PARASITIC MOMENT EFFECT FOR THE THREE SPANS CONTINUOUS

PRESTRESSED CONCRETE BRIDGE

SITI SARAH SALIM

A project report submitted in partial fulfillment of the

requirements for the award of the degree of

Master of Engineering (Civil-Structure)

Faculty of Civil Engineering

Universiti Teknologi Malaysia

JANUARY 2014

iii

To my beloved parents and family

iv

ACKNOWLEDGEMENT

I wish to express my sincere appreciation to my project supervisor, Assoc.

Prof. Dr. Arizu b. Sulaiman, for his encouragement, guidance, advices and critics.

Without his continued support and interest, this project would not have been the

same as presented here.

I also would like to give my special thanks to my Director, Mr Zainal, my

supervisor, Mr S. Baskaran and fellow officemate at SMEC (M) Sdn. Bhd. for

providing assistance and support. They have contributed towards my understanding,

thoughts and useful information for finishing this project.

My fellow friends also are recognized for their support and thanks for their

direct and indirect involvement. My sincere appreciation also extends to others who

have provided assistance at various occasions.

Lastly but not least, I am grateful to my dearest family for their constant

encouragement apart from providing their love and moral support. Words cannot

express my gratitude. Thank you for everything.

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ABSTRACT

In the analysis of a continuous prestressed concrete bridge, Dead Load (self-

weight of bridge), Superimposed Dead Load (Surfacing and Parapet) and Live Load

(HA, HB or combined) are considered as major loadings for bridge structure.

However, there are other factors that should be considered in the analysis such as

Parasitic Moment. The effect from parasitic moment can contribute a significant

value in designing a continuous prestressed concrete bridge. This study focuses on

the effect of parasitic moment for a three spans continuous prestressed concrete

bridge. An analysis of a continuous bridge using Staad Pro software is carried out to

determine the parasitic moments of the bridge. The parasitic moments obtained from

Staad Pro are slightly higher compared to the parasitic moments from Adapt software

with a difference less than 10 percent. The parasitic moment is sagging throughout

the whole bridge and the maximum moment is at the second span. A positive value

of the parasitic moment will increase the value of the sagging moment at the mid

span but will reduce the hogging moment at the support. For the case when parasitic

moment effect is considered, the stress at bottom of beam is lower than the stress at

top of beam. Whereas, the situation is reverse for the case when parasitic moment

effect is not considered. If the same dead load, superimposed dead load and live load

proportions are to be considered, the resultant stress at bottom of the beam will

exceed the tensile stress limit when the parasitic moment proportion is more than

55% of the total moment. Hence, the parasitic moment effect should be considered

in the design of a continuous prestressed concrete bridge especially when it comes to

the value of moment at the mid span of the bridge.

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ABSTRAK

Dalam analisis jambatan konkrit prategasan selanjar, beban mati (berat

sendiri jambatan), beban mati kenaan (permukaan dan dinding jambatan) dan beban

hidup (HA, HB atau gabungan) dianggap beban utama bagi struktur jambatan.

Walau bagaimanapun, terdapat factor-faktor lain yang perlu dipertimbangkan dalam

analisis seperti momen parasitik. Kesan daripada momen parasitik boleh

menyumbang nilai yang signifikan dalam mereka bentuk sesebuah jambatan konkrit

prategasan selanjar. Kajian ini menumpukan kepada kesan momen parasitik terhadap

jambatan konkrit prategasan selanjar yang mempunyai tiga rentang. Analisis

jambatan selanjar menggunakan perisian Staad Pro digunakan untuk menentukan

momen parasitik jambatan tersebut. Momen parasitik yang diperolehi daripada Staad

Pro adalah lebih tinggi berbanding momen parasitik daripada analisis perisian Adapt,

dengan perbezaan kurang daripada 10 peratus. Momen parasitik adalah melendut

pada keseluruhan jambatan dan momen maksimum adalah pada rentang kedua.

Momen parasitik positif akan meningkatkan momen melendut di tengah rentang dan

mengurangkan momen meleding di penyokong. Apabila kesan momen parasitik

diambil kira, tekanan di bahagian bawah rasuk adalah lebih rendah daripada tekanan

di bahagian atas rasuk. Manakala, keadaan adalah sebaliknya bagi kes apabila

momen parasitik tidak dipertimbangkan. Jika bahagian beban mati, beban mati

kenaan dan beban hidup yang sama dipertimbangkan, tekanan di bahagian bawah

rasuk akan melebihi had tegasan tegangan apabila momen parasitik melebihi 55

peratus daripada jumlah momen. Oleh itu, kesan momen parasitik perlu

dipertimbangkan dalam rekabentuk jambatan konkrit pretegasan selanjar terutama

jika melibatkan nilai momen di pertengahan rentang jambatan.

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TABLE OF CONTENTS

CHAPTER TITLE PAGE

DECLARATION ii

DEDICATION iii

ACKNOWLEDGEMENTS iv

ABSTRACT v

ABSTRAK vi

TABLE OF CONTENTS vii

LIST OF TABLES x

LIST OF FIGURES xi

LIST OF SYMBOLS

LIST OF APPENDICES

xvi

xvii

1 INTRODUCTION

1.1 General

1.2 Problem Statement

1.3 Aim and Objectives

1.4 Scope of Work

1.5 Significant of Study

1

1

3

3

4

4

2 LITERATURE REVIEW

2.1 General

2.2 Design Loading

2.2.1 Dead Load

2.2.2 Highway loading according to BD 37/01

5

5

6

6

7

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2.2.3 Highway loading according to JKR

specifications

2.2.3.1 LTAL loading

2.2.3.2 SV loading

2.2.5 Other loading

2.3 Stage of Construction

2.4 Continuity of Prestressed Bridge

2.5 Parasitic Moment

2.5.1 Primary and secondary prestress effects

2.5.2 The nature of prestress parasitic moments

2.5.3 Computation method for secondary prestress

moments

2.5.4 Prestress application in Staad Pro

11

11

12

14

15

19

21

21

24

29

31

3 METHODOLOGY

3.1 Dead Load and Applied Loading Analysis

3.2 Designing Prestressed Concrete Beam

3.3 Deriving the Parasitic Moment

3.3.1 Creating new file

3.3.2 Geometry section

3.3.3 General section

3.3.4 Perform analysis

3.4 Compare Results from Staad Pro and Adapt Software

3.5 Effect of Parasitic Moment

34

34

35

36

37

39

40

52

53

54

4 ANALYSIS AND RESULTS

4.1 Introduction

4.2 Analysis of Bridge Due to Applied Loading

4.3 Parasitic Moment

56

56

57

63

4.4 Effect of Parasitic Moment

4.5 Significant of Parasitic Moment

66

69

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5 CONCLUSIONS AND RECOMMENDATIONS

5.1 Overview

5.2 Conclusions

5.3 Future Recommendations

75

75

76

77

REFERENCES 79

APPENDICES 81

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LIST OF TABLES

TABLE NO TITLE PAGE

2.1 Type HA uniformly distributed load 7

2.2 HA lane factors 8

2.3 Type LTAL uniformly distributed load 11

4.1 Bending moment and shear force for different applied

loadings

62

4.2 Parasitic Moment at different positions 65

4.3 Total moment for analysis of the bridge 67

4.4 The stress check at 0.5L of second span with parasitic

effect

70

4.5 The stress check at 0.5L of second span without parasitic

effect

71

4.6 The stress check at 0.5L of the second span with parasitic

moment value of 6760 kNm

73

xi

LIST OF FIGURES

FIGURE NO TITLE PAGE

2.1 Dimensions of HB vehicle 9

2.2 Plan of SV 12

2.3 Controlled SV movement geometry 13

2.4 Uncontrolled SV movement geometry 13

2.5 Stage 1 for three-span continuous prestressed concrete

bridge construction

15

2.6 Stage 2 for three-span continuous prestressed concrete

bridge construction

16

2.7 Stage 3 for three-span continuous prestressed concrete

bridge construction

16

2.8 Stage 4 for three-span continuous prestressed concrete

bridge construction

17

2.9 Stage 5 for three-span continuous prestressed concrete

bridge construction

18

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2.10 Stage 6 for three-span continuous prestressed concrete

bridge construction

18

2.11 Multi-strand tendon coupler 19

2.12 Prestress bar coupler 20

2.13 Prestressed in continuous decks 22

2.14 Prestress stresses on section 24

2.15 (a) The principal of parasitic moment 27

2.15 (b) The principal of parasitic moment continued 28

3.1 Grillage model of a three-span continuous prestressed

concrete bridge

35

3.2 Estimate number of tendons for a bridge 36

3.3 The home page of Staad Pro. Software 37

3.4 "New" model dialog box 38

3.5 "Where do you want to go?" dialog box 38

3.6 Members of three span continuous prestressed concrete

bridge

39

3.7 Line-beam model for three span continuous prestressed

concrete bridge

40

3.8 The section properties representation in Staad Pro 41

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3.9 Section properties of T10 beam 42

3.10 Section properties of T10 beam (end block) 43

3.11 Section properties of T10 internal beam 44

3.12 Section properties of T10 edge beam 45

3.13 Section properties of edge diaphram 46

3.14 Section properties of stitching and crosshead 47

3.15 The pinned support is assign to the model 48

3.16 Prestress load dialog box 49

3.17 The prestress load assignation 50

3.18 Post stress load dialog box 50

3.19 The post stress load assignation 51

3.20 Load combination dialog box 52

3.21 The parasitic moment diagram 53

3.22 Parasitic moment value from Adapt software 54

3.23 Resultant stress on prestress section 55

4.1 Bending moment due to self weight 57

4.2 Shear force due to self weight 57

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4.3 Bending moment due to parapet load 58

4.4 Shear force due to parapet load 58

4.5 Bending moment due to internal surfacing 59

4.6 Shear force due to internal surfacing 59

4.7 Bending moment due to external surfacing 60

4.8 Shear force due to external surfacing 60

4.9 Bending moment due to live load (HA and HB30) 61

4.10 Shear force due to live load (HA and HB30) 61

4.11 Parasitic moment from Staad Pro analysis 64

4.12 Result of parasitic moment from Adapt software 64

4.13 Resultant moment for the three spans continuous bridge 66

4.14 Percentage of moment at 0.4L of the first span 68

4.15 Percentage of moment at 0.5L of the second span 68

4.16 The resultant stress at 0.5L of second span with parasitic

effect

71

4.17 The resultant stress at 0.5L of second span without

parasitic effect

72

xv

4.18 The resultant stress at 0.5L of the second span with the

parasitic moment value of 6760 kNm

73

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LIST OF SYMBOLS

2-D - Two-dimensional space

A, As - Area of section

d - Diameter

e, ec - Eccentricity

E, Es - Modulus of elasticity

fcu - Concrete strength

I - Moment of inertia

l - Span length

M - Bending moment

NA - Neutral axis

P, Pult - Force

w - Load per meter

yb - Distance of cable from bottom section

Zb, Zt - Section modulus

θ - End rotation

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LIST OF APPENDICES

APPENDIX TITLE PAGE

A General arrangement of the bridge 82

B Drawing of Cable Layout 83

CHAPTER 1

INTRODUCTION

1.1 General

Normal practice in bridge design is to combine the longitudinal and transverse

designs, different load conditions and long term effects in order to suit the design

requirements. However, these criteria are practically analyzed separately. The analysis

that commonly used to derive the forces and moments for bridge design is two- or three

dimensional finite-element modeling or grillage models. This type of analysis can be

applicable for any types of bridge materials as steel, prestressed concrete and many

more.

Prestressed concrete is frequently chosen as the material for bridge constructions.

This is because the development of prestressed concrete bridges has given the bridge

engineers increased flexibility in his selection of bridge form and in the construction

techniques available. Prestressing in bridgeworks is normally applied as an external

force to the concrete by the use of wires, strands or bars, and can greatly increase the

2

strength of concrete alone. This can result in longer or slender spans, which improves

aesthetics while providing economy in the construction (Hewson, 2003).

For prestressed concrete bridge, the prestress effect must be applied within the

model as other loads. The principle of prestress design is to make sure that the resulting

stress came from primary and secondary effects are within the allowable limit. The

stress is generated due to self-weight and loadings from the prestress effect. The

secondary moment such as parasitic moment is one of the prestress effects. If the

resulting stresses are exceeding the allowable limit, adjustments have to be made to the

prestress arrangement. So, it is important to analysis the prestress effects before

determining the final bridge design.

The stresses inside the prestress structure also undergo short and long term losses

such as creep and shrinkage. Since the continuous prestressed concrete bridge generally

constructed stage-by-stage, each stage must be analyzed separately to obtain the

moments, shears and prestress effects for that stage. The total moment and force

distribution at each stage is the combination of the results from the stage and from all the

earlier stages. However, the results from previous stages must be modified to consider

the long term losses. At the final stage, the analysis results for the completed structure

are calculated after all long term losses occurred and these values are used to verify the

final design.

3

1.2 Problem Statement

In analysis of a continuous prestressed concrete bridge, Dead Load (self-weight

of bridge), Superimposed Dead Load (Surfacing and Parapet) and Live Load (HA, HB

or combined) are considered as major loadings for bridge structure. However, there are

other factors that should also be considered in the analysis such as Parasitic Moment.

The effect from parasitic moment may contribute a significant value in designing a

prestressed concrete bridge. If this effect is neglected, improper design of bridges may

be obtained. Furthermore, if the total stresses resulted from the applied loads and this

additional effect exceeded the capacity of the bridge, the bridge may fail.

1.3 Aim and Objectives

The aim of this study is to study the parasitic moment effect for three-span

continuous prestressed concrete bridges. The objectives for this study are:

i. To analyze the three-span continuous prestressed concrete bridge due the

parasitic moment effect with Staad Pro.

ii. To compare the analysis results from Staad Pro. with existing results from Adapt.

iii. To determine the effect of parasitic moment for the three-span continuous

prestressed bridge.

iv. To propose a suitable position for considering the parasitic moment effect that

will have some significant in the design of three-span continuous prestressed

concrete bridge.

v. To determine the limit of parasitic moment's value which will be significant in

the design of three-span continuous prestressed concrete bridge.

4

1.4 Scope of Work

This study only focuses on the Putai Bridge which is a three-span continuous

prestressed concrete bridge. The dimensions, section properties and tendons location of

the bridge will be shown on Appendix section. The bridge will be modelled in Staad

Pro. for different stages. The stages consider will follow the sequences of construction.

This model will be analyzed for self weight, superimposed dead load and highway

loadings at different stages. Parasitic moment effect will be analyzed using line-beam

analysis. The eccentricities and forces of tendons inside the complete prestressed

concrete bridge are applied directly to the model. The analysis results from Staad Pro.

are compared to the existing results from Adapt to determine the accuracy of the model.

The resultant stresses of the prestressed concrete beam is checked against the stress limit

using spreadsheet.

1.5 Significant of Study

i. The study will shows the method to analyze the parasitic moment effects by

using general structural analysis such as Staad Pro.

ii. The study will show the effect of parasitic moment for the continuous prestressed

concrete bridge.

iii. The study will be the basis on whether parasitic moment values will be of some

significant in designing continuous prestressed concrete bridge.

79

REFERENCES

Aalami, B.O. (1998), Hyperstatic (Secondary) Actions in Prestressing and Their

Computation, Technical Notes for Professional Engaged in Post-Tensioning

Design, December 1998

Benaim, R. (2007), Prestressing for Continuous Beam. The Design of Prestressed

Concrete Bridges 6: 139 – 187

Bondy, K.B. (2003), Moment Redistribution: Principles and Practice Using ACI 318-02,

PTI Journal, January 2003

British Design (2001), Loads for Highways Bridge, BD37/01, London: British Standards

Institution

British Standard Institution (1988), Steel, concrete and composite bridges. General

statement. BS 5400-1, London: British Standards Institution

British Standard Institution (2006), Steel, concrete and composite bridges. Specification

for loads. BS 5400-2, London: British Standards Institution

British Standard Institution (1990), Steel, concrete and composite bridges. Code of

practice for design of concrete bridges. BS 5400-4, London: British Standards

Institution

British Standard Institution (2007) Structural Use of Concrete, BS 8110, London: British

Standards Institution

Burgoyne, C. (2005) Analysis of Continuous Prestressed Concrete Beams

Duan L., Chen, K. and Tan, A. (2000), Prestressed Concrete Bridges, Bridge

Engineering Handbook. Boca Raton: CRC Press, 2000

Guo, N., Li, H. and Guo, Y. (2011), Research on Secondary Moment of Prestressed Slab-

Column Structure, Advanced Materials Research Vols. 243-249 (2011) pp 787-792

80

Hewson, N.R. (2003), Analysis of Prestressed Concrete Bridges. Prestressed Concrete

Bridges: Design and Construction 8: 134 - 150

Law, S.S. and Lu, Z.R. (2005), Time domain responses of a prestressed beam and

prestress identification, Journal of Sound and Vibration, 288 (2005) 1011–1025

Lua, Z.R. and Law, S.S. (2005) Identification of prestress force from measured structural

responses, Mechanical Systems and Signal Processing, 20 (2006) pp 2186–2199

Marshall, R.B., Cormie, D. and Lavery, M. (2012), Chapter 10: Loading, ICE Manual of

Structural Design: Buildings 2012 Institution of Civil Engineers

Oh, B.H. and Jeon, S.J. (2002) Limitations and realistic application of equivalent load

methods in pre-stressed concrete structures, Magazine of Concrete Research, 2002,

54, No. 3, June, 223–231

Scollard, C.R. and Bartlett, F.M. (2005), Secondary Prestressing Moments in

Rehabilitated Posttensioned Bridges, Journal of Bridge Engineering, 2005.10:215-

227

Su, X.K., Nan, G. (2012) Analysis Method of Secondary Moment in Prestressed Plane

Structures Applied Mechanics and Materials, Vols. 105-107 (2012) pp 953-956

Tiruchirapalli, V. and Hindi, R. (2009), Secondary Moments of Continuous Prestressed

Concrte Beams Using Closed Form Equation, Structures 2009: Don't Mess with

Structural Engineers 2009 ASCE

Xiong, X. and Xu, S.X. (2005) Computation of Secondary Moments in Prestressed

Concrete Structures, ASCE