Part 3 Typical Superstructures, Substructures and Components

8/11/2019 Part 3 Typical Superstructures, Substructures and Components

1/105

Austroads

Part 4: Design Procurement andConcept Design

GUIDE TO BRIDGE TECHNOLOGY


2/105

Guide to Bridge TechnologyPart 4: Design Procurement and Concept Design


3/105

Guide to Br idge Technology Part 4: Design Procurement and Concept Design

Summary

Part 4 of the Austroads Guide to Bridge Technology provides guidance about effectively specifyingand scoping contractual requirements for bridge design parameters, particularly fordesign/construct and similar contracts for bridge procurement. This guidance is important wherethe design standards require resolution by the authority/owner of many matters about designassumptions or dimensional/detailing information prior to the commencement of design. An actionchecklist identifying all the issues in AS5100 2004 is provided.

It is essential that the design process be error free and result in durable, robust, reliable andaesthetically pleasing bridges, provided at a reasonable cost. It is also essential that theauthority/owner, and the users, costs associated with maintaining the bridge over its full life beminimised. No compromise of this intention should be tolerated.

To ensure the required bridge performance, a significant effort must be put into comprehensively

scoping the design and detailing requirements in the contract documents for a bridge. As manyissues as possible within the authority/owners control need to be resolved before the contract issigned.

For those issues that must be resolved and negotiated during the contract, a robust, formalprocess needs to be specified that ensures the authority/owner does not inherit costly and majormaintenance difficulties during the full 100 year life of the bridge.

The effective management of the design process has a significant bearing on the successfulimplementation and continuing performance of a bridge project over the bridges 100 year life.

Keywords

bridge, bridge design, design procurement, design brief, bridge ownership, owners responsibility,design/construct, contractual claims, waterway, floodway design, scour, durability, geotechnicalinvestigation, foundations, construction methods, maintainability

First Published June 2009

Austroads Inc. 2009

This work is copyright. Apart from any use as permitted under the Copyright Act 1968, no part maybe reproduced by any process without the prior written permission of Austroads.

ISBN 978-1-921551-47-5

Austroads Project No. TP1564

Austroads Publication No: AGBT04/09

Project Manager

Geoff Boully, VicRoads

Prepared by

Don CarterRay Wedgwood


4/105

Published by Austroads IncorporatedLevel 9, Robell House287 Elizabeth StreetSydney NSW 2000 AustraliaPhone: +61 2 9264 7088Fax: +61 2 9264 1657Email: [email protected]

This Guide is produced by Austroads as a general guide. Its application is discretionary. Roadauthorities may vary their practice according to local circumstances and policies.

Austroads believes this publication to be correct at the time of printing and does not acceptresponsibility for any consequences arising from the use of information herein. Readers shouldrely on their own skill and judgement to apply information to particular issues.
mailto:[email protected]:[email protected]:[email protected]


5/105

Guide to Bridge TechnologyPart 4: Design Procurement and Concept Design

Sydney 2009


6/105

Austroads profi le

Austroads purpose is to contribute to improved Australian and New Zealand transport outcomesby:

providing expert advice to SCOT and ATC on road and road transport issues

facilitating collaboration between road agencies

promoting harmonisation, consistency and uniformity in road and related operations

undertaking strategic research on behalf of road agencies and communicating outcomes

promoting improved and consistent practice by road agencies.

Austroads membership

Austroads membership comprises the six state and two territory road transport and trafficauthorities, the Commonwealth Department of Infrastructure, Transport, Regional Developmentand Local Government in Australia, the Australian Local Government Association, and NZ

Transport Agency. Austroads is governed by a council consisting of the chief executive officer (oran alternative senior executive officer) of each of its eleven member organisations:

Roads and Traffic Authority New South Wales

Roads Corporation Victoria

Department of Transport and Main Roads Queensland

Main Roads Western Australia

Department for Transport, Energy and Infrastructure South Australia

Department of Infrastructure, Energy and Resources Tasmania

Department of Planning and Infrastructure Northern Territory

Department of Territory and Municipal Services Australian Capital Territory

Department of Infrastructure, Transport, Regional Development and Local Government

Australian Local Government Association

New Zealand Transport Agency.

The success of Austroads is derived from the collaboration of member organisations and others inthe road industry. It aims to be the Australasian leader in providing high quality information, adviceand fostering research in the road sector.


7/105

GUIDE TO BRIDGE TECHNOLOGY PART 4 : DESIGN PROCUREMENT AND CONCEPT DESIGN

A u s t r o a d s 2 0 0 9

i

CONTENTS

1 INTRODUCTION AND GUIDE STRUCTURE................................................................ 1

1.1 Purpose .......................................................................................................................... 11.2 Guide Structure............................................................................................................... 1

2 BRIDGE DESIGN PROCESS PROCUREMENT MODELS........................................... 3

2.1 General........................................................................................................................... 32.2 Separate Design Followed by Construction.................................................................... 32.3 Integrated Design/Construct ........................................................................................... 32.4 Alliance Arrangements.................................................................................................... 42.5 Further Information about Project Procurement ............................................................. 4

3 SPECIFYING REQUIREMENTS FOR DESIGN............................................................. 5

3.1 Bridge Design Code Issues ............................................................................................ 53.2 Specifying for Local Conditions ...................................................................................... 5

3.3 Geometric Details, Including Clearances........................................................................ 53.4 Gathering and Integrating Data for a Bridge Design....................................................... 63.5 Design Statement ........................................................................................................... 63.6 Requirements of AS5100, Australian Standard for Bridge Design................................. 63.7 Application of Authority Requirements for Road Users, OH&S and Design

Parameters ..................................................................................................................... 73.8 Design Surveillance and Achievement of Design Intent ................................................. 8

4 CONSIDERATIONS IN THE DESIGN PROCESS......................................................... 9

4.1 Design and Delivery Management.................................................................................. 94.1.1 General ............................................................................................................. 94.1.2 Delivery of Design/Construct and Alliance Bridge Projects .............................. 9

4.2 Checking and Review Concepts..................................................................................... 94.2.1 General ............................................................................................................. 94.2.2 Defining Process Terminology........................................................................ 104.2.3 Road Safety Audit........................................................................................... 10

4.3 Standardised Components ........................................................................................... 114.3.1 General ........................................................................................................... 114.3.2 Proprietary Items ............................................................................................ 11

4.4 Aesthetics/Architectural Requirements......................................................................... 114.4.1 General ........................................................................................................... 114.4.2 References for Aesthetics............................................................................... 11

4.5 Presentation of Drawings and Reports ......................................................................... 124.5.1 General ........................................................................................................... 12

4.5.2 Interpretation of Site Data............................................................................... 124.6 Constructability and Maintenance Issues ..................................................................... 12

4.6.1 General ........................................................................................................... 12

5 GENERAL CONSIDERATIONS................................................................................... 13

5.1 Design Process............................................................................................................. 135.2 Construction.................................................................................................................. 145.3 Aesthetics ..................................................................................................................... 145.4 Cost Effective Design ................................................................................................... 155.5 Live Loads .................................................................................................................... 15

5.5.1 Design Live Loads .......................................................................................... 155.5.2 Dynamics........................................................................................................ 15


8/105


A u s t r o a d s 2 0 0 9

ii

5.5.3 Fatigue Data ................................................................................................... 155.5.4 Pedestrian Bridges ......................................................................................... 15

5.6 Location ........................................................................................................................ 165.7 Traffic and Traffic Considerations................................................................................. 16

5.7.1 Road Geometry .............................................................................................. 175.8 Public Utilities ............................................................................................................... 17

5.9 Articulation.................................................................................................................... 185.9.1 Definition......................................................................................................... 185.9.2 Considerations................................................................................................ 19

5.10 Skew............................................................................................................................. 195.11 Information from Existing Bridges................................................................................. 205.12 Temporary Bridging ...................................................................................................... 205.13 Provision of Disabled Access ....................................................................................... 205.14 Terrorist Activity............................................................................................................ 205.15 Construction Safety and Structural Form...................................................................... 205.16 Serviceability Requirements ......................................................................................... 21

5.16.1 Service Life of Bridge and Components ......................................................... 215.16.2 Flood Free or Submersible ............................................................................. 215.16.3 Alignment and Design Speed ......................................................................... 215.16.4 Number of Lanes, Wide Bridges and Thermal Movements............................ 22

5.17 Computer Analysis........................................................................................................ 235.18 Review of Design Concept ........................................................................................... 235.19 Review of Drawings...................................................................................................... 23

6 SPECIFIC DESIGN REQUIREMENTS ........................................................................ 25

6.1 Mining Subsidence ....................................................................................................... 256.2 Earthquake ................................................................................................................... 266.3 Dynamics Stiffness, Deflection, Span/Depth ............................................................. 26

7 ENVIRONMENT........................................................................................................... 28

7.1 Waterway...................................................................................................................... 287.1.1 Basic Considerations ...................................................................................... 287.1.2 Floodway Design ............................................................................................ 307.1.3 Submergence ................................................................................................. 307.1.4 Piers................................................................................................................ 307.1.5 Scour .............................................................................................................. 307.1.6 Minimum Energy Drainage Structures............................................................ 32

7.2 Environmental Constraints............................................................................................ 337.2.1 Noise............................................................................................................... 337.2.2 Pollutants, Flora and Fauna............................................................................ 337.2.3 Disturbance of Sediments............................................................................... 33

7.2.4 Fisheries ......................................................................................................... 347.3 Drainage ....................................................................................................................... 347.4 Site Constraints and Access......................................................................................... 347.5 Durability....................................................................................................................... 34

7.5.1 Marine and Salt Rich Environments ............................................................... 347.5.2 Piles ................................................................................................................ 357.5.3 Concrete and Concreting................................................................................ 357.5.4 Concrete and Concreting Issues .................................................................... 36

7.6 Protection...................................................................................................................... 36


9/105


A u s t r o a d s 2 0 0 9

iii

8 GEOTECHNICAL ......................................................................................................... 37

8.1 Foundation Type and Geology ..................................................................................... 378.2 Investigations................................................................................................................ 37

8.2.1 Preliminary Geotechnical Investigations......................................................... 378.2.2 Geotechnical Strategy and Geology ............................................................... 37

8.3 Investigation Methods................................................................................................... 398.3.1 Site Investigation Methods.............................................................................. 39

8.4 Specific Issues.............................................................................................................. 418.4.1 Soft Soils......................................................................................................... 418.4.2 Black Soils ...................................................................................................... 418.4.3 Soil and Ground Water Aggressivity (RTA Guideline Acid Sulphate

Soils)............................................................................................................... 418.4.4 Pile Relaxation in Fine Sands......................................................................... 428.4.5 Height of Abutments ....................................................................................... 428.4.6 Skew Abutments............................................................................................. 428.4.7 Sensitivity of Design to Changes in Site Conditions ....................................... 42

8.5 Geotechnical Investigations.......................................................................................... 428.5.1 Geotechnical Investigations Design and Construct Contracts..................... 428.5.2 Presentation of Geotechnical Information....................................................... 43

9 FOUNDATION SELECTION ........................................................................................ 44

9.1 Footings, Abutments and Piers..................................................................................... 449.1.1 Spread Footings ............................................................................................. 44

9.2 Piles.............................................................................................................................. 449.2.1 Reinforced Concrete....................................................................................... 449.2.2 Prestressed Concrete..................................................................................... 449.2.3 Steel H Piles ................................................................................................... 459.2.4 Composite Steel and Prestressed Concrete Piles.......................................... 45

9.2.5 Steel H Pile Corrosion .................................................................................... 469.2.6 Cast-in-Place Piles ......................................................................................... 469.2.7 Open-ended Tubular Piles in Dense Sands ................................................... 479.2.8 Proprietary Piling Systems.............................................................................. 47

9.3 Pile Driving.................................................................................................................... 489.3.1 Historical ......................................................................................................... 489.3.2 Dynamic Pile Testing...................................................................................... 489.3.3 Pile Driving Issues .......................................................................................... 49

9.4 Scour Susceptibility ...................................................................................................... 509.5 Damage to Adjacent Properties.................................................................................... 51

10 CONSTRUCTION CONSIDERATIONS ....................................................................... 52

10.1 Construction Form ........................................................................................................ 5210.1.1 Cast-in-situ Concrete...................................................................................... 5210.1.2 Precast Prestressed Concrete Members........................................................ 5410.1.3 Steel Members................................................................................................ 5510.1.4 Precast Prestressed Segmental Construction................................................ 57

10.2 Construction Method..................................................................................................... 5810.2.1 Incrementally Launched.................................................................................. 5810.2.2 Push-out Construction .................................................................................... 6010.2.3 Balanced Cantilever........................................................................................ 6010.2.4 Cable Stayed .................................................................................................. 6310.2.5 Suspension..................................................................................................... 6510.2.6 Stage Construction ......................................................................................... 65

10.2.7 Superstructure Types and Construction Method ............................................ 65


10/105


A u s t r o a d s 2 0 0 9

iv

10.3 Concrete Construction in Marine Environments ........................................................... 6610.3.1 Steel Pipe Culverts ......................................................................................... 66

11 DESIGN FOR CONSTRUCTION ................................................................................. 68

11.1 Special Cases............................................................................................................... 6811.2 Specific Site Constraints............................................................................................... 68

11.3 Location ........................................................................................................................ 6811.4 Physical Location.......................................................................................................... 6911.5 Choice of Bridge Type .................................................................................................. 69

12 DESIGN FOR MAINTAINABILITY............................................................................... 70

12.1 Maintenance Schedule ................................................................................................. 7012.2 Access for Inspection (stairs, ladders, hatches, anchorage points).............................. 7012.3 Access for Maintenance Works .................................................................................... 7012.4 Bearing Replacement (jacking points method, clearances for removal and loads)...... 7012.5 Fitment Materials .......................................................................................................... 7012.6 Provision for Prestressing Tendon Replacement ......................................................... 7012.7 Provision of Stay Cable Maintenance........................................................................... 71

REFERENCES ...................................................................................................................... 72

APPENDIX A ACTION CHECK LIST FOR RESOLUTION OF DESIGNISSUES IN AS5100 2004 .............................................................. 74

APPENDIX B ACTION CHECKLIST FOR ENSURING COVERAGE OFRELEVANT DETAILS FOR THE PREPARATION OF ABRIDGE DESIGN CONCEPT........................................................... 79

APPENDIX C RESOURCES FOR BRIDGE AESTHETICS.................................... 84

APPENDIX D CODE ERRATA................................................................................ 86

APPENDIX E FUTURE CODE REQUIREMENTS.................................................. 91


11/105


A u s t r o a d s 2 0 0 9

v

TABLES

Table 4.1: Process of review and interaction..................................................................... 9

Table 10.1: Construction methods of superstructure types ............................................... 66

FIGURES

Figure 5.1: Simply supported spans ................................................................................. 18

Figure 5.2: Continuous spans........................................................................................... 18

Figure 5.3: Simply supported for dead load, continuous for live load ............................... 18

Figure 5.4: Superstructure and pier integral ..................................................................... 18

Figure 5.5: Bridge built normal to the skew....................................................................... 22

Figure 6.1: Design consideration for mine subsidence..................................................... 25

Figure 7.1: Scoured abutment due to lack of waterway.................................................... 28Figure 7.2: 12 metre high abutment abutment expansion joint jammed due to

horizontal abutment displacement .................................................................. 29

Figure 7.3: Scour at a pile caused by horseshoe and wake vortices................................ 31

Figure 7.4: Cut back scour................................................................................................ 32

Figure 7.5: Minimum energy drainage structure concept.................................................. 33

Figure 8.1: Weathering profile of granite........................................................................... 38

Figure 9.1: Pile driving with hydraulic hammer ................................................................. 44

Figure 9.2: Prestressed concrete pile with Steel H pile section ...................................... 45

Figure 9.3: Prestressed concrete piles with steel stubs.................................................... 46

Figure 9.4: Cast-in-place pile ............................................................................................ 47Figure 9.5: Pile driving analyser equipment...................................................................... 49

Figure 9.6: Pile instrumented with strain reducer.............................................................. 49

Figure 9.7: Pile damage due to overdriving ...................................................................... 50

Figure 10.1: Reinforced concrete slab ................................................................................ 52

Figure 10.2: T-beam ........................................................................................................... 53

Figure 10.3: Reinforced concrete T-beam .......................................................................... 53

Figure 10.4: Prestressed concrete box girder..................................................................... 53

Figure 10.5: Prestressed concrete voided slab................................................................... 54

Figure 10.6: Prestressed precast members........................................................................ 54Figure 10.7: I-girders........................................................................................................... 55

Figure 10.8: Trough girders with cast in situ deck .............................................................. 55

Figure 10.9: Rolled steel universal beam............................................................................ 56

Figure 10.10: Welded plate girder......................................................................................... 56

Figure 10.11: Steel box girder............................................................................................... 56

Figure 10.12: Steel box girders............................................................................................. 57

Figure 10.13: Span-by-span construction segments supported by truss........................... 58

Figure 10.14: Incrementally launching construction process ................................................ 59


12/105


A u s t r o a d s 2 0 0 9

vi

Figure 10.15: Incrementally launched bridge........................................................................ 60

Figure 10.16: Mooney Mooney balanced cantilever bridge nearing completion................... 61

Figure 10.17: Construction steps of balanced cantilever bridge ........................................... 62

Figure 10.18: Cable stayed bridge construction using balanced cantilever method............. 64

Figure 10.19: Anzac Bridge .................................................................................................. 65


13/105


A u s t r o a d s 2 0 0 9

1

1 INTRODUCTION AND GUIDE STRUCTURE

1.1 Purpose

The purpose of the Austroads Guide to Bridge Technology, Part 4: Design Procurement andConcept Design, is two-fold. It provides guidance about effectively scoping and specifying

contractual requirements for bridge design parameters to enable efficient procurement of design.This part also looks at the design process and how it necessitates a series of steps to ensure thatthe final design has addressed the design requirements and various site constraints.

Guidance is particularly important where the design standards require the authority/owner toresolve matters about design assumptions or dimensional/detailing information prior to thecommencement of design. It also discusses philosophical issues about how the bridge designprocurement process should be managed and where responsibilities should lie for various parts ofthe design input and process. For more specific information about project procurement, referenceis made to the companion Austroads Guide to Project Delivery.

The bridge design process necessitates a number of steps to ensure the final design addresses alldesign requirements and site constraints. This outcome is best achieved by preparing designconcepts for a number of options for the client. Depending on the size of the project the conceptdesigns may require preliminary calculations and should set out how each concept addresses thedesign issues. Included in this part are issues of the environment, geotechnical and foundationissues, designing for construction and maintainability considerations and other generalconstruction issues.

1.2 Guide Structure

The Austroads Guide to Bridge Technologyis published in seven parts and addresses a range ofbridge technology issues, each of which is summarised below.

Part 1: Introduction and Bridge Performance

This part covers the scope of the Guide to Bridge Technology, includes factors affectingbridge performance, the relationship to the bridge design standards, and an understanding ofthe evolution of bridges and bridge loadings. Technical and non-technical design influencesare also discussed along with the evolution of bridge construction methods and equipment.Specifications and quality assurance in bridge construction are also included in this part.

Part 2: Materials

The full range of bridge building materials is discussed in Part 2 including concrete, steel,timber and non-metallic components. It also discusses the material characteristics includingthe individual stress mechanisms.

Part 3: Typical Bridge Superstructures, Substructures and Components

Included in this part are superstructure and substructure components - namely timber, steel,wrought iron, reinforced and pre-stressed concrete. Typical bridge types such assuspension, cable stayed and arched types are discussed. Included in this part is a sectionon bridge foundations.


14/105


A u s t r o a d s 2 0 0 9

2

Part 4: Design Procurement and Concept Design

Coverage includes bridge design process procurement models, specification requirements,design and delivery management processes, design checking and review concepts, the useof standardised components, aesthetics/architectural requirements, standard presentation ofdrawings and reports, designing for constructability and maintenance. The service life of the

structure and components, mining and subsidence, flood plains, bridge loadings, andgeotechnical and environmental considerations are also discussed.

Part 5: Structural Drafting

Covers the detailed drawing aspects required to clearly convey to the consultant/constructioncontractor the specifics of the project. It discusses the various standards including detailsrequired for cost estimating and material quantities. Coverage also includes reinforcementidentification details.

Part 6: Bridge Construction

Provides guidance to the bridge owner's representative on site. It focuses on bridge

technology, high-risk construction processes e.g. piling, pre-stressing, and the relevanttechnical surveillance requirements during the construction phase. Bridge geometry and themanagement of existing road traffic and temporary works are also discussed.

Part 7: Maintenance and Management of Existing Bridges

Maintenance issues for timber, reinforced and pre-stressed concrete, steel, wrought and castiron bridges are discussed in this part. Other bridge components including bridge bearingsand deck joints are also referred to. It also covers the monitoring, inspection andmanagement of bridge conditions.


15/105


A u s t r o a d s 2 0 0 9

3

2 BRIDGE DESIGN PROCESS PROCUREMENT MODELS

2.1 General

The processes for the procurement of bridge design by road authorities/owners are determined bytheir in-house design capabilities, the capabilities of the available external design providers and the

availability of both. Emphasis is placed on the importance of the design process to the successfulcompletion of the bridge project. The effective management of risks associated with ensuringtraffic-friendly, durable, robust and reliable bridge performance over the required 100 year life isenhanced by being an informed purchaser of design.

It is essential that the design input information be closely researched and clearly specified toensure minimum change during the design and that the purchasers intent is delivered. Thissection does not seek to endorse one procurement method over another, but simply to give anoutline of the mechanics of each to the reader. Choice of procurement method would depend oncircumstances and the road authoritys policies and objectives.

2.2 Separate Design Followed by ConstructionGenerally, up to the 1980s, the method of bridge design procurement commonly used was toacquire the design separately, in advance of the bridge construction, with the design plans beingpart of the tender (or briefing) documents for the construction of the bridge. Such designs areeither prepared in-house or acquired from an external provider by a procurement arrangement.

An advantage of this process is the time it allows for the design to gestate and be subject to wide-ranging review, both formal and informal, from other contributors to the road/traffic environment inwhich the bridge is to be used. This process usually allows for the development of a conceptdesign proposal, with detailed design not commencing until the concept is signed off by ahierarchy of authority/owner management. By this means, many projects are enhanced by theincorporation of both technical and geometrical refinements, at minimal cost penalty to theauthority/owner. Further advantages of this process are that the design provision is managed bybridge design specialists, with access to a range of collegiate bridge design and constructionexperience to inform the process and the designer owes allegiance to the authority/owner.

2.3 Integrated Design/Construct

Bridge designs are now more often procured as part of the design/construct model (ordesign/construct/maintain, or design/construct/maintain/operate models). In such cases, thedesign procurement phase is managed as part of the overall project procurement, often withminimal input from bridge design specialists and generally under severe time and dollarconstraints, which can disadvantage the project by limiting the input of other road/traffic specialists.Another disadvantage is the relatively short time specified for maintenance, as defects do notbecome obvious for a number of years.

For this procurement arrangement, the owner is obliged to specify at the outset the requirementsfor the design process.

The advantage of this process is that responsibility for all co-ordination of the separate activities isassigned to the contractor. In addition, the suitability of the construction/erection processes maybe tailored to suit each contractors experience and equipment.


16/105


A u s t r o a d s 2 0 0 9

4

2.4 Alliance Arrangements

A recent development for project procurement is the alliance arrangement where the contractor,designer and owner/authority form a management team to manage the project. This processhappens under the separate oversight review of the owner, but involves the owner in ensuring thatfinancial aspects of delays are recognised and minimised, by involvement of the owner in a profit

sharing arrangement.

The important aspect of the alliance process is the assessment by the owner of the competencyand potential performance of the alliance team to produce the desired outcomes and the specificscoping of the works.

Once again, as for the design/construct procedure, it is necessary to specify design requirementsbefore the letting of the tender.

The advantage of the alliance arrangement is that all players (contractor, designer and owner)have an interest in the financial and technical outcome. Another advantage is that the allianceteam takes on an ownership of the project, which can develop an exceptional synergy.

2.5 Further Information about Project Procurement

A more detailed discussion about methods of project procurement generally, including advantagesand disadvantages, is covered in the Guide to Project Delivery Part 2: Project Delivery Planningand Control,Austroads (2007).


17/105


A u s t r o a d s 2 0 0 9

5

3 SPECIFYING REQUIREMENTS FOR DESIGN

3.1 Bridge Design Code Issues

For bridge design to be procured by the same contract as the construction(maintenance/operation) of the bridge, the means to ensure the advantageous outcomes from the

separate design procurement process need to be incorporated into the design/construct tenderprocess. For an effective process, there are many important design and design detail decisions tobe made by the authority/owners representatives prior to the signing of the contract. AS5100 listsall the issues where design input is required or where the approval of the authority/owner isrequired in Appendix A of Part 1 (Scope and General Principles) of theAustralian Bridge DesignCode(Standards Australia). These issues are repeated inAppendix Ato this document.

While AS5100 applies to all Australian bridge design, the Transit New ZealandBridge Manual(Transit NZ 2003) is applicable to all New Zealand bridges. In the case of design/constructcontracts in New Zealand, an interactive tendering and consultation process is used based on theproforma tender documents set out in TransitsState Highway Construction Contract ProformaManual(Transit NZ 2001). The tender documents include a section entitled principalsrequirements, which sets out Transits requirements for the contractors design, construction,completion and correction of defects of the contract works. It describes the relevant standards,design criteria, technical and other requirements and provides information that applies to thecontract, and also includes a specimen design that demonstrates that the principals requirementscan be met. During the tender period, tenderers develop a preliminary conceptual design. Theseare discussed in formalised individual consultation meetings between each tenderer and Transit,with the aim of resolving issues relating to the tenderers preliminary concept design, tenderpreparation and submission. The processes will also address any identified anomalies,ambiguities, errors or omissions in the tender documents, and may result in amendment of theprincipal requirements. A formal submission of the preliminary concept design is then made toTransit. Transit will then issue to tenderers a schedule of supplementary requirements for their

conceptual design proposal, to be taken into account in their tender submission. Final tendersubmissions include drawings of the developed conceptual design together with a correspondingdesign statement.

3.2 Specifying for Local Conditions

If the bridge site is in a remote area where quality of work and supervision is a concern, precastingor prefabrication should be included as a requirement.

3.3 Geometric Details, including Clearances

As a bridge is part of a road network and must operate effectively to carry traffic over a space(waterway, transport corridor), the geometric layout and details of the bridge must be appropriateto its use. Changes to bridge drawings to amend geometric details can extend over many of thedrawings and present the possibility of errors in the drawings when changes are made.

It is important that crossing clearances and road/traffic geometry for a bridge is confirmed byrelevant, authorised personnel from the road authority/owner and, in the case of a bridge over arailway, by relevant authorised personnel from the railway authority. Navigation clearances willrequire the confirmation of the relevant waterway authority. Flood and debris clearances willrequire the confirmation of the relevant local authority.


18/105


A u s t r o a d s 2 0 0 9

6

3.4 Gathering and Integrating Data for a Bridge Design

A formalised process is the most effective way to ensure that all relevant issues are considered,integrated and resolved. Most state road authorities have adopted such a process. The followingchecklists to inform and assist this process need to be assembled:

Checklist 1 A Bridge Site Information Summary that contains the basic data needed for the startof design. It should be completed prior to the commencement of design, asdescribed inAppendix Bto this document.

Checklist 2 Action checklist for comments and/or concurrences to design concept proposal.

Checklist 3 Action check list for comments and/or concurrences and approval to various stagesof design and drawing preparation, including final design and drawings.

3.5 Design Statement

Authorities should require the preparation of a design statement which sets out all the factorsaffecting the design (including those as listed in the Bridge Design Code/Manual) and presentdesign options and a recommended solution, with a recommended construction procedure.

Design codes and standards, and any departures from these and/or alternative methods of designproposed to be adopted are to be stated. The design statement, once endorsed by the authority,sets out the agreed form and nature of the structure to be designed.

3.6 Requirements of AS5100, Australian Standard for Bridge Design

AS5100, the Australian Standard for Bridge Design, recognises that it will be used as the designstandard by the authorities/owners for all forms of bridge design procurement. An increasingnumber of bridges are being procured under the design/construct/{maintain}/{operate} process,with the completed bridge being handed back to the authority/owner to maintain after some yearsof operation. Contract administration for these methods of procurement of bridges, which rely onreferences to AS5100could becompromised by the failure of the authority/owner to determine a

number of matters in AS5100 that require resolution by the authority/owner before commencing thedesign process.

Some of the typical issues which have fallen into this category include confirming:

bridge deck geometry, including deck width (with any allowances for curve widening),superelevation and footway requirements and layouts (including provision for cyclists)

traffic barrier category and geometry and pedestrian barrier details

additional design live traffic loads (including provision for road construction vehicles) andpedestrian loads

extent and comprehensiveness of geotechnical investigations

location and type of deck expansion joint, including width, type and performance parameters.

While AS5100 has not been adopted by Transit New Zealand for use in New Zealand, a similarneed exists to minimise the need for variations because of incomplete resolution of issues prior tothe signing of the contract. In the case of design and construct contracts, the practice is that theprincipals requirements set out the criteria to be met, and a specimen design illustrates how theycan be met. Tenderers are required to submit a conceptual design and corresponding designstatement with their tender submission.


19/105


A u s t r o a d s 2 0 0 9

7

Even more variations can occur when construction is allowed to proceed before these issues areresolved, thus potentially placing the owners representative under pressure to accept a lowerstandard of work.

3.7 Application of Authori ty Requirements for Road Users, OH&S and

Design ParametersThere are a number of bridge details for which the road authority/owner will have specificrequirements to ensure consistency and conformity of the bridge deck appearance for use by roadusers, such as:

traffic barriers

pedestrian barriers

transitions to approach barriers

deck, traffic lane, shoulder and footway widths and geometry

deck drainage

expansion joints

light standards

noise walls

safety screens.

There are also a number of bridge details for which the road authority/owner will have specificrequirements to ensure consistency of OH&S requirements for constructability, replaceability andaccessibility during both construction and maintenance of the bridge, such as:

access gantries, including methods of attachment to the structure

bearings

deck joints, particularly expansion joints

traffic and pedestrian rails

drainage details

access to internal cells of box girders (confined spaces)

maintenance of attached services.

There are also a number of design parameters for which the road authority/owner will have specificrequirements to ensure consistency of design outcomes, such as:

acceptance of relevant geotechnical strength reduction factors for design of retaining walls,

abutments, piers, footings and cast-in place and driven piles, as related to the level ofgeotechnical investigation, as outlined in AS5100 Standard for Bridge Design

fatigue design limits for a particular vehicle route

earthquake resistance requirements.

It is essential that the authority/owner provides its specific requirements for these details before thebridge design procurement tender is let.


20/105


A u s t r o a d s 2 0 0 9

8

3.8 Design Surveillance and Achievement of Design Intent

The design surveillance process adopted should be based on the quality management system ofthe authority/owner or as otherwise agreed by the parties. The achievement of the design intent inconstruction must be certified by the designer. For long span bridges, the control of deflectedshape is also very important.

For the handover of the bridge to the authority/owner a process of inspection and rehabilitationneeds to be negotiated and implemented.


21/105


A u s t r o a d s 2 0 0 9

9

4 CONSIDERATIONS IN THE DESIGN PROCESS

4.1 Design and Delivery Management

4.1.1 General

The action checklist inAppendix Acovers the many aspects related to a bridge design that mustbe considered, reviewed and acted on.

The design process requires continual review in order to ensure that the interaction ofrequirements for traffic-friendliness (safety), durability, robustness, reliability and aesthetics doesnot compromise any of these criteria. For significant and/or complex bridges it may be appropriatefor the owner to conduct a Value Engineering study to review risks to the project.

Value Engineering is defined as the review of bridge drawings and design calculations to identifyopportunities to optimise the structural form and element quantities to achieve economies in designand construction. Value Engineering should not, however, result in a reduction in the designstandards, but rather, an enhanced project outcome

4.1.2 Delivery of Design/Construct and Alliance Bridge Projects

In a design/construct or alliance project the requirements in the contract documents need to reflectthe interaction between the authority/owner and the contractors designers. The design for abridge is developed to satisfy not only the contractors focus on efficiency and economy, but alsothe authority/owners requirements for traffic-friendliness, durability, robustness, reliability andaesthetic values, for the 100 year life of the bridge.

Successful management of the design process has been achieved by a multi-stage process ofreview and interaction, (Table 4.1).

Table 4.1: Process of review and interaction

Stage of process Contractor Authority/Owner

Preliminary investigations and design brief Prepare and submit Review, comment and/or accept

Concept/preliminary design proposal, including verification for100 year durability and aesthetics

Prepare and submit Review, comment and/or accept

Final investigations and final design to 20% Prepare and submit Review, comment and/or accept

Final design to 80% Prepare and submit Review, comment and/or accept

Final design to 100% and related construction documentation Prepare and submit Review, comment and/or accept

Each of these stages needs to be identified in the contract documents, with an associated holdpoint and related time limit for review, comment and/or acceptance for each stage.

4.2 Checking and Review Concepts

4.2.1 General

The requirement for an independent design check is an important part of the quality assuranceprocess for bridge design. The risk management processes for avoiding design and drawingerrors, particularly gross errors, must be foolproof and failsafe and must be at a level to result inthe confidence of road users.


22/105


A u s t r o a d s 2 0 0 9

10

Various procedures have been implemented on different projects, such as design checking, proofengineering, design verification and peer review. These terms are not well defined and havedifferent meanings to different people in terms of the level of comprehensiveness of the designcheck and the level of confidence that any design and drawing errors have been identified.

The authority/owner needs to define precisely the level and quantum of design checking required,

as related to the risk consequences for the project, and also the competency required for bothdesigner and checker, the level of independence of the checker from the designer, and theresponsibility for payment of the checker.

For particularly significant or complex bridges, it may be appropriate to nominate a third level ofindependent checking or verification, particularly to ensure the structural modelling is consistent.

In addition, the authority/owner needs to ensure the checking outcomes are critically reviewed andthat an arbitration process is in place to resolve technical disputes between the designer and thechecker or independent verifier.

4.2.2 Defining Process Terminology

For the purpose of achieving commonality of understanding, the following definitions of activitiesrelated to the design review process are provided:

Design checking a comprehensive, separate, independent preparation of calculations forthe whole of the bridge design by a qualified bridge designer in another part of theorganisation, with subsequent comparison of results and either certified agreement betweendesigner and checker or arbitration by an experienced bridge design manager.

Proof engineering a review of the bridge design calculations and drawings by anexperienced independent bridge designer in another entity, not part of the original designorganisation. Separate calculations need to be undertaken for critical aspects of the design(abutments, piers, main superstructure members) and certified as either agreed with the

bridge designer or arbitrated by an experienced design manager and with investigation andcorrection of any other discrepancies raised.

Design verification a review of the bridge design calculations and drawings by anexperienced independent bridge designer. Investigation and correction of any discrepanciesraised.

Peer review a review of the bridge drawings by an experienced independent bridgedesigner. Investigation and correction of any discrepancies raised.

Where a design review process is applied to a significant road project with a number of similarbridges, the design checking, proof engineering, design verification and peer review processesmay be applied to a selected few representative bridge designs, depending on the risk analysis.

4.2.3 Road Safety Audit

In addition, the final bridge design and any subsequent changes should be subject to a road safetyaudit, to confirm the suitability of road safety issues associated with the bridge alignment andwidth.

For complicated urban interchange bridge geometry, with curved alignments, the safe designspeed and minimum radius of curvature should be determined by the owner as a functionalrequirement, and the final design geometry should be reviewed to ensure it conforms. Whilst itmay be tempting to reduce costs of overbridges by shortening spans, reducing skew and reducingthe radius of curvature at certain locations, these actions can also lower the safe design speed.


23/105


A u s t r o a d s 2 0 0 9

11

Road safety audits need to be certified and the requirements implemented.

4.3 Standardised Components

4.3.1 General

Most road authorities/owners have determined that for some aspects of bridge construction andmaintenance, the use of standardised components results in efficiencies for both themselves andalso for the industry.

Typical examples are the use of a standardised range of mould sizes for laminated elastomericbearings, (AS 5100.4, Appendix A) and the standardised formwork sizes for precast prestressedconcrete bridge girders, both I-girders and Super-T girders (AS 5100.5, Appendix H). Other localexamples are for precast concrete pile sections and joints and for barrier shapes and railingcomponents.

Where the authority/owner requires the adoption of such standardised components, this should benominated in the contract documents, with appropriate requirements for supply and testing.

4.3.2 Proprietary Items

The authority/owner should ensure that any proprietary products that are nominated for use by thedesigner are noted or approved equivalent to enable competition to be applied to the supply ofproprietary items.

In addition, the authority/owner should ensure it specifies the required performance of proprietaryitems to enable a judgement of equivalence.

4.4 Aesthetics/Architectural Requirements

4.4.1 General

Whilst difficult to scope and value, some authorities/owners are nominating that the tenderselection process will include consideration of aesthetic/architectural requirements. The level ofthese requirements will depend on the visibility of the project and issues such as the need forlandmark bridges, overbridges or pedestrian bridges. Issues such as span length, superstructuredepth, pier shape, pile cap visibility and retaining wall configuration are important for landmark oriconic structures. For structures of lesser visibility, the general requirement of attention tosimplicity of line and proportion is emphasised.

Bridge aesthetics last for the life of a bridge. Good aesthetics can be achieved at little or no extracost.

4.4.2 References for Aesthetics

The designer shall give careful consideration to the aesthetics of the structure. Guidance on theprinciples involved may be obtained from the following references, while additional resources arelisted inAppendix Cto this document:

Fdration Internationale du Bton (2000); Highways Agency (1998); Highways Department, HongKong (1997); Roads and Traffic Authority (2004); and Transportation Research Board (1991).


24/105


A u s t r o a d s 2 0 0 9

12

4.5 Presentation of Drawings and Reports

4.5.1 General

A particular source of error or ambiguity can be from a poor standard of presentation with bridgedrawings and reports, whether as hard or soft copies. Such errors and ambiguities cancompromise not only the bridge construction process, but also future maintenance and loadcapacity rating management of the bridge. A standard form of presentation for drawings andreports (e.g. Foundation Investigations, Hydrology Report, Fatigue Studies, etc.) similar to thatused by the authority/owner should be nominated in contract documents.

The drafting standards of the authority/owner should be specified for the production of drawings.

Guide to Bridge Technology Part 5: Structural Drafting, Austroads (2009c) provides full details onthe requirements for the presentation of structural drawings.

4.5.2 Interpretation of Site Data

While the interpretation of spatial geotechnical information is not included on the drawings for

contractual reasons, it may be that such interpretive information would be valuable for otherinterested parties. In such a case, it may be appropriate to request this information with the as-constructed drawings, with a suitable disclaimer.

4.6 Constructability and Maintenance Issues

4.6.1 General

Authorities/owners need to ensure that issues related to the constructability of the structure,replaceability of components of shorter life than the design life of the structure and OH&S issuesfor construction and maintenance are identified and resolved during the design process. Theauthority/owner will have on-going responsibility for OH&S issues over the lifespan of the bridge.

These issues usually, but not exclusively, relate to access to various components of the bridge,such as bearings, deck joints and main load-carrying members. It is essential that these issues beincluded in the Design Statement and in contract documentation.

Constructability and maintenance issues need to be signed off by corporate and local assetmanagers of the authority/owner, at the relevant stages of the design process (Table 4.1).


25/105


A u s t r o a d s 2 0 0 9

13

5 GENERAL CONSIDERATIONS

5.1 Design Process

The bridge design process necessitates a number of steps to ensure the final design addresses alldesign requirements and site constraints.

This outcome is best achieved by preparing design concepts for a number of options for the client.Depending on the size of the project the concept designs may require preliminary calculations andshould set out how each concept addresses the design issues.

In the case of small streams design options should consider either a bridge or a culvert.

Early in the project planning phase the client needs to decide the project delivery mode as this willimpact on the bridge design process. Options for the project delivery mode include:

Bridge design by in-house or external resources. Construction is by public tender usingcontract documents prepared by the designer. The project is funded by the client.

Design and Construct tenders call for the design and construction of the bridge as onepackage. Under this arrangement the construction contractor tendering usually engagesbridge design consultants to carry out the bridge design. The project is funded by the client.

BOOT Project tenders call for the financing, design, construction and operation for theproject as a tolled facility for a specified period. At the end of the specified period theownership reverts to the client. B-Build, O-Own, O- Operate, T- Transfer. The project isfunded by the private sector.

Alliance Contract Tenders call for delivery of the project, including the design andconstruction, under an arrangement where the client and the contractor contribute to theproject. The aim is for the contract to operate under a non-adversarial environment whereby

both parties have input into the project. This is opposed to the adversarial environment thatexists with conventional construction contracts.

Early Contractor Involvement (ECI) essentially a Design and Construct. However, thecontractor/consortium is engaged early and is involved in the design and planning with aview to efficient construction. An estimate is prepared which is audited externally and ifaccepted the consortium is chosen for the final design and construction phase.

In all of the above project delivery modes the concept of Project Partnering needs to be fosteredwhere the client and contractor are to work together in a fair and meaningful way with opencommunication to optimise the project outcomes.

Steps in the design process include:

concept design possible options, global design considerations

preliminary design sufficient calculations carried out to assess the structural and economicfeasibility of each concept

design proposal physical details and dimensions, design basis, loads, cost estimate

client review and feedback

approval to proceed or amend proposal

detailed design

design review this may involve review of the design at stages nominated by the client


26/105


A u s t r o a d s 2 0 0 9

14

final design and preparation of contract documentation drawings and specifications. Thespecifications may include project specific as well as standard documents.

AS 5100 Part 1 Bridge Design (2004), Appendix A Matters for Resolution Before DesignCommences are to be addressed by the designer and the relevant authority or owner of a bridge.

The following sub-sections deal with additional matters for design consideration.

5.2 Construction

Two fundamental concept design considerations are the structural form and the method ofconstruction of the bridge.

The structural form and the method of construction chosen for a particular site will be influenced bya number of factors including:

the height of the bridge above the natural surface or water ease of access

simply supported or continuous spans the need to reduce the number of deck joints and

noise generated by them, structural efficiency longitudinal profile of the site ground slope and height may influence number and location

of piers and hence span lengths

proximity and extent of water location and number of piers on ground and over water tominimise work over water

the geographical location in terms of haulage distances, proximity to concrete batching andprecast concrete plants, urban or rural location, prefabrication options

traffic access requirement in terms of provision of openings and maintaining traffic flow

environmental constraints in terms of minimising disturbance to existing conditions, risk ofpollution

site access in terms of working area, equipment access

site geology in terms of addressing geological issues such as slope stability, settlement

seismic areas in terms of simply supported or continuous spans

mining subsidence areas in terms of simply supported or continuous spans and provision foranticipated movements

location of utilities may influence position of piers and span lengths

comparative costs of options.

The design considerations for each site will provide options for the form and construction methodto be adopted.

5.3 Aesthetics

Aesthetics is an important design consideration. A number of state road authorities have producedguidelines on the aesthetics of bridges. RTA, NSW has published a document titled BridgeAesthetics(RTA 2004a).


27/105


A u s t r o a d s 2 0 0 9

15

5.4 Cost Effective Design

In preparing proposals a number of design options and their cost estimates should be consideredas part of the design process including:

cost comparison between superstructure types and methods of erection, e.g. precast versuscast in situ or segmental construction

identifying site constraints for each method of construction and the cost implications

the cost comparison between increasing the span lengths to reduce the number of piers andfoundation costs

optimisation of girder spacing versus deck slab thickness

the minimisation of the number of piers constructed over water, e.g. minor changes in spanlengths or bridge position may result in piers that are marginally over water being on land

designing members to allow repeated use of formwork, e.g. on a bridge on a vertical curve itmay be possible to make all pier columns the same height by varying the pile cap levelsallowing the use of the same formwork throughout

cost comparison of low level bridge versus high level

overall project costs, which include the cost of approaches and road realignment, may be thedetermining economic factor

minimum whole of life cost.

5.5 Live Loads

Design considerations for live loads should include the following:

5.5.1 Design Live Loads

Notwithstanding the requirements of AS 5100.2 Clause 6 it may be advantageous to thecommunity and industry to design for heavier loads where they are required for specific projectssuch as power stations and dams. Payloads on these projects may include boiler components andheavy construction equipment.

5.5.2 Dynamics

Notwithstanding the requirements of AS 5100.2 Clause 6.7 the dynamic characteristics of a bridgeand/or its components may be sensitive to interaction with the specific traffic using the bridge.Instances have occurred where the dynamic amplification as a result of the interaction of the bridgewith specific vehicle types has resulted in an increase in the dynamic load in excess of theprovisions in AS 5100.2. In addition the possibility of stress reversals occurring when theexcitation force (traffic) is removed need to be considered.

5.5.3 Fatigue Data

The projected number of load cycles for the design life needs to be obtained to enable a fatiguedesign to be carried out. Traffic volumes and make up are required to carry this out.

5.5.4 Pedestrian Bridges

AS 5100.2 Clause 12.4 includes provisions for the dynamic behaviour of pedestrian bridges. Arange is stipulated for the resonant frequency for vertical vibrations for which the serviceability limitstate must be investigated. In addition a limit is set for the dynamic deflection at the first modeflexural frequency and horizontal excitation by pedestrian loads is also considered.


28/105


A u s t r o a d s 2 0 0 9

16

Notwithstanding the provisions in the code, in instances where the dynamic characteristics areclose to the limits set, there is a possibility of producing adverse dynamic behaviour. The provisionof fitments to enable installation of damping devices if required may be an appropriate contingencyprovision. These damping devices may be in the form of hydraulic shock absorbers.

The design may need to consider the possibility of the use of light vehicles being used on the

bridge for maintenance purposes.

Disabled access to pedestrian bridges needs to be addressed. There are legislative requirementsin some jurisdictions. Design considerations will include:

maximum gradient on the bridge and ramps

provision of level landings in the approach ramps

provision of lifts where ramps are not practical because of site constraints.

5.6 Location

The location of the bridge is a key factor in the design considerations. The location will influencedecisions made on a number of key factors including:

type of bridge

foundation details, e.g. steel piles vs concrete piles

availability of materials, e.g. proximity of a concrete batching plant and precast concretefactories

haul distance

material type, e.g. steel or concrete, carbon steel or stainless steel components and fixtures

availability of construction equipment, e.g. crane capacity

durability considerations, e.g. marine environment, aggressive ground water

method of construction, e.g. to address the need to protect or diminish the impact on theenvironment. Sensitive environments may require special consideration

the need for staged construction

proximity of existing bridge or other structures.

5.7 Traffic and Traffic Considerations

Each road authority records data on the make up and volume of traffic on classified roads. Thedata provides the percentage of heavy vehicles in the traffic stream. Terms used in traffic datainclude Average Daily Traffic (ADT) and Average Annual Daily Traffic (AADT). The volume andmake up of traffic on roads set a number of bridge design parameters including the width, thenumber and width of lanes and the type of traffic barrier.

The use of weigh-in-motion systems to obtain traffic data is becoming widespread. These systemsprovide invaluable data on vehicle mass and number which is relevant for design issues such asfatigue. On existing bridges they provide information on changes in traffic patterns and theircumulative effects.

See AS5100 (2004) Part 2 Design Loads.


29/105


A u s t r o a d s 2 0 0 9

17

5.7.1 Road Geometry

Clause 9 of AS5100 (Part 1) sets out the geometric requirements for all bridges. However, thereare other traffic related issues that need to be considered including the following:

Future land use changes may have a significant impact on projected traffic growth figures.The design should provide an adequate number of lanes and overall width.

Every effort should be made to design the vertical and horizontal alignments of a bridge tosimplify the bridge geometry. A bridge on a constant curvature is preferable to havingtransition curves within its length.

For a major incrementally launched bridge a minor redesign of the road alignment to useconstant radius of curvature resulted in significant cost savings and improvedconstructability.

In another case the vertical and horizontal alignments were redesigned to shift the curvetransitions off the bridge. This avoided the need for the bridge planks to be placed onvarying crossfalls across the deck.

For incrementally launched bridges on vertical and horizontal curves a constant curvature

simplifies the segment formwork and the launching process.

It should be noted that a reversal of curvature on a bridge results in a transition from onesuperelevation to the other. This situation results in a length of the deck being level transverselywhich creates an issue in terms of drainage of the deck.

5.8 Public Utilities

The presence and location of public utilities at the site need to be determined early in theinvestigations. The type and location may have a major impact on the design. For example, thepresence of an optical fibre cable may affect the bridge location because of the major cost torelocate it. Details need to be obtained of the provision for utilities as constructed and for future

needs. Provision for utilities may include:

Ducts in barriers.

Attachment water, sewer and gas mains.

In the case of pressure mains, dynamic loads to the bridge caused by any changes in thepipe alignment must be considered.

Provision of trenches below footways for electrical and gas services. Note: There areregulations governing the proximity of gas and electrical services.

Design and installation of fitments to support existing or future utilities.

The utilities must be designed to accommodate the thermal, deflection and rotation

movements of the bridge.

The attachment of utilities must be done in such a way as to allow access for future maintenanceof the bridge, e.g. providing clearance behind mains to allow access to concrete surfaces.

Note: Gas and water mains should not be installed inside box girders.


30/105


5.9 Articulation

5.9.1 Definition

Articulation of a bridge refers to the way the components of a bridge are joined. For example, abridge where the girders are rigidly connected to the piers will behave differently to one where thegirders are supported on the piers. Similarly a bridge that has an expansion joint at each pier willbehave differently as it expands under temperature changes to a bridge where the deck iscontinuous over its full length. The bridge designer can make a bridge behave differently bychanging the way it is articulated (Figure 5.1, Figure 5.2, Figure 5.3, and Figure 5.4).

Figure 5.1: Simply supported spans

Figure 5.2: Continuous spans

Figure 5.3: Simply suppor ted for dead load, continuous for live load

Source for Figures 5.1 to 5.4: D Carter

Figure 5.4: Superstruc ture and pier integral

A u s t r o a d s 2 0 0 9

18


31/105


A u s t r o a d s 2 0 0 9

19

5.9.2 Considerations

Each of the considerations listed below may have an influence on the number and location ofexpansion joints and type of bearings in the bridge, the connection of the substructure to thesuperstructure (pinned, fixed or integral), the distribution of longitudinal and transverse loads tobearings, piers and abutments.

Considerations for the articulation of a bridge will be governed by a number of factors including:

Type of superstructure (form and whether continuous or simply supported)

An alternative to fully continuous spans is to erect the members as simply supported andthen pour the deck slab continuous over the piers. This is referred to as being continuousunder live load

Method of construction

Horizontal alignment

Length of bridge

Span lengths Ride quality

Noise generated by deck joints

Relative heights and stiffness of piers

Type of bearings

Lateral restraints

Stiffness of bearings

Seismic constraints

Mining subsidence Site geology

Skew angle.

5.10 Skew

The adverse effects of skew need to be considered in the design particularly for skew angles inexcess of 20. The effects of large skew angles include:

Non-uniform distribution of loads to bearings, particularly those at the acute corners of adeck. Instances have occurred where the deck at the acute corner has lifted off the adjacentbearing under dead load only.

This has implications for the deck in terms of flexural behaviour. In regard to bearings thissituation results in increased loads to adjacent bearings that will overload them.

In the case of elastomeric bearings the reduced loads at bearings may lead to bearingswalking out under shear displacements because of the lack of friction at the rubber/concreteinterface.

On large skew bridges there is a tendency for decks to rotate due to the fact that anylongitudinal deck movement will cause the piers to deflect normal to their transverse axis.


32/105


A u s t r o a d s 2 0 0 9

20

Circular elastomeric bearings should be used on large skew bridges to provide the same stiffnessin all directions. This will better accommodate the complex movements that occur with large skewbridges.

5.11 Information from Existing Bridge

Review of maintenance records of the existing bridge may highlight other design considerations.These may include:

foundation type and founding levels

foundation performance

stream characteristics

evidence of durability problems that may have relevance to the new bridge. For example,evidence of the presence of acid soils evidenced by deterioration of non-structural concreteor other deleterious agents in the soil or ground water evidenced by deterioration of structuralconcrete.

5.12 Temporary BridgingDepending on the site conditions and traffic requirements temporary bridging may be required toprovide access while an existing bridge is demolished or partly demolished, to allow construction ofa new bridge. A number of road authorities have supplies of proprietary temporary bridgingsystems. Bridging systems are also available from equipment hire companies.

5.13 Provision of Disabled Access

Statutory requirements exist in most jurisdictions for the provision of disabled access, particularlyto pedestrian bridges.

5.14 Terrorist Act ivi tyWith the increased awareness of potential terrorist activity design considerations may need toinclude the following:

high security access to the inside of box girders and hollow piers

considerations of the redundancy of members and in spans

installation of security cameras

design assessment of worst case scenarios.

5.15 Construct ion Safety and Structural Form

The designer must ensure that the form of the bridge and the construction sequence specified willallow it to be constructed in a safe manner. To achieve this special provisions may be requiredincluding:

purpose built construction equipment

purpose built access provisions

purpose built safety equipment

detailed documentation of construction procedures to ensure the safety issues areaddressed.


33/105


A u s t r o a d s 2 0 0 9

21

Liaison between the designer and the construction contractor may be necessary where specialprovisions are required.

Instances have occurred overseas where following a construction safety incident the courts havefound the designer liable for designing a structure that could not have been built safely.

5.16 Serviceabili ty Requirements5.16.1 Service Life of Bridge and Components

The specified design service life in AS 5100 is 100 years. However, the relevant road authorityshould give consideration to the fact that a nominal 100 year design service life will result in somebridges having a service life of less than 100 years due to statistical variation in the constructionquality.

For bridges in aggressive environments this statistical variation will have more serious implicationscompared to bridges in relatively benign environments. It may be more logical to increase thedesign service life to 150 years. This decision would result in additional considerations of thedurability aspects in terms of construction quality provisions and material types. For example, itmay force the use of stainless steel fitments to ensure the extended design service life is achieved.

5.16.2 Flood Free or Submersible

Waterway calculations are aimed at defining the minimum size opening to be able to pass a floodflow for a specific return interval, e.g. 1 in 100 years, 1 in 50 years, 1 in 25 years.

The waterway area provided needs to provide the desired level of service and ensure there are nodetrimental effects to the stream in regard to scour and bank erosion, the adjacent land and thestructural integrity of the bridge.

In addition the structural integrity of the bridge and the effect on adjacent land under the ultimate

design flood (1 in 2000 years) event needs to be assessed.

In some instance the waterway area may be fixed by other considerations such as road grading,navigational or other local requirements.

The bridge waterway will inevitably be smaller than in the natural stream under flood conditions.Therefore the water velocity through the bridge will increase. The acceptable restricted velocitythrough the bridge will depend on the local conditions in terms of the type of material in the streambed and its propensity to scour. The implications of the restricted velocity on the stability ofabutments and road embankments also need to be assessed. Scour protection of abutments andembankments may be required.

5.16.3 Alignment and Design Speed

The vertical and horizontal alignment and design speed will have an impact on the bridge design interms of:

bridge geometry in terms of gradient, vertical curvature, superelevation and horizontalcurvature. For example, for incrementally launched bridges constant vertical and horizontalcurvature is required

drainage of the deck in terms of collection and piping to stilling basins

method used to accommodate the curvature on the bridge, e.g. bridge built as a series ofchords with curved traffic barrier or constructed on the curve


34/105


width to allow for curve effects in terms of vehicle tracking

traffic barrier type

potential vehicular impacts

longitudinal and transverse forces generated by traffic

number of lanes, e.g. climbing lanes, turning movements

transition curves.

5.16.4 Number of Lanes, Wide Bridges and Thermal Movements

The number of lanes and therefore the width of a bridge are generally governed by trafficrequirements. However other considerations may dictate that additional lanes are requiredincluding:

future traffic growth

gradient and the need for climbing lanes

geometric requirements e.g. acceleration and deceleration lanes, overtaking lanes percentage of heavy vehicles

provision of cycle lanes.

In some instances the bridge may be wider than it

Part 3 Typical Superstructures, Substructures and Components

Documents

Transcript of Part 3 Typical Superstructures, Substructures and Components