AS 5100.4-2004(+A2) Bearings and deck joints

This Australian Standard® was prepared by Committee BD-090, Bridge Design. It was approved on behalf of the Council of Standards Australia on 29 July 2003.

This Standard was published on 23 April 2004.

The following are represented on Committee BD-090:

?Association of Consulting Engineers Australia

?Australasian Railway Association

?Austroads

?Bureau of Steel Manufacturers of Australia

?Cement and Concrete Association of Australia

?Institution of Engineers Australia

?Queensland University of Technology

?Steel Reinforcement Institute of Australia

?University of Western Sydney

This Standard was issued in draft form for comment as DR 00377.

Standards Australia wishes to acknowledge the participation of the expert individuals that contributed to the development of this Standard through their representation on the Committee and through the public comment period.

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AS 5100.4—2004

AP-G15.4/04

(Incorporating Amendment Nos 1 and 2)

Australian Standard®

Bridge design

Part 4: Bearings and deck joints

Originated as HB 77.4—1996.

Revised and redesignated as AS 5100.4—2004.

Reissued incorporating Amendment No. 1 (April 2010).

Reissued incorporating Amendment No. 2 (December 2010).

COPYRIGHT

© Standards Australia Limited

All rights are reserved. No part of this work may be reproduced or copied in any form or by any means, ele troni or me hani al, in luding photo opying, without the written permission of the publisher, unless otherwise permitted under the Copyright Act 1968. Published by SAI Global Limited under licence from Standards Australia Limited, GPO Box 476, Sydney, NSW 2001, Australia

ISBN 0 7337 5474 0

AS 5100.4—2004 2

PREFACE

This Standard was prepared by the Standards Australia Committee BD-090, Bridge Design to supersede HB 77.4—1996, Australian Bridge Design Code, Section 4: Bearings and deck joints, and AS 1523, Elastomeric bearings for use in structures.

This Standard incorporates Am endm ent No. 1 (April 2010) and Am endm ent No. 2 (Decem ber 2010). The changes required by the Am endm ent are indicated in the text by a marginal bar and amendment number against the clause, note, table, figure or part thereof affected.

The AS 5100 series represents a revision of the 1996 HB 77 series, Australian Bridge Design Code, which contained a separate Railway Supplement to Sections 1 to 5, together with Section 6, Steel and composite construction, and Section 7, Rating. AS 5100 takes the requirements of the Railway Supplement and incorporates them into Parts 1 to 5 of the present series, to form integrated documents covering requirements for both road and rail bridges. In addition, technical material has been updated.

This Standard is also designated as AUSTROADS publication AP-G15.4/04.

The objectives of AS 5100 are to provide nationally acceptable requirements for—

(a)the design of road, rail, pedestrian and bicycle-path bridges;

(b)the specific application of concrete, steel and composite steel/concrete construction,

which embody principles that may be applied to other materials in association with

relevant Standards; and

(c)the assessment of the load capacity of existing bridges.

These requirements are based on the principles of structural mechanics and knowledge of material properties, for both the conceptual and detailed design, to achieve acceptable probabilities that the bridge or associated structure being designed will not become unfit for use during its design life.

Whereas earlier editions of the Australian Bridge Design Code were essentially administered by the infrastructure owners and applied to their own inventory, an increasing number of bridges are being built under the design-construct-operate principle and being handed over to the relevant statutory authority after several years of operation. This Standard includes clauses intended to facilitate the specification to the designer of the functional requirements of the owner, to ensure the long-term performance and serviceability of the bridge and associated structure.

Significant differences between this Standard and HB 77.4 are the following:

(i) Pot bearings and sliding surfaces Design criteria for pot bearings and sliding

contact surfaces have been specified at the ultimate limit states.

(ii) Mechanical bearings Design provisions for mechanical bearings previously in HB 77.6 have been moved to this Standard.

(iii) Multiple pot bearing Additional clauses have been included relating to the reaction of multiple pot bearings to sliding forces.

(iv) Anchorages The rules for anchorage of pot bearings, laminated elastomeric bearings and deck joints have been revised.

(v) Testing Testing of elastomer and laminated elastomeric bearings has been added.

In line with Standards Australia policy, the words ‘shall’ and ‘may’ are used consistently throughout this Standard to indicate, respectively, a mandatory provision and an acceptable or permissible alternative.

3

AS 5100.4—2004

Statements expressed in mandatory terms in Notes to Tables are deemed to be requirements

of this Standard.

The term ‘normative’ and ‘informative’ have been used in this Standard to define the

application of the appendix to which it applies. A ‘normative’ appendix is an integral part

of the Standard. An ‘informative’ appendix is only for information and guidance.

AS 5100.4—2004 4

CONTENTS

Page

1 SCOPE (5)

2 REFERENCED

DOCUMENTS (5)

3 DEFINITIONS (6)

4 NOTATION (6)

5 FUNCTIONS OF BEARINGS AND DECK JOINTS (9)

6 LOADS, MOVEMENTS AND ROTATIONS (9)

7 GENERAL DESIGN REQUIREMENTS (10)

RESTRAINTS (11)

8 MOVEMENT

9 ALIGNMENT OF BEARINGS AND DECK JOINTS (12)

10 ANCHORAGE OF BEARINGS (12)

11 LOADS RESULTING FROM RESISTANCE TO MOVEMENT (13)

BEARINGS (15)

12 E L ASTOMERIC

BEARINGS (24)

13 POT

14 SLIDING CONTACT SURFACES (25)

15 MECHANICA L BEARINGS (26)

16 BEARINGS SUBJECT TO UPLIFT (28)

JOINTS (29)

17 DECK

APPENDICES

A TABLES OF STANDARD ELASTOMERIC BEARING PROPERTIES (32)

A TESTING OF LAMINATED ELASTOMERIC BEARINGS (60)

B TESTING OF ELASTOMER, CATEGORY 1 TESTS (53)

C MANUFACTURING TOLERANCES FOR LAMINATE

D ELASTOMERIC

BEARINGS (58)

D TESTING OF LAMINATED ELASTOMERIC BEARINGS (60)

5 AS 5100.4—2004

.au © Standards Australia STANDARDS AUSTRALIA

Australian Standard

Bridge design

Part 4: Bearings and deck joints 1 SCOPE

This Standard sets out minimum design and performance requirements for bearings and

deck joints for the articulation and accommodation of movements of bridge structures.

This Standard applies to elastomeric, pot and mechanical bearings and deck joints, all of

which are locations where rotation or translation, or both, can take place. It does not apply

to concrete hinges or PTFE-lined spherical bearings.

2 REFERENCED DOCUMENTS

The following documents are referred to in this Standard:

AS

1683

Methods of test for elastomers 1683.11

Method 11: Tension testing of vulcanized or thermoplastic rubber 1683.12

Method 12: Rubber, vulcanized or thermoplastic—Determination of tear strength (trouser, angle and crescent test pieces) 1683.14.1

Method 14.1: Adhesive strength of vulcanized or thermoplastic rubber—One-plate method 1683.15.1

Method 15.1: International rubber hardness 1683.15.2

Method 15.2: Durometer hardness 1683.22

Method 22: Determination of vulcanization characteristics using the oscillating disc curemeter 1683.24

Method 24: Determination of the resistance of vulcanized or thermoplastic rubbers to ozone cracking—Static strain test 1683.26 Method 26: Rubber, vulcanized or thermoplastic—Accelerated

ageing or heat-resistance tests

5100 Bridge design

5100.2 Part 2: Design loads

5100.5 Part 5: Concrete

5100.6 Part 6: Steel and composite construction

5100.4 Supp 1 Bridge design—Bearings and deck joints—Commentary (Supplement

to AS 5100.4—2003)

ISO

815

Rubber, vulcanized or thermoplastic—Determination of compression set at ambient, elevated or low temperatures 13000

Plastics—Polytetrafluoroethylene (PTFE) semi-finished products 13000-1

Part 1: Requirements and designation 1827

Rubber, vulcanized or thermoplastic—Determination of modulus in shear or adhesion to rigid plates—Quadruple shear method 4661

Rubber, vulcanized or thermoplastic—Preparation of samples and test pieces 4661.1 Part 1: Physical tests

AS 5100.4—2004 6

© Standards Australia .au ASTM

A240/A240M-03b Standard Specification for Chromium and Chromium-Nickel Stainless

Steel Plate, Sheet and Strip for Pressure Vessels and for General

Applications

NCHRP 402

Fatigue Design of Modular Bridge Expansion Joints 3 DEFINITIONS

For the purpose of this Standard, the definitions below apply.

3.1 Bonded layer

A layer of elastomer bonded on both faces to metal plates, achieved by a vulcanization process.

3.2 Deck joint

A structural discontinuity between two elements, at least one of which is a deck element and is designed to permit relative translation or rotation, or both, of abutting structural elements.

3.3 Laminated bearing

An elastomeric bearing with two or more metal plates bonded into the elastomer.

3.4 Plain bearing

A bearing made up of a single unbonded layer of elastomer.

3.5 Pot bearing

A bearing that carries vertical load by compression of an elastomeric disc confined in a steel cylinder and which accommodates rotation by angular deformation of the disc.

3.5A Rated load

The calculated maximum permissible compressive load, which may be applied to a bearing when it is subjected at the same time to specified shear strain and rotation.

3.6 Semi-bonded layer

A layer of elastomer bonded on one face only to a metal plate.

3.7 Strip bearing

A plain bearing pad in which the length is more than 10 times the width.

3.8 Unbonded layer

A single layer of elastomer that is not bonded to metal plates.

4 NOTATION

The symbols used in this Standard are listed in Table 4.

Where non-dimensional ratios are involved, both the numerator and denominator are expressed in identical units.

The dimensional units for length and stress in all expressions or equations are to be taken as millimetres (mm), Newtons (N) and megapascals (MPa) respectively, unless specifically noted otherwise.

An asterisk (*) placed after a symbol as a superscript denotes a design action effect due to the design load for the ultimate limit state. A1

7 AS 5100.4—2004

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TABLE 4 NOTATION

S mbol Description Clause reference A b bonded surface area of an elastomeric bearing

12.5.2 a plan dimension of the edge of the bonded surface of rectangular

bearings parallel to the span of the bridge

12.6.1 A eff effective loaded plan area, that is, projected area common to top and bottom when a bearing is distorted tangentially

12.6.1 A p projected contact area (length of the seating times the diameter of the pin)

15.4.2 A r total rubber plan area 12.5.2 B bulk modulus of elastomer

Table 12.2 b plan dimension of the edge of the bonded surface of a rectangular bearing transverse to the span of the bridge 12.6.1 b e lesser of a and b for rectangular bearings 12.6.5 C 1, C 2 constant dependent on bearing shape

12.6.8, 12.7.3

d plan diameter of circular bearing at edg

e o

f bonded surface 12.6.1

d c total compressiv

e deflection

12.6.4 d 1 diameter of the elastomeric pad within the pot bearing 13.1 E effective compression or rotation modulus of elastomer 12.6.8, 12.7.3

E h homogeneous compression modulus 12.6.8 E s Young’s modulus of elasticity

15.3.2 e shift in the centre of pressure due to rotation

13.1 f o stress used in calculation of anchorage of laminated bearing 12.6.7 f u tensile strength used in design 15.3.2 f y yield strength of metal plates

12.6.6 G chord shear modulus between 5% and 25% shear strain for an elastomer

Table 12.2 H horizontal force or shear force, serviceability limit state 11.4 H * horizontal force or shear force, ultimate limit state

10.1 I second moment of area of the plan area of the elastomer about its axis of rotation

12.7.3 K c compressive stiffness of a bearing

12.7.1 K cn

compressive stiffness of an individual layer of elastomer in a laminated bearing

12.7.1 K h lateral h orizontal stiffness 12.7.4 K r rotational stiffness of bearing

12.7.3

K rn rotational stiffness of a layer n 12.7.3 K s shear stiffness of an elastomeric bearing

11.4 K sn shear stiffness of a layer n of elastomer in a laminated bearing 12.7.2 K v effective compression stiffness 12.7.4 L length of the cylinder 15.3.2 M rotational moment

12.7.3 m

ratio of the sides of a rectangular laminated bearing

12.7.3

(continued )

A1

AS 5100.4—2004 8

© Standards Australia .au

S mbol Description Clause reference N compressive load on a bearing, serviceability limit state; or

design bearing load of a cylinder

12.6.1, 15.3.2

N min. minimum compressive load normal to the bearing anchorage interface concurrent with H , serviceability limit state

12.6.7 N min.PE minimum permanent compressive load normal to the bearing anchorage interface concurrent with H , serviceability limit state 12.6.7 N *

compressive load on bearing, ultimate limit state

12.6, 12.7 *min.N

minimum concurrent load acting in compression normal to the bearing anchorage interface, ultimate limit state

10.1 n a number of bearings contributing to adverse frictional load 11.3 n t number of bearings contributing to relieving frictional load 11.3 P surface perimeter for laminated elastomeric bearings 12.5.2 q ratio 12.6.8

R ua characteristic ultimate shear capacity of mechanical anchors 10.1 r radius of cylindrical roller or rocker; or radius of spherical rocker 15.3.2, 15.3.4

r i radius of the concave seating

15.3.2 S shape factor of a layer of elastomer; or shape factor of the thickest inner layer

12.5.2, 12.6.5

t total thickness of elastomer in a laminated bearing or thickness of plain pad or strip bearing

12.5.2 t c thickness of a cover layer of a laminated bearing

12.5.2 t e effective thickness of an individual elastomer layer in compression (due to vertical load or rotation)

12.5.2 t i thickness of an individual inner layer of elastomer in a laminated bearing

12.5.2, 12.6.6

t n thickness of a typical layer n of elastomer 12.7.1 t s thickness of metal plates 12.6.6 w width of strip

12.5.2, 13.1 α maximum angle of rotation, that is, change in angle between top and bottom surfaces of bearing in critical direction 12.6.1 αa angle of rotation parallel to the span of the bridge 12.6.1, 12.6.3 αb angle of rotation transverse to the span of the bridge

12.6.1, 12.6.3

βa , βr factors dependent on the numbers of bearings n a and n r 11.3 δa

maximum shear displacement tangential to bearing surface in the direction of dimension a due to movements of the structure and tangential forces

12.6.1

δb

maximum shear displacement tangential to bearing surface in the direction of dimension b due to movements of the structure and tangential forces

12.6.1

δs

maximum resultant vector shear displacement tangential to the bearing surface considering movements of the structure and imposed shear force 11.4

φ strength reduction factor

10.1

(continued )

TABLE 4 (continued )

9 AS 5100.4—2004

.au © Standards Australia

S mbol Description Clause reference φf strength reduction factor for friction

10.1 εcl compressive strain due to live load and dynamic load allowance

normal to the bearing surface (based on the effective plan area A eff )12.6.1 εc compressive strain due to loads normal to the bearing surfaces (based on the effective plan area A eff )

12.6.1 εsc shear strain at edge of bonded surface due to loads normal to bearing surfaces

12.6.1 εscl shear strain at edge of bonded surface due to live load and dynamic load allowance only

12.6.1 εsh shear strain at edge of bonded surface due to forces tangential to the bearing surface or movement of the structure, or both 12.6.1 εsr shear strain at edge of bonded surface due to relative rotation of bearing surfaces

12.6.1 μ characteristic coefficient of fiction 11.2 μk min. characteristic low friction coefficient 10.1 μa adverse coefficient of friction 11.3 μr relieving coefficient of friction

11.3 θ

angle of inclination of opposing bearings

12.7.4

5 FUNCTIONS OF BEARINGS AND DECK JOINTS

The function of bearings is to provide a special connection to control the interaction of loads and movements between parts of the structure, usually between superstructure and substructure.

The function of deck joints is to provide a trafficable surface across permanent openings in the bridge deck between parts of the deck or between deck and abutments with the widths of such openings varying with environmental effects, loads and movements. The number of deck joints in a bridge shall be minimized.

NOTE: Preference should be given to continuous deck systems.

6 LOADS, MOVEMENTS AND ROTATIONS

The load and movement capabilities of bearings and deck joints for any bridge shall be compatible with the assumptions made in the overall design of the bridge and the special requirements of this Standard.

The effects of movements of the centre of pressure due to rotation and the moment caused by horizontal loads and friction forces shall be considered in the design of bearings and in the calculation of bearing pressures on substructures and superstructures. Movements including rotations shall be identified for each of the main axes.

Bridge drawings shall include a diagrammatic plan view of all bearings, by indicating the various actions and degrees of restraint for each bearing by using appropriate symbols.

NOTE: Appropriate symbols for bearing actions and degrees of restraint are shown in AS 5100.4 Supp 1.

The loads and movements at the appropriate limit state shall be specified. Bearing loads and any testing requirements, including test loads, shall be specified in the contract documents.

TABLE 4 (continued )

AS 5100.4—2004 10 Bearing loads and bridge movements of skewed and curved bridges shall be rigorously

assessed including variations of bearing loads across piers and abutments.

Detailing and construction of services, pipelines, railings, parapets and other appendages to

the superstructure shall be such as to ensure that movements and rotations of the bridge are

not impeded.

7 GENERAL DESIGN REQUIREMENTS

7.1 Design consideration

The following shall be considered in the design and specification of performance

requirements of bearings and deck joints:

(a)Properties of the materials in the structure, including coefficients of thermal

expansion, modulus of elasticity, Poisson’s ratio, creep and shrinkage.

(b)Tolerances on material properties, including tolerances on compressive, shear and

rotational characteristics.

(c)Effective temperature range of elements of the bridge.

(d)Sizes of structural elements.

(e)Method and sequence of construction including prestressing effects and concrete

creep and shrinkage, as relevant.

(f)Tilt, settlement and movement of piers and abutments.

(g)Construction tolerances of elements of the bridge and bearing.

(h)Properties of the bearing in regard to restraints to translation.

(i)Static and dynamic response of the bridge including traffic, wind, flood, earthquake,

collision and ship impact loads.

(j)Changes to bearing loads due to the longitudinal and transverse effects of differential temperature gradients in statically indeterminate structures.

(k)Fatigue requirements.

Where bearings with differing characteristics are used in the same line of support, the

resulting interactive effects shall be considered in the design of the bearings and the bridge.

Bearing performance requirements shall be specified to allow for all the design

considerations specified in this Clause, and for tolerances and errors in positioning and

aligning bearings based on the specific contract construction and erection tolerances.

Secondary effects resulting from eccentric loads or movements not along bearing axes shall

be considered in both the design of the bearing and adjacent structural elements.

7.2 Design life

Bearings and deck joints, excluding easily replaceable components such as deck joint seals,

shall be designed for the same design life as the bridge.

7.3 Limit state requirements

All bearings and deck joints shall be designed to accommodate the relevant imposed loads,

load effects and movements at the required limit states.

Ultimate limit state movements shall be derived from the nominal movements factored by

the relevant load factors specified in AS 5100.2.

Elastomeric bearings shall be designed for serviceability limit state effects.

© Standards Australia .au

11 AS 5100.4—2004

.au © Standards Australia Mechanical bearings shall be designed to accommodate ultimate limit state movements and

to sustain serviceability and ultimate limit state loads. I n addition, mechanical bearings

shall remain undamaged after ultimate limit state load testing.

Other types of bearings, sliding contact surfaces and deck joints shall be designed to

accommodate ultimate limit state movements and to sustain serviceability and ultimate limit

state loads without damage.

7.4 Provision for replacement

Provision shall be made to facilitate the removal and replacement of bearings. For bridges

where it is not practical to provide staging from the ground, provision shall be made in both

the superstructure and substructure design for jacking points. Sliding parts of bearings and

deck joint components subject to wear shall be detailed, to facilitate their replacement.

7.5 Provision for resetting

When it is known that excessive substructure settlements or rotations, or other movements

due to mining subsidence or other effects are likely to occur in the life of a bridge, then

provision for resetting bearings shall be made and the joints shall be designed to

accommodate these movements or to facilitate resetting.

7.6 Provision for handling

Suitable handling attachments and lifting points shall be provided for heavy bearings and

joints, to facilitate handling, placement and location.

7.7 Access

Adequate space shall be provided around bearings and major deck joints, to facilitate their

inspection and maintenance.

7.8 Durability

All surfaces of bearings and deck joints shall be protected against corrosion.

Bearings shall be placed wherever possible on pedestals, to protect them against water or

dirt spilling from deck joints and against accumulations of dirt and debris.

8 MOVEMENT RESTRAINTS

8.1 General

Where it is required to restrict the movement of a bridge totally, partially or in a selected

direction, restraints shall be provided.

NOTE: These restraints may be provided as part of or separate from the bearings, and may take

the form of keys, keepers or side restraints.

8.2 Design loads

Restraints shall be designed to resist, at the ultimate limit state, either the design load

effects or the relevant component of the minimum lateral restraint capacity as specified in

AS 5100.2, whichever is the greater.

I n addition to forces due to external loads, design load effects due to longitudinal and

transverse movements of the superstructure and misalignment of restraints shall be

considered.

If restraint against translation is to be provided by several bearings, consideration shall be

given to the effects of any clearances between working parts of the bearings and their

guides, and the effects of the stiffness of the structure on the distribution of the resulting

loads between the bearings.

AS 5100.4—2004 12

© Standards Australia .au 9 ALIGNMENT OF BEARINGS AND DECK JOINTS

Bearings and deck joints shall be positioned such that they function as assumed in the design.

Bearings shall normally be set level. Where bearings are required to be set on an incline, allowance shall be made for the longitudinal and transverse components of vertical loads on the bearings.

For all bridges, especially those with wide, skewed or horizontally curved superstructures, due consideration shall be given to the alignment of each bearing in regard to the actual directions of movements and rotations of the superstructure.

10 ANCHORAGE OF BEARINGS

10.1 Pot bearings

Pot bearings shall be anchored at all stages, including construction, by a combination of friction and mechanical anchors. For incrementally launched bridges, pot bearings may be anchored to the superstructure by friction alone.

The anchorage capacity of pot bearings shall be calculated to resist the resultant shear force (H *) as follows:

ua *min.kmin.f *R N H φμφ+≤ . . . 10.1

where

φf = strength reduction factor for friction

= 0.6

μkmin. = characteristic low friction coefficient for the interface as given in

Table 10.1; or

determined by tests to provide a 95% probability of exceedance

*min.N = minimum concurrent load acting in compression normal to the bearing anchorage interface calculated in accordance with AS 5100.2

φ = strength reduction factor

φR ua = design capacity of mechanical anchors calculated in accordance with

AS 5100.5 or AS 5100.6, as appropriate

I n cases of extreme dynamic load fluctuations, e.g., railway bridges and earthquake load cases, μkmin. shall be taken as zero.

In the absence of more precise calculations, *min.

N shall allow for a contingent reduction in vertical load not less than the dynamic load allowance determined in accordance with AS 5100.2.

The requirement specified in this Clause shall be met for the ultimate limit state at all stages, including during construction.

13 AS 5100.4—2004

.au © Standards Australia TABLE 10.1

CHARACTERISTIC LOW FRICTION COEFFICIENT

FOR ANCHORAGE OF BEARINGS Interface

Characteristic low friction coefficient, μkmin. Steel on concrete

0.50 Steel on steel grit blasted, metal zinc

sprayed or zinc silicate primed surfaces

0.30 Steel on steel clean mill scale surfaces

0.20 Hot-dip-galvanized surfaces 0.08

10.2 Elastomeric bearings

Elastomeric bearings to be anchored by friction only shall satisfy the requirements of

Clause 12.6.7 and the contact surface shall be sufficiently rough to ensure that the friction

or restrained force can be developed.

When the use of laminated elastomeric bearings as fixed bearings by the provision of

dowels is being considered, it shall be ensured that—

(a)

the shear and bending stresses in the dowels are properly investigated; and (b) the dowel strength and stiffness are adequate.

Where frictional restraint, as specified in Clause 12.6.7, is inadequate to restrain the bearing

in position and, thus, prevent slippage or crawling, then restraint shall be provided.

Restraints shall be removable to allow bearing replacement.

Adhesives including epoxies shall not be used to provide restraint or fixing of elastomeric

bearings.

10.3 Restraining devices for earthquakes

Where the horizontal restraints of conventional bearings are inadequate under earthquake

effects, additional restraining devices, such as ties, shear keys, stops and dowels, shall be

provided with the specific aim of preventing dislodgment of the superstructure from the

support structure.

10.4 Provision for horizontal movements

Bearings and deck joints shall accommodate the horizontal movements calculated in

accordance with AS 5100.2, including movements due to earthquake effects.

11 LOADS RESULTING FROM RESISTANCE TO MOVEMENT

11.1 General

Bearings and deck joints, their connections and associated supporting elements shall be

designed to transmit forces arising from resistance to movement due to friction of

mechanical and sliding components, and the rotational, compressive and shear stiffnesses of

elastomeric elements.

I n considering the effects of bearings on structures, the force component due to frictional

effects on sliding contact surfaces shall be calculated for permanent effects only.

At the ultimate limit state, the frictional force shall be calculated using the load factors

specified in AS 5100.2.

AS 5100.4—2004 14

© Standards Australia .au 11.2 Frictional restraint of sliding surfaces

For design purposes, the appropriate characteristic maximum and minimum coefficients of friction (μ) for stainless steel sliding on permanently lubricated pure PTFE at the serviceability limit state shall be taken as 0.03 and zero respectively.

The characteristic maximum coefficient of friction (μ) for pure unlubricated PTFE on stainless steel shall be taken as 0.06.

The characteristic coefficient of friction for other types of sliding surfaces shall be based on test data.

11.3 Reaction to sliding of multiple bearings

Where a number of bearings are so arranged that the adverse forces, resulting from reaction to movement by some, are partly relieved by the forces resulting from the reaction to movement by others, the respective coefficients of friction (μa ) and (μr ) shall be estimated as follows, unless a more precise investigation has been made:

μβμa a =

. . . 11.3(1)μβμr r = . . . 11.3(2)where

μa

= adverse coefficient of friction μr

= relieving coefficient of friction μ = characteristic coefficient of friction for the bearing as given in Clause 11.2βa , βr = factors dependent on the numbers of bearings n a and n r , which are exerting

adverse and relieving forces respectively, as given in Tables 11.3(A)

and 11.3(B)

TABLE 11.3(A)

VALUES OF βa

TABLE 11.3(B)

VALUES OF

βr

15 AS 5100.4—2004

.au © Standards Australia 11.4 Shear resistance of elastomeric bearings

For elastomeric bearings where shear movements are accommodated by shear in the

elastomer, the shear force (H ) due to a movement δs shall be calculated as follows:

s s δK H = . . . 11.4

where

K s = shear stiffness of an elastomeric bearing

δs = maximum resultant vector shear displacement tangential to the bearing

surface

12 ELASTOMERIC BEARINGS

12.1 General

This Clause sets out the minimum requirements for the design of single unbonded layer

(plain pads and strips) and laminated elastomeric bearings.

NOTE: Wherever possible, elastomeric bearings should be selected from standard sizes as given

in Appendix A, and checked to meet all the criteria contained in this Standard.

12.2 Physical properties of elastomer

The elastomer used in the manufacture of bridge bearings shall comply with Appendix B.

Values of the shear modulus (G ) and the bulk modulus (B ) relevant to the elastomer

hardnesses detailed in Appendix B are given in Table 12.2.

For plain pads and strips, the durometer hardness shall be IRHD 60 or above.

Appropriate values of G and B shall be adopted for alternative elastomer formulations based

on appropriate test results.

The physical properties of natural rubber vary significantly at temperatures below ?10°C.

For areas where the lowest one-day mean ambient temperatures fall below ?10°C,

variations in the value of G of the elastomer shall be assessed or the use of alternative

formulations considered, or both.

TABLE 12.2

ELASTOMER PROPERTIES Durometer hardness Shear modulus,G Bulk modulus, B

IRHD ±5 MPa MPa

53 0.69 2 000

60 0.90 2 000

12.3 General requirements

Laminated elastomeric bearings shall have a side cover of elastomer with a minimum

design thickness of 6 mm to protect the edges of the steel plates.

Tolerances for the manufacture of laminated elastomeric bearings shall be as given in

Appendix C.

The steel plates shall be bonded to the elastomer during vulcanizing and the edges of all

plates shall be lightly rounded and the corners chamfered. For non-standard bearings having

thicker layers of elastomer under high compression, plate thickness shall be checked to

ensure that the plate does not fail in tension (see Clause 12.6.6).

AS 5100.4—2004 16

© Standards Australia .au Contact surfaces of a bearing shall be dimensioned to allow an edge clearance of at least 25 mm all round. This allows tolerance when positioning bearings and ensures adequate edge support.

Relatively large tolerances shall be provided to meet the specified stiffness properties of elastomeric bearings and also inherent variations of stiffness that occur in elastomers with variations of strain. Where it is significant, the effects of these tolerances and variations shall be considered in the design of the structure. They may be assumed to be of the total order of ±20%.

12.4 Design principles

12.4.1 General

Elastomeric bearings shall be designed to resist serviceability limit state loads and movements.

12.4.2 Bearing rotations

The structural elements of the bridge shall be detailed with the objective that, at completion of construction, the loaded faces of the elastomeric bearing are parallel.

The elastomeric bearing shall then be designed to accommodate rotations due to traffic loading and other transient effects, thermal effects and long-term permanent effects in combination with an initial lack-of-parallelism due to construction tolerances.

Where superstructure members are erected directly on to previously prepared bearings, pre-existing rotations in the superstructure members shall be determined by calculation or measurement and increased by a rotation of not less than 0.005 radians, to permit for construction tolerances. The rotation to account for initial lack of parallelism may be taken as zero where either—

(a)

the superstructure members are initially supported above the bearings and the remaining spaces are then fully grouted; or (b) the superstructure is cast directly on to the installed bearing.

12.5 Basis of design

12.5.1 General

Elastomeric bearings accommodate translation and rotation by elastic deformation. The deflection of the elastomer under compressive load is influenced by its shape and where reinforcing plates are bonded to the elastomer, the design shall be based on the assumption that there is no relative movement at the steel and elastomer interface.

The design of elastomeric bearings shall be in accordance with Clause 12.6. Pads, strips and laminated elastomeric bearings with shape factors outside the limits specified in Clause 12.5.2 require special consideration in the design.

12.5.2 Shape factor

The shape factor (S ) of a layer of elastomer shall be the area under compression divided by the area free to bulge, and shall be calculated for layers without holes as follows:

(a) For laminated elastomeric bearings :

e b Pt A S = . . . 12.5.2(1)

where

A b = bonded surface area

P = surface perimeter

17 AS 5100.4—2004

.au © Standards Australia t e = effective thickness of the individual elastomer layer in compression (due

to vertical load or rotation)

= t i

for an inner layer . . . 12.5.2(2)

= 1.4t c for a cover layer . . . 12.5.2(3)

t i = thickness of the individual inner layer of elastomer in laminated elastomeric bearing

t c = thickness of a cover layer of laminated elastomeric bearing

(b) For plain pad bearings : e r Pt A S = . . . 12.5.2(4)

where

A r = total rubber plan area

t e = 1.8t

. . . 12.5.2(5)

t = total thickness of elastomer in laminated elastomeric bearing or thickness of plain pad or strip bearing

(c) For strip bearings : e 2t w S = . . . 12.5.2(6)

where

w = width of strip

t e = 1.8t . . . 12.5.2(7)

Where dowel holes are to be provided, a special assessment of the shape factor (S ) shall be

made allowing for the holes and the restraint to bulge provided by the dowels.

For the design criteria specified in Clause 12, the shape factor (S ) shall be as follows:

(i) For plain pads and strips.............................................................................1 ≤ S ≤ 4.

(ii) For internal layers of laminated elastomeric bearings.................................4 ≤ S ≤ 12.

12.6 Design requirements

12.6.1 Maximum shear strain in laminated elastomeric bearings

To ensure that the total shear strain developed in the elastomer is not excessive, the following requirement at the edge of the bonded surface shall be satisfied:

G 2.6

sh sr sc ≤++εεε . . . 12.6.1(1)

where

εsc = shear strain at edge of bonded surface due to loads normal to bearing surfaces

εsr = shear strain at edge of bonded surface due to relative rotation of bearing

surfaces

εsh = shear strain at edge of bonded surface due to forces tangential to the bearing

surface or movement of the structure, or both

AS 5100.4—2004 18

© Standards Australia .au The values of shear strains shall be calculated as follows:

c sc 6εεS = . . . 12.6.1(2)where

εc = compressive strain due to loads normal to the bearing surfaces (based on the

effective plan area A eff )

=

()2eff 213S G A N + for internal layers only . . . 12.6.1(3)

N = compressive load on a bearing, serviceability limit state

A eff = effective loaded plan area nominally equal to the projected area common to top and bottom when a bearing is distorted tangentially

= ????????b a A b a b 1δδ for rectangular bearings . . . 12.6.1(4)

= A b ?δs d for circular bearings . . . 12.6.1(5) δa = maximum shear displacement tangential to bearing surface in

the direction of dimension a due to movements of the structure

and tangential forces

a = plan dimension of the edge of the bonded surface of rectangular

bearings parallel to the span of the bridge

δb = maximum shear displacement tangential to bearing surface in

the direction of dimension b due to movements of the structure

and tangential forces

b = plan dimension of the edge of the bonded surface of the

rectangular bearing transverse to the span of the bridge

δs = maximum resultant vector shear displacement tangential to the

bearing surface, e.g., temperature effects and the like, and

tangential force effects, e.g., braking forces and the like in the

directions of the dimensions a and b

d = plan diameter of circular bearing at edg

e o

f bonded surface

εsr = t

t b a i 2

b 2a 2αα+ for rectangular bearings . . . 12.6.1(6) = t t d i 22α for circular bearings . . . 12.6.1(7)εsh =

t s δ for all bearings . . . 12.6.1(8)

αa = angle of rotation parallel to the span of the bridge

αb = angle of rotation transverse to the span of the bridge α = maximum angle of rotation, i.e., change in angle between top and

bottom surfaces of bearing in critical direction

19 AS 5100.4—2004

.au © Standards Australia To limit the effect of fatigue, which is likely to be significant only in short spans, anchor spans and lightweight structures, the following shall also be satisfied:

G 0.69 1.4 scl ≤ε . . . 12.6.1(9)

where

εscl = shear strain at edge of bonded surface due to live load and impact only

= 6S εcl . . . 12.6.1(10)

NOTE: In the calculations for total shear strain, bulk modulus is not included.

12.6.2 Compressive stress on elastomeric bearings

The mean compressive stress on elastomeric bearings shall be determined as follows:

(a)

The mean compressive stress (N /A b ) on laminated elastomeric bearings shall not be greater than 15 MPa. (b) The mean compressive stress (N /A r ) on plain pad and strip bearings shall not be

greater than the lesser of 2GS or 5 MPa.

12.6.3 Shear strain due to tangential movements and forces

To limit tangential distortion and to minimize rolling of the edges of the bearings or

tendency of the steel plates to bend, the following shall be satisfied:

εsh ≤ 0.5

The tangential movements and forces shall not reduce the projected plan area common to

the top and bottom faces of a bearing by more than 20%, i.e.—

(a)

A eff ≥ 0.8A b for laminated elastomeric bearings; and (b) A eff ≥ 0.8A r for plain pads and bearing strips.

12.6.4 Rotational limitation

For plain pads and laminated elastomeric bearings, the total compressive deflection (d c )

shall satisfy the following:

(a) For rectangular bearings :

3 b a c b a d αα+≥ . . . 12.6.4(1)

(b) For circular bearings :

3 c d d α≥ . . . 12.6.4(2)

(c) For plain strip bearings :

3a c w d α≥ . . . 12.6.4(3)

12.6.5 Stability of bearings

The stability of bearings shall be determined as follows:

(a) Plain pad and strip bearings For plain pad and strip bearings, the thickness shall not

be greater than one quarter of the least lateral dimension.

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