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7/23/2019 Pierre Vd Spuy Thesis Draft 2014-11-25 http://slidepdf.com/reader/full/pierre-vd-spuy-thesis-draft-2014-11-25 1/82  A COMPARITIVE STUDY BETWEEN THE SOUTH AFRICAN AND EUROPEAN BRIDGE DESIGN CODES FOR BENDING AND SHEAR PIERRE FRANCOIS VAN DER SPUY BEng (Civil) Cum Laude, US Thesis submitted to the University of Cape Town in partial fulfilment for the degree of Master of Engineering Department of Civil Engineering University of Cape Town November 2014

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A COMPARITIVE STUDY BETWEEN THE SOUTH AFRICAN

AND EUROPEAN BRIDGE DESIGN CODES FOR BENDING

AND SHEAR

PIERRE FRANCOIS VAN DER SPUY

BEng (Civil) Cum Laude, US

Thesis submitted to the University of Cape Town in partial fulfilment for the degree of

Master of Engineering

Department of Civil Engineering

University of Cape Town

November 2014

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DECLARATION

I, Pierre Francois van der Spuy, hereby declare that this thesis is essentially my own work,

except where otherwise indicated, and has not, to the best of my knowledge, been submitted

for a degree at any other university.

………………………………………… 

Pierre Francois van der Spuy

September 2014

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ACKNOWLEDGEMENTS

I would like to thank the following people and institutions for their invaluable support making

this research project a reality:

  My wife, Adele, for her endless patience, support, motivation and sacrifices to afford

me the time to work on my research.

  My parents and my brother for encouraging me to persevere.

  Aurecon, my employer, for providing the funding for my master’s degree. 

  My adviser, A/Prof Pilate Moyo, for his guidance throughout the course of this study.

  My doctors, Dr Louw Fourie and Prof Piet Oosthuizen, without whom I believe I

would not have been in the position to complete my postgraduate studies. Words

cannot describe my gratitude.

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In memory of

Pepper

2009 - 2014

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EXECUTIVE SUMMARY

South African design codes have historically been based on British codes of practice which

have since been replaced by the European standards known as the Eurocodes. Once the

codes on which a specific code is based are replaced it becomes imperative that the specificcode must also be updated. The South African bridge design code, known as TMH7, was

introduced in 1981 and is based on the old CEB-FIP Model Code for Concrete Structures

published in 1978 with reference to BS5400 (since replaced by Eurocodes) and also the

National Building Code of Canada. The introduction of the Eurocodes provides a sound

framework for benchmarking the South African bridge design code.

The Eurocodes have the advantage of incorporating the latest advances in research and

technology. The Eurocodes are further based on probabilistic principles which make them

adaptable and expandable to most parts of the world. With increasing amount of

international work being done from South Africa and the considerable costs involved in

creating a new unique code from scratch, it makes sense to allign the South African bridge

design code to the Eurocodes.

The adoption of the Eurocode principles would imply thath only variables specific to South

 Africa need to be determined.

The aim of this study is to compare the loading on bridges of various numbers of spans and

span lengths between TMH7 and the Eurocodes. This was done by performing a literature

study of the two codes and performing line beam analyses to both codes and comparing the

results. For the purpose of this study the UK national annex to the Eurocodes was used.

The results showed that the Eurocode loading is substantially higher than TMH7 for normal

traffic, especially in shear where the Eurocode is in some instances double that of TMH7.

This can be attributed to the high knife edge loads of the Eurocode compared to TMH7. For

abnormal loading it was found that TMH7 was generally heavier than the Eurocode which

was based on the British annex. The difference was however marginal. In the light of the

differences in normal loading a substantial calibration effort will be needed to allign TMH7 to

the Eurocode.

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Table of contents

DECLARATION ..................................................................................................................... i 

 ACKNOWLEDGEMENTS ......................................................................................................ii 

EXECUTIVE SUMMARY ...................................................................................................... iv 

Table of contents .................................................................................................................. v 

List of tables and figures ...................................................................................................... vii 

1.  Introduction .................................................................................................................... 1 

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

1.2.  Research objectives and methodology .................................................................... 1 

1.3.  Thesis overview ...................................................................................................... 2 

2.  Background to TMH7 and the Eurocodes ...................................................................... 3 

2.1.  Deterministic versus probabilistic design ................................................................. 3 

2.2.  Principles of limit state design ................................................................................. 5 

2.3.  Background of TMH7 .............................................................................................. 8 

2.4.  Background of the Eurocodes ................................................................................. 8 

2.5.  Structure of the codes ............................................................................................. 9 

3.  Comparison between TMH7 and the Eurocodes .......................................................... 11 

3.1.  Comparison of loading models .............................................................................. 11 

3.1.1.  Dead loads .................................................................................................... 11 

3.1.2.  Superimposed dead loads ............................................................................. 11 

3.1.3.  Vehicle loading .............................................................................................. 12 

3.1.3.1.  Transverse positioning ............................................................................ 12 

3.1.3.2.  Longitudinal positioning .......................................................................... 13 

3.1.3.3.  TMH7 vehicle loading models ................................................................. 20 

3.1.3.4.  Eurocode vehicle loading models............................................................ 34 

3.1.3.5.  Comparison between TMH7 NA loading and Eurocode LM1 loading for

worked examples ..................................................................................................... 45 

3.2.  Main study comparison ......................................................................................... 48 

3.2.1.  Description of main study comparative examples .......................................... 48 

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3.2.2.  Loading according to influence lines in LUSAS .............................................. 48 

3.2.3.  How the design values will be compared ....................................................... 52 

3.2.3.1.  Single span configurations ...................................................................... 52 

3.2.3.2.  Two span configurations ......................................................................... 54 

3.2.3.3.  Three span configurations ...................................................................... 60 

3.2.4.  Summary ....................................................................................................... 67 

4.  Conclusions and recommendations ............................................................................. 70 

Bibliography ........................................................................................................................ 73 

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List of tables and figures

Figure 1: Comparison of deterministic and probabilistic design approaches .......................... 4 

Figure 2: Bending moment influence line ............................................................................ 13 

Figure 3: Influence line worked example layout ................................................................... 14 Figure 4: Influence line for endspan sagging moment ......................................................... 14 

Figure 5: Loading arrangement for endspan sagging .......................................................... 16 

Figure 6: Resulting bending moments for endspan sagging ................................................ 17 

Figure 7: Influence line for internal support shear ................................................................ 17 

Figure 8: Loading arrangement for internal support shear ................................................... 18 

Figure 9: Resulting shear force diagram for internal support shear ..................................... 19 

Figure 10: NA load curve for TMH7 ..................................................................................... 21 

Figure 11: NA knife edge loading example .......................................................................... 21 

Figure 12: NA UDL example 1 layout .................................................................................. 23 

Figure 13: NA UDL example 2 layout .................................................................................. 25 

Figure 14: Influence line for NA UDL example 2 .................................................................. 26 

Figure 15: Resultant loading for NA UDL example 2 ........................................................... 29 

Figure 16: NA UDL example 2 Knife Edge loads ................................................................. 30 

Figure 17: Straddling of lanes ............................................................................................. 31 

Figure 18: NB loading arrangement for single unit .............................................................. 32 

Figure 19: NC 30x5x40 loading configuration ...................................................................... 33 

Figure 20: Eurocode notional lanes layout .......................................................................... 35 

Figure 21: Application of Load Model 1 ............................................................................... 37 

Figure 22: Eurocode Load Model 1 example distributed loading ......................................... 38 

Figure 23: Eurocode Load Model 1 example Tandem System loading ................................ 39 

Figure 24: Eurocode load model 2 ...................................................................................... 40 

Figure 25: SV80 special vehicle .......................................................................................... 41 

Figure 26: SV100 special vehicle ........................................................................................ 42 

Figure 27: SV196 special vehicle ........................................................................................ 43 

Figure 28: SOV vehicles ..................................................................................................... 44 

Figure 29: Comparison example of NA (left) and LM1 (right) distributed loads .................... 46 

Figure 30: Comparison example of NA (left) and LM1 (right) concentrated loads ................ 47 

Figure 31: TMH7 notional lane arrangement ....................................................................... 48 

Figure 32: BS EN notional lane arrangement ...................................................................... 48 

Figure 33: LUSAS influence line example model ................................................................. 49 

Figure 34: Influence line shape from LUSAS ....................................................................... 50 

Figure 35: LUSAS NA loading UDL application ................................................................... 50 

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Figure 36: LUSAS NA loading Knife Edge application ......................................................... 50 

Figure 37: LUSAS LM1 loading UDL application ................................................................. 50 

Figure 38: LUSAS LM1 loading Tandem System application .............................................. 51 

Figure 39: LUSAS NB loading moving load example........................................................... 51 

Figure 40: LUSAS NC loading moving load example .......................................................... 51 

Figure 41: LUSAS LM3 loading moving load example ......................................................... 52 

Figure 42: Single span bending moments graph ................................................................. 52  

Figure 43: Single span shear forces graph .......................................................................... 53  

Figure 44: Two span hogging influence line ........................................................................ 54 

Figure 45: Two span hogging bending moments graph ....................................................... 55 

Figure 46: Two span sagging influence line ........................................................................ 56 

Figure 47: Two span sagging bending moments graph ....................................................... 56 

Figure 48: Two span end shear influence line ..................................................................... 57 

Figure 49: Two span end support shear graph .................................................................... 58 

Figure 50: Two span middle support shear influence line .................................................... 59 

Figure 51: Two span internal support shear graph .............................................................. 59  

Figure 52: Three span hogging influence line ...................................................................... 60 

Figure 53: Three span hogging bending moments graph .................................................... 61 

Figure 54: Three span sagging end span influence line ...................................................... 62 

Figure 55: Three span end span sagging moments graph .................................................. 62 

Figure 56: Three span middle span sagging influence line .................................................. 63 

Figure 57: Three span middle span sagging moments graph .............................................. 64 

Figure 58: Three span end support shear influence line ...................................................... 65 

Figure 59: Three span end support shear graph ................................................................. 65 

Figure 60: Three span internal support shear influence line ................................................ 66 

Figure 61: Three span internal support shear graph ............................................................ 67 

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1. Introduction

1.1. Background

The South African bridge design code, known as TMH7, was introduced in 1981 and is

based on the old CEB-FIP Model Code for Concrete Structures published in 1978 with

reference to BS5400 and also the National Building Code of Canada.

The Eurocodes are widely regarded as the most technically advanced suite of structural

engineering design codes in the world today (Zingoni, 2008). British codes, on which a

number of South African structural design codes were based, including TMH7, have now

been replaced by the Eurocodes which necessarily implies that South African design codes

now have to be updated to contain the latest in research and scientific advances. The cost of

creating a new, unique, set of design codes for South Africa will be exorbitant and the

academic resources needed to compose the codes are extremely limited.

The Eurocodes were originally developed for countries of the European Union, but many

countries outside the EU have now started to compose country specific national annexes to

the Eurocodes or by adapting their national codes to take advantage of the technical

benefits of the Eurocodes. South Africa cannot afford to be left behind in this. With the help

of electronic communication technologies and due to the relatively cheap labour cost in

South Africa, South African companies are engaging in an increasing amount of international

projects. It is obvious that having a universal design code across borders is of great

advantage to the success of international projects. Apart from this advantage, it makes

financial sense for South Africa to adopt or allign with a code that has already been

developed and adapt it to South African conditions. The Eurocodes are the perfect answer to

this problem because they were intentionally composed to be generic, where each country

simply produces an annex that gives values for the variables in the base codes.

1.2. Research objectives and methodology

The objective of this research project is to compare TMH7 and Eurocode for various

numbers of bridge spans and various bridge span lengths. A review of the design

philosophies, loading and concrete design of the different codes will be done and described

after which the loadings will be compared by performing a range of line beam analysis using

a finite element software package.

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The study is intended to point out major differences in approaches and results with the intent

to identify broadly what work must be done in South Africa before the Eurocode can be

adopted.

1.3. Thesis overviewChapter 1 investigates the background to TMH7 and the Eurocodes with reference to their

origins and development.

Chapter 2 deals with the differences in design philosophies adopted by the two codes.

In chapter 3 the loading of the two codes are compared in detail as well as the structure of

the two codes.

Chapter 4 contains conclusions that can be made from the study and somerecommendations are presented.

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2. Background to TMH7 and the Eurocodes

To understand the design philosophies of the two codes it is first necessary to get an

understanding of the difference between deterministic and probabilistic design as well as

limit state design.

2.1. Deterministic versus probabilistic design

To understand the different design philosophies on which TMH7 and the Eurocodes are

based it is essential to understand the difference between deterministic and probabilistic

design.

The safety factor method used in the older codes is an example of a deterministic design. In

this method the safety factors are used to account for uncertainties in design parameters

with the aim of generating designs that will ideally avoid failure in service (Booker, Raines

and Swift, 2001). These factors are based on experience and intuition and variability in load

and material parameters are covered by blanket factors. The deterministic design approach

can be show by the following equation

 

where S = Material strength

L = Loading stress

FS = Factor of safety

The deterministic approach is not very precise and tends to produce overly conservative

designs. The deterministic approach is, therefore, not well suited to today’s products where

superior functionality and customer satisfaction (mostly cost based) are the driving

influences.

Probabilistic design introduces the terms  probability and reliability. The variable nature of

loads and material properties are well known to engineers and it is by quantifying the

variable nature of these parameters that designs can be done within acceptable limits of

failure probabilities. Mathematically the scatter of engineering parameters can be modelled

by a Probability Density Function (PDF) that will accurately describe the pattern of the data.

 An example of this is Weigh In Motion data of loadings on bridges. Once a PDF of both the

load and material strength distributions are determined, an acceptable level of reliability can

be used to determine what the characteristic values of the parameters must be. In other

words, the reliability of a component part can be based on the inference of its inherent

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material strength distribution f (S) and its loading stress distribution f (L) where both are

random variables. The probabilistic design approach can be shown by the following equation

which says that the probability of the strength exceeding the loading equals the reliability.

( )  

where P = Probability

S = Material strength

L = Loading stress

R = Reliability level

The difference between deterministic and probabilistic design can be shown by Figure 1 with

the deterministic approach on the left and the probabilistic approach on the right :

Figure 1: Comparison of deterministic and probabilistic design approaches

Without a proper understanding of the variability of strengths of materials and the stresses

imposed on them, the deterministic approach will select a safety factor large enough to

separate the stress and strength distributions without any overlap (see Figure 1 (a)). This

approach leads to conservative design. If, on the other hand, the safety factor is chosen too

low, then a considerable amount of failures will occur (see Figure 1 (b)).

The probabilistic approach can be seen in Figure 1 (c). In this approach the variability of the

stresses and strengths are taken into account and a certain amount of overlap between the

respective distributions are allowed. The reliability (probability of no failure) is inversely

proportionate to the amount of overlap between the two distributions. The more overlap

between the distributions, the higher the probability of failure and vice versa. By using this

approach the safety factor is optimised leading to a structurally adequate and economical

design (Booker, Raines and Swift, 2001). The Eurocode suite of codes are examples of fully

probabilistic design codes (Holicky, Retief and Dunaiski, n.d.).

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2.2. Principles of limit state design

The older bridge design codes were based on the selection of reasonable, upper bound

estimates of normal working loads; the use of elastic methods ofstructural analysis and the

provision of some margin in strength by the selection of allowable working stresses

separated by a factor of safety from some critical stress, such as the yield or ultimate stress

of the material. This procedure is also called Allowable Stress Design (ASD).

For example, the 1973 edition of the American Standard Specifications for Highway Bridges

(the American Association of State Highway Officials, or AASTHO Code), in its section on

working stress design, specified for structural carbon steel a minimum yield stress of 240

MPa, a minimum tensile strength of 400 MPa and a basic allowable stress of 138 MPa. The

implicit factor of safety on yield was 1.8. Earlier, for many years an allowable stress of 124

MPa had been used, corresponding to a factor of safety of 2.0.

However, these factors of safety were not the same for all materials. For example, for a

reinforced concrete beam, the allowable stress in compression in the extreme fibre of the

concrete was specified as 0.4f’c, where f’c was the ultimate strength of the concrete as

determined by tests on concrete cylinders tested at an age of 28 days. The implicit factor of

safety was 2.5, providing for a greater variability in the strength of this material, as compared

with steel. A typical concrete strength at that time was 20 MPa. The 1990 American Railway

Engineering Association (AREA) Specifications for Steel Railway Bridges (AREA Manual:

Ch. 15) gave the same basic allowable stress for steel (138 MPa). However, it is interesting

to observe that older bridge design codes had allowable stresses that varied with the nature

of the loading. A typical ‘working stress’ for steel was

55(1+Min/Max) MPa

where

Min represented the minimum stress caused by the applied loads;

and

Max, the maximum

Often, Min corresponded to the effects of dead load alone, and Max to dead load plus live

load. This clause adds: ‘For combined live, dead, wind and centrifugal stresses, increase the

preceding unit stress 30% above live and dead load unit stresses’. 

For the effects of dead load alone (i.e. Max=Min), the allowable stress became 110 MPa, or

for live load alone (Min=0), 55 MPa. A more typical result would be with Max=2×Min, giving

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an allowable stress of 83 MPa. These values are low compared with later standards, partly

because of the use of lower strength steels, but the principle is of interest: effects such as

impact, fatigue and the greater variability of live load, as compared with dead load, caused

the codes to increase the factor of safety for live load. This also allowed for the unlikelihood

of the combination of extreme values of wind and live loads.

It was in the 1940s that the so-called plastic methods of structural analysis came to be used

in the design of building frames, with the emphasis shifted from behaviour at working loads

to collapse. A major improvement from the safety factor method (which was purely

deterministic in nature) was the development of the limit state design method. For the first

time in structural design proper study was made of loading and material strength

distributions which enabled probability and reliability to be introduced in the development of

design codes. This, in turn, led to safer and more economic designs.

The Limit States Design Method, as currently used in structural design, has two basic

characteristics:

1. it tries to consider all possible limit states; and

2. it is based on probabilistic methods.

The simplest limit state is the failure of a component under a particular applied load. This

depends on two parameters: the magnitude of the load as it impinges on the structure, here

called the load effect, and the resistance or strength of the component. If the load effect

exceeds the resistance, then the component will fail. However, both the magnitude of the

load effect and the resistance may be subject to statistical variation.

The limit states considered by modern bridge design codes are divided into ultimate and

serviceability limit states, where the first refers broadly to incipient collapse, and the second

to undesirable behaviour that does not involve collapse of the primary structure. However,

the first of these must immediately be qualified. It was seen in Section 2.2 that the collapse

of a redundant or indeterminate building frame required the development of uncontrolled

plastic deformation at two or more sections. There is a reserve of strength beyond initial

failure, and this involves a redistribution of actions between the various parts or members of

the structure. Many current bridge codes do not allow for this type of redistribution, and

failure is deemed to occur when the first section reaches the ultimate capacity. (O'Connor

and Shaw, 2000)

With this in view, possible ultimate limit states correspond to the conditions when:

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(a) one or more parts of the structure reach their ultimate capacity, i.e. they are incapable of

carrying additional load;

(b) parts of the structure move by sliding, uplift, or overturning; or

(c) parts of the structure are on the point of failure because of deterioration caused by

corrosion, cracking or fatigue.

The serviceability limit states typically include:

(a) dynamic movements that cause discomfort or public concern;

(b) dynamic movements that cause damage to ancillary parts of the structure, such as lamp

standards or hand railings;

(c) permanent deformations, either of the structure itself or its foundations, that cause public

concern or make the structure unfit for use;

(d) damage by scour;

(e) the flooding or scour of adjacent properties; and

(f) damage due to corrosion or fatigue that is sufficient to cause a significant reduction in the

strength of the structure or in its service life.

The chief advantages of the probabilistic-based, Limit States Design Method are:

(a) the recognition of the different variabilities of the various loads, such as the dead load

versus the live load, for the old working stress method encompassed both in the same factor

of safety;

(b) the recognition of a range of limit states; and

(c) the promise of uniformity by the use of statistical methods to relate all to the probability of

failure.

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2.3. Background of TMH7

TMH7 was the first bridge design code in South Africa to be based on limit state design

principles. This method was based on limit state principles formulated in ISO 2394 “General

Principles for the Verification of the Safety of Structures” and the CIB-FIP Model Code for

Concrete Structures (1978). It replaced the previously used “Permissible Stress” method

which formed the basis of its predecessors (Committee of State Road Authorities, 1981).

 According to TMH7 there are different levels of limit state design. These are:

Level 1

 A semi-probabilistic process where partial safety factors are assigned to load actions and the

strength of materials in order to better define the uncertainties associated with these

variables.

Introducing probability and reliability in the development of design codes led to probabilistic

design methods. The first codes that appeared with limit state design methods were semi-

probabilistic, including TMH7. This meant that probabilistic principles were applied when

determining material and load factors, but the value of these were fixed by the design codes.

This was a big step forward because material and loading characteristics could now be

predicted with more accuracy leading to less conservative designs.

Level 2

 A design process in which the loads or actions and strengths of materials and sections are

represented by their known or postulated distributions (types, means and standard

deviations). TMH7 does not fall into this category.

Level 3

 A design process based upon an exact probabilistic analysis for the entire structural system.

TMH7 does not fall into this category, but as per section 2.4 it will be seen that the Eurocode

does.

2.4. Background of the Eurocodes

The Eurocodes are not based on any specific code. The Eurocode project dates back to

1975 when the Commission of the European Community decided on an action programme in

the field of construction to eliminate technical obstacles to trade and to harmonise technical

specifications in the construction industry. The intended benefits were to provide a common

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understanding of structural design between owners, operators, users, designers, contractors

and construction product manufacturers (Camilleri, 2003).

For fifteen years the Commission, with the help of a Steering Committee with

Representatives from the Member States, conducted the development of the Eurocodesprogramme which led to the first generation of European codes in the 1980’s (CEN EN1990,

2002).

In 1989 the Commission and the Member States decided to transfer the preparation of the

Eurocodes to the European Committee for Standardisation (CEN) in order to provide them

with the future status of European Standard (EN) (CEN EN1990, 2002).

In 2001 the head code EN1990 Eurocode – basis of structural design was published with the

rest of the codes published at later stages as they were completed (CEN EN1990, 2002).

What resulted was an unrivalled set of unified international codes of practice for designing

buildings and other civil engineering structures including bridges.

The Eurocodes are fully probabilistic meaning that they leave room for authorities or users

to specify levels of reliability to determine the material and load factors. Each country that

adopts the Eurocode typically publishes its own national annex specifying these factors.

 According to a report published by ATKINS in the UK (ATKINS Highways and

Transportation, 2005), the UK national annex has been calibrated to give loads close to

BS5400. As stated in section 1.1 of this thesis TMH7 is largely based on BS5400 which

means that material and load factors for the Eurocode in South Africa should be close to that

of the UK. The UK national annex will be a good starting point for South Africa, but still a lot

of research work will have to be done in if we are to adopt the Eurocodes in the future.

2.5. Structure of the codes

To compare TMH7 to the Eurocode it is important to look at the structure of both codes and

compare them.

TMH7 is a basic three part code consisting of the following volumes:

  Part 1 – General Statement

  Part 2 – Specification for Loads

  Part 3 – Design of Concrete Structures

TMH7 is only applicable to bridges.

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The Eurocodes are a comprehensive suite of codes covering all types of structures. The

suite consists of the following volumes:

  EN 1990 – Basis of Structural Design

  EN 1991 – Actions on Structures (sub section 2 specifies bridge loading)

  EN 1992  – Design of Concrete Structures (sub section 2 is applicable to concrete

bridges)

  EN 1993 – Design of Steel Structures (sub section 2 applicable to steel bridges)

  EN 1994  –  Design of Composite Steel and Concrete Structures (sub section 2

applicable to steel bridges)

  EN 1995 – Design of Timber Structures (sub section 2 applicable to steel bridges)

  EN 1996 – Design of Masonry Structures

  EN 1997 – Geotechnical Design

  EN 1998 – Design of Structures for Earthquake Resistance (sub section 2 applicable

to steel bridges)

  EN 1999 – Design of Aluminium Structures

What is clear from looking at the structures of the two code systems is that TMH7 does not

allow for steel bridges, composite bridges or timber bridges. TMH7 does indeed address

seismic loading on bridges, but does not include the modern analysis methods contained in

EN 1998. Geotechnical design is not accounted for in TMH7 and South African designers

tend to fall back on SABS codes for this purpose.

It is clear that if the Eurocodes are adopted in South Africa or alligned with South African

codes a much more comprehensive set of tools will be available to South African bridge

designers.

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3. Comparison between TMH7 and the Eurocodes

3.1. Comparison of loading models

In this section the dead loads and superimposed dead loads are briefly discussed, although

they are more dependant on material properties and therefore similar between the codes. Of

more importance in this chapter is the discussion on vehicle loading. To gain a thoughrough

understanding of veicle loading it is essential to understand the concept of influence lines.

Hence to start off the discussion on live loading the theory behind influence lines is first

discussed followed by a description of the vehicle loading models of both codes.

3.1.1. Dead loads

Dead loads are primarily the self-weight of a structure and are generally independent of

design codes. Both codes make provision for specific material weights used on site which

vary from Table 1 below.

The flexibility provided for the designer to specify actual material weights, however, enables

designer to use exactly the same loading for both codes.

Table 1 : Comparison of dead loads

Material

Self-weight

(kN/m3)

TMH7 Eurocode

Plain concrete 24 24

Reinforced/prestressed concrete 26 25

Unhardened concrete - 26

Steel 78.5 77-78.5

3.1.2. Superimposed dead loads

Superimposed dead loads are self-weight of items that are connected to the deck, but are

not integral with the deck. Examples are balustrades, sidewalks and asphalt surfacing.

These loads are, like dead loads, generally independent of the design codes.

TMH7 superimposed dead loading

TMH7 gives the following values for nominal material weights:

  Normal density bitumen premix : 21 kN/m3 

  Concrete sidewalk : As in section 4.2.1.1

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Generally the weight of a parapet is taken as 10kN/m unless otherwise stated.

The code allows adjustments for actual material weights used in construction.

Eurocodes superimposed dead loading

EN1991-1 Appendix A gives the following nominal densities:

  Hot rolled asphalt : 23kN/m3 

  Concrete sidewalk : As in section 4.2.1.2

Parapet weight can generally be taken as 10kN/m unless other wise stated.

The code also makes provision for specific material weights used on site which vary from the

table above.

Comparison and summary

The flexibility provided for the designer to specify actual material weights, however, enables

designer to use exactly the same loading for both codes.

3.1.3. Vehicle loading

Vehicle loading on bridges consists of different loading models which represents different

types of vehicular loading on bridges. Traffic load models in the design codes cover

  Normal traffic

  Abnormal loading

  Super loading

Normal traffic loading consists of cars and lorries. Abnormal loading consists of above

normal weight vehicles and the number of such vehicles at any one time on the bridge is

limited. Super loading are extreme loads which have to occupy designated areas on the

bridge and which are transported at very slow speed to minimise dynamic actions resulting

from the loading. These loads are normally moved over a bridge during the night and are

escorted by traffic officials while the bridge is closed to normal traffic.

In this section the general principles of load positioning for most adverse effects are

discussed (influence lines) as well as the loading models of both TMH7 and the Eurocode.

3.1.3.1. Transverse pos it ion ing

The transverse positions that traffic loads occupy on the structure for the purpose of design

are defined by the concept of notional lanes. Notional lanes are fictional lanes that are

intended only for design purposes and have no relation to the actual amount of traffic lanes

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on a bridge. These lanes are used to define transversely where the different loading models

need to be applied on the deck during design.

3.1.3.2. Lon gitud inal pos it ion ing

To determine the most adverse loading for a bending moment or shear force at a point along

a structure it is useful to apply the concept of influence lines.

 An influence line represents the variation of a bending moment or shear force at a specific

point on a structure with a unit load placed at different positions on the structure. Once an

influence line has been generated it is easy to place live loading at the most honerous

positions. To illustrate this concept a brief example will follow.

Consider a three span bridge with three equal spans of 10m length.

To determine where the loading must be placed to generate the maximum moment at point

B, an influence line must be generated. A unit load is run along the full length of the structure

from point A to point D, constantly plotting the value of the moment at point B as the unit

load moves along. A plot of the moment at point B as a result of the unit load is as follows.

Figure 2: Bending moment influence line

From the graph above it is clear that to obtain the maximum bending moment at point B both

the first and the second spans must be loaded with the maximum load intensity at

approximately 6m from the start of span one. If a knife edge load is present it must be placed

at the point of maximum load intensity. Loading on span three will cause a reduction of the

-1.2

-1

-0.8

-0.6

-0.4

-0.2

0

0.2

0.4

0 5 10 15 20 25 30

Continuous Beam Influence Lines

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bending moment at B due to the influence line showing a positive effect between points C

and D.

Worked example

In this section a worked example is presented to show how influence lines are used to

calculate maximum bending moments and shear forces. To illustrate the concept of

influence lines it is essential to choose at least a two span structure to explain the

adverse/relieving effect. For this purpose a two span bridge will be analysed with equal

spans of 15m. The total length was chosen as 30m to prevent load reduction (explained in

section 3.1.3.3). The example bridge only carries one notional lane with a UDL of 36kN/m

and a knife edge load of 144kN as per TMH7.

Figure 3: Influence line worked example layout

Endspan sagging moment

To determine the position of the loading the influence line for the sagging moment in the end

span must first be determined. This is obtained by moving a unit load accross the bridge

whilst observing the value of the sagging moment in the end span for every unit load

position. The result can be seen in Figure 4 below.

Figure 4: Influence line for endspan sagging moment

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The influence line above shows that to obtain the maximum sagging moment in the end

span one has to load only the first span with the UDL and the knife edge load. The second

span has a negative value on the influence line and will therefore cause a relieving effect.

The maximum point on the influence line is where the knife edge load has to be placed to

cause the largest moment. This maximum point is located at 6.5m from the end support.

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Figure 5: Loading arrangement for endspan sagging

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Figure 5 above shows the loading arrangement to get the maximum sagging moment in the

end span. Figure 6 below shows the resultant bending moment diagram which indicates a

maximum moment of 1957kNm at 6.5m from the end support.

Figure 6: Resulting bending moments for endspan sagging

Internal support shear

To determine the position of the loading the influence line for the shear force at the internal

support must first be determined. This is obtained by moving a unit load accross the bridge

whilst observing the value of the shear force at the internal support for every unit load

position. The result can be seen in Figure 7 below.

Figure 7: Influence line for internal support shear

The influence line above shows that to obtain the maximum shear force at the internal

support one has to load both spans with the UDL. The knife edge load must be placed

infinitely close to the internal support. This maximum point is located at 0.001m from the

internal support.

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Figure 8: Loading arrangement for internal support shear

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Figure 8 above shows the loading arrangement to get the maximum shear force at the

internal support. Figure 6 below shows the resultant shear force diagram which indicates a

maximum shear force of 540kN at 0.001m from the internal support.

Figure 9: Resulting shear force diagram for internal support shear

The parameters in this worked example that could vary are

  Number of spans

  Span lengths

  Bridge width ie. number of notional lanes

 Although the above three parameters influence the intensity of the loading, the principle of

influence lines remain unchanged irrespective of number of spans, span lengths and the

number of notional lanes.

In the next section the load models of the two codes are discussed.

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3.1.3.3. TMH7 vehic le loading mo dels

In this section the TMH7 vehicle loading models are discussed and then illustrated by

worked examples.

TMH7 specifies three load models which need to be considered in design. These are

  NA loading: Normal traffic loading

  NB loading: Abnormal loading

  NC loading: Super loading

Before these three models can be discussed in detail it is important to first look at the

definitions of notional lanes in TMH7. Notional lanes are purely fictional lanes for design

purposes. They have no relation to the actual traffic lanes on the bridges.

For bridges having a carriageway width of more than 4.8m the number of notional lanes are

determined by the following table from TMH7 Section 2.6.2:

Table 2: Definition of notional lanes in TMH7

For carriageways widths of less than 4.8m the number of notional lanes are given by the

(carriageway width)/3 and this may be a non-integer number (Committee of State Road

 Authorities, 1981).

NA loading (TMH7 Section 2.6.3)

Type NA loading represents normal traffic loading and consists of a distributed load plus a

concentrated load or two 100kN nominal wheel loads only. The 100kN nominal wheel loads

are for local effects and will therefore not be discussed further in this thesis.

The distributed loading is a function of the loaded length and can be applied to the whole or

parts of the length of any notional lane or combination of such lanes. The distributed load for

loaded lengths of up to 36m is 36kN/m. For loaded lengths in excess of 36m the average

distributed load is given by

Q =

√   kN/m where n is the total loaded length

This concept can also be seen in the following figure from TMH7:

Carriageway width (m) Number of notional lanes

4.8 up to and including 7.4 2

above 7.4 up tp and including 11.1 3

above 11.1 up to and including 14.8 4

above 14.8 up to and including 18.5 5

above 18.5 up to and including 22.2 6

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Figure 10: NA load curve for TMH7

It is clear from Figure 10 that the average distributed load decreases as the loaded length

increases for loaded lengths in excess of 36m.

Knife edge loads are point loads that act in conjunction with the distributed NA loading.

These loads are expressed as an axle load of

√   kN where n is the loading sequence

number of the relevant lane. This axle load is split up into two equal wheel loads spaced

1.9m apart and positioned transversely to create the worst situation for the member under

consideration. This principle is explained in Figure 11 below where a deck cross section is

shown with four notional lanes.

Figure 11: NA knife edge loading example

Longitudinal distribution

In the longitudinal direction the distributed part of the NA loading shall be applied to those

parts of any combination of notional lanes which will result in the most severe effect for the

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member under consideration (refer to Section 3.1.3.2). The effective loaded length shall be

taken as the aggregate length of the separate parts loaded in any single notional lane or

combination of notional lanes in one or more carriageways.

The concept of a separate part of a notional lane as used in this context shall mean thatcontinuous length of the notional lane that has entirely a positive (or alternatively negative)

effect on the member being considered. These vehicle positions are best determined by the

use of influence lines or surfaces.

To determine the maximum effect on any structural member an approximate procedure is

adopted whereby the sequence of loading is determined by the ranking of the average

influence values of the abovementioned parts. That part of any notional lane which has the

maximum average influence value is loaded at an intensity determined by the NA loading

curve (Figure 10). Thereafter, that part of the same or any other notional lane with the next

highest average influence value is loaded at an intensity such that the total load on the two

loaded parts corresponds to the formula loading for a loaded length equal to the sum of the

two loaded lengths. This procedure is continued until all the parts of equal influence sign are

loaded (Committee of State Road Authorities, 1981). The following expressions explain this

concept.

If ∑   is the sum of all the loaded lengths up to and including the  part, the

intensity of the loading  on the  part of length  is defined as follows:

 = ( ∑ ∑

with,

  the intensity of loading for a length of ∑  

  the intensity of loading applied to any previously calculated base length

portion i

  the dimension of any previously calculated base length portion i

In this procedure  reduces as p increases with no limiting value.

The concept can be illustrated by the following two worked examples which are unrelated to

the worked example in section 3.1.3.2. 

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NA loading worked example 1

Figure 12: NA UDL example 1 layout

Figure 12 above shows a single span bridge with a length of 20m and three notional lanes.

This span length and total length of 60m was chosen specifically to invoke load reduction

which starts at a total loaded length of 36m. Lane 1 will be loaded the heaviest (rank 1) to

assess the most adverse situation for the edge beam of the fictional deck. Lane 2 (rank 2)

will be loaded next with Lane 3 (rank 3) loaded last with the least intensity.

Lane 1

L = L1  = 20m (<36 m thus Q1 = 36 kN/m)

Lane 2 (Lane 1 + Lane 2 loaded)

L1+2  = 40 m

L2  = 20 m

Q1+2  = 180/sqrt(40) + 6

= 34.460 kN/m

Q2  = (Q1+2*L1+2 – Q1*L1)/L2 

= ((34.460)(40) – (36)(20))/20

= 32.920 kN/m

Lane 3 (Lane 1 + Lane 2 + Lane 3 loaded)

L1+2+3  = 60 m

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Q1+2+3  = 180/sqrt(60) + 6

= 29.238 kN/m

Q3  = (Q1+2+3*L1+2+3 – Q1*L1 – Q2*L2)/L3 

= ((29.238)(60) – (32.920)(20) – (36)(20))/20

= 18.794 kN/m

To summarize Lane 1 must be loaded with 36 kN/m, Lane 2 must be loaded with 32.920

kN/m and Lane 3 with 18.794 kN/m. The knife edge loads for lanes 1, 2 and 3 are 144 kN,

102 kN and 84 kN respectively placed near the supports for maxuimum shear and at

midspan for maximum bending. The calculation method described above is applicable to all

single span bridge decks with any length and any number of notional lanes.

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NA loading worked example 2

Figure 13: NA UDL example 2 layout

Figure 13 shows a three span bridge with equal span lengths of 20 m and three notional

lanes. The objective of this example is to determine the position and the intensity of NA

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distributed loading to determine the maximum edge beam moment in the end span. The

span length of 20m gives a total loaded length of 120m. This was chosen specifically to

illustrate the concept of load reduction where the UDL component of NA loading starts to

reduce after a loaded length of 36m. Three spans were chosen in this instance to illustrate

the concept of loading alternate spans.

The influence line for bending in the end span shows that the end span under consideration

should be loaded the heaviest. The center span has negative influence and should not be

loaded. The other end span has positive influence, but less than the span under

consideration.

Figure 14: Influence line for NA UDL example 2

Through inspection it becomes evidend that the ranking of the lanes should be as in Figure

13. Lane rank 1 must be loaded with the highest intensity and lane rank 6 with the lowest.

The intensities can be calculated as follows:

Lane 1

L = L1  = 20m (<36 m thus Q1 = 36 kN/m)

Lane 2 (Lane 1 + Lane 2 loaded)

L1+2  = 40 m

L2  = 20 m

Q1+2  = 180/sqrt(40) + 6

= 34.460 kN/m

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Q2  = (Q1+2*L1+2 – Q1*L1)/L2 

= ((34.460)(40) – (36)(20))/20

= 32.920 kN/m

Lane 3 (Lane 1 + Lane 2 + Lane 3 loaded)

L1+2+3  = 60 m

Q1+2+3  = 180/sqrt(60) + 6

= 29.238 kN/m

Q3  = (Q1+2+3*L1+2+3 – Q1*L1 – Q2*L2)/L3 

= ((29.238)(60) – (32.920)(20) – (36)(20))/20

= 18.794 kN/m

Lane 4 (Lane 1 + Lane 2 + Lane 3 + Lane 4 loaded)

L1+2+3+4  = 80 m

Q1+2+3+4  = 180/sqrt(80) + 6

= 26.125 kN/m

Q4  = (Q1+2+3+4*L1+2+3+4 – Q1*L1 – Q2*L2 – Q3*L3)/L4 

= ((26.125)(80) – (36)(20) – (32.920)(20) – (18.794)(20))/20

= 16.786 kN/m

Lane 5 (Lane 1 + Lane 2 + Lane 3 + Lane 4 + Lane 5 loaded)

L1+2+3+4+5  = 100 m

Q1+2+3+4+5  = 180/sqrt(100) + 6

= 24 kN/m

Q4  = (Q1+2+3+4+5*L1+2+3+4+5 – Q1*L1 – Q2*L2 – Q3*L3 – Q4*L4 )/L5 

= ((24)(100)  –  (36)(20)  –  (32.920)(20)  –  (18.794)(20)  – 

(16.786)(20))/20

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= 15.5 kN/m

Lane 6 (Lane 1 + Lane 2 + Lane 3 + Lane 4 + Lane 5 + Lane 6 loaded)

L1+2+3+4+5  = 120 m

Q1+2+3+4+5  = 180/sqrt(120) + 6

= 22.432 kN/m

Q4  = (Q1+2+3+4+5+6*L1+2+3+4+5+6 –Q1*L1 –Q2*L2 –Q3*L3 –Q4*L4 –Q5*L5)/L6 

= ((22.432)(120)  –  (36)(20)  –  (32.920)(20)  –  (18.794)(20)  – 

(16.786)(20) – (15.5)(20))/20

= 14.592 kN/m

The resultant NA distributed loading for example 2 can be seen in Figure 15 below with the

Knife Edge loading shown in Figure 16.  This loading arrangement will give the maximum

bending moment in the edge beam of the end span of the bridge. The example described

above is limited to the maximum sagging moment in the end span of a three span structure.

The calculations can, however, be extended and are valid for any number of spans, span

lengths and number of notional lanes.

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Figure 15: Resultant loading for NA UDL example 2

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Figure 16: NA UDL example 2 Knife Edge loads

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Transverse distribution

The above distributed loading shall be split into two separate line loads 1.9m apart each

having an intensity of Qa/2. These line loads shall be positioned transversely in a lane in

such a position to create the worst effect for the member under consideration.

Transverse position

The distributed and knife edge loads occupy one or more notional lanes. The loading on any

specific lane acting in conjunction with the loading on adjacent lanes shall be within the width

of this notional lane except for the distributed loading which can be within 0.5m of the

adjacent distributed loading and within 0.25m from the inside of a kerb. Where an element

can be more severely affected by the lateral translation of the loading the loading on two

notional lanes shall be considered to straddle two or three notional lanes (see Figure 17:

Straddling of lanes). Then straddling takes place, no other lanes shall be loaded (Committee

of State Road Authorities, 1981).

Figure 17: Straddling of lanes

NB loading

NB loading is a unit loading representing a single abnormally heavy vehicle as can be seen

in Figure 18: NB loading arrangement for single unit. 

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Figure 18: NB loading arrangement for single unit

The design wheel loads shall be applied to a circular or square contact area derived by

assuming a uniformly distributed effective pressure of 1 MPa.

The dimension X is selected between 6 m abd 26 m in increments of 5m to produce the

most severe effect.

No dynamic allowance is made for NB loading.

Magnitude of NB loading

NB loading is applied in two magnitudes namely NB24 and NB36 loading. NB24 loading is

24 units of NB loading which equals 60kN per wheel. NB36 is 36 units of NB loading which

equals 90kN per wheel.

 Application of NB loading

Only one NB vehicle is allowed on the bridge at any one time and acts without any other

forms of vehicular loading on the bridge. The NB vehicle can occupy any transverse position

in the carriageway and can come to within 0.6m from the face of a kerb except when the

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distance between the kerb and the balustrade exceeds 0.6m it shall be placed up to within

0.15m from the face of the kerb.

NC loading

NC loading is a loading representing multi-wheeled trailer combinations with controlledhydraulic suspension and steering intended to transport very heavy indivisible payloads. The

standard type NC 30x5x40 is shown in Figure 19: NC 30x5x40 loading configuration

Figure 19: NC 30x5x40 loading configuration

The loading is uniformly distributed over the area shown with an intensity of 30kN/m 2. The

dimensions a, b and c must be chosen to have the most severe effect within the ranges

shown in Figure 19: NC 30x5x40 loading configuration. 

No allowance must be made for impact effects.

 Application of NC loading

Type NC loading shall be directed along the centreline of any carriageway unless otherwise

dictated by road geometrics. Allowance is made for the vehicle to move 1m off centre to

either side so as to cause the most severe effect on the element under consideration.Subject to the above restriction of movement, the loading may be placed hard up against a

kerb, but not closer than 0.45m from a balustrade.

No other traffic loading shall be considered in conjunction with this loading in any single

carriageway, but where dual carriageways are carried by a single superstructure or where a

unified substructure carries separate superstructures of a dual carriageway or carries multi-

level superstructures, an additional loading case shall be considered. This loading case

consists of NC loading only on any one carriageway with two thirds of the intensity of NA

loading on the whole or parts of the other carriageways.

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3.1.3.4. Euroc ode vehic le loading models

In this section the Eurocode vehicle loading models are discussed and then illustrated by

worked examples.

The Eurocode specifies four load models which need to be considered in design. These are:

  Load Model 1: Covers most of the effects of lorries and cars

  Load Model 2: Covers dynamic effects on short structural members

  Load Model 3: Abnormal loads

  Load Model 4: Crowd loading

The definition of notional lanes differs from TMH7. The carriageway width, w, should be

measured between kerbs or between inner limits of vehicle restraint systems. Only kerbs

equal to or lower than 100mm must be included in the carriageway width.

The width wl of notional lanes on a carriageway and the greatest possible whole (integer)

number nl  of such lanes on this carriageway are defined in Error! Reference source not

found..

Table 3: Eurocode definition of notional lanes

For example, the number of notional lanes will be:

  1 where w<5.4m

  2 where 5.4<w<9m

  3 where 9<w<12m etc.

The lane giving the most unfavourable effect is numbered Lane Number 1, the lane giving

the second most unfavourable effect is numbered Lane Number 2, etc.

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Figure 20: Eurocode notional lanes layout

For each individual verification, the load models on each notional lane should be applied on

such a length and so longitudinally located that the most adverse effect is obtained, as far as

this is compatible with the conditions of application defined for each particular load model.

On the remaining area, the associated load model should be applied on such lengths and

widths in order to obtain the most adverse effect, as far as this is compatible with the

conditions of application defined for each particular load model (CEN EN1991-2, 2002).

Load Model 1

Load Model 1 consists of two systems:

  A double axle concentrated load called the Tandem System (TS), each axle having a

weight of αQQk where αQ is an adjustment factor. Axles are spaced 1.2 m apart.

  An uniformly distributed load (UDL) system having a weight per square metre of

notional lane of αqqk where αq is an adjustment factor

The values of the adjustment factors should be selected depending on the expected traffic

and possibly on different classes of routes. In the absence of specification these factors

should be taken equal to unity. These factors can be specified in a national annex.

The characteristic loading values for Load Model 1 are given in Table 4: Characteristic

values for Load Model 1 below.

Table 4: Characteristic values for Load Model 1

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The application of Load Model 1 is subject to the following rules for the Tandem System:

  Only one tandem load permitted per notional lane

  For the assessment of general effects, each tandem system should be assumed totravel centrally along the axes of notional lanes

  Each axle of the tandem system should be taken into account with two identical

wheels, each carrying half of the axle load

  The contact surface of each wheel should be taken as square and of side 0.4m

  For local verifications, a tandem system should be applied at the most unfavourable

position. Where two tandem systems on adjacent notional lanes are taken into

account, they may be brought closer with a distance between wheel axles of 0.5m

minimum

Load Model 1 should be applied to each notional lane and on the remaining areas. The UDL

loads should be applied only in the unfavourable parts of the influence surface, longitudinally

and transversely. A summary of the application of Load Model 1 can be seen in Figure 21:

 Application of Load Model 1 below.

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Figure 21: Application of Load Model 1

Eurocode Load Model 1 example

The aim of this example is to illustrate Eurocode Load Model 1 distributed loading for the

same configuration as example 2 for NA distributed loading in section 3.1.3.3. Assuming the

bridge is 9 m wide this implies three notional lanes of 3 m width each (refer to Error!

Reference source not found.). This width was chosen specifically to invoke three notional

lanes without any remaining width. Between 9 m and 12 m trafficable width there will be a

remaining width that varies from 0 m to 3 m which also carries a load of 2.5 kN/m2, but this

has been ignored for simplicity and conparison purposes   . Load Model 1 of the Eurocode

does not have a ranking and load reduction curve like that of TMH7 and the application

thereof is therefore much simpler. The example described above is limited to the maximum

sagging moment in the end span of a three span structure. The calculations can, however,

be extended and are valid for any number of spans, span lengths and number of notional

lanes. Refer to Figure 22 for the application of the distributed load and to Figure 23 for the

application of the Tandem System loading.

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Figure 22: Eurocode Load Model 1 example distributed loading

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Figure 23: Eurocode Load Model 1 example Tandem System loading

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Load Model 2

Load model 2 consists of a single axle load βQQak  with Qak  equal to 400kN, dynamic

amplification included, which should be applied at any location on the carriageway. When

relevant, only one wheel of 200 βQ (kN) may be taken into account. The value of βQ should

be specified.

In the vicinity of expansion joints, an additional dynamic amplification factor should be

applied.

The contact surface of each wheel should be taken as a rectangle of sides 0.35 m and 0.60

m.

The configuration of Load Model 2 can be seen in Figure 24: Eurocode load model 2 below.

Figure 24: Eurocode load model 2

Load Model 3

Load model 3 refers to special vehicles and is defined in the relevant national annexes. For

comparison purposes it was decided to investigate the special vehicles defined in the British

National Annex (British Standards International, 2003). These are not actual vehicles, but

are calibrated to include the effects of the nominal axle weights and dynamic characteristics

if the Special Types General Order (STGO) and Special Order (SO) vehicles defined by the

British government.

STGO vehicles consist of three variations namely SV80 with a gross weight of 80 tonnes,SV100 with a gross weight of 100 tonnes and SV196 with a gross weight of 196 tonnes.

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The SV80 vehicle type has a maximum axle load of 12.6 tonnes and consists of six axles

grouped in two sets of three axles. The axles are spaced 1.2m apart. The configuration can

be seen in Figure 25 below.

Figure 25: SV80 special vehicle

The SV100 type vehicle has a similar axle configuration, but the axle loading is 165 kN

compared to the 130 kN of SV80. The configuration can be seen in Figure 26 below.

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Figure 26: SV100 special vehicle

The SV196 type load represents the effect of a single locomotive pulling a Category 3 STGO

load with a maximum gross weight of 150 tonnes. The maximum axle load is 16.5 tonnes

with the gross weight of the vehicle train not exceeding 196 tonnes. The load configuration

can be seen in Figure 27 below.

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Figure 27: SV196 special vehicle

There are four Special Order Vehicles (SOV’s). A SOC-250 with a maximum weight of 250

tonnes, a SOC-350 with a maximum weight of 350 tonnes, a SOV-450 with a maximumweight of 450 tonnes and a SOC-600 with a maximum weight of 600 tonnes. The standard

configuration has a trailer with two bogies and two tractors, one pulling and ont pushing. The

configurations can be seen in Figure 28 below.

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Figure 28: SOV vehicles

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Load Model 4

Load Model 4 makes provision for crowd loading and is represented by a uniformly

distributed loading of 5 kPa.

Load Model 4 should be applied on any position of the deck with all reservations included.This load is intended for general verifications and should only be associated with a transient

design situation.

3.1.3.5. Compariso n between TMH7 NA loading and Euro code LM1

loading for work ed examples

In sections 3.1.3.3 and 3.1.3.4 a typical bridge deck configuration was used to illustrate the

application of the normal traffic models for TMH7 and Eurocode. This was achieved through

worked examples, but these examples are not to be confused with the comparativeexamples in section 3.2.3 which are entirely seperate. Figure 29 shows a comparison of the

distributed loading of TMH7 NA loading and Eurocode LM1 loading. It is clear that TMH7’s

distributed loading exceeds LM1 loading by a large margin. Figure 30 below shows a

comparison of the concentrated loading of TMH7 NA loading and Eurocode LM1 loading. It

is clear that the concentrated loading of LM1 exceeds that of NA by a large margin. In

general TMH7’s distributed loading is larger than that of the Eurocode, but the concentrated

loading of the Eurocode is much larger than that of TMH7. The effect of this will be

investigated in the remainder of this document.

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Figure 29: Comparison example of NA (left) and LM1 (right) distributed loads

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Figure 30: Comparison example of NA (left) and LM1 (right) concentrated loads

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3.2. Main study comparison

This section forms the main part of this study. Worked examples in the previous sections

were done to illustrate principles only. This section outlines the different configurations that

were investigated and describes how the modelling was performed in the analysis software

package LUSAS. It goes on to describe the results of the analysis through observations and

gives a summary at the end.

3.2.1. Description of main study comparative examples

In the following sections a comparison will be made between TMH7 and EN 1991-2 for

single-, two- and three span bridges with span lengths of 10 m, 15 m, 20 m, 25 m and 30 m.

The chosen trafficable width is 7.4m. This implies two notional lanes for both TMH7 and EN.

For TMH7 the notional lane width will be 3.7m with no remaining area.

Figure 31: TMH7 notional lane arrangement

For BS EN the notional lane width will be 3m with a remaining area of 1.4m.

Figure 32: BS EN notional lane arrangement

3.2.2. Loading according to influence lines in LUSAS

To determine the most adverse loading positions the loading was done with influence lines

as per Section 3.1.3.2.  Modelling was done with LUSAS finite element software and the

bridges were modelled as line beams with a beam depth of 1 m and a beam width of 7.4 m

as described in Section 3.2. To explain how LUSAS calculates influence lines a simple two

span bridge will be used as in Figure 33 below which is a screenshot from LUSAS.

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Figure 33: LUSAS influence line example model

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LUSAS requires that an influence point be definined. This is the point for which the user

wants LUSAS to calculate the influence line. This point is indicated by the rotational blue

arrow in Figure 33. 

Figure 34: Influence line shape from LUSAS

Figure 34 above shows the influence line shape obtained from LUSAS.

 Application of NA loading in LUSAS

NA is loaded according to the influence line of  Figure 34. Figure 35 shows the application of

the distributed load and Figure 36 shows the application of the knife edge load.

Figure 35: LUSAS NA loading UDL application

Figure 36: LUSAS NA loading Knife Edge application

 Application of LM1 loading in LUSAS

LM1 is loaded according to the influence line of  Figure 34. Figure 37 shows the application

of the distributed load and Figure 38 shows the application of the Tandem System load.

Figure 37: LUSAS LM1 loading UDL application

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Figure 38: LUSAS LM1 loading Tandem System application

 Application of NB loading in LUSAS

 According to section 3.1.3 there can be only one NB vehicle on a bridge at any one time. It

was therefore decided that loading to influence lines was not necessary. A moving load was

run along the length of the bridge which produced an envelope of the moments and shears

at all points on the bridge. Figure 39 shows a typical position of a NB vehicle as it movesalong the deck.

Figure 39: LUSAS NB loading moving load example

 Application of NC loading in LUSAS

 According to section 3.1.3 there can be only one NC vehicle on a bridge at any one time. It

was therefore decided that loading to influence lines was not necessary. A moving load was

run along the length of the bridge which produced an envelope of the moments and shears

at all points on the bridge. Figure 40 shows a typical position of a NC vehicle as it moves

along the deck.

Figure 40: LUSAS NC loading moving load example

 Application of LM3 loading in LUSAS

Similar to NB and NA loading there can be only one LM3 vehicle on a bridge at any one

time. It was therefore decided that loading to influence lines was not necessary. A moving

load was run along the length of the bridge which produced an envelope of the moments

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and shears at all points on the bridge. Figure 41 shows a typical position of a LM3 vehicle as

it moves along the deck.

Figure 41: LUSAS LM3 loading moving load example

3.2.3. How the design values will be compared

When designing a reinforced concrete bridge for flexure and shear it is necessary to check

for both the ultimate limit state (for forces) as well as the serviceability limit state (stresses

and deflections). For this study the nominal actions only were considered to determine howthe individual vehicles compare. For the configurations considered below the values are

given in tabular format and graphs as well as the influence lines are also provided.

To compare the values sensibly NA loading was compared to LM1 and NB36 and NC

loading were compared to LM3. LM2 is given in the graphs and tables but is more intended

for local verifications.

3.2.3.1. Single span con figu rations

 As per section 3.2.1 single span bridges with span lengths of 10 m, 15 m, 20 m, 25 m and 30

m were analysed with a trafficable width of 7.4 m. Table 5 below shows the bending moment

values for the different analyses while Figure 42 shows the results in a graph.

Figure 42: Single span bending moments graph

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Table 5: Single span bending moments values

Table 5 below shows the shear force values for the different analyses while Figure 43 shows

the results in a graph.

Figure 43: Single span shear forces graph

Table 6: Single span shear forces values

Observations:

  LM1 is substantially heavier than NA in bending and shear. In bending LM1 is 77%

heavier than NA for a 10 m span which decreases to 36% more for a 30 m span

Span length NA NB NC LM1 LM2 LM3

10 1515 1440 1884 2675   1000 2040

15 2948 2736 4230   4519 1500 4500

20 4675 4464 7512   6600 2000 8040

25 6452 6246 11727   8919 2500 12420

30 8426 8006 16872   11475 3000 16800

Beding Moments

Span length NA NB NC LM1 LM2 LM3

10 606 610 780 1123   200 880

15 786 936 1178   1234 200 1200

20 935 1008 1530   1346 200 1638

25 1032 1080 1920   1449 200 1980

30 1124 1152 2250   1544 200 2160

Shear 

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length. In shear LM1 is 85% heavier than NA for a 10 m span which decreases to

37% more for a 30 m span length.

  NB is very close to NA loading.

  NC and LM3 compare well for all span lengths with a maximum deviation of 13% for

a 10 m span and a minimum deviation of 2% for a 25 m span length.

3.2.3.2. Two span con figur ations

 As per section 3.2.1 two span bridges with equal span lengths of 10 m, 15 m, 20 m, 25 m

and 30 m were analysed with a trafficable width of 7.4 m. This section describes the results

obtained.

Bending – Hogging

The influence line below (Figure 44) shows that both spans must be loaded equally with the

distributed load and the knife edge load can be placed on either span at the maximum point

on the influence line.

Figure 44: Two span hogging influence line

Table 7 below shows the hogging bending moment values for the different analyses while

Figure 45 shows the results in a graph.

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Figure 45: Two span hogging bending moments graph

Table 7: Two span hogging bending moments values

Observations:

  For hogging NA and LM1 compare well for all span lengths except for 10 m where

the deviation is 29%. This deviation reduces with an increase in span length with a

deviation of 5% at 30 m.

  NB is very close to NA and LM1.

  NC is significantly heavier than LM3 for longer spans. The deviation varies from 7%for a 10 m span length to 51% for a 30 m span.

Beding – Sagging

The influence line shows that only one span should be loaded with a second span having a

relieving effect (Figure 46). The chosen span should also be the one that is loaded with the

knife edge load situated at the maximum point on the influence line.

Span length NA NB NC LM1 LM2 LM3

10   847 1308 1864 1096 381 1991

15   1624 2030 4210 1836 574 3919

20   2582 2728 7453 2690 767 5340

25   3708 3416 10965 3660 959 762930   4991 4102 14394 4748 1152 9550

Beding Moments Hogging

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Figure 46: Two span sagging influence line

Table 8 below shows the sagging bending moment values for the different analyses while

Figure 47 shows the results in a graph.

Figure 47: Two span sagging bending moments graph

Table 8: Two span sagging bending moments values

Span length NA NB NC LM1 LM2 LM3

10   1159 1183 1432 2151 827 1552

15   2252 2202 3210 3642 1239 3432

20   3569 3514 5706 5282 1652 6112

25   4923 4904 8907 7053 2065 9429

30   6429 6424 12827 9005 2477 12966

Beding Moments Sagging

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Observations:

  For sagging NA and NB are very close to each other with the lines on the graph

coinciding.

  LM1 is substantially heavier than NA with a deviation of 86% for a span length of 10m reducing to 40% for a span length of 30 m.

  NC and LM3 compare well for all span lengths with a maximum deviation of 8% for a

span length of 10 m.

Shear – End Support

The influence line shows that one of the end spans should be fully loaded with the other

span unloaded due to relieving effect (Figure 48). The knife edge load should be placed as

close to the support as possible, but not on top of the support.

Figure 48: Two span end shear influence line

Table 9 below shows the end support shear force values for the different analyses while

Figure 49 shows the results in a graph.

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Figure 49: Two span end support shear graph

Table 9: Two span end support shear values

Observations:

  For shear at the end support LM1 is substantially heavier than NA. The deviation

varies from 107% for a span length of 10 m and decreases to 45% for a span length

of 30 m.

  NB is reasonably close to NA with a maximum deviation of 16%.

  NC is reasonably close to LM3 for all span lengths with a maximum deviation of 14%

for a span length of 20 m.

Shear – Middle Support

The influence line shows that both spans must be loaded, the one more heavily than the

other. On the side with the largest distributed load the knife edge loads should be placed as

close to the support as possible, but not on the support.

Span length NA NB NC LM1 LM2 LM3

10   562 548 718 1167 350 774

15   710 776 1043 1200 375 1172

20   850 979 1323 1296 375 150625   935 1089 1700 1386 375 1749

30   1015 1087 2007 1475 380 1936

Shear End

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Figure 50: Two span middle support shear influence line

Table 10 below shows the middle support shear force values for the different analyses while

Figure 51 shows the results in a graph.

Figure 51: Two span internal support shear graph

Table 10: Two span middle support shear values

Span length NA NB NC LM1 LM2 LM3

10   653 681 970 1176 377 1039

15   839 953 1436 1301 389 1341

20   995 1144 1913 1417 389 1855

25   1101 1156 2313 1530 389 2260

30   1200 1239 2599 1642 392 2430

Shear Middle

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Observations:

  For shear at the middle support LM1 is substantially heavier than NA. The deviation

varies from 80% for a span length of 10 m and decreases to 37% for a span length of

30 m.  NB is reasonably close to NA with a maximum deviation of 15%.

  NC is reasonably close to LM3 for all span lengths with a maximum deviation of 7%

at a span length of 30 m.

3.2.3.3. Three span con figur ations

 As per section 3.2.1 three span bridges with equal span lengths of 10 m, 15 m, 20 m, 25 m

and 30 m were analysed with a trafficable width of 7.4 m. This section describes the results

obtained.

Bending – Hogging

The influence line shows that any two adjacent spans must be loaded with the end span

loaded with the highest intensity (Figure 52). The knife edge load should be placed in the

end span at the maximum position on the influence line.

Figure 52: Three span hogging influence line

Table 11 below shows the end support shear force values for the different analyses while

Figure 53 shows the results in a graph.

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Figure 53: Three span hogging bending moments graph

Table 11: Three span hogging bending moments values

Observations:

  For hogging LM1 is substantially heavier than NA with a deviation of 37% for a 10

m span length which reduces to 27% for a 30 m span length.

  NC is substantially higher than LM3 with a maximum deviation of 52% for a spanlength of 30 m. This deviation reduces to 7% for a span length of 10 m.

Bending – Sagging End Span

The influence line shows that both the end spans should be loaded with the span under

consideration being loaded with the highest intensity (Figure 54). The knife edge load should

be placed at the maximum point on the influence line. The middle span should not be loaded

as it has a relieving effect.

Span length NA NB NC LM1 LM2 LM3

10   1045 1241 1738 1433 406 1862

15   1906 1917 3928 2502 612 3705

20   2929 2569 6993 3787 817 5103

25   4146 3246 10300 5289 1023 7169

30   5525 4058 13750 7010 1230 9050

Beding Moments Hogging

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Figure 54: Three span sagging end span influence line

Table 12 below shows the end span sagging moment values for the different analyses while

Figure 55 shows the results in a graph.

Figure 55: Three span end span sagging moments graph

Table 12: Three span end span sagging moments values

Span length NA NB NC LM1 LM2 LM3

10   1223 1229 1522 2146 818 1528

15   2332 2131 3426 3644 1226 3419

20   3669 3503 6084 5338 1636 6016

25   5069 4900 9009 7218 2048 935230   6616 6320 12680 9292 2450 12820

Beding Moments Sagging Endspan

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Observations:

  For end span sagging LM1 is substantially heavier than NA with a maximum

deviation of 75% for a span length of 10 m. This deviation reduces to 47% for a span

length of 30 m.  NA and NB compare well with a maximum deviation of 5% for a span length of 30 m.

  NC and LM3 compare well with a maximum deviation of 4% for a span length of 25

m.

Bending – Sagging Middle Span

The influence line shows that only the center span should be loaded with maximum intensity.

The endspans should not be loaded due to relieving effect. The knife edge loads should be

placed in the center of the middle span.

Figure 56: Three span middle span sagging influence line

Table 13 below shows the internal span sagging moment values for the different analyses

while Figure 57 shows the results in a graph.

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Figure 57: Three span middle span sagging moments graph

Table 13: Three span middle span sagging moments graph

Observations:

  For middle span sagging LM1 is substantially heavier than NA with a maximum

deviation of 79% for a span length of 30 m. This deviation reduces to 43% for a span

length of 10 m.

  NA and NB compare well with a maximum deviation of 11% for a span length of 15

m.

  NC and LM3 compare well with a maximum deviation of 9% for a span length of 25

m.

Shear – End Support

The influence line shows that the two end spans should be loaded with the one span at

maximum intensity and the other at lower intensity (Figure 58). The middle span should not

be loaded as it has a relieving effect. The knife edge load should be placed on the span with

Span length NA NB NC LM1 LM2 LM3

10   976 949 1130 1750 701 1055

15   1870 1679 2539 2980 1036 2693

20   2943 2770 4512 4355 1400 4811

25   4045 3900 6863 5874 1747 7487

30   5268 5089 10130 7537 2100 10330

Beding Moments Sagging Centerspan

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the maximum loading as close as possible to the end support, but not directly above the

support.

Figure 58: Three span end support shear influence line

Table 14 below shows the middle support shear force values for the different analyses while

Figure 59 shows the results in a graph.

Figure 59: Three span end support shear graph

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Table 14: Three span end support shear values

Observations:

  For shear at the end support LM1 is substantially heavier than NA with a maximum

deviation of 100% for a span length of 10 m. This deviation reduces to 53% for a

span length of 30 m.

  The maximum deviation between NC and LM3 is 11% for a span length of 25 m. Theminimum deviation is 4% for a span length of 10 m.

Shear – Internal Support

The influence line shows that two adjacent spans should be loaded with the end span

loaded with the highest intensity. The opposite end span should not be loaded as it has a

relieving effect. The knife edge load should be placed on the end span as close as possible

to the internal support, but not directly above the support.

Figure 60: Three span internal support shear influence line

Table 15 below shows the middle support shear force values for the different analyses while

Figure 61 shows the results in a graph.

Span length NA NB NC LM1 LM2 LM3

10   530 602 736 1064 350 768

15   670 770 1063 1169 366 1162

20   785 1002 1400 1260 375 149325   862 1085 1661 1345 380 1838

30   934 1083 1993 1427 383 2092

Shear End

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Figure 61: Three span internal support shear graph

Table 15: Three span internal support shear values

Observations:

  For shear at the internal supports LM1 is substantially heavier than NA with a

maximum deviation of 81% for a span length of 10 m. This deviation decreases to

36% for a span length of 30 m.

  NA compares well to NB with a maximum deviation of 12% for a span length of 15 m.

  NC compares well to LM3 with a maximum deviation of 8% with NC being the

heavier of the two.

3.2.4. Summary

The following table summarises the data from the previous sections.

Span length NA NB NC LM1 LM2 LM3

10   648 672 967 1175 378 1029

15   840 959 1432 1297 386 136020   991 1111 1850 1396 390 1867

25   1098 1194 2274 1523 392 2206

30   1197 1245 2641 1624 393 2448

Shear Middle

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Table 16: Analysis results summary

   N  o  o   f  s  p  a  n  s

   S  p  a  n   l  e  n  g   t   h   (  m   )   N   A  v  s   (

   L   M   1   )   N   B   &   N   C  v  s   (   L   M   3   )   N   A  v  s   (   L   M   1

   )   N   B   &   N   C  v  s   (   L   M   3   )   N   A  v  s   (   L   M   1   )   N

   B   &   N   C  v  s   (   L   M   3   )   N   A  v  s   (   L   M   1   )   N   B   &   N   C  v  s   (   L   M   3   )

   1   0

   (   7   7

   )

   (   8   )

  -

  -

   (   8   5   )

   (   1   3   )

  -

  -

   1   5

   (   5   3

   )

   (   6   )

  -

  -

   (   5   7   )

   (   2   )

  -

  -

   2   0

   (   4   1

   )

   (   7   )

  -

  -

   (   4   4   )

   (   7   )

  -

  -

   2   5

   (   3   8

   )

   (   6   )

  -

  -

   (   4   0   )

   (   3   )

  -

  -

   3   0

   (   3   6

   )

   1

  -

  -

   (   3   7   )

   4

  -

  -

   1   0

   (   8   6

   )

   (   8   )

   (   2   9   )

   (   7   )

   (   1   0   7   )

   (   8   )

   (   8   0   )

   (   7   )

   1   5

   (   6   2

   )

   (   7   )

   (   1   3   )

   7

   (   6   9   )

   (   1   2   )

   (   5   5   )

   7

   2   0

   (   4   8

   )

   (   7   )

   (   4   )

   4   0

   (   5   2   )

   (   1   4   )

   (   4   2   )

   3

   2   5

   (   4   3

   )

   (   6   )

   1

   4   4

   (   4   8   )

   (   3   )

   (   3   9   )

   2

   3   0

   (   4   0

   )

   (   1   )

   5

   5   1

   (   4   5   )

   4

   (   3   7   )

   7

   1   0

   (   7   5

   )

   (   1   )

   (   3   7   )

   (   7   )

   (   1   0   1   )

   (   5   )

   (   8   1   )

   (   6   )

   1   5

   (   5   6

   )

   1

   (   3   1   )

   6

   (   7   4   )

   (   9   )

   (   5   4   )

   5

   2   0

   (   4   5

   )

   1

   (   2   9   )

   3   7

   (   6   1   )

   (   7   )

   (   4   1   )

   (   1   )

   2   5

   (   4   2

   )

   (   4   )

   (   2   8   )

   4   4

   (   5   6   )

   (   1   1   )

   (   3   9   )

   3

   3   0

   (   4   0

   )

   (   1   )

   (   2   7   )

   5   2

   (   5   3   )

   (   5   )

   (   3   6   )

   8

   N   O   T   E

   T   h  e  v  a   l  u  e  s   i  n   t   h  e   t  a   b   l  e  a   b  o  v  e  a  r  e  r  e   l  a   t   i  v  e  p  e  r  c  e  n   t  a  g  e  s   b  e   t  w  e  e

  n   t   h  e   l  o  a   d   t  y  p  e  s .   N   A  v  s   (   L   M   1   )  =   (   7   7

   )  m  e  a  n  s   t   h  a   t   L   M   1   i  s   7   7   %    h

   i  g   h  e  r   t   h  a

  n   N   A .

   S   i  m   i   l  a  r   l  y   N   A  v  s   (   L   M   1   )  =   5  m  e  a  n  s   t   h  a   t   N   A   i  s   5   %    h

   i  g   h  e  r   t   h  a  n   L   M   1 .

   S   h  e  a  r

   1 2 3

   S  a  g  g   i  n  g

   H  o  g  g   i  n  g

   E

  n   d

   I  n   t  e  r  n  a

   l

   B  e  n   d   i  n  g

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To summarise the analysis data the following:

1. For single span configurations LM1 loading is significantly heavier than NA loading

(77% for bending and 85% for shear). The difference tends to decrease with

increasing span length. Abnormal loading (NB&NC and LM3) give similar results witha maximum difference of 13%, LM3 being heavier.

2. For two span configurations LM1 loading is significantly heavier, especially in shear

where LM1 is more than double NA at the end support (107%). In bending there is a

bigger difference in sagging (86%) than in hogging (29%). The differences tend to

decrease with an increase in span length. For abnormal loads (NB&NC and LM3) NC

is 51% heavier than LM3 for hogging. For sagging the results are close with a

maximum difference of 8%, LM3 being the heavier.

3. For three span configurations LM1 loading is significantly heavier, especially in shear

where where LM1 is more than double NA at the end support (101%). In bending

there is a bigger difference in sagging (75%) than in hogging (37%). The differences

tend to decrease with an increase in span length. For abnormal loads (NB&NC and

LM3) NC is 52% heavier than LM3 for a span length of 30 m. For sagging the results

are close with a maximum difference of 4%, LM3 being the heavier.

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4. Conclusions and recommendations

This thesis was concerned with the comparison of the live load models specified in TMH7

and the Eurocode.

To compare any codes it is important to understand the background to the codes and the

philosophies employed in their composition. This study showed that TMH7 follows a semi-

probabilistic approach while the Eurocode follows a fully probabilistic approach. Semi-

probabilistic means that probabilistic principles were applied when determining material and

load factors for limit state design, but the value of these were fixed by the design codes. The

fully probabilistic approach is a design process based upon an exact probabilistic analysis

for the entire structural system. This means that statistical analyses are performed on actual

traffic data to derive the partial factors used in limit state design. These factors are flexibile

and can be adjusted as traffic demands change.

To understand how vehicle loading is applied to a bridge it is essential to understand to

concept of influence lines. Section 3.1.3.2 explains this concept in detail and defines an

influence line as the variation of a bending moment or shear force at a specific point on a

structure with a unit load placed at diffferent positions on the structure. Influence lines were

used throughout this study to determine the most onerous positions of the live loads. Section

3.2.2 explains how loading was applied in the analyses.

Section 3 dealt with the different loading models of the two codes. It showed that TMH7

consists of three types of loading namely NA  – normal traffic, NB – abnormal traffic and NC

 – super loading. Eurocode consists of LM1  – normal traffic, LM2  – dynamic effects for local

verification and LM3  –  abnormal loads. It was therefore decided that NA traffic would be

compared to LM1. NB and NC traffic was compared to LM3. It was decided to compare one,

two and three span bridges with span lengths ranging from 10 m to 30 m in 5 m increments.

 A width of 7.4m was chosen which rendered two notional lanes of 3.7 m each for TMH7 and

two notional lanes of 3 m each for the Eurocode with a remaining width of 1.4 m. The studyshowed the following:

Single span configurations

For single span configurations LM1 loading is significantly heavier than NA loading (77% for

bending and 85% for shear). The difference tends to decrease with increasing span length.

 Abnormal loading (NB&NC and LM3) give similar results with a maximum difference of 13%,

LM3 being heavier.

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Two span configurations

For two span configurations LM1 loading is significantly heavier, especially in shear where

LM1 is more than double NA at the end support (107%). In bending there is a bigger

difference in sagging (86%) than in hogging (29%). The differences tend to decrease with anincrease in span length. For abnormal loads (NB&NC and LM3) NC is 51% heavier than

LM3 for hogging. For sagging the results are close with a maximum difference of 8%, LM3

being the heavier.

Three span configurations

For three span configurations LM1 loading is significantly heavier, especially in shear where

where LM1 is more than double NA at the end support (101%). In bending there is a bigger

difference in sagging (75%) than in hogging (37%). The differences tend to decrease with an

increase in span length. For abnormal loads (NB&NC and LM3) NC is 52% heavier than

LM3 for a span length of 30 m. For sagging the results are close with a maximum difference

of 4%, LM3 being the heavier.

This study has therefore shown that there are large differences in traffic loading between the

South African bridge design code, TMH7, and the Eurocode. For nomal traffic loading EN is

substantially heavier than TMH7 especially in shear, but also in bending. For abnormal

loading there is less of a difference and the numbers generally compare well within 10%.

To reasonably limit the scope of this work the study has made use of single, two and three

span bridges of varying span length to illustrate the differences. The following

reccommendations can be made for different configurations:

  With an increase in span length the UDL tends to become the governing component

of the loading. TMH7’s UDL is substantially heavier than that of the Eurocode, but the

knife edge loading of the Eurocode is substantially heavier than TMH7. Although LM1

will foreseeably continue to exceed NA loading it can be assumed that, the longer the

span length is, the closer the results of the two load models will become.

  NC is approximately 50% heavier than LM3 in hogging for two and three span

configurations. Although more span lengths have not been analysed it is foreseeable

that this trend will continue for four and more span structures. Further studies are

needed as confirmation.

  For abnormal load sagging the difference decreases with an increase in the number

of spans. For a single span structure the maximum difference is 13%, for two spans

8% and for three spans 4%. Although more span lengths have not been analysed it is

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foreseeable that the difference will become closer to zero. Further studies are

needed as confirmation.

 Adopting the Eurocodes or alligning with the Eurocodes in South Africa for bridge design will

require extensive calibration efforts to compile a South African national annex and this willmost likely have to be done by academic institutions. A traffic study was done by (Anderson,

2006) to determine the validity of the current loading in TMH7 on South African roads. It was

found that the actual loading on South African bridges was noticeably higher than the

provisions given in TMH7. This study can be used to calibrate the Eurocode for South

 African conditions when the opportunity arrises.

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Bibliography

 Anderson, J.R.B. (2006) Review of the South African Live Load Models for Traffic Loading

on Bridge and Culvert Structures using Weigh - In - Motion Data, Cape Town: UCT.

 ATKINS Highways and Transportation (2005) 'Background to the UK National Annexes to

EN1990: Bases of Structural Design'.

Booker, J.D., Raines, M. and Swift, K.G. (2001) Designing Capable and Reliable Products,

1st edition, Oxford: Butterworth Heinemann.

British Standards International (2003) UK National Annex to Eurocode 1: Actions on

structures Part 2: Traffic loads on bridges, BSI.

Camilleri, D. (2003) 'An overview of the structural Eurocodes in the construction industry',

The Structural Engineer , vol. 81, no. 14, July, pp. 14-17.

CEN EN1990 (2002) EN1990 - Basis of structural design, Brussels: CEN.

CEN EN1991-2 (2002) Eurocode 1: Actions on structures - Part 2: Traffic loads on bridges,

Brussels: CEN.

Committee of State Road Authorities (1981) TMH7 : Code of practice for the design of

highway bridges and culverts in South Africa, Pretoria: Department of Transport.

Holicky, M., Retief, J. and Dunaiski, P. (n.d) 'The reliability basis of design for structural

resistance', Structural Engineering Mechanics and Computation, pp. 1735-1740.

O'Connor, C. and Shaw, P. (2000) Bridge Loads, London: Spon Press.

Zingoni, A. (2008) 'The case for the Eurocodes for South Africa', Civil Engineering , March,

pp. 16-18.