chapter 4 experimental investigation -...

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CHAPTER 4

EXPERIMENTAL INVESTIGATION

4.1 GENERAL

This chapter discusses the experimental programme, materials used

and the specimens tested in the current research project. The experimental

work conducted in this project is on the seismic behaviour of exterior beam-

column joints under simulated cyclic and reverse cyclic loading. Comparison

of conventional reinforced concrete joint, seismic reinforced joint, steel fibre

reinforced concrete (SFRC) joint and the hybrid fibre reinforced (HFRC)

joints were performed based on the experimental results on seven beam-

column joint units.

The main objective of this study is to investigate the suitable

percentage of hybrid fibre combination (steel and synthetic fibre) which

gives more load carrying capacity, more energy dissipation capacity, more

joint shear stress and ductility factor.

4.2 EXPERIMENTAL PROGRAMME

Experimental works were carried out in three phases. In the first

phase 18 cubes [150 mm x150 mm x150 mm], 18 cylinders [150 mm

diameter and 300mm hieght] and 28 beam-column joint specimens were cast

by using M20 concrete as per Table 4.1. In the second phase 18 cubes,

18 cylinders and 28 beam-column joint specimens were cast by using M25

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Figure 4.1 Flowchart – Experimental Programme

Studies on Hybrid Fibre Reinforced Beam-Column Joints Under Reverse Cyclic Loading

Experimental Work

Analytical work Using

ABAQUS

M60M25M20

28-BCJ 18-Cubes 12- Cylinders12-Cubes 10-BCJ18- Cylinders

Reverse Cyclic load TestCyclic load Test Compression Test Reverse Cyclic load Test

F.C, 1.5% S.F+0.2% P.F

F.C, 1.5% S.F+0.4% P.F

F.C, 1.5% S.F+0.6% P.F

F.C,1.5% P.F

O.C JointO.C + SeismicDetailing

F.C 1.5% S.F

O.C - Ordinary ConcreteF.C - Fibre ConcreteS.F - Steel FibreP.F - Polypropylene Fibre

B.C.J - Beam-Column Joint

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concrete as per Table 4.2. In the third phase 12 cubes, 12 cylinders and

10 beam-column joint specimens were cast by using M60 concrete. In first

two phases normal strength concrete was used and in third phase high strength

concrete was used. Figure 4.1 shows the flow chart of the experimental

programme.

In phase I and II seven types of exterior beam-column joints were

cast by using M20 and M25 concrete. All the specimens were designed as per

IS 456:2000. The first specimen was reinforced accordingly, without

considering the seismic requirement. The second specimen was detailed as

per IS 13920:1993 for seismic requirements. The remaining five specimens

were similar to the first one but various combinations of hybrid fibre were

mixed with concrete in the joint region. Out of five fibrous specimens four

specimens were cast by using constant 1.5% of steel fibre and 0 to 0.6% of

polypropylene fibre with an increment of 0.2% by volume fraction. The fifth

fibre reinforced specimen was cast by using only 1.5 % of polypropylene

fibre. Tables 4.1 and 4.2 show the details of specimens cast by using M20 and

M25 concrete.

Table 4.1 Specimens with Various Combinations of Hybrid Fibres in

M20 Concrete

Sl.No

Specimen

Identification

Fibre Volume

Fraction No of

BCJCyclic

Load

Reverse Cyclic

LoadingSteel

Polypro

pylene

1 I O1 I O2 - - 4

2 I S1 I S2 - - 4

3 I F11 I F12 1.5% 0% 4

4 I F21 I F22 1.5% 0.2% 4

5 I F31 I F32 1.5% 0.4% 4

6 I F41 I F42 1.5% 0.6% 4

7 I F51 I F52 - 1.5% 4

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M25 Concrete

Sl.No

Specimen IdFibre Volume

Fraction No of

BCJCyclic

Load

Reverse Cyclic

LoadingSteel

Polypr

opylene

1 II O1 II O2 - - 4

2 II S1 II S2 - - 4

3 II F11 II F12 1.5% 0% 4

4 II F21 II F22 1.5% 0.2% 4

5 II F31 II F32 1.5% 0.4% 4

6 II F41 II F42 1.5% 0.6% 4

7 II F51 II F52 - 1.5% 4

In phase III five types of exterior beam-column joints were cast

using M60 concrete. All the specimens were designed as per IS 456:2000. The

first specimen was reinforced accordingly, without considering the seismic

requirement. The second specimen was detailed as per IS 13920:1993 for

seismic requirements. The remaining three specimens were similar to the first

one but various combinations of hybrid fibre reinforeced concrete in the joint

region (constant 1.5% of steel fibre and 0 to 0.4 % of polypropylene fibre

with an increment of 0.2% by volume fraction) were used. The details of

specimen cast using M60 concrete is presented in Table 4.3

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M60 Concrete

Sl.

No

Specimen

Id

Fibre Volume Fraction

No of

BCJSteel Polypropylene

1 III O2 - - 2

2 III S2 - - 2

3 III F12 1.5% 0% 2

4 III F22 1.5% 0.2% 2

5 III F32 1.5% 0.4% 2

4.3 SPECIMEN DETAILS

4.3.1 General

The test sub assemblage is an exterior beam-column joint in the

ground storey of a five storied RC building situated in a place falling under

seismic zone III as per IS 1893: (Part 1 2002). The structure was analysed

using STADD.Pro (2004) software to determine the shear forces, bending

moments and axial forces around the exterior beam-column joint due to

earthquake loading. The specimens were designed as per IS 456-2000. The

second specimen was detailed as per IS 13920: 1993.

4.3.2 Details of Test Specimen and Reinforcement

Test specimen was reduced to a scale (Bayasi 2002) to suit the

loading frame and testing facilities. Original joint design had contained beam

and column sections of 380 mm X 450 mm and 380 mm X 380 mm

respectively. The test specimen joint design includes beam and column with

90 mm X 110 mm and 90 mm X 90 mm respectively. Original joint beam

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reinforcement at top was 1.52 % and at bottom was 1% of gross area. Original

column reinforcement of the joint is 2.4 %. These percentages of steel

reinforcement ratio were also used for the model. Percentage of reinforcement

of hoops at the joint was 2.13 % and other portion was 1.07 %. Figures 4.2

and 4.3 show seismic joint and ordinary & fibrous joint respectively. For

seismic joint this hoop spacing is 20 mm for a distance of 180 mm (2*db)

(db=effective depth of beam) from the face of the column in the beam and at a

distance of 90 mm (db) from the bottom and top of the beam in the column.

The fibrous joints were cast by using fibre reinforced concrete in the joint

region for a distance of two times effective depth from the face of column on

beam and one time the effective depth from the face of the beam on either

side of the column. The effective cover for main reinforcement is 20 mm.

Figure 4.2 Seismic Detailed Joint

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Figure 4.3 Fibre Reinforced Joint

4.4 PROPERTIES OF MATERIALS

4.4.1 General

The properties of materials used for preparing the different grades

of (M20, M25 and M60) concrete will be described in the following sections.

The types of concrete being analysed are normal strength concrete, high

strength concrete, steel fibre reinforced concrete and hybrid fibre reinforced

concrete.

4.4.2 Materials Used

Cement, fine aggregate, coarse aggregate, steel fibre, polypropylene

fibre, fly ash, silica fume, superplasticizer and water were used in this

investigation. The following are the properties of the materials used.

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4.4.2.1 Cement

Ordinary portland cement of grade–53 conforming to Indian

standard IS: 12269-1987 has been used in the present study. The specific

gravity of cement used is 3.15.

4.4.2.2 Fine Aggregate

Sand that is available in nearby locality has been used as fine

aggregate. Other foreign matter present in the sand has been separated before

use. The specific gravity of sand used in this investigation is 2.42.

4.4.2.3 Coarse Aggregate

Crushed stone aggregate of maximum size 10mm available from

local area has been used. Coarse aggregate has been sieved through IS:150-

micron sieve to remove dirt and other foreign materials. The specific gravity

of coarse aggregate used is 2.65.

4.4.2.4 Steel Fibre

For improving the mechanical bond between the fibre and matrix,

indented, crimped, machined and hook ended fibres are normally produced.

The aspect ratio of fibres which have been employed vary from about 30 to

250. Fibres made from mild steel drawn wire conforming to IS: 280-1976

with the diameter of wire varying from 0.3 to 0.5 mm has been practically

used in India. The efficiency of fibre distribution depends on the geometry of

the fibre, the fibre content, the mixing and compaction technique, the size and

shape of the aggregates and the mix proportions. The fibre used in this study

was crimped steel fibre shown in Figure 4.4. As provided by the manufacturer

(Fibre mesh, Product manual, SI Concrete Systems,USA.) the properties of

crimped steel fibre used are given in Table 4.4.

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Table 4.4 Properties of Fibre

Sl.NoProperties Steel fibre

(Crimped)

Polypropylene

Fibre

1. Length 30 mm 20 mm

2. Diameter 0.50 mm 0.008 mm

3. Aspect ratio 60 2500

4 Specific

Gravity

7.850 0.91

4.4.2.5 Polypropylene Fibre

Table 4.4 shows physical properties of polypropylene fibre used in

this study. Figure 4.4 shows the polypropylene fibre used in this investigation.

Figure 4.4 Crimped Steel Fibre and Polypropylene Fibre

4.4.2.6 Flyash

Fly ash which is a by-product of the thermal power plant poses

serious problems of its dumping to the environmentalists. Utilization of flyash

in concrete as partial replacement of cement not only solves the problems of

dumping to some extent but also it is used as mineral admixture in concrete

and helps to attain reduction in cost of concrete by saving cement. This

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pozzolana is beneficially used to attain certain properties in concrete such as

lower water demand for similar workability, reduced bleeding and lower

evolution of heat. The specific gravity of flyash used is 2.32. It has been used

particularly in mass concrete applications and large volume placement to

control expansion due to heat of hydration and also helps in reducing cracking

at early ages. In addition, the chemical reaction that creates Portland cement

produces CO2 as a by-product. By displacing a large percentage of the cement

in concrete, fly ash significantly reduces the associated environmental impacts

of CO2 production and air pollution. Therefore for higher strengths, silica

fume must be used in conjunction with fly ash. For the preparation of high

strength concrete, flyash is used at a dosage of 15 % of cement content.

4.4.2.7 Silica Fume

Silica fume is a waste by-product of the production of silicon and

silicon alloys. Silica fume is available in different forms, of which the most

commonly used is in a densified form. In developed countries it is already

available in blended with cement. With silica fume it is easier to make HPC

of strengths between 60-98 Mpa. In the present study silica fume content of

about 10 % by weight of cement for partial replacement of cement was mixed

to obtain high strength concrete.

4.4.2.8 Water

According to IS: 456-2000 water used for preparing concrete

should be of potable quality. In this investigation ordinary tap water, which is

fit for drinking, has been used in preparing all concrete mixes and curing.

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4.4.2.9 Super Plasticizers

Plasticizers help us to increase the workability of concrete without

addition of extra quantity of water. It means that we can use less water

without reducing the workability at the same cement content. This is added to

avoid formation of flakes, due to less quantity of water. Use of plasticizers is

economical as the cost incurred on them is less than the cost of cement saved.

Use of super plasticizers becomes essential for designing mix to achieve HPC

and also for the preparation of fibre reinforced concrete to increase

workability. Super plasticizer used in this study was Sulphonate Naphthalene

Polymer. (Conplast SP 430).

4.4.2.10 Steel

The main reinforcement used for the specimen was tor steel of

diameter 8 mm. The shear reinforcement was of mild steel of diameter

3.3 mm. The yield stress of steel reinforcement is 420 N/mm2.

4.5 CONCRETE MIX DESIGN

4.5.1 General

The selection of suitable ingredients of concrete and the

determination of their relative proportion were done with an aim to produce

concrete of required strength and durability as economical as possible. Based

on the properties of cement, fine aggregate, coarse aggregate and water, the

mix proportion was calculated as per IS 10262-1982.

4.5.2 Mix Proportion

The mix design for fibre reinforced concrete has been done

according to Indian Standard method by taking into account the quantity of

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fibre (Shetty 1996). Tables 4.5 to 4.7 show the proportions of mix for M20,

M25 and M60 concrete respectively.

Table 4.5 Concrete Mix Proportions (M20)

Material UnitPlain Concrete

1:1.76:2.69

Fibre concrete

1:1.64:2.5 +1.5%

Cement kg/m3

378 378

Fine Aggregarte (Sand) kg/m3

665.6 619.70

Coarse Aggregate

( 6mm to 10mm)kg/m

31020 968.15

Water (0.55) kg/m3

208 208

Steel Fibre (1.5 %) kg/m3

- 117.75

Polypropylene Fibre

(0, 0.2, 0.4, 0.6 and 1.5%)kg/m

3-

(0,1.82,3.64, 5.46

and 13.65)


Material UnitPlain Concrete

1:1.57:2.4

Fibre concrete

1:1.46:2.23+1.5%

Cement kg/m3

416 416


652.60 607.33

Coarse Aggregate ( 6mm to

10mm)kg/m

31001.70 929.2

Water (0.50) kg/m3

208 208


- 117.75

Polypropylene Fibre

(0, 0.2, 0.4, 0.6 and 1.5%)kg/m

3-

(0,1.82,3.64, 5.46

and 13.65)

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HPC mix proportion for M60 grade concrete was obtained based on

the guidelines given in modified ACI 211 method suggested by the author

M.S. Shetty. Portion of the cement was replaced by micro fillers such as silica

fume and flyash. In this study 10% replacement of cement by silica fume and

15% by fly ash were considered. To increase the workability of concrete

superplasticiser was added. The ratio of HPC mix was

1:0.2:0.11:1.4:2.14:0.35:0.02 (cement : fly ash : silica fume : sand : C.A : water:

superplasticiser). The ratio of HPFRC mix was 1:0.2:0.11:1.3:2:0.35:0.024 +

1.5% fibre. Table 4.7 presents the characteristics of two different concrete

mixes used to cast the test specimens.


Material UnitPlain

ConcreteFibre Concrete

Cement kg/m3

449 449

Fly Ash kg/m3

88 88

Silica fume kg/m3

50 50


630 583

Coarse Aggregate

( 6mm to 10mm)kg/m

3963 891

Water Water binder

ratio (0.35)kg/m

3209 207

Superplasticiser Lit/ m3

10.00 11.75


- 117.75

Polypropylene

Fibre (0, 0.2 and 0.4%)kg/m

3- (0,1.82 and 3.64)

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4.6 CASTING AND CURING

The mould was arranged properly and placed over a smooth

surface. The sides of the mould exposed to concrete were oiled well to

prevent the side walls of the mould from absorbing water from concrete and

to facilitate easy removal of the specimen. Figure 4.5 shows the

reinforcements which were tied for casting, seismic reinforced joint and

ordinary and fibre reinforced joint. The reinforcement cages were placed in

the moulds and the cover between cage and form were maintained as 10 mm.

The concrete contents such as cement, sand, aggregate and water were

weighed accurately and mixed. Fibres were carefully mixed with concrete

without balling of fibre. The mixing was done till uniform mix was obtained.

The concrete was placed into the mould immediately after mixing and well

compacted. Figure 4.6 shows the fibrous concrete placed in the joint region.

After placing the fibrous concrete in the joint region the ordinary concrete

was placed in the remaining portion. Control cubes and cylinders were

prepared for all the mixes along with concreting. The test specimens were

removed from the mould at the end of 24 hours of casting. Identification

marks were marked on the specimens. They were cured in water for 28 days.

After 28 days of curing the specimens were dried in air and white washed.

Figure 4.5 Reinforcement Cage of Seismic Detailed Joint and Fibrous

Joint

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Figure 4.6 Fibrous Concrete Placed in the Joint Region and Ordinary

Concrete in the Remaining portion

4.7 TESTING PROCEDURE

The testing of cubes, cylinders and beam-column specimens have

been done after 28 days of curing. The following tests were performed in the

present research work:

Stress strain behaviour of concrete by conducting compression

test on cylinder

Compression test on concrete cubes.

Cyclic load test on beam-column joint

Reverse cyclic load test on beam-column joint

4.7.1 Compressive Strength Test

Compressive strength measurements are primarily concerned in

testing the strength of concrete. Cube specimens were tested using the 3000

kN capacity Automatic Compression Testing Machine (ACTM). This

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machine fulfills the entire requirement for compression testing as per IS: 516-

1959. Cube specimens were placed centrally in the machine in such a manner

that the load is applied perpendicular to the casting faces. The load was

applied in a continuous and uniform fashion without shock. In this test the

maximum load carried by each specimen has been recorded. Compressive

strength is calculated by dividing the maximum load obtained by the cross-

sectional area of the specimen. To get the compressive strength, average value

of three specimens has been used.

4.7.2 Stress Strain Behaviour of Concrete

To get the stress strain behaviour, cylindrical specimens have been

tested in the servo controlled 100 Tonne capacity Universal Testing Machine.

Specimens after the required curing have been tested for compression after

their surfaces became dry. Surface water and grit had been wiped off from the

specimens. The bearing surfaces of the testing machine was wiped clean and

loose sand or other material were removed. Cylindrical specimens were

placed centrally in the machine. The load was applied in a continuous and

uniform fashion without shock with the help of a computer attached to the

machine. The data and graphs saved in computer were used for preparing

stress strain curves. The results displayed on the computer screen were

recorded at the failure of specimens.

4.8 EXPERIMENTAL SETUP

4.8.1 Cyclic loading

Seven beam-column specimens each from M20 and M25 grade

concretes were tested in Universal Testing machine of 100T capacity for

cyclic load test. The test setup is shown schematically in Figure 4.7.

Figure 4.8 shows the photograph of test setup. The specimen was mounted

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such that the column is in vertical position. A constant axial load of 60 kN

was applied to the column to keep it in the vertical position and to stimulate

column axial load. A hydraulic jack was used to apply the load at a distance

of 50 mm from the free end of the beam. To record the load precisely a

proving ring was used. The beam was loaded gradually up to 5mm deflection,

unloaded and reloaded for next increment of deflection and this pattern of

loading was continued for each increment of deflection until failure. The

deflection of the beam at the point of loading during the test was measured by

a dial gauge with a least count of 0.01mm. Strain gauges were fixed on the

beam and column reinforcements to measure the strain in reinforcement.

Figure 4.7 Schematic Diagram of the Experimental Setup-Cyclic Load

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Figure 4.8 Experimental Setup for Cyclic Loading

4.8.2 Reverse Cyclic Load Testing

Seven beam-column specimens each from M20 and M25

concrete and five beam-column specimens from M60 concrete were tested

under reverse cyclic loading which is similar to the seismic loading. The test

setup is shown schematically in Figure 4.9. The Figure 4.10 shows the

photograph of forward and reverse loading. The specimen was mounted such

that the column is in vertical position and beam is in horizontal position. For

strain controlled testing screw jack and hydraulic jack were used to apply

displacement at a distance of 50mm from the beam end. The hydraulic jack

was fixed at the strong floor and screw jack was fixed to the loading frame at

the top.

LVDT

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Figure 4.9 Schematic Diagram of Reverse Cyclic Loading Test set-up

To record the load precisely, proving rings were used. The dial

gauges were used to measure the deflection. Each displacement cycle

consisted of a cycle of upward and downward displacement of beam end

position. Dial gauges were fixed at a distance of db and 2db (db = effective

depth of the beam) from the column face on the beam to measure the beam

deflections. Strain gauges were fitted in the beam top and bottom

reinforcement and column reinforcement to measure the reinforcement strain.

By using these load and displacement values strength, ductility, shear and

energy dissipation capacity were calculated.

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Figure 4.10 Photograph of Forward and Reverse Loading

4.9 INSTRUMENTATION

Figure 4.11 shows the photograph of various instruments fitted on

the specimen during testing. Following are the name of instruments fitted.

Figure 4.11 Photograph Showing the Various Instruments

1

2 34

5

6

7

LVDT

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1 Proving ring

2 Dial gauge used to measure beam deflection at 50 mm from

the beam end

3 Dial gauge used to measure beam deflection at a distance of

2db from the face of the column

4 Dial gauge used to measure beam deflection at a distance db

from the face of the column

5 Strain gauge to measure the column reinforcement strain

6 Strain gauge to measure the beam top reinforcement strain

7 Strain gauge to measure the beam bottom reinforcement strain

4.9.1 Measurement of Load and Deflection

For measuring the load, proving ring was fixed and for measuring

deflection at the free end dial gauge was fixed at a distance of 50 mm from

the free end.

4.9.2 Measurement of Joint Distortion

Two LVDTs mounted diagonally on the rear face on the joint were

used to measure the distortion of the interior core of the joint.

4.9.3 Measurement of Strains

Demec strain gauges were used to measure strain in the reinforcement

bars. Gauge length of demec strain gauge is 100 mm. Demec points were

fixed for the measurement of strain. While casting two small pieces of rods of

length equal to clear cover were welded on the main reinforcement at spacing

of 100mm such that they are projected up to concrete top surface. While

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curing that reinforcement surfaces were covered with water proofing tape.

While testing the strain gauge tips were fixed on the rod surface and thereby

the strain in reinforcement could be measured.

4.10 PROPERTIES OF COMPANION SPECIMEN

4.10.1 Compression Test

The cylinder compressive strength and cube compressive strength

of various grades of concrete such as M20, M25 and M60 with different

proportions of hybrid fibre combinations are presented in Tables 4.8 to 4.10

respectively. It is evident from these tables that the increase in percentage of

polypropylene fibre reduces the compressive strength of fibre reinforced

concrete of grades M20, M25 and M60. Maximum decrease in compressive

strength was observed in the specimen cast by using 1.5 percent of

polypropylene fibre alone in the proportions tried. The specimen in the F1

series (with 1.5% of steel fibre) gave the maximum compressive strength.

Table 4.8 28 days Cube and Cylindrical Compressive Strength of M20

grade Concrete

Sl.

NoType of Fibre

Specimen Identification

I O1 I F11 I F21 I F31 I F41 I F51

1 Steel fibre in % 0 1.5 1.5 1.5 1.5 0

2Polypropylene

Fibre in %0 0 0.2 0.4 0.6 1.5

3Cube compressive

strength in N/mm2

35.4 41.42 39.42 37.95 32.71 15.24

4Cylinder Compressive

Strength in N/mm2

27.26 29.08 28.245 25.88 22.28 10.97

69


Grade Concrete

Sl.

NoType of Fibre

Specimen Identification

II O1 II F11 II F21 II F31 II F41 II F51

1 Steel fibre in % 0 1.5 1.5 1.5 1.5 0

2Polypropylene

Fibre in %0 0 0.2 0.4 0.6 1.5

3Cube compressive

strength in N/mm2 38.4 44.5 43.26 37.53 33.86 22


Strength in N/mm2

31.28 35.13 33.50 27.52 24.34 15.31


Grade Concrete

Sl. No. Name of FibreSpecimen Identification

III O2 III F12 III F22 III F32

1 Steel fibre in % 0 1.5 1.5 1.5

2Polypropylene

Fibre in %0 0 0.2 0.4

3Cube compressive

strength in N/mm2

76.5 84.5 82.6 78.30


Strength in N/mm2 61.2 69.3 66.9 62.8

4.10.2 Stress Strain Curve

Compression test on cylindrical specimens cast with M20, M25 and

M60 grade concretes, were conducted using computerised UTM. Figure 4.12

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shows the load Vs cross head travel curves which were obtained during

testing of IIO2 and II F22 specimens cast using M25 concrete. Tables 4.10 to

4.12 show the cylinder compressive strength of concrete of all the specimens

cast using M20, M25 and M60 respectively.

Figure 4.12 Typical Load Vs Cross Head Travel Curve of II O2 and II

F22 Specimen cast using M25 Concrete obtained from UTM

Figure 4.13 Original Stress Strain Curve of II O2 and II F22 Specimen

cast M25 Concrete

The graph in Figure 4.12 which is obtained during testing is

converted to stress strain curve and is shown in Figure 4.13. The above stress

strain curve is used for the ABAQUS Finite Element Analysis.

71

4.11 SUMMARY

The properties of various materials used and experimental setup of

cyclic and reverse cyclic loading were described. The details of test specimen,

various combinations of fibres used for casting the specimens, their mix

design, testing methods and various instruments used for testing were also

specified. The compression test results of cubes and cylinders show that the

addition of steel fibre increases the compressive strength while the addition of

polypropylene fibre decreases the compressive strength.

chapter 4 experimental investigation -...

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