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5 DETERMINATION OF STRUCTURAL DUCTILITY (μ) AND STRUCTURALPERFORMANCE FACTOR (Sp)

5 DETERMINATION OF STRUCTURAL DUCTILITY (μ) AND STRUCTURALPERFORMANCE FACTOR (Sp)

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39



AS 1170.4—2007



TABLE 6.5(A)

STRUCTURAL DUCTILITY FACTOR (µ) AND STRUCTURAL

PERFORMANCE FACTOR (S p)—BASIC STRUCTURES

Structural

system



µ



Sp



S p/µ



µ/S p



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



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



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



Description



Steel structures



Concrete structures



Accessed by SWINBURNE UNIVERSITY OF TECHNOLOGY on 19 Nov 2007



Timber structures



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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â Standards Australia



AS 1170.42007



40



TABLE 6.5(B)

STRUCTURAL DUCTILITY FACTOR (à) 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.



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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 (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.



© Standards Australia



www.standards.org.au



41



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.



Accessed by SWINBURNE UNIVERSITY OF TECHNOLOGY on 19 Nov 2007



(a)



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© Standards Australia



AS 1170.4—2007



42



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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43



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 (<0.05T1) may be ignored.

7.4.3 Combining modes

The peak member forces, displacements, horizontal earthquake shear forces and base

reactions for each mode shall be combined by a recognized method.

When modal periods are closely spaced, modal interaction effects shall be considered.

7.4.4 Torsion

7.4.4.1 Three-dimensional dynamic analysis



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Three-dimensional dynamic analysis shall take account of torsional effects, including

accidental torsional effects as described in Clause 6.6. Where three-dimensional models are

used for analysis, the effects of accidental torsion shall be accounted for, either by

appropriate adjustments in the model, such as adjustment of mass locations, or by

equivalent static procedures, as described in Clause 6.6.

7.4.4.2 Two-dimensional dynamic analysis with static analysis for torsion

For static analysis for torsional effects, applied torsion at each level shall use either the

actions calculated by the equivalent static method or the combined storey earthquake forces

found in a two-dimensional modal response spectrum analysis for translation. The

eccentricity used shall be as required in Clause 6.6. Action effects arising from torsion shall

be combined with the translational action effects by direct summation, with signs chosen to

produce the most adverse combined effects in the resisting members.

7.5 DRIFT DETERMINATION AND P-DELTA EFFECTS

Storey drifts, member forces and moments due to P-delta effects shall be calculated in

accordance with Clause 6.7, using the deflections, forces and moments calculated from the

dynamic analysis.



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© Standards Australia



AS 1170.4—2007



44



SECT ION



8



DES IG N O F PARTS

COMPONENTS



AND



8.1 GENERAL REQUIREMENTS

8.1.1 General

Non-structural parts and components and their fastenings, as listed in Clause 8.1.4, shall be

designed for horizontal and vertical earthquake forces as defined in Clauses 8.1.2 and 8.1.3.

Base isolation may be used to reduce the forces on a component. Where flexible mounting

devices (such as spring mountings) are used, they shall be fitted with restraining devices to

limit the horizontal and vertical motions, to inhibit the development of resonance in the

flexible mounting system, and to prevent overturning.

8.1.2 Earthquake actions

Design of parts and components shall be carried out for earthquake actions by one of the

following methods:

(a)



Using established principles of structural dynamics.



(b)



Using the general method given in Clause 8.2.



(c)



Using the forces determined by the simplified method given in Clause 8.3.



8.1.3 Forces on components

The horizontal earthquake force on any component shall be applied at the centre of gravity

of the component and shall be assumed to act in any horizontal direction. Vertical

earthquake forces on mechanical and electrical components shall be taken as 50% of the

horizontal earthquake force.



Accessed by SWINBURNE UNIVERSITY OF TECHNOLOGY on 19 Nov 2007



Mechanical connectors from the following shall be designed for 1.5 times the design force

for the supported element:

(a)



Curtain walls.



(b)



External walls.



(c)



Walls enclosing stairs, stair shafts, lifts and required exit paths.



8.1.4 Parts and components

The following parts and components and their connections shall be designed in accordance

with this Section:

(a)



Architectural components:

(i)



Walls that are not part of the seismic-force-resisting system.



(ii)



Appendages, including parapets, gables, verandas, awnings, canopies,

chimneys, roofing components (tiles, metal panels) containers and

miscellaneous components.



(iii) Connections (fasteners) for wall attachments, curtain walls, exterior nonloadbearing walls.

(iv)



Partitions.



(v)



Floors (including access floor systems, where the weight of the floor system

shall be determined in accordance with Clause 6.2.2).



(vi)



Ceilings.



© Standards Australia



www.standards.org.au



45



AS 1170.4—2007



(vii) Architectural equipment including storage racks and library shelves with a

height over 2.0 m.

(b)



Mechanical and electrical components:

(i)



Smoke control systems.



(ii)



Emergency electrical systems (including battery racks).



(iii) Fire and smoke detection systems.

(iv)



Fire suppression systems (including sprinklers).



(v)



Life safety system components.



(vi)



Boilers, furnaces, incinerators, water heaters, and other equipment using

combustible energy sources or high-temperature energy sources, chimneys,

flues, smokestacks, vents and pressure vessels.



(vii) Communication systems (such as cable systems motor control devices,

switchgear, transformers, and unit substations).

(viii) Reciprocating or rotating equipment.

(ix)



Utility and service interfaces.



(x)



Anchorage of lift machinery and controllers.



(xi)



Lift and hoist components including structural frames providing support for

guide rail brackets, guide rails and brackets, car and counterweight members.



(xii) Escalators.

(xiii) Machinery (manufacturing and process).

(xiv) Lighting fixtures.

(xv) Electrical panel boards and dimmers.

(xvi) Conveyor systems (non-personnel).



Accessed by SWINBURNE UNIVERSITY OF TECHNOLOGY on 19 Nov 2007



(xvii) Ducts and piping distribution systems.

(xviii) Supports for ducts and piping distribution systems, except supports in the

following situations:



(c)



(A)



In structures classified as being in EDC I.



(B)



For gas piping less than 25 mm inside diameter.



(C)



For piping in boiler and mechanical rooms less than 32 mm inside

diameter.



(D)



For all other piping less than 64 mm inside diameter.



(E)



For all electrical conduit less than 64 mm inside diameter.



(F)



For all rectangular air-handling ducts less than 0.4 m 2 in cross-sectional

area.



(G)



For all round air-handling ducts less than 700 mm in diameter.



(H)



For all ducts and piping suspended by individual hangers 300 mm or less

in length from the top of the pipe to the bottom of the support for the

hanger.



All other components similar to those listed in Items (a) and (b).



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© Standards Australia



AS 1170.4—2007



46



8.2 METHOD USING DESIGN ACCELERATIONS

Architectural, mechanical and electrical components and their fixings shall be designed for

earthquake actions from the accelerations determined using the design methods given in

Sections 6 and 7, as appropriate for the particular structure in which the component or

fixing is incorporated.

The forces generated on the part or component in the specific structure being considered are

given as follows, based on the principles given in this Standard for design of the structure:

F c = a floor [I cac/Rc]W c ≤ 0.5W c



. . . 8.2(1)



where

a floor = effective floor acceleration at the level where the component is situated,

calculated from the earthquake actions determined for the structure using

Sections 5, 6 and 7 divided by the seismic weight, but not less than k pZC h(0),

where the values of C h (0) are the bracketed values given in Table 6.1

NOTE: The fundamental natural period of vibration of a completed structure may

be determined by measurement.



Ic



= component importance factor, taken as:

= 1.5 for components critical for life safety, which includes parts and

components required to function immediately following an earthquake, those

critical to containment of hazardous materials, storage racks in public areas

and all parts and components in importance level 4 structures

= 1.0 for all other components

= component amplification factor



ac



= 2.5 for flexible spring-type mounting systems for mechanical equipment

(unless detailed dynamic analysis is used to justify lower values)

= 1.0 for all other mounting systems

= component ductility factor



Rc

Accessed by SWINBURNE UNIVERSITY OF TECHNOLOGY on 19 Nov 2007



= 1.0 for rigid components with non-ductile or brittle materials or connections

= 2.5 for all other components and parts

= seismic weight of the component, in kilonewtons



Wc



For objects mounted on the ground, the acceleration should be taken as follows:

a floor = k p ZC h (0)



. . . 8.2(2)



where

C h (0) = bracketed value of the spectral shape factor for the period of zero seconds,

as given in Clause 6.4

8.3 SIMPLE METHOD

Non-structural parts or components and their attachments shall be designed to resist the

horizontal earthquake force determined as follows and applied to the component at its

centre of mass in combination with the gravity load of the element:

F c = [k pZC h (0)]a x [I cac/Rc]W c



but > 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)



© Standards Australia



www.standards.org.au



47



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



Accessed by SWINBURNE UNIVERSITY OF TECHNOLOGY on 19 Nov 2007



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



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© Standards Australia



AS 1170.4—2007



48



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



Accessed by SWINBURNE UNIVERSITY OF TECHNOLOGY on 19 Nov 2007



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



>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:



© Standards Australia



www.standards.org.au



49



(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).



Accessed by SWINBURNE UNIVERSITY OF TECHNOLOGY on 19 Nov 2007



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



FIGURE A1 SECTION GEOMETRY



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