AS-1170-4-2007(encrypted)

AS 1170.4—2007

AS 1170.4—2007

Australian Standard® Structural design actions

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Part 4: Earthquake actions in Australia

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.

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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 Standards may also be withdrawn.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.

AS 1170.4—2007

Australian Standard® Structural design actions Part 4: Earthquake actions in Australia

Accessed by SINCLAIR KNIGHT MERZ on 31 Jan 2011

Originated as AS 2121—1979. Revised and redesignated as AS 1170.4—1993. Second edition 2007.

COPYRIGHT © Standards Australia All rights are reserved. No part of this work may be reproduced or copied in any form or by any means, electronic or mechanical, including photocopying, without the written permission of the publisher. Published by Standards Australia GPO Box 476, Sydney, NSW 2001, Australia ISBN 0 7337 8349 X

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. 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 1170.4

Structural design actions Part 4: Earthquake actions (this Standard)

AS/NZS 1170.0 1170.1 1170.2 1170.3

Part 0: Part 1: Part 2: Part 3:

General principles Permanent, imposed and other actions Wind actions Snow and ice actions

NZS 1170.5

Part 5:

Earthquake actions—New Zealand

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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. (g)

The option to allow no analysis or detailing for some structures has been removed (except for importance level 1 structures).

* 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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AS 1170.4—2007

(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/R f to S p/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.

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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. 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.

* 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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Statements expressed in mandatory terms in notes to tables and figures are deemed to be an integral part of this Standard.

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Notes to the text contain information and guidance. They are not an integral part of the Standard.

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AS 1170.4—2007

CONTENTS Page SECTION 1 SCOPE AND GENERAL 1.1 SCOPE ........................................................................................................................ 6 1.2 NORMATIVE REFERENCES .................................................................................... 6 1.3 DEFINITIONS ............................................................................................................ 7 1.4 NOTATION AND UNITS........................................................................................... 9 1.5 LEVELS, WEIGHTS AND FORCES OF THE STRUCTURE.................................. 11 SECTION 2 DESIGN PROCEDURE 2.1 GENERAL ................................................................................................................ 15 2.2 DESIGN PROCEDURE ............................................................................................ 15 SECTION 3 SITE HAZARD 3.1 ANNUAL PROBABILITY OF EXCEEDANCE (P) AND PROBABILITY FACTOR (kp)............................................................................................................. 18 3.2 HAZARD FACTOR (Z) ............................................................................................ 18 SECTION 4 SITE SUB-SOIL CLASS 4.1 DETERMINATION OF SITE SUB-SOIL CLASS.................................................... 27 4.2 CLASS DEFINITIONS ............................................................................................. 28

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SECTION 5 EARTHQUAKE DESIGN 5.1 GENERAL ................................................................................................................ 30 5.2 BASIC DESIGN PRINCIPLES ................................................................................. 30 5.3 EARTHQUAKE DESIGN CATEGORY I (EDC I)................................................... 31 5.4 EARTHQUAKE DESIGN CATEGORY II (EDC II) ................................................ 31 5.5 EARTHQUAKE DESIGN CATEGORY III (EDC III).............................................. 34 SECTION 6 EQUIVALENT STATIC ANALYSIS 6.1 GENERAL ................................................................................................................ 35 6.2 HORIZONTAL EQUIVALENT STATIC FORCES.................................................. 35 6.3 VERTICAL DISTRIBUTION OF HORIZONTAL FORCES.................................... 36 6.4 SPECTRAL SHAPE FACTOR (Ch(T)) ..................................................................... 37 6.5 DETERMINATION OF STRUCTURAL DUCTILITY (μ) AND STRUCTURAL PERFORMANCE FACTOR (Sp) .................................................... 38 6.6 TORSIONAL EFFECTS ........................................................................................... 40 6.7 DRIFT DETERMINATION AND P-DELTA EFFECTS .......................................... 40 SECTION 7 DYNAMIC ANALYSIS 7.1 GENERAL ................................................................................................................ 42 7.2 EARTHQUAKE ACTIONS ...................................................................................... 42 7.3 MATHEMATICAL MODEL .................................................................................... 42 7.4 MODAL ANALYSIS ................................................................................................ 43 7.5 DRIFT DETERMINATION AND P-DELTA EFFECTS .......................................... 43 SECTION 8 DESIGN OF PARTS AND COMPONENTS 8.1 GENERAL REQUIREMENTS ................................................................................. 44 8.2 METHOD USING DESIGN ACCELERATIONS ..................................................... 46 8.3 SIMPLE METHOD ................................................................................................... 46 APPENDIX A

DOMESTIC STRUCTURES (HOUSING) .......................................... 48

AS 1170.4—2007

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STANDARDS AUSTRALIA Australian Standard Structural design actions Part 4: Earthquake actions in Australia

SECT ION

1

SCOPE

AND

GENERA 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.

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1.2 NORMATIVE REFERENCES The following referenced documents are indispensable to the application of this Standard. AS 1684

Residential timber-framed construction (all parts)

1720 1720.1

Timber structures Part 1: Design methods

3600

Concrete structures

3700

Masonry structures

4100

Steel structures

AS/NZS 1170 1170.0 1170.1 1170.3

Structural design actions Part 0: General principles Part 1: Permanent, imposed and other actions Part 3: Snow and ice actions

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AS 1170.4—2007

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 6.2). 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 6.2). 1.3.6 Connection Mechanical means that provide a load path for actions between structural elements, nonstructural elements and structural and non-structural elements. 1.3.7 Diaphragm

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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. 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.

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1.3.12 Moment-resisting frame, intermediate Concrete or steel moment-resisting frame designed and detailed to achieve moderate structural ductility (see Table 6.2). 1.3.13 Moment-resisting frame, ordinary Moment-resisting frame with no particular earthquake detailing, specified in the relevant material standard (see Table 6.2). 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 6.2). 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-forceresisting 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

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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 (S p) Numerical assessment of the additional ability of the total building (structure and other parts) to survive earthquake motion. 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).

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AS 1170.4—2007

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).

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Unless stated otherwise, the notation used in this Standard shall have the following meanings: ac

= component amplification factor

a floor

= effective floor acceleration at the height of the component centre of mass

ax

= height amplification factor at height h x 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(T 1)

= value of the elastic site hazard spectrum for the fundamental natural period of the structure

C d(T)

= horizontal design response spectrum as a function of period (T)

C d(T1 )

= horizontal design action coefficient (value of the horizontal design response spectrum for the fundamental natural period of the structure)

C h (T)

= spectral shape factor as a function of period (T) (dimensionless coefficient)

C h (T1 )

= value of the spectral shape factor for the fundamental natural period of the structure

C v (T v )

= elastic site hazard spectrum for vertical loading, which may be taken as half of the elastic site hazard spectrum for horizontal loading (C(T))

C vd (T)

= vertical design response spectrum as a function of period (T)

C h (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’

d ie

= deflection at level ‘i’ determined by an elastic analysis

d st

= 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 F i 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 kilonewtons

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

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hn

= height from the base of the structure to the uppermost seismic weight or mass, in metres (see Clause 1.5)

h si

= 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 (T 1)

kc

= factor for determining height amplification factor (a x )

k F,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

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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 + ψc Q) 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

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

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AS 1170.4—2007

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 W n , it shall be treated as the top seismic weight and W n and W n − 1 recalculated. The building height (h n ) is taken as the height of the centre of mass of W n above the base.

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Figure 1.5(C) illustrates the structural base for various situations.

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AS 1170.4—2007

12 Uppermost seismic mass Level n

Force F n Storey n Force F n

- 1

Level n - 1

Force F i

+ 1

Level i + 1 Storey i + 1 hn

Level i

Force F i Storey i

h si h

Force F i

Level i - 1

- 1

Level 1

Force F i Storey 1

Base

Level i + 1 Storey i + 1

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Wi

h si 2 h si 2

Level i Wi Storey i Level i - 1

FIGURE 1.5(A) ILLUSTRATION OF LEVEL, STOREY, WEIGHT AND FORCE

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AS 1170.4—2007 Centre of gravity of W n

Plant

Top Wn Storey n hn Storey n - 1

Base

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FIGURE 1.5(B) EXAMPLE OF DETERMINATION OF THE TOP OF THE STRUCTURE

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AS 1170.4—2007

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Building height, h n

(a) Base shear reaction at ground level

Building height, h n

(b) Base shear reaction below ground level

Building height, h n

(c) Base shear reaction taken as at lowest level

Building height, h n

(d) Base shear reaction at ground level

NOTE: Building height measured from top of slab at relevant level.

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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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S E C T I ON

2

D E S I G N

AS 1170.4—2007

PRO CE D U RE

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 (E u ) 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 (k p) 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.

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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.

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 for importance level 2 structures.

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TABLE 2.1 SELECTION OF EARTHQUAKE DESIGN CATEGORIES Importance level, type of structure (see Clause 2.2)

(k pZ) for site sub-soil class E e or D e

Ce

1

Ae

—

≤0.05

≤0.08

≤0.11

≤0.14

>0.05 to ≤0.08 >0.08 to ≤0.12 >0.11 to ≤0.17 >0.14 to ≤0.21

—

Not required to be designed for earthquake actions

Top of roof ≤8.5

Refer to Appendix A

Top of roof >8.5

Design as importance level 2

≤12 >12, 0.12

>0.17

>0.21

0.12

>0.17

>0.21

3 is outside the scope of this Standard (see Clause 2.2) † These values are taken from AS 3700

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TABLE 6.5(B) STRUCTURAL DUCTILITY FACTOR (µ) AND STRUCTURAL PERFORMANCE FACTOR (S p)—SPECIFIC STRUCTURE TYPES µ

Sp

µ/S p

S p/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

Type of structure

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.

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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 (d i ) at the top and bottom of the storey under consideration. The design deflections (d i) shall be determined from the following equations: d i = d ie μ/S p

. . . 6.7(1)

where d ie = deflection at the ith level determined by an elastic analysis, carried out using the horizontal equivalent static earthquake forces (F i ) 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

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, θ = d st

⎛ W j / ⎜ hsi μ ⎜ j=i ⎝ n

∑

⎞

n

∑ F ⎟⎟ j= i

j

⎠

. . . 6.7(2)

where i

= level of the structure under consideration

h si = 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 forces and moments, the resulting member forces and moments, and the storey drifts that include the P-delta effects shall be determined by— scaling the equivalent static forces and deflections by the factor (0.9/(1 – θ)), which is greater than or equal to 1; or

(b)

using a second-order analysis.

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(a)

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SECT ION

7

DYNAM I C

ANA L YS I S

7.1 GENERAL Dynamic analysis, when used, shall be carried out in accordance with this Section. The analysis shall be based on an appropriate ground-motion representation in accordance with Clause 7.2. The mathematical model used shall be in accordance with Clause 7.3. The analysis procedure may be either a modal-response-spectrum analysis in accordance with Clause 7.4 or a time-history analysis in accordance with Clause 7.2(c). Drift and P-delta effects shall be determined in accordance with Clause 7.5. 7.2 EARTHQUAKE ACTIONS The earthquake ground motion shall be accounted for by using one of the following: (a)

Horizontal design response spectrum (Cd(T)), including the site hazard spectrum and the effects of the structural response as follows: C d(T) = C(T)S p/μ = k pZC h (T)Sp/μ

. . . 7.2(1) . . . 7.2(2)

where values are as given in Section 6, except that—

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T = period of vibration appropriate to the mode of vibration of the structure being considered (b)

Site-specific design response spectra developed for the specific site, which shall be based on analyses that consider the soil profile and apply a bedrock ground motion compatible with the rock spectra given in Clause 6.4.

(c)

Ground-motion time histories chosen for the specific site, which shall be representative of actual earthquake motions. Response spectra from these time histories, either individually or in combination, shall approximate the site design spectrum conforming to Item (a) or (b). A dynamic analysis of a structure by the time-history method involves calculating the response of a structure at each increment of time when the base is subjected to a specific ground-motion time-history. The analysis should be based on well-established principles of mechanics using groundmotion records compatible with the site-specific design response spectra.

Where design includes consideration of vertical earthquake actions, both upwards and downwards directions shall be considered and the vertical design response spectrum shall be as follows: C vd (T) = C v (T v )S p

. . . 7.2(3)

= 0.5C(T v )S p = 0.5k pZC h (T v )S p where C v (T v ) = elastic site hazard spectrum for vertical loading for the vertical period of vibration 7.3 MATHEMATICAL MODEL A mathematical model of the physical structure shall represent the spatial distribution of the mass and stiffness of the structure to an extent that is adequate for the calculation of the significant features of its dynamic response. © Standards Australia

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AS 1170.4—2007

7.4 MODAL ANALYSIS 7.4.1 General A dynamic analysis of a structure by the modal response spectrum method shall use the peak response of all modes having a significant contribution to the total structural response as specified in Clause 7.4.2. Peak modal responses shall be calculated using the ordinates of the appropriate response spectrum curve specified in Clause 7.2(a) or 7.2(b) that corresponds to the modal periods. Maximum modal contributions shall be combined in accordance with Clause 7.4.3. 7.4.2 Number of modes In two-dimensional analysis, sufficient modes shall be included in the analysis to ensure that at least 90% of the mass of the structure is participating for the direction under consideration. In three-dimensional analysis, where structures are modelled so that modes that are not those of the seismic-force-resisting system are considered, then all modes not part of the seismic-force-resisting system shall be ignored. Further, all modes with periods less than 5% of the fundamental natural period of the structure ( 0.05W c

. . . 8.3

where Ic , a c, R c, W c are as given in Clause 8.2; and kp

= probability factor (see Section 3)

Z

= hazard factor (see Section 3)

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ax

AS 1170.4—2007

= height amplification factor at height h x at which the component is attached, given as follows: = (1 + kch x ) k c = 2/h n for h n ≥ 12 m = 0.17 for h n < 12 m h x = height at which the component is attached above the structural base of the structure, in metres

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h n = total height of the structure above the structural base, in metres

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APPENDIX A

DOMESTIC STRUCTURES (HOUSING) (Normative) A1 GENERAL For the purposes of this Appendix, a domestic structure (housing) is a single dwelling or one or more attached dwellings complying with Class 1a or 1b, as defined in the Building Code of Australia (as shown in Figure A1). Domestic structures (housing) exceeding 8.5 m in height (see Figure A1), shall be designed in accordance with Section 2 for Importance Level 2 structures, using the annual probability of exceedance specified for housing. TABLE A1 DESIGN OF DOMESTIC STRUCTURES OF HEIGHT LESS THAN OR EQUAL TO 8.5 METRES Hazard at the kpZ

Provision for lateral resistance

≤0.11

Housing designed and detailed for lateral wind forces in accordance with AS 1684, AS 3600, AS 3700, AS 4100, AS/NZS 1664, AS 1720.1 or NASH Standard Part 1—2005

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>0.11

Housing designed and detailed for lateral wind forces in accordance with AS 1684, AS 3600, AS 3700, AS 4100, AS/NZS 1664, AS 1720.1 or NASH Standard Part 1—2005

Material type

Specific deemed to satisfy limits

Design required

As per the relevant Standard

As per the relevant Standard

No specific earthquake design required

Adobe, pressed earth bricks, rammed earth or other earth-wall material not in accordance with AS 3700

None provided

Use Paragraph A2 or design as for importance level 2 (see Section 2)

Other materials ∗

None provided

Use Paragraph A2 or design as for importance level 2 (see Section 2)

As per the relevant Standard

As per the relevant Standard

Use Paragraph A2 or design as for importance level 2 (see Section 2)

∗ This includes any other materials that are not covered by accepted design Standards such as random stone masonry or hay bale construction

A2 DESIGN AND DETAILING Domestic structures required to be designed in accordance with this Paragraph shall comply with the following requirements: (a)

Where the racking forces calculated in this item are greater than those calculated for wind action, lateral bracing shall be provided in both orthogonal directions, distributed into at least two walls in each orthogonal direction with a maximum spacing between walls of 9 m to resist the following forces:

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(i)

For masonry veneer, reinforced masonry, timber, steel and concrete structures— F r = 1.4 k p Z W

(ii)

AS 1170.4—2007

. . . A2(1)

For unreinforced masonry and other structures— F r = 2.3 k p Z W

. . . A2(2)

where Fr

= horizontal design racking earthquake force applied in each orthogonal direction on the part or component, in kilonewtons

W

= sum of the seismic weight of the building (G + 0.3Q) at the level where bracing is to be determined and above this level (see Figure 1.5(A))

kp

= probability factor appropriate for the limit state under consideration

Z

= earthquake hazard factor, which is equivalent to an acceleration coefficient with an annual probability of exceedance of 1/500 (i.e., a 10% probability of exceedance in 50 years)

(b)

Walls shall be tied to other walls that they abut and shall be anchored to the roof and all floors that provide horizontal in-plane and perpendicular to the plane of the wall support for the wall, with an anchorage capable of resisting 0.5 kN/m. Walls shall be checked for stability under out-of-plane lateral loads of Z times the weight of the wall.

(c)

Non-ductile components, such as unreinforced masonry gable ends, chimneys and parapets shall be restrained to resist a minimum force of 0.1W c , where W c is the weight of the component. Masonry veneer walls tied to framing in accordance with AS 3700 are deemed to comply with this Item (c).

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NOTE: See AS 3700 for detailing requirements for masonry structures.

FIGURE A1 SECTION GEOMETRY

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BIBLIOGRAPHY

Earth retaining structures

NZS 1170 1170.5

Structural design actions Part 5: Earthquake actions—New Zealand

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AS 4678

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NOTES

AS 1170.4—2007

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AS 1170.4—2007 52

NOTES

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