AS 1170.4—2007 (Incorporating Amendment No. 1)
Structural design actions
Part 4: Earthquake actions in Australia
AS
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This Australian Standard® was prepared by Committee BD-006, General Design
Requirements and Loading on Structures. It was approved on behalf of the Council of
Standards Australia on 22 May 2007.
This Standard was published on 9 October 2007.
The following are represented on Committee BD-006:
• Association of Consulting Engineers Australia • Australian Building Codes Board • Australian Steel Institute • Cement Concrete and Aggregates Australia • Concrete Masonry Association of Australia • Department of Building and Housing (New Zealand) • Engineers Australia • Housing Industry Association • Institution of Professional Engineers New Zealand • James Cook University • Master Builders Australia • New Zealand Heavy Engineering Research Association • Property Council of Australia • Steel Reinforcement Institute of Australia • Swinburne University of Technology • Timber Development Association (NSW) • University of Canterbury New Zealand • University of Melbourne • University of Newcastle
Additional Interests:
• Australian Defence Force Academy • Australia Earthquake Engineering Society • Australian Seismological Centre • Building Research Association of New Zealand • Environmental Systems and Services • Geoscience Australia • Institute of Geological and Nuclear Science • New Zealand National Society for Earthquake Engineering • Primary Industries and Resources South Australia • Seismology Research Centre, Australia • University of Adelaide
This Standard was issued in draft form for comment as DR 04303.
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 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 Standards may also be withdrawn.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. A
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AS 1170.4—2007 (Incorporating Amendment No. 1)
Australian Standard®
Structural design actions
Part 4: Earthquake actions in Australia
Originated as AS 2121—1979. Revised and redesignated as AS 1170.4—1993.
Second edition 2007. Reissued incorporating Amendment No. 1 (August 2015).
COPYRIGHT
© Standards Australia Limited
All rights are reserved. No part of this work may be reproduced or copied in any form or by
any means, electronic or mechanical, including photocopying, without the written
permission of the publisher, unless otherwise permitted under the Copyright Act 1968.
Published by SAI Global Limited under licence from Standards Australia Limited, GPO Box
476, Sydney, NSW 2001, Australia
ISBN 0 7337 8349 X
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AS 1170.4—2007 2
PREFACE
This Standard was prepared by the Joint Standards Australia/Standards New Zealand
Committee BD-006, General Design Requirements and Loading on Structures, to supersede
AS 1170.4—1993, Minimum design loads on structures, Part 4: Earthquake loads.
This Standard incorporates Amendment No. 1 (August 2015). 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.
After consultation with stakeholders in both countries, Standards Australia and Standards
New Zealand decided to develop this Standard as an Australian Standard rather than an
Australian/New Zealand Standard.
The objective of this Standard is to provide designers of structures with earthquake actions
and general detailing requirements for use in the design of structures subject to earthquakes.
This Standard is Part 4 of the 1170 series Structural design actions, which comprises the
following parts, each of which has an accompanying Commentary* published as a
Supplement:
AS
1170 Structural design actions
1170.4 Part 4: Earthquake actions (this Standard)
AS/NZS
1170.0 Part 0: General principles
1170.1 Part 1: Permanent, imposed and other actions
1170.2 Part 2: Wind actions
1170.3 Part 3: Snow and ice actions
NZS
1170.5 Part 5: Earthquake actions—New Zealand
This edition differs from AS 1170.4—1993 as follows:
(a) Importance factors have been replaced with the annual probability of exceedance, to
enable design to be set by the use of a single performance parameter. Values of
hazard are determined using the return period factor determined from the annual
probability of exceedance and the hazard factor for the site.
(b) Combinations of actions are now given in the BCA and AS/NZS 1170.0.
(c) Clauses on domestic structures have been simplified and moved to an Appendix.
(d) Soil profile descriptors have been replaced with five (5) new site sub-soil classes.
(e) Site factors and the effect of sub-soil conditions have been replaced with spectral
shape factors in the form of response spectra that vary depending on the fundamental
natural period of the structure.
(f) The five (5) earthquake design categories have been simplified to three (3) new
categories simply described as follows:
(i) I—a minimum static check.
(ii) II—static analysis.
(iii) III—dynamic analysis.
* The Commentary to this Standard, when published, will be AS 1170.4 Supp 1, Structural design actions—
Earthquake actions—Commentary (Supplement to AS 1170.4—2007).
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3 AS 1170.4—2007
(g) The option to allow no analysis or detailing for some structures has been removed
(except for importance level 1 structures).
(h) All requirements for the earthquake design categories are collected together in a
single section (Section 5), with reference to the Sections on static and dynamic
analysis.
(i) The 50 m height limitation on ordinary moment-resisting frames has been removed
but dynamic analysis is required above 50 m.
(j) Due to new site sub-soil spectra, adjustments were needed to simple design rules
throughout the Standard. The basic static and dynamic methods have not changed in
this respect.
(k) The equation for base shear has been aligned with international methods.
(l) Structural response factor has been replaced by the combination of structural
performance factor and structural ductility factor (1/Rf to Sp/μ) and values modified for some structure types.
(m) A new method has been introduced for the calculation of the fundamental natural
period of the structure.
(n) The clause on torsion effects has been simplified.
(o) The clause on stability effects has been removed.
(p) The requirement to design some structures for vertical components of earthquake
action has been removed.
(q) Scaling of results has been removed from the dynamic analysis.
(r) The Section on structural alterations has been removed.
(s) The clauses on parts and components have been simplified.
(t) The ‘informative’ Appendices have been removed.
The Standard has been drafted to be applicable to the design of structures constructed of
any material or combination thereof. Designers will need to refer to the appropriate material
Standard(s) for guidance on detailing requirements additional to those contained in this
Standard.
This Standard is not equivalent to ISO 3010:2001, Basis for design of structures—Seismic
actions on structures, but is based on equivalent principles. ISO 3010 gives guidance on a
general format and on detail for the drafting of national Standards on seismic actions. The
principles of ISO 3010 have been adopted, including some of the detail, with modifications
for the low seismicity in Australia. The most significant points are as follows*:
(i) ISO 3010 is drafted as a guide for committees preparing Standards on seismic actions.
(ii) Method and notation for presenting the mapped earthquake hazard data has not been
adopted.
(iii) Some notation and definitions have not been adopted.
(iv) Details of the equivalent static method have been aligned.
(v) Principles of the dynamic method have been aligned.
Particular acknowledgment should be given to those organizations listed as ‘additional
interests’ for their contributions to the drafting of this Standard.
* When published, the Commentary to this Standard will include additional information on the relationship of
this Standard to ISO 3010:2001.
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AS 1170.4—2007 4
The terms ‘normative’ and ‘informative’ have been used in this Standard to define the
application of the appendix to which they apply. A ‘normative’ appendix is an integral part
of a Standard, whereas an ‘informative’ appendix is only for information and guidance.
Statements expressed in mandatory terms in notes to tables and figures are deemed to be an
integral part of this Standard.
Notes to the text contain information and guidance. They are not an integral part of the
Standard.
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5 AS 1170.4—2007
CONTENTS
Page
SECTION 1 SCOPE AND GENERAL
1.1 SCOPE ......................................................................................................................... 7
1.2 NORMATIVE REFERENCES .................................................................................... 7
1.3 DEFINITIONS ............................................................................................................. 8
1.4 NOTATION AND UNITS ......................................................................................... 10
1.5 LEVELS, WEIGHTS AND FORCES OF THE STRUCTURE .................................. 12
SECTION 2 DESIGN PROCEDURE
2.1 GENERAL ................................................................................................................. 16
2.2 DESIGN PROCEDURE ............................................................................................ 16
SECTION 3 SITE HAZARD
3.1 ANNUAL PROBABILITY OF EXCEEDANCE (P) AND PROBABILITY
FACTOR (kp) ............................................................................................................. 19
3.2 HAZARD FACTOR (Z) ............................................................................................. 19
SECTION 4 SITE SUB-SOIL CLASS
4.1 DETERMINATION OF SITE SUB-SOIL CLASS .................................................... 28
4.2 CLASS DEFINITIONS ............................................................................................. 29
SECTION 5 EARTHQUAKE DESIGN
5.1 GENERAL ................................................................................................................. 31
5.2 BASIC DESIGN PRINCIPLES ................................................................................. 31
5.3 EARTHQUAKE DESIGN CATEGORY I (EDC I) ................................................... 32
5.4 EARTHQUAKE DESIGN CATEGORY II (EDC II) ................................................ 32
5.5 EARTHQUAKE DESIGN CATEGORY III (EDC III) .............................................. 35
SECTION 6 EQUIVALENT STATIC ANALYSIS
6.1 GENERAL ................................................................................................................. 36
6.2 HORIZONTAL EQUIVALENT STATIC FORCES .................................................. 36
6.3 VERTICAL DISTRIBUTION OF HORIZONTAL FORCES .................................... 37
6.4 SPECTRAL SHAPE FACTOR (Ch(T)) ...................................................................... 38
6.5 DETERMINATION OF STRUCTURAL DUCTILITY (μ) AND STRUCTURAL PERFORMANCE FACTOR (Sp) ............................................................................... 39
6.6 TORSIONAL EFFECTS ............................................................................................ 41
6.7 DRIFT DETERMINATION AND P-DELTA EFFECTS ........................................... 41
SECTION 7 DYNAMIC ANALYSIS
7.1 GENERAL ................................................................................................................. 43
7.2 EARTHQUAKE ACTIONS ...................................................................................... 43
7.3 MATHEMATICAL MODEL ..................................................................................... 43
7.4 MODAL ANALYSIS ................................................................................................ 44
7.5 DRIFT DETERMINATION AND P-DELTA EFFECTS ........................................... 44
SECTION 8 DESIGN OF PARTS AND COMPONENTS
8.1 GENERAL REQUIREMENTS .................................................................................. 45
8.2 METHOD USING DESIGN ACCELERATIONS ..................................................... 47
8.3 SIMPLE METHOD ................................................................................................... 47
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AS 1170.4—2007 6
APPENDICES
A DOMESTIC STRUCTURES (HOUSING) ................................................................ 49
BIBLIOGRAPHY ..................................................................................................................... 51
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7 AS 1170.4—2007
www.standards.org.au © Standards Australia
STANDARDS AUSTRALIA
Australian Standard
Structural design actions
Part 4: Earthquake actions in Australia
S E C T I O N 1 S C O P E A N D G E N E R A L
1.1 SCOPE
This Standard sets out procedures for determining earthquake actions and detailing
requirements for structures and components to be used in the design of structures. It also
includes requirements for domestic structures.
Importance level 1 structures are not required to be designed for earthquake actions.
The following structures are outside the scope of this Standard:
(a) High-risk structures.
(b) Bridges.
(c) Tanks containing liquids.
(d) Civil structures including dams and bunds.
(e) Offshore structures that are partly or fully immersed.
(f) Soil-retaining structures.
(g) Structures with first mode periods greater than 5 s.
This Standard does not consider the effect on a structure of related earthquake phenomena
such as settlement, slides, subsidence, liquefaction or faulting.
NOTES:
1 For structures in New Zealand, see NZS 1170.5.
2 For earth-retaining structures, see AS 4678.
1.2 NORMATIVE REFERENCES
The following referenced documents are indispensable to the application of this Standard.
NOTE: Documents referenced for informative purposes are listed in the Bibliography.
AS
1684 Residential timber-framed construction (all parts)
1720 Timber structures
1720.1 Part 1: Design methods
3600 Concrete structures
3700 Masonry structures
4100 Steel structures
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AS 1170.4—2007 8
© Standards Australia www.standards.org.au
AS/NZS
1170 Structural design actions
1170.0 Part 0: General principles
1170.1 Part 1: Permanent, imposed and other actions
1170.3 Part 3: Snow and ice actions
1664 Aluminium structures (all parts)
BCA Building Code of Australia
NASH Standard Residential and low-rise steel framing, Part 1—2005, Design criteria
1.3 DEFINITIONS
For the purpose of this Standard, the definitions given in AS/NZS 1170.0 and those below
apply. Where the definitions in this Standard differ from those given in AS/NZS 1170.0, for
the purpose of this Standard, those below apply.
1.3.1 Base, structural
Level at which earthquake motions are considered to be imparted to the structure, or the
level at which the structure as a dynamic vibrator is supported (see Figure 1.5(C)).
1.3.2 Bearing wall system
Structural system in which loadbearing walls provide support for all or most of the vertical
loads while shear walls or braced frames provide the horizontal earthquake resistance.
1.3.3 Braced frame
Two-dimensional structural system composed of an essentially vertical truss (or its
equivalent) where the members are subject primarily to axial forces when resisting
earthquake actions.
1.3.4 Braced frame, concentric
Braced frame in which bracing members are connected at the column-beam joints
(see Table 6.5(A)).
1.3.5 Braced frame, eccentric
Braced frame where at least one end of each brace intersects a beam at a location away
from the column-beam joint (see Table 6.5(A)).
1.3.6 Connection
Mechanical means that provide a load path for actions between structural elements, non-
structural elements and structural and non-structural elements.
1.3.7 Diaphragm
Structural system (usually horizontal) that acts to transmit earthquake actions to the
seismic-force-resisting system.
1.3.8 Domestic structure
Single dwelling or one or more attached dwellings (single occupancy units) complying with
Class 1a or 1b as defined in the Building Code of Australia.
1.3.9 Ductility (of a structure)
Ability of a structure to sustain its load-carrying capacity and dissipate energy when
responding to cyclic displacements in the inelastic range during an earthquake.
1.3.10 Earthquake actions
Inertia-induced actions arising from the response to earthquake of the structure.
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1.3.11 Moment-resisting frame
Essentially complete space frame that supports the vertical and horizontal actions by both
flexural and axial resistance of its members and connections.
1.3.12 Moment-resisting frame, intermediate
Concrete or steel moment-resisting frame designed and detailed to achieve moderate
structural ductility (see Table 6.5(A)).
1.3.13 Moment-resisting frame, ordinary
Moment-resisting frame with no particular earthquake detailing, specified in the relevant
material standard (see Table 6.5(A)).
1.3.14 Moment-resisting frame, special
Concrete or steel moment-resisting frame designed and detailed to achieve high structural
ductility and where plastic deformation is planned under ultimate actions
(see Table 6.5(A)).
1.3.15 Partition
Permanent or relocatable internal dividing wall between floor spaces.
1.3.16 Parts and components
Elements that are—
(a) attached to and supported by the structure but are not part of the seismic-force-
resisting system; or
(b) elements of the seismic-force-resisting system, which can be loaded by an earthquake
in a direction not usually considered in the design of that element.
1.3.17 P-delta effect
Additional induced structural forces that develop as a consequence of the gravity loads
being displaced horizontally.
1.3.18 Seismic-force-resisting system
Part of the structural system that provides resistance to the earthquake forces and effects.
1.3.19 Shear wall
Wall (either loadbearing or non-loadbearing) designed to resist horizontal earthquake forces
acting in the plane of the wall.
1.3.20 Space frame
A three-dimensional structural system composed of interconnected members (other than
loadbearing walls) that is capable of supporting vertical loads, which may also provide
horizontal resistance to earthquake forces.
1.3.21 Storey
Space between levels including the space between the structural base and the level above.
NOTE: Storey i is the storey below the ith level.
1.3.22 Structural performance factor (Sp)
Numerical assessment of the additional ability of the total building (structure and other
parts) to survive earthquake motion.
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AS 1170.4—2007 10
© Standards Australia www.standards.org.au
1.3.23 Structural ductility factor (μ)
Numerical assessment of the ability of a structure to sustain cyclic displacements in the
inelastic range. Its value depends upon the structural form, the ductility of the materials and
structural damping characteristics.
1.3.24 Top (of a structure)
Level of the uppermost principal seismic weight (see Clause 1.5).
1.4 NOTATION AND UNITS
Except where specifically noted, this Standard uses SI units of kilograms, metres, seconds,
pascals and newtons (kg, m, s, Pa, N).
Unless stated otherwise, the notation used in this Standard shall have the following
meanings:
ac = component amplification factor
afloor = effective floor acceleration at the height of the component centre of mass
ax = height amplification factor at height hx of the component centre of mass
b = plan dimension of the structure at right angles to the direction of the action, in
metres
C(T) = elastic site hazard spectrum for horizontal loading as a function of period (T)
C(T1) = value of the elastic site hazard spectrum for the fundamental natural period of
the structure
Cd(T) = horizontal design response spectrum as a function of period (T)
Cd(T1) = horizontal design action coefficient (value of the horizontal design response
spectrum for the fundamental natural period of the structure)
Ch(T) = spectral shape factor as a function of period (T) (dimensionless coefficient)
Ch(T1) = value of the spectral shape factor for the fundamental natural period of the
structure
Cv(Tv) = elastic site hazard spectrum for vertical loading, which may be taken as half
of the elastic site hazard spectrum for horizontal loading (C(T))
Cvd(T) = vertical design response spectrum as a function of period (T)
Ch(0) = bracketed value of the spectral shape factor for the period of zero seconds
di = horizontal deflection of the centre of mass at level ‘i’
die = deflection at level ‘i’ determined by an elastic analysis
dst = design storey drift
E = earthquake actions (see Clause 1.3 and AS/NZS 1170.0)
Eu = earthquake actions for ultimate limit state
= represented by a set of equivalent static forces Fi at each level (i) or by
resultant action effects determined using a dynamic analysis
Fc = horizontal design earthquake force on the part or component, in kilonewtons
Fi = horizontal equivalent static design force at the ith level, in kilonewtons
Fj = horizontal equivalent static design force at the jth level, in kilonewtons
Fn = horizontal equivalent static design force at the uppermost seismic mass, in
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11 AS 1170.4—2007
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Fr = horizontal design racking earthquake force on the part or component, in
kilonewtons
g = acceleration due to gravity (9.8 m/s2)
G = permanent action (self-weight or ‘dead load’), in kilonewtons
Gi = permanent action (self-weight or ‘dead load’) at level i, in kilonewtons
hi = height of level i above the base of the structure, in metres
hn = height from the base of the structure to the uppermost seismic weight or mass,
in metres (see Clause 1.5)
hsi = inter-storey height of level i, measured from centre-line to centre-line of floor,
in metres
hx = height at which the component is attached above the structural base of the
structure, in metres
Ic = component importance factor
i, j = levels of the structure under consideration
Ks = factor to account for height of a level in a structure
k = exponent, dependent on the fundamental natural period of the structure (T1)
kc = factor for determining height amplification factor (ax)
kF,i = seismic force distribution factor for the ith level
kp = probability factor appropriate for the limit state under consideration
kt = factor for determining building period
mi = seismic mass at each level
N-values = number of blows for standard penetration (Standard Penetration Test)
n = number of levels in a structure
P = annual probability of exceedance
P-delta = second order effects due to amplication of axial loads
Q = imposed action for each occupancy class, in kilonewtons
Qi = imposed action for each occupancy class on the ith level
Rc = component ductility factor
Sp = structural performance factor
T = period of vibration, which varies according to the mode of vibration being
considered
T1 = fundamental natural period of the structure as a whole (translational first
mode natural period)
Tv = period of vibration appropriate to vertical mode of vibration of the structure
V = horizontal equivalent static shear force acting at the base (base shear)
Vi = horizontal equivalent static shear force at the ith level
W = sum of the seismic weight of the building (G + ψcQ) at the level where bracing is to be determined and above this level, in kilonewtons
Wc = seismic weight of the part or component, in kilonewtons
Wi = seismic weight of the structure or component at the ith level, in kilonewtons
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AS 1170.4—2007 12
© Standards Australia www.standards.org.au
Wj = seismic weight of the structure or component at level j, in kilonewtons
Wn = seismic weight of the structure or component at the nth level (upper level), in
kilonewtons
Wt = total seismic weight of the building, in kilonewtons
Z = earthquake hazard factor which is equivalent to an acceleration coefficient
with an annual probability of exceedance in 1/500, (i.e., a 10% probability of
exceedance in 50 years)
μ = structural ductility factor (μ = mu)
θ = stability coefficient
ψc = earthquake imposed action combination factor
1.5 LEVELS, WEIGHTS AND FORCES OF THE STRUCTURE
For the purposes of analysis, the masses of the structure, parts and components are taken as
acting at the levels of the structure (see Figure 1.5(A)).
The seismic weight at a level is determined by summing the weights that would act at that
level, including the weight of the floor plus any items spanning from one level to the next,
e.g., walls, half way to the level above and half way to the level below and adding the
factored imposed actions on that level. This mass is then assumed to act at the height of the
centre of the floor slab (excluding consideration of any beams).
The centre of mass of the uppermost (top) weight (including roofing, structure and any
additional parts and components above and down to half way to the floor below) shall be
considered to act at the centre of the combined mass (see Figure 1.5(B)). For more
complicated situations, the uppermost seismic weight shall be assessed depending on the
effect on the distribution of forces. Where a concentrated weight exists above the ceiling
level that contributes more than 1/3 of Wn, it shall be treated as the top seismic weight and
Wn and Wn − 1 recalculated.
The building height (hn) is taken as the height of the centre of mass of Wn above the base.
Figure 1.5(C) illustrates the structural base for various situations.
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13 AS 1170.4—2007
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Storey n
Storey i + 1
Storey i + 1
Storey i
Storey i
Storey 1
Force Fn
Force Fn - 1
Force F i + 1
Force F i - 1
Force F i
Force F1
Level n
Level n - 1
Level i + 1
Level i - 1
Level i + 1
Level i
Level i - 1
Level i
Level 1
Base
hnhn
hhhsihsi
Uppermost seismic mass
W iW i hsi
2hsi2
FIGURE 1.5(A) ILLUSTRATION OF LEVEL, STOREY, WEIGHT AND FORCE
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AS 1170.4—2007 14
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Storey n - 1
Storey n
Wn
Top
Base
hn
PlantCentre ofgravity of Wn
FIGURE 1.5(B) EXAMPLE OF DETERMINATION OF THE TOP OF THE STRUCTURE
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Building height, hn Building height, hn
(a) Base shear reaction at ground level
(b) Base shear reaction below ground level
Building height, hn Building height, hn
(c) Base shear reaction taken as at lowest level
(d) Base shear reaction at ground level
NOTE: Building height measured from top of slab at relevant level.
FIGURE 1.5(C) EXAMPLES OF DEFINITION OF BUILDING BASE WHERE
EARTHQUAKE MOTIONS ARE CONSIDERED TO BE TRANSMITTED
TO THE STRUCTURE
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AS 1170.4—2007 16
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S E C T I O N 2 D E S I G N P R O C E D U R E
2.1 GENERAL
Earthquake actions for use in design (E) shall be appropriate for the type of structure or
element, its intended use, design working life and exposure to earthquake shaking.
The earthquake actions (Eu) determined in accordance with this Standard shall be deemed to
comply with this provision.
2.2 DESIGN PROCEDURE
The design procedure (see Figure 2.2) to be adopted for the design of a structure subject to
this Standard shall—
(a) determine the importance level for the structure (AS/NZS 1170.0 and BCA);
(b) determine the probability factor (kp) and the hazard factor (Z) (see Section 3);
(c) determine if the structure complies with the definition for domestic structures
(housing) given in Appendix A and whether it complies with the requirements
therein;
(d) determine the site sub-soil class (see Section 4);
(e) determine the earthquake design category (EDC) from Table 2.1; and
(f) design the structure in accordance with the requirements for the EDC as set out in
Section 5.
Importance level 1 structures are not required to be designed to this Standard, (i.e., for
earthquake actions), and domestic structures (housing) that comply with the definition
given in Appendix A and with the provisions of Appendix A are deemed to satisfy this
Standard.
All other structures, including parts and components, are required to be designed for
earthquake actions.
NOTE: During an earthquake, motion will be imposed on all parts of any construction. Therefore,
parts of a structure (including non-loadbearing walls, etc.) should be designed for lateral
earthquake forces such as out-of-plane forces.
A higher level of analysis than that specified in Table 2.1 for a particular EDC may be used.
Domestic structures that do not comply with the limits specified in Appendix A shall be
designed as importance level 2 structures.
NOTE: Structures (including housing) that are constructed on a site with a hazard factor Z of 0.3
or greater should be designed in accordance with NZS 1170.5 (see Macquarie Islands, Table 3.2).
For structures sited on sub-soil Class E (except houses in accordance with Appendix A), the
design shall consider the effects of subsidence or differential settlement of the foundation
material under the earthquake actions determined for the structure.
NOTE: Structures, where the structural ductility factor (μ) assumed in design is greater than 3, should be designed in accordance with NZS 1170.5 and associated New Zealand Standards.
Serviceability limit states are deemed to be satisfied under earthquake actions for
importance levels 1, 2 and 3 structures that are designed in accordance with this Standard
and the appropriate materials design Standards. A special study shall be carried out for
importance level 4 structures to ensure they remain serviceable for immediate use following
the design event associated with importance level 2 structures.
A1
A1
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TABLE 2.1
SELECTION OF EARTHQUAKE DESIGN CATEGORIES
Importance
level, type of
structure
(see
Clause 2.2)
(kpZ) for site sub-soil class
Structure
height, hn
(m)
Earthquake
design
category Ee or De Ce Be Ae
1 — —
Not required to
be designed for
earthquake
actions
Domestic
structure
(housing)
—
Top of
roof
≤8.5
Refer to
Appendix A
Top of
roof
>8.5
Design as
importance
level 2
2
≤0.05 ≤0.08 ≤0.11 ≤0.14 ≤12
>12, 0.05 to ≤0.08 >0.08 to ≤0.12 >0.11 to ≤0.17 >0.14 to ≤0.21 0.08 >0.12 >0.17 >0.21 0.12 >0.17 >0.21
AS 1170.4—2007 18
© Standards Australia www.standards.org.au
1 Determine
2 Look up
3 Determine
4 Apply EDC I
5 Design partsand components
Structure location and importance level
Annual probabil i ty of exceedance (from AS/NZS 1170.0 or BCA)
kp, Z value (Section 3)
Soil class, A, B, C, D or E (Section 4)
EDC (Table 2.1)
Does the structure comply with the definit ion of
domestic structures (Housing) and is hn 8.5
EDC II EDC III
Use Clause 5.2
Clause 5.3
Simple stat ic check
Use Clause 5.2
Clause 5.4
Static analysis
(Section 6)
Use Clause 5.2
Clause 5.5
Dynamic analysis
(Section 7)
EDC I(Clause 5.3)
EDC II(Section 8)
EDC III(Section 8)
No
Appendix AY
FIGURE 2.2 FLOW DIAGRAM—DESIGN PROCEDURE
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S E C T I O N 3 S I T E H A Z A R D
3.1 ANNUAL PROBABILITY OF EXCEEDANCE (P) AND PROBABILITY
FACTOR (kp)
The probability factor (kp) for the annual probability of exceedance, appropriate for the
limit state under consideration, shall be obtained from Table 3.1.
TABLE 3.1
PROBABILITY FACTOR (kp)
Annual probability of exceedance Probability factor
P kp
1/2500
1/2000
1/1500
1.8
1.7
1.5
1/1000
1/800
1/500
1.3
1.25
1.0
1/250
1/200
1/100
0.75
0.7
0.5
1/50
1/25
1/20
0.35
0.25
0.20
NOTE: The annual probability of exceedance in Table 3.1
is taken from the BCA and AS/NZS 1170.0.
3.2 HAZARD FACTOR (Z)
The hazard factor (Z) shall be taken from Table 3.2 or, where the location is not listed, be
determined from Figures 3.2(A) to 3.2(F). A general overview of the hazard factor (Z) for
Australia is shown in Figure 3.2(G).
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AS 1170.4—2007 20
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TABLE 3.2
HAZARD FACTOR (Z) FOR SPECIFIC AUSTRALIAN LOCATIONS
Location Z Location Z Location Z
Adelaide
Albany
Albury/Wodonga
0.10
0.08
0.09
Geraldton
Gladstone
Gold Coast
0.09
0.09
0.05
Port Augusta
Port Lincoln
Port Hedland
0.11
0.10
0.12
Alice Springs
Ballarat
Bathurst
0.08
0.08
0.08
Gosford
Grafton
Gippsland
0.09
0.05
0.10
Port Macquarie
Port Pirie
Robe
0.06
0.10
0.10
Bendigo
Brisbane
Broome
0.09
0.05
0.12
Goulburn
Hobart
Karratha
0.09
0.03
0.12
Rockhampton
Shepparton
Sydney
0.08
0.09
0.08
Bundaberg
Burnie
Cairns
0.11
0.07
0.06
Katoomba
Latrobe Valley
Launceston
0.09
0.10
0.04
Tamworth
Taree
Tennant Creek
0.07
0.08
0.13
Camden
Canberra
Carnarvon
0.09
0.08
0.09
Lismore
Lorne
Mackay
0.05
0.10
0.07
Toowoomba
Townsville
Tweed Heads
0.06
0.07
0.05
Coffs Harbour
Cooma
Dampier
0.05
0.08
0.12
Maitland
Melbourne
Mittagong
0.10
0.08
0.09
Uluru
Wagga Wagga
Wangaratta
0.08
0.09
0.09
Darwin
Derby
Dubbo
0.09
0.09
0.08
Morisset
Newcastle
Noosa
0.10
0.11
0.08
Whyalla
Wollongong
Woomera
0.09
0.09
0.08
Esperance
Geelong
0.09
0.10
Orange
Perth
0.08
0.09
Wyndham
Wyong
0.09
0.10
Meckering region Islands
Ballidu
Corrigin
Cunderdin
0.15
0.14
0.22
Meckering
Northam
Wongan Hills
0.20
0.14
0.15
Christmas Island
Cocos Islands
Heard Island
0.15
0.08
0.10
Dowerin
Goomalling
Kellerberrin
0.20
0.16
0.14
Wickepin
York
0.15
0.14
Lord Howe Island
Macquarie Island
Norfolk Island
0.06
0.60
0.08
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21 AS 1170.4—2007
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Hazard (z)1 in 500 years annual
probabil i ty of exceedance
FIGURE 3.2(A) HAZARD FACTOR (Z) FOR NEW SOUTH WALES, VICTORIA
AND TASMANIA
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AS 1170.4—2007 22
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Hazard (z)1 in 500 years annual
probabil i ty of exceedance
FIGURE 3.2(B) HAZARD FACTOR (Z) FOR SOUTH AUSTRALIA
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FIGURE 3.2(C) HAZARD FACTOR (Z) FOR WESTERN AUSTRALIA
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AS 1170.4—2007 24
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Hazard (z)1 in 500 years annual
probabil i ty of exceedance
FIGURE 3.2(D) HAZARD FACTOR (Z) FOR SOUTH-WEST OF WESTERN AUSTRALIA
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25 AS 1170.4—2007
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Hazard (z)1 in 500 years annual
probabil i ty of exceedance
FIGURE 3.2(E) HAZARD FACTOR (Z) FOR NORTHERN TERRITORY
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AS 1170.4—2007 26
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Hazard (z)1 in 500 years annual
probabil i ty of exceedance
FIGURE 3.2(F) HAZARD FACTOR (Z) FOR QUEENSLAND
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Ha
za
rd (
z)
1 i
n 5
00
ye
ars
an
nu
al
pro
ba
bil
ity
of
ex
ce
ed
an
ce
FIG
UR
E
3.2
(G)
H
AZ
AR
D F
AC
TO
R (Z
)
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AS 1170.4—2007 28
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S E C T I O N 4 S I T E S U B - S O I L C L A S S
4.1 DETERMINATION OF SITE SUB-SOIL CLASS
4.1.1 General
The site shall be assessed and assigned to the site sub-soil class it most closely resembles.
The site sub-soil classes shall be as defined in Clause 4.2, that is, Classes Ae to Ee as
follows:
(a) Class Ae—Strong rock.
(b) Class Be—Rock.
(c) Class Ce—Shallow soil.
(d) Class De—Deep or soft soil.
(e) Class Ee—Very soft soil.
4.1.2 Hierarchy for site classification methods
Site classification shall be determined using the methods in the following list, in order of
most preferred to least preferred:
(a) Site periods based on four times the shear-wave travel-time through material from the
surface to underlying rock.
(b) Bore logs, including measurement of geotechnical properties.
(c) Evaluation of site periods from Nakamura ratios or from recorded earthquake
motions.
(d) Bore logs with descriptors but no geotechnical measurements.
(e) Surface geology and estimates of the depth to underlying rock.
Where more than one method has been carried out, the site classification determined by the
most preferred method shall be used.
4.1.3 Evaluation of periods for layered sites
For sites consisting of layers of several types of material, the low-amplitude natural period
of the site may be estimated by summing the contributions to the natural period of each
layer. The contribution of each layer may be estimated by determining the soil type of each
layer, and multiplying the ratio of each layer’s thickness to the maximum depth of soil for
that soil type (given in Table 4.1) by 0.6 s. In evaluating site periods, material above rock
shall be included in the summation.
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29 AS 1170.4—2007
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TABLE 4.1
MAXIMUM DEPTH LIMITS FOR SITE SUB-SOIL CLASS C
Soil type and description Property Maximum
depth of soil
Representative undrained
shear strengths
Representative
SPT N-values
(kPa) (Number) (m)
Cohesive soils Very soft 30 100
4.2 CLASS DEFINITIONS
4.2.1 Class Ae—Strong rock
Site sub-soil Class Ae is defined as strong to extremely strong rock satisfying the following
conditions:
(a) Unconfined compressive strength greater than 50 MPa or an average shear-wave
velocity over the top 30 m greater than 1500 m/s.
(b) Not underlain by materials having a compressive strength less than 18 MPa or an
average shear wave velocity less than 600 m/s.
4.2.2 Class Be—Rock
Site sub-soil Class Be is defined as rock satisfying the following conditions:
(a) A compressive strength between 1 and 50 MPa inclusive or an average shear-wave
velocity, over the top 30 m, greater than 360 m/s.
(b) Not underlain by materials having a compressive strength less than 0.8 MPa or an
average shear wave velocity less than 300 m/s.
A surface layer of no more than 3 m depth of highly weathered or completely weathered
rock or soil (a material with a compressive strength less than 1 MPa) may be present.
4.2.3 Class Ce—Shallow soil site
Site sub-soil Class Ce is defined as a site that is not Class Ae, Class Be (i.e., not rock site),
or Class Ee site (i.e., not very soft soil site) and either—
(a) the low-amplitude natural site period is less than or equal to 0.6 s; or
(b) the depths of soil do not exceed those listed in Table 4.1.
The low-amplitude natural site period may be estimated from—
(i) four times the shear-wave travel time from the surface to rock;
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AS 1170.4—2007 30
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(iii) recorded earthquake motions; or
(iv) evaluated in accordance with Clause 4.1.3 for sites with layered sub-soil.
Where more than one method is used, the value determined from the most preferred method
given in Clause 4.1.2 shall be adopted.
4.2.4 Class De—Deep or soft soil site
Site sub-soil Class De is defined as a site that is—
(a) not Class Ae, Class Be (i.e., not rock site) or Class Ee site (i.e., very soft soil site); and
(b) underlain by less than 10 m of soil with an undrained shear-strength less than
12.5 kPa or soil with Standard penetration test (SPT) N-values less than 6; and either
(i) the low-amplitude natural site period is greater than 0.6 s; or
(ii) the depths of soil exceed those listed in Table 4.1,
where the low-amplitude natural site period is estimated in accordance with Clause 4.2.3.
4.2.5 Class Ee—Very soft soil site
Site sub-soil Class Ee is defined as a site with any one of the following:
(a) More than 10 m of very soft soil with undrained shear-strength less than 12.5 kPa.
(b) More than 10 m of soil with SPT N-values less than 6.
(c) More than 10 m depth of soil with shear wave velocities of 150 m/s or less.
(d) More than 10 m combined depth of soils with properties as described in Items (a), (b)
and (c) above.
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31 AS 1170.4—2007
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S E C T I O N 5 E A R T H Q U A K E D E S I G N
5.1 GENERAL
Structures required by Section 2 to be designed for earthquake actions shall be designed in
accordance with the general principles of Clause 5.2, the provisions of the appropriate
earthquake design category (see Clauses 5.3, 5.4 or 5.5) and the requirements of the
applicable material design Standards.
5.2 BASIC DESIGN PRINCIPLES
5.2.1 Seismic-force-resisting system
All structures shall be configured with a seismic-force-resisting system that has a clearly
defined load path, or paths, that will transfer the earthquake actions (both horizontal and
vertical) generated in an earthquake, together with gravity loads, to the supporting
foundation soil.
5.2.2 Tying structure together
All parts of the structure shall be tied together both in the horizontal and the vertical planes
so that forces generated by an earthquake from all parts of the structure, including structural
and other parts and components, are carried to the foundation.
Footings supported on piles, or caissons, or spread footings that are located in or on soils
with a maximum vertical ultimate bearing value of less than 250 kPa shall be restrained in
any horizontal direction by ties or other means, to limit differential horizontal movement
during an earthquake.
5.2.3 Performance under earthquake deformations
Stiff components (such as concrete, masonry, brick, precast concrete walls or panels or stair
walls, stairs and ramps) shall be—
(a) considered to be part of the seismic-force-resisting system and designed accordingly;
or
(b) separated from all structural elements such that no interaction takes place as the
structure undergoes deflections due to the earthquake effects determined in
accordance with this Standard.
All components, including those deliberately designed to be independent of the seismic-
force-resisting system, shall be designed to perform their required function while sustaining
the deformation of the structure resulting from the application of the earthquake forces
determined for each limit state.
Floors shall be—
(i) continuous over a series of internal walls at right angles or near right angles; or
(ii) tied to supporting walls at all supported edges.
Provision shall be made for floors to span without collapse if they become dislodged from
edges to which they are not tied.
5.2.4 Walls
Walls shall be anchored to the roof and restrained at all floors that provide horizontal
support for the wall. Walls shall be designed for in-plane and out-of-plane forces.
Out-of-plane forces on walls shall be designed in accordance with Section 8.
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AS 1170.4—2007 32
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5.2.5 Diaphragms
The deflection in the plane of the diaphragm, as determined by analysis, shall not exceed
the permissible deflection of the attached elements. Permissible deflection shall be that
deflection that will permit the attached element to maintain its structural integrity and
continue to support the prescribed forces.
5.3 EARTHQUAKE DESIGN CATEGORY I (EDC I)
This Clause shall not apply to structures of height (hn) over 12 m.
All structures subject to earthquake design category I (EDC I) shall comply with the
requirements of Clause 5.2 and the requirements of this Clause.
The structure and all parts and components shall be designed for the following equivalent
static forces applied laterally to the centre of mass of the part or component being
considered, or to the centres of mass of the levels of the structure (see Figure 5.2), in
combination with gravity loads (see combination [G, Eu, ψcQ] in AS/NZS 1170.0):
Fi = 0.1Wi . . . 5.3
where
Wi = seismic weight of the structure or component at level i as given in Clause 6.2.2
Each of the major axes of the structure shall be considered separately.
Vertical earthquake actions and pounding need not be considered, except where vertical
actions apply to parts and components.
Base
Storey 1
Storey 2
Storey 3
W3F 3
F 2
F 1
W2
W1
FIGURE 5.2 ILLUSTRATION OF EARTHQUAKE DESIGN CATEGORY I
5.4 EARTHQUAKE DESIGN CATEGORY II (EDC II)
5.4.1 General
All structures subject to earthquake design category II (EDC II) shall comply with the
requirements of Clause 5.2 and Clauses 5.4.2 to 5.4.6.
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33 AS 1170.4—2007
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5.4.2 Strength and stability provisions
5.4.2.1 General
The structural system shall be designed to resist the most critical action effect arising from
the application of the earthquake actions in any direction.
Except for structure components and footings that participate in resisting horizontal
earthquake forces in both major axes of the structure, this provision shall be deemed to be
satisfied by applying the horizontal force in the direction of each of the major axes of the
structure and considering the effect for each direction separately.
For structure components and footings that participate in resisting horizontal earthquake
forces in both major axes of the structure, the effects of the two directions determined
separately shall be added by taking 100% of the horizontal earthquake forces for one
direction and 30% in the perpendicular direction.
Forces shall be applied at the centre of mass of each floor except where offset from the
centre of mass is required for the consideration of torsion effects (see Clause 6.6).
Connections between components of the structure shall be capable of transmitting an
internal ultimate limit state horizontal action equal to the values calculated using this
section but not less than 5% of the vertical reaction arising from the seismic weight or 5%
of the seismic weight of the component whichever is the greater.
5.4.2.2 Earthquake forces—Equivalent static method
Earthquake forces shall be calculated using the equivalent static method, in accordance with
Section 6 except where covered by Clause 5.4.2.3.
NOTE: Dynamic analysis, in accordance with Section 7, may be used if desired (see Clause 2.2).
5.4.2.3 Simplified design for structures not exceeding 15 m
Structures not exceeding 15 m tall and structural components within those structures shall
be deemed to meet the requirements of Clause 5.4.2.2 when they have been designed to
resist at the ultimate limit state a minimum horizontal static force given by the following,
applied simultaneously at each level for the given direction in combination with other
actions as specified in AS/NZS 1170.0:
Fi = Ks[kpZSp/μ]Wi . . . 5.4
where kp and Z are as given in Section 3 and Sp and μ are given in Clause 6.5
Ks = factor to account for floor, as given in Table 5.4
Wi = seismic weight of the structure or component at level i
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AS 1170.4—2007 34
© Standards Australia www.standards.org.au
TABLE 5.4
VALUES OF Ks FOR STRUCTURES NOT EXCEEDING 15 m
Total
number of
stories
Sub-soil
class
Ks factor
Storey under consideration
5th 4th 3rd 2nd 1st
5
Ae
Be
Ce
De, Ee
2.5
3.1
4.4
6.1
1.9
2.5
3.5
4.9
1.4
1.8
2.6
3.6
1.0
1.2
1.7
2.5
0.5
0.6
0.9
1.2
4
Ae
Be
Ce
De, Ee
—
—
—
—
2.7
3.5
4.9
5.8
2.0
2.6
3.6
4.4
1.4
1.7
2.5
3.0
0.6
0.9
1.2
1.4
3
Ae
Be
Ce, De, Ee
—
—
—
—
—
—
3.1
3.9
5.5
2.0
2.6
3.6
1.0
1.3
1.8
2
Ae
Be
Ce, De, Ee
—
—
—
—
—
—
—
—
—
3.1
3.9
4.9
1.6
1.9
2.5
1
Ae
Be
Ce, De, Ee
—
—
—
—
—
—
—
—
—
—
—
—
2.3
3.0
3.6
5.4.3 Vertical earthquake actions
Vertical earthquake actions need not be considered.
NOTE: For parts and components, see Clauses 5.4.6 and 8.1.3.
5.4.4 Drift
The inter-storey drift at the ultimate limit state calculated from the forces determined in
Clause 5.4.2 shall not exceed 1.5% of the storey height for each level (see Clause 6.7.2).
Attachment of cladding and facade panels to the seismic-force-resisting system shall have
sufficient deformation and rotational capacity to accommodate the design storey drift (dst).
Stairs required for emergency egress shall be capable of accommodating a drift of 1.5dst.
This Clause is deemed to be satisfied if the primary seismic force-resisting elements are
structural walls that extend to the base.
5.4.5 Pounding
Structures over 15 m shall be separated from adjacent structures or set back from a building
boundary by a distance sufficient to avoid damaging contact.
This Clause is deemed to be satisfied if the primary seismic force-resisting elements are
structural walls that extend to the base, or the setback from a boundary is more than 1% of
the structure height.
5.4.6 Parts and components
Non-structural parts and components shall be designed in accordance with Section 8 except
that for importance level 2 and 3 structures not exceeding 15 m, parts and components of
non-brittle construction may be attached using connectors designed for horizontal capacity
of 10% of the seismic weight of the part.
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35 AS 1170.4—2007
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5.5 EARTHQUAKE DESIGN CATEGORY III (EDC III)
5.5.1 General
All structures subject to earthquake design category III (EDC III) shall comply with the
requirements of Clause 5.2 and Clauses 5.5.2 to 5.5.6.
5.5.2 Strength and stability provisions
5.5.2.1 General
The seismic-force-resisting system shall be designed to resist the most critical action effect
arising from the application of the earthquake actions in any direction.
The design shall consider the earthquake loading applied, as specified in Clause 5.4.2.1.
Connections between elements of the structure shall be capable of transmitting an internal
ultimate limit state horizontal action equal to the values calculated using the dynamic
analysis but not less than 5% of the vertical reaction arising from the seismic weight or 5%
of the seismic weight of the component, whichever is the greater.
5.5.2.2 Earthquake forces—Dynamic analysis
Earthquake forces shall be calculated using the dynamic analysis method given in Section 7.
5.5.3 Vertical earthquake actions
Vertical earthquake actions need not be considered.
NOTE: For parts and components, see Clause 8.1.3.
5.5.4 Drift
The inter-storey drift at the ultimate limit state, calculated from the forces determined in
Clause 5.5.2, shall not exceed 1.5% of the storey height for each level (see Clause 6.7.2).
Attachment of cladding and facade panels to the seismic-force-resisting system shall have
sufficient deformation and rotational capacity to accommodate the design storey drift (dst).
Stairs required for emergency egress shall be capable of accommodating a drift of 1.5dst.
5.5.5 Pounding
Structures shall be separated from adjacent structures or set back from a building boundary
by a distance sufficient to avoid damaging contact.
This Clause is deemed to be satisfied when the setback from a boundary is more than 1% of
the structure height.
5.5.6 Parts and components
Non-structural parts and components shall be designed in accordance with Section 8.
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AS 1170.4—2007 36
© Standards Australia www.standards.org.au
S E C T I O N 6 E Q U I V A L E N T S T A T I C
A N A L Y S I S
6.1 GENERAL
Equivalent static analysis, when used, shall be carried out in accordance with this Section.
The procedure for equivalent static analysis is as follows:
(a) Decide on the form and material of the structure.
(b) Calculate kpZ using Section 3.
(c) Determine T1, Ch(T1), μ, and other structural properties.
(d) Determine the design action coefficients.
(e) Determine the seismic weight at each level (Wi).
(f) Calculate V using Clause 6.2.
(g) Calculate Fi using Clause 6.3.
(h) Apply the forces to the structure at the eccentricities specified in Clause 6.6.
(i) Take P-delta effects into account as specified in Clause 6.7.
6.2 HORIZONTAL EQUIVALENT STATIC FORCES
6.2.1 Earthquake base shear
The set of equivalent static forces in the direction being considered shall be assumed to act
simultaneously at each level of the structure and shall be applied taking into account the
torsion effects as given in Clause 6.6 in combination with other actions as specified in
AS/NZS 1170.0.
The horizontal equivalent static shear force (V) acting at the base of the structure (base
shear) in the direction being considered shall be calculated from the following equations:
V = Cd(T1)Wt . . . 6.2(1)
= [C(T1)Sp/μ]Wt . . . 6.2(2)
= [kpZCh(T1)Sp/μ]Wt . . . 6.2(3)
where
Cd(T1) = horizontal design action coefficient (value of the horizontal design
response spectrum at the fundamental natural period of the structure)
= C(T1)Sp/μ . . . 6.2(4)
C(T1) = value of the elastic site hazard spectrum, determined from Clause 6.4 using
kp appropriate for the structure, Z for the location and the fundamental
natural period of the structure
= kpZCh(T1) . . . 6.2(5)
Ch(T1) = value of the spectral shape factor for the fundamental natural period of the
structure, as given in Clause 6.4
Wt = seismic weight of the structure taken as the sum of Wi for all levels, as
given in Clause 6.2.2
Sp = structural performance factor, as given in Clause 6.5
μ = structural ductility factor, as given in Clause 6.5 Acc
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37 AS 1170.4—2007
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T1 = fundamental natural period of the structure, as given in Clause 6.2.3
6.2.2 Gravity load
The seismic weight (Wi) at each level shall be as given by the following equation:
Wi = ∑Gi + ∑ψcQi . . . 6.2(6)
where
Gi and ψcQi are summed between the mid-heights of adjacent storeys
Gi = permanent action (self-weight or ‘dead load’) at level i, including an allowance
of 0.3 kPa for ice on roofs in alpine regions as given in AS/NZS 1170.3
ψc = earthquake-imposed action combination factor
= 0.6 for storage applications
= 0.3 for all other applications
Qi = imposed action for each occupancy class on level i (see AS/NZS 1170.1)
NOTE: Seismic mass is the weight divided by acceleration due to gravity (mi = Wi/g).
6.2.3 Natural period of the structure
The fundamental period of the structure as a whole (T1, fundamental natural translational
period of the structure) in seconds, including all the materials incorporated in the whole
construction, may be determined by a rigorous structural analysis or from the following
equation:
T1 = 1.25kthn0.75
for the ultimate limit state . . . 6.2(7)
where
kt = 0.11 for moment-resisting steel frames
= 0.075 for moment-resisting concrete frames
= 0.06 for eccentrically-braced steel frames
= 0.05 for all other structures
hn = height from the base of the structure to the uppermost seismic weight or mass,
in metres
The base shear obtained using the fundamental structure period (T1) determined by a
rigorous structural analysis shall be not less than 70% of the value obtained with T1
calculated using the above equation.
6.3 VERTICAL DISTRIBUTION OF HORIZONTAL FORCES
The horizontal equivalent static design force (Fi) at each level (i) shall be obtained as
follows:
Fi = kF,iV . . . 6.3(1)
( )( ) tp1hpn
1j
kjj
kii
WS
TZCk
hW
hW⎥⎦
⎤⎢⎣
⎡=
∑=
μ
. . . 6.3(2)
where
kF,i = seismic distribution factor for the ith level
Wi = seismic weight of the structure at the ith level, in kilonewtons
hi = height of level i above the base of the structure, in metres
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AS 1170.4—2007 38
© Standards Australia www.standards.org.au
k = exponent, dependent on the fundamental natural period of the structure (T1),
which is taken as—
1.0 when T1 ≤ 0.5;
2.0 when T1 ≥ 2.5; or
linearly interpolated between 1.0 and 2.0 for 0.5 < T1 < 2.5
n = number of levels in a structure
The horizontal equivalent static earthquake shear force (Vi) at storey i is the sum of all the
horizontal forces at and above the ith level (Fi to Fn).
6.4 SPECTRAL SHAPE FACTOR (Ch(T))
The spectral shape factor (Ch(T)) shall be as given in Table 6.4 (illustrated in Figure 6.4) for
the appropriate site sub-soil class defined in Section 4.
TABLE 6.4
SPECTRAL SHAPE FACTOR (Ch(T))
Site sub-soil class
Period
(seconds)
Ae
Strong rock
Be
Rock
Ce
Shallow soil
De
Deep or soft soil
Ee
Very soft soil
0.0
0.1
0.2
2.35 (0.8)*
2.35
2.35
2.94 (1.0)*
2.94
2.94
3.68 (1.3)*
3.68
3.68
3.68 (1.1)*
3.68
3.68
3.68 (1.1)*
3.68
3.68
0.3
0.4
0.5
2.35
1.76
1.41
2.94
2.20
1.76
3.68
3.12
2.50
3.68
3.68
3.68
3.68
3.68
3.68
0.6
0.7
0.8
1.17
1.01
0.88
1.47
1.26
1.10
2.08
1.79
1.56
3.30
2.83
2.48
3.68
3.68
3.68
0.9
1.0
1.2
0.78
0.70
0.59
0.98
0.88
0.73
1.39
1.25
1.04
2.20
1.98
1.65
3.42
3.08
2.57
1.5
1.7
2.0
0.47
0.37
0.26
0.59
0.46
0.33
0.83
0.65
0.47
1.32
1.03
0.74
2.05
1.60
1.16
2.5
3.0
3.5
0.17
0.12
0.086
0.21
0.15
0.11
0.30
0.21
0.15
0.48
0.33
0.24
0.74
0.51
0.38
4.0
4.5
5.0
0.066
0.052
0.042
0.083
0.065
0.053
0.12
0.093
0.075
0.19
0.15
0.12
0.29
0.23
0.18
Equations for spectra
0 < T ≤ 0.1 0.1 < T ≤ 1.5
T > 1.5
0.8 + 15.5T
0.704/T but ≤ 2.35 1.056/T2
1.0 + 19.4T
0.88/T but ≤ 2.941.32/T2
1.3 + 23.8T
1.25/T but ≤ 3.681.874/T2
1.1 + 25.8T
1.98/T but ≤ 3.68 2.97/T2
1.1 + 25.8T
3.08/T but ≤ 3.684.62/T2
* Values in brackets correspond to values of spectral shape factor for the modal response spectrum and the
numerical integration time history methods and for use in the method of calculation of forces on parts and
components (see Section 8)
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39 AS 1170.4—2007
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0.00
0.50
1.00
1.50
2.00
2.50
3.00
3.50
4.00
0.0 0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0 4.5 5.0
Soil AeSoil BeSoil CeSoil DeSoil Ee
PERIOD IN SECONDS (T)
SP
EC
TR
AL
OR
DIN
AT
ES
(C
h(T
))
FIGURE 6.4 NORMALIZED RESPONSE SPECTRA FOR SITE SUB-SOIL CLASS
6.5 DETERMINATION OF STRUCTURAL DUCTILITY (μ) AND STRUCTURAL PERFORMANCE FACTOR (Sp)
The ductility of the structure (μ) and the structural performance factor (Sp) shall be determined either—
(a) in accordance with the appropriate material standard where the data is provided; or
(b) as given in Table 6.5(A) or 6.5(B) for the structure type and material where the data
is not provided,
except that, for a specific structure that is first mode dominant, it shall be permissible to
determine μ and Sp by using a non-linear static pushover analysis. When undertaking such a displacement-based approach, the seismic demand shall be based on a response spectrum
defined by 1.5KpZCh(T).
NOTES:
1 Where the design is carried out using other than recognized Australian material design
Standards, then the values given in the last row for each material type in Table 6.5A should
be used.
2 Where the design is carried out in accordance with NZS 1170.5, μ and Sp should be determined as set out therein.
A lower μ value that is specified in this Clause or the relevant material standard may be used. In all cases, the structure shall be detailed to achieve the level of ductility assumed in
the design, in accordance with the applicable material design Standard.
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AS 1170.4—2007 40
© Standards Australia www.standards.org.au
TABLE 6.5(A)
STRUCTURAL DUCTILITY FACTOR (μ) AND STRUCTURAL PERFORMANCE FACTOR (Sp)—BASIC STRUCTURES
Structural
system Description μ Sp Sp/μ μ/Sp
Steel structures
Special moment-resisting frames (fully ductile)* 4 0.67 0.17 6
Intermediate moment-resisting frames (moderately ductile) 3 0.67 0.22 4.5
Ordinary moment-resisting frames (limited ductile) 2 0.77 0.38 2.6
Moderately ductile concentrically braced frames 3 0.67 0.22 4.5
Limited ductile concentrically braced frames 2 0.77 0.38 2.6
Fully ductile eccentrically braced frames* 4 0.67 0.17 6
Other steel structures not defined above 2 0.77 0.38 2.6
Concrete structures
Special moment-resisting frames (fully ductile)* 4 0.67 0.17 6
Intermediate moment-resisting frames (moderately ductile) 3 0.67 0.22 4.5
Ordinary moment-resisting frames 2 0.77 0.38 2.6
Ductile coupled walls (fully ductile)* 4 0.67 0.17 6
Ductile partially coupled walls* 4 0.67 0.17 6
Ductile shear walls 3 0.67 0.22 4.5
Limited ductile shear walls 2 0.77 0.38 2.6
Ordinary moment-resisting frames in combination with a limited
ductile shear walls 2 0.77 0.38 2.6
Other concrete structures not listed above 2 0.77 0.38 2.6
Timber structures
Shear walls 3 0.67 0.22 4.5
Braced frames (with ductile connections) 2 0.77 0.38 2.6
Moment-resisting frames 2 0.77 0.38 2.6
Other wood or gypsum based seismic-force-resisting systems not
listed above 2 0.77 0.38 2.6
Masonry structures
Close-spaced reinforced masonry† 2 0.77 0.38 2.6
Wide-spaced reinforced masonry† 1.5 0.77 0.5 2
Unreinforced masonry† 1.25 0.77 0.62 1.6
Other masonry structures not complying with AS 3700 1.00 0.77 0.77 1.3
* The design of structures with μ > 3 is outside the scope of this Standard (see Clause 2.2)
† These values are taken from AS 3700
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41 AS 1170.4—2007
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TABLE 6.5(B)
STRUCTURAL DUCTILITY FACTOR (μ) AND STRUCTURAL PERFORMANCE FACTOR (Sp)—SPECIFIC STRUCTURE TYPES
Type of structure μ Sp μ/Sp Sp/μ
Tanks, vessels or pressurized spheres on braced or unbraced legs 2 1 2 0.5
Cast-in-place concrete silos and chimneys having walls continuous to
the foundation 3 1 3 0.33
Distributed mass cantilever structures, such as stacks, chimneys, silos
and skirt-supported vertical vessels 3 1 3 0.33
Trussed towers (freestanding or guyed), guyed stacks and chimneys 3 1 3 0.33
Inverted pendulum-type structures 2 1 2 0.5
Cooling towers 3 1 3 0.33
Bins and hoppers on braced or unbraced legs 3 1 3 0.33
Storage racking 3 1 3 0.33
Signs and billboards 3 1 3 0.33
Amusement structures and monuments 2 1 2 0.5
All other self-supporting structures not otherwise covered 3 1 3 0.33
6.6 TORSIONAL EFFECTS
For each required direction of earthquake action, the earthquake actions, as determined in
Clause 6.3, shall be applied at the position calculated as ±0.1b from the nominal centre of mass, where b is the plan dimension of the structure at right angles to the direction of the
action.
This ±0.1b eccentricity shall be applied in the same direction at all levels and orientated to produce the most adverse torsion moment for the 100% and 30% loads.
6.7 DRIFT DETERMINATION AND P-DELTA EFFECTS
6.7.1 General
Storey drifts, member forces and moments due to P-delta effects shall be determined in
accordance with Clauses 6.7.2 and 6.7.3.
6.7.2 Storey drift determination
Storey drifts shall be assessed for the two major axes of a structure considering horizontal
earthquake forces acting independently, but not simultaneously, in each direction. The
design storey drift (dst) shall be calculated as the difference of the deflections (di) at the top
and bottom of the storey under consideration.
The design deflections (di) shall be determined from the following equations:
di = dieμ/Sp . . . 6.7(1)
where
die = deflection at the ith level determined by an elastic analysis, carried out using
the horizontal equivalent static earthquake forces (Fi) specified in Clause 6.3,
applied to the structure in accordance with Clause 6.6
Where applicable, the design storey drift (dst) shall be increased to allow for the P-delta
effects as given in Clause 6.7.3.
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AS 1170.4—2007 42
© Standards Australia www.standards.org.au
6.7.3 P-delta effects
6.7.3.1 Stability coefficient
For the inter-storey stability coefficient (θ) calculated for each level, design for P-delta effects shall be as follows:
(a) For θ ≤ 0.1, P-delta effects need not be considered.
(b) For θ > 0.2, the structure is potentially unstable and shall be re-designed.
(c) For 0.1 < θ ≤ 0.2, P-delta effects shall be calculated as given in Clause 6.7.3.2,
∑ ∑= =
⎟⎟
⎠
⎞
⎜⎜
⎝
⎛=
n
ij
n
ij
jsijst / FhWd μθ . . . 6.7(2)
where
i = level of the structure under consideration
hsi = inter-storey height of level i, measured from centre-line to centre-line of the
floors
6.7.3.2 Calculating P-delta effects
Values of the horizontal earthquake shear f