Final Draft Bridge Design Guidline LLM

GUIDELINES

FOR

MALAYSIA TOLL EXPRESSWAY SYSTEM

- DESIGN STANDARDS

Chapter 6

CHAPTER 6 DETAILED CONTENTS

6 BRIDGES ... 6-1

6.1 Introduction ... 6-1 6.1.1 Overview of Bridges ... 6-1 6.1.2 Government Requirement ... 6-2 6.1.2.1 Required as in Contract Agreement ... 6-2 6.1.2.2 Approved Suppliers of Materials and Specialist Contractors ... 6-2 6.2 Bridges DesignProcedure ... 6-2 6.2.1 General Arrangement of Bridge ... 6-4 6.2.1.1 River Bridges& Marine Bridges ... 6-5 6.2.1.1.1 General... 6-6 6.2.1.1.2 River Bridges ... 6-6 6.2.1.1.3 Marine Bridges ... 6-6 6.2.1.1.4 Materials ... 6-10 6.2.1.2 Road Bridges& Urban Bridges ... 6-10 6.2.1.2.1 Design Consideration ... 6-10 6.2.1.2.2 Details of Carriageway ... 6-12 6.2.1.2.3 National Lanes ... 6-12 6.2.1.2.4 Loadings ... 6-12 6.2.1.2.5 Parapet ... 6-12 6.2.1.2.6 Bridge Supports ... 6-12 6.2.1.2.7 Expention Joints ... 6-12 6.2.1.3 Railway Overbridges (ROB) ... 6-13 6.2.1.3.1 General Requirements ... 6-14 6.2.1.3.2 Consultation Items ... 6-14 6.2.1.3.3 Other Associated Items ... 6-19 6.2.1.3.4 Sample View of Bridge ... 6-21 6.2.2 Selection of Bridge Superstucture ... 6-22 6.2.1.1 Short to Medium Spans Bridges ... 6-22 6.2.1.2 Short to Medium Spans Curved bridges ... 6-23 6.2.1.3 Medium Spans Bridges ... 6-23 6.2.1.3 Long Spans Bridges ... 6-25 6.3 Bridges Substructure ... 6-25 6.3.1 Abutments ... 6-25 6.3.2 Piers ... 6-26 6.3.3 Foundations ... 6-27 6.4 Bridge Accessories ... 6-29 6.4.1 Expansion Joints ... 6-29 6.4.1.1 General ... 6-29 6.4.1.2 Types of Expansion Joints ... 6-29 6.4.1.3 Design of Expension Joints ... 6-31 6.4.1.4 Maintenance of Expansion Joints ... 6-31 6.4.2 Bridge Bearings ... 6-31 6.4.2.1 General ... 6-31 6.4.2.2 Bearing Types ... 6-31 6.4.2.3 Detailing of Bearings ... 6-32

6.4.3 Bridge Waterproofing ... 6-34 6.4.4 Parapets ... 6-34 6.4.4.1 Pedestrian Parapets ... 6-34 6.4.4.2 Restraint Systems On Motorway Bridges ... 6-34 6.4.5 Bridge Drainage ... 6-36 6.5 Bridge Design ... 6-37 6.5.1 Bridge Loadings ... 6-37 6.5.2.1 Dead Load ... 6-38 6.5.2.2 Superimposed Dead Load ... 6-38 6.5.2.3 Live Load ... 6-38 6.5.2.4 Pedestrian Loading ... 6-39 6.5.2.5 Construction Loading ... 6-39 6.5.2.6 Wind Loading ... 6-39 6.5.2.7 Temperature Loading ... 6-39 6.5.2.8 Creep and Shrinkage ... 6-39 6.5.2.9 Differential Settlements ... 6-40 6.5.2.10 Earth Pressure on Retaining Structure ... 6-40 6.5.2.11 Seismic Load ... 6-40 6.5.2.12 Vehicle & Vessel Collision ... 6-40 6.5.2 Materials ... 6-43 6.5.2.1 Concrete ... 6-44 6.5.2.2 Reinforcement ... 6-41 6.5.2.3 Prestressing Strand ... 6-41 6.5.3 Structural Analysis ... 6-41 6.5.3.1 Load Factors and Load Combinations ... 6-41 6.5.3.2 Stability againt Overturning and Check on Bearing Decompressing ... 6-44 6.5.3.3 Cover to Reinforcement ... 6-44 6.5.3.4 Design Crack Widths ... 6-43 6.5.4 Design Life and Durability ... 6-43 6.5.5 Bridge Deck Analysis ... 6-43 6.5.5.1 Grillage Method ... 6-43 6.5.5.2 Three Dimensional Structure ... 6-44 6.5.5.3 Finite Element Method ... 6-44 6.5.6 Joint Free Construction using Precast Prestressed Concrete Beams: ... 6-45 6.5.6.1 General ... 6-45 6.5.6.2 Narrow Insitu Integral Crosshead ... 6-45 6.5.6.3 Continuous Separated Deck Slab ... 6-45 6.5.7 Integral Crosshead ... 6-46 6.5.7.1 Integral Pier Type-1 ... 6-46 6.5.7.2 Integral Pier Type-2 ... 6-48 6.5.8 Integral Abutment ... 6-49 6.5.9 Bridge Design Codes ... 6-51 6.5.9.1 British Codes ... 6-51 6.5.9.2 Eurocodes ... 6-52 6.6 Seismic Effects ... 6-53 6.6.1 Introduction ... 6-53 6.6.2 Tectonic and Seismic Activity ... 6-54 6.6.3 Seismic Loading ... 6-54

6.6.3.1 Earthquake Events ... 6-55 6.6.3.2 Seismic Response Spectra ... 6-56 6.6.3.3 Response Modification Factor-R ... 6-56 6.6.3.4 Combination of Seismic Force Effects ... 6-57 6.6.3.5 Non-Linear Time History Analysis ... 6-57 6.6.3.6 Likehood of Tsunami Event and Resulting Soil Liquefaction Phenomena ... 6-57 6.7 Bridge Aesthetics... 6-57 6.8 Bridge Maintenance... 6-60 6.8.1 Maintenance Bridges and Viaducts ... 6-60 6.8.2 Inspection and Assessment of Bridge ... 6-60 6.8.2.1 Introduction ... 6-61 6.8.2.2 Inspection Equipment ... 6-61 6.8.2.3 Inspection and Assessment ... 6-62 6.8.2.4 Reporting ... 6-63

FIGURES

Figure 6-1 Type Of Bridges Bridges……… 6-1 Figure 6-2 Typical Design Procedure for Bridges……… 6-3 Figure 6-3 General Arrangement of A Bridge ………. 6-5 Figure 6-4 JPS Requirement For Bridge Design ………. 6-7 Figure 6-5 Suggested Horizontal Clearance……… 6-8

Figure 6-6 Protection Island ……….6-9

Figure 6-7 Fender Protection ………6-9

Figure 6-8 Dolphin Protection ………. 6-9

Figure 6-9 Insufficient Sight Distance ………..6-12 Figure 6-10 Sufficient Sight Distance ... 6-12 Figure 6-11 Standard Structure Gauge and Kinematic Envelope from KTM Berhad…... 6-16 Figure 6-12 Typical envelope of vertical clearance and horizontal span……….……… 6-17 Figure 6-13 Typical ballast configuration and position of railway tracks………...6-18 Figure 6-14 Typical Section Of Parapet……….6-19 Figure 6-15 Bridge crossing the KTM Berhad‟s non- electrified railway track……….6-21 Figure 6-16 Bridge crossing the KTM Berhad‟s electrified railway track………...6-21 Figure 6-17 Typical Span Range for Different Deck Types ...6-22 Figure 6-18 Bridge Deck Types ...6-23 Figure 6-19 Precast Segmental Bridges ...6-23 Figure 6-20 Papar Bridge – Steel Trusses ...6-24 Figure 6-21 Malaysia – Singapore 2nd Crossing – Insitu Box Girder Bridge ...6-24 Figure 6-22 Penang Bridge – Cable Stay ...6-24 Figure 6-23 Clifton Suspension Bridge ...6-25 Figure 6-24 Bank Seat Abutment ...6-26 Figure 6-25 Wall Abutment ...6-26 Figure 6-26 Typical Pier Shapes ...6-27 Figure 6-27 Driven Pile ...6-28 Figure 6-28 Asphaltic Plug Joint ...6-29 Figure 6-29 Elastomer Reinforced Joint ...6-30 Figure 6-30 Mechanical Joint ...6-30 Figure 6-31 Modular Joints …… ...6-30 Figure 6-32 Elastometric Bearings ……….6-32 Figure 6-33 Mechanical Bearings ...6-32

Figure 6-34 Bearings on Steep Gradients ...6-33 Figure 6-35 Uplifts of Bearings ...6-33 Figure 6-36 Methods of Preventing Uplift ...6-33 Figure 6-37 Orientation of Bearings ...6-33 Figure 6-38 Concrete Bridge Parapets ...6-35 Figure 6-39 Guard Rails at Bridge Approach ... . 6-35 Figure 6-40 Typical End Treatment of Parapet ...6-35 Figure 6-41 Typical Ducting in Parapets ... 6-36 Figure 6-42 Typical Bridge Drainage ...6-37 Figure 6-43 Properties For Bridge Design……….6-41 Figure 6-44 Grillage Analysis... 6-44 Figure 6-45 3-D Model ... 6-44 Figure 6-46 Finite Element Method ...6-44 Figure 6-47 Typical pier ends embedded in narrow integral cross-head………..….6-45 Figure 6-48 Typical Beam Supported On Elastometric Bearings………..………6-46 Figure 6-49 Contuinity Beams Arrangement……….6-47

Figure 6-50 Continuity Precast Beam Supported On A Widened Pier Cap Withou Support..…6-48 Figure 6-51 Integral Pier Type-2 ... 6-49

Figure 6-52 Typical Integral Abutment Bridge With A Single Span………..… 6-50 Figure 6-53 Integral Frame Model ………..…... 6-51 Figure 6-54 Load Consideration For SStructure Analysis ………..…… 6-51

Figure 6-55 Eurocodes……… 6-53

Figure 6-56 Microzonation Map of Peninsular Malaysia & Sabah Sarawak ... 6-54 Figure 6-57 Damage Performance Level For Bridges ……..………. 6-55 Figure 6-58 Response Spectra ... 6-56 Figure 6-59 The Forth Bridge, Scotland ... 6-58 Figure 6-60 Golden Gate Bridge, San Francisco ... 6-58 Figure 6-61 Millau Viaduct, France ... 6-58 Figure 6-62 Slender Deck and Deeper Upstands ... 6-59 Figure 6-63 On the Selection of Span Lengths ... 6-59 Figure 6-64 Types Of Bridge Inspection……... 6-61 Figure 6-65 Recording Equipment ………. .6-62 Figure 6-66 Measurement Equipment ……….… 6-62 Figure 6-67 Photograph of Two Bridges With A Number Of Bridge Elements Labelled…... 6-63 Figure 6-68 Photograph of Two Bridges With A Number Of Bridge Elements Labelled…..… 6-63

REFERENCES

Reference 6-1 BA. 42/96, Design of Integral Bridges

Reference 6-2 Prestressed Beam Integral Bridges; Hambly, E.C. and Nicholson, B.A. Reference 6-3 Concrete Box-Girder Bridges; Jorg Schlaich & Harmut Scheef. Reference 6-4 Manual Of Bridge Engineering; Ryall, Parke and Harding

Reference 6-5 Prestressed Concrete Bridges – Design and Construction;Nigel R.Hewson

Reference 6-6 Bridge Deck Analysis; Eugene O‟Brien & Damien Keog Reference 6-7 Bridge Engineering – A Global Perspective; Troyano

Reference 6-8 Seismic Hazard And Risk Management of Malaysia; Dr. Azlan bin Adnan, Ir. P.N. Selvanayagam and Others

Reference 6-9 IEM Seminar on “Use of Eurocodes for The Design Of Bridges”; Chris Hendy, Head of Bridge Design And Technology, Atkins

Reference 6-11 Piglet – Pile Group Analysis Software; Dr. M F Randolph, Department of Civil Engineering, University of Western Australia

Reference 6-12 Expressway Maintenance System – Maintenance Manual And Guideline (Civil Works)

APPENDIX A

List of Bridge related Codes

ABBREVIATIONS

AASHTO American Association of State Highway and Transportation Officials JKR Jabatan Kerja Raya

KTMB Keretapi Tanah Melayu Berhad SIM Standards Institute of Malaysia MHA Malaysian Highway Authority

6 BRIDGES

6.1

Introduction

6.1.1 Overview of Bridges

Bridges are an integral part of the road network, which serves as the lifeline of any state. Bridges provide the continuity to the Highway when it traverses obstructions.Obstructions can be Natural: -

 River Crossing

 Soft – Ground

 Ponds

 Expanse of Water (Straits)

 Ravine / Valleys Or Man-made :-

 Railway Crossing

 Road Crossing

 Built-Environment

In other words, bridge is a structure for carrying the road traffic or other moving loads over a depression or obstruction such as channel, road or railway.

The variety of forms of bridges demonstrates the combination of art and technology.Design of bridges vary depending on the function of the bridge, the nature of the terrain where the bridge is constructed, the material used to make it and the funds available to build it. There are six main types of bridges: beam bridges, arch bridges, truss bridges, suspension bridges, cantilever bridges and cable-stayed bridges.

Figure 6-1 Type of Bridges

The major consideration for bridge type selection were sustainability, functionality, value engineering, aesthetic, work cost, maintenance friendly, construction time, and location. Selecting an appropriate superstructure type is a critical factor in the planning and design process.

In order to function as a Bridge, it must be:-

 Designable

 Buildable

 Cost-Effective

 Provides comfort and safety to users

The following sub-sections will deal with the above functions of the bridge and how it can be achieved in the planning, design, construction phases and subsequent maintenance.

6.1.2 Government Requirement

Refer to JKR, JKSB and LLM requirement.

6.1.2.1 Required as in Contract Agreement

Concessions company or main contractors need to submit design brief, detail design, design calculation and etc as in Contract Agreement.

6.1.2.2 Approved Suppliers of Materials and Specialist Contractors

Main contractors engaged on projects involving the supply of special materials or specialist works on highway structures shall either themselves be registered as approved suppliers , or shall be required to engage one of the approved suppliers or specialist contractors registered in the category to supply the special materials or to carry out the specialist works on highway structures.

6.2

Bridges Design Procedure

The design of bridges is a voluminous subject to be dealt in a General Manual. Suffice to say that each individual designer or organisations have established practices based on knowledge and experience.

Generally the procedure to be adopted for the design of bridges can be divided into two main sections.

(A) Planning and Preliminary Design Stage (B) Final Design and Contract Stage

Figure 6-2 Typical Design Procedure For Bridges

(A)

Planning and Preliminary Design Stage

In this stage, the type of bridge, the span, the skew, the widths, the clearances and the loadings to be carried have to be established and a General Arrangement (GA) drawing prepared for submission to the appropriate Authorities and Client for approval.

At this stage generally all survey and soil investigation work should be carried out so that a proper assessment of the bridge type and spans can be made. Investigations should also be undertaken into the cost of various alternatives.

The purpose of the GA drawing is to indicate the intended design of the bridge, the basic dimensions of the bridge. Guidelines for the developments of different bridge crossings are given below.

On completion of this stage, the output would be: -

 Layout of the bridge General Arrangement

 Selection of bridge Substructure and Superstructure

Site Investigation And Location EEstablish : (1) Clients requirements (2) Design criteria (3) Appropriate Authorities requirements Prepare : (1) General Arrangements (2) Preliminary Estimate Establish : (1) Bridge Type (2) Skew (3) Length (4) Span Lengths (5) Foundations Road Alignment --- Preliminary Soil Investigation Submit : Proposals to Clients and appropriate Authorities for approval Preliminary Survey

Stage 1 - Planning And Preliminary Design Complete Survey Complete Foundation Investigation Superstructure design Substructure design Preparation of B of Q and Contract Documents Prepare : Construction drawings and estimates Final submission for approval Supervision and construction

Stage 2 - Final Design And Contract Documents

(B)

Final Design Stage

After approval of the proposals the preparation of the final design and working drawings can commence.

The stage comprises the following:

 Analysis of the selected bridge type

 Design of the bridge elements and the overall bridge

 Detailing of the bridge for construction

 Supervision to ensure that the designers intent and specifications are complied with. A list of drawings required is drawn up by the engineer responsible for the design and the designer of the bridge is held responsible for the accuracy of the drawings and thoroughly checks all details contained in these drawings.

ICE review and certification.

6.2.1 General Arrangement of Bridge

In deriving the General Arrangement of the Bridge the following components of bridge need consideration:-

The bridge structure comprises of the following parts (refer to Figure 6-3):

 Substructure

This comprises piers and abutments, wing walls or returns and their foundation. 1. Piers and Abutments

These are vertical structures supporting deck/bearing provided for transmitting the load down to the bed/earth through foundation.

2. Wing walls and Returns

These are provided as extension of the abutments to retain the earth of approach bank which otherwise has a natural angle of repose.

3. Foundation

This is provided to transmit the load from the piers or abutments and wings or returns to and evenly distribute the load on to the strata. This is to be provided sufficiently deep so that it is not affected by the scour caused by the flow in the river and does not get undermined.

 Bearings

The bearings transmit the load received from the decking on to the substructure and are provided for distribution of the load evenly over the substructure material which may not have sufficient bearing strength to bear the superstructure load directly.

 Superstructure or Decking

This includes slab, girder, truss, etc. This bears the load passing over it and transmits the forces caused by the same to the substructures.

While the above mentioned are structurally operational parts, for safety hand rails or parapets, guard rails or curbs are provided over the decking in order to prevent vehicle or user from falling into the stream or for the separation of traffic streams.

Figure 6-3 General Arrangement of A Bridge

6.2.1.1 River Bridges & Marine Bridges

6.2.1.1.1 General

Hydrological and hydraulic studies of bridge sites are a necessary part of the preliminary design of a bridge. Appropriate investigations shall be carried out to determine the best design. The investigation shall include:-

a) Hydraulic and hydrology data: as required to determine the soffit levels and deck finished levels of the bridges, river training, scour depth estimation, sedimentation, etc.

b) Navigational requirements for navigable bridge: as required to determine soffit levels, minimum navigational spans, protection against ship impact, navigational lighting, etc.

c) Reference is made to Jabatan Pengairan dan Saliran (JPS) Malaysia “Urban Stormwater Management Manual of Malaysia” or MASMA.

d) Headwater depth (HW) at relevant return period (normally 5 years minor storm and 100 years major storm is considered) based on various bridge opening / cross sections.

e) Backwater and mean velocities at bridge opening for various trial bridge lengths and selected discharges;

Design of Bridges for Hydraulic action should be in accordance with BA 59/94.The reference shall also be made to REAM guidelines.

6.2.1.1.2 River Bridges.

Hydrological and hydraulic analysis should be elaborated in accordance with the Jabatan Pengairan dan Saliran requirements. Hydrological Procedures (refer Section 9.1.3 – Estimation of Design Flood) and Design Standards and other local authorities requirements.

Design shall take into consideration of any sedimentation occurs during and after construction. The sediment control shall refer to Jabatan Pengairan dan Saliran, Malaysia of Sediment Control Guideline and Erosion Control in Malaysia. However, the designer should obtain the approval from Jabatan Pengairan dan Saliran for any bridge crossing river.

6.2.1.1.2.1 Site Data

The following data have to be taken in account as a minimum when conducting these studies and analyses:

 topographic maps and/or aerial photographs with geomorphologic features of surrounding land, landuse, river pattern, sand deposits, bank level and others;

 detail survey for stream bed invert levels and cross sections;

 complete data on existing bridges including dates of construction and performances during past floods;

 The historical of flood level/record shall be considered in the design.

 The designer should review with Jabatan Kerja Raya (JKR) or JPS requirement pertaining to the merge river at the surrounding area.

 The consideration on the environment shall also refer to LLM‟s guideline in Section 2 Environmental Consideration.

 available high water marks with dates of occurrence;

 information on navigation, debris and channel stability, flow pattern and constriction of flow;

 factors affecting water stages such as high water from other streams, reservoirs, flood control projects and tides.

6.2.1.1.2.2 Bridge Clearances

For bridge over river the freeboard shall be in accordance to Garispanduan Pembangunan Melibatkan Sungai dan Rezab Sungai by Jabatan Pengairan dan Saliran, Malaysia such as below but not limited to:

 The minimum vertical clearance from bridge soffit shall be 1.0m from 100yrs return period flood level of existing river or flood plain area.

 Access for maintenance vehicle shall be provided.

 Riverbank stability shall be analyzed.

 The abutment wall shall be 2.0m away from edge of river berm.

 Pier shall be out off the deepest river bed and shall be protected from any scour. Especially for river width more than 30m

 Pier pilecaps shall be 1.5m below river bed level.

 Detail of any proposed river protection works shall be submitted to Jabatan Pengairan dan Saliran, Malaysia for approval.

The river waterway for ship/boat shall be considered in the design. However, the data of the frequency ship/boat using waterway, speed and direction shall be obtain with relevant authorities. Generally the Jabatan Pengairan dan Saliran, Malaysia requirement as per Figure 6-4 below.

Figure 6-4 JPS Requirement For Bridge Design. Existing River Profile If Piers on berm 1.0m (min) above water level Q100 Protection Works at 10m Upstream and Downstream Design River Profile

6.2.1.1.3 Marine Bridges.

6.2.1.1.3.1 Navigational Waterways

There are two topography level systems used in Malaysia; the Admiralty Chart Datum (ACD) and Land Survey Datum (LSD). Admiralty Chart Datum (ACD) is generally used for the marine and port facilities while Land Survey Datum is used for the inland facilities. The difference between the two systems shall be verified with the respective Marine Department

AASHTO Guide Specification and Commentary for vessel Collision Design of Highway Bridges (1991) states, “Bridges with main span less than 2 or 3 times the Design vessel length are vulnerable to vessel collision”.

The suggested horizontal clearance to be used in planning stage for important bridges crossing open deep waters is given below:

Vessel Traffic Free Navigation Restricted navigation

One – way Two – way 3.2L 6.7L to 8.2L 1.6L 3.5L to 5L

*Where L is the length of the vessel.

Figure 6-5 Suggested Horizontal Clearance 6.2.1.1.3.2 Aviation Limit

The actual height restriction over the Main Navigation Span could be obtained from the "Aeronautical Information Publication, Malaysia" by the Aeronautical Information Service Department of Civil Aviation. The designer shall check with the relevant Department of Civil Aviation for the height restriction and shall obtain the approval of the relevant Department of Civil Aviation for any deviation or waiver.

6.2.1.1.3.3 Ship Collision Impact Load

For determining vessel collision loads, consideration should be given to Waterway geometry, available water depth, size, type, loading condition and frequency of vessels using waterway, vessel speed, direction and structural response of the bridge to collision.

It must be noted that in addition to above, necessary information pertaining to navigation should be obtained from the authorities, such as Marine Department. However proper judgement, experience and detailed analysis are required to satisfy navigational requirements.

The basic design case for ship collision impact shall consider Dead weight Tonnage (DWT) of the vessel at certain cruising speed. Consideration shall include the distance of piers from the navigation span as well as the depth of water in assessing the risk of ship collision.

Further Information on navigational requirements can be obtained from:

 AASHTO Guide Specifications and Commentary for Vessel Collision Design of Highway Bridges (1991).

In navigable waterways, the two basic protection options available are designing bridge structures to resist vessel collision force and/or protecting by fenders, dolphins, berms or island.

Figure 6-6 Protection Island

Figure 6-7 Fender Protection

Figure 6-8 Dolphins Protection

6.2.1.1.3.4 Bridge Clearances

The bridge over the main navigation channel shall be to satisfy with horizontal and vertical navigation clearances and requirements by the relevant port authority and maritime department.

The height clearance shall be measured above from the MHWS (Mean High Water Sprint), while the required draft shall be measured below the MLWS (Mean Lowest Water Sprint ).

6.2.1.1.4 Materials.

Consideration should be given to the aggressive marine environment and the appropriate concrete mix. The cover to reinforcement should be determined by consideration of durability under the envisaged condition of exposure.

The design of concrete bridges on issues of durability, cover to reinforcement and crack width requirements shall follow as per Clause 6.5 Bridge Design.

Provision of more than minimum concrete cover over the reinforcement is encouraged in elements such as piers and pile caps located in the sea to provide a level of robustness and durability design life in excess of the minimum.

Materials shall be durable and adequate protection shall be provided against environmental deterioration. Minimum grade of concrete allowable is Grade 40 (C40/20). Where the bridge is exposed to chlorides, high performance concrete or equivalent shall be used.

Anti-corrosion protective system: The steel materials used for the bridge structures shall follow BS 5400: Part 6 and shall be protected by a comprehensive anti-corrosion protective system in accordance with BS 5493 or equivalent. The minimum effective life of such protective system shall be in excess of 20 years.

6.2.1.2 Road Bridges& Urban Bridges

A highway structure is a structure intended to carry highway vehicles, and/or bicycles and pedestrians over, under or through a physical obstruction or hazard, and may be abridge (which may be in the form of a culvert exceeding 2 meter in diameter or span), a flyover, a viaduct, and underpass, a subway, a walkway cover, a cantilever noise barrier, a noise enclosure or a sign gantry.

Road bridges and urban bridges are those bridges carriageway highway vehicles such as private cars, bus, lorries and motorcycles.

The difference between road bridges and urban bridges is the localities where these bridges are constructed. Road bridges are generally located in open areas where constraints and restrictions are much lesser. For urban bridges, due to their locations certain constraints and restrictions must be taken into account during planning and design stages of the project.

6.2.1.2.1 Design Consideration

The design of Road Crossing Bridges must take into the consideration of the following factors.

a. Minimum Headroom Clearance – The headroom to be provided is the effective headroom after compensation for vertical curvature and deflection. The headroom specified for new construction includes and allowance of 100mm for subsequent resurfacing. The general practice of 5.4 metre clearance minimum must be adopted. However, under certain circumstances higher headroom clearance will have to be considered. Headroom shall be measured from the lowest point of the overhead structure. The lowest point shall be taken as the lowest lighting fixture, sign, signal or similar protrusion rather than the lowest part of the overhead structure itself.

b. Minimum side clearance – In the absence of raised kerbs, it is the width between concrete and/or metal parapets, less the amount of set-back required for these parapets. This set-back measured from the traffic face of each parapet shall be taken as 0.6 meter on the off-side fast lane. On the near-side slow lane, the set back shall be taken as 0.6 meter or the width of the marginal strip whichever is the greater subject to a maximum set-back of 1.0 meter.

c. Impact of pier from accidental vehicles – The overall structural integrity of the bridge shall be maintained following an impact due to collision of heavy goods vehicles with bridge superstructures, but local damage to a part of the bridge deck can be accepted. The nominal loads shall be considered as acting horizontally on bridge supports. Supports shall be capable of resisting the main and residual load components acting simultaneously. Loads normal to the carriageway shall be considered separately from loads parallel to the carriageway.

d. Impact of Bridge Deck from „over height‟ vehicles – Impact damage due to „over-height‟ vehicle can lead to structure collapse, reinforcement damage, girder misalignment, steel yielding, reinforcement exposure, connection failure, concrete spalling and concrete cracking. After a collision has occurred in which an emergency repair is required, a fast, inexpensive, effective and easy to repair.

e. Minimum sighting distance – Sight distances are measured from a minimum driver‟s eye height of between 1.05m and 2.0m to an object height of between 0.26m and 2.0m, both above the road surface. A possibility therefore exists that the provision of shorter sight distances could sometimes be justified on the grounds that motorists can see through certain types of parapets. However, visibility through a parapet is liable to be obscured and distorted, and thus cannot be relied upon. A parapet of any kind shall accordingly always be treated as opaque for purposes of sight distance design.

For bridges in built-up areas (Urban Bridges), the design must take into the consideration of the following factors other than those mentioned above.

a. Existing Services – Existing services include electric cables, telco cables, sewer lines etc. The design and locations of bridge structures should avoid these services as much as possible so that least disruption to these services can be avoided.

b. Land Constraints – The design of the bridge must consider the availability of the space for the type of structure to be constructed. The new structure must ensure that all the safety aspect of the existing roadway has been taken into consideration in the design.

c. Buildability to minimise the impact to existing traffic flow – Under no circumstances the existing traffic flow (both vehicle and human movement) must be least disrupted during construction. The design and the chosen construction method must be able to accommodate these impact.

d. Existing structures, drains etc. – The effect of existing structures, drains etc must be considered. Minimum disruption to these structures must be exercised and the design must be able to accommodate the existence of these structures.

e. Environmental Constraints – The effect of noise, vibration etc during construction and post construction must be considered during the design and construction of the bridges. The chosen design and construction must avoid the discomfort to the people in the surrounding area. Noise barrier must be considered in the design.

For bridges more than 5km in length, special consideration must be given in providing layby in the event of emergency. The location of the layby must be away from the middle of span and must also avoid the crest of the bridge alignment.

The type of bridges chosen must be able to blend into the surrounding structures. Skyline clearance must be considered in the design.

Figure 6-9 Insufficient Sight Distance

Figure 6-10 Sufficient Sight Distance

6.2.1.2.2 Details of Carriageway

Liaison with highway engineer is required to confirm the function cross section of the bridge in order that the following details are confirmed prior to the design of bridges.

 Number of traffic lane

 Width of each traffic lane

 Presence of hard shoulder

 Presence of marginal or set back

6.2.1.2.3 National Lanes

Notional lanes shall be defined in accordance with BD37/01.

6.2.1.2.4 Loadings

The loadings acting on the bridge shall be generally determined in accordance with BD37/01. Supports exposed in such a way that they may be subject to the collision by vehicle shall be protected by metal or concrete barriers. And those supports shall be designed to resist the vehicle collision loads.

6.2.1.2.5 Parapet

A parapet is a structural component installed along the edge of the bridges to contain vehicles only on the bridges. The design of bridge parapet shall refer to Section 6.4.4 of this guideline.

Loads transmitted by vehicle collision with parapet to structural elements supports parapet shall be dealt with in accordance with Clause 6.7 of BD37/01.

Suitable level of containment shall be determined with due considerations of the following aspects.

 Vehicle type

 Approach angle and speed

 Road conditions.

Height of parapet shall be determined with due considerations of the following aspects.

 Level of containment

 Structures or features underneath the bridges

Sight distances are measured from a minimum driver‟s eye height of between 1.05 m and 2.0 m to an object height of between 0.26 m and 2.0 m, both above the road surface. A possibility therefore exists that the provision of shorter sight distances could sometimes be justified on the grounds that motorists can see through certain types of parapets. However, visibility through a parapet is liable to be obscured and distorted, and thus cannot be relied upon. A parapet of any kind shall accordingly always be treated as opaque for purposes of sight distance design.

6.2.1.2.6 Bridge Supports

The arrangement of bridge supports including the piers, column and abutment shall take account of the sight distance of the road under the overbridges.

6.2.1.2.7 Expansion Joints

The design of expansion joints shall refer section 6.4.1 of this guideline.

6.2.1.3 Railway Over Bridges (ROB)

The purposes of this chapter are to highlight the general requirements, guideline and technical considerations for the new bridges and elevated structures crossing the railway tracks. In general, the railway tracks in Malaysia are under the care of the Keretapi Tanah Melayu (KTM) Berhad. Concurrently, KTM Berhad is the nodal authority representing the Government overseeing the needs that imperative to be considered in the project involving the railway track. KTM Berhad has set forth the criteria essential to be considered in the design and similar requirement shall be adopted in other railway lines in the country.

Similar reference can also be considered in proposing a bridge crossing other than KTM Berhad‟s railway track namely the LRT, ERL, Monorail and also MRT (Similar consideration also can be adopted to bridge crossing over high speed train railway in the future, however it requires further comments and inputs from the relevant authority).

Due to recent development, the Suruhanjaya Pengangkutan Awam Darat (SPAD) has been established by the Government to regulate and enforce all matters relating to land public transport including the implementation process of project involving railway lines in the country. Designer shall refer to the said agency prior to commence design works.

Salient consideration shall be taken into account amongst others, basing on the following items;

6.2.1.3.1 General Requirements

Basic information of bridges and elevated structures crossing railway track are similar to the road crossing, therefore the following items are required to be reviewed beforehand ;

i. About existing railway :

 Class and grade,

 Rail gauge and cross sectional profile,

 Right of way (railway reserve),

 Clearance limit,

 Electrified or conventional track. ii. About future plan :

 Electrification plan,

 Double tracking plan,

 Elevating plan., if any.

6.2.1.3.2 Consultation Items

The following items are to be consulted with the overseeing authority of railway tracks ; i. Bridge structural configuration

Geometric standard of the carriageway including the type & configuration of superstructures to conform with Malaysia Highway Authority (MHA), Suruhanjaya Pengangkutan Awam Darat (SPAD) and other recognized publications requirement

such as Road Engineering Association of Malaysia (REAM) in tandem with Jabatan Kerja Raya (JKR) standard girders.

ii. Bridge length and span

Geometric design of the horizontal and vertical profile of the bridges crossing railway track shall be in accordance with the present JKR Arahan Teknik (Jalan), Malaysia Highway Authority (MHA) or other governing authority requirement.

iii. Clearance limit

The clearance limits of railway are different depending on the type and kind of railways. The railway in Malaysia has been developed based on the British gauge and is now in progress of electrification. Figure in the following items no. 6.2.1.3.4.(a) and 6.2.1.3.4.(b) shown the clearance

below the bridge crossing both the KTM Berhad‟s electrified and non- electrified railway tracks respectively.

However, the new commuter railway system is going to be/has been constructed in the urban areas. To cross with such new system, clearance limit should be consulted with the associated authorities and shall then be continued by individual consultation.

a) Vertical Clearance

It is the designer‟s responsibility of obtaining latest requirement for vertical clearance limit envelope from the KTM Berhad & other governing authorities prior to design. Approval of all clearances below the bridge shall be obtained from the said authority.

In general, KTM Berhad guidelines specified minimum vertical clearance of 7.0m shall be maintained over top of existing & new electrified railway track with „catenary facilities‟ to the lowest soffit of bridge superstructure girders.

Similarly, for new bridges crossing existing & new non-electrified railway track, KTM Berhad guidelines specified a minimum vertical clearance of 6.1m should generally be provided to the lowest soffit of bridge superstructure girders.

b) Horizontal Clearance

It is the designer‟s responsibility of obtaining latest requirement for horizontal clearance limit envelope from the KTM Berhad & other governing authorities prior to design. Approval of all clearances below the bridge shall be obtained from the said authority

In general, KTM Berhad guidelines specified the horizontal clear span for the bridges shall be minimum 25m measured perpendicular or no less than 80 degree to railway track for accommodating future tracks. Minimum 3.5m horizontal clearance shall be maintained between edge of pier cap/abutments and centre line of track nearest to these structures.

Figure 6-11 Standard Structure Gauge and Kinematic Envelope from KTM Berhad Reference to the standard structure gauge and kinematic envelope from the KTM Berhad‟s as illustrated above is necessary prior to the design of bridge crossing railway. The above information are generally govern the minimum vertical headroom and horizontal clearance below the lowest soffit of bridge to the top of rail levels and from the front face of bridge supports to the center line of rails respectively.

Also, a minimum of 3.5m from the front face of bridge‟s pier & abutment to the center line of tracks shall be provided by the designer.

Figure 6-12 Typical envelope of vertical clearance (from soffit of bridge) and horizontal span (from

Figure 6-13 Typical ballast configuration and position of railway tracks. Designer shall be

responsible to liaise with the KTM Berhad and other governing authorities on the above ballast formation requirement prior to the bridge foundation design.

iv. Location of abutments and piers

Abutment walls shall be parallel next to the railway lines after the 25.0 horizontal clearance envelope. If the restraining walls need to be constructed in the vicinity of abutment wall, the restraining wall shall be vertical containing the earth up to the bridge top surface level.

Restraining wall shall be of reinforced earth soil wall type or other approved equivalent wall that aesthetically pleasing.

For the bridge requires intermediate pier supports, the location of pier caps shall be minimum 3.5m perpendicular the to centre line of nearest track.

v. Bridge pile / foundation

Low displacement/bored piles are favorable for bridge in close proximity to the existing railway lines. However, other type of foundations requires proper submission to the KTM Berhad & other authorities for approval / conditional approval.

vi. Embedding depth of foundations

The whole structure shall be supported by piled foundations or spread footings depending on the soil conditions. In general, all top of foundations and pile caps shall be placed 1.5m below the finished ground level (i.e. below rail‟s cess level) unless otherwise constrained by site conditions. Finished ground level at the top of pile cap location shall follow the 1:20 gradient from rail cess levels (edge of ballast at bottom) for future earthworks.

vii. Existing rail levels

Information of existing rail levels shall be provided by the rail operator for reference prior to the design of bridge. Under certain circumstances, additional surveys are necessary to be carried out.

viii. Impact from Collision

Designer shall confirm with KTM Berhad & other railway authorities on the requirement of additional impact loads due to trains collision that needs to be considered for pier supports design of the bridge.

Main primary loads to the bridge shall be referred to the present standards and codes of practice as listed in the appendices.

6.2.1.2.3 Other Associated Items

i. Engineering submission :

Relevant documents require proper submission to the railway authorities are as follows; a) Application forms

b) Conceptual plans including survey data

c) Preliminary and Detailed engineering design plans d) As built plans

ii. Material :

Utilize materials for the bridge structures that are highly resistant to aggressive agents (e.g. climate and traffic generate harmful impacts and vibrations). Protect the more degradable materials with suitable products which are generally customary on all metal structures, shall also be applied to concrete structures especially on those that most exposed.

iii. Parapet :

Bridge parapet shall be of concrete structures. Two (2) types of Parapet – Type A and Type B to be provided as per KTM Berhad‟s and JKR‟s guidelines.

Minimum 1.8m high (measured from top of walkway) Parapet Type B will be extended up to 10.0m on both side from the KTM Berhad reserve area / above 25.0m horizontal clear span / corridor whichever is more. Designer shall ensure that the parapet meets the requirement of high containment wall TL 5 as per Malaysia Highway Authority (MHA) specification.

Parapet Type A will be continued with sufficient distance covering the approaches / departures to & from the bridge. The provision of the extended parapet is necessary as to avert the skidded vehicle from dashing along and jump onto the railway traffic.

All parapets shall be designed to resist the vehicle impact load as per the codes of practice.

Figure 6-14 Typical Section Of Parapet

iv. Deck drainage :

Drainage facility for the bridge deck shall be suitably provided with UPVC pipe at designed interval or required minimum number per sq.m. whichever is applicable, either on both side or on lower side of deck depending upon the cross-fall of deck, except for the 25.0m stretch (envelope) over the railway tracks, not required. Drainage facility for the bridge deck shall be provided in such a way that the drainage collection system will be properly connected to the nearest drain/sump.

Deck drainage shall be designed for a „n‟ year of return period and appropriate hydraulic calculation. All pipes diameter shall be based on the basis of the slope (%) and the capacity (litres/second) where UPVC pipes are used. In any case the pipe diameters cannot be less than 150mm.

Devices, consists of gullies and collector pipes, shall be provided for collection and disposal of rainwater and surface run-off. Similarly, the maintenance of the drainage facilities & systems shall be executed by the relevant authority.

v. Deck Waterproofing :

All top deck slabs are to be waterproofed. Surface run-off from top deck slab will be discharged through the outlets drained out to the nearest sump outside the KTM Berhad‟s and other governing authorities‟ R.O.W. The provision of waterproofing shall only applicable for bridge crossing railway line.

Resurfacing of waterproofing shall be included in the standard operation procedures (SOP) acceptable to the governing authorities.

vi. Expansion Joint :

In the event of the need of expansion centers at deck level at mid pier (i.e. pier support that closes to electrified railway track), the designers are advised to adopt expansion joint composed of two parts that (i) the upper layer able to maintain the continuity of the road surface and (ii) the second lower part designed to prevent infiltration of water into the underlying structures.

vii. Bracket for utility services :

In principle, there will be no bracket allowed to be attached to the outer side of bridge parapet / edge of deck for utility and power cables including water mains, sewer line etc. All utility ducting shall be embedded into the concrete parapet or deck depending on the

design requirement. Proper consultations for these items are necessary with the relevant authorities.

viii. Frontage & service road :

Provision of frontage road shall be outside of the railway line R.O.W. No encroachment of access roads shall be permitted into the track right of way.

ix. Street light

The light pole shall be mounted at median of the bridge. No lighting pole to be erected at the edge of bridge within/above the KTM Berhad‟s R.O.W. and other governing authorities.

x. Signage

No pedestal for the signage board shall be provided at the outer edge & top surface of parapet wall as to avoid falling onto the railway tracks.

ix. Construction requirements (including relocation and protection of existing railway facilities) :

All launching of superstructure girders shall obtain approval from the authority. All proper method statement (with Professional Engineer endorsement) for launching procedures including temporary bracing between installed girders, etc. shall be submitted to the KTM Berhad and other governing authorities for approval. Time block to be given by the rail authority basing on the method of girder launching submitted by the Contractor.

Limit of construction can be highlighted in the design document/drawing as to ensure the safety aspect has been taken into account and protection of existing railway facilities/assets and services are necessary to be considered prior to the construction like providing the sheet piling, safety

net, etc. A minimum distance of 10.0m, or, subject to the present requirement, from the railway centre line shall be provided for the construction equipment.

A minimum acceptable height and approximately 50m long temporary hording shall be provided before and after the proposed bridge location during the construction period.

x. Permits to enter railway line :

All permits shall be applied timely to the relevant authorities before entering the railway track vicinity (R.O.W.).

6.2.1.3.4 Sample View of Bridge

Figure 6-15 Bridge crossing the KTM Berhad‟s non- electrified railway track

Figure 6-16 Bridge crossing the KTM Berhad‟s

6.2.2 Selection of Bridge Superstructure

The selection of the Bridges Superstructure (Deck) depends on:-

 Curvature / Skew / Span / Width / Depth constraints

 Materials availability / suitability eg masonary / concrete / steel composites

 Construction constraints eg Heavily trafficked / ravine / waterways

6.2.2.1 Short to Medium Spans Bridges

 The deck system available for short to medium span bridges are :-

 Cast-insitu concrete

 Precast Beams plus in-situ concrete deck

 Steel Beam plus in-situ concrete deck

Figure 6-17 Typical Span Range for Different Deck Types

No Type Max Span (meters) Min Radius (meters) 1. Pre-Tensioned Precast U-Beams 30 200 2. Post-Tensioned Precast I-Beams 30 200 3. Post-Tensioned T-Beams 40 300

4. Insitu Voided Slab 25 (Reinforced) 30 (Prestressed)

80

5. Insitu Box 30 (Reinforced) 80

CABLE STAYED BRIDGES

INSTU SEGMENTAL BOX GIRDER (VARIABLE DEPTH)

PRECAST SEGMENTAL BOX GIRDER (VARIABLE DEPTH)

PRECAST CONCRETE BEAMS

INSITU CONCRETE SLAB

20 40 60 80 100 200 1000

SPAN LENGTH / METRE

6. Precast Segmental 50 (No Haunch) 70 (Haunch)

100

7. Steel Beams 30 (Standard Beams)

50 (Plate Girders)

200

8. Steel U-Beams 70 100

Figure 6-18 Bridge Deck Types

6.2.2.2 Short to Medium Spans Curved Bridges

For curved bridges, particularly in urban areas the options available are :-

On gentle curves, straight beams can be used provided the spans are kept short. Curved in-situ voided slab box bridges if the curvature of the road is less 100 metre

For longer spans, bridge over, heavy traffic precast segmental bridges can be used using the balanced cantilever method. This type can extend to spans of 70 metres

Figure 6-19 Precast Segmental Bridges

6.2.2.3 Medium Spans Bridges

Figure 6-20 Papar Bridge – Steel Trusses

Figure 6-21 Malaysia – Singapore 2nd Crossing – Insitu Box Girder Bridge

6.2.2.4 Long Spans Bridges

Long span bridges are generally cable stayed bridges or suspension bridges.

Figure 6-23 Clifton Suspension Bridge

There are however hybrid suspension cable stay bridges that can span even longer then suspension bridges.

6.3

Bridges Substructure

Bridge Substructure comprises of:-

Abutments - End Supports.

Piers - Intermediate Supports

6.3.1 Abutments

The selection of Abutments depends on: -

 Embankment Height

 Foundation Condition

There are as number of Abutment Types

The most common are: -

 Bank Seat - Resting on top of embankment slope

Figure 6-24 Bank Seat Abutment

Figure 6-25 Wall Abutment

The selection of abutment depends on the availability of space under the bridge and soil condition.

In weak soil conditions, bank seat abutments are not to be used, as it is unstable due to embankment movements. Wall abutments with retained sidewalls on a piled base are preferred.

If the ground cannot support the embankment, a piled raft to support the embankment adjacent to the bridge is required.

6.3.2 Piers

There are a variety of Pier Types depending on:-

 Support points required for the bridge

Figure 6-26 Typical Pier Shapes

Piers tend to add elegance to the bridge and a variety of Pier shapes are available.

6.3.3 Foundations

The foundation of bridges will depend on ground conditions.

Foundation must be able to support the loads coming from the superstructure and substructure viz. Direct vertical loads, horizontal loads and moments. Considerations must also be given to loads due to seismic activities and ship impact forces where applicable.

Where the grounds can sustain the applied loading (i.e. sand, gravel, rock) within an acceptable tolerance, then pad footings can be considered provided all the loads mentioned above have been designed for.

Where the ground is weak, pile foundations are required. The design of pile foundation must take into consideration of all the possible loading conditions as mentioned above.

Generally, pile foundation can be divided into driven piles, jack-in piles and cast-in-place piles. Driven piles can be of H-steel pile, prestressed spun pile, reinforced concrete square piles. Driven piles shall not be considered in built-up area due to noise pollution. Jack-in pile shall be considered as an alternative to driven pile in built-up area.

Cast-in pile can be in the form of micro piles or bored piles. In area where space constraint is a concern, hand-dug caisson could be an option. However, caisson shall have the minimum diameter of 1.2m due to safety consideration.

Figure 6-27 Driven Pile

Pile Group Analysis using „Piglet‟ or similar software has to be carried out to determine the loads on individual piles. The structural and soil carrying capacity of the pile must be checked against the maximum loaded pile in the group.

6.4

Bridge Accessories

6.4.1 Expansion Joints

6.4.1.1 General

Expansion joints are provided to seal the gap between two parts of the bridge deck, which is subject to movement due to temperature, creep, shrinkage and other forces.

Expansion joints, by virtue of their function, are usually a weak part of the bridge, thus requiring frequent repair and disruption to traffic.

In view of the above, there is currently or tendency to design bridges without expansion joints where feasible. This may be achieved by providing:

 Deck Continuity

 Integral Bridges

Reference is to be made to UK Highway Agency BA 42/96-The Design of Integral Bridges (Incorporating Amendment No. 1 dated May 2003).

Deck continuity involves design of the superstructure as continuous for superimposed dead load and live loads. This will enable joint free deck for as much as 200 metres for a multi-span bridge. Apart from doing away with joints, this improves the riding quality of the bridge deck.

It is now a JKR and MHA requirement for bridge less than 60m and skew less than 30º to be designed as an integral bridge i.e. the abutment is cast-in with the deck. The design of an Integral Bridge involves considering the forces due to the whole bridge as a single structure usually a portal with soil springs representing the soil / structure interaction.

6.4.1.2 Types of Expansion Joints

There are a variety of expansion joints in the market based on the expansion gap to be sealed. Types of expansion joints are:-

i) Asphaltic plug joints - Asphaltic plug joints are suitable for movements up to + 20mm

Figure 6-28 Asphaltic Plug Joint

This type of joint is not suitable where standing traffic is common due to the possibility of diesel leakage from vehicles which then attacks the hydrocarbon compounds within the joint.

Designer should also consider another situation where the longitudinal gradient of the carriageway is steep and the diesel leakage flows back towards joint during thunderstorm.

ii) TransflexElastomeric Joints - An elastomer reinforced with metal plates fixed on both sides of the gap suitable for expansions up to +100m

Figure 6-29 Elastomer Reinforced Joint

iii) Mechanical Joints - A prefabricated joint with metal comb or tooth with plates that slide back and forth between each other suitable for movements as much as + 300mm. . This type of joint is also called cantilever type joint because of the metal comb or tooth plates‟ cantilever action in bridging the gap.

Figure 6-30 Mechanical Joint

iv) Modular Joints - Also called elastomeric in metal runners (as defined in BD 33/94) or lamella joints this type of joint can accommodate large movements in all three directions and rotations about all three axes.

v) Seismic Joints - Modified modular joints to accommodate large longitudinal, transverse and vertical displacements, as well as vertical rotations. These joints will be required where seismic isolation bearings are used.

6.4.1.3 Design Of Expansion Joints

Design of expansion joints shall be carried out as per BD 33/94 and BD 26/94 (UK Highway Agency). The expansion joints must be capable of sustaining loads and movements. It might be prudent in the design of all joints (to be judged by the designer) to increase the point load or axle load as specified in BD 33/94 where there could be cases of overloading by lorries or trucks. Movements of the structure can be longitudinal (predominant), transverse, vertical and rotational. Designer must take into consideration the bridge geometric layout (curve and skew) on all possible movements and rotation. Another consideration is the rotation of the superstructure and the inclination of the carriageway.

6.4.1.4 Maintenance of Expansion Joints

The Concessionaire Company must ensure there is no build-up of grit and other non-compressible matter, vegetation growth near the parapet.

6.4.2 Bridge Bearings

Bridge bearings provide the necessary articulation of the bridge due to applied loads and movements.

Bridge bearings have similar maintenance problems as for joints. Therefore, there is a general trend to avoid bearings, the problem of dealing with movements is real and has to be dealt with in the total structural solution rather than treating the superstructure separate from the substructure.

6.4.2.1 General

Bridge bearings usually allow free rotation but may or may not allow horizontal translation. Bearings can be categorized as follows:-

 Fixed - no horizontal translation allowed

 Free sliding - fully free to move horizontally

 Guided sliding - free to move horizontally in one direction only In many bridges, a combination of the three types of bearings is provided.

6.4.2.2 Bearing Types

There are many type of bearings and the choice of which type to use depends on the forces and movements to be accommodated. Only the more commonly used bearings are described below: -

 Elastomeric Bearings - Suitable where loads and rotations are low eg. Precast beam or steel beams of composite construction where a bearing is placed under each beam. They are made from rubber and can be in single layer (plain) or multiple layer separated by steel plates (laminated). Elastomeric bearings accommodate rotation (by deflecting more on one side than the other) and translation by shearing action.

Elastomeric bearings are also suitable as seismic isolation bearings. Designers must endeavour to use products that utilised our country‟s natural resources as much as possible.

 Mechanical Bearings - Mechanical bearings are either pot bearings or cylindrical bearings designed to accommodate a specific function i.e. fixed, free or guided. Pot bearings contain elastomers to which a force is applied by means of a metal piston. The elastomer effectively acts as a retained fluid and facilitates some rotation whilst preventing translation. They are also used in combination with plane sliding surfaces to provide free sliding bearings.

6.4.2.3 Detailing Of Bearings

Bearings provide the articulation for a bridge. Therefore in the design and installation of the bearings, care hasto be taken so that the intended function is achieved. Some of the important aspects are: -

Figure 6.33 Mechanical Bearings Figure 6.32 Elastomeric Bearings

 Bearings on bridges with steep gradients to be placed so that the contact surfaces are horizontal. Failure to do this may result in „walking‟ bearings.

Figure 6.34 – Bearings On Steep Gradients

 Ensure that there is no uplift on the bearings especially in skew and curved bridges.

 On curved bridges the direction for movement of sliding bearings to be outwards from the fixed bearing.

 The life of bearings is never as long as the bridge structure with an intended design life of 100 years. Provision shall be provided for the replacement of bearings. This may involve providing jacking points on the supporting sub-structure near the bearings to allow for easy removal and replacement. The superstructure shall also be checked for the effects of this jacking force especially the effects due to forced upward movement. These jacking points together with the proposed jack up force must be indicated in the drawings and attached together with the O & M manual.

Plinth, to keep bearing horizontal

Principal Direction of Movement

Figure 6.37 Orientation Of Bearings

Pier Pier

Abutment Abutment

Figure 6.35 - Uplifts Of Bearings

Tied Down

Wider Spacing

 When designing widening of existing bridges care must be taken so that most of the creep and shrinkage have occurred before stitching the old and new superstructures.

Bridge bearings should be designed in accordance with British Standard BS 5400: Part 9: 1983 and BD 20/92 (UK Highway Agency).

6.4.3 Bridge Waterproofing

Waterproofing of bridges are generally of two types:-

 Waterproofing of the deck by the application of a bituminous coating

 Waterproofing of abutment faces in contact with earth. This also done by an approved waterproofing coating.

BD 47/99 and BA 47/99 should be referred for Bridge waterproofing.

Designers shall refer to section on durability for more extensive treatment on elements of bridges (example pile caps and/or columns for piers) in continuous or periodic contact with water (whether fresh or saline) or in aggressive soil conditions.

6.4.4 Parapets

Bridge parapets and safety barriers must comply with BS6779 or DMRB TD 19/06 issued by UK Highways Agency.

6.4.4.1 Pedestrian Parapets

Pedestrians must be protected by parapets not less than 1.0 metre in height. These should not possess footholds or projections to permit climbing over them.

The motorway should be protected from all falling or thrown objects by means of screen.

6.4.4.2 Restraint Systems On Motorway Bridges

The safety barrier shall cover the length of the motorway bridge and the approach zones.

As mentioned previously wherever the motorway passes over a railway or high risk situation, containment concrete parapets should be provided.

The safety barrier shall comply to minimum Test Level 4 as per AASHTO or high containment level (H2) as per TD19/06.

Anti-glare screens shall be provided if so required by Road Safety Auditor.

Figure 6.40 Typical End Treatment Of Parapet

Figure 6.39 Guard Rails At Bridge Approach Figure 6.38 Concrete Bridge Parapets

Bridge parapets should have ducting provisions for services and supporting arrangements for lighting poles, signages and signals, CCTV masts etc.,

The following Design manuals shall be referred for Design of services:

 BD26/04 (Part 1) - Design of Lighting Columns,

 BD 83/01 (Part11) – Design of CCTV Masts,

 BD 88/03 (Part 13) – Design of Cantilever Masts for Traffic Signals and/or Speed Cameras

6.4.3 Bridge Drainage

Devices have to be provided for collection and disposal of rainwater. These devices may consist of gullies, main and secondary pipes and troughs. The number, size and location of the gullies, troughs and the diameters of pipes shall be determined on the basis of appropriate hydraulic calculations. (Refer to Section 9.3 - Surface Drain Design Philosophy and Parameters). ). All pipe runs shall be capable of being rodded. An accessible rodding eye must be provided at each turning point in the drain pipe run.

In all cases, pipe diameters cannot be less than 150mm in order to facilitate maintenance.

Secondary pipes connect the gullies to the main pipes, which in turn conduct and discharge water to discharge points located at the ends of bridges.

In case of very long structures, it is desirable to provide intermediate discharge points through the piers. However detailing must be such that maintenance of discharge pipes can be easily maintained (refer Figure 6.42).