study on safe usage of b amboo and m ixed s caffoldings · study on safe usage of b amboo and m...

Study on Safe Usage of

Bamboo and Mixed Scaffoldings

Occupational Safety & Health Council

2016

Study on Safe Usage of Bamboo and Mixed Scaffoldings

ii

Occupational Safety and Health Council

Table of contents

TITLE PAGE i

TABLE OF CONTENTS ii

LIST OF FIGURES v

LIST OF TABLES viii

Chapter 1 Introduction ................................................................................................... 1

1.1 Background ...................................................................................................... 1

1.2 Research plan and methodology ...................................................................... 1

Chapter 2 Anchorage for Bamboo Scaffolding: Regional Reinforcement .................... 3

2.1 Mechanical properties of connection in bamboo scaffolding .......................... 4

2.1.1 Connection resistance with and without nodes ..................................... 5

2.1.2 Slipping stiffness of connection without nodes .................................... 6

2.1.3 Rotational stiffness of connection ......................................................... 6

2.2 Modeling of bamboo scaffolding ..................................................................... 8

2.2.1 Description of bamboo scaffolding ....................................................... 8

2.2.2 Finite element modeling of bamboo scaffolding .................................. 9

2.3 Regional reinforcement of bamboo scaffolding............................................. 10

2.3.1 Option 1 - Ledger reinforcement ........................................................ 10

2.3.2 Option 2 - Reinforcing two adjacent ledgers ...................................... 11

2.3.3 Option 3 - Platform reinforcement ...................................................... 13

2.3.4 Personal energy absorber (PEA) lanyard and self-retracting lifeline

(SRL)............................................................................................................ 15

2.3.5 Critical cases for experimental test ..................................................... 16

2.4 Full-scale bamboo scaffolding test ................................................................ 17

2.4.1 Description of the scaffolding ............................................................. 18

2.4.2 Test arrangement ................................................................................. 18


iii


2.4.3 Static point load test ............................................................................ 19

2.4.4 Drop load test ...................................................................................... 21

2.5 Scaffoldings with different configuration and dimensions ............................ 22

2.6 Multiple anchorages for Option 2 regional reinforcement ............................ 23

Chapter 3 Anchorage for Bamboo Scaffolding: Other Options ................................... 65

3.1 A safer scaffolding erection process............................................................... 65

3.2 Anchorages for bamboo scaffolding above roof level ................................... 66

3.3 Anchorages for bamboo scaffolding below roof level ................................... 68

Chapter 4 Use of Mixed Scaffolding ........................................................................... 72

4.1 Mechanical properties of connection ............................................................. 72

4.1.1 Normal steel tube-bamboo connection ............................................... 72

4.1.2 Anti-sliding steel tube-bamboo/normal steel tube connection ............ 74

4.1.3 Normal steel tube-normal steel tube connection ................................. 75

4.1.4 Thermal effect of steel tube on connection ......................................... 76

4.2 Design and modeling of mixed scaffolding ................................................... 77

4.2.1 Design of mixed scaffolding ............................................................... 77

4.2.2 Modeling of mixed scaffolding ........................................................... 77

4.3 Comparison among three types of mixed scaffolding ................................... 78

4.3.1 Construction cost and time.................................................................. 79

4.3.2 Weight and weight distribution ........................................................... 81

4.3.3 Load-carrying capacity ....................................................................... 81

4.3.4 Summary ............................................................................................. 85

4.4 Full-scale mixed scaffolding test ................................................................... 87

4.4.1 Description of the scaffolding ............................................................. 87

4.4.2 Test arrangement ................................................................................. 88

4.4.3 UDL test on platform .......................................................................... 88

4.4.4 Static point load test on connection .................................................... 90

4.5 Anchorages for mixed scaffolding ................................................................. 92


iv


Chapter 5 Use of Different Materials for the Working Platform ............................... 135

5.1 Types for the working platform ................................................................... 135

5.2 Mechanical properties of wooden boards and iron planks ........................... 135

5.3 Full-scale test of working platform .............................................................. 136

5.3.1 Test arrangement ............................................................................... 137

5.3.2 Test results......................................................................................... 138

Chapter 6 Conclusions and Recommendations .......................................................... 150

Appendix .................................................................................................................... 152

Appendix A Other types of connection and test fixture ..................................... 152

A1 Column (or beam/bracing) splice test .................................................. 152

A2 A special type of connection called “打戒指” ..................................... 154

A3 Fixture for beam-column connection test ............................................ 155

Appendix B Material properties of bamboo and steel tube ............................... 161

B1 Mechanical properties of bamboo ........................................................ 161

B2 Mechanical properties of steel tube ...................................................... 162

B3 Tube specimens and fixture for tensile test .......................................... 163

Appendix C Column buckling of structural bamboo in bamboo scaffoldings .. 170

C1 Effective length of the post in bamboo scaffoldings [10] .................... 171

C2 Non-prismatic parameter 𝜶 [34] .......................................................... 173

C3 Working example: column buckling of bamboo post using Kao Jue ... 174

Appendix D Allowable compressive load on metal post in mixed scaffoldings 176

References .................................................................................................................. 178


v


Lists of figures

Fig. 2-1 Setup of bamboo connection test ................................................................... 24

Fig. 2-2 Two failure modes for connection with node ................................................. 25

Fig. 2-3 Typical load-displacement curve for conection test with node ...................... 25

Fig. 2-4 Slippage failure for connection test without node .......................................... 25

Fig. 2-5 Vertical testing curves of BP-BP connection.................................................. 26

Fig. 2-6 Modeling of slippage stiffness for bamboo connection ................................. 27

Fig. 2-7 Setup of rotational stiffness test ..................................................................... 27

Fig. 2-8 Rotational test curves of BP-BP connection .................................................. 28

Fig. 2-9 Modeling of rotational stiffness for bamboo connection ............................... 29

Fig. 2-10 Two typical arrangements and configuration of DLBS ................................ 30

Fig. 2-11 Modeling of bamboo scaffolding ................................................................. 30

Fig. 2-12 Deformation of scaffolding after reinforcement .......................................... 31

Fig. 2-13 Reinforcement option: combining two adjacent ledgers with steel tubes .... 31

Fig. 2-14 Load-carrying capacities and moment distribution diagrams ...................... 32

Fig. 2-15 Modeling of contact surface with couplers .................................................. 32

Fig. 2-16 Load cases for Option 2 ............................................................................... 33

Fig. 2-17 Deformation of load case (2) at the position closest to the edge.................. 33

Fig. 2-18 Reinforcement option: installing steel tubes under the work platform ........ 33

Fig. 2-19 Load cases for Option 3.2 near the center of scaffolding ............................. 34

Fig. 2-20 Moment diagram for two types of bamboo failure ...................................... 35

Fig. 2-21 Configuration and dimensions of the scaffolding ........................................ 36

Fig. 2-22 Load positions for anchorage test ................................................................. 37

Fig. 2-23 Setup of static point load test ....................................................................... 38

Fig. 2-24 Static point load test for various test cases ................................................... 39

Fig. 2-25 Bamboo post and standard labelling for Table 2-13 (a)-(f) .......................... 39

Fig. 2-26 Setup of drop load test .................................................................................. 40


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Fig. 2-27 Drop load test and typical drop force-time curves ....................................... 43

Fig. 2-28 Multiple anchorages for Option 2 regional reinforcement ........................... 44

Fig. 3-1 A safer bamboo scaffolding erection process ................................................. 69

Fig. 3-2 Illustration of various options to facilitate the new erection process ............. 70

Fig. 3-3 Bamboo scaffoldings above roof level ........................................................... 71

Fig. 3-4 Configuration of a HLL system with different anchorage options [14] ......... 71

Fig. 3-5 Miller SkyGrip Wire Rope Lifeline and anchorage [15] ................................ 71

Fig. 4-1 Normal steel tube (left) and anti-sliding steel tube (right) ............................. 93

Fig. 4-2 Test setup for normal steel tube-bamboo connection ..................................... 94

Fig. 4-3 Slippage tests for normal steel tube (post)-bamboo (ledger) connection ....... 95

Fig. 4-4 Rotational tests for normal steel tube (post)-bamboo (ledger) connection .... 96

Fig. 4-5 Modeling of normal steel tube-bamboo connection ....................................... 97

Fig. 4-6 Test setup for connection involving anti-sliding steel tube ............................ 97

Fig. 4-7 Five different orientation angles for the anti-sliding steel tube ..................... 98

Fig. 4-8 Splitting of plastic stripes for 0°, 45° and 90° orientation ............................. 98

Fig. 4-9 Load-displacement curves for anti-sliding steel tube-bamboo connection .... 99

Fig. 4-10 Failure mode for 180° orientation of anti-sliding steel tube-bamboo

connection .................................................................................................................. 100

Fig. 4-11 Failure mode for 180° orientation of anti-sliding steel tube-normal steel tube

connection .................................................................................................................. 101

Fig. 4-12 Illustration of anti-sliding steel tube orientation with transom .................. 102

Fig. 4-13 Right-angle coupler (left) and swivel coupler (right) ................................. 102

Fig. 4-14 Typical configuration of a double-layered bamboo scaffolding (DLBS) ... 102

Fig. 4-15 Three different types of mixed scaffolding ................................................ 104

Fig. 4-16 A one-bay unboarded lift of scaffolding .................................................... 104

Fig. 4-17 Two types of platform commonly used in scaffolding ............................... 105

Fig. 4-18 Modeling of scaffolding platforms ............................................................. 105

Fig. 4-19 Dimension and modeling of metal bracket ................................................ 106


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Fig. 4-20 The full-scale mixed scaffolding used for test ........................................... 107

Fig. 4-21 Test arrangement for UDL test on platform ............................................... 108

Fig. 4-22 Test arrangement for static point load test on connection .......................... 109

Fig. 4-23 Setup of UDL test for platform .................................................................. 109

Fig. 4-24 UDL test on platform ................................................................................. 110

Fig. 4-25 Labeling of metal post and bamboo standard............................................. 111

Fig. 4-26 Setup of static point load test on connection .............................................. 112

Fig. 4-27 Load-displacement curves for Connections (1) and (3) (see Fig. 4-22)..... 113

Fig. 4-28 Failure of Connections (1) and (4) under static point load ........................ 113

Fig. 4-29 Comparison of load-displacement curves between test and analysis ......... 114

Fig. 5-1 Three working platform Types ..................................................................... 140

Fig. 5-2 Thin and thick wooden boards made out of plywood .................................. 140

Fig. 5-3 Dimension of pre-fabricated iron plank ....................................................... 141

Fig. 5-4 Three-point loading test on wooden board and iron plank ........................... 141

Fig. 5-5 A typical load-deflection curve for an iron plank ......................................... 141

Fig. 5-6 Dimensions and position of the partial area ................................................. 142

Fig. 5-7 Setup of static point load test on the middle span of platform ..................... 143

Fig. 5-8 Typical load-deflection curves of three platform types ................................ 144

Fig. 5-9 Comparison of load-deflection curves between test and analysis ................ 144

Fig. A-1 Setup of splice test ....................................................................................... 157

Fig. A-2 Test setup of splice with contact length 1.3 m and different number of ties157

Fig. A-3 Test setup of actual connection with six ties ............................................... 158

Fig. A-4 Typical configuration of “打戒指” .............................................................. 158

Fig. A-5 Failure mode and typical load-displacement curve of “打戒指” ................ 159

Fig. B-1 Three sizes of steel tube available in Hong Kong ....................................... 166

Fig. B-2 Setup for the tensile test............................................................................... 167

Fig. B-3 Load-displacement curve for specimen D2 under tensile test ..................... 168


viii


Lists of tables

Table 2-1 Test configurations for bamboo connection ................................................. 45

Table 2-2 Resistance of bamboo connection with node ............................................... 45

Table 2-3 Resistance of bamboo connection without node ......................................... 46

Table 2-4 Rotation stiffness for beam-column connection .......................................... 46

Table 2-5 Load-carrying capacity of ledger after reinforcement ................................. 47

Table 2-6 Load-carrying capacity for Option 2 near the center of scaffolding ............ 47

Table 2-7 Load-carrying capacity for Option 2 near the edge of scaffolding .............. 48

Table 2-8 Effect of tube thickness on load-carrying capacity for Option 2 load case (1)

...................................................................................................................................... 48

Table 2-9 Load-carrying capacity for various options under load case (1) ................. 49

Table 2-10 Load-carrying capacity for Option 3.2 near the center of scaffold ............ 49

Table 2-11 Summary of load-carrying capacity for Option 2 ...................................... 50

Table 2-12 Load-carrying capacity for Option 3.2 with a tube length of 1.2 m .......... 50

Table 2-13 Results of static point load test for test cases (1) to (6) ............................. 51

Table 2-14 Comparison of computer analysis with static point load test .................... 54

Table 2-15 Summary for the static point load test ....................................................... 57

Table 2-16 Results of drop load test ............................................................................ 57

Table 2-17 Anchorages for DLBS with 3 standards and a span of 0.6 m .................... 59

Table 2-18 Reinforced anchorages for different bamboo scaffoldings ........................ 60

Table 2-19 Load-carrying capacity (in kN) of one anchor point for Option 2 with more

steel struts..................................................................................................................... 62

Table 2-20 Load-carrying capacity for Option 2 under two users ............................... 64

Table 4-1 Resistance for normal steel tube-bamboo connection ............................... 115

Table 4-2 Rotational stiffness for normal steel tube-bamboo connection ................. 115

Table 4-3 Test results for anti-sliding steel tube-bamboo/normal steel tube connection

.................................................................................................................................... 115


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Table 4-4 Connection resistance for 0°, case 45° and case 90° orientation ............... 116

Table 4-5 Total displacement for 0°, case 45° and case 90° orientation .................... 116

Table 4-6 Properties for various types of couplers .................................................... 116

Table 4-7 Material required for a one-bay unboarded lift ......................................... 117

Table 4-8 Material cost for scaffoldings .................................................................... 117

Table 4-9 Equivalent density for scaffoldings ........................................................... 117

Table 4-10 Self-weight and weight distribution of a one-bay unboarded lift ............ 118

Table 4-11 Allowable loads for scaffolding platforms ............................................... 118

Table 4-12 Maximum deflections for scaffolding platforms ..................................... 118

Table 4-13 Allowable buckling loads for metal and bamboo posts ........................... 119

Table 4-14 Allowable heights of scaffoldings ............................................................ 119

Table 4-15 Test data for Fook Shing anchor bolts [2, 3] ............................................ 120

Table 4-16 Safety of anchor bolt and bracket for scaffolding with allowable height 120

Table 4-17 Comparison of three mixed scaffoldings and bamboo scaffolding ......... 121

Table 4-18 Results for UDL test on platform............................................................. 122

Table 4-19 Comparison of UDL test results with computer analysis ........................ 126

Table 4-20 Summary of UDL test and analysis ......................................................... 129

Table 4-21 Displacement of connection under 2 kN static point load ....................... 129

Table 4-22 Results for static point load test (2 kN) on connection ............................ 130

Table 4-23 Load-carrying capacity of connections .................................................... 131

Table 4-24 Comparison of connection displacement between test and analysis ....... 132

Table 4-25 Comparison of load-carrying capacity of connection .............................. 132

Table 4-26 Comparison of axial forces under 2.0 kN load ........................................ 132

Table 4-27 Summary of connection test and analysis ................................................ 134

Table 5-1 Mechanical properties for wooden boards ................................................. 145

Table 5-2 Mechanical properties for iron planks ....................................................... 145

Table 5-3 Deflection at the midpoint of inner layer ................................................... 146

Table 5-4 Results for static point load (3 kN) on working platform .......................... 146


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Table 5-5 Comparison of deflection between test and analysis ................................. 147

Table 5-6 Comparison of axial forces under 3 kN load ............................................. 148

Table 5-7 Summary for platform test and analysis .................................................... 149

Table A-1 Effects of presence of nodes and number of round turns on resistance .... 160

Table A-2 Experiments to study the effect of number of ties and contact length ...... 160

Table A-3 Tested resistance of actual splices ............................................................. 160

Table A-4 Resistance of “打戒指” beam-column connection ................................... 161

Table B-1 Summary of physical and mechanical properties of Kao Jue and Mao Jue

.................................................................................................................................... 168

Table B-2 Results of tensile test for three different sizes of steel tube ...................... 169

Table C-1 Buckling design example of Kao Jue with effective length 2 m ............... 175

Table D-1 Allowable compressive load for steel column with 𝐿𝐸 = 1.0 𝐻 ............. 177


1


Chapter 1 Introduction

1.1 Background

The safety and reliability of bamboo scaffoldings have been investigated previously in

three separate studies funded by the Occupational Safety and Health Council [1-3].

Recommendations have been made and published to ensure safe usage of these

temporary structures. Recent feedbacks from the industry however reveal that some

additional issues have surfaced and might hinder the safety of bamboo scaffoldings.

First, it was recommended in [1] that the intersections of the bamboo scaffoldings

cannot be used to anchor safety belts. This restriction unfortunately has created a

rather unfavorable condition for the workers to anchor the independent lifeline and the

safety harness to a reliable anchorage during erection, alteration or dismantling of

bamboo scaffolding, especially for bamboo scaffolding above the roof level. Also,

there appear some scaffoldings constructed using a mixture of both bamboo and metal

tubes. These mixed scaffoldings have created a series of new technical challenges that

need to be addressed. Furthermore, there is a concern that needs to be addressed about

using different materials for the working platform on the scaffoldings. This proposed

study is intended to investigate these three issues and to provide solutions and

practical guidebooks to the industry for the safe erection, usage as well as dismantling

of bamboo and mixed scaffoldings.

1.2 Research plan and methodology

This research aims at conducting a systematic study on the three issues listed above

using both computer analyses and laboratory tests. The computer analyses are

conducted using the finite element analysis program SAP 2000 and the laboratory tests


2


are conducted in the Structural Laboratory of the Hong Kong University of Science and

Technology. Details of the proposed study are discussed in the following.

(1) Anchorages for safety harness

For bamboo scaffolding under roof level, some regions of scaffolding are reinforced by

using either stronger bamboo components or other non-bamboo components such as

metal tubes. For bamboo scaffolding above the roof level, the possibility of using extra

external support or anchorage to improve the safety of bamboo scaffolding is

considered and investigated.

(2) Issues relating to the use of mixed scaffolding

The load-carrying capacity and safe usage of typical mixed scaffolding are investigated

via numerical analyses first. A mixed scaffolding will then be constructed and tested in

the laboratory to verify the results obtained from the numerical analyses.

(3) Use of different materials for the working platform

Recently, there are some discussions about whether different materials such as

prefabricated bamboo panels, wooden boards or metal plate can be used for the

working platform on the scaffoldings. This issue is investigated numerically as well as

experimentally in this study.


3


Chapter 2 Anchorage for Bamboo

Scaffolding: Regional Reinforcement

Anchorage can be defined as an element or series of elements or components which

incorporates an anchor point or anchor points. An anchor point is an element to which

personal protective equipment can be attached after installation of anchor device. Some

basic requirements for fall arrest systems or personal protective equipment are

available in various standards [4-7] and are summarized in the following.

(1) Anchorages selected for fall arrest systems shall have sufficient strength capable of

sustaining static load applied in the directions permitted by system of at least two times

the maximum arrest force (MAF) for certified anchorages [4, 5]. When more than one

fall arrest system is attached to an anchorage, the strength shall be multiplied by the

number of systems attached to the anchorage.

(2) According to the ANSI Z359.6 [6] and CSA Z259.16 [7], MAF imposed on a user’s

body shall not exceed 8 kN. Note that the 8 kN limitation aims at worker’s body mass

of at least 91 kg. A smaller MAF shall be applied to worker whose weight is less than 91

kg. In 2002, the Technical Committee on Fall Protection has actually voted to move

toward a standardized MAF of 6 kN in all standards, thus protecting workers down to

body mass of 67 kg, see Appendix A.6 of ANSI Z359.6 and Annex A.6 of CSA

Z259.16. The static strength test of 12kN required in BS EN 795 [8] is also based on

MAF of 6 kN and a safety factor of 2.

These two main requirements ensure the safety of workers and prevent their injuries

when fall happens. This chapter is focused on exploring possible anchorages for the

workers when they perform their jobs on bamboo scaffoldings. Several regional

reinforcement options are investigated through numerical analysis to explore whether


4


any part of scaffolding after reinforcement could have adequate strength to serve as safe

anchorages. To improve the accuracy of numerical analysis, systematic tests and

statistical analysis have been done to investigate the connection properties firstly. For

those options meeting the requirements, they will then be tested for deformation, static

and dynamic strength and integrity in the laboratory.

2.1 Mechanical properties of connection in bamboo

scaffolding

Connection plays a very important part in the load transfer mechanism for bamboo

scaffolding. External loads acting on a scaffolding will first be carried by its horizontal

transoms and ledgers and then transferred to its vertical posts via connections. The

connections of two bamboo members are fastened manually using plastic stripes. As

not much research has been done about the behavior of this type of connection in the

past, it is necessary to perform a study on the bamboo scaffolding connection in order

to model the scaffolding more accurately. This section presents an experimental

investigation on the resistance and the stiffness of bamboo scaffolding connection.

Through systematic tests and statistical analysis, the characteristic resistance and

stiffness of beam-column connection are proposed for further analysis. For other types

of connection, such as the column or beam splice and “打戒指”, their properties were

also investigated and concluded in Appendix A1 and A2 for practical design. The tests

were carried out in the Structural Engineering Laboratory of HKUST using the MTS

810 Universal Testing Machine. Also, a fixture was made as loading equipment to

simulate the actual load or moment condition. The dimensions of the test fixture are

presented in Appendix A3.

Fig. 2-1 shows a typical setup of beam-column connection test. A total of 75 tests were

conducted to obtain the following parameters:


5


(1) Connection resistance with and without the presence of nodes;

(2) Slipping stiffness of connection without the presence of nodes;

(3) Rotational stiffness of connection.

Possible configurations of bamboo connection are summarized in Table 2-1. It is noted

that the external diameter is fairly uniform over the length of Kao Jue but not so for that

of Mao Jue (noticeably reduces from bottom to top). Some connections involving Mao

Jue can only be fastened with 4 round turns (instead of 5 used for the other conditions)

using one plastic strip due to larger diameter of Mao Jue. This effect on resistance and

stiffness behavior is considered in the experiment.

2.1.1 Connection resistance with and without nodes

Table 2-2 summaries the resistance of bamboo connection with the presence of nodes. It

is seen that the mean connection resistance ranges between 1.89 and 2.21 kN with the

standard deviation (Std) ranges between 0.35 and 0.81 kN. Table 2-3 presents the

experimental results of connection resistance without the presence of nodes. It is seen

that the mean connection resistance ranges between 0.62 and 0.98 kN with the standard

deviation (Std) ranges between 0.06 and 0.22 kN. As a conservative measure, the

connection resistance without nodes was taken as the minimum slipping force during

the initial 30 mm displacement. Results show that the connection resistance is larger

when bamboo nodes are present around the connection.

Fig. 2-2 shows two failure modes for the connection with nodes: (a) rupture of plastic

strip and (b) slippage over the node. Note that these two failure modes could occur at

the same time. Fig. 2-3 shows a typical load-displacement curve for connection with

nodes under loading. It is seen that small initial slippage occurred which caused small

reduction of UTM force as UTM displacement increased. The plastic strip resettled


6


after the initial slippage and provided a bit more resistant force until the final failure.

For connection without the presence of nodes, the connection resistance depends

primarily on the number of turns of plastic stripes and the workmanship of the

scaffolding practitioners. The failure mode for all connection tests without the presence

of nodes is slippage between bamboo members (see Fig. 2-4).

2.1.2 Slipping stiffness of connection without nodes

As a conservative measure, the slipping stiffness of connection between two Kao Jue is

used as a representative value for all connections between bamboo members. Five tests

have been conducted in the laboratory and their load-displacement curves are shown

in Fig. 2-5 (a). It is seen that the force-displacement shows an approximately linear

trend up to about 20 mm. After that slippage occurred, the forces decreased slightly as

the slippage continued. Based on these five test results, the average minimum slipping

force within the initial 30 mm displacement is found to be 0.9 kN, which is used as

the slipping resistance in the further numerical analyses. A linear relation was used to

model the initial slippage through the least square method as shown in Fig. 2-5 (b).

The average slipping stiffness before reaching the maximum slipping resistance is

56.2 kN/m. In SAP 2000, the multi-linear element and panel zone are used to model the

slipping stiffness of the bamboo connection (see Fig. 2-6).

2.1.3 Rotational stiffness of connection

The rotational stiffness of a bamboo connection is non-symmetrical. It would be zero if

the two components rotate toward the direction perpendicular to the direction of the

fastening tie. To obtain the rotational stiffness when the two components rotate toward

the direction of fastening tie, the MTS 810 Universal Testing Machine was again used.

Fig. 2-7 shows the setup for obtaining this rotational stiffness. Load was applied on one

side of horizontal member at a distance of 125 mm from the center of vertical member.


7


The load-displacement relationship was recorded and transformed to

moment-rotational angle plot. The M − θ curve can be obtained through the following

two equations.

θ = arctan(𝑉

𝐻)

𝑀 = 𝐹 × 𝐻

where

𝐹: applied load;

𝑉: vertical displacement of loading point;

𝐻: horizontal distance between loading point and central line of vertical bamboo;

𝜃: rotational angle (rad); and

𝑀: rotational moment (kN·m).

Fig. 2-8 shows three vertical load-displacement curves of the intersection between two

Kao Jue and the corresponding M − θ curves, respectively. It can be found that the

stiffness against rotation approximately follows linear relationship and the rotational

resistance is quite small. The rotational stiffness was obtained as the slope of straight

line though a linear curve fit.

A total of 21 tests were conducted with different configuration of beam-column

connections. Table 2-4 presents the experimental results of rotational behavior of

bamboo connection. It can be found that the rotational stiffness is about the same for

different configuration of connection. The effect of round turns of plastic stripes on

rotational stiffness is not significant. The overall mean value of all tests is 0.113

kN·m/rad and was selected as rotational stiffness against the direction of the fastening

tie in further analysis. In SAP 2000, the multi-linear element and panel zone are also

used to model the bilinear stiffness behavior against rotation, see Fig. 2-9.


8


2.2 Modeling of bamboo scaffolding

This section presents some important points about the modeling of bamboo scaffolding

in SAP 2000. Modeling and analysis of scaffolding have been reported in some

previous studies [2, 9, 10]. Some useful information were extracted and applied in the

current modeling. The experimental results of connection obtained in the previous

section, including both the slipping stiffness and the rotational stiffness of connection,

were adopted to obtain more realistic behavior of scaffolding.

2.2.1 Description of bamboo scaffolding

Bamboo scaffoldings are classified by their applications [11], such as single-layered

scaffolding, double-layered scaffolding, truss-out scaffolding and signage scaffolding.

In this report, the attention was focused on double-layered bamboo scaffolding

(DLBS).

DLBS consists of two layers: an outer layer scaffolding and an inner layer of posts and

ledgers. For the outer layer, Mao Jue is used for both posts and base ledgers, and Kao

Jue is used for the other ledgers, standards, transoms and diagonal bracings. For the

inner layer, all posts and ledgers are Kao Jue and there are no standards, bracings and

secondary ledgers. Transoms are used to connect the inner and the outer layers. These

transoms are also used to support the working platform. Lateral restraints (putlogs) are

provided at regular or staggered interval to prevent inward and outward leaning of the

scaffold. The inner layer is at about 200 – 250 mm from the building face and the outer

layer is at about 600 mm from the inner layer [12].

With the above basic requirements of DLBS, there are several different configurations

and dimensions due to scaffolders’ own experience. Fig. 2-10 shows two typical

arrangements and configuration of DLBS in accordance with [9, 12].


9


2.2.2 Finite element modeling of bamboo scaffolding

Even differences exist in the configuration and dimension of DLBS, the modeling of

scaffolding remains very much the same. Some details and key issues for the modeling

are summarized as follows:

(1) Bamboo members, Kao Jue and Mao Jue, were modeled as prismatic elements

with a circular hollow section using averaged external and internal diameters. Also,

their material properties under natural moisture content were used. The

dimensions and mechanical properties of bamboo were summarized in Appendix

B1.

(2) The vertical, horizontal and rotational stiffness of the joint between bamboo

members were modeled in SAP 2000 using multi-linear elements and panels. For

simplicity, the out-of-plane displacement between bamboo members at connection

was not considered.

(3) It should be noted that in each main ledger-post/standard fastening, there was

always a transom-post/standard fastening connected at the same location. Thus,

the total connection resistance, vertical stiffness and horizontal stiffness should be

doubled. The rotational stiffness was not doubled because the post/standard, main

ledger and transom were orthogonal to each other.

(4) The support condition of transoms linking up the ledgers of inner layer and outer

layer were simulated as a pinned connection.

(5) The putlog was comprised of a short bamboo strut and a metal tie (minimum at 6

mm∅) acting as a prop and a tie respectively to prevent inward and outward leaning

of the scaffold, which was modeled with only inward and outward restraints.

(6) All main posts were assumed to be pinned at the bottom. The braces were only

connected to main posts of outer layer as a conservative consideration.

(7) Nonlinear analysis with P-Delta effect was adopted in the SAP 2000 software. The

P-Delta effect referred specifically to the nonlinear geometric effect under a large


10


tensile or compressive direct stress upon transverse bending and shear behavior. A

compressive stress tends to make a structural member more flexible in transverse

bending and shear, whereas a tensile stress tends to stiffen the member against

transverse deformation [13]. Note that the P-Delta effect was not significant in our

numerical analysis.

We first focused on the alternative arrangement of DLBS as shown in Fig. 2-10 (b),

which actually gave a more conservative results than the configuration of DLBS in

Fig. 2-10 (a). More detailed analysis was considered to ensure the designed anchorage

can be applied on scaffolding with different arrangement and configuration. Fig. 2-11

shows the finite element model in accordance with the alternative arrangement of

DLBS.

2.3 Regional reinforcement of bamboo scaffolding

To anchor personal protective equipment on bamboo scaffolding, the potential

anchorage location must be reinforced to provide a load-carrying capacity of at least

12 kN. Numerical analysis of a full-scale bamboo scaffolding showed that the

commonly used ledger component, Kao Jue (BP), could only sustain a concentrated

load of about 1.9 kN (see Table 2-5). The following possible reinforcement options for

the anchorage were investigated through numerical analysis. The analysis was

conducted on the full-scale model. For simplicity, the force was acted at the middle of

reinforced region to determine the load-bearing capacity of anchorage. For those

options meeting the requirement, more detailed study and experiment were conducted.

2.3.1 Option 1 - Ledger reinforcement

The first option is to reinforce ledger using multiple bamboo members and/or steel

tubes. Note that the dimensions and mechanical properties of steel tubes were


11


experimentally tested and summarized in Appendix B2. Fig. 2-12 shows a partially

enlarged model after reinforcement. The contact surface between reinforced ledgers

was modeled by gap elements with no opening and stiffness of 3 MN/m. To decrease

the relative displacement between ledger and post (standard) at the connection, the

ledger was tied to every standard and post. The mechanical properties of connection

between bamboo and steel tube were also modeled using the multi-linear element and

panel zone according to testing results from Section 4.1. The concentrated load acting

on the anchorage was increased until the stress in ledger reaching its characteristic

strength. The characteristic strength (95% probability) for Kao Jue (BP) and Mao Jue

(PP) are 58.5 N/mm²and 53.4 N/mm² respectively, and the characteristic yield

strength for steel tube is 350 N/mm² (see Appendix B). Table 2-5 presents the

load-carrying capacity of anchorage for ledgers with different composition of BP, PP

and steel tube. It was found that there was no reinforcement cases that could meet the

load requirement.

2.3.2 Option 2 - Reinforcing two adjacent ledgers

The analysis above showed that the ledger consisting of three BP or two steel tubes

could not offer enough strength for an anchorage. Considering the load-carrying

capacity of ledger consisting of one steel tube and one BP could reach 6.9 kN, the

option of strengthening two adjacent ledgers using steel tubes was investigated. The

steel tubes were tied to bamboo standards/posts through plastic stripes and the two

ledgers were combined together though a linked steel tube. Two types of connection

between steel ledgers were considered: Type 1: an anti-sliding steel tube was used as

the linked strut connecting the two steel ledgers through 5-round plastic stripes; and

Type 2: a normal steel tube was used as the linked strut connecting the two steel

ledgers through metal couplers (swivel coupler). Fig. 2-13 shows the configuration of

this reinforcement option. The load-carrying capacity for Type 1 and Type 2 was

found to be 12.2 kN and 7.9 kN, respectively. Their corresponding moment


12


distribution diagrams in the ledgers are shown in Fig. 2-14. It should be noted that the

contact surface was modeled by gap elements with no opening and stiffness of 3000

kN/m in Fig. 2-14 (a). In Fig. 2-14 (b), due to the use of couplers, the contact surface

at coupler position (width of coupler 50mm) was modeled by gap elements with no

opening and stiffness of 3000 kN/m and the gap elements at other position have an

opening of 10 mm (thickness of coupler) and stiffness of 3000 kN/m (see Fig. 2-15).

It seems that metal coupler can ensure the applied force could be shared equally by the

connected ledgers which helps to obtain a larger load-carrying capacity. Further

analysis on this type of reinforcement was performed and three load cases near the

center as shown in Fig. 2-16 (a) were analyzed. For each load case, the load-carrying

capacities of reinforcement with different steel tube length at each side were studied.

Results obtained were summarized in Table 2-6. It is seen that the length of steel tube

at each side of reinforcement should be at least 0.6 m and the load case (3) seems to

offer the lowest load-carrying capacity of 12.1 kN under steel tubes failure. It should

be noted that the thickness of tube in Table 2-6 and Table 2-7 is 4 mm and the size

effect of tube will be investigated in the following.

Next, the load-carrying capacities of this reinforcement near the edge of scaffolding

were analyzed. Fig. 2-16 (b) shows the three load positions near the edge of

scaffolding with steel tube length of 0.6 m (1’, 2’, 3’) and 1.2 m (1’’, 2’’, 3’’),

respectively. Table 2-7 summarizes their load-carrying capacities. It is seen that the

length of steel tube at each side of anchor point should be at least 2.4 m and the load

case (3) seems to offer the lowest load-carrying capacity of 12.35 kN under steel

tubes failure. The load case (1) offers the highest load-carrying capacity among the

three load cases and the required length of steel tube at each side of anchor point is

0.6 m. Note that the load case (2) with steel tube length 0.6m at the position most

close to the edge (marked as ‘2’ in Fig. 2-16 (b)) will generate a very large

displacement when reaching the load-carrying capacity, which is not allowed and is


13


not considered in this report (see Fig. 2-17). Considering all three load cases near the

edge of scaffolding, at least 4.8 m long of steel tube (a total mass about 21 kg) should

be used to provide a safe anchorage, which is not practical.

Based on the analysis results and considering practical feasibility, the connection

between bamboo post (Mao Jue) and ledger corresponding to load case (1) could be

recommended as an anchor location for the personal protective equipment. It should

be noted that such an anchorage shall be used with at least 0.6 m long of steel tube at

each side of the anchor point.

It was noted that there were three steel tubes available in the market that have the same

outside diameter of 48.3 mm but different thickness of 2.3 mm, 3.2 mm and 4 mm

respectively. As the anchorages near the edge of scaffolding have smaller

load-carrying capacity than those in the middle region, the load-carrying capacities of

anchorages under load case (1) near the edge with different tube length and different

tube thickness were analyzed and summarized in Table 2-8. Results suggest that the

thickness of tube shall be at least 3.2 mm to provide a safe anchorage for this

reinforcement option.

2.3.3 Option 3 - Platform reinforcement

The principle behind Option 2 is to transform the external point load into uniformly

distributed load which can be shared by a long span of bamboo ledger with a smaller

stress. Following the same principle, a steel tube was added underneath the work

platform as shown in Fig. 2-18. The steel tube was fastened to transoms using plastic

stripes. This steel tube has a potential to be used to anchor safety harness for the worker

at the platform below and for the whole range of platform.

As stated above, the safety factors for the steel tube and the bamboo member were


14


assumed to be 2. Hence the load-carrying capacity of the whole reinforced region shall

be at least 12 kN considering a MAF of 6 kN. In addition to installing one steel tube

underneath the platform, additional options were also investigated through numerical

analysis: Option 3.1: adding an additional transom to each existing one; Option 3.2:

using Option 3.1 plus adding one more steel tube (a total of two steel tubes) underneath

the platform.

The analysis was first conducted on a full-scale scaffolding with the anchorage

assumed to be around the middle of platform. For simplicity, the load-carry capacity

was calculated by imposing a static force at the connection between steel tube and the

transom which was connected to two posts (see load case (1) in Fig. 2-19). For those

options meeting the load requirement, more specific load cases covering the whole

platform were then conducted. Table 2-9 summaries the results obtained for the two

options (Option 3.1 and Option 3.2). The load-carrying capacity of the original design

with just one steel tube underneath the platform was also provided for comparison

(denoted as “Option 3” in Table 2-9). Results show that only Option 3.2 can offer a

load-carrying capacity larger than 12 kN (MAF of 6 kN and a safety factor of 2.0).

Hence this option was chosen for further analysis to determine whether this option can

offer sufficient load-carrying capacity under different loading conditions.

For Options 3.2 (adding two steel tubes underneath the platform and an additional

transom to each existing one), five load cases near the center as shown in Fig. 2-19

were analyzed. For each load case, the load-carrying capacities of anchorage with

different length of steel tube at two sides were analyzed. It should be noted that the

maximum stress in the outer layer ledger is always smaller than that of the inner layer

ledger due to additional standards at the outer layer. Results obtained are summarized

and shown again in Table 2-10. It is seen that only load case (1) with full tube length

of 6 m offers the load-carrying capacity larger than 12 kN. So this option cannot

provide safe anchorages along the whole length of platform.


15


2.3.4 Personal energy absorber (PEA) lanyard and self-retracting

lifeline (SRL)

When anchoring safety harness to a location, a connecting subsystem need be used to

link the safety harness to the anchor point. Lots of connecting subsystems found in

market incorporate some forms of energy absorbing device, such as personal energy

absorber (PEA) lanyard and self-retracting lifeline (SRL). They are designed to

comply with requirements in various standards such as ANSI Z359 and CSA Z259

standards. These energy absorbing subsystems can limit the MAF to 4 kN for workers

below 141 kg [14, 15]. That is to say, the anchorage could be reinforced to have a

load-carrying capacity of 8 kN instead of 12 kN (assumed MAF = 4 kN and a safety

factor of 2) when these energy absorbing device are used.

From above analysis, these two options can both meet the load requirements and have

better performance than other choice: (a) Option 2: reinforcing two adjacent ledgers

with steel tubes and linking them through a steel strut; (b) Option 3.2: reinforcing

platform with two steel tubes and adding an additional transom to each existing one.

For Option 2, when the steel tube length is 0.6 m at each side of anchor point, the

load-carrying capacity is mostly determined by failure of bamboo ledger. Failure

could happen at the loading location or at the end of steel tube depending on load

cases and steel tube thickness. When the tube length is more than 1.2 m at two sides

of anchor point, the load-carrying capacity would be larger with longer tube and is

determined by the failure of tube or bamboo ledger at loading position. Also,

anchorages at more central region of scaffolding will have larger load-carrying

capacity. The load-carrying capacity of three load cases for Option 2 near the edge

with two critical tube length (0.6 m and 1.2 m) and three different tube size (thickness

= 2.3 mm, 3.2 mm and 4 mm) are summarized in Table 2-11. It is found that the

load-carrying capacities for all cases could be all larger than 8 kN.


16


For Option 3.2, the length of steel tube (thickness = 4 mm) at two sides of anchor

point shall be at least 1.2 m to provide safe anchorages with load-carrying capacity

larger than 8 kN as seen in Table 2-10. Also, the load-carrying capacity of anchorage

would increase as the tube length increases. The results near the edge of scaffolding

are summarized in Table 2-12. It is found that all cases with different tube size and

with tube length of at least 1.2 m can withstand a load larger than 8 kN.

2.3.5 Critical cases for experimental test

A series of tests are devised to validate the reinforcement options determined above.

The tests are divided into two groups depending on whether the connecting subsystem

incorporating an energy absorbing device. These two groups are indicated by their

target load-carrying capacity of “12 kN” and “8 kN” respectively. These critical test

cases are described as follows.

12 kN anchorage tests:

The load case (1) for Option 2 (thickness of tube at least 3.2 mm and tube length at

least 0.6 m at each side of anchor point) was designed to provide safe anchorages with

12 kN load-carrying capacity in Section 2.3.2. From Table 2-8, all load-carrying

capacities with tube thickness of at least 3.2 mm were under bamboo failure. There

are two types of bamboo failure: (a) when tube length at each side of anchor point is

0.6 m, the bamboo failure occurred at the tube end; (b) when tube length at each side

of anchor point is at least 1.2 m, the bamboo failure occurred at the loading position

(see Fig. 2-20). These two types of bamboo failure with lowest load-carrying capacity

will be considered.

8 kN anchorage tests:

For load cases (2) and (3) of Option 2 from Table 2-11, only when the tube length was


17


0.6 m with tube thickness at least 3.2 mm, the load-carrying capacity was determined

by bamboo failure and happened at the tube end. The failure mode of load cases (2)

and (3) for other situations were tube failure at loading position. So, these two failure

modes (bamboo failure at tube end and tube failure at loading point) with lowest

load-carrying capacity will be considered.

From Table 2-12 for Option 3.2, there were two failure modes when reaching their

load-carrying capacities, one was bamboo failure of main inner ledger for load case (2)

and the other one was steel tube failure for all other situations. These two failure

modes with lowest load-carrying capacity will be considered.

In summary, the following six critical cases will be investigated in the experimental

study:

(1) The load case (1) for Option 2 with 0.6 m tube length (tube size: 48.3 mm × 4 mm)

at both sides of anchor point.

(2) The load case (1) for Option 2 with 1.2 m tube length (tube size: 48.3 mm × 3.2

mm) at both sides of anchor point.

(3) The load case (3) for Option 2 with 0.6 m tube length (tube size: 48.3 mm × 4 mm)

at both sides of anchor point.

(4) The load case (3) for Option 2 with 1.2 m tube length (tube size: 48.3 mm × 2.3


(5) The load case (2) for Option 3.2 with 1.2m tube length (tube size: 48.3 mm × 3.2


(6) The load case (5) for Option 3.2 with 1.2m tube length (tube size: 48.3 mm × 2.3


2.4 Full-scale bamboo scaffolding test

The objective of the full-scale scaffolding tests is to experimentally validate the safety


18


of anchorages. Both static load test and drop load test will be performed for the six

critical loading cases mentioned above. The description of full-scale scaffolding, test

setup and test results are presented in the following.

2.4.1 Description of the scaffolding

The scaffolding used for the test was a double-layer bamboo scaffolding (DLBS) with

dimensions of 4.8 m × 5.6 m × 0.6 m (length × height × width). Fig. 2-21 shows

configuration and dimension of scaffolding. Details of this scaffolding are described

below.

(1) Outer layer: Mao Jue was used as the main posts and base ledger of the outer layer.

Three Kao Jue were then erected in between two Mao Jue as standards which

were overhung from the ledgers but not resting on the ground. Kao Jue was used

as secondary and the other main ledgers as well as the diagonal members.

(2) Inner layer: Kao Jue was used throughout the inner layer. There was no bracing for

the inner layer.

(3) Platform: There were two platforms and their heights were 2.3 m and 3.95 m

respectively. The inner and outer ledgers were connected by transoms.

2.4.2 Test arrangement

12kN anchorage test cases:

The two critical cases (1) and (2) for 12 kN anchorage were tested at the center of

scaffolding with a static point load of 12 kN and a drop load (free fall of a 100 kg

dead weight achieving at least a drop force of 9 kN [8]). Fig. 2-22 (a) shows the

location of the load position for the two cases.

8kN anchorage test cases:

The four critical cases (3) to (6) for 8 kN anchorage were tested at the edge of


19


scaffolding with a point load of 8 kN and a drop load (free fall of a 100 kg dead

weight achieving at least a drop force of 8 kN). The testing positions for critical cases

are shown in Fig. 2-22 (b) shows the location of the load position for the four cases. It

should be noted that the required drop force of 8 kN is to maintain a general safety

factor of 2 [4, 5].

2.4.3 Static point load test

The static point load test was performed to check whether the anchor point can hold the

load about twice the maximum arrest force statically. Fig. 2-23 depicts details for the

test setup. The equipment used in the test included a tensile jack with load cell, data

logger and computer and strain gauges. Strain gauges were installed at bottom

locations of all the bamboo standards, posts and bracings. For metal tubes, strain

gauges were also installed to measure the bending moment in horizontal metal tube

and axial force in metal strut. Note that the bending moment in horizontal metal tubes

was measured at a distance of 10 or 5 cm from loading point depending on installing

convenience. There were a total 20 ports in data logger for strain gauges to connect so

that only the force in total ten bamboos or metal tubes could be measured every time.

Under this limitation, the main load-bearing components were selected for force

measurement. The load cell was mounted on ground through four expansion bolts,

which could sustain a pullout load over 20 kN.

The load generated by tensile jack was applied on a reinforced anchor point through

steel wire. Load was increased from 0 kN to a specified value (either 12 kN or 8 kN)

slowly to avoid dynamic effects. When the load reached the specified value, the load

would be maintained for 3 minutes to observe whether failure would occur in the

reinforced region. For each test case, three independent tests were conducted. Fig.

2-24 (a)-(c) show the anchor points under the specified loads for test cases (2), (3) and

(6), respectively. Axial forces and bending moments in selected components were


20


calculated by multiplying the measured strain values with the bamboo cross sectional

area and the section of modulus of area, respectively. The mean values and standard

deviations of strains and calculated forces for every test case were summarized in

Table 2-13 (a)-(f). The numbering of posts and standards are shown in Fig. 2-25. The

outside diameter of each selected bamboo component in Table 2-13 was obtained

through measurement. The thickness of bamboo was calculated by assuming a linear

relationship between thickness and outside diameter as following:

𝐶𝑎𝑙𝑐𝑢𝑙𝑎𝑡𝑒𝑑 𝑡ℎ𝑖𝑐𝑘𝑛𝑒𝑠𝑠

𝑀𝑒𝑎𝑠𝑢𝑟𝑒𝑑 𝑜𝑢𝑡𝑠𝑖𝑑𝑒 𝑑𝑖𝑎𝑚𝑒𝑡𝑒𝑟=

𝐴𝑣𝑒𝑟𝑎𝑔𝑒 𝑣𝑎𝑙𝑢𝑒 𝑜𝑓 𝑡ℎ𝑖𝑐𝑘𝑛𝑒𝑠𝑠

𝐴𝑣𝑒𝑟𝑎𝑔𝑒 𝑣𝑎𝑙𝑢𝑒 𝑜𝑓 𝑜𝑢𝑡𝑠𝑖𝑑𝑒 𝑑𝑖𝑎𝑚𝑒𝑡𝑒𝑟

Note that the average value of thickness and outside diameter of Kao Jue and Mao Jue

are listed in Appendix B1. Based on the test results, the following observations can be

made:

(1) All reinforced anchor points could resist the required load for 3 minutes without

causing any damage to the scaffolding. The whole scaffolding remained stable and

intact during and after test.

(2) The deformation of bamboo ledger and metal tube was rather small.

(3) The relative slipping distance between connections at anchor point was negligible.

(4) The measured forces in bamboo standards was much smaller than those in bamboo

posts.

(5) The standard deviations of the measured strain for the same critical case were

quite small suggesting that the test results were quite consistent.

In this section, the results obtained from the finite element program SAP 2000 were

compared with that obtained from the static point load test. Table 2-14 (a)-(f) show

the comparison of axial force and bending moment in selected components between

the measured and the analyzed values. Results summarized in Table 2-15 show that

the average difference between the numerical analysis and the test results was about 26%


21


for the bamboo members and 8% for the metal components.

2.4.4 Drop load test

Drop load test was performed to investigate the performance of reinforced anchor

points and the safety of scaffolding under dynamic loads. The procedure of drop load

test followed the test methods described in BS EN 795 [8] and BS EN 364 [16]. A

sand bag was used to simulate a person falling from a height. The six critical cases

mentioned above were all tested under free fall a 100 kg sand bag which generated a

required drop force as specified in Section 2.4.2.

The test equipment and setup is shown in Fig. 2-26. A load cell was attached to the

anchor point. One end of the lanyard was attached to the load cell and the other end to

the sand bag. During the test, the sand bag was raised to a free fall height that could

generate a drop force larger than the required drop force and hold at no more than 300

mm horizontally from the anchor point [8]. The sampling rate of the load cell was set

at 50 Hz to capture the dynamic load induced by the free fall of sand bag. For

simplicity, the strain values in components are not measured in the drop test.

For test cases (1) and (2), the free fall aimed at generating a peak load larger 9 kN at

the anchor point. For test cases (3) to (6), the peak load due to free fall should be

larger than 8 kN at the anchor point. For each test case, three independent tests were

conducted. Fig. 2-27 (a)-(c) show the anchor points before and after drop test for test

cases (2), (3) and (6), respectively. Also shown are their corresponding drop

force-time curves. Table 2-16 (a)-(f) show the test results with maximum drop force

and corresponding free fall for six critical cases respectively. From these results, the

following observations can be seen:

(1) The anchor points of all six test cases could withstand the free fall of a100 kg sand


22


bag without damaging any part of the scaffolding. All designed anchor points can

sustain a drop load larger than its designed load-carrying capacity.

(2) A small vibration of the scaffolding was observed which did not seem to affect the

stability and the safety of the scaffolding. The deformation of the anchor point

after the drop load test was negligible.

(3) For test case (3), the reinforced anchor point could withstand a drop load larger

than 8 kN which was the intended load-carrying capacity. When the drop load

increased to 11.96 kN, it was noted that the bamboo ledge at tube end fractured.

This failure mode coincided with the result obtained from the numerical result.

2.5 Scaffoldings with different configuration and dimensions

Note that the above findings and summaries were obtained on the scaffolding with the

configuration and dimensions specified in Fig. 2-21 (three standards between posts and

span of about 0.6 m between standards), which are concluded in Table 2-17. As the

configuration and dimension of scaffoldings vary from site to site, more detailed

analysis is needed to provide more general recommendations for these reinforcement

options. In this section, finite element numerical analyses were performed on three

additional scaffoldings with different configuration and dimensions as follow:

(1) Double layered bamboo scaffolding with three standards between posts of outer

layer and a larger span of 0.75 m between standards: results summarized in Table

2-18 (a);

(2) Double layered bamboo scaffolding with one standard between two posts of outer

layer and different spans of 0.6 m, 0.75 m or 0.9 m between standards respectively:

results summarized in Table 2-18 (b); and

(3) Single layered bamboo scaffolding (SLBS) with one standard between two posts

of outer layer and different spans of 0.6 m, 0.75 m or 0.9 m between standards

respectively: results summarized in Table 2-18 (c).


23


2.6 Multiple anchorages for Option 2 regional reinforcement

Above analysis for Option 2 only use one steel strut to link the two adjacent ledgers at

the anchor points. In this section, we further explore the possibility of accommodate

multiple anchorages for Option 2 regional reinforcement by connecting the two

adjacent ledgers with additional steel struts as shown in Table 2-19. The load-carrying

capacity of the anchor points at the middle of reinforcement as well as additional

potential anchor points on the reinforcement were obtained through finite element

analysis presented above and are shown in Table 2-19. The load-carrying capacities of

the original Option 2 regional reinforcement (Table 2-11) are also listed for

comparison. It is seen that the additional steel struts do not seem to affect the

load-carrying capacity of the two anchor points at the middle of reinforcement.

Furthermore, the load-carrying capacity of those additional potential anchor points

produced due to the additional vertical steel struts can be larger than 8 kN as long as

these points are not located at the edges of the reinforcement.

Next, the load-carrying capacities for Option 2 regional reinforcement with different

length and additional steel struts under two users simultaneously were obtained and

are shown in Table 2-20. It is seen that Option 2 regional reinforcement with

additional steel struts can offer a load-carrying capacity larger than 8 kN for both

users simultaneously as long as the spacing between the two users is equal or larger

than two spans. This conclusion is now summarized in Fig. 2-28. The analysis results

show that it is possible to generate an anchorage region using Option 2 regional

reinforcement with additional steel struts. This anchorage region can accommodate

multiple users simultaneously as long as the spacing between the users is equal or

larger than two spans. The anchor points inside the reinforcement region can provide

a load-carrying capacity larger than 8 kN. It is recommended that energy absorbing

devices with a MAF of 4 kN be used on these anchor points so that these anchor

points can protect the users with a safety factor of two.


24


Fig. 2-1 Setup of bamboo connection test

(a) Rupture of plastic strip

(b) Slippage over the node


25


Fig. 2-2 Two failure modes for connection with node

Fig. 2-3 Typical load-displacement curve for conection test with node

Fig. 2-4 Slippage failure for connection test without node

0

0.5

1

1.5

2

2.5

0 20 40 60 80

UT

M F

orc

e (k

N)

UTM Displacement (mm)

Slipping distance

Small initial slippage


26


(a) Load-displacement curves

(b) Initial slippage and linear regression

Fig. 2-5 Vertical testing curves of BP-BP connection

0

0.2

0.4

0.6

0.8

1

1.2

1.4

1.6

0 10 20 30 40 50 60

UT

M F

orc

e (k

N)


1

2

3

4

5

y = 0.066x

y = 0.055x

y = 0.052x

y = 0.059x y = 0.049x

0

0.2

0.4

0.6

0.8

1

1.2

1.4

1.6

0 5 10 15 20 25

UT

M F

orc

e (k

N)



27


Fig. 2-6 Modeling of slippage stiffness for bamboo connection

Fig. 2-7 Setup of rotational stiffness test

-16, -0.9

16, 0.9

-1

-0.8

-0.6

-0.4

-0.2

0

0.2

0.4

0.6

0.8

1

-60 -40 -20 0 20 40 60

Fo

rce

(kN

)

Relative displacement (mm)


28


(a) UTM load-displacement curve

(b) Corresponding M − θ curves

Fig. 2-8 Rotational test curves of BP-BP connection

0

0.1

0.2

0.3

0.4

0.5

0.6

0 10 20 30 40 50 60 70

UT

M F

orc

e (k

N)


1

2

3

y = 0.121x

y = 0.103x

y = 0.112x

0

0.01

0.02

0.03

0.04

0.05

0.06

0.07

0 0.1 0.2 0.3 0.4 0.5

M (

kN

·m)

θ (rad)

0

0.05

0.1

0.15

0.2

0.25

0.3

0.35

0.4

-4 -3 -2 -1 0 1 2 3 4

M (

kN

·m)

θ (rad)

M=0.113× θ

M= 0


29


Fig. 2-9 Modeling of rotational stiffness for bamboo connection

(a) Configuration of DLBS according to code [12]

Ledger: Kao Jue

Ledger on the first

lift: Mao Jue

Bracing (outer

layer): Kao Jue

Post (inner layer):

Kao Jue

Post (outer layer):

Mao Jue

Standard (outer

layer): Kao Jue

1.3 m

Transom: Kao Jue

Ledger: Kao Jue

Ledger on the first

lift: Mao Jue

Bracing (outer

layer): Kao Jue

Post (inner layer):

Kao Jue

Post (outer layer):

Mao Jue

Standards (outer

layer): Kao Jue

2.4 m

Transom: Kao Jue


30


(b) An alternative arrangement of DLBS according to [9]

Fig. 2-10 Two typical arrangements and configuration of DLBS

Fig. 2-11 Modeling of bamboo scaffolding

Typical length of bamboo/steel tube = 6 m


31


Fig. 2-12 Deformation of scaffolding after reinforcement

Steel tube

Bamboo member

Connection between tubes (plastic stripes or coupler)

Fig. 2-13 Reinforcement option: combining two adjacent ledgers with steel tubes

(a) Using anti-sliding tube as linked strut

F

v

v

F=7.90 kN

5-round plastic stripes Anti-sliding tube


32


(b) Using normal steel tube as linked strut

Fig. 2-14 Load-carrying capacities and moment distribution diagrams

Fig. 2-15 Modeling of contact surface with couplers

(a) Near the center of scaffolding

F=12.20 kN

Metal couplers Normal steel tube

50 mm

Coupler

(2) (3) (1) Normal steel tube


33


(b) Near the edge of scaffolding

Fig. 2-16 Load cases for Option 2

Fig. 2-17 Deformation of load case (2) at the position closest to the edge

Fig. 2-18 Reinforcement option: installing steel tubes under the work platform

10.3 kN

Relative displacement＞ 200 mm

1’ (1’’)

2

3’ (3’’) 2’ (2’’)

Edge


34


Fig. 2-19 Load cases for Option 3.2 near the center of scaffolding

(a) Bamboo failure at the position of tube end (tube length at each side of anchor point

is 0.6 m)

(b) Bamboo failure at the position of loading point (tube length at each side of anchor

point is at least 1.2 m)

Largest moment in bamboo

ledger is at one of tube ends

Largest moment in bamboo

ledger is at loading point

Two steel tubes

Two transoms


35


Fig. 2-20 Moment diagram for two types of bamboo failure

(a) Front view of the scaffolding (b) Side view of the scaffolding

(c) Dimensions of scaffolding (m)


36


Fig. 2-21 Configuration and dimensions of the scaffolding

(a) 12 kN anchorage

(b) 8 kN anchorage

Critical cases (1) and (2)

Critical case (6)

Critical cases (3) and (4)

Critical case (5)


37


Fig. 2-22 Load positions for anchorage test

(a) Tensile jack and load cell (b) Data logger and computer

(c) Stain gauges attached on bamboo components

Strain gauges

on metal tubes


38


(d) Strain gauges attached on metal components

Fig. 2-23 Setup of static point load test

(a) Test case (2) under static point load ≥ 12 kN

`

(b) Test case (3) under static point load ≥ 8 kN

Small slipping


39


(c) Test case (6) under static point load ≥ 8 kN

Fig. 2-24 Static point load test for various test cases

Fig. 2-25 Bamboo post and standard labelling for Table 2-13 (a)-(f)

Brace 1

Post 6

Post 8 Post 4

Post 1 Post 2

Standard 1

Post 3

Standard 4 Standard 3

Standard 2

Brace 2

Post 5

Post 7


40


Fig. 2-26 Setup of drop load test

Anchor point

Load cell

Data logger

& computer


41


Before drop load test After drop load test

(a) Test case (2): before and after drop test and typical drop force-time curve

12.80

-2

0

2

4

6

8

10

12

14

0 2 4 6 8

Forc

e (k

N)

Time (s)

Typical drop force-time curve

3.2 m


42


Before drop load test (free fall: 2.9 m) Before drop load test (free fall: 3.1 m)

Bamboo failure at tube end with free fall 3.1 m (no failure with free fall of 2.9 m)

(b) Test case (3): before and after drop test and typical drop force-time curve

11.96

-2

0

2

4

6

8

10

12

14

0 1 2 3 4 5 6 7

Forc

e (k

N)

Time (s)

Corresponding drop force-time curve with bamboo

failed at tube end

Upper ledger Under ledger


43


Before drop load test After drop load test

(c) Test case (6): before and after drop test and typical drop force-time curve

Fig. 2-27 Drop load test and typical drop force-time curves

8.19

-1

0

1

2

3

4

5

6

7

8

9

0 2 4 6 8 10

Forc

e (k

N)

Time (s)

Typical drop force-time curve

2.0 m


44


Fig. 2-28 Multiple anchorages for Option 2 regional reinforcement

≥ 1 span ≥ 4 spans ≥ 1 span

≥ 1 span ≥ 1 span Anchorage region for energy absorbing devices

with MAF ≤ 4 kN

Horizontal spacing between two users ≥ 2 spans


45


Table 2-1 Test configurations for bamboo connection

H: Kao Jue V: Kao Jue H: Kao Jue V: Mao Jue

H: Mao Jue V: Kao Jue H: Mao Jue V: Mao Jue

Note: H: horizontal member; V: vertical member.

Table 2-2 Resistance of bamboo connection with node

Type of connection No. of

turns for

strips

No. of

tests

Connection resistance (kN)

Horizontal

member

Vertical

member Mean Std

BP BP 5 4 2.12 0.35

BP PP 4 or 5 4 2.21 0.81

PP PP 4 or 5 4 2.11 0.63

PP BP 4 or 5 4 1.89 0.46


46


Table 2-3 Resistance of bamboo connection without node

Type of connection No. of

turns for

strips

No. of

tests

Connection resistance (kN)

Horizontal

member

Vertical

member Mean Std

BP BP 5 5 0.90 0.15

BP PP 5 5 0.98 0.12

4 5 0.70 0.09

PP BP 5 5 0.92 0.08

4 5 0.62 0.12

PP PP 5 5 0.90 0.22

4 5 0.66 0.06

Table 2-4 Rotation stiffness for beam-column connection

Type of connection No. of turns

for strips

No. of

tests

Rotational stiffness (kN·m/rad)

Horizontal

member

Vertical

member Mean Std

BP BP 5 3 0.112 0.007

BP PP 5 3 0.118 0.003

4 3 0.107 0.007

PP PP 5 3 0.116 0.019

4 3 0.113 0.014

Overall overage 0.113 0.012


47


Table 2-5 Load-carrying capacity of ledger after reinforcement

Reinforcement of ledger Load-carrying

capacity (kN)

Maximum

stress(N/mm²)

Relative displacement

between ledger and

standard (mm)

One BP 1.90 58.4 20.5

Two BP Upper BP

3.50 58.9

15.1 Under BP 54.8

Three BP

Upper BP

4.45

58.6

11.9 Middle BP 53.2

Under BP 50.8

One PP 4.05 53.3 38.2

Two PP Upper PP

7.75 53.4

22.0 Under PP 50.2

One BP &

One PP

Upper BP 4.90

58.6 15.4

Under PP 39.4

Steel tube 5.10 349.9 57.4

Steel tube and

BP

Steel tube 6.90

350.2 12.6

BP 26.6

Two Steel

tubes

Upper tube 9.80

350.5 36.5

Under tube 312.0

Note: The tested yield strength 350 N/mm² and young’s modulus 200 GPa of steel tube with external

diameter 48.3 mm and thickness 4 mm are used in this table.

Table 2-6 Load-carrying capacity for Option 2 near the center of scaffolding

load-carrying capacity (kN) and corresponding maximum stress (N/mm²)

Length of tube at each

side of anchor point

(No. of connections)

0.6 m (1) 1.2 m (2) 1.8 m (3) 2.4 m (4) 3.0 m (5)

Load case

(1) 12.95 13.15 13.20 13.20 13.20

298.9 58.9 313.2 59.0 312.8 58.9 312.4 58.8 304.9 58.1

(2) 12.90 13.10 13.10 13.15 13.20

303.8 58.5 348.1 58.4 342.1 58.3 333.9 58.5 325.4 58.5

(3) 12.80 12.10 12.10 12.40 12.50

298.0 58.1 350.6 47.0 349.5 47.0 350.8 46.5 349.9 50.1

Note 1: For each case, the upper value is load-carrying capacity and the under left and right values are

corresponding maximum stress in metal tube and bamboo ledger, respectively.

Note 2: Bold font represents failed component and its maximum stress.


48


Table 2-7 Load-carrying capacity for Option 2 near the edge of scaffolding

Load-carrying capacity (kN) and corresponding maximum stress (N/mm²)




0.6 m (1) 1.2 m (2) 1.8 m (3) 2.4 m (4) 3.0 m (5)

Load case

(1) 12.80 13.05 13.10 13.10 13.20

290.6 58.5 306.8 58.1 312.5 58.9 310.2 58.6 305.3 58.2

(2) 12.50 13.00 13.00 13.10 13.20

286.9 59.0 350.5 57.2 349.5 55.8 333.9 58.4 325.8 58.8

(3) 10.70 11.50 11.80 12.35 12.45

257.5 58.9 351.1 46.1 350.6 47.1 350.9 46.4 350.5 47.1




Table 2-8 Effect of tube thickness on load-carrying capacity for Option 2 load case (1)





0.6 m (1) 1.2 m (2) 1.8 m (3) 2.4 m (4) 3.0 m (5)

Tube

thickness

4.0 mm 12.80 13.05 13.10 13.10 13.20

290.6 58.5 306.8 58.1 312.5 58.9 310.2 58.6 305.3 58.2

3.2 mm 12.85 12.20 12.30 12.30 12.55

345.4 58.6 312.9 58.3 315.3 58.7 314.9 58.6 318.8 58.4

2.3 mm 11.70 11.20 11.20 11.40 11.60

350.0 46.3 333.2 58.5 332.8 58.5 335.4 58.7 340.9 58.6

Note 1: For each case, the upper value is load-carrying capacity and the under left and right values

are corresponding maximum stress in metal tube and bamboo ledger, respectively.



49


Table 2-9 Load-carrying capacity for various options under load case (1)

Reinforcement

options

Load-carrying

capacity

Maximum

Stress in

transom

Maximum

Stress in

ledger of

outer layer

Maximum

Stress in

ledger of

inner layer

Maximum

Stress in steel

tube

kN N/mm² N/mm² N/mm² N/mm²

Option 3 4.25 58.2 5.2 17.4 148.3

Option 3.1 8.80 56.3 16.2 39.7 350.1

Option 3.2 12.15 57.6 21.1 50.0 350.4

Note: Bold font represents failed component and its maximum stress.

Table 2-10 Load-carrying capacity for Option 3.2 near the center of scaffold


Length of tube at

each side of anchor

point (No. of pairs

of transoms)

0.6m (1) 1.2m (2) 1.8m (3) 2.4m (4) 3.0m (5)

Load

case

(1) 7.00 11.35 11.40 11.65 12.15

140.1 58.8 44.4 350.7 55.0 56.5 350.5 53.8 56.9 350.6 54.2 56.9 350.4 50.0 57.6

(2) 7.80 10.50 10.55 10.70 11.10

185.2 38.2 58.3 340.8 58.4 43.1 338.7 58.2 45.8 339.1 58.5 45.8 336.2 58.4 46.1

(3) 7.00 11.00 11.05 11.25 11.60

149.0 58.7 52.0 350.1 44.5 46.1 350.5 44.9 46.1 350.7 45.2 46.1 350.5 44.7 46.4

(4) 9.40 10.65 10.90 11.20 11.50

266.4 58.4 49.7 350.1 58.3 52.9 351.0 53.4 53.6 349.9 56.7 53.9 350.7 57.8 53.9

(5) 9.00 10.40 10.60 11.10 11.40

263.0 58.6 141.5 351.0 52.6 42.8 349.7 52.4 42.5 350.6 52.5 42.8 350.4 52.4 43.1

Note 1: For each case, the upper value is load-carrying capacity and the under left, middle and right values

are corresponding maximum stress in metal tube, main ledger of inner layer and transom, respectively.



50


Table 2-11 Summary of load-carrying capacity for Option 2


Tube Size 48.3 × 4.0 mm 48.3 × 3.2 mm 48.3 × 2.3 mm




0.6m (1) 1.2m (2) 0.6m (1) 1.2m (2) 0.6m (1) 1.2m (2)

Load case

(1) 12.80 13.05 12.85 12.20 11.70 11.20

290.6 58.5 306.8 58.1 345.4 58.6 312.9 58.3 350.0 46.3 333.2 58.5

(2) 12.50 13.00 12.50 12.00 11.45 10.45

286.9 59.0 350.5 57.2 336.2 58.0 349.4 54.5 350.6 41.6 349.2 53.1

(3) 10.70 11.50 10.90 10.10 10.20 8.20

257.5 58.9 351.1 46.1 303.7 58.5 350.9 44.6 349.7 48.9 349.7 42.0




Table 2-12 Load-carrying capacity for Option 3.2 with a tube length of 1.2 m


Tube size 48.3 × 4.0 mm 48.3 × 3.2 mm 48.3 × 2.3 mm

Load case

(1) 11.10 10.55 9.30

349.9 56.2 56.9 349.2 50.6 57.2 350.9 45.6 57.2

(2) 9.75 9.60 8.60

307.3 58.1 43.8 338.4 58.2 44.4 349.5 54.4 44.8

(3) 10.90 9.90 9.05

350.6 50.3 43.8 350.2 45.9 44.8 350.1 44.5 46.1

(4) 10.65 9.80 8.70

350.3 56.7 53.9 350.3 56.1 52.9 351.0 51.3 52.3

(5) 10.20 9.40 8.20

349.5 51.3 42.5 350.4 48.9 42.8 350.1 43.9 41.8

Note 1: For each case, the upper value is load-carrying capacity and the under left, middle and right

values are corresponding maximum stress in metal tube, main ledger of inner layer and transom,

respectively.



51


Table 2-13 Results of static point load test for test cases (1) to (6)

(a) Test case (1) under 12 kN static point load

Component

Strain Young's

modulus 𝐸

Cross section area 𝐴 Measured axial

force

Mean Std Outside

diameter Thickness 𝐴 Mean Std

× 10−6𝜀 kN/mm² mm mm mm² kN

Axial

force

(front)

Post 1 -37.1 6.1 7.60 112.0 11.6 3659.5 -1.03 0.17

Standard 3 -42.8 6.8 8.55 43.6 5.6 665.8 -0.24 0.04

Post 2 -382.8 41.4 7.60 102.2 10.6 3043.3 -8.85 0.96

Standard 4 -35.6 7.9 8.55 45.2 5.8 715.3 -0.22 0.05

Post 3 -13.6 3.8 7.60 107.9 11.2 3394.2 -0.35 0.10

Brace 2 -81.6 19.1 8.55 51.9 6.6 942.5 -0.66 0.15

Metal strut -62.5 7.6 200 48.3 3.2 453.4 -5.67 0.69

Component

Strain Young's

modulus 𝐸

Section of modulus of area 𝑍 Measured

bending moment

Mean Std Outside

diameter Thickness 𝑍 Mean Std

× 10−6𝜀 kN/mm² mm mm cm³ kN·m

Bending

moment

Upper tube 1238.5 127.5 200 48.3 4.0 5.7 1.42 0.15

Under tube 1107.8 80.7 200 48.3 4.0 5.7 1.27 0.09

(b) Test case (2) under 12 kN static point load

Component

Strain Young's

modulus 𝐸


force

Mean Std Outside



Axial

force

(front)

Post 1 -38.8 7.0 7.60 112.0 11.6 3659.5 -1.08 0.19

Standard 3 -37.1 5.9 8.55 43.6 5.6 665.8 -0.21 0.03

Post 2 -365.9 64.3 7.60 102.2 10.6 3043.3 -8.46 1.49

Standard 4 -37.9 5.4 8.55 45.2 5.8 715.3 -0.23 0.03

Post 3 -17.7 3.9 7.60 107.9 11.2 3394.2 -0.46 0.10

Brace 2 -77.3 14.2 8.55 51.9 6.6 942.5 -0.62 0.11

Metal strut -63.8 5.3 200 48.3 3.2 453.4 -5.79 0.48

Component

Strain Young's

modulus 𝐸


bending moment

Mean Std Outside



Bending

moment

Upper tube 1461.1 89.1 200 48.3 3.2 4.8 1.40 0.09

Under tube 1353.2 102.7 200 48.3 3.2 4.8 1.30 0.10


52


(c) Test case (3) under 8 kN static point load

Component

Strain Young's

modulus 𝐸


force

Mean Std Outside



Axial

force

(front)

Post 1 -105.8 9.7 7.60 112.0 11.6 3659.5 -2.94 0.27

Standard 1 -45.8 6.4 8.55 44.9 5.7 705.2 -0.28 0.04

Standard 2 -89.3 12.6 8.55 44.2 5.7 685.4 -0.52 0.07

Standard 3 -48.0 7.8 8.55 43.6 5.6 665.8 -0.27 0.04

Post 2 -142.5 17.1 7.60 102.2 10.6 3043.3 -3.30 0.40

Metal strut -46.3 4.7 200 48.3 3.2 453.4 -4.19 0.42

Component

Strain Young's

modulus 𝐸


bending moment

Mean Std Outside



Bending

moment

Upper tube 806.0 62.4 200 48.3 4.0 5.7 0.92 0.07

Under tube 628.3 72.0 200 48.3 4.0 5.7 0.72 0.08

(d) Test case (4) under 8 kN static point load

Component

Strain Young's

modulus 𝐸


force

Mean Std Outside



Axial

force

(front)

Post 1 -104.6 14.7 7.60 112.0 11.6 3659.5 -2.91 0.41

Standard 1 -33.0 5.0 8.55 44.9 5.7 705.2 -0.20 0.03

Standard 2 -35.0 7.1 8.55 44.2 5.7 685.4 -0.21 0.04

Standard 3 -31.0 6.5 8.55 43.6 5.6 665.8 -0.18 0.04

Post 2 -164.5 20.2 7.60 102.2 10.6 3043.3 -3.80 0.47

Metal strut -39.6 4.9 200 48.3 3.2 453.4 -3.59 0.45

Component

Strain Young's

modulus 𝐸


bending moment

Mean Std Outside



Bending

moment

Upper tube 1467.7 137.6 200 48.3 2.3 3.6 1.07 0.10

Under tube 1339.5 100.3 200 48.3 2.3 3.6 0.98 0.07


53


(e) Test case (5) under 8 kN static point load

Component

Strain Young's

modulus 𝐸


force

Mean Std Outside



Axial

force

(front)

Post 1 -33.4 5.2 7.60 112.0 11.6 3659.5 -0.93 0.15

Standard 1 -13.1 2.2 8.55 44.9 5.7 705.2 -0.08 0.01

Standard 2 -20.0 4.3 8.55 44.2 5.7 685.4 -0.12 0.03

Standard 3 -14.6 3.1 8.55 43.6 5.6 665.8 -0.08 0.02

Post 2 -114.3 15.1 7.60 102.2 10.6 3043.3 -2.64 0.35

Axial

force

(back)

Post 4 -34.0 5.9 8.55 49.0 6.3 841.3 -0.24 0.04

Post 5 -177.5 20.4 8.55 49.3 6.3 852.2 -1.29 0.15

Post 6 -169.0 11.8 8.55 51.6 6.6 930.9 -1.35 0.09

Component

Strain Young's

modulus 𝐸

Section of modulus of area 𝑍 Measured bending

moment

Mean Std Outside



Bending

moment

Outer tube 993.2 112.6 200 48.3 3.2 4.8 0.95 0.11

Inner tube 1217.0 88.7 200 48.3 3.2 4.8 1.17 0.09

(f) Test case (6) under 8 kN static point load

Component

Strain Young's

modulus 𝐸


force

Mean Std Outside



Axial

force

(front)

Post 1 -44.0 7.8 7.60 112.0 11.6 3659.5 -1.22 0.22

Standard 1 -16.0 3.3 8.55 44.9 5.7 705.2 -0.10 0.02

Standard 2 -19.0 4.3 8.55 44.2 5.7 685.4 -0.11 0.03

Standard 3 -17.0 2.9 8.55 43.6 5.6 665.8 -0.10 0.02

Post 2 -106.1 12.1 7.60 102.2 10.6 3043.3 -2.45 0.28

Axial

force

(back)

Post 4 -65.6 7.1 8.55 49.0 6.3 841.3 -0.47 0.05

Post 5 -175.6 30.0 8.55 49.3 6.3 852.2 -1.28 0.22

Post 6 -147.2 12.6 8.55 51.6 6.6 930.9 -1.17 0.10

Component

Strain Young's

modulus 𝐸

Section of modulus of area 𝑍 Measured bending

moment

Mean Std Outside



Bending

moment

Outer tube 1321.0 96.5 200 48.3 2.3 3.6 0.96 0.07

Inner tube 1407.0 143.7 200 48.3 2.3 3.6 1.03 0.10


54


Table 2-14 Comparison of computer analysis with static point load test

(a) Test case (1) under 12 kN static point load

Component Measured mean

value Analyzed value

Difference

|𝑎𝑛𝑎𝑙𝑦𝑧𝑒𝑑 − 𝑚𝑒𝑎𝑠𝑢𝑟𝑒𝑑

𝑚𝑒𝑎𝑠𝑢𝑟𝑒𝑑| × 100%

Axial force

(front)

(kN)

Post 1 -1.03 -1.29 25%

Standard 3 -0.24 -0.37 52%

Post 2 -8.85 -9.68 9%

Standard 4 -0.22 -0.33 51%

Post 3 -0.35 -0.37 5%

Brace 2 -0.66 -0.82 25%

Metal strut -5.67 -6.00 6%

Bending

moment

(kN·m)

Upper tube 1.42 1.26 11%

Under tube 1.27 1.39 10%

(b) Test case (2) under 12 kN static point load



Difference


𝑚𝑒𝑎𝑠𝑢𝑟𝑒𝑑|

× 100%

Axial force

(front)

(kN)

Post 1 -1.08 -1.30 20%

Standard 3 -0.21 -0.33 56%

Post 2 -8.46 -9.41 11%

Standard 4 -0.23 -0.34 47%

Post 3 -0.46 -0.61 34%

Brace 2 -0.62 -0.85 37%

Metal strut -5.79 -5.99 3%

Bending

moment

(kN·m)

Upper tube 1.40 1.49 6%

Under tube 1.30 1.37 5%


55


(c) Test case (3) under 8 kN static point load



Difference



Axial force

(front)

(kN)

Post 1 -2.94 -3.74 27%

Standard 1 -0.28 -0.34 23%

Standard 2 -0.52 -0.36 31%

Standard 3 -0.27 -0.33 21%

Post 2 -3.30 -4.26 29%

Metal strut -4.19 -3.98 5%

Bending

moment

(kN·m)

Upper tube 0.92 0.87 6%

Under tube 0.72 0.77 7%

(d) Test case (4) under 8 kN static point load



Difference



Axial force

(front)

(kN)

Post 1 -2.91 -3.74 29%

Standard 1 -0.20 -0.20 1%

Standard 2 -0.21 -0.31 51%

Standard 3 -0.18 -0.20 13%

Post 2 -3.80 -4.26 12%

Metal strut -3.59 -3.99 11%

Bending

moment

(kN·m)

Upper tube 1.07 1.16 8%

Under tube 0.98 1.08 11%


56


(e) Test case (5) under 8 kN static point load



Difference



Axial force

(front)

(kN)

Post 1 -0.93 -1.09 17%

Standard 1 -0.08 -0.09 14%

Standard 2 -0.12 -0.14 19%

Standard 3 -0.08 -0.12 44%

Post 2 -2.64 -2.87 9%

Axial force

(back)

(kN)

Post 4 -0.24 -0.25 2%

Post 5 -1.29 -1.80 39%

Post 6 -1.35 -1.80 34%

Bending

moment

(kN·m)

Outer tube 0.95 0.91 4%

Inner tube 1.17 0.99 15%

(f) Test case (6) under 8 kN static point load



Difference



Axial force

(front)

(kN)

Post 1 -1.22 -1.40 14%

Standard 1 -0.10 -0.09 7%

Standard 2 -0.11 -0.15 35%

Standard 3 -0.10 -0.13 34%

Post 2 -2.45 -2.63 7%

Axial force

(back)

(kN)

Post 4 -0.47 -0.53 12%

Post 5 -1.28 -1.80 41%

Post 6 -1.17 -1.75 49%

Bending

moment

(kN·m)

Outer tube 0.96 1.10 14%

Inner tube 1.03 1.12 9%


57


Table 2-15 Summary for the static point load test

Reinforcement options and

test cases

Assigned

load

𝐷𝑖𝑓𝑓𝑒𝑟𝑒𝑛𝑐𝑒 = |𝑎𝑛𝑎𝑙𝑦𝑧𝑒𝑑 − 𝑚𝑒𝑎𝑠𝑢𝑟𝑒𝑑


Bamboo Metal tube

Max Mean Std Max Mean Std

Option 2 Test case (1)

12 kN 52% 28% 18% 11% 9% 2%

Test case (2) 56% 34% 15% 6% 5% 1%

Option 2 Test case (3)

8 kN 31% 26% 4% 7% 6% 1%

Test case (4) 51% 21% 17% 11% 10% 1%

Option 3.2 Test case (5)

8 kN 44% 22% 14% 15% 10% 6%

Test case (6) 49% 25% 16% 14% 12% 3%

Total 56% 26% 16% 15% 8% 3%

Table 2-16 Results of drop load test

(a) Test case (1)

Test

series

Test

mass

Free

fall

Drop

force (kN) Results Test Standards Pass/Fail

1

100kg 3.2m

12.38 No

component

failed

EN 795 (2012) & ANSI

Z359.1 (2007) & OSHA

1926.502

Pass 2 12.35

3 12.08

(b) Test case (2)

Test

series

Test

mass

Free

fall

Drop


1

100kg 3.2m

12.80 No

component

failed

EN 795 (2012) & ANSI

Z359.1 (2007) & OSHA

1926.502

Pass 2 12.94

3 12.14

(c) Test case (3)

Test

series

Test

mass

Free

fall

Drop force

(kN) Results Test Standards Pass/Fail

1

100kg

2.9m 9.18 No component

failed ANSI Z359.1 (2007)

& OSHA 1926.502 Pass

2 2.9m 8.87

3 3.1m 11.96 Bamboo ledger

failed at tube end


58


(d) Test case (4)

Test

series

Test

mass

Free

fall

Drop


1

100kg


failed

ANSI Z359.1 (2007) &

OSHA 1926.502 Pass 2 2.8m 8.69

3 3.1m 11.86

(e) Test case (5)

Test

series

Test

mass

Free

fall

Drop


1

100kg


failed

ANSI Z359.1 (2007) &

OSHA 1926.502 Pass 2 2.0m 8.58

3 2.0m 8.04

(f) Test case (6)

Test

series

Test

mass

Free

fall

Drop force

(kN) Results Test Standards Pass/Fail

1

100kg

2.0m 8.10 No

component

failed

ANSI Z359.1 (2007) &

OSHA 1926.502 Pass 2 2.0m 8.32

3 2.0m 8.19


59


Table 2-17 Anchorages for DLBS with 3 standards and a span of 0.6 m

Reinforcement

options

Load-carrying

capacity

Minimum tube

thickness T &

length L

Location of

anchor point

Connecting

devices Illustration

Option 2:

adding two

steel tubes to

two adjacent

bamboo

ledgers

12 kN T=3.2 mm,

L=0.6 m

Only the

intersection

between post

and ledger

No specific

requirements

8 kN T=2.3 mm,

L=0.6 m

All

intersections

between

post/standard

and ledger

Using energy

absorber

lanyard/

Self-retracting

lifeline

marked with

MAF ≤ 4 kN

Option 3.2:

platform

reinforcement

8 kN T=2.3 mm,

L=1.2 m

All anchor

points in the

middle region

of tube

Note 1: The tube length represents minimum tube length at each side of anchor point;

Note 2: The load case (2) with steel tube length 0.6m at the position most close to the edge shouldn’t be

used as anchorage, see Section 2.3.2.

Anchor

points

Anchor

points

Anchor

region


60


Table 2-18 Reinforced anchorages for different bamboo scaffoldings

(a) Anchorages for DLBS with 3 standards between posts and span of 0.75 m

Reinforcement

options

Load-carrying

capacity

Minimum tube

thickness T &

length L

Location of

anchor point

Connecting


Option 2:

adding two

steel tubes to

two adjacent

bamboo

ledgers

12 kN T=4.0 mm,

L=0.75 m

Only the

intersection

between post

and ledger

No specific

requirements

8 kN T=4.0 mm,

L=1.5 m

All

intersections

between

post/standard

and ledger

Using energy

absorber

lanyard/

Self-retracting

lifeline

marked with

MAF ≤ 4 kN

Option 3.2:

platform

reinforcement

8 kN T=3.2 mm,

L=1.5 m

All anchor

points in the

middle region

of tube


Note 2: The load case (2) with steel tube length 0.6m at the position most close to the edge shouldn’t be used

as anchorage, see Section 2.3.2.

Anchor

points

Anchor

points

Anchor

region


61


(b) Anchorages for DLBS with 1 standard between posts and span of 0.6, 0.75 or 0.9

m

Span Load-carrying

capacity

Minimum tube

thickness T &

length L

Location of

anchor point

Connecting


0.6 m

8 kN

T=2.3 mm,

L=1.2 m

All anchor

points in the

middle region

of tube

Using energy

absorber

lanyard/

Self-retracting

lifeline

marked with

MAF ≤ 4 kN

0.75 m T=3.2 mm,

L=1.5 m

0.90 m T=4.0 mm,

L=1.8 m


Note 2: This table only shows analytical results of Option 3.2 and the application of Option 2 for this table is

the same as in Table 2-18 (c).

Anchor

region 0.6/0.75/0.9 m


62


(c) Anchorages for SLBS with 1 standard between posts and span of 0.6, 0.75 or 0.9

m

Table 2-19 Load-carrying capacity (in kN) of one anchor point for Option 2 with more

Span Load-carrying

capacity

Minimum tube

thickness T &

length L

Location of

anchor point

Connecting


0.6 m

12 kN T=3.2 mm,

L=0.6 m

Only the

intersection

between post

and ledger

No specific

requirements

8 kN T=2.3 mm,

L=0.6 m

All

intersections

between

post/standard

and ledger

Using energy

absorber

lanyard/

Self-retracting

lifeline marked

with MAF ≤ 4

kN

0.75 m

12 kN T=4.0 mm,

L=1.5 m

Only the

intersection

between post

and ledger

No specific

requirements

8 kN T=2.3 mm,

L=0.75 m

All

intersections

between

post/standard

and ledger

Using energy

absorber

lanyard/

Self-retracting

lifeline marked

with MAF ≤ 4

kN

0.90 m 8 kN T=2.3 mm,

L=0.9 m

All

intersections

between

post/standard

and ledger

Using energy

absorber

lanyard/

Self-retracting

lifeline marked

with MAF ≤ 4

kN


Note 2: The connection at the position most close to the edge is also not recommended as anchorage.

Anchor

points

Anchor

points

0.6 m

0.6 m

Anchor

points

0.75 m

Anchor

points

0.75 m

Anchor

points

0.9 m


63


steel struts

Critical

case Configuration

Steel strut covering whole

reinforced region

Only one

steel strut

connecting

anchor

points Anchor point A B

(1)

12.8 6.0 - 12.8

(2)

12.5 12.5 5.8 12.2

(3)

10.3 5.7 - 10.7

(4)

8.0 10.0 6.5 8.2

Anchor

point

A

Anchor

point

A

Anchor

point

A

Anchor

point

A B

B


64


Table 2-20 Load-carrying capacity for Option 2 under two users

Configuration

No. of spans

between the

two users

Load-carrying

capacity for each

anchor point (kN)

1 6.5

2 8.7

3 10.3

4 10.6

Note: The load case (3) near the edge of scaffolding was chosen as the anchorage for “user 1”

because it offers the minimum load-carrying capacity among all three load cases for Option 2.

User 1 User 2

User 1 User 2

User 1 User 2

User 1 User 2


65


Chapter 3 Anchorage for Bamboo

Scaffolding: Other Options

3.1 A safer scaffolding erection process

It is noted that Clause 5.3.1 (n) of the Code of Practice for Bamboo Scaffolding Safety

[17] states that “No shock loading on the platforms should be allowed.” It is believed

that such a restriction might have been originated from the consideration that any shock

loading acting on the platforms would result in vibration of the platforms and endanger

workmen on the platforms. Despite that the reinforcement options presented in the

previous chapter have been validated numerically and experimentally. Such a concern

remain valid and might hinder the overall acceptance of these reinforcement options.

Also Clause 5.3.1 (t) “When a scaffolder or workman has to work in a place where it is

impracticable to erect a safe working platform or to provide safe access and egress, the

use of safety nets and safety belt attached to a secure anchorage point or an

independent lifeline throughout the work is required.” suggests that safety belt attached

to a secure anchorage point or an independent lifeline is an alternative option to a safe

working platform. Such a safe working platform is usually not available till the last

stage of erection due to the reason that it appears to be more time efficient to construct

the outer layer as a whole before erecting inner layer and the working platforms [11].

In this section, a safer scaffolding erection process is proposed to address the safety

issue during the erection of bamboo scaffolding. This erection process ensures that a

safe working platform and necessary guardrails are available during the erection such

that the safety of scaffolders and workmen can be better protected without the need of

attaching safety belt to a secure anchorage or an independent lifeline. This proposed

erection process complies with the erection sequence for metal scaffolding described

in [18]. This erection sequence consists of the following steps:


66


(1) Fig. 3-1 (a): the standards and posts for the next lift above are installed from a fully

planked platform (the existed lift);

(2) Fig. 3-1 (b): the main ledgers of both inner and outer layer for the next lift above

are installed;

(3) Fig. 3-1 (c): the guardrails (intermediate guardrail and top guardrail) and edge

protection for the lift above are then installed;

(4) Fig. 3-1 (d): the transoms and planks for the lift above are installed to form

working platform above;

(5) Fig. 3-1 (e): access the new working platform and install toe-boards; and

(6) Fig. 3-1 (f): install other components such as putlogs or metal brackets from the

new working platform.

Note that when working from a fully planked platform to erect standards/posts (where

the standard/post joint is 1 to 1.5 m above the existed platform level) and guardrails

for the lift above, several possible options such as a temporary ladder or platform as

shown in Fig. 3-2 are possible for the scaffolders to reach the desired height [18]. This

proposed erection process complying with the scaffolding requirements has been

modeled using a BIM software, Revit and Navisworks, for illustrative purpose.

3.2 Anchorages for bamboo scaffolding above roof level

For some special conditions, regional reinforcement on the scaffolding itself as

described in the previous chapter may not be applicable. These conditions include

when the scaffolding is erected above any permanent structure. The portion of

bamboo scaffoldings is more flexible and not suitable for any regional reinforcement

option proposed above. According to Clause 5.3.1 (b): “The height of the bamboo

scaffold erected at any side should not be higher than the topmost part of the

building/structure by one storey.” These above-the-roof-top scaffolding might be


67


several ledges’ height (see Fig. 3-3) and could pose a threat to scaffolders or workmen

as a secure anchorage point or an independent lifeline above the height of

scaffolders/workmen is almost non-existent.

It could be anticipated that the work above roof level would require mostly horizontal

movement. Hence, a horizontal lifeline (HLL) system will be an efficient way to

protect workmen from the consequence of falling. This HLL system can be either

permanent or temporary. As summarized in various standards including ANSI Z359.6

[6], CSA Z259.16 [7] and CSA Z259.13 [19], a good HLL system should meet the

following requirements:

(1) Their components and anchorages are of adequate strength to withstand the

maximum arrest load (MAL) or maximum arrest force (MAF).

(2) The MAF experienced by the user is within acceptable limits (such as 6 kN as

described above) to minimize the possibility of injury.

(3) Clearance in the fall path is adequate to prevent the user from hitting the ground or

any other obstruction.

(4) For a HLL system used to support bamboo scaffolding, the anchorage device should

be fixed on a permanent structure. Expansion bolts or rebar can be used to fix the

anchorages.

(5) A HLL system could be temporary or permanent and should allow at least two

workmen attached to it simultaneously.

(6) A stanchion can also be considered as a possible option for offering anchorage

points above the roof top.

According to the above requirement for selection of a HLL system, Fig. 3-4 shows a

typical HLL system produced by DBI-SALA [14]. The system consists of multi-span

horizontal lifeline, 2.3 m tall posts, different types of bases and various components

which make it more flexible to suit different types of structures.


68


3.3 Anchorages for bamboo scaffolding below roof level

When workers perform jobs on platform below roof level, the HLL system is also an

effective way to provide anchorages for needed horizontal movement. The stanchion

is not necessary and the configuration of the HLL system could be simpler. The

requirements (1)-(5) described above should be followed for choosing an applicable

system. When the HLL system is fixed on vertical concrete wall, the worker should be

able to reach the lifeline easily with his/her arm in order to travel across the scaffolding.

Most commercially available HLL products are single-span and allow a maximum

span up to 18 m. If the largest span allowed by manufacturer is not enough for worker

to perform their jobs, another single-span HLL system can be used independently. Fig.

3-5 gives an example of this type of system produced by Miller [15]. A Miller SkyGrip

Wire Rope Lifeline may be used in conjunction with approved Miller brand anchorage

connectors to provide a temporary HLL system that is quick and easy to install.


69


(a) Standards and posts (b) Main ledgers

(c) Guardrails and edge protection (d) Transoms and planks

(e) Toe-boards (f) Other components

such as putlogs and metal bracket

Fig. 3-1 A safer bamboo scaffolding erection process


70


(a) Temporary ladder used for erection

(b) Temporary platform supported on ledgers/guardrails

(c) Proprietary temporary edge protection system

Fig. 3-2 Illustration of various options to facilitate the new erection process


71


Fig. 3-3 Bamboo scaffoldings above roof level

Fig. 3-4 Configuration of a HLL system with different anchorage options [14]

Fig. 3-5 Miller SkyGrip Wire Rope Lifeline and anchorage [15]


72


Chapter 4 Use of Mixed Scaffolding

Recently, there are some scaffoldings constructed using a mixture of both bamboo and

metal tubes. While there are respective codes of practice for bamboo scaffolding safety

[17] and metal scaffolding safety [20], there is no specific guideline governing the safe

usage of this hybrid type of scaffoldings. These mixed scaffoldings have created a

series of new technical challenges that need to be addressed. In this chapter, issues

relating to the safe usage of mixed scaffoldings were investigated numerically and

validated experimentally. These issues are reported in the following.

4.1 Mechanical properties of connection

In mixed scaffoldings, steel tube is the primary load-bearing component while

bamboo serves as the secondary component. Kao Jue (BP) is commonly used in the

mixed scaffolding as it has similar external diameter as that of steel tube. There are

generally two types of steel tube used in mixed scaffolding (see Fig. 4-1): steel tube

with smooth surface (normal steel tube) and steel tube with anti-sliding bumps on the

surface (anti-sliding steel tube). There are a few possible types of connection in mixed

scaffoldings: (a) bamboo-bamboo; (b) normal steel tube-bamboo; (c) anti-sliding steel

tube-bamboo; (d) anti-sliding steel tube-normal steel tube; and (e) normal steel

tube-normal steel tube. Note that except type (e), all the other types of connection are

fastened using the same plastic stripes as used in bamboo scaffoldings. Metal couplers

are used for type (e) connection. While the mechanical properties for bamboo-bamboo

connection have been reported in Section 2.1, the mechanical properties for the other

types of connection were obtained experimentally and summarized in the following.

4.1.1 Normal steel tube-bamboo connection

A series of tests were conducted to obtain the slippage stiffness and rotational stiffness


73


of connection between normal steel tube and bamboo component (BP). Also, the effect

of bamboo node was considered in the tests. Fig. 4-2 shows the test setup for the

slippage stiffness and the rotational stiffness. In most normal steel tube-bamboo

connections, the bamboo serves as a horizontal member while the steel tube is used as

a vertical load-bearing column. A total of five load-displacement curves were obtained

and plotted in Fig. 4-3 for the slippage stiffness. The mean slippage stiffness before

reaching the maximum slippage resistance is 60.6 kN/m and the average minimum

resistive force during slippage and up to 30 mm displacement is 0.76 kN. Three

load-displacement curves and the corresponding M − θ curves were obtained and

plotted in Fig. 4-4 for the rotational stiffness. The mean rotational stiffness against the

direction of the fastening tie is found to be 0.11 kN∙m/rad.

Table 4-1 summaries the resistance for the normal steel tube-bamboo connection. As a

conservative measure, the connection resistance without nodes was taken as the

minimum slipping force during the initial 30 mm displacement. For connection with

the presence of bamboo node, there were two possible failure modes: (a) fracture of

plastic stripes and (b) the plastic stripes slipping over the node. For connection without

the presence of bamboo nodes, the failure mode was the slipping between two

members. Table 4-2 summaries the rotational stiffness for the normal steel-bamboo

connection. It is noted that the connection between two normal steel tubes fastened by

plastic stripes were also shown in the two tables for comparison. For simplicity, the

slippage stiffness of normal steel tube (vertical)-bamboo (horizontal) connection was

used as the representative mechanical property for this type of connection in the

modeling. In SAP2000, the multi-linear element and panel zone are also used to model

the bilinear stiffness behavior against rotation and the multi-linear slippage stiffness

behavior of the connection as shown in Fig. 4-5 (a) and (b).


74


4.1.2 Anti-sliding steel tube-bamboo/normal steel tube connection

For connection involving anti-sliding steel tube, the anti-slide steel tube is always used

as a vertical component such that the anti-sliding bump can take effect to prevent

slippage of horizontal component which can be either bamboo (BP) or normal steel

tube. Fig. 4-6 shows a typical setup for anti-sliding steel tube-bamboo/normal steel

tube connection test. For this type of connection, the orientation of anti-sliding bumps

would be an issue affecting its mechanical properties. Hence, tests were conducted with

different orientation angles of the bumps with respect to the perpendicular direction of

the post-ledger plane. A total of five different angles, 0°，45°, 90°, 135° and 180° were

selected to represent different connecting situations. Each angle was tested at least 5

times (see Fig. 4-7).

For connection tests with 0°, 45°, 90°, the failure modes was always splitting and

slipping of plastic stripes over the bump as seen in Fig. 4-8. Two typical

load-displacement curves with initial slippage and without initial slippage for

connection test with 0° are shown in Fig. 4-9. For the 135° orientation, the test results

obtained were very similar to those of normal steel tube-bamboo connection shown in

the previous section. This was due to the reason that the plastic strip was not in direct

contact with the bumps. For 180° orientation of anti-sliding steel tube-bamboo

connection, the failure mode was the damage of bamboo surface at the connection

between bamboo and the anti-sliding steel tube as shown in Fig. 4-10. For 180°

orientation of anti-sliding steel tube-normal steel tube connection, the failure mode was

the rotation of horizontal tube as shown in Fig. 4-11.

The slippage resistance and corresponding slippage displacement are summarized in

Table 4-3. The average ultimate slippage resistance decreased as the orientation angle

increasing from 0° to 135°. Results show that 135° orientation angle has the smallest

connection resistance among all cases considered for the anti-sliding steel


75


tube-bamboo/normal steel tube connection. Based on these results, it is recommended

that the orientation angle of the anti-sliding steel tube for this type of connection should

be within [-90°, 90°]. When a transom is also present at the connection, the orientation

of the anti-sliding steel tube is recommended to be within [0°, 90°] or [-90°, 0°]

depending the configuration as shown in Fig. 4-12.

For the modeling of this type of connection, the average connection resistance and

average total displacement of 0°, 45° and 90° orientation were adopted. Linear

elements were selected to model the slippage behavior including the average

connection resistance and the average total displacement. Table 4-4 and Table 4-5

summarize the connection resistance and the total displacement, respectively. Note

that bilinear stiffness behavior against rotation for connection between anti-sliding

tube and bamboo or normal steel tube is assumed to be the same as described in

Section 4.1.1. In summary, the linear slippage stiffness of the connection was modeled

as follows:

For anti-sliding tube (vertical)-bamboo (horizontal) connection:

Slippage force = 51.21 kN/m × displacement

For anti-sliding tube (vertical)-normal steel tube (horizontal) connection:

Slippage force = 57.83 kN/m × displacement

4.1.3 Normal steel tube-normal steel tube connection

All connections between two normal steel tubes were fastened by couplers as shown

in Fig. 4-13. Various types of couplers are available such as the right angle coupler

which is used to join tubes at right angles and the swivel coupler for connecting

components at flexible angles. Mechanical properties for different types of couplers

are summarized in Table 4-6 based on BS EN 74-1 [21] and BS 12811-1 [22].


76


4.1.4 Thermal effect of steel tube on connection

In this section, the thermal expansion effect of steel tube on scaffolding connection

due to temperature change was investigated. The change in circumference of steel tube

due to temperature change could be approximated as:

𝑑𝐶 = 𝜋𝑑1 − 𝜋𝑑0 = 𝜋𝑑0(𝑑𝑡)𝛼

where

𝑑𝐶 is change in circumference (mm);

𝑑0 and 𝑑1 are initial diameter and final diameter (mm), respectively;

𝑑𝑡 is temperature change (oC); and

𝛼 is linear thermal expansion coefficient (10 × 10-6/°C according to Annex E of BS

5975 [23]).

For a steel pipe with outer diameter 𝑑0 = 48.3 𝑚𝑚 and an assumed temperature

change of 𝑑𝑡 = ±25℃, the final outer diameter 𝑑1 would be 48.3 ± 0.012 𝑚𝑚.

According to previous research [1], the dimension of the fastening tie was width = 6

mm and thickness = 1 mm. The Young’s modulus of fastening tie was about 𝐸 =

2 𝑘𝑁/𝑚𝑚² . The force change ∆𝐹 in the fastening tie of steel tube-bamboo

connection due to temperature changing of 25℃ is about:

∆𝐹 = (𝑑1 − 𝑑0) × 𝜋 × 𝐸 × 𝐴/(𝑑0 × 𝜋 × 2) = 1.49 𝑁

Note that the outer diameter of bamboo is assumed to be the same as steel tube. The

force change in the fastening tie of an anti-sliding steel tube and normal steel tube

connection due to a temperature change of 25℃ should be doubled (2.98 kN). In

previous report [1], it was also found that the mean tensile force in the fastening tie

during fixing the joints is about 23 N and the ultimate tensile force of fastening tie is


77


1,135 N. In summary, a temperature change of ±25℃ would not affect the property

of scaffolding connections very much.

4.2 Design and modeling of mixed scaffolding

4.2.1 Design of mixed scaffolding

The design of mixed scaffolding was based on the structural form of traditional double

layered bamboo scaffoldings (DLBS) such as the one shown in Fig. 4-14 [12]. As

shown in Fig. 4-15, there are three possible types for the mixed scaffolding:

Type 1: Posts and bracings of a DLBS are replaced by anti-sliding steel tubes.

Type 2: Type 1 plus main ledgers replaced by normal steel tubes.

Type 3: Posts, main ledgers and bracings of a DLBS are replaced by normal steel

tubes and connected using couplers.

In this study, the size of steel tube is 48.3 × 2.3 mm (outer diameter × thickness) and

its characteristic yield strength = 235 N/mm² and young’s modulus E = 200 GPa.

4.2.2 Modeling of mixed scaffolding

As the design of mixed scaffolding was based on the traditional DLBS, the finite

element modeling of bamboo components was the same as that in Section 2.2.2. Also,

nonlinear analysis with P-Delta effect has been considered in the analysis. Details of

the modeling are outlined as follow:

(1) The posts, main ledgers, and diagonal bracings substituted by steel tubes were

modeled as members with circular hollow cross sections.

(2) The vertical, horizontal and rotational stiffness of the joint between bamboo


78


members or between bamboo and steel tube members were modeled using

multi-linear elements and panel zones. For simplicity, the out-of-plane relative

displacement at connection was ignored.

(3) It should be noted that in each main ledger-post/standard fastening, there was

always a transom-post/standard fastening connected at the same location. Thus,

the total connection resistance, vertical stiffness and horizontal stiffness should be

doubled. The rotational stiffness was not doubled because the post/standard, main

ledger and transom were orthogonal to each other.

(4) For Type 3 mixed scaffolding, the joints between steel tubes fastened by right angle

couplers were assumed to be rigid connections. Those non-orthogonal connections

fastened by swivel couplers were modeled as panel zones with a simple constraint

which could not transmit moments.

(5) The bamboo transoms linking up the inner layer and outer layer ledgers were

simulated as pinned connection.

(6) For Type 1 and Type 2 mixed scaffolding, putlogs were anti-sliding steel tubes

fastened to scaffolding by plastic stripes and connected to wall by anchor bolts.

For Type 3 mixed scaffolding, putlogs were normal steel tubes fastened to

scaffolding by metal couplers and connected to wall with specific anchorages.

These putlogs were modeled with only inward and outward restraints and were

used to prevent inward and outward movement of the scaffoldings.

(7) All the main posts were assumed to be pinned at the bottom. The braces were only

connected to main posts of the outer layer.

4.3 Comparison among three types of mixed scaffolding

In this section, the three mixed scaffolding types were compared with regard to the

following aspects:

(1) Construction cost and time;


79


(2) Weight and weight distribution; and

(3) Load-carrying capacity.

The analytical result of pure bamboo scaffolding was also provided for comparison.

The configuration and dimensions of bamboo scaffolding and mixed scaffoldings

were assumed to be the same with a platform height of 2 m and width of 0.6 m as

shown respectively in Fig. 4-14 and Fig. 4-15.

4.3.1 Construction cost and time

To compare the cost of these mixed scaffoldings, a one-bay (1.3 m) unboarded lift as

shown in Fig. 4-16 was selected for analysis. The work platform board and toe-board

were not included as they could all be used on these scaffoldings. Table 4-7 summaries

the material required for constructing a one-bay unboarded lift for the bamboo

scaffolding and the three mixed scaffoldings. The actual length of a scaffolding

component was calculated by multiplying its net length (physical size of the

scaffolding) with an overlap factor. The overlap factors were determined according to

the requirements in relevant scaffolding codes. To calculate the material consumption,

the following assumptions have been made:

(1) Bracings of outer layer was assumed to be 0.5 m/m².

(2) Bamboo and tube were assumed to be 6 m/piece [12].

(3) For connection between 2 bamboo members, the length of overlap was assumed to

be 2 m [17]. Hence the overlap factor for bamboo (1.5) was based on that only 4

m out of a 6 m bamboo component could contribute to the physical size of

scaffolding.

(4) For both Type 1 and Type 2, the overlap of connection in continuous anti-sliding

tubes was negligible [24].

(5) For Type 2, the overlap of connection in horizontal normal steel tubes was


80


assumed to be 1.5 m. The overlap factor (1.1) for steel tube in this type was based

on that every 4.5 m increase of horizontal normal steel tube required 1.5 m

overlap, and then this increase is averaged to all tube length.

(6) For Type 3, the normal steel tubes for continuous diagonal brace were joined by 2

swivel or parallel couplers with an overlap length of 0.3 m [20]. The overlap

factor of 1.01 for steel tube was based on that every 5.7 m increase of brace

required 0.3 m overlap, and such an overlap is averaged by the total tube length.

(7) For Type 3, joints between posts and main ledgers should be made with sleeve

couplers or expanding joint pins [20] with no overlap. So, a total of 4.5 couplers (2

right angle couplers for post-ledger connection, 0.5 swivel or parallel couplers for

brace overlap, 1 sleeve coupler or expanding joint pin for ledgers and posts, and 1

swivel coupler for connection between steel brace and post) were required for a

one-bay lift.

A comparison of the material costs of three different mixed scaffoldings and bamboo

scaffolding is summarized in Table 4-8. It is seen that the material costs of Type 1, 2

and 3 mixed scaffoldings are 6, 8.4 and 7.7 times of that of bamboo scaffolding. It

should be noted that metal tube and fittings are recyclable which was not reflected in

this table. Furthermore, the labor cost of the three mixed scaffolding types and the

bamboo scaffolding should be in the following order: bamboo scaffolding ﹤ Type 1 ≈

Type 2 ﹤ Type 3.

There are no specific researches or data about the construction time of three different

mixed scaffolding and bamboo scaffolding. Obviously, the erection and dismantling of

bamboo scaffolding is faster than that of mixed scaffoldings as bamboo components are

much lighter than metal components. Comparing Type 1 and Type 2, moving, installing

and dismantling metal main ledgers would not be convenient and easy for a single

worker due to their relatively heavy weight (15.6 kg/piece). Hence constructing Type 1

should be faster than Type 2. Furthermore, the using of couplers in Type 3 would need


81


more time. In summary, the construction time of the three mixed scaffolding types and

the bamboo scaffolding should be in the following order: bamboo scaffolding ﹤ Type

1 ﹤ Type 2 ﹤ Type 3.

4.3.2 Weight and weight distribution

For comparison, the density of bamboo (Kao Jue and Mao Jue) under natural

condition was used, which was obtained according to average dry density, moisture

content for natural condition and geometric dimensions from Appendix B1. The

increased self-weight due to overlap and the using of coupler described in Section

4.3.1 has been considered in an equivalent density by applying corresponding

increasing factors, as shown in Table 4-9. The equivalent density (kg/m) of Kao Jue,

Mao Jue and steel tube were used to calculate the self-weight of a one-bay unboarded

lift for these scaffoldings and are summarized in Table 4-10 for comparison. It is seen

that the weight of a mixed scaffolding is about 2 to 3 times that of a bamboo

scaffolding.

4.3.3 Load-carrying capacity

This section compared the load-carrying capacity including allowable load (UDL) on

platform and allowable height of the three mixed scaffolding types and bamboo

scaffolding. Load-carrying capacity of a scaffolding and its components was

determined based on the method of permissible stress design for scaffoldings according

to BS 5975 [23] and BS EN 12811-1 [22]. In this method, all loads are unfactored loads

and all characteristic resistances are reduced to working resistances by dividing them

by a single factor: 1.1 (material factor) × 1.5 (load factor) = 1.65 for steel components

and 1.5 (material factor [9]) × 1.5 (load factor) = 2.25 for bamboo components. It

should be noted that the mechanical properties of bamboo under normal supply

condition from Appendix B1 was used in analysis.


82


Allowable loads (UDL) on scaffolding platforms:

There are two types of platform commonly used in both bamboo scaffolding and

mixed scaffolding: Type 1: placing wooden boards or iron planks on transoms; Type 2:

fastening longitudinal bamboos to transoms at a closer spacing (≤ 150 mm) to form a

platform (see Fig. 4-17). For Type 1 platform, scaffolding boards contribute bending

strength to the platform and load is transferred from boards to transoms in the form of

uniformly distributed load (UDL). For Type 2 platform, the longitudinal bamboo (Kao

Jue) would contribute bending strength to the platform and load is transferred from

longitudinal bamboos to transoms through a series of point loads. Loads acting on

transoms would be transferred to ledgers and then to posts/standards. The allowable

load on platform would be determined considering all components involved in the load

transfer based on limit state design.

The deflection of platform under two scaffolding duties (light duty 1.5 kN/m² and

special duty 3 kN/m²) was analyzed for the serviceability design. The deflection of

platform mainly comes from the relative slippage at the connections and the bending

deformation of components. The maximum member deflection across all components

supporting platform was recorded as the maximum deflection of platform. Due to

different configuration between the inner and outer layer, load on platform may not be

shared equally by all transoms and main ledgers. So, the allowable load and deflection

of these two types of platform were determined using a full-scale scaffolding model.

For Type 1 platform, wooden boards are fairly popular due to their lower price. For

simplicity, wooden boards were chosen as representative for Type 1 platform in this

section. In the full-scale model, Type 1 platform was modelled by two thick shell

element placing on bamboo transoms through gap elements and each shell element

represents one 225 mm (width) × 25 mm (thick) piece of wooden board as seen in Fig.

4-18 (a). The young's modulus and bending strength of wooden boards were obtained

from the test to be reported in Chapter 5. For Type 2 platform, usually five


83


longitudinal bamboos (Kao Jue) were fastened to transoms using plastic stripes as

seen in Fig. 4-18 (b). Based on these assumptions, the allowable loads and the

maximum deflections for the two types of platform for the bamboo scaffolding and

the three mixed scaffolding types are presented in Table 4-11 and Table 4-12,

respectively. It is seen that the allowable loads on the two types of platform are between

3.23 and 4.0 kN/m2 for all types of scaffolding considered. The allowable loads for

Type 1 mixed scaffolding are the same as those of bamboo scaffolding, while Types 2

and 3 mixed scaffolding have almost the same but slightly higher allowable loads.

Overall speaking, there is no significant difference among the allowable loads for the

two types of platform for all scaffoldings considered. As for the maximum deflection, it

is seen that, except that Type 3 mixed scaffolding has significantly the smallest

deflection, all the other scaffoldings (bamboo and Types 1 and 2 mixed scaffoldings)

have about the same maximum deflections.

Allowable height of scaffoldings:

Next, the allowable height of a scaffolding was determined based on allowable

compressive buckling load of vertical posts. The scaffolding configuration and

dimension corresponding to Figs. 4-15 and 4-16 were used, where the platform width

was 0.6 m, the lift height h was 2 m and the lift width (length of ledger between two

posts) was 1.3 m. Also, assume the vertical distance between lateral restraints was

𝐻 = 2ℎ = 4 𝑚 and the lateral restraints were arranged regularly. The maximum

forces in the posts were obtained through nonlinear full-scale model analysis in SAP

2000. The allowable buckling loads of posts were calculated and summarized in Table

4-13 (detailed calculations presented in Appendices C and D). Based on these results,

the allowable heights of scaffoldings are summarized and presented in Table 4-14. It

is seen that the allowable heights for mixed scaffoldings are considerably larger than

that of bamboo scaffolding under light duty condition.

Safety of metal bracket


84


Metal brackets are used to support posts in tall scaffoldings. Fig. 4-21 shows the

dimensions and the modeling of a commonly used metal bracket for bamboo

scaffolding [12]. Test data about metal brackets obtained from previous research [2, 3]

were used in the modeling. The properties of the metal brackets were assumed to be:

young’s modulus E = 210 GPa and yield strength Fy = 350 MPa. These metal brackets

were assumed to be anchored using Fook Shing expansion bolts with properties

summarized in Table 4-15 [3]. The anchor bolts were modeled by two springs with

coefficients of KH and KV. The contact surface between the metal bracket and the

concrete panel was modeled by gap elements. The failure of an expansion bolt under

combined pull-out and shear forces is determined by the following formula [25]:

(𝑁𝑆

𝑁𝑅𝑢,𝑚)

1.5

+ (𝑉𝑆

𝑉𝑅𝑢,𝑚)

1.5

≤ 1

where

𝑁𝑅𝑢,𝑚 and 𝑉𝑅𝑢,𝑚 are the pull-out and shear strength (Table 4-15 (b)), respectively;

𝑁𝑠 and 𝑉𝑠 are the pull-out force and shear force under loading, respectively.

For simplicity and conservative consideration, the concrete was assumed to have a low

strength of 25 MPa. The maximum axial forces in posts of inner layer and outer layer

under allowable height shown in Table 4-14 were used as external load for a

conservative consideration. Table 4-16 shows the analysis results for different types of

scaffolding. It is seen that values of (𝑁𝑆

𝑁𝑅𝑢,𝑚)

1.5

+ (𝑉𝑆

𝑉𝑅𝑢,𝑚)

1.5

are all smaller than 0.5 and the

maximum stress in steel is smaller than half of the yield strength under the condition

that the scaffolding was erected up to its allowable height. These results indicate that

the metal bracket has adequate strength to support either light-duty or heavy-duty

scaffoldings.

Safety of lateral restraint (putlog)


85


The load generated on putlogs is mainly from the wind load. Wind loads shall be

calculated by assuming that there is a velocity pressure on a reference area of the

working scaffolding, which is in general the projected area perpendicular to the wind

direction. According to the Code of Practice on Wind Effects in Hong Kong [26], the

total wind force 𝐹 acting on a scaffolding is determined by the following equation:

𝐹 = 𝐶𝑓 ∑ 𝑞𝑧 × 𝐴𝑧

where 𝐶𝑓 is the force coefficient for open framework, 𝐶𝑓 = 1.85 when the solidity

ratio φ = 0.15; 𝑞𝑧 is the design wind pressure at height 𝑧, determined in accordance

with Table 1 in [26]; and 𝐴𝑧 is the effective projected area of that part of the building

corresponding to 𝑞𝑧. The solidity ratio φ equaling to the effective projected area 𝐴𝑧

of the open framework building divided by the area 𝐴 enclosed by the boundary of the

frame normal to the direction of the wind, i.e, 𝐴𝑧 = 𝜑 × 𝐴. In this study, it was

assumed that φ = 0.15 according to [27]. Note that a factor of 0.7 may be applied to

wind pressures for temporary buildings or structures. To calculate the load on putlogs,

area 𝐴 should be taken as the area enclosed by the boundary of a quadrangle with

four putlogs at four corners. The top portion of scaffolding should be used to

determine the maximum pull-out load. As an example, the maximum allowable height

62 m in Table 4-14 was used and the putlogs were arranged every 4 m vertically and

2.6 m horizontally, the pull-out load acting on a putlog was calculated to be 5.35 kN.

For a putlog using steel wire of 6 mm diameter, the unfactored stress in the steel wire

was 188 MPa which was smaller than the required yield strength of 250 MPa

specified in [12].

4.3.4 Summary

The material cost, construction time, self-weight, sensitivity of materials to the

environment, typical connection properties and load-carrying capacity of three


86


different mixed scaffoldings and bamboo scaffoldings are summarized in Table 4-17.

Those of a pure metal scaffolding according to code [20] was also provided for

comparison. This pure metal scaffolding was assumed to have platform height of 2 m,

width of 0.6 m and bay length of 1.3 m. All components in the metal scaffolding are

consisted of normal steel tubes same as those used in the mixed scaffoldings and there

is no standard between posts. The transoms are fixed to the inside and outside ledgers

with couplers at each pair of posts. The joint between tubes in metal scaffolding are

similar to Type 3 mixed scaffolding. From this table, the following findings can be

concluded:

(1) All three types of mixed scaffolding can meet the load requirements specified in

the bamboo scaffolding code [17] and the metal scaffolding code [20]. The mixed

scaffoldings have a better performance than bamboo scaffolding in terms of

load-carrying capacity. However, in terms of costs (material cost and labor cost),

self-weight and construction time, bamboo scaffolding is still much better than the

mixed scaffoldings. Metal scaffolding is the most costly but can offer a more

robust performance under different environmental condition.

(2) The allowable load (UDL) on platform of bamboo scaffolding and mixed

scaffoldings are all larger than 3 kN/m², which is determined by the failure of

bamboo transom between posts. Metal scaffolding gives the largest allowable load

(UDL) on platform among all scaffoldings, which is determined by the failure of

wooden boards. The allowable loads (UDL) on platform of Type 2 and Type 3 are

slightly larger than that of Type 1 and bamboo scaffolding.

(3) The deflection of platform under designed load is smallest in Type 3 mixed

scaffolding, which is slightly smaller than that of metal scaffolding. Bamboo

scaffolding and Type 1 and Type 2 mixed scaffoldings show a larger but similar

deflection behavior. Also, two different types of platform (wooden board and

closely-spaced bamboo members) give a similar load-carrying capacity and

deflection for all three mixed scaffoldings and bamboo scaffolding.


87


(4) Bamboo scaffolding can only be used as light-duty scaffolding (two working

platforms rated at 1.5 kN/m²) and both mixed and metal scaffoldings can serve as

heavy-duty scaffolding (two working platforms rated at 2.50 kN/m² plus one

working platform rated at 0.75 kN/m²). Considering the allowable height within a

single zone (a separate zone between metal brackets), all mixed scaffoldings have

a larger erection height (more than twice) than the bamboo scaffolding.

4.4 Full-scale mixed scaffolding test

The objective of the full-scale scaffolding test is to experimentally validate the

load-carrying capacity of scaffolding, anchorage issue as well as the accuracy of

numerical modeling. From above analysis and comparison, it seems that Type 1 offers

a smaller allowable load (UDL) and a larger deflection of platform of all three mixed

scaffoldings. Type 1 mixed scaffolding was chosen as the candidate for validation.

4.4.1 Description of the scaffolding

The full-scale mixed scaffolding used for testing is a scaffolding with dimensions of

6.3 m×4.6 m×0.65 m (height×length×width) erected by the Sinoscaff (Hong Kong)

Limited. The properties of the anti-sliding tubes provided by this company were: 48.2

mm×2.23 mm (outer diameter×thickness), E = 204 GPa and a yield strength of 220

N/mm²[28]. The outer layer consisted of four anti-sliding steel tube posts and 3

bamboo standards (Kao Jue). The inner layer had four anti-sliding steel tube posts.

There were three platforms at the height of 1.1 m, 3.1 m and 5.1m, respectively. The

scaffolding was X-braced by two anti-sliding tubes at the outer layer and connected to

building façade through five putlogs. The configuration and dimension of mixed

scaffolding is shown in Fig. 4-20.


88



On this scaffolding, two types of test were performed: UDL test on platform and static

point load test on connection. Details of these tests are provided in the following.

UDL test on platform:

Two sets of UDL test were performed to validate the behavior and the load-carrying

capacity of scaffolding (see Fig. 4-21):

(1) UDL of 5 kN/m² (equivalent point load of 10 kN) and 7.6 kN/m² (equivalent point

load of 15 kN) acting on two spans of platform, respectively.

(2) UDL of 5.1 kN/m2 (equivalent point load of 5 kN) and 10.3 kN/m2 (equivalent

point load of 10 kN) on the middle span of platform respectively.

Static point load test on connection:

The point load test were performed to obtain the behavior and the load-carrying

capacity of connection. Two types of connection were tested:

(1) Connection of bamboo ledger and bamboo standard (load position (1) and (2) in

Fig. 4-22).

(2) Connection of bamboo ledger and anti-sliding steel tube post (load position (3)

and (4) in Fig. 4-22).

4.4.3 UDL test on platform

The equipment used in the tests were the same as that reported in Section 2.4. Strain

gauges were installed at the bottom of all bamboo standards and steel tube posts. For

each test case described in above, loads were conducted on both the upper platform

and the bottom platform separately. To create the UDL condition, a loading device


89


made by steel tubes and coupler was used to convert the applied point load to UDL as

shown in Fig. 4-23. For the UDL test on two spans of both the upper and the bottom

platform, a point load up to 10 kN (5.0 kN/m²) and 15 kN (7.6 kN/m²) was applied,

respectively. For UDL test on the middle span of both the upper and the bottom

platform, a point load up to 5 kN (5.1 kN/m²) and 10 kN (10.3 kN/m²) was applied,

respectively. Fig. 4-24 shows two of the loading conditions: middle span of the

bottom platform under 10 kN (10.3 kN/m²) load and two spans of the upper platform

under 15 kN (7.6 kN/m²) load. For each case, 3 independent tests were conducted.

Table 4-18 summarizes the test results according to the post number and standard

number labelling as shown in Fig. 4-25. Based on these testing results, the following

observations can be made:

(1) There were no notable deformation nor any sign of damage in any part of the

scaffolding even under an UDL with a magnitude twice as large as the required

value for all cases. The measured axial forces in posts were all much less than

their compressive buckling strength.

(2) Under UDL, the middle steel posts (posts 4, 6 of back layer and posts 3, 5 of front

layer) carried larger axial loads than the other posts.

(3) The axial forces in bamboo standards were much smaller than those in steel posts.

(4) For the same loading condition, the axial forces in the posts and standards were

approximately linearly proportional to the UDL magnitude.

(5) The standard deviations of the measured strains were quite small which suggested

that the test results were quite consistent and reliable.

To compare the test results obtained above, finite element analysis using SAP 2000

reported in Section 4.2 was performed for all the UDL cases tested above. Table 4-19

presents the comparison between the UDL test and the computer analysis results. Note

that strain gauges used in the test had a precision of 1 × 10−6𝜀, hence comparison of

those axial forces obtained from strain values smaller than or around this precision


90


was not made. Table 4-20 further summarizes the average differences obtained

between the full-scale test and the numerical analysis. It shows that the average

difference in the axial forces between the full-scale UDL test and the numerical

analysis of Type 1 mixed scaffolding was about 33% for the bamboo members and

about 20% for the metal members.

4.4.4 Static point load test on connection

The static point load tests were performed to obtain the deformation behavior and the

load-carrying capacity of connection and check whether the connection could be used

as an anchorage for safety harness. The setup of static point load test was similar to

that of UDL test. The load generated by tensile jack was applied on connection

through a steel wire. Two types of point load test were performed to obtain the

deformation behavior and the load-carrying capacity of scaffolding connection,

respectively. First, the point load applied on connection was slowly increased from 0

kN to 2 kN to obtain the deformation behavior of connection. The deformation at

about 10 cm away from the connection was measured by the LVDT as illustrated in

Fig. 4-26. Each of four connections as shown in Fig. 4-22 were tested three times.

Then, load acting on connection was increased gradually until some sign of

connection failure occurred to obtain its load-carrying capacity.

Fig. 4-27 shows the load-displacement curves for Connection (1) and Connection (3).

It is seen that the load-displacement relation is rather linear indicating that the

scaffolding remains linear elastic up to 2 kN load applied to these locations. Table

4-21 summaries the displacement measured near the four connections under 2 kN

static point load. Table 4-22 summarizes the mean values and standard deviations of

measured strains and axial forces for vertical posts and standards under 2 kN static

point load acting on each of the four connections. It is seen that the load acting on

connection was mainly carried by the posts directly underneath. The axial force in a


91


post decreases as the distance between the post and the connection increases. The

axial forces in the bamboo standards were generally very small comparing to those in

the posts.

Fig. 4-28 shows the failure of Connections (1) and (4) under static point load. The

ultimate failure loads corresponded to the maximum point loads attained during the

loading process. Table 4-23 summarizes the failure loads of these four connections.

Results show that the connections can only sustain around 4 kN load before failure.

This is not sufficient to be used as an anchorage for safety harness even an energy

absorbing connecting device is used (requiring a minimum of 8 kN). This indicates

that the connections in Type 1 mixed scaffolding cannot be used as an anchorage for

safety harness.


reported in Section 4.2 was performed for all the static point load cases tested above.

Fig. 4-29 shows the comparison of load-displacement curves between test and

analysis for Connection (1) and (3). It is seen that the computer analysis results

coincided with the first test results very well at both connections, both of which

exhibited linear behavior. Tables 4-24 and 4-25 further summarize the comparison of

displacement and load-carrying capacity of connections between test and analysis,

respectively. It is seen that the displacement difference between test and analysis

ranges between 10 to 45 % if the average diameter from Appendix B1 was used in the

analysis. The difference becomes smaller (between 1 to 23%) if the diameters of

bamboo ledges were measured in-situ and used in the computer model. Similarly, the

difference of load-carrying capacity between test and analysis ranges between 15 to

30% if the measured diameters were used in the model. Table 4-26 compares the axial

forces in some of the posts and standards between test and analysis under 2 kN point

load acting on the four connections. Table 4-27 further summarizes the difference

between test and analysis results. It can be concluded that the axial force difference


92


between full-scale test and numerical analysis was about 38% for the bamboo members

and about 22% for the metal members.

4.5 Anchorages for mixed scaffolding

As revealed experimentally and numerically in Table 4-25, the four connections on a

Type 1 mixed scaffolding were found not suitable to anchor safety harness. We have

conducted a similar numerical analysis on a Type 2 mixed scaffolding with span 1.3 m

and using normal steel tube (size: 48.3 × 2.3 mm; E = 200 GPa; characteristic yield

strength = 235 N/mm²) as main ledgers, the load-carrying capacity of main ledger-post

connection was found to be around 4.75 kN. This suggests that the connection on

Type 2 mixed scaffolding is also not a good anchorage location for safety harness.

For Type 3 mixed scaffolding, the steel ledger (48.3×2.3 mm) has a larger

load-carrying capacity due to the use of right angle couplers. Assume that the support

condition of the metal ledger are clamped supports with a span of 1.3m, the

load-carrying capacity at the midpoint is 5.3 kN under the yield strength of 235

N/mm² (or 7.95 kN under the yield strength 350 N/mm²). It can be briefly concluded

that the Type 3 mixed scaffolding also cannot provide safe anchorages to resist the

drop force of 4 kN with a safety factor of 2 even when an energy absorber lanyard or

SRL/Fall limiter is used.


93


Fig. 4-1 Normal steel tube (left) and anti-sliding steel tube (right)


94


(a) Test for slippage stiffness (b) Test for rotational stiffness

Fig. 4-2 Test setup for normal steel tube-bamboo connection


0

0.2

0.4

0.6

0.8

1

1.2

0 10 20 30 40 50 60 70

UT

M F

orc

e (k

N)


1

2

3

4

5


95


(b) Initial slippage

Fig. 4-3 Slippage tests for normal steel tube (post)-bamboo (ledger) connection


y = 0.063x

y = 0.068x y = 0.053xy = 0.063x

y = 0.056x

0

0.2

0.4

0.6

0.8

1

1.2

0 5 10 15 20 25

UT

M F

orc

e (k

N)


1

2

3

4

5

-0.1

0

0.1

0.2

0.3

0.4

0.5

0.6

0 10 20 30 40 50 60 70

UT

M F

orc

e (k

N)


1

2

3


96


(b) M − θ curves

Fig. 4-4 Rotational tests for normal steel tube (post)-bamboo (ledger) connection

(a) Slippage stiffness

y = 0.124x

y = 0.100x

y = 0.109x

-0.01

0

0.01

0.02

0.03

0.04

0.05

0.06

0.07

0 0.1 0.2 0.3 0.4 0.5

M (

kN

·m)

θ (rad)

1

2

3

-12.5, -0.76

12.5, 0.76

-1

-0.5

0

0.5

1

-60 -40 -20 0 20 40 60

Forc

e (k

N)

Relative displacement (mm)

0

0.05

0.1

0.15

0.2

0.25

0.3

0.35

-4 -2 0 2 4

M (

kN

·m)

θ (rad)

M=0.11× θ

M=0


97


(b) Rotational stiffness

Fig. 4-5 Modeling of normal steel tube-bamboo connection

Fig. 4-6 Test setup for connection involving anti-sliding steel tube

(a) 0° orientation (b) 45° orientation (c) 90° orientation


98


(d) 135° orientation (e) 180° orientation

Fig. 4-7 Five different orientation angles for the anti-sliding steel tube

(a) 0° orientation (b) 45° orientation (c) 90° orientation

Fig. 4-8 Splitting of plastic stripes for 0°, 45° and 90° orientation


99


(a) With initial slippage

(b) Without initial slippage

Fig. 4-9 Load-displacement curves for anti-sliding steel tube-bamboo connection

0

0.5

1

1.5

2

2.5

3

3.5

4

0 20 40 60 80 100 120 140 160

UT

M F

orc

e (k

N)


Horizontal member: BP & 0° orientation

0

0.5

1

1.5

2

2.5

3

3.5

4

0 10 20 30 40 50 60 70 80

UT

M F

orc

e (k

N)



Initial slippage

Slipping force

Connection resistance

First bump

Second bump


100


(a) Damage of bamboo for 180° orientation

(b) Load-displacement curve for 180° orientation

Fig. 4-10 Failure mode for 180° orientation of anti-sliding steel tube-bamboo

connection

0

0.5

1

1.5

2

2.5

0 10 20 30 40 50 60

UT

M F

orc

e (k

N)




101


(a) Rotation failure of horizontal tube for 180° orientation

(b) Load-displacement curve for 180° orientation

Fig. 4-11 Failure mode for 180° orientation of anti-sliding steel tube-normal steel tube

connection

0

0.5

1

1.5

2

2.5

3

0 10 20 30 40 50 60

UT

M F

orc

e (k

N)


Horizontal member: normal steel tube &

180° orientation

Inner layer


102


Fig. 4-12 Illustration of anti-sliding steel tube orientation with transom

Fig. 4-13 Right-angle coupler (left) and swivel coupler (right)

Fig. 4-14 Typical configuration of a double-layered bamboo scaffolding (DLBS)

Post (inner layer):

Kao Jue

Post (outer layer):

Mao Jue

Standard (outer

layer): Kao Jue

1.3 m

Ledger: Kao Jue

Ledger on the first

lift: Mao Jue

Bracing (outer

layer): Kao Jue


103


(a) Type 1 mixed scaffolding

(b) Type 2 mixed scaffolding

1.3 m

Tube size: 48.3×2.3 mm.

Vertical tube (anti-sliding)

Horizontal tube (normal)

1.3 m

Ledger on the first

lift: Mao Jue

Ledger: Kao Jue

Standard (outer

layer): Kao Jue

Anti-sliding tube


104


(c) Type 3 mixed scaffolding

Fig. 4-15 Three different types of mixed scaffolding

Fig. 4-16 A one-bay unboarded lift of scaffolding

1.3 m

One bay 1.3m

2m


105


(a) Type 1 platform: wooden boards or iron planks placed on transoms

(b) Type 2 platform: closely-spaced bamboo members

Fig. 4-17 Two types of platform commonly used in scaffolding

(a) Type 1 platform (b) Type 2 platform

Fig. 4-18 Modeling of scaffolding platforms


106


(a) Dimension of metal bracket

(b) Modeling of metal bracket

Fig. 4-19 Dimension and modeling of metal bracket


107


(a) Front view of the scaffolding

(b) Dimension of the scaffolding

Fig. 4-20 The full-scale mixed scaffolding used for test


108


(a) UDL test on two spans of platform

(b) UDL test on single span of platform

Fig. 4-21 Test arrangement for UDL test on platform

5 kN/10 kN

10 kN/15 kN

(1)

(3)

(4)

(2)


109


Fig. 4-22 Test arrangement for static point load test on connection

(a) Two spans of bottom platform (b) Two spans of upper platform

(c) Middle span of bottom platform (d) Middle span of upper platform

Fig. 4-23 Setup of UDL test for platform


110


(a) Middle span of the bottom platform under 10 kN (10.3 kN/m²) load

(b) Two spans of the upper platform under 15 kN (7.6 kN/m²) load

Fig. 4-24 UDL test on platform


111


Fig. 4-25 Labeling of metal post and bamboo standard

Post 1

Post 2 Post 8

Post 5 Post 7 Post 3

Post 6 Post 4

Standard 1 Standard 2 Standard 3

Brace 1 Brace 2


112


Fig. 4-26 Setup of static point load test on connection

(a) Load-displacement curve for Connection (1)

(b) Load-displacement curve for Connection (3)

0

5

10

15

20

25

30

0 0.5 1 1.5 2 2.5

Dip

lace

men

t (m

m)

Point load (kN)

1st Test

2nd Test

3rd Test

0

5

10

15

20

25

0 0.5 1 1.5 2 2.5

Dis

pla

cem

ent

(mm

)

Point load (kN)

1st Test

2nd Test

3rd Test


113


Fig. 4-27 Load-displacement curves for Connections (1) and (3) (see Fig. 4-22)

(a) Failure of Connection (1)

(b) Failure of Connection (4)

Fig. 4-28 Failure of Connections (1) and (4) under static point load

3.23

0

0.5

1

1.5

2

2.5

3

3.5

0 10 20 30 40 50 60

Po

int

loa

d (

kN

)

Displacement (mm)

4.55

0

0.5

1

1.5

2

2.5

3

3.5

4

4.5

5

0 10 20 30 40 50

Po

int

loa

d (

kN

)

Displacement (mm)


114


(a) Load-displacement curve for Connection (1)

(b) Load-displacement curve for Connection (3)

Fig. 4-29 Comparison of load-displacement curves between test and analysis

0

5

10

15

20

25

30

0 0.5 1 1.5 2 2.5

Dip

lace

men

t (m

m)

Point load (kN)

SAP 2000

1st Test

2nd Test

3rd Test

0

5

10

15

20

25

0 0.5 1 1.5 2 2.5

Dis

pla

cem

ent

(mm

)

Point load (kN)

SAP 2000

1st Test

2nd Test

3rd Test


115


Table 4-1 Resistance for normal steel tube-bamboo connection

Test series Presence

of nodes

No. of

round

turns

No. of

tests

Connection resistance

(kN)

Horizontal member Vertical member Mean Std

BP Normal steel tube No 5 5 0.76 0.09

Normal steel tube BP No 5 5 0.80 0.14

Normal steel tube Normal steel tube No 5 5 0.74 0.13

Normal steel tube BP Yes 5 4 2.20 0.36

Table 4-2 Rotational stiffness for normal steel tube-bamboo connection

Test series No. of

round

turns

No. of

tests

Rotational stiffness

(kN·m/rad)

Horizontal member Vertical member Mean Std

BP Normal steel tube 5 3 0.111 0.01

Normal steel tube Normal steel tube 5 3 0.109 0.003

Total 0.110 0.007

Table 4-3 Test results for anti-sliding steel tube-bamboo/normal steel tube connection

Test series

Total

No. of

tests

𝑁

No. of

test with

initial

slippage

𝑛

Initial

slippage

distance

(average over

𝑁)

Connection

resistance

(kN)

Slippage

displacement

(mm) Horizontal

member

Vertical

member

Angle

(°)

mm Mean Std Mean Std

Bamboo

Anti-

sliding

steel tube

0 5 4 10.92 3.36 0.11 61.33 5.69

45 5 3 4.20 2.81 0.24 54.05 6.28

90 5 4 7.95 2.60 0.25 55.68 7.11

135 5 / / 0.82 0.10 / /

180 5 1 1.20 1.81 0.45 20.24 9.81

Normal

steel tube

Anti-

sliding

steel tube

0 5 2 2.95 3.42 0.23 52.08 5.80

45 5 3 2.70 2.94 0.28 49.95 6.20

90 5 4 5.85 2.50 0.43 51.00 4.93

135 5 / / 0.88 0.16 / /

180 5 1 1.80 2.02 0.56 10.16 6.01


116


Table 4-4 Connection resistance for 0°, case 45° and case 90° orientation

Horizontal

member

Bamboo Normal steel tube

0° 45° 90° 0° 45° 90°

Connection

resistance

(kN)

3.42 2.36 2.39 3.57 2.59 2.80

3.55 2.75 3.01 2.98 2.78 2.58

3.24 2.99 2.73 3.65 3.22 3.04

3.26 2.96 2.33 3.47 2.79 2.28

3.34 2.97 2.52 3.41 3.33 1.81

Mean (kN) 3.36 2.81 2.60 3.42 2.94 2.50

Std (kN) 0.11 0.24 0.25 0.23 0.28 0.43

Overall (kN) Mean = 2.92 Std = 0.39 Mean = 2.95 Std = 0.49

Table 4-5 Total displacement for 0°, case 45° and case 90° orientation

Horizontal

member

Bamboo Normal steel tube

0° 45° 90° 0° 45° 90°

Total

Displacement

(mm)

65.05 64.48 51.04 56.33 46.10 55.52

62.39 44.79 59.56 43.36 44.28 52.96

51.88 54.36 47.88 47.53 55.38 56.12

58.84 54.16 52.27 54.01 44.67 43.90

68.48 52.45 67.66 59.15 59.33 46.49

Mean (mm) 61.33 54.05 55.68 52.08 49.95 51.00

Std (mm) 5.69 6.28 7.11 5.80 6.20 4.93

Overall (mm) Mean = 57.02 Std = 7.11 Mean = 51.01 Std = 5.73

Table 4-6 Properties for various types of couplers

Coupler type Resistance

Characteristic

values

Safe load or

moment

Class A Class B Class A Class B

Right angle coupler Slippage force Fs (kN) 10.0 15.0 6.1 9.1

Swivel coupler Slippage force Fs (kN) 10.0 15.0 6.1 9.1

Parallel coupler Slippage force Fs (kN) 10.0 15.0 6.1 9.1

Friction type sleeve

coupler

Slippage force Fs (kN) 6.0 9.0 3.6 5.5

Bending moment

(kN·m) 2.4

1.5

Internal joint pin

(expanding spigot

coupler)

Slippage force (kN) Safe load = 0 kN A)

Shear strength (kN) Safe load = 21.0 kN A)

Putlog coupler Slippage force Fs (kN) Safe load = 0.63 kN A)

Note 1: These figures are extracted from Annex C of BS EN 12811-1 [22].

Note 2: A) From BS 5975 [23].


117


Table 4-7 Material required for a one-bay unboarded lift

Scaffolding

type

Mao Jue Kao Jue Steel tube

Number of

couplers

Net

length

(m)

Overlap

factor

Net

length

(m)

Overlap

factor

Net

length

(m)

Overlap

factor

Bamboo 2

1.5

11.7

1.5

/ / 0

Type 1 / 8.4 5.3 1.0 0

Type 2 / 5.8 7.9 1.1 0

Type 3 / 5.8 7.9 1.01 4.5

Note: The consumption of plastic stripes is not included.

Table 4-8 Material cost for scaffoldings

Material price of an unboarded lift one bay long (1.3 m)

Scaffolding

type

Length of tube or Mao

Jue (m)

Length of

Kao Jue

(m)

Cost of

fittings

(HKD)

Total price

(HKD)

Ratio to

bamboo

scaffold

Bamboo 3 (PP) 17.6 4 39 1.0

Type 1 5.3 (anti-sliding steel

tube) 12.6 4 235 6.0

Type 2

8.7 (normal steel tube

3.4 m; anti-sliding

steel tube 5.3 m)

8.7 4 331 8.4

Type 3 8.0 (normal steel tube) 8.7 47 300 7.7

Note: The price of Kao Jue, Mao Jue, normal tube and anti-sliding tube are HK$1.5/m, HK$3.0/m,

HK$30/m and HK$40/m respectively; The price of coupler is HK$10/Unit; The price of plastic

stripes is HK$0.83/m² based on quantity analysis by WLS Scaffolding Works Co. Ltd. [29].

Table 4-9 Equivalent density for scaffoldings

Material

Density under natural

condition

(kN/m³)

Increasing

factor

Equivalent density

kN/m³ kg/m

Kao Jue 7.82 1.5 11.7 0.69

Mao Jue 9.35 1.5 14.0 1.95

Steel

tube

Type 1

77.00

1.0 77.0 2.60

Type 2 1.1 84.7 2.86

Type 3 1.23 94.7 3.20

Note: The mass of coupler is assumed to be 1 kg each.


118


Table 4-10 Self-weight and weight distribution of a one-bay unboarded lift

Scaffolding type Outer layer (kg) Inner layer (kg) Ratio Total weight (kg)

Bamboo 9.28 2.69 3.45 11.97

Type 1 13.07 6.51 2.01 19.58

Type 2 16.74 9.85 1.70 26.59

Type 3 18.31 10.97 1.67 29.28

Note: Ratio = weight of outer layer / weight of inner layer.

Table 4-11 Allowable loads for scaffolding platforms

Platform type Scaffolding type Allowable UDL on

platform (kN/m²) Failure components

Type 1:

wooden boards

Bamboo 3.23

Bamboo transom

between posts

Type 1 3.23

Type 2 3.75

Type 3 3.75

Type 2:

closely-spaced

bamboo members

Bamboo 3.50

Type 1 3.50

Type 2 4.00

Type 3 3.95

Note: Considering a single factor of 2.25 for bamboo, the maximum allowable stress against

bending for Kao Jue is 26.0 N/mm² under normal supply condition.

Table 4-12 Maximum deflections for scaffolding platforms

Platform type Scaffolding

type

Maximum member

deflection under 1.5 kN/m²

Maximum member

deflection under 3.0 kN/m²

Deflection

(mm) Member

Deflection

(mm) Member

Type 1:

wooden

boards

Bamboo 6.8 Ledger of inner

layer

13.6 Ledger of inner

layer Type 1 6.8 13.6

Type 2 6.1 12.3

Type 3 1.1 Transom

(midpoint) 2.2

Transom

(midpoint)

Type 2:

closely-spaced

bamboo

members

Bamboo 6.7 Ledger of inner

layer

13.3 Ledger of inner

layer Type 1 6.7 13.3

Type 2 6.2 12.3

Type 3 1.1

Middle

longitudinal

bamboo or

transom

(midpoint)

2.2

Middle

longitudinal

bamboo or

transom

(midpoint)


119


Table 4-13 Allowable buckling loads for metal and bamboo posts

Material Buckling strength

(kN) Safety factor

Allowable buckling

load

(kN)

Metal post

(48.3×2.3 mm) 9.13 1.65 5.53

Bamboo inner post

(Kao Jue) 2.31 2.25 1.54

Bamboo outer post

(Mao Jue) 9.33 2.25 6.22

Note: The material factor (𝑟𝑚=1.5) of bamboo column was considered in buckling strength.

Table 4-14 Allowable heights of scaffoldings

Duty Scaffolding

type

Allowable

height (m)

Maximum force in posts for a zone (kN)

Inner layer Outer layer

Self-weight Live

load Total Self-weight

Live

load Total

Light

duty

Bamboo 16 0.22 1.32 1.54 0.72 1.37 2.09

Type 1 62 1.98 1.32 3.30 4.31 1.23 5.54

Type 2 48 2.33 1.35 3.68 4.29 1.24 5.53

Type 3 52 2.82 1.33 4.15 4.24 1.26 5.50

Heavy

duty

Bamboo scaffolding cannot be used for heavy-duty purpose

Type 1 44 1.42 2.47 3.89 3.20 2.29 5.49

Type 2 36 1.72 2.51 4.23 3.26 2.31 5.57

Type 3 40 2.17 2.47 4.64 3.21 2.34 5.55

Note 1: For simplicity, only the working platforms are boarded in calculation of height and this

assumption is acceptable for the purpose of comparison.

Note 2: The real erection height of scaffolding can be increased by separating the whole

scaffolding into different zones by installing brackets at corresponding levels.


120


Table 4-15 Test data for Fook Shing anchor bolts [2, 3]

(a) Spring coefficients for Fook Shing anchor bolts

Concrete panel Low strength (25 MPa) Standard strength (65 MPa)

𝐾𝐻 (kN/cm) 15 25

𝐾𝑉 (kN/cm) 30 50

(b) Average pull-out and shear strengths for Fook Shing anchor bolts

Concrete panel Pull-out strength 𝑁𝑅𝑢,𝑚 (kN) Shear strength 𝑉𝑅𝑢,𝑚 (kN)

Low strength (25 MPa) 11.3 18.7

Standard strength (65 MPa) 18.2 30.1

Table 4-16 Safety of anchor bolt and bracket for scaffolding with allowable height

Duty Scaffolding

type

Maximum axial

force in posts (kN)

Safety check of anchor bolts and metal bracket

Force in top anchor bolt Maximum

stress in steel

(MPa)

Inner

layer

Outer

layer

Pull-out

force (kN)

Shear

force (kN) (

𝑁𝑆

𝑁𝑅𝑢,𝑚

)

1.5

+ (𝑉𝑆

𝑉𝑅𝑢,𝑚

)

1.5

Light

duty

Bamboo 1.54 2.09 1.55 1.20 0.07 35.89

Type 1 3.3 5.54 3.94 2.93 0.27 81.64

Type 2 3.68 5.53 4.02 3.05 0.28 88.16

Type 3 4.15 5.50 4.10 3.20 0.29 96.14

Heavy

Duty

Bamboo scaffolding cannot be used for heavy-duty purpose

Type 1 3.89 5.49 4.04 3.11 0.28 91.61

Type 2 4.23 5.57 4.16 3.25 0.30 97.83

Type 3 4.64 5.55 4.23 3.38 0.31 104.83


121


Table 4-17 Comparison of three mixed scaffoldings and bamboo scaffolding

Issue Bamboo

scaffolding

Mixed scaffolding Pure metal

scaffolding Type 1 Type 2 Type 3

Material cost for a one-bay unboarded lift

(HKD) 39 235 331 300 405

Self-weight for a one-bay unboarded lift

(kg) 11.97 19.58 26.59 29.28 36.08

Sensitive to the environment Yes Middle No No No

Construction time Fast Middle Middle Slow Slow

Allowable load (UDL) on wooden-board

platform (kN/m²) 3.23 3.23 3.75 3.75 6.00

Allowable height within

a single zone (m)

Light duty 16 62 48 52 42

Heavy duty - 44 36 40 32

Max. deflection of wooden-board

platform under UDL of 3.0 kN/m² (mm) 13.6 13.6 12.3 2.2 5.5

Typical beam-column

connection

Resistance (kN) 0.9 2.92 2.95 10.0 10.0

Slippage

stiffness (kN/m) 56.2 51.2 57.8 - -


122


Table 4-18 Results for UDL test on platform

(a) 5 kN (UDL = 5.1 kN/m²) on the middle span of upper platform

Component

Strain Young's

modulus

𝐸

Cross section area 𝐴 Measured

axial force

Mean Std Outside



Back

Post 2 -1.1 0.7 204 48.2 2.23 322.1 -0.07 0.04

Post 4 -19.1 0.9 204 48.2 2.23 322.1 -1.26 0.06

Post 6 -20.0 1.3 204 48.2 2.23 322.1 -1.31 0.08

Post 8 0.4 0.3 204 48.2 2.23 322.1 0.03 0.02

Front

Post 1 1.4 4.4 204 48.2 2.23 322.1 0.09 0.29

Post 3 -16.1 0.8 204 48.2 2.23 322.1 -1.06 0.05

Post 5 -17.4 2.6 204 48.2 2.23 322.1 -1.14 0.17

Post 7 0.6 0.4 204 48.2 2.23 322.1 0.04 0.02

Standard 1 -0.4 0.2 8.55 49.7 6.34 863.3 -0.003 0.001

Standard 2 -8.2 1.4 8.55 43.3 5.53 656.1 -0.05 0.01

(b) 5 kN (UDL = 5.1 kN/m²) on the middle span of bottom platform

Component

Strain Young's

modulus

𝐸


axial force

Mean Std Outside



Back

Post 2 -1.00 0.7 204 48.2 2.23 322.1 -0.07 0.05

Post 4 -14.77 0.3 204 48.2 2.23 322.1 -0.97 0.02

Post 6 -24.66 1.3 204 48.2 2.23 322.1 -1.62 0.08

Post 8 0.78 0.2 204 48.2 2.23 322.1 0.05 0.01

Front

Post 1 1.62 0.3 204 48.2 2.23 322.1 0.11 0.02

Post 3 -13.42 1.6 204 48.2 2.23 322.1 -0.88 0.10

Post 5 -14.47 0.8 204 48.2 2.23 322.1 -0.95 0.05

Post 7 0.57 0.3 204 48.2 2.23 322.1 0.04 0.02

Standard 1 -0.33 0.4 8.55 49.7 6.34 863.3 -0.002 0.003

Standard 2 -9.06 3.2 8.55 43.3 5.53 656.1 -0.05 0.02


123


(c) 10 kN (UDL = 10.3 kN/m²) on the middle span of upper platform

Component

Strain Young's

modulus

𝐸


axial force

Mean Std Outside



Back

Post 2 -0.9 0.4 204 48.2 2.23 322.1 -0.06 0.03

Post 4 -36.3 0.9 204 48.2 2.23 322.1 -2.38 0.06

Post 6 -38.6 0.5 204 48.2 2.23 322.1 -2.54 0.03

Post 8 -1.0 1.2 204 48.2 2.23 322.1 -0.07 0.08

Front

Post 1 2.3 0.6 204 48.2 2.23 322.1 0.15 0.04

Post 3 -34.1 2.1 204 48.2 2.23 322.1 -2.24 0.14

Post 5 -35.5 1.5 204 48.2 2.23 322.1 -2.33 0.10

Post 7 1.0 0.8 204 48.2 2.23 322.1 0.066 0.05

Standard 1 -1.1 0.3 8.55 49.7 6.34 863.3 -0.008 0.002

Standard 2 -17.4 4.2 8.55 43.3 5.53 656.1 -0.098 0.02

(d) 10 kN (UDL = 10.3 kN/m²) on the middle span of bottom platform

Component

Strain Young's

modulus

𝐸


axial force

Mean Std Outside



Back

Post 2 -1.7 0.7 204 48.2 2.23 322.1 -0.11 0.04

Post 4 -35.2 0.6 204 48.2 2.23 322.1 -2.31 0.04

Post 6 -40.0 3.1 204 48.2 2.23 322.1 -2.63 0.20

Post 8 -0.6 0.8 204 48.2 2.23 322.1 -0.04 0.06

Front

Post 1 2.5 0.7 204 48.2 2.23 322.1 0.16 0.05

Post 3 -26.3 0.8 204 48.2 2.23 322.1 -1.73 0.06

Post 5 -33.9 0.4 204 48.2 2.23 322.1 -2.23 0.03

Post 7 1.0 0.8 204 48.2 2.23 322.1 0.07 0.05

Standard 1 -0.5 0.7 8.55 49.7 6.34 863.3 -0.004 0.005

Standard 2 -14.8 4.7 8.55 43.3 5.53 656.1 -0.08 0.03


124


(e) 10 kN (UDL = 5.0 kN/m²) on the two spans of upper platform

Component

Strain Young's

modulus

𝐸


axial force

Mean Std Outside



Back

Post 2 -14.7 1.4 204 48.2 2.23 322.1 -0.96 0.09

Post 4 -34.3 0.5 204 48.2 2.23 322.1 -2.26 0.03

Post 6 -13.5 1.2 204 48.2 2.23 322.1 -0.89 0.08

Post 8 1.0 1.2 204 48.2 2.23 322.1 0.07 0.08

Front

Post 1 -12.0 2.8 204 48.2 2.23 322.1 -0.79 0.19

Post 3 -36.3 2.9 204 48.2 2.23 322.1 -2.38 0.19

Post 5 -14.2 1.3 204 48.2 2.23 322.1 -0.93 0.09

Post 7 1.8 0.6 204 48.2 2.23 322.1 0.12 0.04

Standard 1 -11.1 2.4 8.55 49.7 6.34 863.3 -0.08 0.02

Standard 2 -10.8 3.1 8.55 43.3 5.53 656.1 -0.06 0.02

(f) 10 kN (UDL = 5.0 kN/m²) on the two spans of bottom platform

Component

Strain Young's

modulus

𝐸


axial force

Mean Std Outside



Back

Post 2 -20.8 0.5 204 48.2 2.23 322.1 -1.37 0.03

Post 4 -29.7 0.5 204 48.2 2.23 322.1 -1.95 0.03

Post 6 -22.1 0.3 204 48.2 2.23 322.1 -1.45 0.02

Post 8 -1.3 0.7 204 48.2 2.23 322.1 -0.08 0.05

Front

Post 1 -11.4 0.9 204 48.2 2.23 322.1 -0.75 0.06

Post 3 -34.9 5.4 204 48.2 2.23 322.1 -2.29 0.36

Post 5 -22.0 4.6 204 48.2 2.23 322.1 -1.45 0.30

Post 7 1.5 0.8 204 48.2 2.23 322.1 0.10 0.05

Standard 1 -13.8 4.0 8.55 49.7 6.34 863.3 -0.10 0.03

Standard 2 -12.6 3.1 8.55 43.3 5.53 656.1 -0.07 0.02


125


(g) 15 kN (UDL = 7.6 kN/m²) on the two spans of upper platform

Component

Strain Young's

modulus

𝐸


axial force

Mean Std Outside



Back

Post 2 -24.2 1.0 204 48.2 2.23 322.1 -1.59 0.07

Post 4 -52.6 1.0 204 48.2 2.23 322.1 -3.45 0.07

Post 6 -22.1 0.8 204 48.2 2.23 322.1 -1.45 0.05

Post 8 0.5 2.9 204 48.2 2.23 322.1 0.03 0.19

Front

Post 1 -20.2 0.6 204 48.2 2.23 322.1 -1.32 0.04

Post 3 -57.3 1.3 204 48.2 2.23 322.1 -3.76 0.09

Post 5 -22.3 1.0 204 48.2 2.23 322.1 -1.46 0.07

Post 7 2.0 0.7 204 48.2 2.23 322.1 0.13 0.05

Standard 1 -18.2 4.0 8.55 49.7 6.34 863.3 -0.13 0.03

Standard 2 -15.8 6.1 8.55 43.3 5.53 656.1 -0.09 0.03

(h) 15 kN (UDL = 7.6 kN/m²) on the two spans of bottom platform

Component

Strain Young's

modulus

𝐸


axial force

Mean Std Outside



Back

Post 2 -29.0 0.8 204 48.2 2.23 322.1 -1.91 0.05

Post 4 -49.3 1.0 204 48.2 2.23 322.1 -3.24 0.07

Post 6 -31.8 0.2 204 48.2 2.23 322.1 -2.09 0.02

Post 8 -1.4 0.3 204 48.2 2.23 322.1 -0.09 0.02

Front

Post 1 -16.2 0.8 204 48.2 2.23 322.1 -1.06 0.06

Post 3 -48.4 8.3 204 48.2 2.23 322.1 -3.18 0.55

Post 5 -35.4 0.5 204 48.2 2.23 322.1 -2.33 0.03

Post 7 2.7 0.5 204 48.2 2.23 322.1 0.18 0.03

Standard 1 -11.3 3.5 8.55 49.7 6.34 863.3 -0.08 0.03

Standard 2 -15.5 4.1 8.55 43.3 5.53 656.1 -0.09 0.02


126


Table 4-19 Comparison of UDL test results with computer analysis

(a) 5 kN (UDL = 5.1 kN/m²) on the middle span of upper platform

Component Measured axial force

(mean value) (kN)

Analyzed

value (kN)

Difference



Back Post 4 -1.26 -1.1 12%

Post 6 -1.31 -1.08 18%

Front

Post 3 -1.06 -1.29 22%

Post 5 -1.14 -1.29 13%

Standard 2 -0.05 -0.06 31%

Note: Axial forces obtained from strain values smaller than or around its precision (1 × 10−6𝜀) was

not considered in comparison.

(b) 5 kN (UDL = 5.1 kN/m²) on the middle span of bottom platform


(mean value) (kN)

Analyzed

value (kN)

Difference



Back Post 4 -0.97 -1.2 24%

Post 6 -1.62 -1.21 25%

Front

Post 1 0.11 0.07 34%

Post 3 -0.88 -1.18 34%

Post 5 -0.95 -1.20 26%

Standard 2 -0.05 -0.06 18%



(c) 10 kN (UDL = 10.3 kN/m²) on the middle span of upper platform


(mean value) (kN)

Analyzed

value (kN)

Difference



Back Post 4 -2.38 -2.18 9%

Post 6 -2.54 -2.17 15%

Front

Post 1 0.15 0.09 40%

Post 3 -2.24 -2.58 15%

Post 5 -2.33 -2.59 11%

Standard 2 -0.098 -0.13 33%




127


(d) 10 kN (UDL = 10.3 kN/m²) on the middle span of bottom platform


(mean value) (kN)

Analyzed

value (kN)

Difference



Back

Post 2 -0.11 -0.15 34%

Post 4 -2.31 -2.42 5%

Post 6 -2.63 -2.43 8%

Front

Post 1 0.16 0.14 15%

Post 3 -1.73 -2.35 36%

Post 5 -2.23 -2.39 7%

Standard 2 -0.08 -0.12 45%



(e) 10 kN (UDL = 5.0 kN/m²) on the two spans of upper platform


(mean value) (kN)

Analyzed

value (kN)

Difference



Back

Post 2 -0.96 -1.11 15%

Post 4 -2.26 -2.2 2%

Post 6 -0.89 -1.15 30%

Front

Post 1 -0.79 -1.11 41%

Post 3 -2.38 -2.85 20%

Post 5 -0.93 -1.25 34%

Post 7 0.12 0.10 14%

Standard 1 -0.08 -0.08 2%

Standard 2 -0.06 -0.09 49%




128


(f) 10 kN (UDL = 5.0 kN/m²) on the two spans of bottom platform


(mean value) (kN)

Analyzed

value (kN)

Difference



Back

Post 2 -1.37 -1.29 6%

Post 4 -1.95 -2.43 25%

Post 6 -1.45 -1.34 8%

Front

Post 1 -0.75 -0.92 23%

Post 3 -2.29 -2.65 16%

Post 5 -1.45 -1.08 25%

Post 7 0.10 0.12 22%

Standard 1 -0.10 -0.07 31%

Standard 2 -0.07 -0.09 28%



(g) 15 kN (UDL = 7.6 kN/m²) on the two spans of upper platform


(mean value) (kN)

Analyzed

value (kN)

Difference



Back

Post 2 -1.59 -1.67 5%

Post 4 -3.45 -3.31 4%

Post 6 -1.45 -1.73 19%

Front

Post 1 -1.32 -1.67 26%

Post 3 -3.76 -4.27 14%

Post 5 -1.46 -1.88 29%

Post 7 0.13 0.15 14%

Standard 1 -0.13 -0.11 18%

Standard 2 -0.09 -0.14 58%




129


(h) 15 kN (UDL = 7.6 kN/m²) on the two spans of bottom platform


(mean value) (kN)

Analyzed

value (kN)

Difference



Back

Post 2 -1.91 -1.95 2%

Post 4 -3.24 -3.66 13%

Post 6 -2.09 -2.01 4%

Front

Post 1 -1.06 -1.37 29%

Post 3 -3.18 -3.96 24%

Post 5 -2.33 -1.62 30%

Post 7 0.18 0.19 8%

Standard 1 -0.08 -0.11 32%

Standard 2 -0.09 -0.13 50%



Table 4-20 Summary of UDL test and analysis

UDL test cases Applied

UDL



Metal tube Bamboo

Max Average Std Max Average Std

Middle span

Upper

platform

5 kN 22% 16% 4% 31% / /

10 kN 40% 18% 11% 33% / /

Bottom

platform

5 kN 34% 29% 4% 18% / /

10 kN 36% 18% 13% 45% / /

Two spans

Upper

platform

10 kN 41% 22% 13% 49% 26% 24%

15 kN 29% 16% 9% 58% 38% 20%

Bottom

platform

10 kN 25% 18% 8% 31% 29% 2%

15 kN 30% 16% 11% 50% 41% 9%

Total 41% 19% 11% 58% 33% 15%

Note: “/” means there is only one bamboo member with strain value larger than its precision (1 ×

10−6𝜀), see Table 4-19 (a)-(d).

Table 4-21 Displacement of connection under 2 kN static point load

Connection Displacement (mm)

1st test 2nd test 3rd test

(1) Bamboo-bamboo 22.81 18.10 17.87

(2) Bamboo-bamboo 25.27 17.17 16.30

(3) Bamboo-anti-sliding steel tube 19.87 14.48 13.59

(4) Bamboo-anti-sliding steel tube 22.63 15.75 15.27


130


Table 4-22 Results for static point load test (2 kN) on connection

(a) Connection (1)

Component

Strain Young's

modulus

𝐸


axial force

Mean Std Outside



Front

Post 1 1.4 1.1 204 48.2 2.23 322.1 0.09 0.08

Post 3 -14.1 0.3 204 48.2 2.23 322.1 -0.92 0.02

Post 5 -12.1 1.1 204 48.2 2.23 322.1 -0.80 0.07

Post 7 1.1 0.6 204 48.2 2.23 322.1 0.07 0.04

Standard 1 0.9 0.7 8.55 49.7 6.34 863.3 0.007 0.01

Standard 2 -7.2 1.9 8.55 43.3 5.53 656.1 -0.04 0.01

Standard 3 -0.9 0.3 8.55 50.0 6.38 874.4 -0.007 0.00

Brace 1 -3.3 0.6 204 48.2 2.23 322.1 -0.21 0.04

Brace 2 -4.0 0.4 204 48.2 2.23 322.1 -0.26 0.03

(b) Connection (2)

Component

Strain Young's

modulus

𝐸


axial force

Mean Std Outside



Front

Post 1 1.7 0.4 204 48.2 2.23 322.1 0.11 0.02

Post 3 -13.7 0.2 204 48.2 2.23 322.1 -0.90 0.01

Post 5 -10.9 1.1 204 48.2 2.23 322.1 -0.72 0.07

Post 7 1.2 0.5 204 48.2 2.23 322.1 0.08 0.03

Standard 1 1.1 0.8 8.55 49.7 6.34 863.3 0.008 0.01

Standard 2 -13.7 1.5 8.55 43.3 5.53 656.1 -0.08 0.01

Standard 3 -0.4 0.2 8.55 50.0 6.38 874.4 -0.003 0.001

Brace 1 -2.0 0.4 204 48.2 2.23 322.1 -0.13 0.03

Brace 2 -2.3 0.2 204 48.2 2.23 322.1 -0.15 0.01


131


(c) Connection (3)

Component

Strain Young's

modulus

𝐸


axial force

Mean Std Outside



Front

Post 1 -2.3 0.4 204 48.2 2.23 322.1 -0.15 0.03

Post 3 -25.6 1.3 204 48.2 2.23 322.1 -1.68 0.08

Post 5 -1.0 1.2 204 48.2 2.23 322.1 -0.06 0.08

Post 7 -1.0 0.9 204 48.2 2.23 322.1 -0.07 0.06

Standard 1 -0.7 0.8 8.55 49.7 6.34 863.3 -0.005 0.01

Standard 2 -0.7 1.4 8.55 43.3 5.53 656.1 -0.004 0.01

Standard 3 -0.5 1.2 8.55 50.0 6.38 874.4 -0.004 0.01

Brace 1 -1.5 0.4 204 48.2 2.23 322.1 -0.10 0.02

Brace 2 -1.4 0.3 204 48.2 2.23 322.1 -0.09 0.02

(d) Connection (4)

Component

Strain Young's

modulus

𝐸


axial force

Mean Std Outside



Front

Post 1 -1.4 0.5 204 48.2 2.23 322.1 -0.09 0.04

Post 3 -25.7 0.2 204 48.2 2.23 322.1 -1.69 0.01

Post 5 -0.9 0.4 204 48.2 2.23 322.1 -0.06 0.02

Post 7 -1.1 0.5 204 48.2 2.23 322.1 -0.07 0.03

Standard 1 -1.0 0.6 8.55 49.7 6.34 863.3 -0.007 0.005

Standard 2 -1.3 0.5 8.55 43.3 5.53 656.1 -0.007 0.003

Standard 3 -0.2 0.5 8.55 50.0 6.38 874.4 -0.002 0.004

Brace 1 -3.0 0.7 204 48.2 2.23 322.1 -0.20 0.05

Brace 2 -2.1 0.3 204 48.2 2.23 322.1 -0.14 0.02

Table 4-23 Load-carrying capacity of connections

Connection Tested failure load (kN)

(1) Bamboo-bamboo 3.23

(2) Bamboo-bamboo 4.57

(3) Bamboo-anti-sliding steel tube 4.82

(4) Bamboo-anti-sliding steel tube 4.55


132


Table 4-24 Comparison of connection displacement between test and analysis

Connection

Displacement

from 1st test

(mm)

SAP 2000 with average

bamboo ledger diameter

SAP 2000 with measured


Displacement

(mm)

Difference

(%)

Displacement

(mm)

Difference

(%)

(1) 22.81 30.2 32.4 19.7 -13.6

(2) 25.27 36.5 44.4 19.4 -23.2

(3) 19.87 25.3 27.3 21.3 7.2

(4) 22.63 25.1 10.9 22.3 -1.5

Note 1: The measured outside diameter and thickness of bamboo ledger is determined by the same

procedure as in Section 2.4.3

Note 2: Difference= (Model-Test) / Test.

Table 4-25 Comparison of load-carrying capacity of connection

Connection Testing

results (kN)

SAP 2000 with average


SAP 2000 with measured


Load-carrying

capacity (kN)

Difference

(%)

Load-carrying

capacity (kN)

Difference

(%)

(1) 3.23 2.05 -36.5 2.75 -14.9

(2) 4.57 2.0 -56.2 3.25 -28.9

(3) 4.82 3.0 -37.8 4.0 -17.0

(4) 4.55 3.0 -34.1 3.75 -17.6

Note: Difference= (Model-Test) / Test.

Table 4-26 Comparison of axial forces under 2.0 kN load

(a) Connection (1)


(mean value) (kN)

Analyzed

value (kN)

Difference



Front

Post 1 0.09 0.08 8%

Post 3 -0.92 -0.84 9%

Post 5 -0.80 -0.96 21%

Standard 2 -0.04 -0.064 58%

Brace 1 -0.21 -0.26 20%

Brace 2 -0.26 -0.23 12%




133


(b) Connection (2)


(mean value) (kN)

Analyzed

value (kN)

Difference



Front

Post 1 0.11 0.10 14%

Post 3 -0.90 -1.01 12%

Post 5 -0.72 -1.03 43%

Standard 2 -0.08 -0.063 18%

Brace 1 -0.13 -0.10 24%

Brace 2 -0.15 -0.09 38%



(c) Connection (3)


(mean value) (kN)

Analyzed

value (kN)

Difference



Front

Post 1 -0.15 -0.09 -42%

Post 3 -1.68 -1.58 -6%

Brace 1 -0.10 -0.13 31%

Brace 2 -0.09 -0.08 -14%



(d) Connection (4)


(mean value) (kN)

Analyzed

value (kN)

Difference



Front

Post 1 -0.09 -0.08 -15%

Post 3 -1.69 -1.61 -5%

Brace 1 -0.20 -0.13 -36%

Brace 2 -0.14 -0.08 -42%




134


Table 4-27 Summary of connection test and analysis

Connection Static

point load



Metal tube Bamboo


(1)

2.0 kN

21% 14% 5% 58% / /

(2) 43% 26% 12% 18% / /

(3) 42% 23% 14% / / /

(4) 42% 25% 15% / / /

Total 43% 22% 13% 58% 38% 20%

Note: “/” means there is only one or no bamboo member with strain value larger than its precision

(1 × 10−6𝜀), see Table 4-26 (a)-(d).


135


Chapter 5 Use of Different Materials for the

Working Platform

5.1 Types for the working platform

There are two types of working platform commonly used in the industry. First one is

formed by placing wooden boards or pre-fabricated iron planks on transoms. The

other one is by fastening bamboo members (Kao Jue) on transoms at a closely-spaced

distance (≤ 150 mm) to form an integrated bamboo platform, above which thin

wooden boards are usually placed for ease of work as well as to prevent debris/objects

falling through. In this chapter, the safety of the following three commonly used

platform Types were investigated numerically and experimentally:

(1) Type 1: Integrated bamboo members with thin wooden boards, see Fig. 5-1 (a);

(2) Type 2: Thick wooden boards, see Fig. 5-1 (b);

(3) Type 3: Pre-fabricated iron planks, see Fig. 5-1 (c).

5.2 Mechanical properties of wooden boards and iron planks

The material properties of bamboo (Kao Jue) have been studied in previous

investigations. Please see Appendix B1 for a summary. The wooden boards used in

this study were purchased from the market and were made of plywood as seen in Fig.

5-2. Both the thick and thin wooden boards have a width of 200 mm and with a

thickness of 25 mm and 12 mm, respectively. The iron planks were provided by the

Sinoscaff (HK) Ltd. with dimensions shown in Fig. 5-3.

Three-point loading tests were used to evaluate the flexure modulus and the ultimate

bending strength of the wooden boards and the iron planks. Specimens were placed in


136


the Dartec loading machine with round pin supports at both ends. Load was added at

the middle of specimens through a round tube as shown in Fig. 5-4. The distance

between two simply supported pins for wooden board test and iron plank test was set

as 0.6 m and 1.6 m, respectively. For the thick and thin wooden boards, six tests were

performed each. Four tests were performed for the iron planks. Fig. 5-5 shows a

typical load-deflection curve for the iron plank. The flexural modulus 𝐸 can be

obtained through the formula:

𝑃

∆=

48𝐸𝐼

𝐿3

where

P is load in the initial load-deflection curve;

△ is the corresponding deflection;

L is the distance between the two simply supported pins;

I is the moment of area.

The ratio of P over △ can be obtained from a linear regression of the initial slope of the

load–deflection curve as shown in Fig. 5-5. Table 5-1 summarizes the mechanical

properties for the thin and thick wooden boards. It is seen that the ultimate load for

the thin wooden board is about 1 kN, while that for the thick wooden board is about

four times. Both of them have about the same ultimate bending strength 30-35 MPa

and about the same flexural modulus 4.5-4.8 GPa. Table 5-2 summarizes the

mechanical properties for the iron planks. It is seen that its ultimate load is about 2 kN,

ultimate bending strength is about 376 MPa and flexural modulus is about 167 GPa.

5.3 Full-scale test of working platform

After obtain the properties of wooden boards and iron planks, the structural behavior


137


of three types of platform was investigated experimentally and numerically.


The Type 1 mixed scaffolding tested in Chapter 4 was used for the full-scale test of

working platform with three different types: integrated bamboo members with thin

wooden boards; thick wooden boards and iron planks. From the UDL test and

load-carrying capacity analysis of platform in Chapter 4, the platform boards would

not fail under the UDL and the load-carrying capacity is dominated by the failure of

bamboo transom. In this section, the safety and deflection behavior of three different

types on real support under partial area load or point load would be investigated.

According to BS EN 12811-1 [22], the working area for load classes 5 and 6 shall be

capable of supporting a uniformly distributed partial area load of 7.5 kN/m² and 10

kN/m², respectively. The partial area for load classes 5 and 6 is obtained by

multiplying the area of the bay by the partial area factor 0.4 and 0.5, respectively. The

dimensions and position of the partial area shall be chosen to give the most

unfavourable codition (maximum moment and deflection), as shown in Fig. 5-6. For

simplicity, an equivalent point load was used in test instead of the partial area load,

which gives a larger moment and deflection. The equivalent point load for load

classes 5 and 6 is 2.93 kN and 4.88 kN when testing in Type 1 mixed scaffolding with

bay length 1.5 m and platform width 0.65 m. A loading device made of the steel tube

and couplers was used to form a static point load condition (equivalent line UDL). The

static point load was applied in the middle working area of platform. The setup of

static point load test for the three platform types is shown in Fig. 5-7. The loading

device was set to apply a point load up to 3 kN or 5 kN on the middle of working area.

Each type was tested four times. The displacement at the midpoint of the inner layer

was recorded by LVDT for comparison.


138


5.3.2 Test results

Table 5-3 summaries the deflection of the midpoint of the inner layer for the three

platform types under 3 kN and 5 kN point load for comparison. Fig. 5-8 shows the

load-deflection curves for the three types under a static point load larger than 3 kN. It

is seen that all three platform types have about the same linear elastic deflection

behavior under loads. This shows that the platform with all three types remained very

much intact during the tests. No noticeable damage on the platform and the

scaffolding was observed after all the tests. The measured axial force in bamboo

standards and steel posts were calculated by multiplying the measured strain values

with the calculated cross sectional area of bamboo and steel tube respectively. Table

5-4 summarizes the mean values and standard deviations of strains and axial forces

under recorded static point load of 3 kN. The post number and standard number are

the same as in Fig. 4-25. It is seen that the point load acting on the platform was

mainly carried by the posts directly under the loading position.


reported in Section 4.2 was performed for all the static point load cases tested above.

Fig. 5-9 shows the comparison of load-deflection curves between test and analysis for

all three platform types. It is seen that the displacements estimated from the numerical

analysis are in general higher than those measured from the test. Both of them show

linear elastic behavior. Table 5-5 summarizes the comparison of displacement at the

midpoint of inner layer of the bottom platform for the three platform types under 3

and 5 kN load. It is seen that the difference between test and analysis ranges between

30 to 67%. Table 5-6 compares the axial forces in some of the posts and standards

between test and analysis under 3 kN point load acting on the platform. Table 5-7

further summarizes the difference between test and analysis results. It can be

concluded that the axial force difference between full-scale test and numerical analysis

was about 32% for the bamboo members and about 14% for the metal members. In


139


summary, both the test and analysis results confirm that all three platform types:

integrated bamboo members with thin wooden boards, thick wooden boards, and iron

planks, have similar mechanical behavior on real support and seem to be able to be

used as a safe platform for the scaffolding.

(a) Type 1: Integrated bamboo members (thin wooden boards are not shown)

(b) Type 2: Thick wooden boards


140


(c) Type 3: Prefabricated iron planks

Fig. 5-1 Three working platform Types

Fig. 5-2 Thin and thick wooden boards made out of plywood


141


Fig. 5-3 Dimension of pre-fabricated iron plank

(a) Test on a wooden board (b) Test on an iron plank

Fig. 5-4 Three-point loading test on wooden board and iron plank

Fig. 5-5 A typical load-deflection curve for an iron plank

y = 0.0488x + 0.2925

0

0.5

1

1.5

2

2.5

0 20 40 60 80 100 120 140 160

Mid

load

(k

N)

Mid deflection (mm)

0.6 m

1.6 m

P

△


142


Fig. 5-6 Dimensions and position of the partial area

(a) Type 1: Integrated bamboo members with thin wooden boards

Area of the bay

Partial area


143



(c) Type 3: Iron planks

Fig. 5-7 Setup of static point load test on the middle span of platform


144


Fig. 5-8 Typical load-deflection curves of three platform types

Fig. 5-9 Comparison of load-deflection curves between test and analysis

0

2

4

6

8

10

12

14

0 0.5 1 1.5 2 2.5 3 3.5 4

Def

lect

ion

(m

m)

Line UDL (kN)

Bamboo +

thin wooden

board

Thick

wooden

board

Iron plank

0

2

4

6

8

10

12

14

16

18

0 1 2 3 4

Def

lect

ion

(m

m)

Line UDL (kN)

Bamboo + thin

wooden board

Model

Test

Thick wooden

board Model

Test

Iron plank

Model

Test


145


Table 5-1 Mechanical properties for wooden boards

Specimen Width

(mm)

Thickness

(mm)

Ultimate

test load

(kN)

Ultimate

bending

strength

(MPa)

Initial slope of

the load–

deflection

curve (kN/mm)

Flexural

rigidity

(N·m²)

Flexural

modulus

(GPa)

Thin wooden board

1 200 11.6 1.22 40.4 0.0285 128.3 4.88

2 199 11.6 0.95 31.7 0.0258 116.1 4.46

3 200 11.6 0.92 30.4 0.0306 137.7 5.24

4 200 11.6 1.02 33.7 0.0275 123.8 4.71

5 200 11.7 1.01 33.3 0.0273 122.9 4.65

6 200 11.7 1.26 41.6 0.0299 134.6 5.11

Average 200 11.6 1.06 35.2 0.0283 127.2 4.84

Thick wooden board

7 200 23.7 4.50 35.9 0.2090 940.5 4.22

8 201 24.2 3.83 29.2 0.2490 1120.5 4.71

9 200 23.4 3.28 26.9 0.2070 931.5 4.36

10 200 23.5 3.16 25.8 0.2030 913.5 4.24

11 200 23.9 4.79 37.7 0.2260 1017.0 4.46

12 200 23.9 3.65 28.7 0.2390 1075.5 4.73

Average 200 23.8 3.86 30.7 0.2222 999.8 4.45

Table 5-2 Mechanical properties for iron planks

Specimen Width

(mm)

Thickness

(mm)

Ultimate

test load

(kN)

Ultimate

bending

strength

(MPa)

Initial slope of

the load–

deflection

curve (kN/mm)

Flexural

rigidity

(N·m²)

Flexural

modulus

(GPa)

1 221 1.20 2.17 414.3 0.0408 3481.6 149.9

2 220 1.21 1.89 360.7 0.0456 3891.2 167.5

3 220 1.18 1.88 358.8 0.0470 4010.7 172.6

4 220 1.22 1.95 372.2 0.0488 4164.3 179.2

Average 220 1.20 1.97 376.5 0.0456 3886.9 167.3

Note: Due to complexity of the section of iron planks, the second moment of area and section

modulus based on average measured dimensions are used for all specimens.


146


Table 5-3 Deflection at the midpoint of inner layer

Platform Type Under line UDL: 3 kN (mm) Under line UDL: 5 kN (mm)

1st 2nd 3rd 4th 3rd 4th

Integrated bamboo

members with thin wooden

boards

10.74 9.49 10.59 8.94 18.14 16.59

Thick wooden boards 10.82 8.14 8.58 8.12 16.21 15.08

Iron planks 10.63 9.45 8.97 9.21 15.57 15.18

Table 5-4 Results for static point load (3 kN) on working platform


Component

Strain Young's

modulus

𝐸


axial force

Mean Std Outside


× 10−6𝜀 GPa mm mm mm² kN

Back

Post 2 0.4 1.0 204 48.2 2.23 322.1 0.03 0.07

Post 4 -13.7 0.3 204 48.2 2.23 322.1 -0.90 0.58

Post 6 -14.5 1.0 204 48.2 2.23 322.1 -0.95 0.52

Post 8 0.7 0.8 204 48.2 2.23 322.1 0.05 0.05

Front

Post 1 1.2 0.7 204 48.2 2.23 322.1 0.08 0.05

Post 3 -9.7 1.9 204 48.2 2.23 322.1 -0.64 0.12

Post 5 -9.0 2.4 204 48.2 2.23 322.1 -0.59 0.16

Post 7 1.2 0.8 204 48.2 2.23 322.1 0.08 0.05

Standard 1 0.3 0.6 8.55 49.7 6.34 863.3 0.003 0.004

Standard 2 -8.6 2.7 8.55 43.3 5.53 656.1 -0.05 0.01


147



Component

Strain Young's

modulus

𝐸


axial force

Mean Std Outside



Back

Post 2 0.8 1.5 204 48.2 2.23 322.1 0.05 0.10

Post 4 -13.7 0.3 204 48.2 2.23 322.1 -0.90 0.02

Post 6 -11.6 0.8 204 48.2 2.23 322.1 -0.76 0.05

Post 8 1.3 1.1 204 48.2 2.23 322.1 0.08 0.07

Front

Post 1 2.0 0.9 204 48.2 2.23 322.1 0.13 0.06

Post 3 -9.5 0.6 204 48.2 2.23 322.1 -0.63 0.04

Post 5 -10.9 0.7 204 48.2 2.23 322.1 -0.72 0.05

Post 7 1.4 0.3 204 48.2 2.23 322.1 0.09 0.02

Standard 1 -0.3 0.3 8.55 49.7 6.34 863.3 -0.002 0.002

Standard 2 -6.7 0.9 8.55 43.3 5.53 656.1 -0.04 0.01


Component

Strain Young's

modulus

𝐸


axial force

Mean Std Outside



Back

Post 2 0.7 1.3 204 48.2 2.23 322.1 0.04 0.09

Post 4 -11.0 1.5 204 48.2 2.23 322.1 -0.72 0.10

Post 6 -15.1 2.1 204 48.2 2.23 322.1 -1.00 0.14

Post 8 1.2 0.9 204 48.2 2.23 322.1 0.08 0.06

Front

Post 1 2.6 1.2 204 48.2 2.23 322.1 0.17 0.08

Post 3 -11.4 3.6 204 48.2 2.23 322.1 -0.75 0.24

Post 5 -10.7 1.8 204 48.2 2.23 322.1 -0.70 0.12

Post 7 1.3 0.2 204 48.2 2.23 322.1 0.08 0.01

Standard 1 0.4 0.7 8.55 49.7 6.34 863.3 0.003 0.01

Standard 2 -11.3 4.1 8.55 43.3 5.53 656.1 -0.06 0.02

Table 5-5 Comparison of deflection between test and analysis

Platform Type

Under line UDL: 3 kN (mm) Under line UDL: 5 kN (mm)

Testing

result SAP model Difference

Testing

result SAP model Difference

Type 1 10.74 14.1 31.3% 18.14 23.5 29.5%

Type 2 10.82 16.2 49.7% 16.21 27.1 67.2%

Type 3 10.63 13.8 29.8% 15.57 23.0 47.7%


148


Note: Difference= (Model-Test) / Test.

Table 5-6 Comparison of axial forces under 3 kN load



(mean value) (kN)

Analyzed

value (kN)

Difference



Back Post 4 -0.90 -0.88 2%

Post 6 -0.95 -0.88 8%

Front

Post 3 -0.64 -0.71 12%

Post 5 -0.59 -0.66 11%

Standard 2 -0.05 -0.04 17%





(mean value) (kN)

Analyzed

value (kN)

Difference



Back Post 4 -0.90 -0.82 9%

Post 6 -0.76 -0.82 7%

Front

Post 1 0.13 0.09 32%

Post 3 -0.63 -0.78 24%

Post 5 -0.72 -0.79 10%

Post 7 0.09 0.08 12%

Standard 2 -0.04 -0.06 59%





(mean value) (kN)

Analyzed

value (kN)

Difference



Back Post 4 -0.72 -0.79 9%

Post 6 -1.00 -0.80 20%

Front

Post 1 0.17 0.11 35%

Post 3 -0.75 -0.80 7%

Post 5 -0.70 -0.79 13%

Post 7 0.08 0.08 5%

Standard 2 -0.06 -0.05 21%




149


Table 5-7 Summary for platform test and analysis

Platform Type Static point

load



Metal tube Bamboo


Type 1

3 kN

12% 8% 4% 17% / /

Type 2 32% 16% 9% 59% / /

Type 3 35% 15% 10% 21% / /

Total 35% 14% 9% 59% 32% 19%

Note: “/” means there is only one bamboo member with strain value larger than its precision (1 ×

10−6𝜀), see Table 5-6 (a)-(c).


150


Chapter 6 Conclusions and

Recommendations

The aim of this study is on the safe usage of bamboo and mixed scaffoldings using

combination of laboratory tests and computer analysis. The computer analyses were

conducted using the finite element analysis program SAP 2000 and the laboratory tests

were conducted in the Structural Laboratory of the Hong Kong University of Science

and Technology. Conclusions and recommendations obtained from this study can be

summarized as follows.

(1) Anchorages for the safety harness

Two regional reinforcement options that can meet the anchorage requirements for

safety harness are proposed to serve as safe anchorages:

Option 1: Reinforce ledgers of two layers by adding two steel tubes and linking

them though a steel strut; and

Option 2: Reinforce platform by adding an additional transom and two steel tubes

underneath the platform.

Both reinforcement options can resist more than 8 kN of static load and 100 kg of

drop load without causing any damage to the scaffolding. Furthermore, it is feasible to

form a reinforcement region by adding additional vertical steel struts to Option 1. This

reinforcement region can accommodate multiple users simultaneously as long as the

spacing between the users is equal or larger than two spans. The anchor points inside

the reinforcement region can provide a load-carrying capacity larger than 8 kN. It is

recommended that energy absorbing devices with a MAF of 4 kN be used on these

anchor points so that these anchor points can protect the users with a safety factor of

two. A safer erection and dismantling procedure is presented for bamboo scaffolding

to ensure that there are guardrails up to the chest of workers at all time and the

maximum falling height is limited to less than 2 meters to prevent any serious injury


151


to workers in case of accident. This erection and dismantling procedure is animated

and illustrated using the building information modeling (BIM) software. Note that this

procedure could also be applied to mixed scaffoldings. For those scaffoldings that

extend beyond roof top, horizontal lifeline systems (HLLs) with stanchions appear to

be a good option for anchoring safety harness. For those platforms below the roof

level, HLLs fixed on vertical concrete wall is also an effective way to provide safe

anchorage.

(2) Issue relating to the use of mixed scaffoldings

Three different types of mixed scaffolding are established:

Type 1: Anti-sliding vertical tube with bamboo ledger;

Type 2: Anti-sliding vertical tube with steel main ledger; and

Type 3: Mixed scaffolding incorporating couplers.

Studies show that all three types of mixed scaffolding can meet the load requirements

(3 kN/m² for masonry or special duty) specified in the bamboo or metal scaffolding

codes. Among the three types of mixed scaffolding, Type 1 is the least expensive and

is more suitable for short term usage. Type 3 is the most costly but can offer a more

robust performance under different environmental condition.

(3) Use of different materials for the working platform

Three commonly used platform types have been investigated and compared

numerically and experimentally:

Type 1: Bamboo members with thin wooden boards (thickness 12 mm);

Type 2: Thick wooden boards (thickness 25 mm); and

Type 3: Prefabricated iron planks.

All three types of platform exhibit good integrity under full-scale scaffolding tests.

None of them show any sign of damage under a static load larger than 5 kN acting at

the middle of platform. Results suggest that all three types can function very well as a

platform for the scaffolding.


152


Appendix

Appendix A Other types of connection and test fixture

A1 Column (or beam/bracing) splice test

The splice in scaffolding is the type of connection used to join or overlap same units

together. In this chapter, the experiments and analysis will be focused on four

parameters which affect the characteristic resistance of splice for bracings, ledgers and

standards used in the erection of bamboo scaffold. Firstly, we will analyze the effect of

presence of nodes, the contact length, number of ties and number of round turns on

resistance. Then the resistance of actual splice between bamboos according to Hong

Kong bamboo scaffolding codes [12, 17] will be investigated. The controlling variable

method was used to arrange experiments and analyze their different degrees of

influence. The setup of splice test is shown in Fig.A-1. In the test, one bamboo member

was hold in position and the load was applied parallel to the other one.

The effect of presence of nodes and number of round turns:

Firstly, two same bamboo members (BP) were used in experiments to find the effect of

presence of nodes and number of round turns on resistance of splice between bamboos.

All of these tests maintain the same contact length and single tie between bamboo

members. The contact length between two bamboo members is 0.45 m. Three cases of

presence of node were studied: case 1: the tie is far away from nodes; case 2: the tie is

close to only one node; case 3: the tie is closely between two nodes. Different number

of round turns to fasten splice was analyzed for case 1: (1) splice was fastened with five

round turns; (2) splice was fastened with four round turns. Table A-1 shows the

arrangement of experiments and the testing results. From experimental data, following

observations can be seen:


153


(1) The resistance of splice under case 1 with 5 round turns and case 2 is very close.

The failure mode of these two cases is always slipping between bamboo members.

(2) Comparing case 1 with different round turns to fasten splice, the number of round

turns shows a big impact on the resistance.

(3) The splice fastened closely between two nodes (case 3) shows a very large

resistance, and the failure mode is always splitting of plastic stripes.

The effect of number of ties and contact length:

This section focused on the effect of contact length and number of ties on resistance

between two bamboo members. Also, two same bamboo members (BP) were used in

experiment to eliminate the effect of other factors. During the tests, the situation that

ties closely between two nodes was intentionally avoided to prevent the buckling

failure of bamboo. Fig. A-2 shows test set up of splice between two BP with same

contact length 1.3m and different number of ties. Table A-2 shows the results of the

experiments and the following conclusions can be drawn:

(1) The influence of number of ties on resistance is far greater than the contact length

between two bamboo members.

(2) The resistance of splice shows approximately multiple relationships with the

number of ties.

Resistance of actual column (or beam/bracing) splice in bamboo scaffoldings:

Resistance of actual splice between bamboo members for bracings, ledgers and

standards used in the erection of bamboo scaffolding was studied in this section. The

contact length between two bamboo members are 1.8 m and total six ties were arranged

at an approximate distance of 30 cm [12, 17] (see Fig. A-3). In experiments, the ties

between two close nodes were artificially avoided for conservative consideration. This

practice also helps to avoid the buckling destruction of bamboo members in test. Every


154


five tests were conducted for splice between two BP and two PP respectively. The

bamboo members were selected randomly and two different bamboo members were

used for each test. This arrangement can give a more realistic experimental result.

Tested resistance data is concluded in Table A-3, and from which, following

observations can be seen:

(1) The resistance of splice between two PP is smaller than which between two BP. This

is mainly because of the larger diameter of PP so that the number of round turns is

less than it in the splice between two BP.

(2) During tests, the occurrence of loose of stripes under loading for actual splice is

more often than above four-ties splice. This due to the bending effect is more

important in long bamboo members and this effect may cause the loose of plastic

strips during the deformation of strips under loading. Thus, the resistance of six-ties

splice didn’t show a larger resistance compared with four-ties splice.

(3) Due to the different shape (cross-section area, initial curvature) and surface property

of different bamboo members, a larger variation of resistance is shown compared

with previous tests.

A2 A special type of connection called “打戒指”

“打戒指” is a commonly used type of beam-column connection in bamboo scaffolding.

Fig. A-4 shows a typical configuration of this type of connection. It is commonly used

to avoid slipping between two bamboo members caused by shrink of new bamboos.

The slipping stiffness behavior and resistance of this type connection were investigated

through experiments. Table A-4 presents the experimental results of this type of

connection. It should be noted that the resistance of connection with a slipping of 100

mm was selected and shown in this table.

It can be found that the failure mode of this type of connection is always the large


155


deformation of plastic stripes and slipping between bamboo members. The resistance

will increase as the slipping between two orthotropic members increased, and a relative

displacement larger than 100 mm will always happen without splitting and looseness of

plastic stripes. The failure mode of “打戒指” and a corresponding load-displacement

curve are shown in Fig. A-5 (a) and (b), respectively. This type of connection has a

larger connection resistance and smaller slipping stiffness compared with the

connection fastened by 5-round plastic stripes. The connection behavior of “打戒指”

has also been considered in design of bamboo scaffolding reinforced anchorages but it

couldn’t improve the safety of connection as anchorage due to its small slipping

stiffness.

A3 Fixture for beam-column connection test

CAD view of connection test fixture


156


Front view and dimensions (mm) of connection test fixture

Top view and dimensions (mm) of connection test fixture


157


Fig. A-1 Setup of splice test

Fig. A-2 Test setup of splice with contact length 1.3 m and different number of ties

0.3 m 0.3 m 0.3 m

0.9 m

0.2 m 0.2 m

0.2 m 0.2 m


158


(a) Actual connections between two PP

(b) Actual connections between two BP

Fig. A-3 Test setup of actual connection with six ties

Fig. A-4 Typical configuration of “打戒指”


159


(a) Failure mode of “打戒指” (before and after loading)

(b) Typical load-displacement curve of “打戒指”

Fig. A-5 Failure mode and typical load-displacement curve of “打戒指”

y = 0.0239x

0

0.5

1

1.5

2

2.5

3

0 20 40 60 80 100 120

UT

M F

orc

e (

kN

)



160


Table A-1 Effects of presence of nodes and number of round turns on resistance

Test

series

No.

of

tests

Contact

length(m)

No. of

round

turns

Presence

of nodes

Resistance(kN) Illustration

Failure

Mode Mean Std

Case

1 5 0.45 5 None 0.53 0.128

Relative

slippage

between

bamboo

members

Case

1 5 0.45 4 None 0.37 0.074

Case

2 5 0.45 5 One side 0.52 0.044

Case

3 5 0.45 5

Two

sides 4.18 0.296

Splitting

of

plastic

strips

Table A-2 Experiments to study the effect of number of ties and contact length

No. of tests Contact

length(m)

No. of round

turns No. of ties

Resistance(kN)

Mean Std

5 0.65 5 2 1.02 0.237

5 1.3 5 2 1.38 0.275

5 1.3 5 4 2.20 0.179

Table A-3 Tested resistance of actual splices

Test series No. of

tests

Contact

length(m)

No. of round

turns No. of ties

Resistance(kN)

Mean Std

BP-BP 5 1.8 5 6 2.83 0.53

PP-PP 5 1.8 4 6 2.28 0.65


161


Table A-4 Resistance of “打戒指” beam-column connection

Test series Presence of

nodes

No. of

tests

Resistance (kN)

Horizontal

member

Vertical

member

Mean

(Disp. = 100 mm) Std

BP BP None 3 2.30 0.28

BP PP None 3 2.52 0.31

Steel tube BP None 3 2.36 0.19

Appendix B Material properties of bamboo and steel tube

B1 Mechanical properties of bamboo

There were two bamboo species, namely Bambusa Pervariabilis (or Kao Jue) and

Phyllostachys Pubecens (or Mao Jue), commonly used in bamboo scaffoldings. Recent

scientific investigations on bamboo as construction materials were published by Chung

and Yu in 2002 [30]. Compression and bending tests were conducted to establish the

characteristic strengths and the Young’s modulus of these bamboo species. Table B-1

summaries the physical and mechanical properties of Kao Jue and Mao Jue under

different moisture. The experimental results have been verified with an average model

factor about 2 ( 𝑚𝑜𝑑𝑒𝑙 𝑓𝑎𝑐𝑡𝑜𝑟 =𝑀𝑒𝑎𝑠𝑢𝑟𝑒𝑑 𝑓𝑜𝑟𝑐𝑒 𝑎𝑛𝑑 𝑐𝑎𝑝𝑎𝑐𝑖𝑟𝑦

𝐷𝑒𝑠𝑖𝑔𝑛 𝑓𝑜𝑟𝑐𝑒 𝑎𝑛𝑑 𝑐𝑎𝑝𝑎𝑐𝑖𝑡𝑦) when using a proposed

material partial safety factor 1.5 against the characteristic strength (at fifth percentile)

to get the design strength of bamboo. So the proposed mechanical properties with the

appropriate material partial safety factor were used in analysis for this report.


162


B2 Mechanical properties of steel tube

According to material requirements of loose tubes (BS EN 12811-1 [22]), loose tubes

connected by couplers (BS EN 74-1 [21]) shall have a minimum nominal yield

strength of 235 N/mm², nominal external diameter of 48.3 mm and a minimum

nominal wall thickness of 3.2 mm. It should however be noted that the steel tubes

with the same external diameter but a thickness of 2.3mm are commonly used in

mixed scaffoldings in Hong Kong.

There are three sizes of steel tube commonly available in Hong Kong (see Fig. B-1):

(a) 48.3 mm (external diameter) × 4 mm (thickness) complying with BS EN 10255

[31]; (b) 48.3 mm × 3.2 mm complying with [31] and (c) 48.3 mm × 2.3 mm with no

specific standards. To determine their mechanical properties, tensile test were carried

out in accordance with ASTM E8 [32]. Dimensions of the test specimens are shown in

Appendix B3. Due to the curved surface of tube, a pair of testing fixture with the same

curved surface shape was made for the test. The dimensions of the fixture are also

presented in Appendix B3. The tensile test was carried out in the Structural

Engineering Laboratory of HKUST using a MTS Universal Testing Machine with

MTS 647 hydraulic wedge grip (see Fig. B-2). Fig. B-3 (a) and (b) show the

load-displacement curve and the enlarged initial stress-strain curve of specimen D2

for obtaining the yield strength and the young’s modulus of the specimen,

respectively.

Results obtained from the tensile test are shown in Table B-2. It can be see that the

characteristic yield strength, which is about 350 MPa for all three sizes of steel tube,

is much larger than the minimum yield strength of 235 N/mm² (235 MPa) as specified

in [22]. Also, the average Young’s modulus was tested to be about 200 GPa. In this

report, the yield strength 350 MPa (characteristic value) and Young’s modulus 200

GPa were adopted in the finite element numerical analysis for steel tubes from Hong


163


Kong market. In Table B-2, the original cross-section area 𝑆0 of a test specimen is

calculated according to the formula given in [32]:

𝑆0 = (𝑏

4) × √𝐷2 − 𝑏2 + (

𝐷2

4) × 𝑎𝑟𝑐𝑠𝑖𝑛 (

𝑏

𝐷) − (

𝑏

4) × √(𝐷 − 2𝑎)2 − 𝑏2 − (

𝐷 − 2𝑎

2)

2

× 𝑎𝑟𝑐𝑠𝑖𝑛 (𝑏

𝐷 − 2𝑎)

where

𝑎: thickness of the tube wall;

𝑏: average width of the stripe; and

𝐷: external diameter of the tube.

The percentages of elongation after fracture under a fixed gauge length of 50 mm were

obtained in test. These elongation values should be converted to those corresponding to

a gauge length of 𝐿 = 5.65√𝑆0 using the formula given in BS EN ISO 2566-1 [33]:

𝐴𝑟 =𝐴

2(

√𝑆0

𝐿0)

−0.4

where

𝐴𝑟: required elongation on gauge length of 5.65√𝑆0;

𝐴: elongation on gauge length 50 mm;

𝐿0: original gauge length; and

𝑆0: original cross-sectional area of test piece.

B3 Tube specimens and fixture for tensile test

Metal tube specimens for tensile test:


164


Dimensions (mm) of tube specimens

Side view of the specimens Front view of the specimens

Tensile test fixture:

CAD view of tensile test fixture


165


Top view of the specimens and test fixture

Front view and dimensions (mm) of tensile test fixture


166


Top view and dimensions (mm) of tensile test fixture

Fig. B-1 Three sizes of steel tube available in Hong Kong


167


Fig. B-2 Setup for the tensile test

0

5

10

15

20

25

0 5 10 15 20

UT

M f

orc

e (k

N)

Displacement (mm)


168


(a) Load-displacement curve

(b) Initial stress-strain curve

Fig. B-3 Load-displacement curve for specimen D2 under tensile test

Table B-1 Summary of physical and mechanical properties of Kao Jue and Mao Jue

Bamboo Moisture content

Avg.

external

diameter

(mm)

Avg.

internal

diameter

(mm)

95% characteristic

strength (N/mm²)

Avg. Young's

modulus (kN/mm²)

Compression Bending Compression Bending

Kao Jue

(BP)

Dry < 5.0%

40.7 30.4

79.0 80.0 10.3 22.0

Natural 12.5% 57.0 58.5 8.6 19.2

Wet > 20.0% 35.0 37.0 6.8 16.4

Mao

Jue (PP)

Dry < 5.0%

68.6 54.5

117.0 51.0 9.4 13.2

Natural 20.0% 73.2 53.4 7.6 11.0

Wet > 30.0% 44.0 55.0 6.4 9.6

Note: Based on a total of 364 compression and 91 bending tests reported in [30].

y = 202.29x

0

0.05

0.1

0.15

0.2

0.25

0.3

0.35

0.4

0 0.0005 0.001 0.0015 0.002

Str

ess

(GP

a)

Strain ε


169


Table B-2 Results of tensile test for three different sizes of steel tube

Specimen

Dimensions Testing Properties

External

diameter

𝐷

Thick

𝑇

Width

of

strip

𝑏

Cross

section

area

𝑆0

Lower

yield

strength

𝑅𝑒𝐿

Tensile

strength

𝑅𝑚

Young’s

modulus

𝐸

Percentage

elongation after

fracture on

50mm

gauge

length

5.65√𝑆0

(mm) (mm) (mm) (mm²) (MPa) (MPa) (GPa) ( %)

48.3×2.3 mm (no standards)

A1 48.3 2.2 12.5 28.3 367 469 199 28% 34%

A2 48.3 2.3 12.5 28.6 381 472 188 25% 31%

B1 48.4 2.3 12.5 28.8 377 472 182 23% 28%

B2 48.4 2.2 12.6 28.7 362 468 243 25% 30%

C1 48.3 2.3 12.6 28.8 375 469 215 20% 24%

C2 48.3 2.3 12.5 29.1 380 470 201 21% 25%

Average 48.3 2.3 12.6 28.7 374 470 205 24% 29%

48.3×3.2 mm (BS EN 10255)

D1 48.4 3.3 12.5 41.8 381 473 181 20% 23%

D2 48.4 3.2 12.6 41.3 385 473 202 21% 24%

E1 48.6 3.3 12.5 41.8 388 477 185 21% 24%

E2 48.6 3.3 12.6 41.9 394 472 176 22% 25%

F1 48.4 3.2 12.5 40.9 388 476 196 20% 23%

F2 48.4 3.2 12.5 40.3 391 481 209 21% 24%

Average 48.5 3.3 12.5 41.3 388 475 192 21% 24%

48.3×4.0 mm (BS EN 10255)

G1 48.7 3.9 12.5 49.1 358 436 198 25% 27%

G2 48.7 3.9 12.6 49.7 347 411 198 26% 29%

H1 48.7 3.9 12.5 49.2 351 418 186 26% 28%

H2 48.7 3.8 12.6 49.1 365 437 188 26% 28%

I1 48.7 4.0 12.6 50.6 353 406 203 20% 22%

I2 48.7 4.0 12.5 51.2 360 426 212 20% 22%

Average 48.7 3.9 12.5 49.8 356 422 197 24% 26%

Summary

(1) Yield strength: Average = 372.5 MPa; Std = 14.4 MPa; Characteristic strength

(95%) = 348.8 MPa;

(2) Young’s modulus: Average = 197.9 GPa; Std = 15.3 MPa.


170


Appendix C Column buckling of structural bamboo in

bamboo scaffoldings

The buckling of structural bamboo in bamboo scaffoldings is mostly determined by the

arrangement of ties and mechanical properties and geometrical dimensions of bamboo

members. In previous researches [10, 34, 35], a design method based on

Perry-Robertson interaction formula was proposed for column buckling of both Kao

Jue and Mao Jue. The predicted the axial buckling resistances of the bamboo columns

by this method have been proved through experimental investigation with an averaged

model factor of 1.65. It may be used effectively to design against column buckling of

structural bamboo in bamboo scaffoldings. The main points of the proposed method

are described as follows:

(1) The effective length of structural bamboo in bamboo scaffolding was determined

through advanced non-linear finite element analysis using Nonlinear Integrated

Design and Analysis software (NIDA). It is shown that the axial buckling

resistances of the bamboo columns are affected significantly by the presence or the

absence of lateral restraints. It was also found that due to the presence of bracing

members and secondary ledgers in the outer layer and larger dimensions of post

(Mao Jue) of outer layer, the post of the inner layer (Kao Jue) always fails against

buckling firstly.

(2) The Robertson constant of Mao Jue and Kao Jue should be selected as 15 and 28

respectively [34], which represent initial imperfection of bamboo members.

(3) Also, the non-prismatic effect of bamboo is considered by incorporating a

non-prismatic parameter, 𝛼 , to the elastic Euler buckling load of the bamboo

member, see Appendix C2.


171


C1 Effective length of the post in bamboo scaffoldings [10]

According to previous research [10], it was recommended that the effective length of

a structural bamboo may conservatively be taken as follows.

Effective length of post in single layered bamboo scaffoldings (SLBS):

In single layered bamboo scaffoldings, the recommended effective length of a

post ℎ𝑒 may be taken as follows:

ℎ𝑒 = 𝑘𝑒 × 𝐻

where

𝑘𝑒 is the effective length coefficient

= 1.0 for SLBS with regular lateral restraints with H = 1.0 h to 3.0 h;

= 0.7 for SLBS with staggered lateral restraints with H = 2.0 h to 3.0 h;

𝐻 is the system length between lateral restraints; and

ℎ is the height of a platform, or the vertical distance between two platforms.

Effective length of post in double layered bamboo scaffoldings(DLBS):

In double layered bamboo scaffoldings, the recommended effective length of a

post ℎ𝑒 may be taken as follows:

Inner layer

ℎ𝑒 = 𝑘𝑒 × ℎ

where

𝑘𝑒 is the effective length coefficient, 𝑘𝑒 = 𝑘𝑖 × 𝑘𝑏;

𝑘𝑖 is the secondary effective length coefficient which depends on the restraint


172


arrangement provided at the posts of the outer layer as follows:

H/h 1.00 1.50 2.00 2.667 3.00

𝑘𝑖 1.00 1.10 1.25 1.50 1.75

𝑘𝑏 = 1.0 for DLBS with regular lateral restraints, or 0.7 for DLBS with staggered

lateral restraints;



Modified effective length of post of inner layer

If the lateral restraints are provided to the base ledger of bamboo scaffoldings, the

column member at the base level will be most critical regardless of distance between

lateral restraints according to the experimental and numerical results in [10]. The

comparison between test and design results also showed that above design method is

fairly conservative for bamboo scaffoldings. Consequently, above proposed method to

determine the effective length of the post of inner layer is modified as follows:

ℎ𝑒 = 𝑘𝑒 × ℎ

where

𝑘𝑒 is the effective length coefficient, = 1.0 for DLBS with 𝐻 = 1.0ℎ 𝑡𝑜 3.0ℎ;

ℎ is the height of base column, but not less than height of a platform; and

𝐻 is the system length between lateral restraints.

Outer layer

ℎ𝑒 = 𝑘𝑒 × 𝐻

where


173


𝑘𝑒 is the effective length coefficient, 𝑘𝑒 = 𝑘0 × 𝑘𝑏;

𝑘0 =0.7 for DLBS with H = 1.0 h to 2.667 h to allow for the restraint effect provided

by both ledgers and standards;

𝑘𝑏 =1.0 for DLBS with regular lateral restraints, or 0.7 for DLBS with staggered

lateral restraints;



Based on the predicted structural performance of DLBS from the non-linear analysis,

the maximum value of 𝐻 should not exceed 2.667 h in practice.

C2 Non-prismatic parameter 𝜶 [34]

As natural non-homogenous organic materials, large variations of physical properties

along the length of bamboo members such as external and internal diameters are

shown. Thus, the non-prismatic effect is significant in the buckling analysis of

bamboo column. And this may be considered by incorporating a non-prismatic

parameter, 𝛼, to the elastic Euler buckling load of the bamboo member [34]. The

non-prismatic parameter 𝛼 is a function of the change of the second moment of area

along member length, and it could be evaluated through the minimum energy method

[34].

The elastic critical buckling strength of the bamboo column 𝑝𝑐𝑟 is given by:

𝑝𝑐𝑟 = 𝛼𝜋2𝐸𝑏

𝜆12

where the non-prismatic parameter 𝛼 is the minimum root of the following cubic

function,


174


𝑔(𝛼) = 𝑐3𝛼3 + 𝑐2𝛼2 + 𝑐1𝛼 + 𝑐0 = 0

where

𝑐3 = −0.2880

𝑐2 = 2.016(2 + 𝜌)

𝑐1 = −(14.11 + 14.11𝜌 + 3.098𝜌2)

𝑐0 = 10.37 + 15.55𝜌 + 7.047𝜌2 + 0.932𝜌3

𝜌 =𝐼2−𝐼1

𝐼1

If the value of ρ lies between 0 and 3, the value of 𝛼 may be calculated approximately

as follows:

α = 1.005 + 0.4751ρ − 0.011𝜌2

where α lies between 1.00 and 2.35.

It should be noted that the value of non-prismatic parameter 𝛼 for Kao Jue is found

to range from 1.00–1.28 [10], and thus, the variation of external diameter and

thickness along the length of Kao Jue is considered not to be significant. In assessing

axial buckling resistances of Kao Jue, the external and the internal diameters are

considered to be constant along the length of the bamboo so that non-prismatic

parameter is 1.0 for Kao Jue.

C3 Working example: column buckling of bamboo post using Kao Jue

For simplicity, the vertical distance between ties in bamboo scaffolding are assumed to

equal to 𝐻 = 2ℎ = 4𝑚, ℎ is the vertical distance between lifts. Assume the lateral

restraints are provided to the base ledger of bamboo scaffoldings and this is the


175


common practice in real scaffolding construction. The calculations of the allowable

compressive load of Kao Jue under natural moisture content are shown in Table C-1.

Table C-1 Buckling design example of Kao Jue with effective length 2 m

Calculation methods and steps Results or values

i) Section properties

Characteristic compressive

strength (95% prob.) 𝑝𝑐,𝑘 From Table B-1 𝑝𝑐,𝑘 = 57 𝑁/𝑚𝑚²

Young's Modulus against

bending Eb From Table B-1 𝐸𝑏 = 19.2 𝑘𝑁/𝑚𝑚²

Cross section area 𝐴1 and 𝐴2 𝐴 = 𝜋(𝐷𝑒2 − 𝐷𝑖

2)/4 𝐴1 = 𝐴2 = 5.75 𝑐𝑚2

Moment of inertia 𝐼1 and 𝐼2 𝐼 = 𝜋(𝐷𝑒4 − 𝐷𝑖

4)/64 𝐼1 = 𝐼2 = 9.28 𝑐𝑚4

Radius of gyration 𝑟1 𝑟1 = √𝐼1/𝐴1 𝑟1 = 12.70 𝑚𝑚

ii) Elastic critical buckling strength considering non-prismatic effect

Effective length 𝐿𝐸 Effective length should be determined

from Appendix C1 Assumed 𝐿𝐸 = 2 𝑚

Slenderness ratio 𝜆1 𝜆1 = 𝐿𝐸/𝑟1 𝜆1 = 157.48

Non-prismatic parameter 𝛼 See Appendix C2 𝜌 = 0; α = 1.0

Elastic critical buckling strength

𝑝𝑐𝑟 𝑝𝑐𝑟 = 𝛼(𝜋2𝐸𝑏/𝜆1

2) 𝑝𝑐𝑟 = 7.64 𝑁/𝑚𝑚²

iii) Compressive buckling strength using Perry-Robertson interaction formula

Design compressive strength

𝑝𝑐,𝑑 𝑝𝑐,𝑑 =

𝑝𝑐,𝑘

𝑟𝑚 Where 𝑟𝑚 = 1.5 𝑝𝑐,𝑑 = 38 𝑁/𝑚𝑚²

Perry factor 𝜂

𝜂 = 0.001𝑎(𝜆1 − 𝜆0)

where 𝑎 is Robertson constant;

𝜆0 = 0.2𝜋𝐸𝑏

𝑝𝑐,𝑑 is Limiting slenderness

𝑎 = 28

𝜆0 = 14.12

𝜂 = 4.01

Design compressive buckling

strength 𝑝𝑐𝑐,𝑑

𝑝𝑐𝑐,𝑑 =𝑝𝑐𝑟 × 𝑝𝑐,𝑑

∅ + (∅2 − 𝑝𝑐𝑟 × 𝑝𝑐,𝑑)0.5

where ∅ =𝑝𝑐,𝑑+(1+𝜂)𝑝𝑐𝑟

2

∅ = 38.16𝑁/𝑚𝑚²

𝑝𝑐𝑐,𝑑 = 4.016𝑁/𝑚𝑚²

Permissible axial load 𝑃 𝑃 =

𝑝𝑐𝑐,𝑑 × 𝐴1

𝛾𝑚

where 𝛾𝑚 = 1.5

𝑃 = 1.54𝑘𝑁

Note 1: Above design method is based on [9].

Note 2: Subscripts 1 and 2 denote the upper (smaller) cross-section and the lower (larger)

cross-section, respectively.

Note 3: 𝛾𝑓 = 1.5 is a single partial safety factor for loads and 𝛾𝑚 = 1.5 is a single partial safety

factor for resistances.


176


Appendix D Allowable compressive load on metal post in

mixed scaffoldings

In metal scaffolding or mixed scaffolding, the effective length 𝐿𝐸 of a compression

member should be derived from its actual centre-to-centre, between the intersections

with supporting members in accordance with the conditions of restraint in the

appropriate plane. Effective joint restraint is only likely to exist in riveted or bolted

structural connections, or with welded joints combined with reasonable continuity of

members [23]. So, an effective length of 1.0 𝐻 is selected as conservative value to

calculate the permissible stress on the gross section of steel tube for axial compression,

𝐻 is the vertical distance between the lateral restraints. According to Annex B of BS

5975 [23] or BS EN 1993-1-1 [36], the characteristic compressive strength 𝑁 of a

tubular strut with an effective length 𝐿𝐸 is given by:

N = χA𝑓𝑦

Where

χ =1

𝜙 + (𝜙2 − �̅�2)0.5

where

𝜙 = 0.5[1 + 0.49(�̅� − 0.2) + �̅�2]

�̅� =𝜆

√𝜋2𝐸

𝑓𝑦

𝜆 =𝐿𝐸

𝑟

Where

χ is the reduction factor for the relevant buckling mode;

A is the cross-sectional area of the post;

𝜆 is the slenderness ratio;


177


𝑟 is the radius of gyration;

𝐸 is the elastic modulus (= 200 kN/mm²);

𝑓𝑦 is the yield stress; and

�̅� is non-dimensional slenderness.

The allowable compressive load of a steel column may be obtained by applying a

single factor: 1.1 (material factor) × 1.5 (load factor) = 1.65:

P𝑐 =𝑁

1.65

Here, assume the vertical distance between lateral restraints 𝐻 = 2ℎ and the platform

height ℎ is 2 m. The effective length 𝐿𝐸 of steel column is taken as 1.0 𝐻. Note that

a distance of 4 m between lateral restraints is actually the maximum vertical distance

between ties allowed in bamboo scaffolding code [17]. The allowable compressive

load for steel tube column is given in Table D-1.

Table D-1 Allowable compressive load for steel column with 𝐿𝐸 = 1.0 𝐻

Effective

length

Outside

diameter

Wall

thickness

Modulus

of

elasticity

Characteristic

yield strength

Characteristic

compressive

strength

Single

factor

Permissible

axial load

m mm mm N/mm² N/mm² kN kN

𝐿𝐸 = 2.0 ℎ 48.3 2.3 200000 235 9.13 1.65 5.53

Note: The Characteristic compressive strength 9.13 kN is the same in Table B.2 of BS 5975 [23].


178


References

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179


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180


[21] British Standards Institution, BS EN 74: Couplers, Spigot Pins and Baseplates

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181


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