The Town Lattice Truss: An Appropriate Bridge Technology for Developing Countries

300 Pages·2009·17.04 MB·English

The Town Lattice Truss: An Appropriate Bridge Technology for
Developing Countries

by

Todd Craig Radford

B.Sc.Eng (Civil Engineering)
University of New Brunswick, 2000

S.M. Civil and Environmental Engineering
Massachusetts Institute of Technology, 2003

Submitted to the Department of Civil and Environmental Engineering in partial
fulfillment of the requirements for the degree of

Doctor of Philosophy
at the
Massachusetts Institute of Technology

February 2010

© 2009 Todd C. Radford. All rights reserved.

The author hereby grants to MIT permission to reproduce and to distribute publicly
paper and electronic copies of this thesis document in whole or in part in any medium
now known or hereafter created.

Signature of Author: ____________________________________________________
Department of Civil and Environmental Engineering
September 8, 2009

Certified by: ___________________________________________________________
Jerome Joseph Connor, Jr.
Professor of Civil and Environmental Engineering
September 8, 2009

Signature of Author: ____________________________________________________
Daniele Veneziano
Chairman, Departmental Committee for Graduate Students

The Town Lattice Truss: An Appropriate Bridge Technology for
Developing Countries

by

Todd Radford

Submitted to the Department of Civil and Environmental Engineering on
September 8, 2009 in partial fulfillment of the requirements for the degree of
Doctor of Philosophy in the field of Structures and Materials

ABSTRACT

The Town lattice truss is proposed as an appropriate technology for the Tshumbe
Diocese of the Democratic Republic of Congo. This proposal is made based on an
understanding of rural transport and appropriate technology and an in-depth analysis of
the details of the Town lattice truss.

The nature and importance of rural transport and accessibility are presented, and
bridges are identified as a key component in rural transport development. The concept
of appropriate technology is presented along with a framework consisting of required
and desired characteristics of any appropriate technology, including bridges. Structural
materials are compared for use in bridges in rural areas of developing countries and
timber is selected as the appropriate choice for the Tshumbe Diocese. Three existing
timber bridges systems for developing countries are analyzed and compared, and the
Town lattice truss is proposed as an alternative to all three.

The Town lattice truss is presented and described in detail with reference to a study of
forty existing bridges in the northeastern United States that was conducted as a part of
this work. Appropriate characteristics of the truss are identified and used to compare
the truss with other timber bridge systems. The wooden pegged connections and chord
structure are identified as unique components of the Town lattice truss and are the
subjects of further analysis. Equations are developed for strength prediction and
stiffness estimation for the wooden pegged connections. The chord structure is
analyzed for strength and stiffness, which are determined to be combinations of
underlying component properties based on the chord termination pattern that is used. A
comprehensive set of possible chord termination patterns is developed and the best
patterns are proposed for use in design. Finally, truss moment capacity is determined
as a function of chord strength and stiffness properties and a simple methodology is
proposed for the design of new Town lattice truss bridges.

Thesis Supervisor: Jerome Joseph Connor, Jr.
Title: Professor of Civil and Environmental Engineering

Acknowledgements

This thesis has been a major part of my life for a number of years, and I would like to
gratefully thank the many people who helped me along the way, including

- my supervisor, Dr. Jerome Connor, who has provided unwavering support and
consistent enthusiasm for my research despite its nontraditional nature,

- my thesis committee, Dr. John Ochsendorf, Dr. Herbert Einstein, and Amy Smith, who
inspired my work and provided invaluable feedback,

- Dr. Eduardo Kausel, Dr. Jack Germaine, Dr. Harry Hemond, and Dr. Dennis
McLaughlin, who have taught me so much in the process of teaching others,

- my many officemates and friends, Paul, Chu, Misha, Hervé, Simon, and Pierre, who
have acted as wonderful sounding boards and motivators,

- my parents, whose patience may have been tested but never broke,

- and, finally, my lovely wife, Dana, without whose love, support, and patience I could
never have finished.

Table of Contents

Title Page..................................................................................................................1

Abstract....................................................................................................................3

Acknowledgements....................................................................................................5

Table of Contents 7

Chapter 1 – Introduction 11
1.1 - Background..................................................................................................11
1.2 - Overview.....................................................................................................12
1.3 - References...................................................................................................13

Chapter 2 – Appropriate Bridge Technology 15
2.1 - Rural Transport in Developing Countries........................................................15
2.1.1 - What is Being Accessed?.........................................................................16
2.1.2 - The Current State of Access....................................................................17
2.1.3 - Measuring Accessibility...........................................................................20
2.1.4 - Components of Access and Strategies for Improving Accessibility..............22
2.1.5 - Special Role of Bridges...........................................................................24
2.1.6 - Summary of rural transport in developing countries..................................24
2.2 - Appropriate Technology................................................................................25
2.2.1 - History of the Appropriate Technology Movement ....................................25
2.2.2 - Defining Appropriate Technology.............................................................30
2.2.3 - A New Definition and Assessment Framework for Appropriate Technology.36
2.2.4 - Summary...............................................................................................44
2.3 - Consideration of Appropriate Technology in Rural Transport Infrastructure......44
2.3.1 - Required elements.................................................................................44
2.3.2 - Desired elements ...................................................................................47
2.4 - Appropriate Bridge Technology......................................................................49
2.4.1 - Bridge-building organizations..................................................................49
2.4.2 - Comparison of general delivery methodologies.........................................53
2.4.3 - General Discussion of Approaches...........................................................54
2.4.4 - Trail Bridges vs. Road Bridge..................................................................55
2.5 - Summary and Conclusions............................................................................56
2.6 - References...................................................................................................57

Chapter 3 – An Appropriate Bridge Technology for the Tshumbe Diocese 59
3.1 - General Comparison of Building Materials for Use in Bridges...........................59
3.1.1 - Timber ..................................................................................................60
3.1.2 - Steel......................................................................................................61
3.1.3 - Reinforced Concrete...............................................................................62
3.1.4 - Comparison of Materials.........................................................................63
3.2 - The Appropriate Choice of structural material for the Tshumbe Diocese of the
Democratic Republic of Congo...............................................................................64
3.3 - Bridge Systems ............................................................................................69
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3.3.1 - Functional Characteristics.......................................................................70
3.3.2 - Loads....................................................................................................71
3.3.3 - Material Properties.................................................................................78
3.3.4 - Timber bridge systems...........................................................................79
3.4 - Timber Bridge System for the Tshumbe Diocese.............................................92
3.5 - References...................................................................................................93

Chapter 4 – The Town Lattice Truss: Overview 95
4.1 - Background and History of the Town Lattice Truss.........................................95
4.1.1 - A History of Timber Bridges in the United States......................................95
4.1.2 - Background ...........................................................................................99
4.2 - The Town Lattice Truss Structure................................................................101
4.2.1 - Overview.............................................................................................101
4.2.2 - Bridge Components..............................................................................102
4.2.3 - Summary of properties in existing Town lattice truss bridges..................123
4.3 - Appropriate Characteristics of the Town Lattice Truss...................................124
4.3.1 - Exclusively timber truss........................................................................125
4.3.2 - Small timbers.......................................................................................126
4.3.3 - Connections.........................................................................................126
4.3.4 - Redundancy and repetition...................................................................130
4.3.5 - Covering the bridge..............................................................................131
4.3.6 - Summary of appropriate characteristics.................................................132
4.4 - The functionality of the Town lattice truss....................................................133
4.5 - Summary...................................................................................................134
4.6 - References.................................................................................................135

Chapter 5 – The Town Lattice Truss: Connections 137
5.1 - Connection Strength...................................................................................138
5.1.1 - Literature.............................................................................................138
5.1.2 - Verification of equations from literature.................................................149
5.1.3 - Town Lattice Truss Connections............................................................151
5.1.4 - Strength results ...................................................................................154
5.2 - Connection Stiffness...................................................................................155
5.2.1 - Literature.............................................................................................156
5.2.2 - Beam on Elastic Foundation..................................................................159
5.2.3 - Analytical Model...................................................................................159
5.2.4 - Experimental Models ............................................................................161
5.2.5 - Results................................................................................................165
5.2.6 - Stiffness results....................................................................................170
5.3 - Summary...................................................................................................170
5.4 - References.................................................................................................171

Chapter 6 – The Town Lattice Truss: Chords 173
6.1 - Development of patterns.............................................................................173
6.1.1 - Description of pattern lengths...............................................................174
6.1.2 - Basic rules of valid patterns..................................................................175
6.1.3 - Description of pattern making procedure...............................................178
6.1.4 - Pattern results .....................................................................................180
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6.2 - Strength of patterns...................................................................................181
6.2.1 - Component strength.............................................................................181
6.2.2 - Determination of failure planes.............................................................182
6.2.3 - Comparison between patterns...............................................................185
6.2.4 - Results and conclusions........................................................................187
6.3 - Stiffness of patterns ...................................................................................189
6.3.1 - Component stiffness.............................................................................189
6.3.2 - Procedure for determination of stiffness ................................................189
6.3.3 - Comparison between results.................................................................194
6.3.4 - Results and Conclusions .......................................................................196
6.4 - Summary...................................................................................................196
6.5 - References.................................................................................................197

Chapter 7 – The Town Lattice Truss: Design 199
7.1 - Relationship between maximum chord capacity and maximum moment capacity
.........................................................................................................................199
7.2 - Example capacity analysis...........................................................................202
7.2.1 - Truss properties...................................................................................202
7.2.2 - Component properties..........................................................................203
7.2.3 - Chord properties..................................................................................205
7.2.4 - Moment capacity..................................................................................207
7.2.5 - Determination of dead load...................................................................207
7.2.6 - Live load capacity and allowable span....................................................210
7.3 - Design methodology...................................................................................212
Single peg......................................................................................................213
Connection strength........................................................................................213
7.4 - Example designs with comparison and assessment.......................................217
7.5 - Summary...................................................................................................222

Chapter 8 – Summary and Future Work 223
8.1 - Summary...................................................................................................223
8.2 - Future work...............................................................................................225

Appendix A - Structural Testing of Wood Samples from Tshumbe Diocese of the
Democratic Republic of Congo 227

Appendix B - Calculations for Timber Bridges 235
B.1 - Timber Beam Bridge...................................................................................235
B.2 - Allotey Built-up Timber Girder.....................................................................238
B.3 - Kenyan Low-Cost Modular Timber Bridge.....................................................243
B.4 - References.................................................................................................255

Appendix C - Connection Strength Results 257
C.1 - Material Properties.....................................................................................257
C.2 - Modified Yield Model Results.......................................................................259

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Appendix D - Yield Mode Comparison Factor Calculations 271
D.1 - Mode Yield Equations.................................................................................271
D.2 - Comparison Factors....................................................................................271
D.3 - Yield Mode Equalities .................................................................................272

Appendix E - Chord Termination Patterns 275
E.1 - Pattern Diagrams.......................................................................................275
E.2 - Pattern Results...........................................................................................283

Appendix F - Draft Design Guide 295

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