AS 5100.2—2004 AP-G15.2/04 (Incorporating Amendment No. 1) AS 5100.2—2004
Australian Standard® Bridge design
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Part 2: Design loads
This Australian Standard® was prepared by Committee BD-090, Bridge Design. It was approved on behalf of the Council of Standards Australia on 4 November 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 00375. 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.
Keeping Standards up-to-date
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Australian Standards® are living documents that reflect progress in science, technology and systems. To maintain their currency, all Standards are periodically reviewed, and new editions are published. Between editions, amendments may be issued. Standards may also be withdrawn. It is important that readers assure themselves they are using a current Standard, which should include any amendments that may have been published since the Standard was published. Detailed information about Australian Standards, drafts, amendments and new projects can be found by visiting www.standards.org.au Standards Australia welcomes suggestions for improvements, and encourages readers to notify us immediately of any apparent inaccuracies or ambiguities. Contact us via email at
[email protected], or write to Standards Australia, GPO Box 476, Sydney, NSW 2001.
AS 5100.2—2004 AP-G15.2/04 (Incorporating Amendment No. 1)
Australian Standard® Bridge design Part 2: Design loads
Accessed by SMEC AUSTRALIA on 11 Sep 2011
Originated as HB 77.2—1996. Revised and redesignated as AS 5100.2—2004. Reissued incorporating Amendment No. 1 (April 2010).
COPYRIGHT © Standards Australia All rights are reserved. No part of this work may be reproduced or copied in any form or by any means, electronic or mechanical, including photocopying, without the written permission of the publisher. Published by Standards Australia GPO Box 476, Sydney, NSW 2001, Australia ISBN 0 7337 5628 X
AS 5100.2—2004
2
PREFACE This Standard was prepared by the Standards Australia Committee BD-090, Bridge Design, to supersede HB 77.2—1996, Australian Bridge Design Code, Section 2: Design loads. This Standard incorporates Amendment No. 1 (April 2010). The changes required by the Amendment 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-G15.2/04. 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 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 structure.
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Significant differences between this Standard and HB 77.2 are the following: (i)
Highway bridge design loads The design model for road traffic loads has been completely redefined to make provision for potential future increases in legal load limits. Not only does the design load reflect the projected increased loads but it has also been modified so that it more closely represents the full spectrum of vehicle configurations and traffic patterns. It no longer ‘looks like’ a semi-trailer but is purely a mathematical model. This new model incorporates both moving traffic loads and stationary traffic loads, and also incorporates the effects of special vehicles. The width of the design load, the standard design load and the standard design lane have been increased to 3.2 m, to reflect future loads and truck configurations. Provision has been made for the heavy load platform (HLP) design load, which may be specified by the relevant authority if required.
(ii)
Dynamic load allowance The dynamic load allowance for railway bridges has been modified to incorporate the results of experience and investigations of fatigue in transom top steel railway bridges. The dynamic load allowance for road bridges has been adapted to reflect the recent changes in the Canadian Highway Bridge Design Code, modified to suit Australian conditions.
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AS 5100.2—2004
(iii) Bridge barriers The clauses for design loads of road bridge barriers have been updated to be consistent with performance level definition and selection specified in AS 5100.1. Many of the clauses are based on recently developed AASHTO* documentation, suitably modified to reflect local Australian conditions. (v)
Earthquake loading The earthquake loading clause has been updated to reflect the intent of AS 1170.4 as applicable to bridges.
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. Statements expressed in mandatory terms in Notes to Tables are deemed to be requirements of this Standard.
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The term ‘informative’ has been used in this Standard to define the application of the appendix to which it applies. An ‘informative’ appendix is only for information and guidance.
* American Association of State Highway and Transportation Officials
AS 5100.2—2004
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CONTENTS
1
Page SCOPE AND GENERAL ........................................................................................... 5
2
REFERENCED DOCUMENTS.................................................................................. 6
3
DEFINITIONS............................................................................................................ 6
4
NOTATION................................................................................................................ 6
5 6
DEAD LOADS ......................................................................................................... 10 ROAD TRAFFIC ...................................................................................................... 12
7
PEDESTRIAN AND BICYCLE-PATH LOAD ........................................................ 21
8
RAILWAY TRAFFIC............................................................................................... 22
9
MINIMUM LATERAL RESTRAINT CAPACITY .................................................. 30
10
COLLISION LOADS ............................................................................................... 31
11 12
KERB AND BARRIER DESIGN LOADS AND OTHER REQUIREMENTS FOR ROAD TRAFFIC BRIDGES .................................................................................... 33 DYNAMIC BEHAVIOUR........................................................................................ 37
13
EARTH PRESSURE................................................................................................. 40
14 15
EARTHQUAKE FORCES........................................................................................ 42 FORCES RESULTING FROM WATER FLOW ...................................................... 48
16
WIND LOADS ......................................................................................................... 57
17
THERMAL EFFECTS .............................................................................................. 60
18 19
SHRINKAGE, CREEP AND PRESTRESS EFFECTS ............................................. 64 DIFFERENTIAL MOVEMENT OF SUPPORTS ..................................................... 64
20
FORCES FROM BEARINGS ................................................................................... 65
21
CONSTRUCTION FORCES AND EFFECTS.......................................................... 65
22 23
LOAD COMBINATIONS ........................................................................................ 66 ROAD SIGNS AND LIGHTING STRUCTURES .................................................... 67
24
NOISE BARRIERS .................................................................................................. 69
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APPENDIX A
DESIGN LOADS FOR MEDIUM AND SPECIAL PERFORMANCE LEVEL BARRIERS.................................................................................. 71
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AS 5100.2—2004
STANDARDS AUSTRALIA Australian Standard Bridge design Part 2: Design loads 1 SCOPE AND GENERAL 1.1 Scope This Standard sets out minimum design loads, forces and load effect for road, railway, pedestrian and bicycle bridges, and other associated structures. 1.2 General Structures shall be proportioned for the design loads, forces and load effects in accordance with Clauses 5 to 24, as appropriate. NOTE: If the authority approves, the designer may vary any of the loads set out in this Standard on the basis of engineering measurements and calculations, provided the provisions of AS 5100.1 are complied with.
The design loads and forces shall be considered as acting in combinations as set out in Clause 22. Each individual bridge shall be assessed to ascertain whether any other loads, forces or load effects are applicable for that particular design. The magnitude of these additional forces or load effects, and their combination with other loads shall be consistent with the principles set out in AS 5100.1.
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On the front sheet of the bridge drawings, the following details relating to design loads shall be shown where relevant: (a)
The Standard used.
(b)
Any significant variation to the minimum design loads as set out in this Standard.
(c)
Traffic load, e.g., 300LA and SM1600, including lateral position, if critical, and the number of design lanes.
(d)
Design traffic speed.
(e)
Fatigue criteria, including number of cycles and route factor.
(f)
Pedestrian load.
(g)
Collision load on piers, where applicable, or alternative load paths provided.
(h)
Design wind speeds.
(i)
Flood data, e.g., design velocities, levels, debris, and the like.
(j)
Earthquake zone.
(k)
Differential settlements and mining subsidence effects allowed for in the design.
(l)
Foundation data where not shown elsewhere.
(m)
Barrier performance level.
Where required, the construction methods and sequence, or any other specific limitations, shall be indicated on the bridge drawings. www.standards.org.au
© Standards Australia
AS 5100.2—2004
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2 REFERENCED DOCUMENTS The following documents are referred to in this Standard: A1
AS 1170 1170.4*
Minimum design loads on structures Part 4: Earthquake loads
1726
Geotechnical site investigations
4678
Earth-retaining structures
5100 5100.1 5100.3 5100.4 5100.5 5100.6 5100.7
Bridge design Part 1: Scope and general principles Part 3: Foundations and soil-supporting structures Part 4: Bearings and deck joints Part 5: Concrete Part 6: Steel and composite construction Part 7: Rating of existing bridges
AS/NZS 1170 1170.0 1170.1 1170.2
Structural design actions Part 0: General principles Part 1: Permanent, imposed and other actions Part 2: Wind actions
Austroads Vehicle Classification Scheme TRB-NCHRP 350
Recommended Procedures for the Safety Performance Evaluation of Highway Features
3 DEFINITIONS For the purpose of this Standard, the definitions in AS 5100.1 apply. 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 units for length and load in all expressions or equations are to be taken as metres (m) and kilonewtons (kN) respectively, unless specifically noted otherwise. The unit for velocity is in metres per second, unless specified otherwise.
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An asterisk ( * ) placed after a symbol as a superscript denotes a design action effect due to the design load for either the ultimate limit state or the serviceability limit state.
* This Standard refers to the superseded 1993 edition of AS 1170.4 and not to the current edition of AS 1170.4, published in 2007. © Standards Australia
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AS 5100.2—2004
TABLE 4 NOTATION Symbols
Clause reference
A
axle load
8.6.1
Ad
area, equal to the thickness of the pier normal to the direction of the water flow, multiplied by the height of the water flow
15.3.1
projected area of debris
15.5.4
area, equal to the width of the pier parallel to the direction of the water flow, multiplied by the height of the flow; or plan deck area of the superstructure
15.3.2
A deb AL
15.4.3
Ap
bridge area in plan
As
wetted area of the superstructure, including any railings or parapets, projected on a plane normal to the water flow; or projected area of debris
At
area of the structure for calculation of wind load
16.3.1
a
acceleration coefficient
14.3.3
b
width between traffic barriers; or overall width of the bridge between outer faces of parapets
6.5 16.3.3
C
earthquake design coefficient
14.5.4
Cd
drag coefficient
15.3.1
Ch
earthquake design coefficient
14.5.7
CL
lift coefficient
15.3.2
Cm
moment coefficient
15.4.4
CT
base number of load cycles
8.7.4
depth of the superstructure, including solid parapet, if applicable
16.3.3
d sp
wetted depth of the superstructure (including any railings or parapets) projected on a plane normal to the water flow (see Figure 15.4.2(B))
15.4.2
d ss
wetted depth of the solid superstructure, excluding any railings but including solid parapets, projected on a plane normal to the water flow
15.4.2
d wgs
vertical distance from the girder soffit to the flood water surface upstream of the bridge
15.4.2
d
F Accessed by SMEC AUSTRALIA on 11 Sep 2011
Description
Froude number
16.5 15.4.2 and 15.4.4
15.5.4(B)
F BM
braking force applied by multiple vehicles
6.8.2
F BS
braking force applied by a single vehicle
6.8.2
Fc
centrifugal force
6.8.1
FL
ultimate longitudinal or transverse inward load
12.3
FT
ultimate transverse outward load
12.3
FV
ultimate vertical downward load
12.3
* Fds
serviceability design drag force
15.3.1
* Fdu
ultimate design drag force
15.3.1
* FLs
serviceability design lift force
15.3.2 (continued)
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AS 5100.2—2004
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TABLE 4 (continued) Symbols * FLu
Clause reference
ultimate design lift force
15.3.2
f*
fatigue design stress range
8.7.3
GB
distance of wheel load to the track centre-line
10.5.2
Gg
total unfactored dead load including superimposed dead load
14.5.2
g
acceleration due to gravity
6.8.1
H CF
centrifugal force resulting from railway loads
8.6.1
He
minimum effective height
H u*
horizontal design earthquake force
14.5.2
h
height of the top rail; or depth of fill cover, in millimetres
11.5 6.12
Table 11.2.3
14.7.3
hd
average height of the columns or piers supporting the superstructure length (Ld )
k
coefficient
I
importance factor
14.5.3
L
effective span; or loaded length; or span of the member between posts
6.9 8.6.2 11.5
L bs
minimum support length measured normal to the face of an abutment or pier
14.7.3
Ld
length of the superstructure to the next expansion joint
14.7.3
Lf
span of main girders, trusses or stringers; or cross-girder spacing for cross-girders
8.7.4
LL
vehicle contact length for longitudinal loads
11.3
largest of the values L1 , L 2, ……L n
8.4.2
LT
vehicle contact length for transverse loads
11.3
Lv
distance between centres of axle groups; or vehicle contact length for vertical loads
8.7.1 12.3
span lengths of a continuous structure
8.4.2
Lα
characteristic length
8.4.1
Mi
importance factor
24.2
Ms
shielding multiplier
24.1.4
* M gs
serviceability design superstructure moment
15.4.4
* M gu
ultimate design superstructure moment
15.4.4
mi
discrete mass
14.5.4
n
number of standard design loads; or effective number of cycles; or number of continuous main girder spans
nT
number of equivalent stress cycles of amplitude (f *) per train, which depends on L f and L v
8.7.4
Pr
proximity ratio
15.4.2
pn
net pressure for hoardings and freestanding walls
24.5
design wind pressure
23.4
L max.
L 1, L 2, L n
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Description
q
*
22.3
6.5 8.7.4 Table 8.4.2
(continued)
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AS 5100.2—2004
TABLE 4 (continued) Symbols
Clause reference
Rf
structural response factor
14.5.5
r
radius of curve
8.6.1
S
site factor
14.3.4
Sr
relative submergence
15.4.2
T
structure period of the first dominant mode of free vibration, in the direction under consideration; or temperature
14.5.4 Figure 17.3
V
design speed
8.6.1
Vs
mean velocity of water flow for serviceability limit states at the level of the superstructure or debris as appropriate; or design wind speed for serviceability limit states
15.3.1
Vu
mean velocity of water flow for ultimate limit states at the level of the superstructure or debris as appropriate
15.3.1 16.3
Vw
design wind speed for the ultimate limit states, or serviceability limit state
23.4
operating speed
6.8.1
W BM
load due to multiple lanes of the M1600 moving traffic load for the length under consideration
6.8.2
W BS
load due to a single lane of the M1600 moving traffic load for the length under consideration, up to a maximum of 1600 kN
6.8.2
Wc
load due to multiple lanes of the M1600 moving traffic load for the length under consideration
6.8.1
Wts*
serviceability design transverse wind load
16.3
Wtu*
ultimate design transverse wind load
16.3
* Wvs
serviceability design vertical wind load
16.5
* Wvu
ultimate design vertical wind load
16.5
v
y
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Description
average flow depth
16.3
15.5.4(A)
y gs
average vertical distance from the girder soffit to the bed assuming no scour at the span under consideration
15.4.2
α
dynamic load allowance
6.7.2
δ
displacement under self weight
14.5.4
γg
load factor for dead load
5.2
γ ge
load factor for the density of soils and groundwater
5.4
γ gb
load factor for railway ballast and track loads
5.5
γ gs
load factor for superimposed dead load
5.3
γ LL
load factor for live load
10.4.4
γ WF
ultimate load factor for water flow
15.2.1
θ
superelevation of the road
6.8.1
θs
angle of skew of the support measured from a line normal to the span
14.7.3
θw
angle between the direction of the water flow and the transverse centre-line of the pier
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Figure 15.3.1
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AS 5100.2—2004
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5 DEAD LOADS 5.1 General The nominal dead load shall be calculated from the dimensions shown on the drawings and the mean value of the weight per unit volume of the materials. A figure based on the densities of the materials, the percentage of reinforcement and other appropriate factors shall be adopted. Wherever possible, design densities shall be based on measurements of the materials to be used. Selecting a high value of density may be conservative when considering some limit states, but may not be conservative when considering stability, stresses at transfer of prestress and the like. If insufficient information is available to accurately assess the mean weight per unit volume, calculations shall be performed using a range of values and the most critical case shall be used for the design. 5.2 Dead load of structure Dead load shall be considered as the weight of the parts of the structure that are structural elements and any non-structural elements that are considered unlikely to vary during construction and use of the structure, such as parapets and kerbs of steel or concrete. To obtain the design dead loads for ultimate and serviceability limit states, the nominal dead load shall be multiplied by the appropriate load factor (γ g ) given in Table 5.2. For all types of structures, except structures of balanced cantilever or anchor cantilever design, or similar, the appropriate value of γ g shall be applied to the dead load of all parts of the structure. For the exceptions, the values of γ g given in Item (b) or Item (c) of Table 5.2 for unfavourable or favourable dead load shall be applied to the appropriate parts of the structure. TABLE 5.2 LOAD FACTORS (γg) FOR DEAD LOAD OF STRUCTURE
Type of structure
(a)
All structures, except for Items (b) and (c)
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(b) Balanced cantilever structures At a section subjected to approximately equal favourable and unfavourable dead loads (c)
Anchor cantilever structures At a section subjected to unequal favourable and unfavourable dead loads
Type of construction
Ultimate limit states where dead load
Serviceability limit states
Reduces safety
Increases safety
Steel Concrete
1.1 1.2
0.9 0.85
1.0 1.0
All
1.1
1.0
1.0
All
1.2
1.0
1.0
NOTE: For large segmental cantilever construction, where appropriate control and monitoring are exercised over dimensions, the authority may allow a reduction of γ g to not less than 1.1 for ultimate limit states, for the case where the dead load reduces safety.
5.3 Superimposed dead load Superimposed dead load shall be considered as the weight of all materials forming the loads on the structure, which are not structural elements and which vary during construction and use of the structure. NOTE: Examples of superimposed dead load include surfacing material, footway filling, tram tracks, pipes, conduits, cables and other utility services, and additional concrete to compensate for the hog of prestressed beams. © Standards Australia
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AS 5100.2—2004
If a separate wearing surface is to be placed when the bridge is constructed or if placement of a separate wearing surface is anticipated in the future, allowance shall be made for its weight in the superimposed dead load. The design superimposed dead loads for ultimate and serviceability limit states shall be obtained by applying the appropriate load factor (γ gs), given in Table 5.3, to the nominal superimposed dead loads on the structure. For special cases, and subject to the approval of the relevant authority, the values of γ gs to be applied to the nominal superimposed dead load may be reduced to an amount not less than those given in Item (b) of Table 5.3. It shall be ensured that the nominal superimposed dead load is not exceeded during the life of the bridge. TABLE 5.3 LOAD FACTORS (γgs) FOR SUPERIMPOSED DEAD LOAD (SDL)
Type of structure
A1
Type of load
Ultimate limit states where SDL Reduces safety
Increases safety
Serviceability limit states
(a)
All structures, except for Item (b)
Permanent Removable
2.0 2.0
0.7 0
1.3 1.3
(b)
Special cases On major structures where superimposed dead loads are controlled by the relevant authority.
Permanent Removable
1.4 1.4
0.8 0
1.0 1.0
5.4 Soil loads on retaining walls and buried structures Soil loads and properties of the soil shall be obtained from AS 4678. The design of foundations and soil-supporting structures shall be carried out in accordance with this Standard and AS 5100.3. Where required during the design, the density of soils shall be factored by the load factor (γge ) given in Table 5.4. TABLE 5.4 LOAD FACTORS (γge) FOR THE DENSITY OF SOILS AND GROUNDWATER
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Type of soil
Ultimate limit states where soil Increases load
Reduces load
Serviceability limit state
Controlled fill with regular testing of soil density
1.25
0.85
1.0
All other fills and in-situ soils
1.5
0.7
1.2
Groundwater
1.0
1.0
1.0
NOTE: Variation in water levels shall be taken into account by using design levels based on a return period of 1000 years for the ultimate limit state or 100 years for the serviceability limit state.
5.5 Railway ballast and track loads Railway ballast and track shall be considered as removable superimposed dead loads. The design loads for the ultimate and serviceability limit states shall be obtained by applying the appropriate load factor (γ gb ) given in Table 5.5 to the nominal ballast and track loads. For bridges such as half through structures, if it is possible to fill with ballast to a much greater depth than normally specified, the maximum amount of ballast possible on the bridge shall also be determined and the nominal amount of ballast shall be taken as not less than 0.7 times that maximum amount.
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AS 5100.2—2004
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TABLE 5.5 LOAD FACTORS (γgb) FOR RAILWAY BALLAST AND TRACK LOADS Type of structure All structures
Ultimate limit states where load Reduces safety
Increases safety
Serviceability limit states
Ballast and track
1.7
0.7
1.3
Transom track
1.4
0.9
1.2
Type of load
6 ROAD TRAFFIC 6.1 General Road traffic load is the load resulting from the passage of vehicles, either singly or in groups, or pedestrians. The magnitude, direction and positioning of loads in this Standard produce effects in structures that approximate the effects of vehicles or groups of vehicles. The load models are not intended to be the same as actual vehicles. 6.2 SM1600 loads The abbreviation SM1600 represents the design loads W80, A160, M1600 and S1600 traffic design loads. All road bridges shall be designed to resist the following: (a)
The traffic loads specified in this Standard, which approximate the effects induced by moving traffic, stationary queues of traffic and pedestrian traffic.
(b)
The most adverse effects induced by the following loading elements, combinations of these elements and their corresponding load factors: (i)
W80 wheel load.
(ii)
A160 axle load.
(iii) M1600 moving traffic load. (iv)
S1600 stationary traffic load.
(v)
HLP320 or HLP400, if required by the authority.
(vi)
Dynamic load allowance (α).
(vii) Number and position of traffic lanes.
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(viii) Accompanying lane factors (ALF). (ix)
Centrifugal forces (F c).
(x)
Braking forces (F BS , F BM).
(xi)
Fatigue load.
(xii) Pedestrian load. 6.2.1 W80 wheel load The W80 wheel load models an individual heavy wheel load. It shall consist of an 80 kN load uniformly distributed over a contact area of 400 mm × 250 mm. The W80 wheel load shall be applied anywhere on the roadway surface and to all structural elements for which the critical load is a single wheel load. 6.2.2 A160 axle load The A160 load models an individual heavy axle. It shall consist of the load shown in Figure 6.2.2. © Standards Australia
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AS 5100.2—2004
FIGURE 6.2.2 A160 AXLE LOAD
6.2.3 M1600 moving traffic load The M1600 moving traffic load models the loads applied by a moving stream of traffic. The M1600 load shall be positioned laterally within a 3.2 m standard design lane as shown in Figure 6.2.3. The moving traffic load shall consist of a uniformly distributed load together with a truck load as shown in Figure 6.2.3. The uniformly distributed component of the M1600 moving traffic load continues under the truck and shall be considered as uniformly distributed over the width of a 3.2 m standard design lane. The uniformly distributed component of the M1600 moving traffic load shall be continuous or discontinuous and of any length as may be necessary to produce the most adverse effects. Likewise, the truck position and variable spacing shall be determined so as to produce the most adverse effects. Where a single tri-axial group from the M1600 moving traffic load, including the UDL component, controls, the dynamic load allowance (α) shall be as given in Table 6.7.2. The UDL component shall be continuous or discontinuous and of any length as necessary to produce the most adverse effects.
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A1
FIGURE 6.2.3 M1600 MOVING TRAFFIC LOAD
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AS 5100.2—2004
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6.2.4 S1600 stationary traffic load The S1600 stationary traffic load models the loads applied by a stationary queue of traffic. The S1600 stationary traffic load shall consist of a uniformly distributed load together with a truckload as shown in Figure 6.2.4. The uniformly distributed component of the S1600 stationary traffic load continues under the truck and shall be considered as uniformly distributed over the width of a 3.2 m standard design lane. The S1600 truck shall be positioned laterally within a 3.2 m standard design lane as shown in Figure 6.2.4. The uniformly distributed component of the S1600 stationary traffic load shall be continuous or discontinuous and of any length as may be necessary to produce the most adverse effects. Likewise, the truck position and variable spacing shall be determined so as to produce the most adverse effects. A1
FIGURE 6.2.4 S1600 STATIONARY TRAFFIC LOAD
6.3 Heavy load platform The heavy load platform design load HLP320 or HLP400, or an alternative platform design load, may be specified by the authority. Details of HLP320 and HLP400 load configurations are specified in AS 5100.7. The HLP320 and HLP400 heavy load platform loads shall be assumed to centrally occupy two standard design lanes or the road carriageway width, whichever is the lesser.
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The heavy load platform loads shall be positioned laterally on a bridge as specified by the authority. To account for errors in the positioning of actual vehicles, bridges shall be designed for the effects of the heavy load platform loads positioned up to 1.0 m laterally in either direction from the specified position. Where the two standard design lanes containing the heavy load platform loads are positioned such that one or more design traffic lanes are unobstructed, then a load of half of either the M1600 moving traffic load or the S1600 stationary traffic load, to create the worst effect, shall be placed in those lanes, unless the authority specifies otherwise. 6.4 Tramway and railway loads Where road bridges are to carry tramway or railway traffic, the operating authority for the utility shall be consulted to determine the appropriate design loads and load factors.
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AS 5100.2—2004
6.5 Number of lanes for design and lateral positioning The A160, M1600 and S1600 loadings shall be assumed to occupy one standard design lane of 3.2 m width. The number and position of standard design lanes shall be as follows: n =
b (rounded down to next integer) 3. 2
. . . 6.5
where n = number of standard design loads b = width between traffic barriers, in metres, unless specified otherwise These standard design lanes shall be positioned laterally on the bridge to produce the most adverse effects. 6.6 Accompanying lane factors If more than one lane is loaded, the A160, M1600 or S1600 loading applied to the additional lanes shall be multiplied by the accompanying lane factors given in Table 6.6. TABLE 6.6 ACCOMPANYING LANE FACTORS Standard design lane number, n
Accompanying lane factor, ALFi
1 lane loaded
1.0
2 lanes loaded
1.0 for first lane; and 0.8 for second lane
3 or more lanes loaded
1.0 for first lane; 0.8 for second lane; and 0.4 for third and subsequent lanes
NOTES: 1
First lane—the loaded lane giving the largest effect.
2
Second lane—the loaded lane giving the second largest effect.
3
Third lane—the loaded lane giving the third largest effect.
The number of standard design lanes loaded and the load patterning (standard design lane numbering) shall be selected to produce the most adverse effects. For bridges that support vehicle and pedestrian traffic, the accompanying load factors shall be applied to both the vehicle and the pedestrian traffic. The total pedestrian load shall be considered as one standard design lane. Accessed by SMEC AUSTRALIA on 11 Sep 2011
6.7 Dynamic load allowance 6.7.1 General The dynamic load allowance (α) set out in this Clause specifies an increase in the traffic load resulting from the interaction of moving vehicles and the bridge structure, and shall be described in terms of the static equivalent of the dynamic and vibratory effects. For design purposes, α shall be specified as a proportion of the traffic load and shall be applied as specified in Clause 6.7.2. The dynamic load allowance applies to both the ultimate and serviceability limit states. The dynamic load allowance models the dynamic effects of vehicles moving over bridges with typical road profile irregularities. 6.7.2 Magnitude The design action is equal to (1 + α) × the load factor × the action under consideration.
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The value of α for the appropriate loading shall be as given in Table 6.7.2. For deck joints, the values for α specified in AS 5100.4 shall be used. TABLE 6.7.2 DYNAMIC LOAD ALLOWANCE (α) Loading
Dynamic load allowance (α)
W80 wheel load
0.4
A160 axle load
0.4
M1600 tri-axle group (see Note 2)
0.35
M1600 load (see Note 2)
0.30
S1600 load (see Note 2)
0
HLP loading
0.1
NOTES: 1
Dynamic load allowance is not required for centrifugal forces, braking forces or pedestrian load.
2
Including the UDL component of the traffic load.
6.7.3 Application The dynamic load allowance shall be applied to all parts of the structure extending down to the ground level. For parts of the structure below the ground level, the dynamic load allowance to be applied to each part shall be— (a)
the ground level value for a cover depth of zero;
(b)
zero for a cover depth of 2 m or more; or
(c)
a linear interpolation between depths of zero and 2 m.
For buried structures such as culverts and soil-steel structures, the dynamic load allowance to be applied to the entire structure shall be— A1
(i)
the ground level value for a cover depth of zero;
(ii)
0.1 for a cover depth of 2 m or more for loads excluding S1600. For S1600 loads, the dynamic load allowance is zero; or
(iii) a linear interpolation between depths of zero and 2 m. Accessed by SMEC AUSTRALIA on 11 Sep 2011
6.7.4 Dynamic load reversal Consideration shall be given to the reversal of the dynamic response to live load. Vibrations may continue and slowly decay after passing of traffic. In particular, the minimum reaction on bearings shall take into consideration any reduction that may occur as a result of dynamic effects. 6.8 Horizontal forces 6.8.1 Centrifugal forces For bridges on horizontal curves, allowance shall be made for the centrifugal effects of traffic load on all parts of the structure. The bridge shall be designed to resist the most adverse co-existing effects induced by the M1600 moving traffic load and the centrifugal force (Fc), in kilonewtons.
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AS 5100.2—2004
The centrifugal force (Fc) shall be assumed to act at deck level and shall be applied in accordance with the distribution of load in the M1600 moving traffic load. The centrifugal force (Fc) shall be calculated as follows: Fc =
V2 Wc rg
. . . 6.8.1(1)
≤ (0.35 + θ )Wc
. . . 6.8.1(2)
where V
= design speed, in metres per second
r
= radius of curve, in metres
g
= acceleration due to gravity (9.81 m/s2)
Wc
= load due to multiple lanes of the M1600 moving traffic load for the length under consideration, in kilonewtons. No dynamic load allowance is to be considered. Accompanying lane factors shall be applied, i.e.— j
Σ ALF
=
i
i =1
θ
× M1600 i
j
= number of design lanes
ALF i
= accompanying lane factor (see Table 6.6)
. . . 6.8.1(3)
= superelevation of the road, expressed as a ratio, e.g., 4% superelevation is expressed as 0.04
6.8.2 Braking forces Braking effects of traffic shall be considered as a longitudinal force. Braking forces shall be applied in either direction. The restraint system shall be designed to resist the most adverse co-existing effects induced by the braking force and the vertical traffic load. The braking force shall be applied in accordance with the distribution of mass of the vertical traffic load. The braking force shall be assumed to act at the road surface. The most adverse effects from the following scenarios shall be considered: (a)
Single vehicle stopping The braking force for single vehicle stopping (F BS) shall be calculated as follows:
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FBS = 0.45W BS
. . . 6.8.2(1)
200 kN < F BS < 720 kN where F BS
= braking force applied by a single vehicle
W BS = load due to a single lane of the M1600 moving traffic load for the length under consideration, in kilonewtons, up to a maximum of 1600 kN. No dynamic load allowance is to be included F BS shall be applied to any lane of a multi-lane bridge to produce the most adverse effects. (b)
Multi-lane moving traffic stream stopping The braking force for multi-lane moving traffic stream stopping (FBM ) shall be calculated as follows: FBM = 0.15WBM
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. . . 6.8.2(2)
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where F BM = braking force applied by multiple vehicles W BM = load due to multiple lanes of the M1600 moving traffic load for the length under consideration, in kilonewtons. No dynamic load allowance is to be included. Accompanying lane factors shall be applied, i.e.— j
=
Σ ALF
i =1
i
× M1600 i
. . . 6.8.2(3)
The number of lanes to be included shall be limited to those likely to carry traffic in a single direction, unless specified otherwise by the relevant authority. When assessing the effects of longitudinal forces on bridge bearings and substructures, the friction or shear displacement characteristics of expansion bearings and the stiffness of the substructure shall be taken into account. 6.9 Fatigue load effects The fatigue design traffic load effects shall be determined from 70% of the effects of a single A160 axle or 70% of a single M1600 moving traffic load, without UDL, whichever is more severe. In both cases, a load factor of 1.0 shall be used and the load effects shall be increased by the dynamic load allowance (α). The single A160 axle load or M1600 moving traffic load, without UDL, shall be placed within any design traffic lane to maximize the fatigue effects for the component under consideration. Unless determined otherwise by the relevant authority, the number of fatigue stress cycles to be used for the calculation of the fatigue capacity of the structural element under consideration shall be as follows: (a)
For the fatigue design load of 0.70 × (A160 axle load) × (1 + α): (current number of heavy vehicles per lane per day) × 4 × 10 4 × (route factor).
(b)
For the fatigue design load of 0.70 × (M1600 moving traffic load without UDL) × (1 + α): (current number of heavy vehicles per lane per day) × 2 × 10 4(L−0.5 ) × (route factor).
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Unless specified otherwise by the relevant authority, the route factor shall be— (i)
for principal interstate freeways and highways ..................................................... 1.0;
(ii)
for urban freeways............................................................................................... 0.7;
(iii) for other rural routes......................................................................................0.5; and (iv)
for urban roads other than freeways...................................................................... 0.3.
On interstate and other rural routes where there are two or more lanes in one direction, the number of heavy vehicles per lane per day shall be the total of the heavy vehicles travelling in that direction. On urban routes where there are two or more lanes in one direction, the number of heavy vehicles per lane per day shall be 65% of the total number of heavy vehicles in that direction. The fatigue design traffic load effects and relevant stress cycles shall be applied to each design lane independently. L is the effective span in metres and is defined as follows:
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AS 5100.2—2004
(A)
For positive bending moments, L is the actual span in which the bending moment is being considered.
(B)
For negative moment over interior supports, L is the average of the adjacent spans.
(C)
For end shear, L is the actual span.
(D)
For reactions, L is the sum of the adjacent spans.
(E)
For cross-girders, L is twice the longitudinal spacing of the cross-girders.
A fatigue stress cycle shall be taken to be the maximum peak to peak stress from the passage of the relevant fatigue design load. Heavy vehicles shall be as defined by the Austroads Vehicle Classification Scheme, i.e., Classes 3 to 12. The current number of heavy vehicles shall be based on the year the bridge is to be put into service. This Clause does not apply to fatigue design of roadway expansion joints. 6.10 Load factors For ultimate and serviceability limit state design loads, the load factors for design road traffic loads shall be as given in Table 6.10(A). TABLE 6.10(A) LOAD FACTORS FOR DESIGN ROAD TRAFFIC LOADS Limit state
Traffic load Ultimate
Serviceability
W80 wheel load
1.8
1.0
A160 axle load
1.8
1.0
M1600 moving traffic load
1.8
1.0
S1600 stationary traffic load
1.8
1.0
Heavy load platform load
1.5
1.0
The load factor to be applied in calculating the design centrifugal and braking forces shall be as given in Table 6.10(B).
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TABLE 6.10(B) LOAD FACTORS FOR DESIGN CENTRIFUGAL AND BRAKING FORCES Limit state
Force Ultimate
Serviceability
Centrifugal force
1.8
1.0
Braking force
1.8
1.0
Each of the design horizontal forces due to road traffic load shall be applied simultaneously with the vertical road traffic load and such load cases or any combination thereof shall be considered as a single vehicular traffic load specified in Clause 22.1.3.
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6.11 Deflection The deflection limits of a road bridge under traffic for serviceability limit state shall be appropriate to the structure and its intended use, the nature of the loading and the elements supported by it. Notwithstanding this requirement, the deflection for serviceability limit state under live load plus dynamic load allowance shall be not greater than 1/600 of the span or 1/300 of the cantilever projection, as applicable. The live load to be used for calculating deflection shall be one M1600 moving traffic load, without UDL, including dynamic load allowance, placed longitudinally in each design lane to produce the maximum deflection, taking into account the accompanying lane factors. NOTE: In calculating the deflection, the following assumptions may be made: (a)
The deflection of the bridge may be averaged across all beams.
(b)
The design cross-section of the bridge may include continuous portions of road furniture contributing to stiffness, provided that adequate connection is included to ensure composite action with the bridge deck.
In addition, road traffic bridges shall be designed so that— (a)
deflections do not infringe on clearance diagrams;
(b)
hog deflection does not exceed 1/300 of the span; and
(c)
no sag deflection occurs under permanent loads.
6.12 Distribution of road traffic loads through fill For all types of roadway pavements above structures, the distribution of SM1600 design loads, with the factors and allowances applied in accordance with this Standard, shall be as specified below, unless calculated otherwise by an analytical modelling procedure approved by the authority. This requirement shall apply to all types of roadway pavements. SM1600 design wheel loads shall be distributed through the fill cover over the structure, from the imprint of the rectangular wheel contact area at the road surface to a rectangular distribution area on the surface of the structure, proportioned in accordance with the wheel contact area dimensions.
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The length of the sides of the distribution rectangle shall be determined as follows: (a)
For depths of fill cover from 0 to 200 mm—sides of distribution rectangle = sides of wheel contact rectangle + 0.5 h, where h is the depth of fill cover in millimetres.
(b)
For depths of fill cover greater than 200 mm—sides of distribution rectangle = sides of wheel contact rectangles + 100 mm + 1.2 × (h − 200).
Where distribution areas from several wheel loads overlap, the total load may be considered to be evenly distributed on the surface over the total area of distribution. The uniformly distributed component of the SM1600 design load shall be applied with no longitudinal distribution. Transverse distribution shall be as for wheel loads. The total width of transverse distribution shall not exceed the total width of the structure supporting the fill. For single spans, the road traffic loads may be neglected when the depth of fill is more than 2.5 m and exceeds the span length. For multiple spans, road traffic loads may be neglected when the depth of fill exceeds the distance between faces of the end abutments.
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AS 5100.2—2004
7 PEDESTRIAN AND BICYCLE-PATH LOAD 7.1 General Pedestrian and bicycle-path bridges, and walkways on road and railway traffic bridges that provide public access shall be designed for the loads per square metre of loaded area as shown in Figure 7. The loaded area shall be the area related to the structural element under consideration. Dynamic load allowance need not be applied to pedestrian load. Road and rail traffic bridges with access walkways not intended for public use are not required to be designed for the simultaneous occurrence of the road and railway live load and the walkway live load. Where it is possible for a vehicle, such as a park tractor, to mount the walkway, the walkway shall be designed to carry a concentrated load of 20 kN, with no dynamic load allowance, unless specified otherwise by the authority. Where the authority requires that a pedestrian bridge or walkway be designed for crowd loading, such as for special events, a design load of 5 kPa shall be used.
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FIGURE 7 PEDESTRIAN LOADS
7.2 Service live load on walkways For structures fitted with walkways or service platform, or both, a total load of 2.2 kN shall be distributed over any 0.6 m length of walkway or platform, and multiplied by the load factors given in Table 7.3 to obtain the appropriate design load. 7.3 Load factors For ultimate and serviceability limit state design loads, the load factors for design pedestrian loads shall be as given in Table 7.3. A1
NOTE: Where a pedestrian bridge is not located above a road or railway, the authority may approve a load factor for pedestrian loads of not less than that required by AS/NZS 1170.1.
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AS 5100.2—2004
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TABLE 7.3 LOAD FACTORS FOR DESIGN PEDESTRIAN AND SERVICE LIVE LOADS Limit state
Load
Ultimate
Serviceability
Pedestrian load
1.8
1.0
Service live loads
2.0
1.0
8 RAILWAY TRAFFIC 8.1 General Railway bridges shall be designed for the loads specified in Clause 8, unless specified otherwise by the rail authority. Bridges carrying light rail, cane railways and the like shall be designed for loads specified by the relevant authority. 8.2 300LA railway traffic load The 300LA load shall consist of groups of vehicles with four axles each having a load of 300 kN, and have axle spacings of 1.7 m, 1.1 m and 1.7 m. To simulate coupled locomotives, a 360 kN axle load shall be added 2 m in front of the axle group, as shown in Figure 8.2(A). The spacing between the centres of each vehicle axle group shall vary between 12 m and 20 m to give maximum effect in the member under consideration, as shown in Figure 8.2(B).
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The position of the loads and the number of axle groups shall be selected so as to give maximum load effects in the member under consideration.
FIGURE 8.2(A) 300LA RAILWAY TRAFFIC LOADS—AXLE LOADS
FIGURE 8.2(B) 300LA RAILWAY TRAFFIC LOADS—AXLE GROUP SPACINGS © Standards Australia
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AS 5100.2—2004
8.3 Multiple track factor for railway bridges When loading a number of tracks simultaneously, the multiple track factors given in Table 8.3 shall be used, as appropriate. These factors shall be applied to the total railway traffic loads, depending on the number of loaded tracks being considered. The selection of the number of tracks to be loaded with railway traffic loads shall be such as to give the greatest live load effects in the member under consideration. TABLE 8.3 MULTIPLE TRACK FACTORS Number of tracks loaded
Multiple track factor
1
1.00
2
1.00
3
0.85
4
0.70
5 or more
0.60
8.4 Dynamic load allowance 8.4.1 General The dynamic load allowance (α) for railway live load effects shall be a proportion of the static railway live load, and shall be calculated by the methods specified in this Clause. It shall have the same value for structures of reinforced or prestressed concrete, steel, or composite construction. The value of α shall depend upon the characteristic length (L α). A distinction is made between different methods of supporting the track, i.e., with ballast or transom top structures. The dynamic load allowance applies to both the ultimate and serviceability limit states. The design action is equal to (1 + α) × the load factor × the action under consideration. In cases where a member acts in two different modes, e.g., as a deck support and also as part of the main girder, the dynamic load allowance shall be calculated separately for the structural actions in each mode, and the actions summed. 8.4.2 Characteristic length (Lα )
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For main girders and components of railway bridge superstructures, the characteristic length (L α) for each component shall be dependent on the structural geometry. The values of L α for superstructure elements shall be as given in Table 8.4.2. For bridge bearings and abutments, L α shall be the length of the supported span. For intermediate piers, L α shall be the sum of the lengths of the adjacent spans. For bearings supporting floor members, L α shall be as given in Table 8.4.2.
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TABLE 8.4.2 CHARACTERISTIC LENGTH (Lα) Case No.
Characteristic length (L α) m
Bridge members, types of bridge Floor members
1
Stringers
Cross-girder spacing +3.0
2
End stringers
Cross-girder spacing
3
Cantilevered stringers
0.5
4
Cross-girders, including cantilevered crossgirders, loaded by simply supported stringers and continuous deck elements
Twice the cross-girder spacing +3.0
5
End cross-girders, including cantilevered end cross-girders
4.0
6
Deck slabs between supports
Span of the main girders or twice the span of the deck slab, whichever is less
7
Cantilevered deck slabs
Span of the main girders or twice the distance between each support, whichever is less
8
Suspension bars or supports loaded by crossgirders only
The values to be used shall correspond to those applying to the cross-girder, as given in Cases 4 and 5
Main girders 9 10
Simply supported main girders
Span of main girders
Continuous main girders over n spans where—
for—
L m = 1/n (L 1 + L 2……+L n )
n
=
2
3
4
≥5
x
=
1.2
1.3
1.4
1.5
L α = xL m , but ≤ L max. 11
Cantilever portions of cantilever bridges
Length of the cantilevered portion plus the span of any suspended girder supported by the cantilever
12
Suspended girders of suspended span bridges
Span of the suspended girder
13
Arches
Half span
14
Plate web girders at bottom of welded stiffeners
0.5
15
Truss members:
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(a)
16
Top and bottom chords
Three times the length from adjacent panel points
(b)
Verticals
Three times the length between chords
(c)
Diagonals not intersected by members complying with this Standard
Three times the horizontal or vertical projection, whichever is the shorter
(d)
Diagonals intersected by members complying with this Standard
Six times the horizontal or vertical projection of the overall length, whichever is the shorter
Lattice girder members: (a)
Top and bottom flanges and webs
As for main girders
(b)
Lattice members
Six times the horizontal or vertical projection of the overall length from web to web, whichever is the shorter (continued)
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AS 5100.2—2004
TABLE 8.4.2 (continued) Case No.
Characteristic length (L α) m
Bridge members, types of bridge
17
Bracing members: (a)
Horizontal or vertical members parallel to or perpendicular to the track
Three times the member length
(b)
Diagonal members with respect to Item (a), Three times the projected length horizontally or if not intersected by members complying vertically, parallel to or perpendicular to the track, with this Standard whichever is the shorter
(c)
Diagonal members, with respect to Item (a), if intersected by members complying with this Standard
Six times the projected overall length horizontally or vertically, parallel to or perpendicular to the track, whichever is the shorter
where n
=
number of continuous main girder spans
L 1, L 2, L n =
span lengths of a continuous structure, in metres
L max.
largest of the values L1 , L 2, L n , in metres
=
8.4.3 Dynamic load allowance for bending effects 8.4.3.1 Ballasted deck spans The value of the dynamic load allowance (α) for bending moment for ballasted deck spans shall be as given in Table 8.4.3.1. TABLE 8.4.3.1 VALUES OF α FOR BENDING MOMENT FOR BALLASTED DECK SPAN Characteristic length (L α) m
Dynamic load allowance (α)
≤3.6
1.0
>3.6
Lα0.5 − 0.20
2.16
− 0.27
NOTE: The value of α shall not be less than 0.
8.4.3.2 Open deck spans and spans with direct rail fixation
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The value of the dynamic load allowance (α) for bending moment for open deck spans or spans with direct rail fixation shall be as given in Table 8.4.3.2. TABLE 8.4.3.2 VALUES OF α FOR BENDING MOMENT FOR OPEN DECK SPANS AND SPANS WITH DIRECT RAIL FIXATION Characteristic length (Lα) m
Dynamic load allowance (α)
≤ 2.0
1.6
> 2.0
L0.5 α − 0.20
2.16
− 0.17
NOTE: The value of α shall not be less than 0.
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8.4.4 Application For all parts of the structure extending down to the ground level, the dynamic load allowance (α) shall be as specified in Clauses 8.4.3. For culverts and soil steel structures below the ground level, α shall be linearly transitioned from the ground level value to zero at a cover depth of 2 m. For structures in embankments, the ground level shall be taken as the underside of the ballast. The dynamic load allowance established for the appropriate cover depth shall apply to the entire structure. The depth of the cover shall be measured from the underside of the ballast. 8.4.5 Dynamic load allowance for other load effects The dynamic load allowance (α) for shear, torsion and reactions shall be taken as 2/3 of the value for bending moment. Where the application of the dynamic load allowance leads to greater safety or stability, e.g., against overturning, α shall be taken as 0. Where deflections are to be calculated for serviceability loads, including dynamic load allowance, 2/3 of the dynamic load allowance shall be used. 8.4.6 Dynamic load reversal Consideration shall be given to the reversal of the dynamic response to live load. Vibrations may continue and slowly decay after passing of traffic. The frequency and rate of strain in dynamic load reversal are critical in fatigue damage accumulation. In particular, the minimum reaction on bearings shall permit for the reduction, which may occur from the results of the dynamic effects. 8.4.7 Application to dedicated lines and traffic Where detailed information is available for specific structures and track standard, and where train speeds are known, α may be determined as required by the authority. NOTE: A procedure for the determination of α is described in AS 5100.2 Supp 1.
8.5 Distribution of railway traffic load 8.5.1 General The distribution of railway live load to the supporting members shall be calculated using a rigorous analysis in accordance with the appropriate clauses of the relevant material Section of the Standard. A1
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A1
In the absence of a rigorous analysis, railway traffic loads shall be distributed as set out in Clauses 8.5.2 to 8.5.5, as appropriate. 8.5.2 Open deck steel railway bridges Timber bridge transoms shall be designed on the assumption that the maximum wheel load on each rail shall be distributed equally to all transoms or fractions thereof within a length of 1.2 m, but shall not be greater than three transoms, and the load shall be applied with a dynamic load allowance of 1.0. For the design of beams, the live load shall be distributed and shall be applied via the transoms as above. In such cases, additional longitudinal distribution of such loads shall not be assumed, and the full dynamic load allowance shall be applied to the beams.
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AS 5100.2—2004
8.5.3 Ballasted deck steel railway bridges Provided that sleepers are spaced at no more than 700 mm centres, and not less than 150 mm of ballast is provided under them, the load from each axle may be uniformly distributed longitudinally over a length of 1.1 m, and uniformly distributed laterally over a width equal to the length of the sleeper plus the minimum distance from the bottom of sleeper to the top of the beams. This width shall be not greater than 4.0 m, the distance between track centres of multiple track bridges, or the width of the deck between ballast retainers. 8.5.4 Ballasted deck concrete railway bridges Railway traffic loads on ballasted deck railway bridges shall be uniformly distributed longitudinally over a length of 1 m, plus the depth of ballast under the sleeper, plus twice the effective depth of slab. The total length shall be not greater than the axle spacing. The loads shall be uniformly distributed laterally over a width equal to the length of the sleepers plus the depth of ballast below the bottom of the sleepers, plus twice the effective depth of the concrete slab, unless limited by the extent of the structure. This width shall not be greater than the distance between centres of adjacent tracks on multiple track railway bridges. 8.5.5 Direct fixation The distribution of rail wheel loads through directly fixed track shall be determined on the basis of the relative stiffness of the rail, the rail fixing supports and the superstructure. For the determination of the rail wheel load forces, the dynamic load allowance (α) shall be based on a value of L α equal to the longitudinal distance between centre-lines of the rail track supports. 8.6 Horizontal forces 8.6.1 Centrifugal forces For railway bridges on horizontal curves, allowance shall be made for the centrifugal effects of railway traffic load by applying a centrifugal force (H CF ) corresponding to each axle load horizontally through a point 2 m above the top of the rail. The horizontal centrifugal force shall be proportional to the design railway traffic load, and for each axle, H CF , in kilonewtons, shall be calculated as follows: H CF =
0.0077V 2 A r
. . . 8.6.1
where Accessed by SMEC AUSTRALIA on 11 Sep 2011
V = design speed, in kilometres per hour A = axle load, in kilonewtons r = radius of curve, in metres The specified centrifugal force shall not be increased by the dynamic load allowance. 8.6.2 Braking and traction forces Railway bridges shall be designed for the forces arising from braking and traction forces applied to the top of the rails. They shall be proportional to the specified railway traffic load and, for 300LA load, shall have the values given in Table 8.6.2. The specified longitudinal force shall not be increased by the dynamic load allowance.
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TABLE 8.6.2 BRAKING AND TRACTION FORCES FOR 300LA LOAD Track type
Loaded length (L) m
Horizontal force kN
All
200 + 20L
L < 50 m
100
L > 50 m
100 + 15(L − 50)
Discontinuous Continuous
For continuous track, the loaded length shall be taken to be the full length of the bridge. The total longitudinal load on the bridge, as calculated from Table 8.6.2, shall be distributed to the supports in proportion to their stiffnesses. For bridges with discontinuous track, the loaded length shall be taken as the length between the discontinuity and an abutment, or as the length between discontinuities. The longitudinal load shall be distributed to the supports under the loaded length, in proportion to their stiffnesses. Continuous tracks, for the purpose of determining the longitudinal forces specified in this Clause, shall be those tracks that have no rail discontinuities either on the bridge or within 20 m of either end of the bridge. Where a structure or element carries two tracks, both tracks shall be considered as being occupied simultaneously. Loads in either direction shall be applied simultaneous to both tracks. Where elements carry more than two tracks, longitudinal loads shall be applied simultaneously to two tracks only. 8.6.3 Nosing loads Railway bridges that are intended to carry 300LA traffic loads shall be designed to resist a lateral nosing load of 100 kN applied at top of rail level in either direction and at any point along the structure. This load shall be adjusted in proportion to the actual design traffic load. Nosing loads shall not be increased by the dynamic load allowance. Nosing loads are independent from the speed and shall not be reduced at low speeds. 8.7 Fatigue load
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8.7.1 Fatigue design traffic load The fatigue design traffic load for railway bridges shall be the design railway traffic load and half of the design dynamic load allowance, with a load factor of 1.0. The distance between the centre of the axle groups (L v) shall be varied between 12 m and 20 m to produce the maximum fatigue design stress range (f* ) (see Clause 8.7.3). 8.7.2 Fatigue design stress range (f * ) The fatigue design stress range (f * ) in any element of a bridge structure, shall be derived from the passage of the fatigue design traffic load over the bridge. It shall be the algebraic difference between the maximum and minimum stresses caused by that load. Stresses and stress ranges caused by other load effects need not be included. 8.7.3 Effective number of stress cycles (n) The effective number of cycles (n) of the fatigue design stress range (f * ) to be considered in the design of the structure shall be calculated as follows: n = C Tn T
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. . . 8.7.3
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where C T = base number of load cycles for the track category as given in Table 8.7.4 n T = number of equivalent stress cycles of amplitude (f * ) per train, which depends on L f and L v (see Table 8.7.3) L f = span of main girders, trusses or stringers; or cross-girder spacing for cross-girders L v = distance between the centres of the axle groups (i.e., the length of the vehicle) TABLE 8.7.3 VALUES OF nT Lf
nT
< 2.5
240
2.5 < L f < 9.0
60.0
9.0 < L f < 25.0
⎛ ( 2 L v − Lf ) ⎞ ⎟⎟ + 2 60 ⎜⎜ Lf ⎝ ⎠ Max . 60 Min . 2
> 25.0
2.0
3
8.7.4 Track category for fatigue load The base number of load cycles (C T) for fatigue load depends on the track category and shall be as given in Table 8.7.4. TABLE 8.7.4 VALUES OF CT Track category
CT
Heavy haul
6 × 10 5
Main line freight
1 × 10 5
Branch line
1 × 10 4
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8.7.5 Multiple track bridges For elements of multiple track railway bridges that are subject to loads from more than one track, the fatigue loads, both the fatigue design traffic load specified in Clause 8.7.1 and the fatigue design stress range specified in Clause 8.7.2, shall be determined from the full fatigue design traffic load on one track, and a load on the other track(s) of 80% of their full fatigue design traffic load with no dynamic load allowance. NOTE: A more accurate calculation may be carried out by estimating the number of load events in the life of the element in which two or more trains will be loading the element under consideration at any one time. If the effect of the load from multiple tracks results in a stress range more severe than that due to a single track, a cumulative damage calculation for the cases of single-track and multiple-track loads should be performed.
8.8 Load factors For ultimate and serviceability limit state design loads, the load factors for the design railway traffic load shall be as given in Table 8.8(A).
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TABLE 8.8(A) LOAD FACTORS FOR DESIGN RAILWAY TRAFFIC LOADS Limit state Loads 300LA railway traffic load
Ultimate
Serviceability
1.6
1.0
The load factors to be applied in calculating centrifugal, nosing and longitudinal forces shall be as given in Table 8.8(B). TABLE 8.8(B) LOAD FACTORS FOR DESIGN RAILWAY TRAFFIC LOADS Limit state
Traffic load
Ultimate
Serviceability
Centrifugal forces
1.6
1.0
Nosing forces
1.6
1.0
Longitudinal braking and traction forces
1.6
1.0
Each of the design horizontal forces due to railway load shall be applied simultaneously with the vertical railway load and such load cases shall be considered a single load, as specified in Clause 22.1.3. Centrifugal forces and nosing loads shall not be applied simultaneously. 8.9 Deflection limits The deflection limits of a railway bridge under traffic for serviceability limit state shall be appropriate to the structure and its intended use, the nature of the loading and the elements supported by it. Notwithstanding this requirement, the deflection of railway bridges for serviceability limit state under live load plus dynamic load allowance shall be not greater than 1/640 of the span and 1/320 of the cantilever projection. NOTE: In order not to detract from their appearance, bridges should be designed so that their hog does not exceed 1/300 of the span and they do not sag under permanent loads.
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Railway bridges shall not deflect so that they infringe clearance diagrams. 9 MINIMUM LATERAL RESTRAINT CAPACITY To ensure that the superstructure has sufficient lateral restraint to resist lateral forces not otherwise accounted for in the design, a positive lateral restraint system between the superstructure and the substructure shall be provided at piers and abutments. For continuous superstructures, lateral restraints may be omitted at some piers provided each continuous section of the superstructure between expansion joints is adequately restrained. The restraint system for each continuous section of the superstructure shall be capable of resisting an ultimate design horizontal force normal to the bridge centre-line of 500 kN or 5% of the superstructure dead load at that support, whichever is greater. Supports providing this lateral restraint shall also be designed to resist this design force. A load factor of 1.0 shall be used.
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Restraints shall have sufficient lateral clearance to allow thermal movements, especially on wide and curved superstructures. If the transverse load requirement specified in other Parts of AS 5100 is greater than the requirements of this Clause, then the restraints may be deemed to satisfy the requirements of this Clause. 10 COLLISION LOADS 10.1 General Collision protection shall be considered in accordance with AS 5100.1. The design collision loads shall be as specified in Clauses 10.2 to 10.4, where applicable. 10.2 Collision load from road traffic Where the supports for a road bridge or a railway bridge are not located behind appropriate protective traffic barriers, they shall be designed to resist a minimum equivalent static load of 2000 kN applied at an angle of 10° from the direction of the road centre-line passing under the bridge. The load shall be applied 1.2 m above ground level. This load, in conjunction with the ultimate design dead loads on the structure, shall be considered at ultimate limit states, with a load factor of 1.0. 10.3 Loads on protection beams Where required by the relevant authority, protection beams shall be installed to protect the superstructure of low clearance bridges from impact from road vehicles. They shall be designed for the ultimate loads given in Table 10.3, with a load factor of 1.0. TABLE 10.3 ULTIMATE LOADS ON PROTECTION BEAMS Ultimate limit state kN
Loads Horizontal loads
1000 (towards the bridge) 750 (away from the bridge)
Vertical load (uplift)
500
Protection beam supports shall be capable of resisting loads 25% greater than the capacity of the protection beam itself. 10.4 Collision load from rail traffic
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10.4.1 General This Clause applies to all structures above the railway track including railway bridges over other railways, overbridges, pedestrian bridges, air space developments, developments adjacent to railways and similar structures in underground railways. This Clause does not apply to— (a)
structures that only support signals, overhead wiring, lighting or communications equipment;
(b)
gang sheds adjacent to tracks; or
(c)
waiting rooms and ticket offices on platforms.
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10.4.2 Provision of alternative load path Where an alternative load path is to be provided, the superstructure shall be designed with sufficient redundancy to be capable of supporting the deck load plus 20% of the live load at the ultimate limit state with one or more piers or columns removed. The number of supports to be removed shall be determined by a risk analysis approved by the relevant rail authority. In the case of railway bridges over other railways and where determined by the relevant rail authority, the live load for the redundancy action shall be increased from 20% to 60%. 10.4.3 Collision loads on support elements Unless specified otherwise by the rail authority, supports for bridges and structures located within 10 m of the centre-line of the railway track, not complying with the redundancy requirements of Clause 10.4.2, shall be designed to resist the following minimum collision loads applied simultaneously as an ultimate design load with a load factor of 1.0: (a)
3000 kN parallel to rails.
(b)
1500 kN normal to rails.
The loads specified in Items (a) and (b) shall be applied horizontally, 2 m above rail level and shall be applied in conjunction with the ultimate design dead loads on the structure. Where supporting elements are located between 10 m and 20 m from the centre-line of the railway track, a risk analysis shall be carried out by the relevant rail authority, which shall determine the required level of protection. If the level of redundancy does not meet the requirements of Clause 10.4.2, the piers and columns shall be designed to resist a minimum collision load applied as an ultimate load of 1500 kN, at any angle in the horizontal plane, 2 m above the rail level. NOTE: Some rail authorities permit relaxation of this loading where platforms, under certain conditions, provide protection to the columns.
10.4.4 Bridge and structural components within 10 m of the centre-line of the railway track Any part of any structure specified in Clause 10.4.1, including the superstructure, within 10 m horizontally and 5 m vertically of the centre-line of the nearest railway track, shall be designed for a 500 kN minimum collision load applied as an ultimate design load. The collision load shall be applied in any direction. Above 5 m and up to 10 m vertically above the railway track level, this collision load shall vary linearly from 500 kN at 5 m to zero at 10 m. When applied vertically upwards, the force shall be distributed over an area of one square metre, to allow for roof crushing of the railway vehicle.
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The 500 kN force may act in conjunction with the ultimate design dead load and either— (a)
γ g DL +1.0 × collision load ................................................(min. γ g shall be used); or
(b)
γ g DL + 0.4γ LL LL + 1.0 × collision load ................................. (max. γ g shall be used);
whichever gives the worst case. Relaxation of the 500 kN collision load on supporting members complying with the redundancy provisions of Clause 10.4.2 is permitted, but not for members of the superstructure. Platforms shall not be assumed to provide a degree of protection to permit reduction of the 500 kN collision load. The 500 kN collision load shall not be applied in conjunction with the loads specified in Clause 10.4.3.
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10.4.5 Underground railway, air space developments and similar situations For all underground railways and air space developments, except on platforms, the 500 kN collision load specified in Clause 10.4.4 shall be increased to 1500 kN. When applied vertically upwards, this 1500 kN collision force shall be distributed over an area of 2 m2. 10.4.6 Other design requirements In addition to the design requirements specified herein, any other design requirements of the relevant rail authority shall be satisfied. The loads specified herein shall also be applied to deflection walls. A load factor of 1.0 for the ultimate limit state shall be used. Piers and columns shall be designed for the same load combinations specified in Clause 10.4.4. 10.5 Derailment loads 10.5.1 General Railway bridges designed to carry 300LA loads shall be designed for two separate train derailment load cases as set out in Clauses 10.5.2 and 10.5.3. The loads shall be proportioned if a different live load is specified. Derailment loads shall only be considered for the ultimate limit state without dynamic load allowance, and shall act in combination with long-term permanent effects. 10.5.2 Derailment load Case A In derailment load Case A, a bridge shall be designed for the more unfavourable of the following loads: (a)
300LA load applied as wheel loads, separated by the track gauge, parallel to the track, and in the most unfavourable position within a distance G B of track centre-line.
(b)
A single point load of 200 kN, acting in the most unfavourable position within a distance G B of the track centre-line;
where G B is equal to 1.5 times the railway gauge. For the loads specified in Items (a) and (b), an ultimate load factor of 1.2 shall be used. 10.5.3 Derailment load Case B
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In derailment load Case B, a bridge shall be designed for an equivalent line load of 100 kN/m, over a length of up to 20 m, acting on the edge of the superstructure, using an ultimate load factor of 1.0. 11 KERB AND BARRIER DESIGN LOADS AND OTHER REQUIREMENTS FOR ROAD TRAFFIC BRIDGES 11.1 Kerb design loads Kerbs shall be designed to resist an ultimate design load of 15 kN per metre applied laterally at the top of the kerb. 11.2 Barriers 11.2.1 General A1
The design criteria, including loads and geometric requirements, provided in this Clause 11 and in AS 5100.1, shall be used for the following: (a)
Developing a prototype barrier for a crash test program to validate vehicle/barrier interaction performance.
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Designing minor modifications to a barrier system which has been validated by either crash testing or performance review to develop a geometrically and structurally equivalent barrier. The modified barrier shall not have features that are absent in the validated configuration, which might detract from the performance of the barrier system.
The design of any modified barrier system shall ensure that the locations and capacities of components are capable of safely redirecting all vehicles nominated in the crash test vehicle criteria for that barrier performance level in AS 5100.1. In order to minimize damage to bridge decks and for safety considerations, bridge barriers shall be designed as progressive strength systems in which barriers and then their connections fail prior to the failure of the supporting elements. 11.2.2 Traffic barrier design loads The ultimate design loads and load distribution lengths for low and regular traffic barrier performance levels as defined in AS 5100.1 are given in Table 11.2.2. The ultimate design loads and load distribution lengths for the barrier performance levels, medium and special, shall be the subject of specific investigations consistent with the criteria specified in Clause 11 and AS 5100.1, and shall be determined by the authority. NOTE: Typical design loads for medium and special performance level barriers are given in Appendix A.
A load factor of 1.0 shall apply to the design of bridge barriers. TABLE 11.2.2 TRAFFIC BARRIER DESIGN LOADS AND CONTACT LENGTHS Ultimate transverse outward load (F T)
Ultimate longitudinal or transverse inward load (F L)
Vehicle contact length for transverse loads (L T) and longitudinal loads (L L)
Ultimate vertical downward load (F V)
Vehicle contact length for vertical loads (LV )
kN
kN
m
kN
m
Low
125
40
1.1
20
5.5
Regular
250
80
1.1
80
5.5
Barrier performance level
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NOTE: The data given in the Table is based on a lateral combined barrier/vehicle deformation of 0.3 m for the low and regular performance levels.
The design of a barrier system using Table 11.2.2 requires a detailed analysis, such as a yield line analysis for a concrete parapet or an inelastic plastic moment analysis for a steel post and rail barrier. The following load combinations shall be considered: (a)
Transverse and longitudinal loads applied simultaneously.
(b)
Vertical loads only.
The loads given in Table 11.2.2 shall be applied uniformly over the relevant specified contact lengths. All loads shall be applied to the longitudinal barrier elements. The distribution of the longitudinal loads to posts shall be consistent with the continuity of rail elements. Distribution of transverse loads shall be consistent with the assumed failure mechanism of the barrier system.
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11.2.3 Effective height The effective height of a barrier is defined as the height of the resultant of the lateral resistance forces of the individual components of the barrier. Traffic barriers shall have sufficient height to ensure that the minimum effective height is achieved. Traffic barriers shall have an effective height greater than or equal to the required minimum effective height given in Table 11.2.3. The minimum effective height for the medium and special performance levels shall be the subject of specific investigation consistent with the criteria specified in Clause 11 and AS 5100, and shall be determined by the authority. The equivalent actual heights for rigid concrete parapets may be marginally higher than, but not less than, the minimum effective height. For low performance level traffic barriers, the minimum effective height given in Table 11.2.3 is 500 mm. For concrete, metal or combined concrete and metal barriers with a vertical face, the minimum actual height shall be 700 mm unless prototype testing indicates that a lower height system fulfils the requirements of the TRB-NCHRP 350 Specification. For regular performance level traffic barriers, the minimum actual height above the reference surface shall be 800 mm. For low and regular traffic performance level barriers, the effective barrier height may not be sufficient to prevent a vehicle with a high centre of gravity from tipping over. In this case, a higher actual barrier may be required, as specified by the authority. NOTE: Typical minimum effective heights for medium and special performance level barriers are given in Appendix A.
TABLE 11.2.3 MINIMUM EFFECTIVE HEIGHT OF TRAFFIC BARRIER Barrier performance level
Minimum effective height (H e) mm
Low
500
Regular
800
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11.2.4 Anchorage The yield strength of steel anchor bolts for the barrier shall be fully developed by bond, hooks, attachment to embedded plates or any combination thereof. Other means of anchorage shall be as approved by the authority. Reinforcing steel for concrete barriers shall have sufficient embedment length to develop the yield strength. A load factor of 1.05 shall apply to the design of anchor bolts and anchorage reinforcement. 11.2.5 Continuity Full lateral strength shall be provided throughout the barrier length. In the case of steel railing, splices may be provided by bolted sleeve joints or full penetration butt welds. In the splice section, for bending and shear, full rail continuity shall be provided. For tension, a minimum of 75% rail continuity shall be provided in the splice section.
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11.3 Bridge deck cantilevers The loads transmitted to the bridge deck shall be determined from the results of load testing and ultimate strength analysis of the barrier system using the loads given in Table 11.2.2. A load factor of 1.1 shall apply to the design of deck cantilevers for the effects of barrier loads. The barrier impact loads and traffic loads on the deck need not be applied simultaneously when designing the deck. 11.4 Expansion joints and end parapets 11.4.1 Post and rail type barriers Joints providing continuity between lengths of rails or across expansion or rotational joints, where the total longitudinal movement at rail level is 50 mm or less, shall be capable of transmitting 75% of the tensile strength of the theoretical gross rail section. The joints shall be capable of transmitting the full design requirement of the rail in bending at any extension of the joint. Joints across expansion or rotational joints, where the total longitudinal movement at rail level is greater than 50 mm, shall be capable of transmitting the full design requirement of the rail in bending and shear at any extension up to the full design movement at the joint plus 100 mm. Special end posts shall be provided at each side of the joint spaced as closely together as is practicable to compensate for the loss in beam action of the barrier over the joint. Joints where significant movements take place in a vertical or transverse horizontal direction shall, where possible, comply with this Clause. Where compliance is not possible, a discontinuity of the barrier is permitted. The gap between the ends of the rail shall be not greater than the calculated maximum joint gap plus 25 mm. It is emphasized that this discontinuity is only permitted in extreme cases. Some form of bridging of the ends of the rails shall be devised to prevent a vehicle that is in contact with a deflected length of barrier directly striking the end of an undeflected length. When a bridging piece is used, it shall be securely attached to the end of the rail on the approach end.
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11.4.2 Rigid parapets Panels on either side of movement joints shall be designed to stand alone and shall not have any shear transfer arrangements incorporated across the joint. Where large movements take place, which would produce a gap greater than 25 mm between panels, a bridging plate shall be incorporated. Any such bridging plate shall be securely fixed at the traffic approach end, and shall be corrosion resistant and replaceable. 11.5 Pedestrian barriers Pedestrian barriers shall be designed for a static load of 0.75 kN/m, acting simultaneously in a transverse and vertical direction on each longitudinal member, or the appropriate wind load, whichever produces the most adverse effects. Where the authority requires pedestrian barriers to restrain crowds or people under panic conditions, simultaneously acting transverse and vertical design loads of 3.0 kN/m shall be used. The static deflection of a pedestrian barrier subject to the above serviceability loadings shall not exceed— (a)
for longitudinal members, L/800; and
(b)
for post, h/300,
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where L = span of the member between posts h = height of the top rail The load factor to be applied in calculating the design barrier loadings shall be as given in Table 11.5. TABLE 11.5 LOAD FACTOR FOR DESIGN PEDESTRIAN BARRIER LOAD Limit state Load Pedestrian load
Ultimate
Serviceability
1.8
1.0
12 DYNAMIC BEHAVIOUR 12.1 General Vibration induced in bridges by the passage of vehicles and in pedestrian bridges by pedestrians may constitute a serviceability limit state if the level of vibration causes alarm or public unease as to the safety of the structures. 12.2 Road bridges 12.2.1 With walkways The vibration of a road bridge shall be investigated as a serviceability limit state if the structure is fitted with a walkway intended for public use. The serviceability design load of 0.7 × (M1600 moving traffic load without UDL), including dynamic load allowance, shall be positioned along the spans and within any design traffic lane to produce the maximum static deflection of the walkway. The deflection at the centre of the walkway shall be not greater than that shown in Figure 12.2.1, unless an investigation complying with Clause 12.2.3 is undertaken.
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This Clause shall be applied to bridges and similar structures that support platforms or other areas intended for public use.
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FIGURE 12.2.1 STATIC DEFLECTION LIMITS FOR ROAD BRIDGES WITH WALKWAYS
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12.2.2 Without walkways Where the deflection of a road bridge without a public walkway complies with the limits specified in Clause 6.11, the vibration behaviour of the bridge need not be specifically investigated. 12.2.3 Detailed dynamic analysis Where the deflection limits specified in Clause 6.11 and Clause 12.2.1 are exceeded, the vibration behaviour of the bridge shall be assessed by a rational method of analysis, using acceptance criteria appropriate to the structure and its intended use, as approved by the authority. 12.3 Railway bridges Where required by the relevant railway authority, vibration behaviour shall be assessed by a rational method of analysis using acceptance criteria appropriate to the structure and its intended use, as approved by the authority. 12.4 Pedestrian bridges For pedestrian bridges with resonant frequencies for vertical vibration inside the range 1.5 Hz to 3.5 Hz, the vibration of the superstructure shall be investigated as a serviceability limit state. Superstructures shall be proportioned such that, with one pedestrian traversing the structure, the maximum dynamic amplitude shall be not greater than the limit shown in Figure 12.4. The design pedestrian load shall have a weight of 700 N and be assumed to cross the structure at an average walking speed, i.e., 1.75 to 2.5 footfalls per second. This Clause shall also apply to bridges and similar structures that support access routes to platforms or other areas intended for public use. When the fundamental frequency of horizontal vibration is less than 1.5 Hz, special consideration shall be given to the possibility of excitation by pedestrians of lateral movements of unacceptable magnitude.
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NOTE: Bridges with low mass and damping, and expected to be used by crowds of people, are particularly susceptible to such vibrations. Refer to specialist literature.
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A1
FIGURE 12.4 DYNAMIC AMPLITUDE LIMITS FOR PEDESTRIAN BRIDGES
12.5 Special structures This Standard does not provide acceptance criteria for the dynamic behaviour of bridges with spans in excess of 100 m, or suspension and cable-stayed bridges. The dynamic behaviour of such structures under the action of traffic, wind or other loadings shall be the subject of special investigations. 13 EARTH PRESSURE 13.1 General The load effects on a retaining structure due to earth pressure loads shall be determined in accordance with AS 5100.3.
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13.2 Surcharge loads from road traffic loads Where highway live loads can approach within a distance equal to the effective height of the wall from the backface of the structure, an equivalent load caused by an additional height of fill, which diminishes over the height of the wall, as shown in Figure 13.2, shall be assumed for the purpose of calculating design earth pressure. This load shall be assumed to act above the finished grade and over the entire length of the retaining structure. The effect of foundations or other loads placed in or on the backfill, within a distance equal to the effective height of the wall, shall also be included. The live load surcharge shall be applied irrespective of whether or not there is provision for an approach slab in the bridge design.
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FIGURE 13.2 EQUIVALENT LOAD DUE TO LIVE LOAD SURCHARGE
13.3 Surcharge loads from railway loads Where sleepers supporting railway traffic load are located within a distance from the back face of a retaining wall or abutment equal to the effective height of the retaining structure, an additional surcharge load equal to the railway traffic load shall be applied as a uniform load at the level of the underside of the sleepers as shown in Figure 13.3. An equivalent load caused by an additional height of fill shall be applied, or an alternative method of allowing for surcharge shall be used. In determining the distribution of rail loads at the underside of sleepers, it is assumed that the total train load over any given length of track shall be uniformly distributed over the area defined by the length of sleepers and the length of track considered. The length of track shall be selected to produce the worst design effects. The resulting distributed loads shall be considered in the design as discrete areas of surcharge.
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These areas of surcharge shall be distributed with increasing depth below the underside of sleepers. The width of the distribution perpendicular to the track centre-line shall be increased in each direction at a slope of 1 horizontally to 2 vertically, to a maximum width of 4.5 m, to determine the maximum vertical earth pressures at depth as a result of surcharge. When adjacent rail traffic load distributions overlap, the total load shall be considered to be uniformly distributed over the area defined by the outside limits of the individual rail load distributions at that depth. The total width of the distribution so determined shall not exceed the total width of the structure supporting the fill and, if the centroid of the load is not coincident with the loaded area, the load distribution shall be taken to vary linearly to satisfy statics. When determining lateral earth pressures on retaining walls and abutments, the areas of surcharge at the underside of sleepers shall be taken to apply pressures to the structure if they are located within the zone of a 45° projection from the heel or base of the retaining structure.
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FIGURE 13.3 SURCHARGE LOADS FOR RAILWAY TRAFFIC LOADS
14 EARTHQUAKE FORCES 14.1 General
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For the design of bridge structures, earthquake effects shall be considered in accordance with this Clause. However, some factors to be used in the calculation of earthquake effects, which are in common with those given in AS 1170.4, are not repeated in this Clause. When specifically referred to, the factors given in AS 1170.4 shall be used. Other parts of AS 1170.4 shall not be used for earthquake design of bridges. The provisions for earthquake design in this Clause are applicable to bridges of conventional superstructure types, such as slab, beam and slab, box girder and truss types, with spans not greater than 100 m. For other bridges, specialist advice shall be sought for the assessment of earthquake effects. Not all bridges are required to be designed for earthquake forces. Where required, earthquake forces shall be determined by either— (a)
static analysis; or
(b)
dynamic analysis (response spectrum analysis or time history analysis).
The method of analysis depends on the bridge earthquake design category and the bridge structural configuration, as specified in Clause 14.4. The bridge earthquake design category depends on the following: (i)
The bridge classification (see Clause 14.3.2).
(ii)
The acceleration coefficient (see Clause 14.3.3).
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14.2 Limit state The earthquake effects calculated in accordance with Clause 14 shall be considered as design effects at the ultimate limit state, for member strengths, overall stability of both the structure and its components and horizontal movements. 14.3 Bridge earthquake design category 14.3.1 General The bridge earthquake design category (BEDC) shall be as given in Table 14.3.1, for the appropriate value of the product of acceleration coefficient and site factor (aS), where a is the acceleration coefficient and S is the site factor and the bridge classification. TABLE 14.3.1 BRIDGE EARTHQUAKE DESIGN CATEGORY (BEDC) Product of acceleration coefficient and site factor (aS)
Bridge classification Type III
Type II
Type I
aS ≥ 0.2
BEDC-4
BEDC-3
BEDC-2
0.1 ≤ aS < 0.2
BEDC-3
BEDC-2
BEDC-1
aS < 0.1
BEDC-2
BEDC-1
BEDC-1
14.3.2 Bridge classification Bridges and associated structures, such as approach retaining walls, shall be classified as follows: (a)
Type III Bridges and associated structures that are essential to post-earthquake recovery, as determined by the relevant authority.
(b)
Type II Bridges that are designed to carry large volumes of traffic or bridges over other roadways, railways or buildings.
(c)
Type I Bridges not of Type II or Type III.
14.3.3 Acceleration coefficient The acceleration coefficient (a) shall be as specified in AS 1170.4.
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14.3.4 Site factor The site factor (S) shall be as specified in AS 1170.4 for the appropriate soil profile below the founding level. The soil profile shall be established from geotechnical data and classified in accordance with AS 1726. Interpolation for soil profiles in between those given in AS 1170.4 is permitted. 14.4 Requirements for earthquake design 14.4.1 General The method of analysis of earthquake effects and any additional requirements shall be as specified in Clauses 14.4.2 to 14.4.5, depending on the bridge earthquake design category. Where the relevant authority considers that a bridge structure is particularly important or has unusual or special features, the requirements for earthquake design for a more severe BEDC may be adopted. 14.4.2 Requirements for BEDC-1 Bridge structures in BEDC-1, where the maximum span is less than or equal to 20 m, need not be analysed for earthquake forces. www.standards.org.au
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For bridge structures in BEDC-1, where the maximum span exceeds 20 m, effects of horizontal earthquake forces, determined using static analysis in accordance with Clause 14.5, shall be considered. For bridge structures in BEDC-1, which do not require analysis for earthquake forces, the minimum lateral restraint provisions of Clause 9 apply. For other bridges in BEDC-1, the detailing of restraining devices, bearings and deck joints shall be in accordance with Clause 14.7. 14.4.3 Requirements for BEDC-2 For bridge structures in BEDC-2, the effects of earthquake forces shall be determined using either static analysis, in accordance with Clause 14.5, or a dynamic analysis in accordance with Clause 14.6. Where the maximum span is less than or equal to 35 m, the effects of horizontal earthquake forces only need be considered. Where the maximum span exceeds 35 m, the effects of both horizontal and vertical earthquake forces shall be considered. For all bridges in BEDC-2, the detailing of structural members, restraining devices, bearings and deck joints shall be in accordance with Clause 14.7. 14.4.4 Requirements for BEDC-3 For bridge structures in BEDC-3, the effects of both horizontal and vertical earthquake forces shall be considered. Where there is one dominant mode of free vibration in a particular direction, horizontal or vertical, the effects of earthquake forces in that direction shall be determined using either static analysis in accordance with Clause 14.5, or a dynamic analysis in accordance with Clause 14.6. Where more than one mode of free vibration contributes to the dynamic response or the bridge structure is complicated or irregular in its mass or stiffness distribution in any direction, or both, the effects of earthquake forces shall be determined using a dynamic analysis in accordance with Clause 14.6. For all bridges in BEDC-3, the detailing of structural members, retaining devices, bearings and deck joints shall be in accordance with Clause 14.7. 14.4.5 Requirements for BEDC-4
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For bridge structures in BEDC-4, the effects of both horizontal and vertical earthquake forces shall be determined using a dynamic analysis in accordance with Clause 14.6, and the detailing of structural members, restraining devices, bearings and deck joints shall be in accordance with Clause 14.7. 14.5 Static analysis 14.5.1 General Horizontal design earthquake forces shall be determined in the direction of each principal axis or in the major orthogonal directions of the structure. These horizontal forces shall be assumed to act non-concurrently and shall be considered as separate load cases. Where required, a vertical design earthquake force shall be determined, and shall be considered independently of the horizontal design earthquake forces. 14.5.2 Horizontal earthquake force
( )
The total horizontal design earthquake force H u* in each direction shall be applied at a vertical level that corresponds to the mass centroid of the bridge deck when considered in elevation. The design force shall be distributed along the length of the bridge, in accordance with the distribution of the mass of the bridge deck. A separate design force shall be © Standards Australia
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determined for and applied to each continuous section of the bridge deck considered in each principal direction. The horizontal design earthquake force equation:
(H ) * u
shall be determined from the following
⎛ CS ⎞ ⎟⎟G g H u* = I ⎜⎜ ⎝ Rf ⎠
. . . 14.5.2(1)
within the limits— H u* ≥ 0.02G g ; and
. . . 14.5.2(2)
⎛ 2.5a ⎞ ⎟⎟G g H u* ≤ I ⎜⎜ ⎝ Rf ⎠
. . . 14.5.2(3)
where I
= importance factor (see Clause 14.5.3)
C
= earthquake design coefficient (see Clause 14.5.4)
S
= site factor (see Clause 14.3.4)
R f = structural response factor (see Clause 14.5.5) G g = total unfactored dead load including superimposed dead load (see Clause 5) a
= acceleration coefficient (see Clause 14.3.3)
14.5.3 Importance factor The importance factor (I) shall be as given in Table 14.5.3. TABLE 14.5.3 IMPORTANCE FACTOR Structure type
Importance factor, I
III
1.25
II and I
1.00
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14.5.4 Earthquake design coefficient The earthquake design coefficient (C) shall be determined for each horizontal and vertical direction separately from the following equation: C=
1.25a T
2
. . . 14.5.4(1)
3
where T (in seconds) is the structure period of the first dominant mode of free vibration in the direction under consideration. The structure period (T) shall be determined by structural analysis based on a recognized theoretical approach. For bridge structures in BEDC-1 only, T may be approximated from— T = 0.063 δ
. . . 14.5.4(2)
where δ is the displacement under self-weight, in millimetres, with gravity applied in the direction of interest, i.e., horizontal or vertical. www.standards.org.au
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For bridge structures in BEDC-1 only and with a more general mass distribution, T may be approximated from— Σmi (δ i )
2
T = 2π
. . . 14.5.4(3)
gΣ (miδ i )
The structure is represented by a number of discrete masses (m i) in kilograms, while δ i , in metres, is the deflection at the centroid of mass (m i ) due to a force of (m i g) applied at the centroid in the direction of interest. 14.5.5 Structural response factor The structural response factor (R f ) shall be the minimum value given in Table 14.5.5 for the appropriate bridge structural system. TABLE 14.5.5 STRUCTURAL RESPONSE FACTOR Bridge structural system
Structural response factor (R f)
Piers and deck form a continuous frame to resist horizontal earthquake force
6.0
Deck continuous over piers, supported on bearings
5.0
Bridges with single column piers to resist horizontal earthquake force
3.5
Bridges with simply supported spans
3.0
14.5.6 Vertical earthquake force The total vertical design earthquake force, acting either up or down, shall be determined using the procedures of Clause 14.5.2, considering the structure period of the dominant mode of free vibration in the vertical direction. The vertical design force shall not be less than 50% of the maximum horizontal design earthquake force in either direction. The vertical design earthquake force does not include normal gravity force. Vertical earthquake forces shall be applied to the structure in accordance with the distribution of mass. The distribution of forces between the superstructure and the substructure shall be in accordance with the stiffness of the bearings or connections. Where vertical earthquake forces do not produce adverse critical effects, they shall be ignored.
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The vertical earthquake force shall be considered independently of the horizontal earthquake forces. 14.5.7 Abutments and retaining walls The seismic design of abutments and retaining walls shall take into account forces from static earth pressures, seismically induced lateral earth pressures, additional forces arising from wall and backfill inertia effects and the transfer of seismic forces from the bridge deck. The effects of vertical acceleration shall be omitted. The calculation of seismically induced lateral earth pressures shall be in accordance with accepted engineering principals such as the pseudo-static Mononobe-Okabe method. For freestanding abutments or retaining walls that may displace horizontally without significant restraint, the earthquake design coefficient equals to one half the acceleration coefficient (C h = 0.5a). Abutments shall be proportioned to slide rather than tilt and provisions shall be made to accommodate horizontal seismically induced abutment displacements of up to 250a mm.
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For freestanding abutments and retaining walls that are restrained from horizontal displacement by anchors or batter piles, the earthquake design coefficient (C h) equal to 1.5a. 14.6 Dynamic analysis Dynamic analysis, when used, shall be performed generally in accordance with AS 1170.4. The analysis method may be either a response spectrum analysis or a time history analysis. For the response spectrum analysis method in accordance with AS 1170.4, scaling of results, directional effects and torsion are not applicable to bridge structures, and shall be ignored. A sufficient number of modes of free vibration shall be included in the total response so that, for each direction, at least 90% of the structure’s mass has been accounted for in the participating mass. The effects of dynamic earthquake forces shall be considered in the horizontal directions corresponding to the direction of each principal axis, or in the major orthogonal directions of the structure and the vertical direction, as specified in Clause 14.4. The effects in each direction shall be considered independently. The analysis shall take account of torsional effects by use of a suitable three-dimensional mathematical model of the structure, which represents the spatial distribution of the mass and stiffness of the structure to an extent which is adequate for the determination of the significant features of its dynamic response. 14.7 Structural detailing requirements for earthquake effects 14.7.1 General
A1
For all bridges, good detailing practices and design for ductile behaviour shall be employed where practicable, to guard against the effects of unexpected seismic disturbances. Sufficient ductility to deal with unexpected seismic disturbances shall be deemed to be achieved in bridges with a Bridge Design Category of BEDC-1 or BEDC-2 if the structure is analysed using a response factor (R f ) equal to 2.0, and the elements designed for the resulting actions. Particular attention shall be given to the prevention of dislodgment of the superstructure from its support system and the provision of viable, continuous and direct load paths from the level of the bridge deck to the foundation system.
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14.7.2 Restraining devices Where the horizontal restraints of conventional bearings are inadequate under earthquake effects, 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. Restraining devices and connections shall be designed to withstand the horizontal design earthquake forces calculated in accordance with Clause 14.5 or Clause 14.6, but not less than the minimum lateral restraint force specified in Clause 9. Vertical restraint devices shall be provided at all supports where the vertical design earthquake force opposes and is greater than 50% of the static reaction under permanent loads. The vertical restraint device shall be designed to resist not less than 10% of the vertical reaction from the permanent effects of the support. Due to the nature of earthquake loads, horizontal restraints cannot be assumed to rely on any component of friction. For assessment of the structure under any load combination which includes earthquake effects, the friction coefficient between any material types shall be equal to zero. 14.7.3 Provision for horizontal movements Bearings and deck joints shall accommodate the horizontal movements due to earthquake effects calculated in accordance with Clause 14.5 or Clause 14.6.
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Where excessive movements, which are outside the range of conventional bearings or deck joints are expected, additional devices may be used to limit movements under earthquake loadings only. These special devices, such as buffer bearings, shall be designed to be activated after a large, but tolerable, horizontal movement to prevent failure of sliding bearings and deck joints. Bearing seats supporting expansion ends of the superstructure for bridges in BEDC-2, BEDC-3 and BEDC-4 shall be designed to provide a minimum support length measured normal to the face of an abutment or pier (Lbs ) of—
(
)
Lbs = (200 + 1.7 Ld + 6.7 hd ) 1 + 0.000125θ 2s × 10 −3
. . . 14.7.3
where L d = length of the superstructure to the next expansion joint h d = average height of the columns or piers supporting the superstructure length Ld θ s = angle of skew of the support measured from a line normal to the span
14.7.4 Soil behaviour For soil behaviour, the following shall be taken into consideration: (a)
The effects of excessive settlement of approach embankments and allowances made for increased earth pressure on earth retaining structures.
(b)
Loose granular soils, when subjected to seismic loading of sufficient duration and intensity, may suddenly lose their strength and behave as viscous liquids. This possibility of soil liquefaction shall be investigated where saturated sandy and silty soils within 10 m of the ground surface have a standard penetration test value of 10 or less.
14.7.5 Ductile behaviour 14.7.5.1 General requirements For bridge structures in BEDC-2, BEDC-3 and BEDC-4, a clearly defined collapse mechanism shall be established. The structural members shall be ductile at the potential plastic hinge locations defined in the mechanism. Minimum ductility requirements for the design of these structural members under earthquake design loads shall be as specified in AS 5100.5 and AS 5100.6. These requirements are to ensure that the required ductility at potential plastic hinges can be achieved.
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14.7.5.2 Pile to pile cap connection For bridge structures in BEDC-2, BEDC-3 and BEDC-4, the connection between each pile and its pile cap shall be designed to resist a tensile force of not less than 10% of N * for the pile. 15 FORCES RESULTING FROM WATER FLOW 15.1 General When a bridge crosses a river, stream or any other body of water, it shall be designed to resist the effects of water flow and wave action, as applicable. The design shall include an assessment of how the water forces may vary in an adverse manner under the influence of debris, log impact, scour and buoyancy of the structure. Tidal and wave actions shall be considered on bridges across large bodies of water, estuaries and open sea.
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15.2 Limit states 15.2.1 Ultimate limit states The ultimate limit states define the capability of a bridge to withstand, without collapse, any flood of a magnitude up to and including that with a 2000 year average return interval, whichever produces the most severe effect. It can be accepted that scour of the stream bed and considerable damage to approaches and embankments may take place, provided that the structural integrity of the bridge is maintained. As the critical design condition may occur at the flood level which just causes overtopping of the superstructure, an estimate of the return interval of such a flood shall be made and, if appropriate, this condition shall be considered in the design. Where the critical design condition occurs at an average return interval of less than 2000 years, the ultimate load factor (γWF ) shall be obtained from Figure 15.2.1, but shall be not greater than 2.0. A1
FIGURE 15.2.1
ULTIMATE LOAD FACTOR (γWF)
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15.2.2 Serviceability limit states The serviceability limit states define the capability of the road and bridge systems to remain open during a serviceability design flood or to sustain an overtopping flood without damage to bridges, culverts, floodways or embankments within the system. The serviceability design flood shall be that with a 20 year average return interval. 15.3 Forces on piers due to water flow 15.3.1 Drag forces on piers In bridge structures subjected to water flow effects, the fluid forces on the piers are dependent on the pier shape, the water velocity and the direction of the water flow. The design drag forces parallel to the plane containing the pier (as shown in Figure 15.3.1) shall be calculated as follows: (a)
( )
Ultimate design drag force Fdu* : Fdu* = 0.5 CdVu2 Ad
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. . . 15.3.1(1)
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( )
Serviceability design drag force Fds* :
(b)
Fds* = 0.5 C dVs2 Ad
. . . 15.3.1(2)
where C d = drag coefficient, depending upon pier shape Vu
= mean velocity of water flow for ultimate limit states at the level of the superstructure or debris as appropriate
Vs
= mean velocity of water flow for serviceability limit states at the level of the superstructure or debris as appropriate
Ad
= area, equal to the thickness of the pier normal to the direction of the water flow, multiplied by the height of the water flow
In the absence of more exact estimates, the value of C d shall be assumed as follows: C d = 0.7 (semi-circular pier nosing) = 1.4 (square end pier nosing) = 0.8 (wedge, sharper than 90°, nosing) 15.3.2 Lift forces on piers The design lift forces, perpendicular to the plane containing the pier (as shown in Figure 15.3.1) shall be calculated as follows: (a)
( )
* : Ultimate design lift force FLu * FLu = 0.5C LVu2 AL
(b)
. . . 15.3.2(1)
( )
Serviceability design lift force FL*s : FL*s = 0.5C LVs2 AL
. . . 15.3.2(2)
where C L = lift coefficient, which depends on the angle between the water flow direction and the plane containing the pier AL
= area, equal to the width of the pier parallel to the direction of the water flow, multiplied by the height of the flow
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In the absence of more exact estimates, the value of C L shall be assumed as follows: C L = 0.9 for θw ≤ 30° = 1.0 for θw > 30° where θ w is the angle between the direction of the water flow and the transverse centre-line of the pier. NOTE: In plate or wall-type piers angled to the direction of flow, transverse lift-type forces can be significant.
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FIGURE 15.3.1 DRAG AND LIFT FORCES ON PIERS
15.4 Forces on superstructures due to water flow 15.4.1 General A superstructure that is partially or fully submerged in a flood is subjected to— (a)
a drag force normal to its longitudinal axis;
(b)
a vertical lift force (positive upwards); and
(c)
a moment about the girder soffit level (clockwise positive with the water flow from left to right).
The loads specified in Items (a), (b) and (c) shall be determined in accordance with Clauses 15.4.2, 15.4.3 and 15.4.4, as appropriate. 15.4.2 Drag force on superstructures The drag force on superstructures shall be calculated as follows:
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(a)
( )
Ultimate design drag force Fd*u : Fdu* = 0.5C dVu2 As
(b)
. . . 15.4.2(1)
Serviceability design drag force ( Fds* ): Fds* = 0.5C dVs2 As
. . . 15.4.2(2)
where C d = drag coefficient As
= wetted area of the superstructure, including any railings or parapets, projected on a plane normal to the water flow
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The value of C d for superstructures shall be obtained from Figure 15.4.2(A). The relative submergence (S r) and the proximity ratio (P r) shall be calculated as follows: Sr = Pr =
d wgs
. . . 15.4.2(3)
d sp y gs
. . . 15.4.2(4)
d ss
where d wgs = vertical distance from the girder soffit to the flood water surface upstream of the bridge (see Figure 15.4.2(B)) d sp
= wetted depth of the superstructure (including any railings or parapets) projected on a plane normal to the water flow (see Figure 15.4.2(B))
y gs
= vertical average distance from the girder soffit to the bed assuming no scour at the span under consideration (see Figure 15.4.2(B))
d ss
= wetted depth of the solid superstructure (excluding any railings but including solid parapets) projected on a plane normal to the water flow (see Figure 15.4.2(B))
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FIGURE 15.4.2(A) SUPERSTRUCTURE Cd
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FIGURE 15.4.2(B) DIMENSIONS
15.4.3 Lift force on superstructures The lift force on a superstructure shall be calculated as follows: (a)
( )
* Ultimate design lift force FLu : * FLu = 0.5 C LV u2 AL
(b)
. . . 15.4.3(1)
( )
Serviceability design lift force FLs* : FLs* = 0.5 C L Vs2 AL
. . . 15.4.3(2)
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where C L = lift coefficient A L = plan deck area of the superstructure The value of C L shall be obtained from Figure 15.4.3. Two lift forces shall be calculated at each S r . The upper value of C L shall be used when determining the resistance of the structure to overturning and the tie down requirements for the superstructure. Where upward lift forces on the superstructure are possible, a positive tie-down system shall be provided. The lower value of C L , a downward force, shall be considered in the design of the deck, girders, substructure and foundations. In determining the design flood load for each of these components, the downward force shall be combined with the moment as described in Clause 15.4.4.
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FIGURE 15.4.3 SUPERSTRUCTURE CL
15.4.4 Moment on a superstructure The drag and lift forces generate a moment about the longitudinal axis of the superstructure. The moment at the soffit level at the centre-line of the superstructure shall be calculated as follows: (a)
(
)
Ultimate design moment M g* u : * M gu = 0.5 C m Vu2 As d sp
(b)
. . . 15.4.4(1)
(
)
Serviceability design moment M g*s : M g*s = 0.5 C m Vs2 As d sp
. . . 15.4.4(2)
where C m = moment coefficient
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The value of C m shall be obtained from Figure 15.4.4.
FIGURE 15.4.4 SUPERSTRUCTURE Cm
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15.4.5 Loads on superstructures with superelevation The loads on a superstructure with a positive superelevation (upstream face raised) of up to 4% shall be calculated as described in Clauses 15.4.2 to 15.4.4. The loads on a superstructure with a negative superelevation of up to −4% shall be calculated as described in Clauses 15.4.2 to 15.4.4, but with the following adjustments to the coefficients: (a)
The value of C d shall be increased by 5%.
(b)
The magnitude of C L shall be increased by 20%.
(c)
The value of C m shall be the same as for a level superstructure.
If the superelevation is greater than 4%, the upward lift force shall be calculated in the same manner as for wall type piers (see Clause 15.3.2) except that A L shall be taken as the plan deck area. Values of C L shall be calculated by interpolation of the values given in Clause 15.3.2. For superelevations outside this range, study of specialist literature or physical model testing shall be undertaken. 15.5 Forces due to debris 15.5.1 Depth of debris mat The depth of a debris mat varies depending on factors such as catchment vegetation, available water flow depth and superstructure span. In the absence of more accurate estimates, the minimum depth of debris mat for design shall be 1.2 m and the maximum depth shall be 3 m. 15.5.2 Debris acting on piers A debris load acting on piers shall be considered for bridges where the flood level is below the superstructure. The length of a debris mat shall be taken as one half the sum of the adjacent spans or 20 m, whichever is the smaller. The debris load shall be applied at midheight of the debris mat, assuming the top of the debris mat is at the flood level. 15.5.3 Debris acting on superstructures A debris load acting on superstructures shall be considered for bridges where the flood level is above a level of 600 mm below the soffit level. The length of the debris mat shall be the projected length of the superstructure. The debris load shall be applied at mid-height of the superstructure, including any railing or parapets. 15.5.4 Calculation of debris load
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The ultimate and serviceability design forces due to debris shall be calculated using Equations 15.5.4(1) and 15.5.4(2) respectively: (a)
( )
Ultimate design drag force Fdu* : . . . 15.5.4(1)
Fdu* = 0.5 C d Vu2 Adeb
(b)
( )
Serviceability design force Fds* : Fds* = 0.5 C d Vs2 Adeb
. . . 15.5.4(2)
where Cd
= obtained from Figure 15.5.4(A), for debris acting on piers obtained from Figure 15.5.4(B), for debris acting on superstructures
A deb = projected area of debris NOTE: The depth of debris varies depending on the catchment vegetation.
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Debris forces shall not be used concurrently with water flow forces except that, in determining the resistance of the structure to overturning, an upward lift force shall be assumed when the debris is acting on the superstructure. The upward lift force shall be the sum of the lift force, calculated using Equations 15.4.3(1) and 15.4.3(2) given in Clause 15.4.3 and the buoyancy force. A value of 0.5 for C L shall be used.
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FIGURE 15.5.4(A) PIER DEBRIS C d
FIGURE 15.5.4(B) SUPERSTRUCTURE DEBRIS C d
15.6 Forces due to log impact Where floating logs are possible, the ultimate and serviceability design forces exerted by such logs directly hitting piers or superstructure shall be calculated on the assumptions that a log with a minimum mass of 2 t will be stopped in a distance of 300 mm for timber piers, 150 mm for hollow concrete piers, and 75 mm for solid concrete piers. If fender piles or sheathing, to absorb the energy of the blow, are placed upstream from the pier, the stopping © Standards Australia
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AS 5100.2—2004
distance shall be increased. The design forces shall be calculated using the mean velocity of water flow at flood level V s for serviceability limit states, or V u for ultimate limit states, as appropriate. The forces due to log impact and debris shall not be applied concurrently. Log impact shall be applied with such other water flow forces as appropriate. 15.7 Effects due to buoyancy and lift In assessing the effects of buoyancy and lift on bridge structures, consideration shall be given to the following: (a)
The effects of buoyancy and lift on substructure, including piling, and superstructure dead loads. Buoyancy shall be applied concurrently with other water flow forces.
(b)
For beam and slab or box girder bridges, the provision of horizontal bleed holes in webs or diaphragms, or both, or vertical bleed holes in the deck to dissipate air, which may be trapped between high water level and the underside of the deck slab. Several escape paths and a minimum diameter of 50 mm for vertical bleed holes and 75 mm for horizontal bleed holes shall be used.
(c)
Provision of drainage from internal cells.
The provision of a positive tie-down system for the superstructure shall be provided for an * + Buoyancy − γ g DL , where γ g shall be the lower value given ultimate force equal to 1.5 FLu in Table 5.2. 16 WIND LOADS 16.1 General This Clause specifies design wind loads for conventional bridge structures. For windsensitive structures, such as suspension or long-span cable-stayed bridges, which may be subject to wind excited oscillations, special investigations into the dynamic behaviour of the structure shall be carried out. Wind loads on lighting, traffic signal and traffic sign structures shall be in accordance with Clause 23. Wind loads on noise barriers shall be in accordance with Clause 24. 16.2 Design wind speed 16.2.1 General
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The design wind speed shall be derived from the appropriate regional basic design wind speeds, after adjustment for— (a)
average return interval;
(b)
geographical location;
(c)
terrain category;
(d)
shielding; and
(e)
height above ground.
The average return interval shall be as specified in this Clause. The values and factors for Items (b) to (e) shall be obtained from AS/NZS 1170.2. 16.2.2 Average return interval The average return interval to be adopted shall be as follows: (a)
For ultimate limit states ........................................................................... 2000 years. The regional basic design wind speed for a 2000 year average return interval shall be as specified in AS/NZS 1170.2 for that interval.
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58
For serviceability limit states ....................................................................... 20 years, (for wind in conjunction with permanent effects only). For serviceability limit state wind loads in conjunction with road traffic loads on a structure, the selection of a wind speed for a specified return interval is not appropriate and the design wind speed shall be taken as 35 m/s in all locations. The effect of wind on road traffic load need not be considered.
16.3 Transverse wind load 16.3.1 Calculation of transverse wind load The transverse wind load shall be taken as acting horizontally at the centroids of the appropriate areas, and shall be calculated as follows: (a)
Ultimate design transverse wind load ( W tu* ): W tu* = 0.0006 Vu2 At C d
(b)
. . . 16.3(1)
Serviceability design transverse wind load ( W ts* ): W ts* = 0.0006 Vs2 At C d
. . . 16.3(2)
where Vu
= design wind speed for ultimate limit states
Vs
= design wind speed for serviceability limit states
At
= area of the structure for calculation of wind load
Cd
= drag coefficient
16.3.2 Area of structure for calculation of transverse wind load (A t)
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The area of the structure or element under consideration shall be the solid area in normal projected elevation subject to the following: (a)
Superstructures with solid parapets The area of the superstructure shall include the area of the solid windward parapet, but the effect of the leeward parapet need not be considered.
(b)
Superstructures with open parapets The total load shall be the sum of the loads for the superstructure, the windward barrier and the leeward barrier considered separately. Where there are more than two parapets or safety fences, irrespective of the width of the superstructure, only those two elements having the greatest unshielded effect shall be considered.
(c)
Piers Shielding shall not be considered.
16.3.3 Drag coefficient (Cd) The drag coefficient (C d) shall be determined as follows: (a)
Drag coefficient for all superstructures with solid elevation For superstructures with or without traffic load, C d shall be as shown in Figure 16.3.3— where b = overall width of the bridge between outer faces of parapets d = depth of superstructure, including solid parapet, if applicable
(b)
Aerodynamic shape factor for truss girder superstructures The wind force on truss girder superstructures shall be calculated by considering each component individually, using the aerodynamic shape factor specified in AS/NZS 1170.2.
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(c)
Drag coefficients for beams during erection The drag coefficient for beams and girders during erection shall be calculated for individual beams as shown in Figure 16.3.3. Shielding shall not be considered for individual beams, but may be allowed for when two or more beams are connected, provided the ratio of the clear distance between beams to the depth is not be greater than 7. Where the ratio of the clear distance between connected beams to the depth is greater than 7, the drag coefficient for the combination shall be taken as 1.5 times the value for an individual beam.
(d)
Aerodynamic shape factor for parapet railings, parapet barriers and substructures Aerodynamic shape factors shall be obtained from AS/NZS 1170.2.
A1
NOTES: 1
The values given assume a vertical elevation and a horizontal wind.
2
Where the windward face is inclined to the vertical, the drag coefficient (Cd ) may be reduced by 0.5% per degree of inclination from the vertical, subject to a maximum reduction of 30%.
3
Where the windward face consists of a vertical and a sloping part or two sloping parts inclined at different angles, the wind load shall be derived as follows: (a) The basic drag coefficient (C d) shall be calculated using the total depth of the structure. (b) For each non-vertical face, the basic drag coefficient calculated above shall be reduced in accordance with Note 2.
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(c) The total wind load shall be calculated by applying the appropriate drag coefficients to the relevant areas. 4
Where a superstructure is superelevated, Cd shall be increased by 3% per degree of inclination to the horizontal, but not by more than 25%.
5
Where a superstructure is subject to wind inclined at not more than 5° to the horizontal, C d shall be increased by 15%. Where the angle of inclination exceeds 5°, the drag coefficient shall be derived from tests.
6
Where a superstructure is superelevated and also subject to inclined wind, the drag coefficient shall be the subject of special investigation.
FIGURE 16.3.3 DRAG COEFFICIENT (Cd ) FOR SUPERSTRUCTURES WITH SOLID ELEVATION
16.4 Longitudinal wind load For piers, truss bridges and other superstructure forms, which present a significant surface area to wind loads parallel to the longitudinal centre-line of the structure, a longitudinal wind load shall be considered. The ultimate and serviceability design longitudinal wind loads shall be calculated in a manner similar to those for transverse wind loads. NOTE: Longitudinal wind loads on the superstructure may also be significant during the construction stage of some bridge types, which are not affected by these loads during service.
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16.5 Vertical wind load An upward or downward vertical wind load, acting at the centroid of the appropriate area, shall be calculated as follows: (a)
Ultimate design vertical wind load ( W vu* ): W vu* = 0.6 V u2 Ap C L 10 −3
(b)
. . . 16.5(1)
Serviceability design vertical wind load ( W vs* ): W vs* = 0.6 Vs2 Ap C L 10 −3
. . . 16.5(2)
where V u = design wind speed for ultimate limit states V s = design wind speed for serviceability limit states A p = bridge area in plan C L = lift coefficient = 0.75 Equations 16.5(1) and 16.5(2) may be used provided the angle of inclination of the wind to the structure is less than 5°. For inclinations greater than 5°, the lift coefficient shall be investigated by testing. 16.6 Wind on railway live load The effect of wind on railway live load shall be included in both ultimate and serviceability limit state load combinations and shall be considered to act with the design railway traffic load. The area to be considered in the calculation of the wind load on railway live load shall be the solid area in normal projected elevation of the train area where it protrudes beyond the projected elevation of the bridge structure. For the calculation of the projected area, a train on the bridge shall be assumed to be 3.7 m in height, taken from the top of rails. The point of application shall be taken as 1.85 m above the top of the rails. The drag factor to be used in calculating the force for wind on the bridge plus live load shall be obtained from Clause 16.3.3(a), with the height d taken as the projected area of the train and the bridge, and the width b as specified in Clause 16.3.3(a).
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17 THERMAL EFFECTS 17.1 General Daily and seasonal fluctuations in air temperature and solar radiation cause both variations in average bridge temperature and differential temperature gradients across structural members. Variation in average bridge temperature shall be used as a basis for— (a)
assessment of bearing and deck joint movement requirements; and
(b)
evaluation of design loads or load effects resulting from the restraint of associated expansion or contraction by either the form of the structure, e.g., as in portal frames and arches, or by the support and bearing stiffnesses.
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Differential temperatures within bridge superstructures result in load effects within the section. In the case of statically indeterminate or restrained structural forms, these differential temperatures also cause both longitudinal and transverse parasitic load effects, which shall be taken into account in the design. 17.2 Variation in average bridge temperature Extremes of shade air temperature appropriate to the structure location shall be as given in Table 17.2(1). Consideration shall be given to particular site characteristics, e.g., frost pockets and sheltered low-lying areas where the minimum shade air temperature may be substantially lower; and in urban and coastal areas where the minimum values may be higher than the values given in Table 17.2(1). For major or special structures, extreme shade air temperatures for the actual site shall be determined. For minor structures, consideration shall be given to increase displacements determined for the range of average bridge temperatures to allow for limited supervision and control of setting bearings and deck joints. For concrete superstructures (Types 1 and 2 shown in Figure 17.3), the minimum and maximum average bridge temperatures shall be derived from the minimum and maximum shade air temperatures by reference to Table 17.2(2). Average temperature values indicated relate to bridge cross-sections with a depth of up to 2 m. Where sections are greater than 2 m in depth, an allowance shall be made in average temperatures to account for the heat sink effect. For superstructures consisting of a concrete deck on steel girders (Type 3 shown in Figure 17.3), the range of average bridge temperatures given in Table 17.2(2) shall be extended by reducing the minimum average temperature by 5°C and increasing the maximum average by 10°C. For superstructures consisting of a steel deck on steel girders, such as pedestrian bridges, the range of average bridge temperatures given in Table 17.2(2) shall be extended by reducing the minimum average temperature by 10°C and increasing the maximum average by 20°C. TABLE 17.2(1) SHADE AIR TEMPERATURES
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Location
Height above sea level m
Inland
Coastal
Shade air temperature °C Region I North of 22.5°S
Region II South of 22.5°S
Region III Tasmania
Max.
Min.
Max.
Min.
Max.
Min.
≤1000
46
0
45
−5
37
−5
>1000
36
−5
36
−10
32
−10
≤1000
44
4
44
−1
35
−1
>1000
34
−1
34
−6
30
−6
NOTE: Coastal locations are locations that are less than 20 km from the coast.
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TABLE 17.2(2) AVERAGE BRIDGE TEMPERATURES Min. Shade air temp °C
Average bridge temp °C
−8
2
−2
4
4
8
10
12 Max.
NOTE: Linear permitted.
50
54
46
50
42
46
38
43
34
40
30
37
interpolation
of
intermediate
values
is
17.3 Differential temperature The effects of vertical differential temperature gradients through a bridge superstructure shall be derived for both positive temperature differential conditions, where solar radiation has caused a gain in top surface temperatures, and negative temperature differentials, where re-radiation of heat from the section results in relatively low top surface temperatures. Design effective vertical temperature gradients, appropriate to various regions and superstructure types, shall be as shown in Figure 17.3. These design temperature gradients have been derived for cases where decks are unsurfaced or where surfacing will be limited to 50 mm of bituminous concrete. For substantially greater thicknesses of surfacing, some reduction in design temperature gradients may be warranted. For those parts of rail bridge decks covered by ballast greater than 100 mm thick, the differential temperature distribution shall be as given in Figure 17.3, but in such cases the maximum temperature of the temperature profiles given shall apply at the top of the ballast, with a corresponding reduced temperature applying at the top of the bridge deck.
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The effects of transverse differential temperature gradients across the superstructure also needs to be considered for some structures, such as very wide bridges.
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Bridge type A1
1
Concrete beam and slab, or slab
2
Concrete box girders
3
Concrete slab on steel trough, box or I girders
AS 5100.2—2004
Typical cross-section
Effective temperature gradient
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Regional values for T Key
Region Positive differential temperature gradients Negative differential temperature gradients
T
Regional category
1
20°C Continental-inland of Great Dividing Range or further than 200 km from coast (typical Canberra, Alice Springs)
2
18°C Coastal temperature—No further than 200 km from coast (typical Perth, Adelaide. Melbourne, Sydney)
3
14°C Coastal sub-tropical, monsoonal (typical Brisbane, Darwin)
NOTE: The temperature gradient given for deck slabs forming closed box cells should only apply for slab thicknesses, including any internal fillets, of d less than 300 mm. Therefore, any deck slab, or part thereof, over a box cell with a thickness greater than 300 mm, should be subject to the general effective vertical temperature gradient shown.
FIGURE 17.3 DESIGN EFFECTIVE VERTICAL TEMPERATURE GRADIENTS www.standards.org.au
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17.4 Limit states Thermal effects shall be considered, where they adversely affect a structure, as follows: (a)
For ultimate limit states The thermal effects that are applicable to the structure, as determined from the relevant material Section of this Standard, shall be considered, and the ultimate design effects shall be determined using a load factor of 1.25.
(b)
For serviceability limit states All thermal effects shall be considered, and the serviceability design effects shall be determined using a load factor of 1.0.
The effects of vertical and transverse differential temperatures shall be considered separately. 18 SHRINKAGE, CREEP AND PRESTRESS EFFECTS 18.1 Shrinkage and creep effects Consideration shall be given to the effects of shrinkage and creep in concrete structures. The characteristics of different types and different ages of concrete shall be considered. Shrinkage and creep strains shall be calculated in accordance with AS 5100.5. The design effects shall be calculated using the nominal dead loads of the structure and a load factor of 1.2 for ultimate limit states, and 1.0 for serviceability limit states. Shrinkage and creep effects shall be included in serviceability design checks for stresses, cracking and deflection. Where shrinkage and creep affect the strength or stability of a structure or its components, these effects shall be taken into consideration. 18.2 Prestress effects The secondary effects of prestress induced in restrained components and indeterminate structures shall be considered in the design of prestressed concrete structures. These effects shall be included in the ultimate and serviceability limit states using a load factor of 1.0. The case of dead loads plus prestress at transfer shall be considered as an ultimate limit state using the load factors given in Table 5.2 for unfavourable and favourable dead load, as applicable, and an ultimate load factor of 1.0 for all prestress effects. 19 DIFFERENTIAL MOVEMENT OF SUPPORTS 19.1 Differential settlement effects
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Where differential settlement of the supports, especially in continuous span configurations, affects the structure in whole or in part, the effects shall be taken into consideration. Differential settlement shall be calculated assuming permanent loads only acting, and using the nominal dead loads of the structure, except that for railway bridges, the additional settlement due to traffic load, including the dynamic load allowance, shall be included. The differential settlement or rotation shall take account of the relief afforded by creep and soil-structure interaction. Design differential settlement effects shall be included in the serviceability limit states for the structure, including bearings and deck joints, using a load factor of 1.0. For railway bridges, spans shall be proportioned such that there is no net uplift at bearings. Consideration shall be given to whether differential settlement effects need to be included in the ultimate limit states loads for the structure. Where a structure has negligible plastic capacity, differential settlement effects shall be included in the ultimate limit states using a load factor of 1.5.
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AS 5100.2—2004
19.2 Mining subsidence effects Bridge structures in areas underlain by known coal deposits shall be designed to cater for anticipated mining subsidence effects, which may include a vertical displacement or change in the slope of the ground, or the development of surface strains. Mining subsidence effects shall be included in the serviceability limit state checks of the superstructure, bearings, deck joints and substructure, using a load factor of 1.0. The foundations shall be designed for mining subsidence effects at ultimate limit states, using a load factor of 1.5. 20 FORCES FROM BEARINGS Bridges shall be designed for the forces arising from the friction of sliding and rolling bearings, and the load-displacement characteristics of elastomeric bearings. The forces due to friction on bearings shall be calculated considering permanent loads only acting. Characteristic values of the coefficient of friction, under normal operating conditions of bearings, shall be as specified in AS 5100.4. For ultimate limit states, the design friction force shall be calculated using the characteristic coefficient of friction, the nominal dead loads of the structure and a load factor of 1.3, in combination with other ultimate limit state loads. For serviceability limit states, the average design friction forces, calculated using the characteristic coefficient of friction, the nominal dead loads of the structure and a load factor of 1.0, shall be treated as a permanent effect, acting in either direction. The coefficient of friction of any surface intended for sliding to accommodate movements of a structure shall be taken as zero as one of the ultimate limit states. The effects of a seized bearing in conjunction with permanent loads and thermal movements shall be considered. 21 CONSTRUCTION FORCES AND EFFECTS 21.1 General The permanent forces and effects introduced during construction shall be considered in the design. Allowance shall also be made for the weight of any falsework or plant that may be carried by the structure, resulting from the anticipated method or sequence of construction.
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Forces arising during possible methods of construction and the stability and serviceability of the component parts shall be considered. Where the design is dependent on a particular method of construction, the structure shall be capable of safely sustaining all construction loads, and these constraints inherent in the design shall be clearly detailed in the drawings and specifications. The ability of bridge supporting members to withstand the effect of flood and wind forces occurring during construction shall also be investigated. Time related relaxation of construction effects shall be considered where appropriate. 21.2 Temporary structures Temporary structures shall be designed in accordance with the appropriate Standards.
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22 LOAD COMBINATIONS 22.1 Classification of loads and load effects Loads and load effects are divided into permanent effects (PE), thermal effects and transient effects. 22.1.1 Permanent effects (PE) Permanent effects shall include the following: (a)
Structure dead load.
(b)
Additional permanent loads (superimposed dead loads).
(c)
Earth pressure loads.
(d)
Normal water flow loads and buoyancy.
(e)
Shrinkage and creep effects (zero effects and full effects).
(f)
Prestress effects (before and after losses).
(g)
Bearing friction or stiffness forces and effects.
(h)
Differential settlement and/or mining subsidence effects.
22.1.2 Thermal effects Thermal effects shall include the following: (a)
Effects due to variation in average bridge temperature.
(b)
Differential temperature effects.
22.1.3 Transient effects Transient effects shall include the following: (a)
Vehicular traffic loads, including dynamic effects.
(b)
Pedestrian traffic loads.
(c)
Wind loads.
(d)
Earthquake loads.
(e)
Flood loads including debris and impact loadings.
Wind on both the structure and the railway live load, in combination with the railway traffic load, shall be considered to be a single transient effect.
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22.2 Ultimate limit state load combinations The ultimate limit state load combinations to be considered for ultimate analyses shall include the following: (a)
PE + ultimate thermal effects.
(b)
PE + ultimate traffic loads.
(c)
PE + ultimate collision load.
(d)
PE + ultimate pedestrian traffic loads.
(e)
PE + ultimate wind load.
(f)
PE + ultimate flood load.
(g)
PE + earthquake.
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AS 5100.2—2004
For Items (a) and (f), where they produce more severe loading, the serviceability traffic loads shall be included in these combinations, provided that the structure is open to traffic under ultimate conditions. For Items (b) and (e), where they produce more severe loading, the serviceability thermal effects shall be included in these combinations, if they produce an adverse effect. Permanent effects and ultimate wind load on the structure together with the railway traffic load using a load factor of 1.0, and no dynamic load allowance shall be one of the ultimate limit state load combinations considered. If the effect of the vertical railway traffic load is beneficial to the structure, a load factor of 0.25 on the railway traffic load shall be considered. 22.3 Serviceability limit state load combinations At serviceability limit states, more than one transient load can co-exist at any time. The basic combination to be considered for serviceability limit states shall be as follows: PE + (serviceability design load for one transient effect) + k (serviceability design load for one or more other transient or thermal effect) where k = coefficient = 0.7 for one additional effect = 0.5 for two additional effects 22.4 Design loads specific to an element Many elements of a bridge, such as traffic barriers and piers have a specified accidental collision load. In such cases, in addition to any other applicable load combination, the element shall be designed for— PE + collision load 23 ROAD SIGNS AND LIGHTING STRUCTURES 23.1 General This Clause shall apply to lighting support structures, traffic signal supports and traffic sign structures, whether post-mounted or attached to overhead gantries or other structures. 23.2 Limit states
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23.2.1 Ultimate limit state Ultimate limit state shall be defined as a loss of static equilibrium, inelastic instability and failure to further sustain the design load. 23.2.2 Serviceability limit state Serviceability limit state shall be defined as excessive vibration from lateral or cross-wind effects induced by vortex shedding, leading to fatigue or failure of electrical components or other functional problems. The critical wind speed, where the frequency of vortex shedding equals a structure resonance frequency, shall be greater than the maximum serviceability design wind speed or low enough to produce very small vibratory amplitudes only.
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23.3 Design wind speeds 23.3.1 Ultimate limit state The ultimate limit state design wind speed shall be determined as follows: (a)
For sign structures which span over traffic, including traffic signal mast arms, the design wind speed shall be as specified in AS/NZS 1170.2 for a 1000 year return period.
(b)
For light poles, signs and signals over 5 m, the design wind speed shall be as specified in AS/NZS 1170.2 for a 200 year return period.
(c)
For minor sign structures less than 5 m in height, the design wind speed shall not be less than 35 m/s.
23.3.2 Serviceability limit state The serviceability limit state design wind speed shall be determined as follows: (a)
For sign structures which span over traffic, traffic signal mast arms, light poles and signs over 5 m, the design wind speed shall be as specified in AS/NZS 1170.2 for a 20-year return period.
(b)
For minor sign structures less than 5 m in height, the design wind speed shall not be less than 20 m/s.
23.4 Design wind pressure The design wind pressure (q * ) (kPa) for ultimate limit states or, serviceability limit state, shall be calculated using an equivalent dynamic pressure approach as follows: q * = 0.6 C dV w2 10 −3
. . . 23.4
where C d = drag coefficient given in Table 23.4 or determined in accordance with AS/NZS 1170.2, as appropriate V w = design wind speed for the ultimate limit states or serviceability limit state determined in accordance with Clause 23.3, as appropriate
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NOTE: For tall slender structures, such as high masts, the equivalent dynamic pressure approach may be unconservative. As an alternative, the dynamic response factor method of determining design wind loads may be used in accordance with AS/NZS 1170.2.
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AS 5100.2—2004
TABLE 23.4 DRAG COEFFICIENTS FOR ELEVATED SIGN PANELS, LUMINAIRES AND TRAFFIC SIGNALS Sign panels (more than 2 m above ground level) Width to height ratio of sign (see Note)
Drag coefficient (C d)
1.0
1.18
2.0
1.19
5.0
1.20
10.0
1.23
15.0
1.30 Luminaires
With rounded surface
0.5
With rectangular, flat-sided shape
1.2
Traffic signals
1.2
NOTE: For immediate values, use linear interpolation.
23.5 Design loads The design loads shall consist of a combination of the appropriate limit state design dead load and wind load. The wind load shall be assumed to come from any direction at the design wind speed specified in Clause 23.3. 23.6 Service live load on walkways In structures fitted with walkways or service platforms, or both, the design load shall be as specified in Clause 7.2. This design load shall be applied in conjunction with design dead and wind loads for serviceability limit states. For ultimate limit states, it shall be applied with design dead loads only. 24 NOISE BARRIERS 24.1 Wind pressure on noise barriers Wind pressures on noise barriers shall be determined in accordance with AS/NZS 1170.2 and subject to the requirements of Clauses 24.2 to 24.8 and this Standard. Accessed by SMEC AUSTRALIA on 11 Sep 2011
24.2 Average return interval A1
A1
The average return interval to be used for the calculation of the ultimate limit state wind forces for design shall conform to the situation descriptions given as follows, subject to approval by the authority: (a)
200 for noise barriers that are located on road or rail authority property and cannot fall onto or slide down a slope onto other property, roadway, walkway or onto traffic areas;
(b)
2000 for noise barriers that can fall onto railways and onto roadways designated as essential to post-disaster functions; and
(c)
500 for all other noise barriers.
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24.3 Design life The design life for noise barriers shall be 50 years. 24.4 Change in terrain category Any change in terrain category shall be taken into consideration in accordance with AS/NZS 1170.2. 24.5 Shielding multiplier (Ms) The shielding multiplier (Ms) specified in AS/NZS 1170.2 shall be taken as 1.0. 24.6 Topographic multiplier AS/NZS 1170.2 accounts for sites in relation to the topographic features of hills, ridges and escarpments. Where the topography along a length of noise barriers varies, then each situation shall be assessed taking into account its location relative to the prevailing topographic feature. Road embankments shall be treated as a hill or an escarpment. A road embankment shall be treated as an escarpment provided it meets the requirements for an escarpment and, additionally, the top width of the embankment is greater than or equal to the greater of— (a)
5 times the upwind height of the embankment; and
(b)
5 times the height of the upwind noise barrier.
24.7 Net pressure for hoardings and freestanding walls The pressure coefficient shall be determined in accordance with AS/NZS 1170.2. Noise barriers on bridges shall be treated as hoardings. Other noise barriers shall be treated as freestanding walls. Where gates and gaps occur in the noise barrier, the barrier adjacent to the gap or gate shall be treated as a free end. 24.8 Free ends
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Special consideration shall be given to the design of free ends.
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AS 5100.2—2004
APPENDIX A
DESIGN LOADS FOR MEDIUM AND SPECIAL PERFORMANCE LEVEL BARRIERS (Informative) A1 GENERAL This Appendix provides guidance for the authority to assist in determining the ultimate design loads and load distribution lengths for medium and special performance level barriers. The loads given in Tables A1 and A2 are based on a lateral combined vehicle/barrier deformation of 0.5 m. A2 DESIGN LOADS A2.1 Medium performance level barriers For medium performance level barriers, the loads and distribution lengths given in Table A1 may be adopted unless the authority determines that other values are appropriate. TABLE A1 DESIGN LOADS FOR MEDIUM PERFORMANCE LEVEL BARRIERS
Barrier performance level
Medium
Ultimate transverse outward load (F T)
Ultimate longitudinal or transverse inward load (F L)
Vehicle contact length for transverse loads, L T and longitudinal loads (L L)
Ultimate vertical downward load (F V)
Vehicle contact length for vertical loads (LV )
kN
kN
m
kN
m
500
170
2.4
350
12.0
A2.2 Special performance level barriers For special performance level barriers, the loads and distribution lengths given in Table A2 may be adopted unless the authority determines that other values are appropriate. TABLE A2
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DESIGN LOADS FOR SPECIAL PERFORMANCE LEVEL BARRIERS
Barrier performance level
Test level 6 (36 t articulated tanker) Greater than test level 6 (44 t articulated van)
Ultimate transverse outward load (F T)
Ultimate longitudinal or transverse inward load (F L)
Vehicle contact length for transverse loads, L T and longitudinal loads (L L)
Ultimate vertical downward load (F V)
Vehicle contact length for vertical loads (LV )
kN
kN
m
kN
m
750
250
2.4
350
12.0
1000
330
2.5
450
15.0
For other special performance level barriers, the loading criteria are to be determined by the authority.
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A3 EFFECTIVE HEIGHTS The minimum effective heights given in Table A3 may be adopted for medium and special performance level barriers unless the authority determines that other values are appropriate. TABLE A3 MINIMUM EFFECTIVE HEIGHT OF TRAFFIC BARRIER Barrier performance level
Minimum effective height (H e ) mm
Medium
1100
Special (TL6–36 t Articulated tanker)
1400
Special (> TL6–44 t Articulated tanker)
1400 To be specified by the authority
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Special—Other
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AMENDMENT CONTROL SHEET AS 5100.2—2004 Amendment No. 1 (2010)
CORRECTION SUMMARY: This Amendment applies to the Preface, Clauses 2, 5.4, 6.7.3(ii), 7.3, 8.5.1, 8.5.2, 11.2.1, 14.7.1, 24.2, Figures 6.2.3, 6.2.4, 12.4, 15.2.1, 16.3.3 and 17.3.
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Published on 19 April 2010.
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AS 5100.2—2004 74
NOTES
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75
NOTES
AS 5100.2—2004
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AS 5100.2—2004 76
NOTES
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