Structural design actions Accessed by CURTIN UNIVERSITY …AS 1170.4—2007 (Incorporating Amendment No. 1) Structural design actions Part 4: Earthquake actions in Australia AS 1170.4—2007

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 Standards may also be withdrawn.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®



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



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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9 AS 1170.4—2007


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


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


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


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


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


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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15 AS 1170.4—2007


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


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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17 AS 1170.4—2007


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


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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19 AS 1170.4—2007


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


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


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




FIGURE 3.2(B) HAZARD FACTOR (Z) FOR SOUTH AUSTRALIA

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23 AS 1170.4—2007


FIGURE 3.2(C) HAZARD FACTOR (Z) FOR WESTERN AUSTRALIA

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AS 1170.4—2007 24




FIGURE 3.2(D) HAZARD FACTOR (Z) FOR SOUTH-WEST OF WESTERN AUSTRALIA

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25 AS 1170.4—2007




FIGURE 3.2(E) HAZARD FACTOR (Z) FOR NORTHERN TERRITORY

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AS 1170.4—2007 26




FIGURE 3.2(F) HAZARD FACTOR (Z) FOR QUEENSLAND

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27 AS 1170.4—2007


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


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


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


(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


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


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


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


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.


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


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.


Non-structural parts and components shall be designed in accordance with Section 8.

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AS 1170.4—2007 36


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


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


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


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


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


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


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