As 4673 - 2001 Cold Formed Stainless Steel Structures Unlocked

AS/NZS 4673:2001

A S / N Z S 4 6 7 3

Aust Austra ralilian an/N /New ew Zeal Zealan and d Stan Standa dard rd™ Cold-formed stainless steel structures ) d e t n i r p n e h w d e e t n a r a u g t o n y c n e r r u c t n e m u c o D ( 7 1 0 2 v o N 4 1 n o D N A L S N E E U Q N R E H T U O S F O Y T I S R E V I N U y b d e s s e c c A

AS/NZS 4673:2001 This Joint Australian/New Zealand Standard was prepared by Joint Technical Committee BD-086, Stainless Steel Structures. It was approved on behalf of the Council of Standards Australia on 22 June 2001 and on behalf of the Council of Standards New Zealand on 24 August 2001. It was published on 9 November 2001.

The following interests are represented on Committee BD-086:

) d e t n i r p n e h w d e e t n a r a u g t o n y c n e r r u c t n e m u c o D ( 7 1 0 2 v o N 4 1 n o D N A L S N E E U Q N R E H T U O S F O Y T I S R E V I N U y b d e s s e c c A

Association of Consulting Engineers Australia Australasian Railway Association Australian Industry Group Australian Stainless Steel Development Association Bureau of Steel Manufacturers of Australia Institution of Engineers Australia New Zea land lan d S tainle tai nless ss Steel St eel Develo Dev elopme pment nt Ass ociati oci ati on The University of Sydney Welding Technology Institute of Australia

Keeping Standards up-to-date Standards are living documents which 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 Standards may also be withdrawn.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 which may have been published since the Standard was purchased. Detailed information about joint Australian/Ne w Zealand Standards can ca n be found by visiting the Standards Australia web site at www.standards.com.au or Standards New Zea land lan d web sit e at a t www.sta www. sta ndards nda rds .co.nz .co .nz and loo kin g u p t he rel evant eva nt Sta ndar d in the on-line catalogue. Alternatively, both organizations publish an annual printed Catalogue with full details of all current Standards. For more frequent listings or notification of revisions, amendments and withdrawals, Standards Australia and Standards New Zealand offer a number of update options. For information about these services, users should contact their respective national Standards organization. We also welcome suggestions for improvement in our Standards, and especially encourage readers to notify us immediately of any apparent inaccuracies or ambiguities. Please address your comments to the Chief Executive of either Standards Australia International or Standards New Zealand at the address shown on the back cover.

This Standard was issued in draft form for comment as DR 00011.

AS/NZS 4673:2001

Aust Austra ralilian an/N /New ew Zeal Zealan and d Stan Standa dard rd™ Cold-formed stainless steel structures ) d e t n i r p n e h w d e e t n a r a u g t o n y c n e r r u c t n e m u c o D ( 7 1 0 2 v o N 4 1 n o D N A L S N E E U Q N R E H T U O S F O Y T I S R E V I N U y b d e s s e c c A

First published as AS/NZS 4673:2001.

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© Standards Australia/Standards New Zealand All righ ts are rese rved . N o pa rt of t his work may be repr oduc ed or cop ied in any for m o r b y any means, electronic or mechanical, including photocopying, without the written permission of the publisher. Jointly published by Standards Australia International Ltd, GPO Box 5420, Sydney, NSW 2001 and Standards New Zealand, Private Bag 2439, Wellington 6020 ISBN 0 7337 3979 2

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PREFACE This Standard was prepared by the Joint Standards Australia/Standards New Zealand Committee BD-086, Stainless Steel Structures. The objective of this Standard is to provide designers of stainless steel structures with specifications for cold-formed stainless steel structural members used for load-carrying purposes i n buildings and other structures. Sections 1, 2, 3, 4 and 5 of this Standard are based on ANSI/ASCE-8-90 Specification for the Design of Cold-formed Stainless Steel Structural Members. Section 6 is based on AS/NZS 4600 and AS/NZS 1664.1. Statements expressed in mandatory terms in notes to tables are deemed to be requirements 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. ) d e t n i r p n e h w d e e t n a r a u g t o n y c n e r r u c t n e m u c o D ( 7 1 0 2 v o N 4 1 n o D N A L S N E E U Q N R E H T U O S F O Y T I S R E V I N U y b d e s s e c c A

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CONTENTS Page SECTION 1 SCOPE AND GENERAL 1.1 SCOPE......................................................................................................................... 5 1.2 REFERENCED DOCUMENTS................................................................................... 5 1.3 DEFINITIONS.............................................................................................................5 1.4 NOTATION............................................................................................................... 11 1.5 MATERIALS............................................................................................................. 19 1.6 DESIGN REQUIREMENTS...................................................................................... 22 1.7 NON-CONFORMING SHAPES AND CONSTRUCTION ....................................... 24


SECTION 2 ELEMENTS 2.1 SECTION PROPERTIES ..........................................................................................25 2.2 EFFECTIVE WIDTHS OF STIFFENED ELEMENTS.............................................. 27 2.3 EFFECTIVE WIDTHS OF UNSTIFFENED ELEMENTS........................................ 31 2.4 EFFECTIVE WIDTHS OF UNIFORMLY COMPRESSED ELEMENTS WITH AN EDGE STIFFENER OR ONE INTERMEDIATE STIFFENER .......................... 32 2.5 EFFECTIVE WIDTHS OF EDGE-STIFFENED ELEMENTS WITH ONE OR MORE INTERMEDIATE STIFFENERS, OR STIFFENED ELEMENTS WITH MORE THAN ONE INTERMEDIATE STIFFENER..................................... 37 2.6 STIFFENERS ............................................................................................................ 38 SECTION 3 MEMBERS 3.1 GENERAL................................................................................................................. 41 3.2 MEMBERS SUBJECT TO TENSION....................................................................... 41 3.3 MEMBERS SUBJECT TO BENDING...................................................................... 41 3.4 CONCENTRICALLY LOADED COMPRESSION MEMBERS............................... 50 3.5 COMBINED AXIAL COMPRESSIVE LOAD AND BENDING.............................. 53 3.6 TUBULAR MEMBERS ............................................................................................ 54 SECTION 4 STRUCTURAL ASSEMBLIES 4.1 BUILT-UP SECTIONS.............................................................................................. 57 4.2 MIXED SYSTEMS.................................................................................................... 58 4.3 LATERAL RESTRAINTS......................................................................................... 58 SECTION 5 CONNECTIONS 5.1 GENERAL................................................................................................................. 60 5.2 WELDED CONNECTIONS ...................................................................................... 60 5.3 BOLTED CONNECTIONS ....................................................................................... 64 SECTION 6 TESTING 6.1 TESTING FOR DETERMINING MATERIAL PROPERTIES ................................. 71 6.2 TESTING FOR ASSESSMENT OR VERIFICATION.............................................. 72

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Page APPENDICES A LIST OF REFERENCED DOCUMENTS ................................................................. 75 B MECHANICAL PROPERTIES ................................................................................. 77 C STAINLESS STEEL PROPERTIES.......................................................................... 83 D STAINLESS STEEL FASTENERS......................................................................... 101 E FLEXURAL MEMBERS SUBJECTED TO POSITIVE AND NEGATIVE BENDING ................................................................................. 104 F FATIGUE ................................................................................................................ 105 G FIRE ........................................................................................................................ 111 H SECTION PROPERTIES ........................................................................................ 113 I UNSTIFFENED ELEMENTS WITH STRESS GRADIENT................................... 117 J HOLLOW SECTION LATTICE GIRDER CONNECTIONS.................................. 118 K DETERMINATION OF THE CAPACITY [STRENGTH REDUCTION] FACTOR .................................................................. 130


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STANDARDS AUSTRALIA/STANDARDS NEW ZEALAND Australian/New Zealand Standard Cold-formed stainless steel structures

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 minimum requirements for the design of stainless steel structural members cold-formed to shape from annealed or temper-rolled sheet, strip, plate or flat bar stainless steels used for load-carrying purposes in buildings. It may also be used for structures other than buildings provided appropriate allowances are made for dynamic effects. ) d e t n i r p n e h w d e e t n a r a u g t o n y c n e r r u c t n e m u c o D ( 7 1 0 2 v o N 4 1 n o D N A L S N E E U Q N R E H T U O S F O Y T I S R E V I N U y b d e s s e c c A

For the purpose of this Standard, steels with at least 10.5% chromium and up to 1.2% carbon are considered as stainless steels. 1.2

REFERENCED DOCUMENTS

The documents referred to in this Standard are listed in Appendix A. 1.3 DEFINITIONS

For the purpose of this Standard, the definitions below apply. Definitions peculiar to a particular clause or secti on are also given in that clause or secti on. NOT E: In thi s Standar d, ter ms in squar e br ackets rel ate to New Zea land use.

1.3.1

Action [Effect]

The cause of stress, dimensional change, or displ acement in a structure or a component of a structure. 1.3.2

Action effect [Action] or load effect [action]

The internal force, moment, deformation, crack, or like effect caused by one or more actions [effects]. 1.3.3

Arched compression element

A circular or parabolic arch-shaped compression element having an inside radius-tothickness ratio greater than 8, stiffened at both ends by ed ge stiffeners. (See Figure 1.3(d).) 1.3.4

Bend

Portion adjacent to flat elements and having a maximum inside radius-to-thickness ratio (r i/t ) of 8. (See Figure 1.1.) 1.3.5

Braced member

One for which the transverse displacement of one end of the member relative to the other is effectively prevented. 1.3.6

Can

Implies a capability or possibility and refers to the ability of the user of the Standard, or to a possibility that is available or that might occur.

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1.3.7

Capacity [Strength reduction] factor

A factor used to multiply the nominal capacity to obtain the design capacity. 1.3.8

Cold-formed stainless steel structural members

Shapes that are manufactured by press-braking blanks sheared from sheets, cut lengths of coils or plates, or by roll-forming cold- or hot-rolled coils or sheets; both forming operations being performed at ambient room temperature, that is, without manifest addition of heat as required for hot-forming. 1.3.9

Design action effect [Design action] or design load effect [design action]

The action [effect] or load effect [action] calculated from the design actions [design forces] or design loads. 1.3.10

Design action [Design force] or design load

The combination of the nominal actions [nominal effects] or loads and the load factors, as specified in the relevant loading Standard. 1.3.11

Design capacity

The product of the nominal capacity and the capacity [strength reduction] factor. ) d e t n i r p n e h w d e e t n a r a u g t o n y c n e r r u c t n e m u c o D ( 7 1 0 2 v o N 4 1 n o D N A L S N E E U Q N R E H T U O S F O Y T I S R E V I N U y b d e s s e c c A

1.3.12

Effective design width

Where the flat width of an element is reduced for design purposes, the reduced design width is termed the effective width or effective design width. 1.3.13

Elements

Simple shapes into which a cold-formed structural member is considered divided and may consist of the following shapes: (a)

Flat elements—appearing in cross-section as rectangles. (See Figure 1 .2.)

(b)

Bends—appearing in cross-section as sectors of circular rings, having the inside ≤ 8). (See Figure 1.2.) radius-to-thickness ratio less than or equal to eight (r /t i

(c)

Arched elements—circular or parabolic elements having the inside radius-tothickness ratio greater than eight (r /t i > 8). (See Figure 1.2.)

1.3.14

Feed width ( w f )

Width of coiled or flat steel used in the production of a cold-formed product. 1.3.15

Flat-width-to-thickness ratio

The flat width of an element measured along its plane, divided by its thickness. 1.3.16

Flexural-torsional buckling

A mode of buckling in which compression members can bend and twist simultaneously without change of cross-sectional shape. 1.3.17

Initial Young’s modulus

The initial slope of the stress-strain curve. (See Appendix B.) 1.3.18

Length (of a compression member)

The actual length (l ) of an axially loaded compression member, taken as the length centreto-centre of intersections with supporting members, or the cantilevered length in the case of a freestanding member. 1.3.19

Limit state

A state beyond which the structure no longer satisfies the design performance requirements. NOT E: Limit sta tes separate desired s tates [no fai lur e] from unde sired sta tes [failure]. COPYRIGHT

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1.3.19.1 Limit state, serviceability

A state that corresponds to conditions beyond which specified service requirements for a structure or structural element are no longer met. NOT E: Requir ements are based on the int ended use and may inc lud e limi ts on deformati on, vibratory response, degradation or other physical aspects.

1.3.19.2 Limit state, stability

A limit state corresponding to the loss of static equilibrium of a structure considered as a rigid body. NOT E: In New Zea land, the stabilit y limit sta te is part o f t he ult imate limit state.

1.3.19.3 Limit state, ultimate

A state associated with collapse, or with other similar forms of structural failure. NOT E: This gene rally cor responds to the maxi mum loa d-c arr ying res ist ance of a str uct ure or structural element but in some cases to the maximum applicable strain or deformation.

1.3.20

Load

An externally applied limit state force including self -weight. ) d e t n i r p n e h w d e e t n a r a u g t o n y c n e r r u c t n e m u c o D ( 7 1 0 2 v o N 4 1 n o D N A L S N E E U Q N R E H T U O S F O Y T I S R E V I N U y b d e s s e c c A

1.3.21

Local buckling

A mode of buckling involving plate flexure alone without transverse deformation of the line or lines of intersection of adjoining plates. 1.3.22 May

Indicates the existence of an option. 1.3.23

Multiple-stiffened element

An element that is stiffened between webs, or between a web and a stiffened edge, by means of intermediate stiffeners that are parallel to the direction of stress. (See Figure 1.3(c).) 1.3.24

Nominal action [Nominal effect] or nominal load

An unfactored action [effect] or load determined in accordance with the relevant loading Standard. 1.3.25

Nominal capacity

The capacity of a member or connection calculated using the parameters specified in this Standard. 1.3.26

Point-symmetric section

A section symmetrical about a point (centroid) such as a Z-section having equal flanges. (See Figure 1.5(b).) 1.3.27

Proof stress

The stress at a nominated plastic strain. (See Appendix B.) 1.3.28

Proof testing

The application of test loads to a structure, sub-structure, member or connection to ascertain the structural characteristics of only that one unit un der test. 1.3.29

Prototype testing

The application of test loads to one or more structures, sub-structures, members or connections to ascertain the structural characteristics of that class of structures, substructures, members or connections that are nominally identical to the units tested.

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1.3.30

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Segment (in a member subjected to bending)

The length between adjacent cross-sections that are fully or partially restrained, or the length between an unrestrained end and the adjacent cross-section that is fully or partially restrained. 1.3.31

Secant modulus

The slope of a line from the origin t o a point on the stress-strain curve. (See Appendix B.) 1.3.32

Shall

Indicates that a statement is mandatory. 1.3.33

Should

Indicates a recommendation. 1.3.34

Special study

A procedure for the analysis or design, or both, of the structure, agreed between the authority having statutory powers to control the design and erection of a structure, and the design engineer. ) d e t n i r p n e h w d e e t n a r a u g t o n y c n e r r u c t n e m u c o D ( 7 1 0 2 v o N 4 1 n o D N A L S N E E U Q N R E H T U O S F O Y T I S R E V I N U y b d e s s e c c A

1.3.35

Stiffened or partially stiffened compression element

A flat compression element (i.e. a plane compression flange of a flexur al member or a plane web or flange of a compression member) of which both edges parallel to the direction of stress are stiffened by a web, flange, edge stiffener, intermediate stiffener, or the like. (See Figure 1.3(a).) 1.3.36

Stiffener(s)

1.3.36.1 Edge stiffener

Formed element at the edge of a flat compression element. (See Figure 1.4(a).) 1.3.36.2 Intermediate stiffeners

Formed elements, employed in multiple stiffened segments, and located between edges of stiffened elements. (See Figure 1.4(b).) 1.3.37

Structural ductility factor

A numerical assessment of the ability of a structure to sustain cyclic inelastic displacements. 1.3.38

Structural performance factor

A numerical assessment of the ability of a building t o survive cyclic displacements. 1.3.39

Structural response factor

The level of force reduction available for a given system compared with an elastic structural system. 1.3.40

Sub-element

The portion between adjacent stiffeners, or between web and intermediate stiffener, or between edge and stiffener. 1.3.41

Tangent modulus

The slope tangential to the stress-strain curve. (See Appendix B.) 1.3.42

Temper rolling

Cold-working of annealed stainless steel by rolling to achieve increased strength.

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1.3.43

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Tensile strength

The minimum ultimate strength in tension specified for the grade of steel in the appropriate Standard. 1.3.44

Thickness

The base steel thickness (t ), exclusive of coatings. 1.3.45

Unformed steel

Steel as received from the steel producer or warehouse before being cold-worked as a result of fabricating operations. 1.3.46

Unformed steel properties

Mechanical properties of unformed steel, such as yield stress, tensile strength and ductility. 1.3.47

Unstiffened compression element

A flat compression element that is stiffened at only one edge parallel to the direction of stress. (See Figure 1.3(b).) 1.3.48 ) d e t n i r p n e h w d e e t n a r a u g t o n y c n e r r u c t n e m u c o D ( 7 1 0 2 v o N 4 1 n o D N A L S N E E U Q N R E H T U O S F O Y T I S R E V I N U y b d e s s e c c A

Yield stress

In the absence of a yield plateau, the yield stress is taken as the 0.2% proof stress, which is the stress at 0.2% plastic strain. (See Appendix B.) NOT E: The yield str ess varies with the rolli ng dir ection, tra nsv ers e or longit udinal , and is different in tension and compression.

FIGURE 1.1

BENDS

NOTE: The member illustrated consists of the following nine elements: (a)

Elements 1, 3, 7, 9 are flat elements (flats).

(b)

Elements 2, 4, 6, 8 are bends (r i/t ≤ 8).

(c)

Element 5 is an arched element (r i/t > 8).

FIGURE 1.2

ELEMENTS

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FIGURE 1.3


STIFFENING MODES

FIGURE 1.4

STIFFENERS

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FIGURE 1.5

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EXAMPLES OF SECTION SYMMETRY

1.4 NOTATION

The symbols used in this Standard are listed in Table 1.4. Where non-dimensional ratios are involved, both the numerator and denominator are expressed in identical units. The dimensional units for length and stress in all expressions or equations are to be taken as millimetres (mm) and megapascals (MPa) respectively, unless specifically noted ot herwise. An asterisk placed after a symbol denotes a design action effect [design action] due to the design load for the strength [ulti mate] limit state.

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TABLE 1.4 NOTATION Symbol


Description

Clause reference

A

area of the full, unreduced cross-section; or gross cross-sectional area of a channel or Z-section

3.3.3

A b

gross cross-sectional area of the bolt

5.3.8.2

A bs

tensile stress area of the bolt

5.3.8.2

Ae

effective area calculated at buckling stress f n

3.4.1

A ef

e ff ec ti ve ar ea of ed ge st iff en er or in ter me di at e st iff en er s

2. 5

A f

gross cross-sectional area of the stainless steel bolt

5.3.7.2

An

net area of the cross-section; or net area of the connected part at the line of bolts transverse to the line of the applied force

3.2, 5.3.5

Ao

reduced area of the cross-section

3.6.3

As

reduced area of a stiffener; or cross-sectional area of a transverse stiffener

2.4.1, 2.6.1

Ase

effective area of a stiffener

2.4.1

A st

gross area of a shear stiffener

2.6.2

area of a member in compression consisting of the transverse stiffeners and a portion of t he web

2.6.1

distance between transverse stiffeners

2.6.2

constant

1.5.2.4

b

flat width of element excluding radii; or flat width of th e compression flange

2.2.1.2, 2.4.1, 3.6.2

be

effective width of uniformly compressed stiffened and unstiffened elements used for determining the load capacity [strength]

2.2.1.2, 2.3.1.2, 2.3.1.3

b ed

effective width of uniformly compressed stiffened and unstiffened elements used for determining the deflection

2.2.1.3, 2.3.2.3

b es

effective width of a sub-element or element to be used in design calculations

2.5

effective width of uniformly compressed stiffened element with stress gradient

2.2.2.1, 2.2.2.2

b f

flat width of the beam flange that contacts the bearing plate

3.3.7

b1

width of the compression and tension flanges, either s tiffened or unstiffened, projecting beyond the web for I-beams and similar sections; or maximum half the distance between webs for box- or U-type sections; or sum of the flange projection beyond the web and the depth of the lip for I-beams and similar sections; or flat width of th e narrowest unstiffened compression element tributary to the connections

2.1.3.2, 2.1.3.3, 4.1.2

b2

flat width of element with intermediate stiffener excluding radii 2.4.1

A s1 , A s2 a Bc

b e1 , b e2

(continued )

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TABLE 1.4 (continued ) Symbol

Description

C

for compression members, ratio of the total bend crosssectional area to the total cross-sectional area of the full section; and for flexural members, ratio of the total bend cross-sectional area of the controlling flange to the full cross-sectional area of the controlling flange; or ratio of the proportionality stress to the yield stress

1.5.2.4, 3.6.2

C b

bending coef fici ent

3.3. 3

C m

coefficient for unequal end moment

3.5

C s

coefficient for moment causing compression or tension on the shear centre side of the centroid

3.3.3

C y

compression strain factor

3.3.2.3

C w

torsional warping constant of the cross-section

3.3.3

coefficient

2.4.1, 3.3.6

cf

amount of curling

2.1.3.2

d

depth of a section; or actual stiffener dimension

2.1.3.2, 2.4.1

d f

nominal diameter of a bolt

5.3.2

d h

standard hole diameter

5.3.2

d l

depth of the flat portion of the web measured along the plane of 2.1.3.4, 2.4.1 the web; or actual stiffener dimension

d m

mean of the across points and across flats dimensions of the bolt head or the nut, wh iche ver is smaller

5.3.8.3

d o

outside diameter of a chord

Paragraph J3

d s

reduced effective width of a stiffener; or effective stiffener dimension

2.4.1

d se

effective width of a stiffener

2.4.1

d w

depth of the compressed portion of the web

3.3.2.3

d 1

depth of the flat portion of a web measured along the plane of the web

2.1.3.4

E o

Initial Young’s modulus of elasticity

1.3.17

E r

reduced modulus of elasticity

2.2.1.3

E s

secant modulus for normal stress

Paragraph B1

E sc

secant modulus corresponding to stress in compression flange

2.2.1.3

E st

secant modulus corresponding to stress in tension flange

2.2.1.3

E t

tangent modulus in compression; or tangent modulus for normal stress

3.4.2, Paragraph B1

e

distance measured in the line of the applied force from centreline of an arc spot weld, arc seam weld or from centre of a bolt hole to the nearest edge of an adjacent weld or bolt hole, or to the end of the connected part toward which the force is directed; or eccentricity

5.3.3, Paragraph J3

ey

yield strain

3.3.2.3

C 1 to C 11 , and C θ ) d e t n i r p n e h w d e e t n a r a u g t o n y c n e r r u c t n e m u c o D ( 7 1 0 2 v o N 4 1 n o D N A L S N E E U Q N R E H T U O S F O Y T I S R E V I N U y b d e s s e c c A

Clause reference

(continued )

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Description

Clause reference

f

normal engineering stress

Paragraph B1

f b

permissibl e co mpressive s tress for local distortion

3.3.2.4

f c

stress at service load in the cover plate or sheet

4.1.2

f cr

critical buckling stress

3.3.2.4

f n

buckl ing str ess

2.6. 1

f nt′

nominal tensile strength for bolts subject to combined shear and 5.3.7.4 tension

f nt

nominal tensile strength of the stainless steel bolt

5.3.8.3

f nv

nominal shear strength of the stainless steel bolt

5.3.7.2

f oc

flexural buckling stress

3.4.2

f pc

offset proportional limit in compression

Paragraph B1

f t

tensile strength for connections with washers under bolt, bolt head and nut

5.3.5

f u

minimum tensile strength used in the design; or tensile or compressive strength of the connected part in the direction of the applied force

1.5.2.2, 5.3.5, 5.3.6

f ua

tensile or compressive strength of the annealed base metal

5.2.2.2

f ut

tensile strength of the connected part tr ansverse to the direction of the applied force

5.3.4

f uv

tensile strength of unformed steel

1.5.2.4

f v

shear stress resulting from the design shear force

5.3.7.4

f wy

lower yield stress value of a beam web ( f y) or of a stiffener section ( f ys )

2.6.1

f xx

tensile strength obtained from all-weld-metal tensile test

5.2.3.2

f y

minimum tensile or compressive yield stress used in design; or 1.5.2.2, 5.3.5, Paragraph B1 yield stress of web steel; or yield stress of stiffener; or specified yield stress in longitudinal compression or tensile strength of the connected part in the direction of the applied force; or offset yield stress in compression

f ya

average design yield stress of the steel in the full section of compression members or full flange sections of flexural members

1.5.2.4

f yc

tensile yield stress of bends; or compressive yield stress

1.5.2.4, 6.1.4

f yf

yield stress of flat portions; or yield stress of unformed steel if tests are not made; or yield stress of flat coupons of formed members

1.5.2.4, 6.1.5.1

f ys

yield stress of stiffener steel

2.6.1

f yt

minimum tensile yield stress

1.5.3

f yv

tensile yield stress of unformed steel; or specified shear yield stress

1.5.2.4, Appendix B

f *

design stress in the compression element calculated on the basis 2.2.1.2 of the effective design width (continued )

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Clause reference

a ve ra ge des ign st re ss in th e fu ll , u nr edu ced fl an ge wi dt h

2. 1. 3. 2

f d*

design compressive stress in the element being considered based on the effecti ve s ecti on at the load for which defle ctio ns are determined

2.2.1.3

f 1* , f 2*

web stresses calculated on the basis o f the effective section or on the full section

2.2.2.1

f 3*

stress in edge stiffener with stress gradient for which load capacities are determined

2.3.2.2

Go

initial shear modulus

3.3.3

Gs

secant modulus for shear stress

Paragraph B1

Gt

tangent modulus for shear stress

Paragraph B1

g

distance measured along the length of the connected face of t he chord, between the toes of the adjacent members

Paragraph J2.1

ho

depth of the chord in the plane of the lattice girder

Paragraph J3

I a

adequate second moment of area of a stiffener, so that each component element behaves as a stiffened element

2.4.1

I b

second moment of area of the full, unreduced cross-section about the bending axis

3.5

I s

second moment of area of a full stiffener about its own centroidal axis parallel to the element to be stiffened

2.4.1

I sf

second moment of area of the full area of a multiple-stiffened element, including the intermediate stiffeners, about its own centroidal axis

2.5

I w

warping constant for a cross-section

Paragraph H1

I x

second moment of area of the cross-section about it s centroidal axis perpendicular to the web

4.3.3.3

I xy

produ ct o f se cond moment o f area of the full sect ion about its centroidal axes and perpendicular to the web

4.3.3.3

I yc

second moment of area of the compression portion of a section about the centroidal axis of the full section parallel to the web, using the full unreduced section

3.3.3

J

St. Venant torsion constant of the cross-section

3.3.3

k

plat e buckli ng coef fici ent; or effective length factor

2.2.1.2, 3.4.2

k f

total population variation due to fabrication

6.2.2.3

k m

total population of variation due to material

6.2.2.3

k s

shear stiffener coefficient

2.6.2

k sc

coefficient of variation of structural characteristic

6.2.2.3

k st

stiffener type coefficient

2.6.2

k t

effective length factor for twisting; or factor to allow for variability of structural units

3.3.3, 6.2.2.2

k v

shear buckling coefficient

2.6.2

effective length factors for bending about the x- and y-axes, respectively

3.3.3

* f av


Description

k x, k y

(continued )

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k ′

Description * coefficient used to d etermine N ib where neither flange is

Clause reference

4.3.3.3

connected to the sheeting or connected to the sheeting with concealed fasteners


l

actual length of an axially loaded compression member; or unbraced length of a member in compression

1.3.18, 3.3.3

l b

actual length of bearing

3.3.6

l eb

effective length in the plane of bending

3.5

l st

length of transverse stiffener

2.6.1

l t

un br aced len gt h o f t he co mpr es si on me mb er fo r t wi st in g

3. 3. 3

l w

length of the full size of the weld

5.2.2.3

l x, l y

unbraced lengths of the compression member for bending about the x- and y-axes, respectively

3.3.3

M b

nominal member moment capacity

2.2.1.2

nominal member moment capacities about the x- and y- axes, respectively

3.5

M c

critical moment

3.3.3

M l d

nominal flexural capacity of the member

3.3.2.4

M m

mean value of the measured yield stress to the nominal yield stress of the finished product

Appendix K

absolute value of the maximum moment in the unbraced segment

3.3.3

M s

nominal section moment capacity

2.2.1.2

M y

moment causing initial yield

2.2.1.2

M 3

absolute value of the moment at quarter point of the unbraced segment

3.3.3

M 4

absolute value of the moment at centre-line of the unbraced segment

3.3.3

M 5

absolute value of the moment at th ree-quarter point of the unbraced segment

3.3.3

M *

design bending moment

3.3.1

M x* , M y*

design bending moment about the x- and y-axes, r especti vel y

3.5

m

constant; or non-dimensional thickness; or distance from the shear centre of one channel to the mid-plane of its web; or distance from the concentrated load to the brace

1.5.2.4, 3.3.6, 4.1.1, 4.3.3.3

N c

nominal member cap acit y o f a memb er in compr ession

2.6 .1

N e

elastic buckling load

3.5

N f

nominal tensile capacity of the connected part

5.3.5

N s

nominal section capacity of a member in compression

2.6.1

N t

nominal section capacity of a member in tension

3.2

N w

nominal tensile or compressive capacity of a butt weld or a resistance spot weld, welded from one or both sides

5.2.1.2, 5.2.3.3

N *

design concentrated load or r eaction; or design axial force, tensile or compressive

2.6.1, 3.4.1

M bx , M by

M m ax.

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Description

Clause reference

N f *

design tensile force in the connected part

5.3.5

N ft*

design tensile force on a bolt

5.3.7.4

* N ib

desi gn force to be r es isted by i nt ermedi at e beam br ace

4.3 .3.3

* N w

design tensile or compressive force normal to the area of a butt weld or on a resistance spot weld

5.2.2.2, 5.2.4.3

n

constant

Paragraph B1

q

intensity of the design load on a beam

4.1.1

R b

nominal capacity for concentrated load or reaction for one solid web connecting top and bottom flanges; or nominal capacity for concentrated load or reaction in the absence of bending moment

3.3.6, 3.3.7

Rd

design capacity of members and connections

1.6.2.2, 6.2.2.7

R f

structural response factor

1.6.3

minimum value of the test results

6.2.2.7

Rt

target test loads for the number of units to be tested

6.2.2.2

Ru

nominal capacity of members and connections

1.6.2.2

R*

design concentrated load or reaction in the presence of bending moment

3.3.7

R b*

design concentrated load or reaction

3.3.6

radius of gyration o f the ful l, u nr educed cross-sect ion

3.4.2

r cy

radius of gyration of one channel about its centroidal axis parallel t o the web

4.1.1

r f

ratio of the force transmitted by the bolt or bolts at the section considered, divided by the tensile force in the member at that section

5.3.5

r i

inside bend radius

1.3.4

r o

pola r radiu s of gyration of th e cr oss- sect ion about the shear centre

3.3.3

r x, r y

radii of gyration of the cross-section about the centroidal axes

3.3.3

r 1

radius of gyration of an I-section about the axis perpendicular to the direction in which buckling occurs for the given conditions of end support and intermediate bracing

4.1.1

S

slenderness factor

2.4.1

S p

structural performance factor; or plastic se ction modul us

1.6.3, 3.6.2

S *

design action effects [design actions]

1.6.2.2

s

spacing in line of the stress of welds and bolts, connecting a cover plate or sheet in compression, to a non-integral stiffener or another element

4.1.2

sf

spacing of bolts transverse to the line of the force; or width of the connected part, in the case of a single bolt

5.3.5

sg

vertical distance between two rows of connections nearest to the top and bottom flanges

4.1.1

smax.

maximum longitudinal spacing of welds or other connectors joining two chann els to form an I -section

4.1.1

R min.

r

(continued )

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sw


Description

Clause reference

weld spacing

4.1.1

t

nominal base steel thickness of any element or section exclusive of coatings; or thickness of the uniformly compressed stiffened elements; or base thickness o f beam web; or thickness of the thinnest welded part; or thickness of the thinnest connected part

1.5.2.8, 2.1.3.1, 2.2.1.2, 2.6.1, 5.2.2.2, 5.3.4

t f

thickness of the flange

2.1.3.2

t p

thickness of the plate under the bolt head or the nut

5.3.8.3

t s

thickness of the stiffener steel

2.5

t w

thickness of a web; or effective throat

2.1.3.4, 5.2.3.2

V b

nominal bearing capacity per bolt of the connected part, where bolt s have washers under bo th bold head and nut

5.3.6

V f

nominal shear capacity per bolt

5.3.4

V fv

nominal shear capacity of a stainless steel bolt

5.3.7.2

V M

coefficient of variation of the ratio of the measured yield stress to the nominal yield str ess of the finished product

Appendix K

V v

nominal shear capacity of the beam

3.3.4

V w

nominal shear capacity of a butt, fillet, or resistance weld, welded from one or both sides; or nominal shear force transmitted by the weld

5.2.2.3, 5.2.3.2, 5.2.3.3, 5.2.4.2

V *

design shear force

3.3.2.3

V b*

design bearing force at a bolt

5.3.6

V f *

design shear force per bolt

5.3.4

* V fv

design shear force for bolts loaded in shear

5.3.7.2

V w*

design shear force on a butt, fillet or resistance weld; or design longitudinal or transverse shear force on a fill et weld

5.2.2.3, 5.2.3.2, 5.2.3.3, 5.2.4.2

leg sizes of the weld

5.2.3.2

xo

distance from the shear centre of the cross-section to the centroid along the principal x-axis, taken as negative

3.3.3

Z c

elastic section modulus of the effective section calculated at a stress M c/ Z f in the extreme compression fibre

3.3.3

Z e

effective section modulus calculated with the extreme compression or tension fibre at f yc or f yt , respectively, whichever initiates yield

3.3.2.2

Z f

elastic section modulus of the full, unreduced cross-section

3.3.2.4

reduction factor

2.5

moment amplification factor

3.5

ε

normal strain

Paragraph B1

ε y

offset yield strain

Paragraph B1

ε p

offset proportional limit strain

Paragraph B1

η

plasticity bu ckling stress

3.3.2.4

w 1, w 2

α α nx , α ny

(continued )

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Description

θ

angle between the plane of the web and the plane of the bearing surface

3.3.6

overlap

Paragraph J2.3

slenderness ratio

2.2.1.2, 3.3.2.3

µ

structural ductility factor

1.6.3

ν

Poisson’s ratio in elastic range of 0.3

3.3.2.4

ρ

quantity for load capacity [strength]; or effective width factor

1.5.2.4, 2.2.1.2

φ

capacity [strength reduction] factor

1.6.2.2

φ b

capacity [strength reduction] factor for bending

3.3.1

φ c

capacity [strength reduction] factor for members in compression

2.6.1

φ d

c ap aci ty [ st ren gt h r ed uct ion ] f act or f or lo cal d ist or ti on

3. 3. 2. 4

φ o

reference value

Appendix K

φ t

capacity [strength reduction] factor for members in tension

3.2

φ v

capacity [strength reduction] factor for shear

3.3.5

φ w

capacity [strength reduction] factor for bearing

3.3.6

ψ

stress ratio f 2* / f 1*

2.2.2.1

λ ov λ , λ 1, λ 2


Clause reference

1.5 MATERIALS 1.5.1

Selection of stainless steel grade

1.5.1.1 Factors to be considered

The selection of the most appropriate grade of stainless steel shall take into account the mechanical properties, effect of welding on mechanical properties and corrosion resistance, the environment of the application, the surface finish and appearance, and the maintenance of the structure. Detailed consideration needs to be given to design for corrosion resistance when a material is selected for use in a corrosive environment. 1.5.1.2 Corrosion resistance

An appropriate grade of stainless steel shall be selected in accordance with the corrosion resistance required for the environment in which the structural members are to be used and in accordance with the fabrication, strength and finish requirements for the specific application. NOT E: For ini tia l guid ance on grade selection for corr osi on res istance, see App endix C.

1.5.1.3 Surface finish and appearance

Consideration shall be given to restitution of the surface after fabrication, and to maintenance during service. NOT E: A variety of s urf ace finish es i s desc rib ed in Appe ndi x C.

1.5.1.4 Cosmetic applications

In cosmetic applications, the possible minor changes in surface appearance that might take place as a result of dirt deposits, which in adverse circumstances can create crevices and lead to surface micro-pitting, shall also be taken into account. A suitable corrosion-resistant grade of stainless steel shall be used to ensure that only superficial surface attack takes place within the desi gn life of the component. COPYRIGHT

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1.5.1.5 Maintenance

If necessary, a suitable cleaning regime shall be specified to maintain the surface appearance. 1.5.2

Stainless steels

1.5.2.1 Applicable stainless steel grades

Structural members or steel used in manufacturing shall comply with AS 1449, ASTM A167, ASTM A176, ASTM A240, ASTM A276, ASTM A480, ASTM A666, EN 10088 and JIS G4305, as applicable. 1.5.2.2 Other stainless steel grades

Clause 1.5.2.1 shall not be interpreted to exclude the use of other steels, the properties and suitability of which shall be determined in accordance with Clause 1.5.2.6. The yield stress ( f y) and tensile strength ( f u) used in design shall be determined in accordance with Section 6. The steel shall conform to the chemical and other mechanical requirements, and shall have been subjected by either the producer or purchaser to analyses, tests and other controls as prescribed by one of the Standards listed in Clause 1.5.2.1 or in accordance with Clause 1.5.2.6. ) d e t n i r p n e h w d e e t n a r a u g t o n y c n e r r u c t n e m u c o D ( 7 1 0 2 v o N 4 1 n o D N A L S N E E U Q N R E H T U O S F O Y T I S R E V I N U y b d e s s e c c A

1.5.2.3 Availability of stainless steel grades and product forms

Not all grades are readily availabl e in all product forms. Appendi x C describes the commonly available grades and tempers of stainless steel by product form. 1.5.2.4 Strength increase resulting from cold-forming ( ferritic stainless st eels)

The increase in yield stress due to cold-forming or temper-rolling, or both, may be partly or completely lost by processes such as welding, annealing or other heat treatment carried out after forming (see Clause 1.5.2.5). The equations given in this Clause are only applicable to the ferritic stainless steels type 409, type 430, type 439 and to type 1.4003 (EN 10088) steel. The increase in strength due to cold for ming for the austenitic stainless steels type 201, type 301, type 304 or type 316, shall be determined by a rational method or b y tests. Strength increase resulting from cold-forming shall be permitted by substituting the average design yield stress ( f ya) of the full section for f y. Such increase shall be limited to Clauses 3.3 (excluding Clause 3.3.3.2), 3.4, 3.5, 3.6 and 4.4. The limitations and methods for determining f ya shall be as follows: (a)

For axially loaded compression members and flexural members whose proportions are such that the quantity (ρ) for load capacity [strength] is unity, as determined in accordance with Clause 2.2 for each of the component elements of the sections, the average design yield stress ( f ya) shall be determined on the basis of one of the following: (i)

Full section tensile tests (see Section 6).

(ii)

Stub column tests (see Section 6).

(iii)

Calculated as follows: f ya

= Cf yc + (1 − C ) f yf

. . . 1.5.2.4(1)

where f ya =

average design yield stress of the steel in the full section of compression members or full flange sections of flexural members

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C =

for compression members, ratio of the total bend cross-sectional area to the total cross-sectional area of the full section; and for flexural members, ratio of the total bend cross-sectional area of the controlling flange to the full cross-sectional area of the controlling flange

f yc =

tensile yield stress of bends

=

Bc f yv (r i / t )

. . . 1.5.2.4(2)

m

Equation 1.5.2.4(2) is applicable only if— (A) f uv/ f yv is greater than or equal to 1 .2; (B) r i/t is less than or equal to 7; and (C) the minimum included angle is less than or equal to 120° . Bc = constant 2


=

 f   f  1.486  uv  − 0.210  uv  − 0.128  f yv   f yv     

. . . 1.5.2.4(3)

f yv = tensile yield stress of unformed steel r i

= inside bend radius

m = constant

 f uv   − 0.068   f yv 

= 0.123  f uv

. . . 1.5.2.4(4)

= tensile strength of unformed steel

f yf = yield stress of the flat portions (see Clause 6.1.5); or yield stress of unformed steel if tests are not made (b)

For axially loaded tension members, f ya shall be determined by either Item (a)(i) or Item (a)(iii). The value of C shall be calculated as fo r compression members.

1.5.2.5 Effect of welding and heat treatment

The increase in yield stress due to cold-forming or temper-rolling, or both, may be partly or completely lost by processes such as welding, annealing or other heat treatment carried out after forming. The effect of any welding and heat treatment on the mechanical properties of a member shall be determined on the basis of tests on specimens of the full section containing the weld within the gauge length. Any necessary allowance for such effect shall be made in the structural use of the member. In the absence of specified testing, the annealed properties shall be used. Surface finishing of the weld is normally required to restore full corrosion resistance. Surface finishing shall be in accordance with AS/NZS 1554.6. NOT E: For initia l g uidance o n the effect o f we ldi ng and heat trea tment, see Appendix C.

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1.5.2.6 Ductility

Stainless steels not specifically conforming to the Standards listed in Clause 1.5.2.1 shall comply with one of the following requirements: (a)

The ratio of tensile strength to yield stress in both longitudinal and transverse directions shall be not less than 1.08.

(b)

The total elongation shall be not less than 10% for a 50 mm gauge length, or 7% for a 200 mm gauge length.

(c)

The elongation shall be determined in accordance with Section 6.

1.5.2.7 Acceptance of steels

Certified mill test reports, or test certificates issued by the mill, shall constitute sufficient evidence of compliance with the Standards referred to in this Standard. 1.5.2.8 Delivered minimum thickness

The minimum thickness of the cold-formed stainless steel product in the structure shall not at any location be less than 95% of the thickness (t ) used in its design, except at bends and corners where the thickness may be less due to cold-forming effects. ) d e t n i r p n e h w d e e t n a r a u g t o n y c n e r r u c t n e m u c o D ( 7 1 0 2 v o N 4 1 n o D N A L S N E E U Q N R E H T U O S F O Y T I S R E V I N U y b d e s s e c c A

1.5.2.9 Unidentified steel

Unidentified steel may only be used when sufficient samples have been subjected by either the producer or purchaser to analyses, tests and other controls as prescribed by one of the Standards listed in Clause 1.5.2.1 or in accordance with Clause 1.5.2.6. 1.5.3

Design stresses

The minimum yield stress ( f y) used in design shall be the proof stress determined at a plastic strain of 0.2%. The minimum tensile yield stress ( f yt ) or compressive yield stress ( f yc ), and tensile strength ( f u) used in design shall not be greater than the higher of the following: (a)

The specified minimum values given in the Standards listed in Clause 1.5.2.1.

(b)

The values given in Appendix B.

(c)

The values determined by tests in accordance with Section 6.

1.5.4

Fasteners

1.5.4.1 Bolts, nuts and washers

Bolts, nut s and washers complying with ASTM A 193, ASTM A 276, ASTM F 593 or ISO 3506 may be used. A manufacturer’s test report, test certificate or letter of conformance, shall constitute sufficient evidence of compliance with the Standard used. NOT E: App endix D des cri bes the commo nly availa ble grades and temp ers of sta inl ess steel fasteners.

1.5.4.2 Welding consumables

All welding consumables shall comply with AS/NZS 1554.6. 1.6 DESIGN REQUIREMENTS 1.6.1

Loads and load combinations

A structure and its components shall be designed for the loads and load combinations as specified in the appropriate limit state loading Standard. 1.6.2

Structural analysis and design

NOT E: Guidance on the applicabi lity of elasti c str uctura l anal ysi s to contin uou s bea ms and frames is given in Appendix E.

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1.6.2.1 General

The following types of limit states shall be considered for the design of structures and its components: (a)

The ultimate and stability limit states.

(b)

The serviceability limit state.

1.6.2.2 Ultimate limit state

The structure and its component members and connections shall be designed for the ultimate limit state as follows: (a)

All members and connections shall be proportioned so that the design capacity ( Rd) is not less than the design action effect [design action] (S *), i.e.— S * ≤ Rd

(b)


(c)

The design action effects [design actions] (S *) resulting from the ultimate limit state design loads shall be determined by an elastic structural analysis unless— (i)

member strength is established by testing in accordance with Section 6; or

(ii)

it is ensured that any plastic hinges have adequate strength and ductility to perform thei r intended purpose, in which case the forces and moments may be determined by a plastic analysis.

The design capacity ( Rd) shall be determined by either— (i)

the nominal capacity ( Ru) in accordance with Sections 2 to 5, and the capacity [strength reduction] factor (φ), i.e.— Rd

(ii)

= φ Ru; or

testing in accordance with Section 6.

1.6.2.3 Stability limit state

The structure as a whole (and any part of it) shall be designed to prevent instability due to overturning, uplift or slidin g as specified in the appropriate loading Standard. 1.6.2.4 Serviceability limit state

The structure and its components shall be designed for the serviceability limit state by controlling or limiting deflection, vibration, bolt slip and corrosion, as appropriate. 1.6.2.5 Fatigue NOT E: Guidance on the des ign of stainless ste el str ucture s f or fatigu e i s g ive n i n Ap pend ix F.

1.6.2.6 Fire NOT E: Guidance on the des ign of stainless ste el str ucture s f or fir e i s g ive n i n Ap pendix G .

1.6.3 Earthquake

Where applicable, the following shall be considered for earthquake design: (a)

For Aust rali a All structures shall be designed for the loads and load combinations specified in AS 1170.4. If stainless steel members are used as the primary earthquake resistance element then the structural response factor ( Rf ) shall be less than or equal to 2.0 unless specified otherwise.

(b)

For New Zealand All structures shall be designed for the loads and load combinations specified in NZS 4203 but subject to the following limitations: (i)

For the ultimate limit state, the structural ductility factor (µ) shall be less than or equal to 1.25, unless a greater value (but not greater than 4.0) is justified by a special study. The structural ductility factor ( µ) depends upon the structural form, the ductility of the material and structural damping characteristics.

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1.6.4

(ii)

For the serviceability limit state, the structural ductility factor (µ) shall be equal to 1.0.

(iii)

The structural performance factor (S ( S p) shall be equal to 0.67, unless a lower value (but not less than 0.4) is determined as appropriate by a special study. The structural performance factor (S ( S p) depends on the material, form and period of the earthquake resisting system, damping of the structure and the interaction of the structure with the ground.

Durability

A structure shall be designed to perform its required functi ons during its expected life. NOT E: For fur ther the r i nforma nfo rmatio tio n, see Appen dix C.

1.7

NON-CONFORMING SHAPES AND CONSTRUCTION

This Standard shall not be interpreted to prevent the use of alternative shapes or constructions not specifically prescribed in this Standard. Such alternatives shall comply with Section 6.


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E L E M E N T S

2.1 SECTION PROPERTIES 2.1.1

General

Properties of sections, such as cross-sectional area, second moment of area, section modulus, radius of gyration, and centroid, shall be determined in accordance with conventional methods by division of the section shape into simple elements, including bends. bend s. Properties shall be based on nominal dimensions and nominal base steel thickness. 2.1.2

Design procedures

2.1.2.1 Full section properties

Properties of full, unreduced sections shall be based on the entire simplified shape with the flats and the bends located along the element mid-lines, unless the manufacturing process warrants consideration of a more accurate method. ) d e t n i r p n e h w d e e t n a r a u g t o n y c n e r r u c t n e m u c o D ( 7 1 0 2 v o N 4 1 n o D N A L S N E E U Q N R E H T U O S F O Y T I S R E V I N U y b d e s s e c c A

To calculate the stability of members, a simplified shape, where the bends are eliminated and the section is represented by straight mid-lines, may be used when calculating the following properties: (a)

Location of shear centre (see Paragraph H1 of Appendix H).

(b)

Warping constant (see Paragraph H1 of Appendix H).

(c)

Monosymmetry section constant (see Paragraph H2 of Appendix H).

2.1.2.2 Effective section properties

For the design of cold-formed stainless steel members with slender elements, the area of t he sections shall be reduced at specified locations. The reduction of the area is required to— (a)

compensate for the effects of shear lag (see Clause 2.1.3.3); and

(b)

compensate for local instabilities of elements in compression (see Clauses 2.2 to 2 .5).

2.1.2.3 Location of reduced width

The location of reduced width shall be determined as follows: (a)

For the design of uniformly compressed stiffened elements, the location of the lost portio por tion n shall sh all be taken t aken at the middle midd le of the element ele ment (see (se e Figur Fi gures es 2.2.1 2.2 .1 and a nd 2.4.1(b 2.4. 1(b)). )).

(b)

For the design of stiffened elements under a stress gradient or where only a part of the element is in compression, e.g. the webs, the location of the lost portion shall be as shown in Figure 2.2.2.

(c)

For unstiffened elements, under either a stress gradient or uniform compression, the lost portion shall be taken at the unstiffened edge as shown in Figure 2.3.1. Where the unstiffened element is subjected to both tension and compression across its width, the lost portion may be taken as set out i n Appendix I.

(d)

For the design of elements with an edge stiffener, the location of the lost portion shall be as show s hown n in i n Figu F igure re 2.4.2. 2.4 .2.

2.1.2.4 Effective section for determining determining deflection

The effective second moment of area used to determine deflection may be obtained in accordance with Clause 2.2.1.3. COPYRIGHT

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2.1.3

Dimensional limits

2.1.3.1 Maximum flange flat-width-to-thickness ratios

The maximum overall flat-width-to-thickness ratios (b ( b / t ), ), disregarding intermediate stiffeners and taking t as the nominal base thickness of the element exclusive of coatings, shall be as follows: (a)


For stiffened compression element having one longitudinal edge connected to a web or flange element and the other stiffened by— (i) (i )

simple simple lip ................................... .................................................... .................................. .................................. ........................ ....... 50; and

(ii)

any other kind of stiffener having I having I s > I a and d l l / b < 0.8 in accordance with Clause Clause 2.4.3 ................................. .................................................. .................................. .................................. ......................90. .....90.

(b)

For stiffened compression element with both longitudinal edges connected to other stiffened stiffened elements elements .................................. ................................................... .................................. .................................. ...........................400. ..........400.

(c)

For unstiffened compression element and elements with an edge stiffener having I s < I < I a and d l l /b ≤ 0.8 in accordan accordance ce with Clause 2.4.3 .................................. .............................................50. ...........50. NOT E: Unsti Uns tiffe ffe ned compre com pre ss ion elements ele ments with wit h b / t ratios greater than 30 and stiffened compression elements with b /t ratios greater than 75 are likely to develop noticeable deformation at the full design load, without affecting the ability of the member to carry the design load. Stiffened elements with b /t ratios greater than 400 can be used with adequate design capacity [strength] to sustain the design loads; however, substantial deformations of such elements usually will invalidate the design equations of this Standard.

2.1.3.2 Flange curling

Where the flange of a flexural member is unusually wide and it is desired to limit the maximum amount of curling or movement of the flange toward the neutral axis, the maximum width (b (b1) of the compression and tension flanges, either stiffened or unstiffened projec pro jectin ting g beyond beyo nd the web for I-beams I-be ams and simi lar section sect ionss or the maximum maxi mum half hal f distan dis tance ce (b1) between webs for box- or U-type beams, shall be determined from the following Equation: b1

=

0.061 t f dE o f *av

4

100 c f

. . . 2.1.3.2

d

where t f f

= thic thickn knes esss of the the fla flang ngee

d

= dept depth h of of the the sect sectio ion n

E o

= initial initial Young’s Young’s modulus modulus of elasticity elasticity (given in Appendix Appendix B)

average design design stress stress in the full, full, unreduced unreduced flange flange width width (see (see Note 1) f av* = average c f

= amount amount of curl curling ing (see (see Note Note 2) 2)

NOT ES: 1

Where members are designed by the effective design width procedure, the average stress equals the maximum stress multiplied by the ratio of the effective design width to the actual width.

2

The amount of curling that can be tolerated will vary with different kinds of sections and should be established by the designer. Amount of curling in the order of 5% of the depth of the section is usually not considered excessive.

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2.1.3.3 Shear lag effects (usually short spans supporting concentrated loads)

Where the span of the beam (l ) is less than 30b1 and the beam carries one concentrated load, or several loads spaced greater than 2 b 1, the effective design width of any flange, whether in tension or compression, shall be limited to t he values given in Table 2.1.3.3. For flanges of I-beams and similar sections stiffened by lips at the outer edges, b1 shall be taken as the sum of the flange projection beyond the web and t he depth of the lip.

TABLE 2.1.3.3 MAXIMUM RATIO OF EFFECTIVE DESIGN WIDTH TO ACTUAL WIDTH FOR SHORT WIDE FLANGE BEAMS


l/b1

Ratio

l/b1

Ratio

30

1.00

14

0.82

25

0.96

12

0.78

20

0.91

10

0.73

18

0.89

8

0.67

16

0.86

6

0.55

NOTE : l is the full span for simple beams; or distance between inflection points for continuous beams; or twice the length of cantilever beams.

2.1.3.4 Maxi mum web depth-t o-thickness ratio

The maximum web depth-to-thickness ratio (d 1/t w) of flexural members shall not exceed the following: (a)

For unreinforced webs d 1/t w .................................................................................200.

(b)

For webs with transverse stiffeners complying with Clause 2.6.1— (i)

if using bearing stiffeners only d 1/t w .................................................... 260; and

(ii)

if using bearing stiffeners and intermediate stiffeners d 1/t w .........................300;

where d 1 = depth of the flat portion of the web measured along the plane of the web t w = thickness of web Where a web consists of two or more sheets, the ratio d 1/t w shall be calculated for each sheet. 2.2 2.2.1

EFFECTIVE WIDTHS OF STIFFENED ELEMENTS Uniformly compressed stiffened elements

2.2.1.1 General

For uniformly compressed stiffened elements, the effective widths for section or member capacity and deflection calculations shall be determined in accordance with Clauses 2.2.1.2 and 2.2.1.3, respectively.

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2.2.1.2 Effective width for capacity calculati ons

For determining the section or member capacity [strength], the effective widths ( b e) of uniformly compressed stiffened elements shall be determined from either one of the following Equations, as appropriate: For λ ≤ 0.673

be = b

. . . 2.2.1.2(1)

For λ > 0.673

be = ρ b

. . . 2.2.1.2(2)

where b = flat width of element excluding radii (see in Figure 2.2.1(a))

ρ = effective width factor =

 1 − 0.22    λ   ≤ 1.0

. . . 2.2.1.2(3)

λ

The slenderness ratio ( λ) shall be determined as follows:


 1.052   b    λ =       k   t  

f * E o

   

. . . 2.2.1.2(4)

where k

= plate buckling coefficient = 4 for stiffened elements supported by a web on each longitudinal edge (k values for different types of elements are given in the appli cable clauses)

t

= thickness of the uniformly compressed stiffened elements

f * = design stress in the compression element calculated on the basis of the effective design width (see Figure 2.2.1(b)) E o = initial Young’s modulus of elasticity given in Appendix B. Alternatively, the plate buckling coefficient (k ) for each flat element may be determined from a rational elastic buckling analysis of the whole section as a plate assemblage subjected to the longitudinal stress distribution in the section prior to buckling.

FIGURE 2.2.1

STIFFENED ELEMENTS WITH UNIFORM COMPRESSION

For determining the nominal section or member capacity of flexural members, the design stress ( f * ) shall be taken as follows: (a)

Where the nominal section moment capacity ( M s) is based on initiation of yielding as specified in Clause 3.3.2.2, and the initial yielding of the element being considered is in compression, then f * shall be equal to f yc. If the initial yielding of the section is in tension, then f * of the element being considered shall be determined on the basis of the effective section at M y (moment causing initial yield). COPYRIGHT

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(b)

AS/NZS 4673:2001

Where the nominal section moment capacity ( M s) is based on inelastic reserve capacity as specified in Clause 3.3.2.3, then f * shall be the stress of the element being considered at M s. The basis of the effective section shall be used to determine M s.

(c)

Where the nominal member moment capacity ( M b) is based on lateral buckling as specified in Clause 3.3.3, then f * shall be equal to M c / Z f as described in Clause 3.3.3 in determining Z c.

For compression members, f * shall be taken equal to f n determined in accordance with Clause 3.4. 2.2.1.3 Effective width for deflection calculations

For determining the deflection, the effective widths (b ed ) shall be determined from either one of the following Equations, as appropriate. For λ ≤ 0.673

bed = b

. . . 2.2.1.3(1)

For λ > 0.673

bed = ρ b

. . . 2.2.1.3(2)

The effective width factor ( ρ) shall be determined from Equations 2.2.1.2(3) and 2.2.1.2(4), ) d e t n i r p n e h w d e e t n a r a u g t o n y c n e r r u c t n e m u c o D ( 7 1 0 2 v o N 4 1 n o D N A L S N E E U Q N R E H T U O S F O Y T I S R E V I N U y b d e s s e c c A

except that f d* shall be substituted for f * , where f d* is the design compressive stress in the element being considered based on the effective section at the load for which deflections are determined, and the reduced modulus of elasticity ( E r ) shall be substituted for E o in Equation 2.2.1.2(4). E r

=

E st + E sc

. . . 2.2.1.3(3)

2

where E st

= secant modulus corresponding to stress in tension flange

E sc = secant modulus corresponding to stress in compression flange The values of E st and E sc shall be obtained from Appendix B, as appropriate. 2.2.2

Effective widths of webs and stiffened elements with stress gradient

2.2.2.1 Effective widths f or capacity calculations

For determining the section or member capacity, the effective width ( be1 ) (see Figure 2.2.2) shall be determined from the following Equation: be1

=

be

. . . 2.2.2.1(1)

3 − ψ

The effective width (be2 ) (see Figure 2.2.2) shall be determined from Equation 2.2.2.1(2) or Equation 2.2.2.1(3), as appropriate. For ψ ≤ −0.236:

be2

=

be 2

. . . 2.2.2.1(2)

where (be1 + be2 ) shall not be greater than the compression portion of the web calculated on the basis of effective section. For ψ > −0.236

be2

= be

− be1

. . . 2.2.2.1(3)

where be

= effective width determined in accordance with Clause 2.2.1.2 with f * 1 substituted for f * and with k determined as follows:

k

= 4 + 2(1

− ψ )3 + 2(1 − ψ ) COPYRIGHT

. . 2.2.2.1(4)

30

AS/NZS 4673:2001

ψ

= stress ratio =

f 2*

. . . 2.2.2.1(5)

f 1*

f 1* , f 2* = web stresses calculated (see Figure 2.2.2)

on

the

basis

of

the

effective

section

f 1* is compression (+) and f 2* can be either tension ( − ) or compression. In case f 1* and f 2* are both compression, f 1* shall be greater than or equal to f 2* . 2.2.2.2 Effective width for deflection calculations

For determining the deflection, the effective widths (b e1 ) and (b e2 ) shall be determined in * * accordance with Clause 2.2.2.1 except that f d1 and f d2 shall be substituted for f 1* and f 2* .

The calculated stresses f 1* and f 2* (see Figure 2.2.2) shall be used to determine f d1* and f d2* , respectively. Calculations shall be based on the effective section for the load for which deflections are determined. ) d e t n i r p n e h w d e e t n a r a u g t o n y c n e r r u c t n e m u c o D ( 7 1 0 2 v o N 4 1 n o D N A L S N E E U Q N R E H T U O S F O Y T I S R E V I N U y b d e s s e c c A

FIGURE 2.2.2 STIFFENED ELEMENTS WITH STRESS GRADIENT AND WEBS

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2.3 2.3.1

AS/NZS 4673:2001

EFFECTIVE WIDTHS OF UNSTIFFENED ELEMENTS Uniformly compressed unstiffened elements

2.3.1.1 General

For uniformly compressed unstiffened elements (see Figure 2.3.1), the effective widths for section or member capacity and deflection calculations shall be determined in accordance with Clauses 2.3.1.2 and 2.3.1.3, respectively. 2.3.1.2 Effective width for capacity calculati ons

For determining the section or member capacity, the effective widths (b e) of uniformly compressed unstiffened elements shall be determined in accordance with Clause 2.2.1.2 with the exception that k shall be taken as 0.5 and b shall be as shown in Figure 2 .3.1. 2.3.1.3 Effective width for deflection calculations

For determining the deflection, the effective widths (b e) shall be determined in accordance with Clause 2.2.1.3 except that f d* shall be substituted for f * and k is equal to 0.5.


FIGURE 2.3.1

2.3.2

UNSTIFFENED ELEMENT WITH UNIFORM COMPRESSION

Unstiffened elements and edge stiffeners with stress gradient

2.3.2.1 General

For unstiffened elements and edge stiffeners with stress gradient, the effective widths for section or member capacity and deflection calculations shall be determined in accordance with Clauses 2.3.2.2 and 2.3.2.3, respectively. 2.3.2.2 Effective width for capacity calculati ons

For determining the section or member capacity, the effective widths (b e) of unstiffened compression elements and edge stiffeners with stress gradient shall be determined in accordance with Clause 2.2.1.2 with f * equal to f 3* as shown in Figures 2.3.2 and 2.4.2, and k equal to 0.5. Values of the plate buckling coefficient (k ) given in Appendix I may be used in lieu of 0.5. Alternatively, the plate buckling coefficient (k ) for each flat element may be determined from a rational elastic buckling analysis of the whole section as a plate assemblage subjected to the longitudinal stress distribution in the section prior to buckling. 2.3.2.3 Effective width for d eflection calculations

For determining the deflection, the effective widths (b ed ) of unstiffened compression elements and edge stiffeners with stress gradient shall be determined in accordance with * Clause 2.2.1.3 except that f d3 shall be substituted for f * and k is equal to 0.5. Values of the plat e buckling coeffi cient (k ) given in Appendix I may be used in lieu of 0.5.

Alternatively, the plate buckling coefficient (k ) for each flat element may be determined from a rational elastic buckling analysis of the whole section as a plate assemblage subjected to the longitudinal stress distribution in the section prior to buckling. COPYRIGHT

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AS/NZS 4673:2001

FIGURE 2.3.2 ) d e t n i r p n e h w d e e t n a r a u g t o n y c n e r r u c t n e m u c o D ( 7 1 0 2 v o N 4 1 n o D N A L S N E E U Q N R E H T U O S F O Y T I S R E V I N U y b d e s s e c c A

UNSTIFFENED COMPRESSION ELEMENTS SUBJECT TO A STRESS GRADIENT

2.4 EFFECTIVE WIDTHS OF UNIFORMLY COMPRESSED ELEMENTS WITH AN EDGE STIFFENER OR ONE INTERMEDIATE STIFFENER 2.4.1

Notation

For the purpose of this Clause— As

= reduced area of the stiffener. As shall be used in calculating the overall effective section properties. The centroid of the stiffener shall be considered located at the centroid of the full area of the stiffener, and the second moment of area of the stiffener about its own centroidal axis shall be that of the full section of the stiffener

Ase

= effective area of the stiffener = d se t (for stiffener shown in Figure 2.4.2)

. . . 2.4.1(1)

b

= flat width of element excluding radii (see Figures 2.4.1(a) and 2.4.2(a))

b2

= flat width of element (see Figure 2.4.1(a))

C 1, C 2

= coefficients (see Figure 2.4.2(b))

with

intermediate

stiffener

excluding

radii

d , d l = actual stiffener dimension (see Figure 2.4.2(a)) d s

= reduced effective width of the stiffener (see Figure 2.4.2(a)). The value of d s calculated in accordance with Clause 2.4.3, shall be used in calculating the overall effective section properties

d se

= effective width of the stiffener calculated in accordance with Clause 2.3.1 (see Figure 2.4.2(a))

I a

= adequate second moment of area of the stiffener, so that each component element behaves as a stiffened element

I s

= second moment of area of the full stiffener about its own centroidal axis parallel to the element to be stiffened

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=

d 3 t sin 2θ 12

(for stiffener shown in Figure 2.4.2)

k

= plate buckling coefficient

S

= slenderness factor = 1.28

E o

AS/NZS 4673:2001

. . . 2.4.1(2)

. . . 2.4.1(3)

f *

For edge stiffeners, the round corner between the stiffener and the element to be stiffened shall not be considered as part of the stiffener.


FIGURE 2.4.1

ELEMENTS WITH INTERMEDIATE STIFFENER

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FIGURE 2.4.2

2.4.2

ELEMENTS WITH EDGE STIFFENER

Elements with an intermediate stiffener

2.4.2.1 General

For uniformly compressed elements with an intermediate stiffener, the effective widths for section or member capacity and deflection calculations shall be determined in accordance with Clauses 2.4.2.2 and 2.4.2.3, respectively. 2.4.2.2 Effective width for capacity calculations

For determining the section or member capacity, the effective widths (b e) of uniformly compressed elements with an intermediate stiffener shall be determined for the following cases: (a)

Case I:

b2 t

≤ S

I a = 0 (no intermediate stiffener is required) be = b

. . 2.4.2.2(1)

As = Ase

. . 2.4.2.2(2)

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(b)

Case II: S <

I a 4

t

=

b2 t

AS/NZS 4673:2001

< 3S

 b2    t  − 50

50 

. . . 2.4.2.2(3)

S

b e shall be calculated in accordance with Clause 2.2.1.2 where k

 = 3  

  + 1 ≤ 4 I a  

As

  = Ase  I s  ≤ Ase   I a 

I s

. . . 2.4.2.2(4)

. . . 2.4.2.2(5)

Ase shall be calculated in accordance with Clause 2.2.1.2. ) d e t n i r p n e h w d e e t n a r a u g t o n y c n e r r u c t n e m u c o D ( 7 1 0 2 v o N 4 1 n o D N A L S N E E U Q N R E H T U O S F O Y T I S R E V I N U y b d e s s e c c A

(c)

Case III:

I a t 4

b2 t

≥ 3S

  =   

128

 b2        t   − 285  S  

. . . 2.4.2.2(6)

b e shall be calculated in accordance with Clause 2.2.1.2 where 1/ 3

k

 I  3  s    I a 

As

Ase

+1

≤4

. . . 2.4.2.2(7)

 I s    ≤ Ase   I a 

. . . 2.4.2.2(8)

Ase shall be calculated in accordance with Clause 2.2.1.2. 2.4.2.3 Effective width for deflection calculations

For determining the deflection, the effective widths (b e) shall be determined in accordance with Clause 2.4.2.2, except that f d* shall be substituted for f *. 2.4.3

Elements with an edge stiffener

2.4.3.1 General

For uniformly compressed elements with an edge stiffener, the effective widths for section or member capacity and deflection calculations shall be determined in accordance with Clauses 2.4.3.2 and 2.4.3.3, respectively. 2.4.3.2 Effective width for capacity calculati ons

For determining the section or member capacity, the effective widths (b e) of uniformly compressed elements with an edge stiffener shall be determined for the foll owing cases:

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AS/NZS 4673:2001

(a)

b

Case I:

t

≤ S 3

I a = 0 (no edge stiffener is required)

(b)

be = b

. . . 2.4.3.2(1)

d s = d se (for simple lip stiffener)

. . . 2.4.3.2(2)

As = Ase (for other stiffener shapes)

. . . 2.4.3.2(3)

S

Case II:

3

I a t 4 n

<

t

< S

 (b / t ) = 399  − S 

k u 4

3  

. . . 2.4.3.2(4)

= 0.5

C 2 = ) d e t n i r p n e h w d e e t n a r a u g t o n y c n e r r u c t n e m u c o D ( 7 1 0 2 v o N 4 1 n o D N A L S N E E U Q N R E H T U O S F O Y T I S R E V I N U y b d e s s e c c A

b

I s

≤1

. . . 2.4.3.2(5)

− C 2

. . . 2.4.3.2(6)

I a

C 1 = 2

b e shall be calculated in accordance with Clause 2.2.1.2, where k shall be determined as follows: k = C 2n (k a

− k u ) + k u

. . . 2.4.3.2(7)

k u = 0.43 For simple lip stiffener with 140° Figure 2.4.2:

≥ θ ≥ 40° and

d l/b ≤ 0.8, where

θ is

as shown in

k a = 5.25 − 5 (d l b ) ≤ 4.0

. . . 2.4.3.2(8)

d s = C 2d s

. . . 2.4.3.2(9)

For stiffener shape other than simple lip : k a = 4.00 As = C 2 Ase (c)

Case III: I a t 4

b t

=  

≤ Ase ’

. . . 2.4.3.2(10)

≥ S 115 (b t ) S

 + 5

. . . 2.4.3.2(11)

C 1, C 2, be, k , d s , As shall be calculated in accordance with Case II with n equal to 0.333. 2.4.3.3 Effective width for d eflection calculations

For determining the deflection, the effective widths (b e) shall be determined in accordance with Clause 2.4.3.2, except that f d* shall be substituted for f * .

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AS/NZS 4673:2001

2.5 EFFECTIVE WIDTHS OF EDGE-STIFFENED ELEMENTS WITH ONE OR MORE INTERMEDIATE STIFFENERS, OR STIFFENED ELEMENTS WITH MORE THAN ONE INTERMEDIATE STIFFENER

For determining the effective width (b e), the intermediate stiffener of an edge-stiffened element or the stiffeners of a stiffened element with more than one stiffener shall be disregarded unless each intermediate stiffener has the f ollowing minimum I s : I s,

= 3.66t

4

min.

 b 2  0.119 E    o     ≥ 18.4t 4   −    t   f y    

. . . 2.5(1)

where I s b t

= second moment of area of the full stiffener about its own centroidal axis parallel t o the element to be stiffened = width-to-thickness ratio of the larger stiffened sub-element.

In addition, the following shall be considered: ) d e t n i r p n e h w d e e t n a r a u g t o n y c n e r r u c t n e m u c o D ( 7 1 0 2 v o N 4 1 n o D N A L S N E E U Q N R E H T U O S F O Y T I S R E V I N U y b d e s s e c c A

(a)

Where the spacing of intermediate stiffeners between two webs is such that for the sub-element between the stiffeners, be is less than b as determined in accordance with Clause 2.2.1.2, only t wo intermediate stiffeners, those nearest each web, shall be considered effective.

(b)

Where the spacing of intermediate stiffeners between a web and an edge stiffener is such that for the sub-element between the stiffeners, be is less than b as determined in accordance with Clause 2.2.1.2, only one intermediate stiffener, that nearest the web, shall be considered effective.

(c)

Where intermediate stiffeners are spaced so closely that for the elements between the stiffeners, b e is equal to b as determined in accordance with Clause 2.2.1.2, all the stiffeners may be considered effective. In calculating the flat-width-to-thickness ratio of the entire multiple-stiffened element, such element shall be considered as replaced by an equi valent element without i nter mediate stiffeners whose width (b 2) shall be the full width between webs or from web to edge stiffener, and whose equivalent thickness of the stiffener (t s) shall be determined from the following Equation: t s

=3

12 I sf

. . . 2.5(2)

b2

where I sf is the second moment of area of the full area of the multiple-stiffened element, including the intermediate stiffeners, about its own centroidal axis. The second moment of area of the entire section shall be calculated assuming the equivalent element to be located at the centroidal axis of the multiple stiffened element, including the intermediate stiffener. The actual extreme fibre distance shall be used in calculating the section modulus. (d)

If b/t is greater than 60, the effective width (be) of the sub-element or element shall be determined from the following Equation: bes t

  b  =   be  − 0.1  − 60   t   t 

. . . 2.5(3)

where b/t = flat-width ratio of the sub-element or element bes = effective width of the sub-element or element to be used in design calculations be = effective width determined in accordance with Clause 2.2.1.2 COPYRIGHT

38

AS/NZS 4673:2001

To calculate the effective structural properties of a member having compression subelements or element subjected to the above reduction in effective width, the area of stiffeners (edge stiffener or intermediate stiffeners) shall be considered reduced to an effective area as follows: (i)

For 60 <

b t

Aef = α As

< 90:

. . . 2.5(4)

where

 

α =  3 −

(ii)

For

b t

≥ 90 :

2bes b

Aef

 − 1  − bes   b   1    30 b     t 

 =   bes  As  b 

. . . 2.5(5)

. . . 2.5(6)

In Equations 2.5(4) and 2.5(6), Aef and As apply only to the area of the stiffener section, exclusive of any portion of adjacent elements.


The centroid of the stiffener shall be considered at the centroid of the full area of the stiffener, and the second moment of area of the stiffener about its own centroidal axis shall be that of the full section of the stiffener. 2.6 STIFFENERS 2.6.1

Transverse stiffeners

Transverse stiffeners attached to beam webs at points of concentrated loads or reactions shall be designed as compression members. Concentrated loads or reactions shall be applied directly into the stiffeners, or each stiffener shall be fitted accurately to the flat portion of the flange to provide direct loadbearing into the end of the stiffener. Means for shear transfer between the stiffener and the web shall be provided in accordance with Section 3. The design concentrated loads or reactions ( N *) shall satisfy the following: (a)

N * ≤ φ c N s

. . . 2.6.1(1)

(b)

N * ≤ φ c N c

. . . 2.6.1(2)

Where

φ c

= capacity [strength reduction] factor for members in compression = 0.85

N s

= nominal section capacity of a member in compression (see Clause 3.4) = f wy As1

N c

= nominal member capacity of a member in compression (see Clause 3.4) = f n As2

f wy

= lower yield stress value of the beam web ( f y) or of the stiffener section ( f ys)

f n

= buckling stress (see Clause 3.4)

As1 , As2

= area of a member in compression consisting of the transverse stiffeners and a portion of the web

As1

= 18t 2 + As (for transverse stiffeners at interior support and under concentrated load)

. . . 2.6.1(3)

= 10t 2 + As (for transverse stiffeners at end support)

. . . 2.6.1(4)

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As2

AS/NZS 4673:2001

= b1t + As (for transverse stiffeners at interior support under concentrated load)

. . . 2.6.1(5)

= b2t + As (for transverse stiffeners at end support)

. . . 2.6.1(6)

t

= base thickness of beam web

As

= cross-sectional area of transverse stiffeners

b1

= 25t  0.0024

 

 l s t  + 0.72 ≤ 25t    t  

. . . 2.6.1(7)

b2

= 12t  0.0044

 

 l s t  + 0.83 ≤ 12t    t  

. . . 2.6.1(8)

l st

= length of transverse stiffener

The b/t s ratio for the stiffened and unstiffened elements of cold-formed steel transverse stiffeners shall not exceed 1.28 E o / f y s and 0.37 E o / f y s , respectively, where f ys is the ) d e t n i r p n e h w d e e t n a r a u g t o n y c n e r r u c t n e m u c o D ( 7 1 0 2 v o N 4 1 n o D N A L S N E E U Q N R E H T U O S F O Y T I S R E V I N U y b d e s s e c c A

yield stress and t s is the thickness of the stiffener st eel. 2.6.2

Shear stiffeners

Where shear stiffeners are required, the spacing shall be such that the design shear force shall not be greater than the design shear capacity ( φ vV v) specified in Clause 3.3.4, and the ratio a/d 1 shall not be greater than [260/(d 1/t )]2 and 3.0. The actual second moment of area ( I s,min.) of a pair of attached shear stiffeners, or of a single shear stiffener, with reference to an axis in the plane of the web, shall have a minimum value as follows: I s , min.

=

3

5d 1t

 d 1  a    d 1  4  − 0.7     ≥  50  d   a  1  

. . . 2.6.2(1)

The gross area of shear sti ffeners ( Ast ) shall be not less than—

Ac

  1 − k s    a  =    2   d 1  

−   

a d 1

 a  2     d 1  2   a    + 1 +  d     1 

    ψ k st d 1 t   

. . . 2.6.2(2)

where k s = shear stiffener coefficient 1.53 E o k v =

=

2

 d  f y  1   t 

0.00248   k v E o

 d 1      t 

f y

   

if k s ≤ 0.8

. . . 2.6.2(3)

> 0 .8

. . . 2.6.2(4)

if k s

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ψ =

yield stress of web yield stress of stiffener

k st = stiffener type coefficient = 1.0 for stiffeners in pairs = 1.8 for single-angle stiffeners = 2.4 for single-plate stiffeners k v = shear buckling coefficient = 4.00 +

= 5.34


+

5.34

 a      d 1 

2

4.00

 a      d 1 

2

if

if

a d 1

a d 1

≤ 1.0

. . . 2.6.2(5)

> 1.0

. . . 2.6.2(6)

a = distance between transverse stiffeners 2.6.3

Non-conforming stiffeners

The design capacities of members with transverse stiffeners that do not comply with Clause 2.6.1 or 2.6.2, such as stamped or rolled-in transverse stiffeners, shall be determined by test s in accordance with Section 6.

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S E C T I O N

3

AS/NZS 4673:2001

M E M B E R S

3.1 GENERAL

Section properties used for the determination of structural performance, moment capacity of beams or capacity of axial members in compression , shall b e those calculated in accordance with Section 2. Both full and effective section properties, where applicable, shall be required. Full section propert ies shall be used for the determinati on of buckling moments or stresses. Effective section properties shall be used for the determination of section and member capacities. 3.2 MEMBERS SUBJECT TO TENSION

The design tensile force ( φ N t t ) for axially loaded tension members shall be determined as follows:

φ t = 0.85 ) d e t n i r p n e h w d e e t n a r a u g t o n y c n e r r u c t n e m u c o D ( 7 1 0 2 v o N 4 1 n o D N A L S N E E U Q N R E H T U O S F O Y T I S R E V I N U y b d e s s e c c A

N t = An f y

. . . 3.2

where

φ t = capacity [strength reduction] factor for members in tension N t = nominal section capacity of the member in tension An = net area of the cross-section, obtained by deducting from the gross area of the sectional area of all penetrations and holes, including fastener holes f y = yield stress used in design (see Appendix B) When mechanical fasteners are used in connections for tension members, the design tensile strength shall also be limited by Clause 5.3.5. 3.3 MEMBERS SUBJECT TO BENDING 3.3.1

Bending moment

The design bending moment ( M *) of a flexural member shall satisfy the follo wing: (a) (b)

≤ φ b M s M * ≤ φ b M b M *

where

φ b = capacity [strength reduction] factor for bending = 0.90 for sections with stiffened compression flanges = 0.85 or sections with unstiffened compression flanges M s = nominal section moment capacity calculated in accordance with Clause 3.3.2 M b = nominal member moment capacity calculated in accordance with Clause 3.3.3 3.3.2

Nominal section moment capacity

3.3.2.1 General

The nominal section moment capacity ( M s ) shall be calculated either on the basis of initiation of yielding in the effective section specified in Clause 3.3.2.2 or on the basis of the inelastic reserve capacity specified in Clause 3.3.2.3.

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3.3.2.2 Based on initiation of yielding

The nominal section moment capacity ( M s) shall be determined as follows: M s = Z e f y

. . . 3.3.2.2

where Z e is the effective section modulus calculated with the extreme compression or tension fibre at f yc or f yt respectively, whichever initiates yield. 3.3.2.3 Based on inelasti c reserve capacity

The inelastic flexural reserve capacity may be used if the following conditions are met: (a)

The member is not subject to twisting or to lateral, torsional, distortional or flexuraltorsional buckling.

(b)

The effect of cold-forming is not included in det ermining the yield stress ( f y).

The ratio of the depth of the compressed portion of the web ( d w) to its thickness (t w) does not exceed the slenderness ratio ( λ 1). The design shear force (V *) does not exceed 0.35 f y times the web area (d 1t w). ) d e t n i r p n e h w d e e t n a r a u g t o n y c n e r r u c t n e m u c o D ( 7 1 0 2 v o N 4 1 n o D N A L S N E E U Q N R E H T U O S F O Y T I S R E V I N U y b d e s s e c c A

The angle between any web and the vertical does not exceed 30 ° . The nominal section moment capacity ( M s ) shall not exceed either 1.25 Z e f y, where Z e f y shall be determined in accor dance with Clause 3.3.2.2 or that causing a maximum compression strain of C ye y, where C y = compression strain factor e y = yield strain =

f y

. . . 3.3.2.3(1)

E o

NOT E: The re is no limi t f or the maxi mum ten sil e s train.

The compression strain factor (C y) shall be determined as follows: (i)

(ii)

For stiffened compression elements without intermediate stiffeners: For b/t ≤ λ 1:

C y = 3

For λ 1 < b/t < λ 2:

C y = 3 − 2[((b/t )

For b/t ≥ λ 2:

C y = 1

. . . 3.3.2.3(2)

− λ 1)/( λ 2 − λ 1)]

. . . 3.3.2.3(3) . . . 3.3.2.3(4)

1.11

λ 1

=

λ 2

=

f yc / E o

. . . 3.3.2.3(5)

1.28 f yc / E o

. . . 3.3.2.3(6)

For unstiffened compression elements: C y = 1

(iii)

For multiple-stiffened compression elements and compression elements with edge stiffeners: C y = 1

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Where applicable, effective design widths shall be used in calculating section properties. M s shall be calculated considering equilibrium of stresses, assuming an ideally elastic plastic stress-strain curve that is the same in tension as in compr ession, small deformation and that plane sections remain plane during bending. Combined bending and bearing shall be in accordance with Clause 3.3.7. 3.3.2.4 Local distortion

Where local distortions in flexural members under nominal service loads shall be limited, the design flexural capacity ( φ d M ld) shall be determined as follows:

φ d

= 1.0

M ld = Z f f b

. . . 3.3.2.4(1)

Where

φ d

= capacity [strength reduction] factor for local distortion

M l d = nominal flexural capacity of the member


Z f

= elastic section modulus of the full, unreduced cross-section

f b

= permissible compressive stress for local distortion, determined as follows: (a)

If small, barely permissible— (i)

perceptible

amounts

(ii)

for stiffened compression elements:

(ii)

. . . 3.3.2.4(4)

for unstiffened compression elements: f b = 0.75 f cr

. . . 3.3.2.4(5)

= critical buckling stress =

π 2 k η E o

. . . 3.3.2.4(6)

12 (1 − ν 2 ) (b t )

2

= plasticity reduction factor =

for stiffened compression elements

E t / E o

for unstiffened compression elements

= E s E o

3.3.3

. . . 3.3.2.4(2)

. . . 3.3.2.4(3)

f b = 0.9 f cr

ν

are

If no local distortions are permissible— (i)

η

distortions

for unstiffened compression elements: f b = f cr

f cr

local

for stiffened compression elements: f b = 1.2 f cr

(b)

of

= Poisson’s ratio in the elastic range equal to 0.3

Nominal member moment capacity

The design strength of the laterally unbraced segments of doubly or singly symmetric sections subjected to lateral buckling ( φ b M b ) shall be determined as follows:

φ b =

0.85

M b =

 M Z c  c  Z f

   

. . . 3.3.3(1)

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where Z c = elastic section modulus of the effective section calculated at a stress M c /S f in the extreme compression fibre Z f = elastic section modulus of the full, unreduced section for the extreme compression fibre M c = critical moment M c shall be calculated as follows, with a maximum value of M y: (a)

For doubly symmetric I-sections bent about the centroidal axis perpendicular to the web ( x-axis)—

 E t 2 M c = π E o C b   E o

dI yc        l 2     

. . . 3.3.3(2)

Alternatively, M c can be calculated using Equation 3.3.3(4). (b) ) d e t n i r p n e h w d e e t n a r a u g t o n y c n e r r u c t n e m u c o D ( 7 1 0 2 v o N 4 1 n o D N A L S N E E U Q N R E H T U O S F O Y T I S R E V I N U y b d e s s e c c A

For point-symmetric Z-sections bent about the centroidal axis perpendicular to the web ( x-axis)—

 E t 2 M c = 0.5π E o C b   E o

  dI yc     l 2     

. . . 3.3.3(3)

Alternatively, M c can be calculated as half the value using Equation 3.3.3(4). (c)

For singly symmetric sections, where the x-axis is assumed to be the axis of symmetry— (i)

for bending about the symmetry axis, where the x-axis is the axis of symmetry oriented such that the shear centre has a negative x- coordinate— M c = C b r o A σ eyσ t

. . . 3.3.3(4)

Alternatively, M c can be calculated using Equation 3.3.3(2) for doubly symmetric I-sections. (ii)

for bending about the centroid axis perpendicular to the symmetry axis—

 M c = C s C b Aσ ex  j + C s 

j 2

+ r o2 (σ t

/ σ ex )  



. . . 3.3.3(5)

where M y

= moment causing initial yield at the extreme compression fibre of the full section = Z f f y

. . . 3.3.3(6)

l

= unbraced length of the member

I yc

= second moment of area the compression portion of the section about the centroidal axis of the full section parallel to the web, using the full unreduced section

C s

=

+ 1 for the moment causing compression on the shear centre side of the centroid

C s

=

−1

for the moment causing tension on the shear centre side of the centroid

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=

 π 2 E o   E t       2  E ( ) k l / r  x x x   o 

. . . 3.3.3(7)

=

 π 2 E o   E t       2  E  (k y l y /r y )   o 

. . . 3.3.3(8)

σ t

=

 π 2 E o C w    E t   1        2  Go J +  2     Ar     o    (k t l t )    E o 

. . . 3.3.3(9)

A

= area of the full, unreduced cross-section

σ ex

σ ey

E t/ E o = plasticity reduction factor given in Appendix B C b

= bending coefficient =


12.5 M max. 2.5 M max.

+ 3 M 3 + 4 M 4 + 3 M 5

. . . 3.3.3(10)

C b is permitted to be conservatively taken as unity for all cases. For cantilevers or overhang where the free end is unbraced, C b shall be taken as unity. For members subject to combined axial load and bending moment (see Clause 3.5), C b shall be taken as unity. M max. = absolute value of the maximum moment in the unbraced segment M 3

= absolute value of the moment at the quarter point of the unbraced segment

M 4

= absolute value of the moment at the centre-line of the unbraced segment

M 5

= absolute value of the moment at the three-quarter point of the unbraced segment

d

= depth of the section

r o

= polar radius of gyration of the cross-section about the shear centre =

r x2

+ r y2 + xo2

. . . 3.3.3(11)

r x, r y = radii of gyration of the cross-section about the centroidal axes Go

= initial shear modulus (see Appendix B)

k x, k y = effective length factors for bending about the x- and y-axes, respectively k t

= effective length factor for twisting

l x, l y = unbraced lengths of the compression member for bending about the x- and y axes, respectively l t

= unbraced length of the compression member for twisting

x o

= distance from the shear centre of the cross-section to the centroid along the principal x-axis, taken as negative

J

= St. Venant torsion constant of the cross-section COPYRIGHT

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3.3.4

C w

= torsional warping constant of the cross-section

j

=

1 2 I y

(∫ A x 3 dA + ∫ A xy 2 dA) − xo

. . . 3.3.3(12)

Shear

The design shear force ( φ vV v) at any cross-section shall be calculated as follows:

φ v

= 0.85 3

V v

4.84 E o t w (Gs Go )

=

. . . 3.3.4(1)

d 1

In no case shall the design shear force ( φ vV v) be greater than 0.95d 1t w f yv, where


φ v

= capacity [strength reduction] factor for shear

V v

= nominal shear capacity of the beam

t w

= thickness of web

Gs/Go = plasticity reduction factor given in Appendix B d 1

= depth of the flat portion of the web measured along the plane of the web

f yv

= specified shear yield stress given in Appendix B

When the web consists of two or more sheets, each sheet shall be considered as a separate element carrying its share of the shear force. For beam webs with transverse stiffeners satisfying the requirements of Clause 2.6.1, the nominal shear capacity (V v) shall be calculated as follows: 3

V v

=

0.904k v E o t w (Gs /G o )

. . . 3.3.4(2)

d 1

where k v is the shear buckling coefficient and shall be determined in accordance with Clause 2.6.2. 3.3.5

Combined bending and shear

For beams with unstiffened webs, the design bending moment ( M *) and the design shear force (V *) shall satisfy— 2

 M *     φ M  b s 

2

 V *   ≤ 1.0 +   φ V  v v 

. . . 3.3.5(1)

For beams with transverse web stiffeners, the design bending moment ( M *) shall satisfy— M *

≤ φ b M b

. . . 3.3.5(2)

The design shear force (V *) shall satisfy— V * If

M *

φ b M s

≤ φ vV v > 0.5 and

. . . 3.3.5(3) V *

φ bV v

> 0.7 ; then M * and V * shall satisfy—

 M *   V *     ≤ 1.3 +    φ M V φ  b s   v v 

0.6

. . . 3.3.5(4)

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where

φ b

= capacity [strength reduction] factor for bending (see Clause 3.3.1)

φ v

= capacity [strength reduction] factor shear (see Clause 3.3.4)

M s

= nominal section moment capacity about the centroidal axes determined in accordance with Clause 3.3.2

V v

= nominal shear capacity when shear alone exists determined in accordance with Clause 3.3.4

M b = nominal member moment capacity when bending alone exists determined in accordance with Clause 3.3.3 3.3.6

Bearing

This Clause applies to webs of flexural members subject to concentrated loads or reactions, or the components thereof, acting perpendicular to the longitudinal axis of the member and in the plane of the web under consideration, and causing compressive stresses in the web. To avoid failure of unstiffened flat webs of flexural members having a flat width ratio

( ) *


(d 1/t w) less than or equal to 200, the design concentrated loads and reactions R b shall satisfy— R b*

. . . 3.3.6(1)

≤ φ w R b

where

φ w = capacity [strength reduction] factor for bearing = 0.70 for single unstiffened webs and I-sections R b = nominal capacity for concentrated load or reaction for one solid web connecting top and bottom flanges The values of R b for stiffened and unstiffened flanges, and for the appropriate type and posi tion of load s, are given in Table 3.3.6. Webs of flexural members for which d 1/t w is greater than 200 shall be provided with means of transmitting concentrated loads and reactions directly into the webs. The equations in Table 3.3.6 apply, if— (a)

l b/t w ≤ 210 and l b/d 1 ≤ 3.5;

(b)

r i/t w ≤ 6 for beams; and

(c)

r i/t w ≤ 7 for decking and cladding;

where l b = actual length of bearing. For the case of two equal and opposite concentrated loads distributed over unequal bearing lengths, the smaller value of l b shall be taken t w = thickness of web r i = inside bend radius For two or more webs, R b shall be calculated for each individual web and the results added to obtain the nominal concentrated load or reaction for the multiple web. Where two webs of a beam are inclined in opposite directions, the R b equations may be applied to such webs only if they are restrained against spreading. For built-up I-sections, or similar sections, the distance between the web connector and beam flange shall be kept as small as practicable. COPYRIGHT

Accessed by UNIVERSITY OF SOUTHERN QUEENSLAND on 14 Nov 2017 (Document currency not guaranteed when printed)

A S / N Z S 4 6 7 3 : 2 0 0 1

TABLE 3.3.6 NOMINAL VALUES OF R b I-sections or similar sections

Shapes with single webs

(See Note 1)

Type and position of loads

C O P Y R I G H T

Stiffened, partially stiffened and unstiffened

Stiffened or partially stiffened flanges

Unstiffened flanges

End reaction Opposing loads (see Note 3) spaced greater Interior than 1.5d 1 reaction (see Note 2) (see Note 4)

t 2C 3C 4C θ (2.28 - 0.0042 (d 1 t )) (1 + 0.01 (l b t ))

t 2C 3C 4C θ (1.51 - 0.002 (d 1 t ))(1 + 0.01(l b t ))

t 2 f y c b 0.01 + 0.00125 l b t

t 2C 1C 2C θ (3.71 - 0.005 (d 1 t ))(1 + 0.007 (l b t ))

t 2C 1C 2C θ (3.71 - 0.005 (d 1 t ))(1 + 0.007 (l b t ))

t 2 f yC 5 (0.88 + 0.12m) 0.015 + 0.00325 l b t

Opposing loads End reaction spaced less than or equal to Interior 1.5d 1 reaction (see Note 5) (see Note 4)

t 2C 3C 4C θ (1.68 - 0.004 (d 1 t ))(1 + 0.01(l b t ))

t 2C 3C 4C θ (1.68 - 0.004(d 1 t ))(1 + 0.01(l b t ))

t 2 f yC 8 (0.64 + 0.31m ) 0.01 + 0.00125 l b t

2

2

t C 1C 2C θ (5.32 - 0.016 (d 1 t ))(1 + 0.0013(l b t ))

t C 1C 2C θ (5.32 - 0.016 (d 1 t )) (1 + 0.0013(l b t ))

flanges

(

)

(

)

(

(

)

t 2 f yC 7 (0.82 + 0.15m ) 0.015 + 0.00325 l b t

NOTE S: 1

I-sections made of two channels connected back-to-back, or similar sections that provide high degree of restraint against rotation of the web, such as I-sections made by welding two angles t o t he channel.

2

At locations of one concentrated load or reaction acting either on top or bottom flange, if clear distance between bearing edges of this and adjacent opposite concentrated loads or reactions is greater than 1.5 d 1 .

3

For end reactions of beams or concentrated loads on end of cantilevers if distance from edge of bearing to end of beam is less than 1.5 d 1 .

4

For reactions and concentrated loads if distance from edge of bearing to end of beam is greater than or equal to 1.5 d 1 .

5

At locations of two opposite concentrated loads or of concentrated load and opposite reaction acting simultaneously on top and bottom flanges, if clear distance between thei r ad jacent bear ing edges is l ess than or equal to 1 .5 d 1 .

6

If l b/t > 60, the factor (1 + 0.01 (l b/t )) may be increased to (0.71 + 0.015 ( l b /t )).

7

If l b/t > 60, the factor (1 + 0.07 (l b/t )) may be increased to (0.75 + 0.011 ( l b /t )).

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The following applies to the equations given in Table 3.3.6:

φ w = capacity [strength reduction] factor for bearing


R b

= nominal capacity for concentrated load or reaction for one web connecting top and bottom flanges

C 1

= (1.22 − 0.22k )k

if f y ≤ 631 MPa

= 1.69

if f y

. . . 3.3.6(2)

> 631 MPa

C 2

= (1.06 − 0.06(r i/t )) ≤ 1.0

C 3

= (1.33 − 0.33k )k

if f y ≤ 459 MPa

= 1.34

if f y > 459 MPa

. . . 3.3.6(3) . . . 3.3.6(4)

C 4

= (1.15 − 0.15(r i/t )) ≤ 1.0 but not less than 0.50

. . . 3.3.6(5)

C 5

= (1.49 − 0.53k ) ≥ 0.6

. . . 3.3.6(6)

C 6

= 1+ 

if d 1/t ≤ 150

= 1.20

if d 1/t > 150

= 1/k

if d 1/t ≤ 66.5

. . . 3.3.6(8)

if d 1/t > 66.5

. . . 3.3.6(9)

C 7

C 8

 d 1 t    750 

=

 1.10 − d 1 t   1      665   k  

=

 0.98 − d 1 t   1      865   k  

. . . 3.3.6(7)

. . . 3.3.6(10)

2

C θ =

 θ  0.7 + 0.3    90 

. . . 3.3.6(11)

f y

= specified yield stress in longitudinal compression

d 1

= depth of the flat portion of the web measured along the plane of the web

k

= f y/228

m

= non-dimensional thickness

. . . 3.3.6(12)

= t /1.91 l b

. . . 3.3.6(13)

= actual length of bearing

For the case of two equal and opposite concentrated loads distributed over unequal bearing lengths, the smaller value of l b shall be taken. r i

= inside bend radius

θ

= angle between the plane of the web and the plane of the bearing surface. shall be within the following limits: 90 °

≥ θ ≥ 45 °

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3.3.7

Combined bending and bearing

Unstiffened flat webs of shapes subjected to a combination of bending and reaction or concentrated load shall be designed as follows: (a)

Shapes having single unstiffened webs shall satisfy—

 R *   M *    +  1.07    ≤ 1.42 φ φ R M w b b s     (b)

At the interior supports of continuous spans, the above interaction is not applicable to deck or beams with two or more single webs, where the compression edges of adjacent webs are laterally supported in the negative moment region by continuous or intermittently connected flange elements, rigid cladding, or lateral bracing, and the spacing between adjacent webs does not exceed 250 mm.

(c)

Back-to-back channel beams and beams with restraint against web rotation, such as I-sections made by welding two angles to a channel, shall sati sfy— 0.82


. . . 3.3.7(1)

If d 1/t w

≤

 R *   M *     +  φ M   ≤ 1.32 R φ  w b   b s 

2.33 f y E o and

λ ≤ 0.673,

. . . 3.3.7(2)

the nominal concentrated load or reaction strength

may be determined in accordance with Clause 3.3.6. In Items (a) and (b), the f ollowing applies: R*

= design concentrated load or reaction in the presence of bending moment

R b

= nominal capacity for concentrated load or reaction in the absence of bending moment determined in accordance with Clause 3.3.6

M * = design bending moment at, or immediately adjacent to, the point of application of the design concentrated load or reaction ( R*) M s

= nominal section moment capacity about the centroidal axes determined in accordance with Clause 3.3.1, excluding Clause 3.3.3

bf

= flat width of the beam flange which contacts the bearing plate

t w

= thickness of the web

λ

= slenderness ratio (see Clause 2.2.1.2)

3.4

CONCENTRICALLY LOADED COMPRESSION MEMBERS

3.4.1

General

This Clause applies to members in which the resultant of all loads acting on the member is an axial load passing through the centroid of the effective section calculated at the stress ( f n). The design compressive axial force ( φ c N c ) shall be calculated as follows: (a)

φ c

= 0.85

(b)

N c

= Ae f n

. . . 3.4.1(1)

where

φ c = capacity [strength reduction] factor for members in compression N c = nominal member capacity of the member in compression Ae = effective area calculated at buckling stress f n f n = the least of the flexural, torsional and flexural-torsional buckling stress determined in accordance with Clauses 3.4.2 to 3.4.5 COPYRIGHT

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Where local distortions in compression members under service loads shall be limited, the design compressive axial force ( φ d N ld) shall be determined as follows:

φ d

= 1.0

N l d = Af b

. . . 3.4.1(2)

where f b

= permissible compressive Clause 3.3.2.4

stresses

determined

in

accordance

with

Angle sections shall be designed for the design axial force ( N *) acting simultaneously with a moment equal to N *l /1000 applied about the minor principal axis causing compression in the tips of the angle legs. NOT E: The sle nder nes s rat io (le/r ) of all compression members should not be greater than 200, except that during construction only, le/r should not be greater than 300.

3.4.2


Sections not subject to torsional or flexural-torsional buckling

For doubly symmetric sections, closed cross-sections and any other sections that can be shown not to subject to torsional or flexural-torsional buckling, the flexural buckling stress ( f oc ) shall be determined as follows:

f oc

=

π 2 E t

≤ f y

(kl r )2

. . . 3.4.2(1)

where E t = tangent modulus in compression corresponding to the buckling stress given in Appendix B k = effective length factor l = unbraced length of the member r = radius of gyration of the full, unreduced cross-section Alternatively, the design compressive axial force can be calculated as follows:

φ c = 0.9 N c = Ae f n

. . . 3.4.2(2)

where f y

f n =

φ + φ

2

1

φ =

2

− λ

2

≤ f y

. . . 3.4.2(3)

(1 + η + λ 2 )

. . . 3.4.2(4)

β η = α ((λ − λ 1 ) − λ o )

λ =

 kl     r 

. . . 3.4.2(5)

f y . . . 3.4.2(6)

π 2 E o

Values for α , β , λ o and λ 1 shall be as given in Table 3.4.2, and values for E o shall be as given in Appendix B.

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TABLE 3.4.2 VALUES OF α α, β β , λ λ 0 AND λ λ 1 FOR TYPES 304, 304L, 316, 316L, 4 09, 1.4003, 430 AND S31803 Types Property 304, 316

340L, 316L

409

1.4003

430

S31803

α

1.59

1.59

0.77

0.94

1.04

1.16

β

0.28

0.28

0.19

0.15

0.14

0.13

λ o

0.55

0.55

0.51

0.56

0.59

0.65

λ 1

0.20

0.20

0.19

0.27

0.33

0.42

NOTES:


3.4.3

1

In frames where lateral stability is provided by diagonal bracing, shear walls, attachment to an adjacent structure having adequate lateral stability, or floor slabs or roof decks secured horizontally by walls or bracing systems parallel to the plane of the frame, and in trusses, the effective length factor ( k ) for compression members, which do not depend upon their own bending stiffness for lateral stability of the frame or truss, should be taken as equal to the unbraced length ( l ) , unless analysis shows that a smaller value may be used.

2

In a frame that depends upon its own bending stiffness for lateral stability, the effective length ( kl ) of the compression members should be determined by a rational method and should not be less than the actual unbraced length.

Doubly symmetric or point-symmetric sections subject to torsional buckling

For doubly or point-symmetric sections subject to torsional buckling, f n shall be taken as the smaller of f n calculated in accordance with Clause 3.4.2 and f n calculated as follows: f n = σ t =

. . . 3.4.3(1)

 1   E t  π 2 E o C w      2  Go J +    E  2  Ar    ( ) k l  o   t t   o 

where

σt is specified in Clause 3.3.3.

3.4.4

Singly symmetric sections subject to flexural-torsional buckling

. . . 3.4.3(2)

For sections subject to flexural-torsional buckling, f n shall be taken as the smaller of f n calculated in accordance with Clause 3.4.2 and f n calculated as follows: f n =

  σ ex + σ t − (σ ex + σ t ) 2 − 4 βσ ex σ t    2 β  1

. . . 3.4.4(1)

Alternatively, a conservative estimate of f n can be obtained using the following equation: f n =

σ t σ ex σ t

. . . 3.4.3(2)

+ σ ex

where 2

β =

 x  1 −  o    r o 

. . . 3.4.3(3)

σ t , σ ex , r o and xo shall be as specified in Clause 3.3.3. For singly symmetric sections, the x-axis shall be assumed to be the axis of symmetry. COPYRIGHT

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3.4.5

AS/NZS 4673:2001

Non-symmetric sections

For shapes whose cross-sections do not have any symmetry, either about an axis or about a point, f n shall be determined by a rational analysis. Alternatively, compression members composed of such shapes may be tested in accordance with Section 6. 3.5

COMBINED AXIAL COMPRESSIVE LOAD AND BENDING

The design axial compressive load ( N *), and the design bending moments ( M x* and M y* ) about the x- and y-axes of the effective section, respectively, shall satisfy the following: N *

(a)

φ c N c N *

(b)


φ c N s

+

+

C mx M x*

φ b M bx α nx M x*

+

φ b M bx

+

C my M y*

φ b M byα ny

M y*

φ b M by

≤ 1.0

≤ 1.0

. . . 3.5(1)

. . . 3.5(2)

If N */ φ c N c ≤ 0.15, the following may be used in lieu of Items (a) and (b): N *

φ c N c

+

M x*

φ b M bx

+

M y*

φ b M by

≤ 1.0

. . . 3.5(3)

where N c

= nominal member capacity of the member in compression determined in accordance with Clause 3.4

C mx, C my = coefficients for unequal end moment whose value shall be taken as follows: (i)

For compression members in frames subject to joint translation (side-sway): C m = 0.85

(ii)

For restrained compression members in frames braced against joint translation and not subject to transverse loading between their supports in the plane of bending: C m = 0.6 − 0.4 ( M 1/ M 2)

. . . 3.5(4)

M 1/ M 2 is the ratio of the smaller to the larger moment at the unbraced in the plane of bending. M 1/ M 2 is positive if the member is bent in reverse curvature and negative if it is bent in single curvature. (iii)

For compression members in frames braced against joint translation in the plane of loading and subject to transverse loading between their supports, the value of C m may be determined by rational analysis. However, in lieu of such analysis, the following values may be used: (A)

For members whose ends are restrained: C m = 0.85

(B)

For members whose ends are unrestrained: C m = 1.0

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M bx , M by = nominal member moment capacity about the x- and y-axes, respectively, determined in accordance with Clause 3.3.3

φ b

= capacity [strength reduction] factor for bending = 0.90 for beam sections with stiffened and partially stiffened compression flanges = 0.85 for beam sections with unstiffened compression flanges; or = 0.85 for laterally unbraced beam

φ c

= capacity [strength reduction] factor for members in compression = 0.85

N s

= nominal section capacity of the member in compression determined in accordance with Clause 3.4, with f n equal to f y

α nx, α ny = moment amplification factors = ) d e t n i r p n e h w d e e t n a r a u g t o n y c n e r r u c t n e m u c o D ( 7 1 0 2 v o N 4 1 n o D N A L S N E E U Q N R E H T U O S F O Y T I S R E V I N U y b d e s s e c c A

N e

 N *   1 −   N  e 

. . . 3.5(5)

= elastic buckling load 2 = λ 2 E o I b /l eb

3.6 3.6.1

. . . 3.5(6)

I b

= second moment of area of the full, unreduced cross-section about the bending axis

l eb

= effective length in the plane of bending

TUBULAR MEMBERS General

This Clause applies to rectangular, square and circular hollow sections. For circular hollow sections, the ratio of outside diameter to wall thickness (d o/t ) shall not be greater than 0.881 E o/ f y. 3.6.2

Bending

The design bending moment ( φ b M s ) shall be determined using —

φ b = 0.9. The nominal member moment capacity ( M s ) shall be determined as follo ws: (a)

Rectangular and square h ollow sections: (i)

For compact sections that satisfy b/t = λ 1 —

λ 1 =

1.11 . . . 3.6.2(1)

f ye / E o

where b is the flat width of the compression flange, and for which the compressed portion of the web to its thickness is no t greater than λ 1, M s shall be calculated as follows: M s = f yS p

. . . 3.6.2(2)

where S p is the plastic section modulus. (ii)

For non-compact sections (b/t > λ 1), the design bending moment ( φ b M s ) shall be determined in accordance with Clause 3.3.1. COPYRIGHT

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(b)

AS/NZS 4673:2001

Circular hollow sections: (i)

For compact sections satisfying d o /t ≤ 0.078 E o/ f y — M s = f yS p

(ii)

. . . 3.6.2(3)

For non-compact sections satisfying 0.078 E o/ f y

< d o/t < 0.31 E o/ f y —

M s = f y Z f (iii)

. . . 3.6.2(4)

For slender sections satisfying 0.31 E o/ f y

< d o/t < 0.881 E o/ f y —

M s = K c f y Z f

. . . 3.6.2(5)

where f y = specified yield stress, given in Appendix B Z f = elastic section modulus of the full, unreduced cross-section K c =


(1 − C ) E o / f y 0.178 C + (3.226 − λ c )(d o / t ) 3.226 − λ c

C = ratio of the proportionality (see Appendix B)

. . . 3.6.2(6) stress

to

the

yield

stress

= f p/ f y

λ c = limiting value of

E o f y

(d o t )

, based on specified ratio C

= 3.048C 3.6.3 Compression

This Clause applies to members in which the resultant of all design loads and design bending moments acting on the member is equival ent to a single force in the direction of the member axis passing through the centroid of the section. The design axial load ( φ c N c) shall be determined as follows: (a)

Rectangular and square h ollow sections φ c N c shall be determined in accordance with Clause 3.4.1.

(b)

Circular hollow sections φ c N c shall be determined as follows: (i)

For compact sections, where Ae equals A as given in Equation 3.6.3(3), φ c N c shall be determined in accordance with Clause 3.4.1.

(ii)

For slender sections, where Ae is less than A as given in Equation 3.6.3(3), φ c N c shall be determined as follows:

φ c = 0.8 N c = f n Ae

. . . 3.6.3(1)

where f n = flexural buckling Clause 3.4.2

stress

determined

in

accordance

with

Ae = effective area at buckling stress f n 1 − 1 − ( E t / E o )

2

[1 − ( Ao / A)] A

. . . 3.6.3(2)

Ao = reduced area of the cross-section = K c A ≤ A for (d o / t ) ≤ 0.881 E o / f y A = area of the full, unreduced cross-section COPYRIGHT

. . . 3.6.3(3)

AS/NZS 4673:2001

3.6.4

56

Combined compression and bending

Combined compression and bending shall satisfy the provisions of Clause 3 .5. 3.6.5

Shear

The design shear capacity of rectangular hollow sections shall satisfy the provisions of Clause 3.3.4. NOT E: Design shear requir ements for c irc ular hollow sec tio ns are not pro vided in thi s Sta ndar d.

3.6.6

Combined shear and bending

Combined shear and bending in rectangular hollow sections shall be determined as follows: (a)

For compact sections as specified in Clause 3.6.2(a), the design bending and shear capacities shall not be reduced b y the presence of combined actions.

(b)

For slender sections, the combined bending and shear capacity shall be determined in accordance with Clause 3.3.5.

NOT E: Design req uirements for shear and bending for cir cul ar hol low sec tio ns are not pro vid ed in this Standard. ) d e t n i r p n e h w d e e t n a r a u g t o n y c n e r r u c t n e m u c o D ( 7 1 0 2 v o N 4 1 n o D N A L S N E E U Q N R E H T U O S F O Y T I S R E V I N U y b d e s s e c c A

3.6.7

Welded connections

The design capacity of welded connections in rectangular and circular hollow sections shall be deter mined in accordance with Appendix J.

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S E C T I O N

4

S T R U C T U R A L

AS/NZS 4673:2001

A S S E M B L I E S

4.1 BUILT-UP SECTIONS 4.1.1

Sections composed of two channels

The maximum longitudinal spacing of welds ( smax. ) or other connectors joining two channels to form an I-section shall be determined as follows: (a)

For compression members— s max.

=

lr cy

. . . 4.1.1(1)

2 r 1

where


(b)

l

= unbraced length of the member in compression

r cy

= radius of gyration of one channel about its centroidal axis parallel to the web

r 1

= radius of gyration of the I-section about the axis perpendicular to the direction in which buckling occurs for the given conditions of end support and intermediate bracing.

For flexural members— s max .

=

l

. . . 4.1.1(2)

6

≤

2 s g N *

. . . 4.1.1(3)

mq

where l

= span of beam

sg

= vertical distance between two rows of connections nearest to the top and bottom flanges

N

= design tensile force of the connection (see Section 5)

q

= intensity of the design load on the beam

m

= distance from the shear centre of one channel to the mid-plane of its web (see Appendix H).

The intensity of the design load (q) shall be obtained by dividing the magnitude of the design concentrated loads or reactions by the length of bearing. For beams designed for a uniformly distributed load, q shall be equal to three times the intensity of the uniformly distributed design load. If the length of bearing of a concentrated load or reaction is less than the weld spacing ( s w), the design tensile force of the welds or connections closest to the load or reaction shall be determined as follows: *

N

=

mR b*

. . . 4.1.1(4)

2 s g

where R b* is the design concentrated load or reaction.

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The maximum longitudinal spacing of connections ( smax. ) depends upon the intensity of the load applied directly at the connection. Therefore, if uniform spacing of connections is used over the whole length of the beam, it shall be determined at the point of maximum local load intensity. In cases where this procedure may result in uneconomically close spacing, either of the following methods may be adopted: (i) The connection spacing may be varied along the beam in accordance with the variation of the load intensity. (ii) The reinforcing cover plates may be welded to the flanges at points where concentrated loads occur. The design shear force of the connections joining these plates to the flanges shall then be used for N * and s g shall be taken as the depth of the beam. 4.1.2

Spacing of connections in compression elements

The spacing ( s) in the line of stress of welds and bolts connecting a cover plate or sheet in compression, to a non-integral stiffener or another element shall not be greater than— (a) that which is required to transmit the shear between the connected parts on the basis of the design shear force per connection specified in this Clause; ) d e t n i r p n e h w d e e t n a r a u g t o n y c n e r r u c t n e m u c o D ( 7 1 0 2 v o N 4 1 n o D N A L S N E E U Q N R E H T U O S F O Y T I S R E V I N U y b d e s s e c c A

(b)

1.11t E t / f c , where t is the thickness of the cover plate or sheet, E t is the tangent

(c)

modulus in compression and f c is the stress at service load in the cover plate or sheet. three times the flat width (b 1) of the narrowest unstiffened compression element tributary to the connections, but not less than 1.03t E o / f y if b/t < 0.50 E o / f y , or 1.24t E o / f y

if b/t ≥ 0.50 E o / f y , unless closer spacing is required by Item (a) or

Item (b). In the case of intermittent fillet welds parallel to the direction of stress, the spacing shall be taken as the clear distance between welds plus 12 mm. In all other cases, the spacing shall be taken as the centre-to-centre distance between connecti ons. This Clause does not apply to cover sheets that act only as sheeting material, and shall not be considered as l oad-carryin g elements. 4.2 MIXED SYSTEMS

The design of members in mixed systems using cold-formed stainless steel components in conjunction with other materials shall conform to this Standard and to the relevant material Standard. 4.3 4.3.1

LATERAL RESTRAINTS General

Restraints shall be designed to restrain lateral bending or twisting of a loaded beam or column, and to avoid local buckling at t he points of attachment. 4.3.2

Symmetrical beams and columns

Restraints and restraint systems, including connections, shall be designed in accordance with the strength and stiffness requirements. 4.3.3

Channel and Z-section beams

4.3.3.1 General

The requirements for bracing to restrain twisting of channels and Z-sections used as beams and loaded in the plane of the web, apply onl y if— (a)

the top flange is connected to the deck or sheeting material in such a manner as effectively to restrain lateral deflection of the connected flange; or

(b) neither flange is connected. If both flanges are connected, further bracing is not required. COPYRIGHT

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4.3.3.2 Bracing when one flange is connected

Channels and Z-sections, which are used to support attached covering material and loaded in a plane parallel to the web, shall be designed taking into account the restraining effects of covering materials and fasteners. Provisions shall be made for the forces from each beam which accumulate in the covering material. These forces shall be transferred from the covering material to a member or assembly of sufficient strength and stiffness to resist these forces. The design of braces shall be in accordance with Clause 4.3.3.3. In addition, tests in accordance with Section 6 shall be performed to ensure that the type or spacing, or both, of the braces selected is such that the strength of the braced beam assembly tested in accordance with Section 6 is greater than or equal to its no minal flexural strength. 4.3.3.3 Neither flange connected to sheeting

Each intermediate brace, at the top and bottom flange, shall be designed to resist a horizontal design force ( N ib* ) determined as follows:


(a)

For uniformly distributed loads, N ib is equal to 1.5k ′ times the design load within a distance 0.5l b each side of the brace, where l b is the distance between the centre-line of braces.

(b)

For concentrated loads, N ib is equal to 1.0k ′ times each design concentrated load within a distance 0.3l b each side of the brace, plus 1.4k ′ [1 − (m/l b)] times each design concentrated load located farther than 0.3l b but not farther than 1.0l b from the brace, where m is the distance from the concentrated load to the brace.

*

*

For channels: k ′ =

m

. . . 4.3.3.3(1)

d

For Z-sections: k ′ =

I x y

. . . 4.3.3.3(2)

I x

where k ′ = coefficient used to determine N * where neither flange is connected to the ib sheeting or connected to the sheeting with concealed fasteners I xy = product of second moment of area of the full section about its centroidal axes parallel and perp endicular to the web I x = second moment of area of the cross-section about its centroidal axis perpendicular to the web Braces shall be designed to avoid local buckling at the points of attachment to the member. Where braces are provided, they shall be attached in such a manner to effectively restrain the section against lateral deflection of both flanges at the ends and at any intermediate brace points. When all loads and reactions on a beam are transmitted through members that frame into the section, in such a manner as to effectively restrain the section against torsional rotation and lateral displacement, no additional braces will be required except those required for strength in accordance with Clause 3.3.3. 4.3.3.4 Laterally unbraced box beams

For closed box-type sections used as beams subject to bending about the major principal axis, the ratio of the laterally unsupported length to the distance between the webs of the section shall not be greater than 0.086 E o / f y . COPYRIGHT

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S E C T I O N

5

C O N N E C T I O N S

5.1 GENERAL

Connections shall be designed to transmit the design action effects derived for the structure at that connection, or joint, from analysis in accordance with accepted principles of structural mechanics. Connections and joints shall be proportioned so as to be consistent with the assumptions made in the analysis of the structure and comply with this Section. Consideration shall be given to load paths and eccentricity. There are a number of suitable fastening systems to join stainless steel structural members or component parts such as welding, bolting, screwing, riveting, clinching, pinning or structural adhesive. These systems may be used singly or in combination This Section applies to welded and bolted connections. Design capacities of specific connections may be obtained by prototype testing in accordance with Section 6. ) d e t n i r p n e h w d e e t n a r a u g t o n y c n e r r u c t n e m u c o D ( 7 1 0 2 v o N 4 1 n o D N A L S N E E U Q N R E H T U O S F O Y T I S R E V I N U y b d e s s e c c A

5.2 WELDED CONNECTIONS 5.2.1

General

This Clause applies to welded connections for cold-formed stainless steel structural members in which the weld is produced by the electric arc welding or resistance welding process. The design capacity of arc welds determined in accordance with this Clause applies only to welds complying with AS/NZS 1554.6. The design capacity of resistance welds determined in accordance with this Section applies only to welds complying with AWS C1.1. For members made from material other than in the annealed condition, allowance shall be made for design strength reduction near welds. The effect of any welding on the mechanical properties of a member shall be determined on the basis of tests on specimens of the full section containing the weld within the gauge length. Any necessary allowance for such effect shall be made in the structural use of the member. In the absence of specified testing, the annealed properties shall be used. Surface finishing of the weld is normally required to restore full corrosion resistance and shall be in accordance with AS/NZS 1554.6. NOT ES: 1

With the exception of 1.4003 (EN 10088), most grades of ferritic and martensitic stainless steels are not suitable for use in welded connections. Information regarding applicability for such uses should be sought from the steel manufacturer or supplier.

2

Austenitic stainless steels used at temperatures above of welds.

3

For other stainless steels, see AS 1210 for guidance on toughness testing of structural welds.

5.2.2

− 30°C do not require toughness testing

Butt welds

5.2.2.1 General

This Clause applies to butt welds between stainless steel structural elements loaded in tension, compression or shear, welded from one or both sides, provided that an effective throat of matching weld greater than or equal to the thickness of the thinnest material is provided throughout t he weld. COPYRIGHT

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5.2.2.2 Tension or compression

A butt weld subjected to a tensile or co mpressive force shall satisfy—

N w*

≤ φ N w

. . . 5.2.2.2

where design tensile or compressive force normal to the area of the butt weld

φ

= =

0.6

N w

= =

N w*

l w t ) d e t n i r p n e h w d e e t n a r a u g t o n y c n e r r u c t n e m u c o D ( 7 1 0 2 v o N 4 1 n o D N A L S N E E U Q N R E H T U O S F O Y T I S R E V I N U y b d e s s e c c A

f ua

capacity [strength reduction] factor of a butt weld for tensile or compressive force

nominal tensile or compressive capacity of a butt weld, welded from one or both sides

=

l w t f ua

= = =

length of weld thickness of the thinnest welded part tensile or compressive strength of the annealed base metal

5.2.2.3 Shear

A butt weld subjected to a shear force shall satisfy— V w*

≤ φ V w

. . . 5.2.2.3(1)

where

= = = = = =

V w* φ

V w

l w

design shear force capacity [strength reduction] factor of a butt weld for shear 0.6 nominal shear capacity of a butt weld, welded from one or both sides l w t (0.6 f ua )

. . . 5.2.2.3(2)

length of the full size of the weld

5.2.3 Fillet welds 5.2.3.1 General

This Clause applies to fillet welds in lap or T joints between stainless steel structural elements, loaded either longitudinal (parallel) or transverse to the line of the weld. 5.2.3.2 Longitudinal loading

A fillet weld subjected to a longitudi nal shear force shall satisfy— V w*

≤ φ V w

. . . 5.2.3.2(1)

where

V w* φ

= = =

design longitudinal shear force on a fillet weld capacity [strength reduction] factor of a fillet weld 0.55

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=

V w

nominal longitudinal shear capacity of a fillet weld, determined as follows: For l w/t < 30

(a)

V w

 0.009l w   = 0.7 −     t l w f ua  t   

. . . 5.2.3.2(2)

For l w/t ≥ 30

(b)

V w

= 0.43tl w f ua

. . . 5.2.3.2(3)

In addition, the value of V w shall not be greater than— V w

= 0.75t w l w f xx

. . . 5.2.3.2(4)

where t w

= effective throat = 0 .70 7w 1 or 0.707w2, whichever is smaller w1, w2 = leg sizes of the weld


f xx

= tensile strength obtained from all-weld-metal tensile test.

NOT E: Tab le B2 of Appe ndi x B giv es value s o f f xx for manual metal arc welding (MMAW).

5.2.3.3 Transverse loading

A fillet weld subjected to a transverse shear force shall satisfy— V w*

≤ φ V w

. . . 5.2.3.3(1)

where V w*

= design transverse shear force on a fillet weld

φ

= 0.55

V w

= nominal transverse shear capacity of a fillet weld = tl w f ua

. . . 5.2.3.3(2)

In addition, the value of φ V w shall not be greater than—

φ V w 5.2.4

= 0.65t w l w f xx

. . . 5.2.3.3(3)

Resistance spot welds

5.2.4.1 General

This Clause applies to Types 301, 304 and 316 stainless steel sheets joined by electric resistance single impulse spot welding or pulsation spot welding. 5.2.4.2 Shear

A resistance spot weld subjected to a shear force shall satisfy— V w*

≤ φ V w

. . . 5.2.4.2

where V w*

= design shear force on a resistance spot weld

φ

= capacity [strength reduction] factor of a resistance spot weld for shear = 0.60

V w

= nominal shear capacity of a resistance spot weld (see Tables 5.2.4(1) and 5.2.4(2)), as appropriate. COPYRIGHT

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5.2.4.3 Tension

A resistance spot weld subjected to a tensile force shall satisfy—

N w*

≤ φ N w

. . . 5.2.4.3

where

N w* φ

N w

5.2.5

= = = =

design tensile force on a resistance spot weld capacity [strength reduction] factor of a resistance spot weld for tensile force 0.60 nominal tensile capacity of a resistance spot weld, taken conservatively as 25% of the nominal shear capacity given in Table 5.2.4(A) for single impulse spot welding, or Table 5.2.4(B) for pulsation spot welding, for the appropriate thickness of the thinnest outside sheet.

Tubular connections

The design capacity of welded connections in rectangular, square and circular hollow sections shall be determined in accordance with Appendix J. ) d e t n i r p n e h w d e e t n a r a u g t o n y c n e r r u c t n e m u c o D ( 7 1 0 2 v o N 4 1 n o D N A L S N E E U Q N R E H T U O S F O Y T I S R E V I N U y b d e s s e c c A

TABLE 5.2.4(A) NOMINAL SHEAR CAPACITY ( V w) OF SINGLE IMPULSE SPOT WELDS Thickness of thinnest outside

V W per spot weld

sheet

kN

mm

Annealed

1/4 Hard

1/2 Hard

0.152

0.27

0.31

0.40

0.203

0.44

0.58

0.67

0.254

0.67

0.76

0.93

0.305

0.85

0.93

1.11

0.356

1.07

1.11

1.42

0.406

1.25

1.33

1.69

0.457

1.42

1.60

2.09

0.533

1.64

2.09

2.22

0.635

2.22

2.67

3.02

0.787

3.02

3.56

4.13

0.864

3.56

4.09

4.89

1.016

4.45

5.65

6.23

1.118

5.34

6.45

7.56

1.222

6.45

7.56

8.89

1.422

7.56

8.90

10.90

1.575

8.67

10.68

12.90

1.778

10.68

12.45

15.79

1.981

12.01

15.12

17.79

2.388

15.79

18.68

23.57

2.769

18.68

22.24

28.47

3.175

22.24

26.69

33.80

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TABLE 5.2.4(B) NOMINAL SHEAR CAPACITY ( V w) OF PULSATION SPOT WELDS Thickness of thinnest outside

V W per spot weld

sheet

kN

mm

1/ 4 Ha rd

1/ 2 H ar d

3. 962

3 3. 8

44. 48

4. 75

4 3. 3 7

54. 71

5. 156

4 7. 1 5

57. 82

6. 35

5 7. 8 2

75. 62

NOT E: The rang e of thickne thi ckne sses given give n for puls atio n spot welding weld ing is not int ended to indicate that single-impulse spot welding cannot be used for welding these thicknesses.

5.3 BOLTED CONNECTIONS 5.3.1 ) d e t n i r p n e h w d e e t n a r a u g t o n y c n e r r u c t n e m u c o D ( 7 1 0 2 v o N 4 1 n o D N A L S N E E U Q N R E H T U O S F O Y T I S R E V I N U y b d e s s e c c A

General

This Clause applies to bolted connections in cold-formed stainless steel structural members propor pro portio tioned ned in accordan acco rdance ce with w ith this thi s Stand S tandard ard.. Bolts, washers and nuts shall be installed and tightened so as to achieve the design performa perf ormance nce intende int ended d for f or the connecti conn ecti on. 5.3.2

Holes

Standard holes for bolts shall be used for joining members unless otherwise specified. Standard holes shall not be greater than the values given in Table 5.3.2. Oversized or slotted holes not greater than the sizes given i n Table 5.3.2 may be used, provid pro vided ed all bolts bol ts are loaded loa ded in shear and the length len gth of such a slotte slo tted d hole hol e is normal nor mal to the direction of the applied shear force. Larger holes may be used, provided backup plate washers of appropriate size and thickness are used. Backup plate washers shall have a standard hole to suit the bolt t hat is to be used. Where a holing and washer arrangement for a bolted connection does not comply with the requirements of this Clause, its performance may be established by testing in accordance with Section 6. NOT E: Gui dance dan ce on ste el backup bac kup pla te washer was herss spe cified cif ied in AS 4100 and NZS 3404 .2 is applicable to stainless steel backup plate washers.

TABLE 5.3.2 MAXIMUM SIZE OF BOLT HOLES Nominal bolt

Standard hole

Oversized

diameter

diameter

hole diameter

(d f f )

(d h)

( d h)

mm

mm

< 12 ≥ 12

Short-slotted hole

Long-slotted hole

dimension

dimension

mm

mm

mm

d f f + 1. 0

d f f + 2. 2 . 0

( d f f + 1.0) by (d (d f f + 6. 6. 0 )

( d f f + 1.0) by 2.5d 2.5 d f f

d f f + 2. 0

d f f + 3. 3 . 0

( d f f + 2.0) by (d (d f f + 6. 6. 0 )

( d f f + 2.0) by 2.5d 2.5 d f f

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5.3.3

AS/NZS 4673:2001

Spacing and edge distance

In addition to the requirements of Clause 5.3.4, the minimum distance between centres of bolt bol t holes hol es shall shal l provid pro videe suffici suf ficient ent clearan cle arance ce for bolt bol t heads, head s, nuts, nut s, washers wash ers and the wrench, wren ch, but shall shal l not be less les s than tha n 3d f f . Also, the distance from the centre of any standard hole to the end or other boundary of t he connecting member shall not be less than 1.5d 1.5d f f . For oversized and slotted holes, the distance between the edges of two adjacent holes and the distance from the edge of the hole to the end or other boundary of the connecting member in the line of force shall not be less than [e − (d h 2)] , where e is the distance measured in the line of the applied force from the centre of a standard hole to the nearest edge of an adjacent hole or to the end of t he connected part. The clear distance between the edges of two adjacent holes shall not be less than 2 d f f and the distance between the edge of the hole and the end of the member shall not be less than d f f . 5.3.4

Tear out capacity of the connected part

For lapped joints between structural members in which bolts are loaded in shear, both the spacing between bolts and the edge distance from a bolt in the line of the applied force shall be such s uch that tha t in i n a connecte conn ected d part— p art— ) d e t n i r p n e h w d e e t n a r a u g t o n y c n e r r u c t n e m u c o D ( 7 1 0 2 v o N 4 1 n o D N A L S N E E U Q N R E H T U O S F O Y T I S R E V I N U y b d e s s e c c A

V f *

≤ φ V f

. . . 5.3.4(1)

where

V f *

=

design shear force per bolt

φ

= = = = =

0.70

V f f

t f ut ut 5.3.5

nominal shear capacity per bolt te f ut

. . . 5.3.4(2)

thickness of the thinnest connected part tensile strength of the connected part transverse to the direction of the applied force.

Net section tensile capacity capacity of the connected part

For lap joints between structural members in which bolts are loaded in shear, both the spacing between bolts and the edge distance from a bolt transverse to the line of the applied force shall be such that in a connected part—

N f *

≤ φ N f

. . . 5.3.5(1)

where

N f *

=

design tensile force in the connected part

φ

= = =

0.70

N f f

A n

=

nominal tensile capacity of the connected part An f t

. . . 5.3.5(2)

net area of the connected part at the line of bolts transverse to the line of the applied force

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=

f t

tensile strength for connections with washers under both bolt head and nut, determined as follows: (a)

For single shear connections: f t

(b) (b )

= (1.0 − r f + (2.5r f d f / sf ) ) f u ≤ f u

. . . 5.3.5(3)

For double shear connection: f t

= (1.0 − 0.9r f + (3r f d f / s f ) ) f u ≤ f u

. . . 5.3.5(4)

r f f

=

ratio of the force transmitted by the bolt or bolts at the section considered, divided by the tensile force in th e member at that section. If r f f is less than 0.2, it may be taken as zero

s f

=

spacing of bolts transverse to the line of the force, or in the case of a single bolt, bol t, the width wid th of the connect con nected ed part

f u

=

tensile strength of the connected part in the direction of the applied force. *

In addition, N f shall not be greater than 0.85 A n f y, where f y is the specified yield stress in tension of the connected part. ) d e t n i r p n e h w d e e t n a r a u g t o n y c n e r r u c t n e m u c o D ( 7 1 0 2 v o N 4 1 n o D N A L S N E E U Q N R E H T U O S F O Y T I S R E V I N U y b d e s s e c c A

5.3.6

Bearing capacity of the connected part

For lapped joints between structural members in which bolts are loaded in shear, the design bearing bear ing force for ce V b at a bolt shall be such that in a connected part— V b*

≤ φ V b

φ

= =

. . . 5.3.6(1)

where

V b

0.65 nominal bearing capacity per bolt of the connected part, where bolts have washers under both bolt head and nut, determined as follows: (a) (a)

For For sin singl glee she shear ar conn connec ecti tion ons: s: V b

(b) (b)

5.3.7

=

. . . 5.3.6(2)

For For dou doubl blee she shear ar conn connec ecti tion on:: V b

f u

= 2.0d f t f u = 2.75d f t f u

. . . 5.3.6(3)

compressive strength of the connected part in the direction of the applied force.

Stainless steel bolts bolts to ASTM Standards

5.3.7.1 General

The design capacity of bolts determined in accordance with Clause 5.3.7 applies to bolts complying with ASTM A 193/A 193 M, ASTM A 276 and ASTM F 593. The design capacity described in this Clause is based on the provisions of ANSI/ASCE-890. The nominal shear strength ( f nv nv ) and the nominal tensile strength ( f nt nt ) for stainless steel bolts bol ts complyi comp lying ng with ASTM Standar Sta ndards ds s hall be obtaine obt ained d from f rom Table Tabl e 5.3.7, 5.3. 7, as a s appr a ppropri opriate ate.. 5.3.7.2 Bolts Bolt s in i n shear s hear

( ) *

The design shear force V fv for bolts loaded in shear shall satisfy— V fv*

≤ φ V fv

. . . 5.3.7.2(1)

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where

φ V fv

= = =

0.65 nominal shear capacity of the stainless steel bolt . . . 5.3.7.2(2)

Af f nv

Af = gross cross-sectional area of the stainless steel bolt f nv = nominal shear strength of the stainless steel bolt given in Table 5.3.7. 5.3.7.3 Bolt s in tension

( ) *

The design tensile force N ft shall satisfy— N ft*

≤ φ N ft

. . . 5.3.7.3(1)

where

φ N ft ) d e t n i r p n e h w d e e t n a r a u g t o n y c n e r r u c t n e m u c o D ( 7 1 0 2 v o N 4 1 n o D N A L S N E E U Q N R E H T U O S F O Y T I S R E V I N U y b d e s s e c c A

= =

75 Af f nt

f nt

. . . 5.3.7.3(2)

= nominal tensile strength of the stainless steel bolt given in Table 5.3.7

The pull-over (pull-through) capacity of the connected part at the bolt head, nut or washer shall be considered where bolt tension is concerned. The increase in pull-out force resulting from bending moments or prying forces transmitted into the bolt from various adjacent structural components shall be taken into account. 5.3.7.4 Bolts in combined shear and tension

For a bolt subjected simultaneously to a design shear force (V fv* ) and a design tensile force

( N ) , the design tensile force ( N ) shall satisfy— * ft

* ft

N ft*

≤ φ N ft′

. . . 5.3.7.4(1)

where

φ

=

0.75

N ft*

=

Af f nt′

. . . 5.3.7.4(2)

f nt′ shall be determined as follows:

(a)

Threads in the shear plane— f nt′

(b)

= 1.25 f nt − 2.4 f v ≤ f nt

. . . 5.3.7.4(3)

No t hreads in the shear plane— f nt′

= 1.25 f nt − 1.9 f v ≤ f nt

. . . 5.3.7.4(4)

where f nt′ = nominal tensile strength for bolts subject to combined shear and tension

f nt

= nominal tensile strength given in Table 5.3.7

f v

=

( ) *

shear stress resulting from the design shear force V fv

= f nv

=

V fv* Af

≤ f nv

. . . 5.3.7.4(5)

nominal shear strength given in Table 5.3.7 COPYRIGHT

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TABLE 5.3.7 NOMINAL SHEAR AND TENSILE STRENGTHS FOR STAINLESS STEEL BOLTS COMPLYING WITH ASTM STANDARDS Nominal shear strength

Nominal tensile

Diameter

( f nv )

strength

( d f )

(see Note 1)

( f nt )

MPa

(see Note 1)

Type of stainless steel

mm


No threads in

Threads in

shear plane

shear plane

MPa

201 (see Note 2)

All

311

232

386

304, 316 (see Note 3)

All

311

232

386

304, 316 (see Notes 5)

≤ 12.7

372

279

465

304, 316 (see Note 7)

≤ 19.1

517

388

646

304, 316 (see Note 4)

6.4

≤ d f ≤ 38.1

290

217

362

304, 316 (see Note 6)

6.4

≤ d f ≤ 15.9

393

295

491

304, 316 (see Note 6)

19.1

331

248

414

248

186

310

290

217

362

430 (see Note 2) 430 (see Note 4)

≤ d f ≤ 38.1 All

6.4

≤ d f ≤ 38.1

NOTE S: 1

Reduction of the nominal strength given in this Table is required for d f < 12.7 mm. For d f < 12.7 mm, the value shall be reduced to 0.9 f nv for nominal shear strength and to 0.9 f nt for nominal tensile strength.

2

Condition A in ASTM A 276, hot-finished or cold-finished.

3

Condition A in ASTM A 276, hot-finished and Class 1(solution-treated) in ASTM A 193/A 193M, hot-finished.

4

Condition A in ASTM F 593, machined from annealed or solution-annealed stock or hot-formed and solution-annealed. The minimum tensile strength is based on tests on the machined specimen.

5

Condition A in ASTM A 276, cold-finished.

6

Condition CW in ASTM F 593, headed and rolled from annealed stock thus acquiring a degree of cold work. Sizes 19.05 mm diameter and larger may be hot-worked. The minimum tensile strength is based on tests on the machined specimen.

7

Condition B (cold-worked) in ASTM A 276 cold-finished and Class 2 (solution-treated and strainhardened) in ASTM A 193/A 193M.

5.3.8

Stainless steel bolts to ISO 3506

5.3.8.1 General

The design capacity of bolts determined in accordance with Clause 5.3.8 applies only to bolts and nuts complyi ng with ISO 3506, with washers of austenitic stainless steel complying with ISO 7089 or ISO 7090, as appropriate.

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The design capacity described in this Clause is based on the provisions of ENV 1993-1-1 and ENV 1993-1-4. For items resisting shear or tension through the threaded portion with cut threads, such as anchor bolts or tie rods fabricated from round stainless steel bars where the threads are cut by the steelwork fabricator and not by a speciali st bolt manufacturer , the relevant values given in Table 5.3.8 shall be reduced by multiplying t hem by a factor of 0.85. The nominal yield stress ( f ny ) and the nominal tensile strength ( f nt ) for stainless steel bolts complying with ISO 3506 shall be obtained from Table 5.3.8, as appropriate. The specified properties shall be verified by a recognized quality control system, with samples from each batch of fasteners.

TABLE 5.3.8 BOLTS COMPLYING WITH ISO 3506 Property class to ) d e t n i r p n e h w d e e t n a r a u g t o n y c n e r r u c t n e m u c o D ( 7 1 0 2 v o N 4 1 n o D N A L S N E E U Q N R E H T U O S F O Y T I S R E V I N U y b d e s s e c c A

Material groups

ISO 3506

Range of sizes

(see Note 1)

Austenitic and austenitic ferritic

50 70 80

≤ M39 ≤ M20 (see Note 2)

≤ M20 (see Note 2)

Nominal yield

Nominal tensile

stress ( f ny )

strength ( f nt )

MPa

MPa

210

500

450

700

600

800

NOTES: 1

In addition to the various steel types specified in ISO 3506 under property classes 50, 70 and 80, other steel types to EN 10088-3 may also be used.

2

For bolts of property classes 70 and 80 with lengths greater than 8 diameters or with sizes larger than M20, the values of the mechanical properties shall be obtained from the bolt manufacturer.

5.3.8.2 Bolts in shear

The design shear force ( V fv* ) shall satisfy— V fv*

≤

φ V fv

Where

φ V fv

= =

A b f nt

=

A bs f nt if the shear plane passes through the threaded portion of t he bolt

0.44

A b

if the shear plane passes through the unthreaded portion of t he bolt; or

= gross cross-sectional area of the bolt

A bs = tensile stress area of the bolt f nt


The shear strength of a bolt in a lapped joint shall be the lesser of the shear capacity of the bolt ( φ V fv) or the bearing capacity per bolt ( φ V b ), specified in Clause 5.3.6.

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5.3.8.3 Bolts in tension

The design tensile force ( N ft* ), inclusive of any force due to pryi ng action, shall satisfy— N ft*

≤ φ N ft

where

φ

=

0.67

N ft

=

A bs f nt nt


The tensile capacity of a bolt in a joint shall be the lesser of the tensile capacity of the bolt (φ N ft ) or the pull through (punching shear) resistance of the bolt head and nut ( N pt* ) calculated as follows: N pt*

= 0.44φ d m t p f u

where ) d e t n i r p n e h w d e e t n a r a u g t o n y c n e r r u c t n e m u c o D ( 7 1 0 2 v o N 4 1 n o D N A L S N E E U Q N R E H T U O S F O Y T I S R E V I N U y b d e s s e c c A

d m

=

mean of the across points and across flats dimensions of the bolt head or the nut, whichever is smaller

t p

=

thickness of the plate under the bolt head or the nut

5.3.8.4 Bolts in combined shear and tension

A bolt subjected simultaneously to a design shear force ( V fv* ) and a design tensile force ( N ft* ) shall satisfy— V fv* 0.44V fv

+

N ft* 0.94 N ft

≤ 1.0

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S E C T I O N

6

AS/NZS 4673:2001

T E S T I N G

6.1 TESTING FOR DETERMINING MATERIAL PROPERTIES 6.1.1

Design based on measured values of yield stress

Where the design is based on measured values of yield stress as determined from mill certificates or in accordance with Clauses 6.1.2, 6.1.3, 6.1.4 and 6.1.5.2, the capacity [strength reduction] factors (φ ) shall be reduced by 6%. Alternatively, the reduction in capacity [strength reduction] factor may be determined in accordance with Appendix K when statistical values of the mean and coefficient of variation of the ratio of measured to nominal yield stress is available, as it may apply to production runs of specific product s. 6.1.2


Testing of unformed steel

Where the stainless steels specified in Clause 1.5.2.2 are used or the yield stress of stainless steel is required for the purpose of Clause 6.1.4, unformed stainless steel tensile properties shall be determined by tests in accordance with AS 1 391. Test specimens shall be taken from positions located one quarter of the coil width from either edge near the outer end of the coil or other location to determine the lowest strength of the material in the coil. At the option of the manufacturer, the test specimens may be cut longitudinally or transversely and may be tested in tension or compression, provided the manufacturer demonstr ates that such tests reli ably indicate the yield stress of the section when subjected to the kind of stress under which the member is to be used. 6.1.3

Compression testing

Compressive mechanical properties may be obtained from coupon or stub column tests. Compressive coupon tests shall be in accordance with ASTM E9. For coupon tests of unformed steel, test specimens shall be taken as specified in Clause 6.1.2. Stub column tests shall be made on flat-end specimens whose length shall not be less than three times the largest dimension of the section but no more than 20 times the least radius of gyration. If tests of ultimate compressive strength are used to determine yield stress for quality control purposes, the length of the section shall be not less than 15 times the least radius of gyration. In making the compression tests, the specimen in the testing machine shall be centred so that the load is applied concentrically with respect to the centroidal axis of the section. NOT E: For fur ther inf ormati on reg ard ing comp ression testing u sin g coup ons or stub columns , reference may b e made to ASTM E9, and to Technical Memor anda Nos 2 and 3 o f the Column Research Council, ‘Notes on Compression Testing of Materials’, and ‘Stub-Column Test Procedure’, reprinted in the Column Research Council Guide to Stability Design Criteria for Metal Structures, Fifth Edition, 1998. Where tangent or secant moduli are to be derived from compression tests, reference is made to ASTM E111.

6.1.4

Testing of full sections

This Clause applies only to the determination of the mechanical properties of a fully formed section for the purposes specified in Clause 1.5.2.4. It shall not be interpreted as forbidding the use of test procedures instead of the usual design calculations. The procedure shall be as follo ws: (a)

Determine the tensile yield stress ( f yt ) in accordance with AS 1391 or the compressive yield stress ( f yc) by coupon testing in accordance with ASTM E9.

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(b)

Determine the compressive yield stress ( f yc ) by means of compression tests as specified in Clause 6.1.3.

(c)

Where the principal effect of the loading to which the member will be subjected in service is to produce bending stresses, determine the yield stress for the flanges. In determining the yield stress, carry out tests on specimens cut from the section. Each such specimen shall consist of one complete flange plus a portion of the web of such flat width ratio so that the section is fully effective.

(d)

For acceptance and control purposes, make two full section tests from formed material lots. Material lots shall be considered as parcels, as defined in the relevant Standard’s material specification in the Clauses on selection and preparation of test samples for mechanical testing.

(e)

Use either tension or compression tests for routine acceptance and control purposes, pro vided it is demonstr ated that such tests reli ably indicate the yield stress of the section when subjected to the kind of stress under which t he member is to be used.

6.1.5

Testing of flat coupons of formed members

6.1.5.1 Assessment of strength increase ) d e t n i r p n e h w d e e t n a r a u g t o n y c n e r r u c t n e m u c o D ( 7 1 0 2 v o N 4 1 n o D N A L S N E E U Q N R E H T U O S F O Y T I S R E V I N U y b d e s s e c c A

Tests for determining material properties of flat coupons of formed members and material properties of unformed steel for the purpose of assessing strength increase resulting from cold-forming as specified in Clause 1.5.2.4 shall be made as follows: (a)

The yield stress of flats ( f yf ) shall be established by means of a weighed average of the yield stresses of standard tensile coupons taken longitudinally from the major flat portions of a cold-formed member. The weighted average shall be the sum of the products of the average yield stress for each major flat portion times its cross-sectional area, divided by the total area of the major flats in the crosssection.

(b)

Where the actual yield stress of the unformed steel exceeds the specified minimum yield stress, the yield stress of the flats ( f yf ) shall be adjusted by multiplying the test values by the ratio of the specified minimum yield stress to the actual yield stress of the unformed steel.

6.1.5.2 Design properties

Tests for determining material properties of flat coupons of formed members for the purpose of establishing design properties of the formed members as specified in Clause 1.5.2.2 shall be made as follows: (a)

The test specimens shall be taken longitudinally from a major flat portion of the section midway between corners (excluding the corners) or midway between a corner and a free edge (excluding the corner).

(b)

The test specimen shall be taken from the flat portion with the least strength increase from cold-forming.

(c)

The minimum yield stress ( f y) and the minimum tensile strength ( f u) used in design shall be determined in accordance with AS 1391.

6.2 6.2.1

TESTING FOR ASSESSMENT OR VERIFICATION General

The methods of test specified in this Clause apply to prototype units of complete structures, parts of structures, individual members or connections for design verification as an alternative to calculation. The methods do not apply to the testing of structural models nor to the establishment of general design criteria. COPYRIGHT

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6.2.2 Static tests for strength or serviceability 6.2.2.1 Test specimens

The prototype test specimens shall be identical nominally to the class of units for which structural verification is required. The materials and fabrication of the prototype specimens shall comply with the relevant specifications used in production. Any additional requirements of a manufacturing specification shall be complied with. The method of assembly used shall simulate that which is used in production. 6.2.2.2 Test loads

The target test loads ( Rt) for the number of units to be tested shall be equal to the design action effects [design actions] (S *) for the relevant strength or serviceability requirements, multiplied by the appropriate factor (k t) to allow for variability of structural units, given in Table 6.2.2, i.e. Rt is equal to k t S *. The design action effects [design actions] shall be determined in accordance with AS 1170.1, AS 1170.2, AS 1170.3, AS 1170.4 or NZS 4203, as appropriate.


TABLE 6.2.2 FACTORS ( k t) TO ALLO W FOR VARIABILITY OF STRUCTURAL UNITS Coefficient of variation of structural characteristics ( k sc )

No. of units to be tested

5%

10%

15%

20%

25%

30%

1

1.20

1.46

1.79

2.21

2.75

3.45

2

1.17

1.38

1.64

1.96

2.36

2.86

3

1.15

1.33

1.56

1.83

2.16

2.56

4

1.15

1.30

1.50

1.74

2.03

2.37

5

1.13

1.28

1.46

1.67

1.93

2.23

10

1.10

1.21

1.34

1.49

1.66

1.85

100

1.00

1.00

1.00

1.00

1.00

1.00

6.2.2.3 Coefficient of variation of structural characteristics

The coefficient of variation of structural characteristics (k sc ) refers to the variability of the total population of the production units. This includes the total population variation due to fabrication (k f ) and material (k m). It can be approximated as follows: k sc

=

k f 2

+ k m2

. . . 6.2.2.3

6.2.2.4 Test requirements

Loading devices shall be calibrated and care shall be taken to ensure that no unintentional restraints on the specimen are applied by the loading systems. The distribution and duration of the forces applied in the test shall represent those forces to which the structure is deemed to be subjected. For short-term static test, the test load shall be applied at a uniform rate such that t he test duration shall be not less than 5 min. Deformations shall, as a minimum, be recorded at the following times: (a)

Prior to the application of the test load.

(b)

After the test load has been applied.

(c)

After the removal of the test load. COPYRIGHT

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6.2.2.5 Criteria for acceptance

Criteria for acceptance shall be as f ollows: (a)

Acceptance for static strength.

(b)

All test units shall be capable of resisting the target test load.

(c)

Acceptance for serviceability.

(d)

All test units shall be capable of sustaining the target test load while remaining within the limiting serviceability value appropriate for the required performance level and the elastic recovery (after the removal of the test load) is 95% complete.

6.2.2.6 Test report

The report of the test of each unit shall contain, in addition to the test results, a clear statement of the conditions of testing, including the method of loading and of measuring deflection, together with any relevant data. The report shall also contain a statement as to whether the units tested satisfy the acceptance criteria. 6.2.2.7 Design capa city of specific products and assemblies ) d e t n i r p n e h w d e e t n a r a u g t o n y c n e r r u c t n e m u c o D ( 7 1 0 2 v o N 4 1 n o D N A L S N E E U Q N R E H T U O S F O Y T I S R E V I N U y b d e s s e c c A

The design capacity ( Rd) of a specific product or a specific assembly may be established by prototype testing of that specific product or assembly. The desi gn capacity ( Rd ) shall satisfy—

Rd

 R  ≤  min.    k t 

. . . 6.2.2.7

where Rmin. is the minimum value of the test results and k t is as given in Table 6. 2.2.

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APPENDIX A

LIST OF REFERENCED DOCUMENTS (Normative) The following documents are referred to in this Standard:


AS 1170 1170.1 1170.2 1170.3 1170.4

Minimum design loads on structures Part 1: Dead and live loads and load combinations Part 2: Wind loads Part 3: Snow loads Part 4: Earthquake loads

1210

Pressure vessels

1391

Methods for tensile testing of metals

1449

Wrought alloy-steels—Stainless and heat-resisting steel plate, sheet and strip

4100 4100 Supp 1

Steel structures Steel structures — Commentary (Supplement to AS 4100 — 1998)

AS/NZS 1554 1554.1 1554.5 1554.6

Structural steel welding Part 1: Welding of steel structures Part 5: Welding of steel structures subject to high levels of fatigue loading Part 6: Welding stainless steels for structural purposes

NZS 3404 3404.2

Steel structures Standard Part 2: Commentary to the steel structures Standard

4203 ASTM A167

Code of practice for general structural design and design loadings for buildings (Volume 1 Code of pract ice; Volume 2 Commentary) Standard Specification for Stainless and Heat-resisting Chromium Nickel Steel Pl ate, Sheet and Strip

A176

Standard Specification for Stainless and Heat-Resisting ChromiumSteel Plate, Sheet and Strip

A193

Standard Specification for Alloy-Steel and Stainless Steel Bolting Materials for High-Temperature Service

A240

Standard Specification for Heat-Resisting Chromium and Chromium Nickel Stai nless Steel Plate, Sheet and Strip for Pressure Vessels

A276

Standard Specification for Stainless Steel Bars and Shapes

A480

Standard Specification for General Requirements for Flat-Rolled Stainless and Heat-Resisting Steel Plate, Sheet and Strip

A666

Standard Specification for Annealed or Cold-Worked Austenitic Stainless Steel Sheet, Strip, Plate and Flat Bars

E9

Standard Test Methods of Compression Testing of Metallic Materials at Room Temperature

E111

Standard Specification for Young’s modulus, tangent modulus and chord modulus

F593

Standard Specification for Stainless Steel Bolts, Hex Cap Screws and Studs COPYRIGHT

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ANSI ANSI/AWS D1.3 Structural Welding Code—Sheet Steel ANSI/ASCE-8-90 Specification for the Design of Cold-Formed Stainless Steel Structural Members ANSI/AWS C1.1 EN 10088 10088-1 10088-2 10088-3 ENV 1993-1-1 1993-1-4 ) d e t n i r p n e h w d e e t n a r a u g t o n y c n e r r u c t n e m u c o D ( 7 1 0 2 v o N 4 1 n o D N A L S N E E U Q N R E H T U O S F O Y T I S R E V I N U y b d e s s e c c A

Recommended Practices for Resistance Welding Stainless Steels Part 1: List of Stainless Steels Part 2: Technical Deli very Condi tions for Sheet/Plate and Strip for General Purposes Part 3: Technical D elivery C onditions f or S emi-Finished P roducts, Bars, Rods and Sections for General Purposes Eurocode 3: Design of steel structures Part 1-1: General rules and rules for buildings Eurocode 3: Design of steel structures Part:1-4: General rules—Supplementary rules for stainless steels

ISO 3506 3506-1 3506-2 3506-3

Mechanical properties of corrosion-resistant stai nless-steel fasteners Part 1: Bolts, screws and studs Part 2: Nuts Part 3: Set screws and similar fasteners not under tensile stress

7089

Plain washers—Normal series—Product grade A

7090

Plain washers, chamford—Normal series—Product grade A

JIS G4305

Cold-rolled stainless steel plates, sheets and strip

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APPENDIX B

MECHANICAL PROPERTIES (Normative) B1 MECHANICAL PROPERTIES OF STAINLESS STEELS

The stress-strain relationships for annealed and cold-rolled stainless steels are non-linear and anisotropic and this shall be considered in design. (See Figure B1.)


FIGURE B1

TYPICAL STRESS-STRAIN RELATIONSHIP FOR STAINLESS STEEL

The stress-strain relationship for stainless steels can be expressed analytically by the Ramberg-Osgood equation as follows:

ε =

f E o

n

 f  + 0.002    f y 

. . . B1(1)

where

ε = normal strain f = normal engineering stress E o = initial elastic modulus n = constant =

ε y

= =

log ε y ε p

. . . B1(2)

log ( f yc f pc ) offset yield strain 0.002 COPYRIGHT

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= = f y = f pc = ε p

offset proportional limit strain 0.0001 offset yield stress in compression offset proportional limit in compression

The tangent and secant moduli to be used for design can be calculated as follows: E t

= =

tangent modulus for normal stress d f dε f y E o

=

n -1

f y E s ) d e t n i r p n e h w d e e t n a r a u g t o n y c n e r r u c t n e m u c o D ( 7 1 0 2 v o N 4 1 n o D N A L S N E E U Q N R E H T U O S F O Y T I S R E V I N U y b d e s s e c c A

= =

=

 f  + 0.002nE o     f y 

. . B1(3)

secant modulus for normal stress f

. . . B1(4)

ε E o

 f n -1  1 + 0.002 E o  n   f y   

. . . B1(5)

Gt = tangent modulus for shear stress =

. . . B1(6)

df v d γ

=

f yv Go n −1

 f  f yv + 0.003Go  v   f yv   

Gs = secant modulus for shear stress = =

f v

γ Go

 f vn -1  1 + 0.003Go  n   f yv    Mechanical properties of cold-formed stainless steels for design calculation are given in Tables B1(A) to B1(E).

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TABLE B1(A) MECHANICAL PROPERTIES FOR LONGITUDINAL TENSION 304,

304L,

316

316L

409

1.4003

430

S31803

Initial elastic modulus

E o

GPa

195

195

185

195

185

200

Yield stress

f y

MPa

205

205

205

280

275

430

n

—

7.5

7.5

11

9

8.5

5.5

Proportional limit

f p

MPa

140

140

155

180

195

245

Ultimate strength

f u

MPa

520

485

380

435

450

590

Ramberg–Osgood parameter

TABLE B1(B) MECHANICAL PROPERTIES FOR LONGITUDINAL COMPRESSION


304,

304L,

316

316L

409

1.4003

430

S31803


E o

GPa

195

195

185

210

185

195

Yield stress

f y

MPa

195

195

205

260

275

435

n

—

4

4

9.5

7.5

6.5

5

f p

MPa

90

90

150

170

170

245

Ramberg–Osgood parameter Proportional limit

TABLE B1(C) MECHANICAL PROPERTIES FOR TRANSVERSE TENSION 304,

304L,

316

316L

409

1.4003

430

S31803


E o

GPa

195

195

200

220

200

205

Yield stress

f y

MPa

205

205

240

320

310

450

n

—

5.5

5.5

16

11.5

14

5

Proportional limit

f p

MPa

118

118

200

215

250

245

Ultimate strength

f u

MPa

520

485

380

460

450

620

Ramberg–Osgood parameter

TABLE B1(D) MECHANICAL PROPERTIES FOR TRANSVERSE COMPRESSION 304,

304L,

316

316L

409

1.4003

430

S31803


E o

GPa

195

195

200

230

200

205

Yield stress

f y

MPa

205

205

240

285

310

445

n

—

7

7

16

11.5

15

5.5

f p

MPa

135

135

200

220

255

265

Ramberg–Osgood parameter Proportional limit

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TABLE B1(E) MECHANICAL PROPERTIES FOR SHEAR

Initial elastic modulus Yield stress Ramberg–Osgood parameter

304,

304L,

316

316L

409

1.4003

430

S31803

G

GPa

75

75

75

75

75

75

f yv

MPa

115

115

130

130

165

255

n

—

6

6

13

10

11

5.5

B2 MECHANICAL PROPERTIES OF WELDS

Many different welding processes may b e used to j oint stainless steels. Table B2 gives tensile properties which can be used for mechanical design of welds made by the manual metal arc (MMAW) welding process.


Other welding processes such as gas metal arc welding (GMAW), gas tungsten arc welding (GTAW) and flux cored arc welding (FCAW) are frequently used with corrosion resistance productivity. Welding consumables for these processes are available, which give tensile str engths at least equivalent to the tensile strengths given in Table B2. Consult suppliers of welding consumables for design properties of weld deposits made by these processes. AS/NZS 1554.6 specifies methods for the selection of welding consumables, details of welded connections, qualifications of procedures and personnel, workmanship, quality of welds and inspections.

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TABLE B2 TENSILE PROPERTIES OF DEPOSITED WELD METAL FOR ALL-WELD-METAL SPECIMENS COVERED ELECTRODES FOR MANUAL METAL ARC WELDING (MMAW) Designation


Minimum tensile strength

Minimum elongation

MPa

%

Heat treatment

E209-XX

690

15

None

E219-XX

620

15

None

E240-XX

690

15

None

E307-XX

590

30

None

E308-XX

550

35

None

E308H-XX

550

35

None

E308L-XX

520

35

None

E309Mo-XX

550

35

None

E308MoL-XX

520

35

None

E309-XX

550

30

None

E309L-XX

520

30

None

E308Nb-XX

550

30

None

E309Mo-XX

550

30

None

E309MoL-XX

520

30

None

E310-XX

550

30

None

E310H-XX

620

10

None

E310Nb-XX

550

25

None

E310Mo-XX

550

30

None

E312-XX

660

22

None

E316-XX

520

30

None

E316H-XX

520

30

None

E316L-XX

490

30

None

E317-XX

550

30

None

E317L-XX

520

30

None

E318-XX

550

25

None

E320-XX

550

30

None

E320LR-XX

520

30

None

E330-XX

520

25

None

E330H-XX

620

10

None

E347-XX

520

30

None (continued )

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TABLE B2 (continued ) Designation

Minimum tensile strength

Minimum elongation

MPa

%

Heat treatment

E49

690

25

None

E383

520

30

None

E385

520

30

None

E410

450

20

(See Note 1)

E410NiMo

760

15

(See Note 2)

E430

450

20

(See Note 3)

E630

930

7

(See Note 4)

E16-8-2

550

35

None

E2209-XX

690

20

None

E2553-XX

760

15

None

NOTES: ) d e t n i r p n e h w d e e t n a r a u g t o n y c n e r r u c t n e m u c o D ( 7 1 0 2 v o N 4 1 n o D N A L S N E E U Q N R E H T U O S F O Y T I S R E V I N U y b d e s s e c c A

1

Specimen shall be heated to between 840 ° C and 870 ° C, held for 2 h, furnace-cooled at a rate not greater than 55 K/h to 595 ° C and air-cooled to ambient temperature.

2

Specimen shall be heated to between 595 ° C and 620 ° C, held for 1 h, and air-cooled t o ambient temperature.

3

Specimen shall be heated to between 760 ° C and 790 ° C, held for 2 h, furnace-cooled at a rate not greater than 55 K/h to 55 ° C and air-cooled to ambient temperature.

4

Specimen shall be heated to between 1025 ° C and 1050 ° C, held for 1 h, air-cooled to less than 15 ° C, and then precipitation-hardened at 610 ° C to 630 ° C, held for 4 h, and air-cooled to ambient temperature.

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APPENDIX C

STAINLESS STEEL PROPERTIES (Informative) C1 INTRODUCTION

This Appendix gives general guidance only on the use of stainless steels in structures. Specialist advice should always be obtained in relation to specific applications to ensure that all relevant factors have been properly accounted for. Figure C1 shows schematically the processes that are used to produce cold-formed structural members. The steel thickness in these members is generally limited by the capacity of cold-forming equipment to about 6 mm.


NOTE: BA (2R) fini sh designat ions are in accordance with ASTM A480/ AS1449, with EN 10088 designation shown in parentheses.

FIGURE C1 PRODUCTION PROCESSES AND SURFACE FINISHES FOR COLD-FORMED STAINLESS STEEL STRUCTURES

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C2 STAINLESS STEEL GRADES C2.1 Introduction

There are many grades of stainless steel, as defined in various national and international standards. Many of these steels are effectively equivalents, the slight differences in specification between different specifying authorities generally being negligible. Stainless steels can be classified into five groups in accordance with their microstructure, which results primarily from their chemical composition. Each group has different properties, particularly in respect of strengt h, corrosi on resistance and ease of fabrication.


FIGURE C2 CLASSIFICAT ION OF STAINLESS STEELS BY THEIR CHROMIUM AND NICKEL CONTENT

C2.2

Classification of stainless steels by microstructures

The five groups can be summarized as follows: (a)

Austenitic stainless steels These are the most commonly used stainless steels. They have an austenitic microstructure at room temperature, stabilized by relatively high amounts of nickel (greater than 7%). Cast austenitic stainless steels may contain significant amount of ferrite. Austenitic stainless steels have high ductility, are easily formed, are readily weldable, and offer good corrosion resistance. Their strengths are reasonable when compared to carbon steel, but they can only be hardened, i.e. made stronger, by cold-working, not by heat treatment. Considerable strength levels can be achieved in austenitic stainless steels by cold working. Austenitic stainless steels are available in all product forms. Steels of this group are the most common in structures, particularl y grades 304 and 316 and thei r low carbo n variants, 304L and 316L. These steels are based on 18% chromium and 8% nickel, 316 being slightly leaner in chromium but with an addition of 2% molybdenum to give higher resistance to localized corrosion. COPYRIGHT

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The low carbon ‘L’ variants of grades 304 and 316 contain a maximum of 0.03% carbon. This greatly reduces their susceptibility to sensitization by the heat of welding (see Paragraph C6.3.5). The use of ‘L’ grades generally gives no significant advantage for section thicknesses less than about 6 mm.


(b)

Ferritic stainl ess steels The ferritic stainless steels contain relatively little nickel and have a ferritic microstructure, as do plain carbon and carbon manganese steels. They are readily available in flat rolled and cast forms. Strength in the annealed condition is similar to austenitic grades, but ductility, formability and weldability are not as good as in the austenitic steels. Although generally not as corrosion resistant as the austenitic grades, their resistance to stress corrosion cracking is superior. As with austenitic grades, they can be hardened by cold working, not by heat treatment, but the strength achieved is much less than for the austenitic grades. It is generally difficult to produce reliable structural welds in ferritic stainless steels. An exception are a group of corrosion resistant steels containing ~12% chromium, conforming to 1.4003 (EN 10088), which are widely used in mildly corrosive environments for nondecorative applications in machinery and rail wagons for minerals; however, specialist assessment of suitability for specific application and fabrication processes is still required.

(c)

Mart ensitic stainless steels These steels can be hardened by heat treatment. They are readily available in flat rolled and cast forms. Great strengths can be achieved. Toughness may not be adequate for structural application and should be considered in design. They are not normally used structurally in welded fabrication. They are used for bolts, connecting nodes and as wear components.

(d)

Duplex (austenitic-ferritic) stai nless steels These steels have a mixed microstructure of austenite and ferrite, and combine some of the best properties of the austenitic and ferritic groups. They are readily available in flat rolled and cast forms. Compared to the austenitic group, they have higher mechanical strengths, slightly inferior weldability, lower formability and similar or higher corrosion resistance especially with respect to stress corrosion cracking. They can be hardened by cold-working. Several of the grades in this group have higher alloy content and hence better corrosion resistance than the most common austenitic grades, 304 and 316. The most common duplex grade in structures is UNS S31803 (1.4462 in EN 10088), which contains 22% chromium, 5% nickel and 3% molybdenum.

(e)

Precipitation hardeni ng stainless steels These offer the highest strengths, obtained by suitable heat treatments, which precipitate second phase particles which increase strength. They are readily available in cast rolls and vast forms. Very high strength levels, with yield stress greater than 1000 MPa, may be obtained in some grades. Precipitation hardening stainless steels may have an austenitic or ferritic matrix. They are not normally used in welded fabrications, as they require heat treatment and surface finishing after welding. The most common grade of precipitation hardening stainless steel is UNS S17400, also known as grade 630.

Further information on the various groups and types of stainless steels may be found in standard t exts (e.g. Ref. 1 given i n Paragraph C9). Table C1 gi ves t he availability of stainless steel products by grade. C2.3

Effect of product form

This Appendix applies mainly to the wrought forms of the selected alloys. Cast forms generally have corrosion resistance equivalent to the wrought forms, but several differences exist. One of the more important is that the microstructure of cast austenitic stainless steels generally contains more ferrite than the wrought form. This facilitates the casting process and weld repair, and also increases the resistance to stress corrosion cracking (see Paragraph C7.3.7). Cast steels also differ in mechanical properties, physical properties COPYRIGHT

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and chemical composition. Because of the formation of larger grain sizes and other differences in microstructure, mechanical properties of cast steels exhibit a wider range and may be inferior to wrought steels. Cast stai nless steels are often manufactured for a specific application, and properties may vary to suit the application. Note that Standards are available for cast stainless steels and should be referred to.

TABLE C1 AVAILABILITY OF STAINLESS STEEL PRODUCTS BY GRADE Plate, sheet and coil Grade


Rod and

Welded

Circular and

Hot-rolled

rectangular hollow

angles and

sections

shapes

Fasteners

H ot-r oll ed

C old-r oll ed

bars

tubes

304

✔

✔

✔

✔

✔

✔

✔

304L

✔

—

—

✔

—

—

—

310

✔

✔

✔

—

—

—

✔

316

✔

✔

✔

✔

✔

✔

✔

316L

✔

—

—

—

—

—

—

409

—

✔

—

✔

—

—

—

1.4003

✔

✔

—

—

—

—

—

430

—

✔

—

—

—

—

—

S31803

✔

✔

✔

—

—

—

—

C3 EFFECT OF ALLOYING ELEMENTS IN STAINLESS STEELS

Chromium is the alloying element by which stainless steels are defined, a minimum of about 10.5% chromium is required. The principal function of chromium is to confer corrosion and high temperature oxidation resistance; both properties arise from the strong affinity of chromium with oxygen. When in contact with aqueous media, chromium contributes to the development of a chromium rich passive layer on the surface. In high temperature environments, chromium contributes to the formation of a protective, slow growing chromium-rich oxide layer on the surface. Nickel is added to stai nless steels mainly to counter act the tendency of chromium to stabilize the ferritic crystal structure. Nickel promotes the for mation of the more ductile and weldable austenitic crystal microstructure, and about 8% of nickel is required to ensure a fully austenitic microstructure in the most common stainless steels, which contain about 18% chromium. Higher levels of nickel may be added to promote resistance to stress corrosion cracking. Molybdenum is added in small amounts (up to about 7%) to stainless steels principally to improve the resistance to corrosion. It is particularly effective in improving resistance to pitting and crevi ce corrosion. Molybdenum also increases the high temperature strength of austenitic grades, and increases room temperature strength and tempering resistance of martensitic grades. Carbon is always present in stainless steels. The carbon content is controlled for an optimum balance of strength to which it contributes, and corrosion resistance and weldability, which it may impair if present at excessive levels. Some grades intended for service at high temperatures or for high strength or wear resistance may have a minimum level of carbon. COPYRIGHT

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Nitrogen behaves i n a simi lar way to carbon i n st ainless steels, although the s ame content of nitrogen is less damaging than carbon to corrosion resistance and weldability. Elements such as titanium, niobium and tantalum may be added, particularly to the austenitic and ferritic grades, to reduce susceptibility to sensitization and hence intergranular corrosion particularly in the welded condition. This approach to the improvement of corrosion properties has largely been superseded in the austenitic grades by limitation of the carbon content to a maximum of 0.03%. This can be readily achieved by modern steelmaking equipment, and is sufficiently low to avoid sensitization even in welded heavy sections of the austenitic grades. Elements such as sulphur, selenium and calcium may be added to improve machinability, although this may be at the expense of corrosion and oxidation resistance. The deleterious effect of calcium is less than that of sulphur. C4 SURFACE FINISH


In many applications, surface finish and appearance are important. Manufacturers offer a range of standard finishes, from mill finish through dull finishes to bright polish. They may also offer proprietary textured finishes. Mill finishes result from the operations used to produce th e product form, while decorative finishes are a ppli ed after wards. Mill finishes are often difficult to repair after damage or fabrication, while decorative finishes can generally be match ed satisfactorily. The most common mill and decorative finishes on cold-formed structural sections are 2B and No. 4 respectively. 2B finish results from the sequence of operations used to produce the section (see Figure C1). No. 4 is produced by a further surface finishing operation, using abrasive grit with a particle size of about 120 to 150 grade. It may be applied either to the flat product used to manufacture cold-formed sections, or to the cold-for med sections. It should be noted that although the various finishes are standardized, variability in processing introduces differences in appearan ce between manufacturers and even within a single producer. Bright finishes are frequently used in architectural applications and it should be noted that bright finishes will exaggerate any out-of-flatness of the material, particularl y on panel surf aces. Rigi dized, embossed, text ured, patterned, or profiled sheets with a rigid supporting frame will alleviate this tendency. Stainless steel may also be given colour, either chemically, or by painting. Consult stainless steel suppliers for the full range of finishes available. C5 MECHANICAL BEHAVIOUR AND DESIGN VALUE OF PROPERTIES C5.1 Basic stress-strain behaviour

The stress-strain behaviour of stainless steels differ from that of carbon steels, such as grade 300 structural steel, in a number of respects (see Figure C3). C5.1.1 Non-linearity

The most important difference between stainless and carbon steels is in the shape of the stress-strain curve. Carbon steel typically exhibits linear elastic behaviour up to the yield stress and a plateau before strain hardening is encountered, while stainless steel has a more rounded r esponse with no well-defined yield stress (see Figure B1 of Appendix B). Therefore, stainless steel ‘yield’ stresses are generally quoted as a proof strength defined for a particular offset permanent strain, typically 0.2% strain, as shown in Figure B1.

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NOTE: Structural steel strain hardens at larger strains than show.

FIGURE C3 TYPICAL INITIAL STRESS-STRAIN CURVES FOR STAINLESS STEELS AND GRADE 300 ST RUCTURAL STEEL (FOR LONGITUDINAL TENSION)

C5.1.2

Non-symmetry of tensile and compressive behaviour

Stainless steel may exhibit quite different stress-strain behaviour in tension and compression. This is especially the case for austenitic grades, where the compressive yield stress is often substantially lower than the tensile yield str ess, particularly in the temper-rolled condition. C5.1.3 Anisotropy

Stainless steel often has different stress-strain behaviour for test coupons aligned parallel and transversely to the rolling direction; i.e. it may be anisotropic. For the austenitic grades transverse tensile tests tend to be weaker than longitudinal tests. This is recognized by product codes, where tran sverse coupons are normally specified for proving t ests; however, for duplex grades the transverse tensile strength is greater than the longitudinal strength (by about 5%). Thus, when non-linearity, non-symmetry and anisotropy are considered, material behaviour is characterized by four stress-strain curves. This leads to relatively complex design. This subject is covered in detail in Appendix B.

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C5.2 Factors affecting stress-strain behaviour

There are factors that can change the form of the four basic curves for any given grade of stainless steel. These factors are to some extent interdependent and include the following: (a)

Cold working Strength is increased by cold working, such as during cold-forming operations including roller levelling/flattening. The reduction in ductility associated with the increase in strength is normally unimportant as the initial ductility is high, especially in the austenitic stainless steels. All stainless steel products should meet minimum ductility requirements, as specified in product Standards. The 0.2% proof strength is typically increased by about 50% in cold-formed corners of cross-sections. However, the effect is localized and the increase in member capacity is dependent on the location of the corners within the section; e.g. in a beam little benefit would be obtained for corners close to the neutral axis. The strength enhancement more than offsets any effect due to thinning of the material at coldworked corners. Cold working, which is normally applied unidirectionally, affects the four basic curves to different extents, though all curves are enhanced.


Subsequent welding of the member will partially anneal the heat-affected zone, reducing the strength increase arising from cold working. Hence, if members are to be welded, annealed or heat treated, the increase in strength resulting from cold-forming can only be used if tests of the structural elements are conducted in accordance with Section 6. (b)

Strain-rate sensitivity, creep and cyclic stressing Strain-rate sensitivity is more pronounced in stai nless steels than in carbon steels; that is, a proportionally greater strength can be realized at fast strain rates for stainless steel than for carbon steel. Conversely, the effects of strength reduction at very low loading rates, including the effects of room temperature creep under static loading, should be recognized. For strain rates differing by two orders of magnitude, over the range used in tensile coupon testing, there is no evidence that the relationship between the four basic curves is altered. Since strength limit states normally correspond to short-term overload conditions, creep need only be considered for high levels of long-term serviceability loads. Creep may be manifested by increased beam deflection. If long-term deflection is an issue, it is tentatively recommended to restrict the long-term serviceability stresses to 0.6 σ 0.2 , where σ 0 .2 is the actual 0.2% proof stress of the material. For very long-term, say 100 years, an even lower figure may be applicable, say 0.5 σ 0. 2. At high levels of cyclic stressing, stainless steel may exhibit ratcheting, with the strain incrementing, though at a decreasing rate, on each cycle. This phenomenon will only rarely be a consideration for structural applications and to a large extent it is accounted for in the partial factors of safety.

(c)

Effects of temperature The austenitic grades are used for cryogenic applications, where they remain tough and ductile. They also retain higher strengths than carbon steel at elevated temperatures; however, the design of structures subject to long-term exposure at cryogenic or elevated temperatures is outside the scope of this Standard. Nevertheless, the short-ter m properties may be of importance, for instance when considering fire resistance. For further information on the design of fire, see Appendix G.

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C6 PHYSICAL PROPERTIES

Typical room temperature physical properties of some grades in the annealed condition are given in Table C2. Physical properties may vary slightly with product form and size but such variations are usually not of critical importance to t he application. In structures, an important physical property is the coefficient of linear expansion (CLE). The CLE of austenitic grades is considerably higher than that for carbon steel (12 × 10 −6/ 0C). The effects of differential thermal expansion should be considered in design and fabrication. The austenitic grades are usually considered non-magnetic, but may show low levels of ferromagnetism (magnetic susceptibility greater than or equal to 1.003) due to the presence of delta ferrite or martensite. The former is usually present in castings and weld metals, the latter may be induced by cold work, such as levelling or forming strains, or at sheared edges. Where non-magnetic properties are important, care should be exercised in selecting appropriate grades and welding consumables, or a post-weld heat treatment applied. It is recommended to obtain further advice for non-magnetic applications.


TABLE C2 TYPICAL ROOM TEMPERATURE PHYSICAL PROPERTIES OF SOME STAINLESS STEELS IN THE ANNEALED CONDITION Density Grade

Mean coefficient of linear

Thermal

Specific

Electrical

expansion

conductivity

heat

resistivity

× 10 −6 / oC

W/m. oK

J/kg. o K

nΩ .m

UNS No kg/m3

0 – 100 o C

0 – 315 o C

0 – 540 o C

100 o C

500 o C

303

S30300

8000

17.2

17.8

18.4

16.2

21.5

500

720

304

S30400

8000

17.2

17.8

18.4

16.2

21.5

500

720

304L

S30403

8000

17.2

17.8

18.4

16.2

21.5

500

720

310

S31000

8000

15.9

16.2

17.0

14.2

18.7

500

780

316

S31600

8000

15.9

16.2

17.5

16.2

21.5

500

740

316L

S31603

8000

15.9

16.2

17.5

16.2

21.5

500

740

321

S32100

8000

16.6

17.2

18.6

16.1

22.2

500

720

409

S40900

7800

11.7

12.0

12.4

24.9

—

460

1.4003

S41003

7800

10.8

11.3

12.0

31.0

32.0

480

570

410

S41000

7800

9.9

11.4

11.6

24.9

28.7

460

570

430

S43000

7800

10.4

11.0

11.4

26.1

26.3

460

600

—

S31803

7800

13.7

14.7

—

—

19.0

—

480

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C7 DURABILITY — CORROSION C7.1 Introduction

In most stainless steel structural applications, corrosion resistance is of primary importance, for appearance, minimal maintenance or long-term durability. Hence, corrosion resistance is often the main consideration in choosing a grade. Because stainless steels are usually used in corrosion conditions that are challenging, appropriate design of the structure may be required, to minimize or eradicate corrosion. If careful consideration is given to this aspect of design, in addition to the mechanical considerations required for other materials, long and economic lives can be achieved, often in service conditions that would give limited life or more expensive maintenance, replacement or repair requirements for other materials. Stainless steels are generally very corrosion resistant and will perform satisfactorily in most environments. The limit of corrosion resistance of a given stainless steel depends on a number of factors but in general the higher the alloy content, particularly chromium and molybdenum, the higher the resistance, and cost.


Careful selection of the appropriate grade for a given application is, therefore, of economic importance. The maintenance and repair schedules should also be resolved at the design stage. As with all metals, stainless steel can be subject to corrosion under specific conditions and details of the major individual types of corrosion are given in the following section. It should be emphasized that the presence of moisture, including that due to condensation, is necessary for corrosion to occur. For atmospheric corrosion, the t ime of wetness is a critical variable for the extent of corrosion experienced. There is a critical relative humidity of the atmosphere, below which condensation will not form on the metal surface, and hence corrosion cannot take place. The actual critical relative humidity will change, depending on the surface condition of the metal. The presence of dust particles and other contamination on the surface will reduce the critical relative humidity, usually t o about 50 to 70%. In some cases, the corrosion mechanism itself may not be as significant as consequences arising from it. For example, corrosion pitting would directly limit the life of pipework, but may not be a problem in a structure unless the pits also affect fatigue life. Where stainless steels are used for their appearance, minor corrosion can produce stains, which constitute failure in a structure of unimpaired integrity. The existence of corrosion mechanisms does not imply that the stainless steels are unduly restricted in use, or that they are ‘delicate’ materials, but simply that these sophisticated materials demand intelligent use in order to avoid certain well-known conditions, and to get the most out of their very considerable advantages. In nearly all cases, grade selection and the design of the structure are the keys to good performance, and appropriate selection and features will eradicate or minimize corrosion. With intelligent use, stainless steels can give long and economic lives, often in service conditions that would give limited life or more expensive maintenance and repair requirements for other materials. C7.2 Mechanism of corrosion resistance

The corrosion resistance of stainless steels results from a passive surface film, which, with adequate access to oxygen or oxidizing agents, is self-healing when damaged. This film is rich in chromium, and the corrosion resistance is strongly related to the chromium content of the steel. The addition of nickel and other alloying elements can substantially enhance the protection offered by the film. In particular, a few percent of molybdenum improves the pitting r esistance (see Paragraph C7.3.3) of t he steel . Corrosion initiates when the passive film is damaged, by electro-chemical attack or by mechanical damage. Corrosion resistance is promoted by conditions that facilitate repair of the passive film,

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92

Types of corrosion and performance of steel grades

C7.3.1

General (uniform) corrosion

The passive chromium-rich surface film makes general corrosion much less severe in stainless steels than for carbon steels. General corrosion on stainless steels normally takes the form of surface staining rather than bulk substrate dissolution . This form of corrosion is not a problem for most austenitic and duplex grades in onshore structural appli cations and for grades 316 and duplex S31803 in marine applications. Ferritic grades should not be used in environments where they can become wet unless they are protected by painting, or surface staining can be tolerated. Where stainless steel is used aesthetically in exposed locations, routine maintenance by washing is normally sufficient to retain the surface finish. Stainless steels are resistant to many chemicals; they are often used for their containment. For these applications, reference should be made to tables in manufacturers’ literature, or the advice of a competent corrosion engineer should be sought (see Paragraph C8). C7.3.2 ) d e t n i r p n e h w d e e t n a r a u g t o n y c n e r r u c t n e m u c o D ( 7 1 0 2 v o N 4 1 n o D N A L S N E E U Q N R E H T U O S F O Y T I S R E V I N U y b d e s s e c c A

Abrasion corrosion

Where there is flow of abrasive particles across a stainless steel surface, the rate of removal of the passive film may exceeds its re-formation. Erosion-corrosion results, and loss rates of the steel can be relatively high. However, the corrosion resistance and strength of stainless steels are higher than many other materials, and they are especially useful where problems have been encountered with abrasion corrosion of other materials. C7.3.3

Pitting corrosion

Pitting corrosion occurs as localized pits. It results from local breakdown of the passive layer, normally by chloride ions, although the other halides, sulphates and other anions can have a similar effect. Since the chloride ion is by far the most common cause of pitting, coastal and marine environments are rather aggressive. Besides the chloride content, the probability of a particular mediu m causi ng pitting depends on factors such as the temperat ure, acidity or alkalinity and the presence of the oxidizing agents needed to maintain the passive film. In most structural applications, the extent of pitting is likely to be only superficial and reduction in section negligible. Stainless steels containing molybdenum have higher resistance to this form of corrosion and, where pitting cannot be tolerated, are recommended for aggressive marine, coastal, and industrial areas. The pitting resistance of a stainless steel is dependent on its chemical composition. Chromium, molybdenum and nitrogen all enhance the resistance to pitting. An approximate measure of pitting resistance is given by the pitting index or pitting resistance equivalent (PRE) defined as follows: (a)

PRE = wt% Cr + 3.3(wt% Mo) + 30(wt% N) for austenitic stainless steels.

(b)

PRE = wt% Cr + 3.3(wt% Mo) + 16(wt% N) for duplex stainless steels.

The PRE of a stainless steel is a useful guide to its ranking with other stainless steels, but has no absolute significance. The 12% chromium ferritic steels, and the austenitic grades that do not contain molybdenum have lower PRE and are not suitable for architectural applications in marine environments except for internal structural components effectively shielded from sea spray and mist. These grades may also show unacceptable levels of pitting in severe industrial atmospheres. Austenitic grades containing molybdenum (316, 316L) or duplex grades are preferred. COPYRIGHT

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C7.3.4

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Crevice corrosion

Crevice corrosion occurs in the same environments as pitting corrosion. Corrosion initiates more easily in a crevice than on a free surface because the diffusion of oxidants necessary for maintaining the passive film is restricted. The severity of a crevice is greatly dependent on its geometry; the narrower the crevice, the more severe the restriction of diffusion of oxidants. Corrosion conditions are more severe, and chlorides may concentrate in the crevice. Crevices may result from a metal to metal joint, a gasket, biofouling, deposits and surface damage such as deep scratches. Every effort should be made to eliminate crevices, although it is often not possible to eliminate them entirely. In particular, intermittent or partial penetration welds shoul d be avoided. There are similar equations to those for pitting corrosion relating crevice corrosion resistance to the contents of the alloying elements chromium, molybdenum and nitrogen, and the ranking of grades for resistance to crevice corrosion is similar to pitting corrosion. C7.3.5


Intergranular corrosion (sensitization)

Where parts of the microstructure are depleted of chromium, the protective passive layer can prove ineffective. This can occur when precipitates form, usually in the range of sensitization temperatures 450 to 850oC, which could be due to the heat of welding, or due to service in that temperature range. Sensitization depends on carbon content and time, and occurs as a result of diffusion of chromium atoms to chromium carbide precipitate particles. These form preferentially at grain boundaries, and in the early stages of formation the grain boundaries are surrounded by a layer of material of lower chromiu m cont ent. On exposur e to corr osive envi ronments, these chromium-depleted zones may suffer preferential attack, and intergranular corrosion results. Intergranular corrosion has been avoided by using steels containing small additions of elements which are stronger carbide formers than chromium, preventing the formation of chromium carbides. Titanium, niobium and tantalum have been commonly used. This approach may still be used for steels that are used in the sensitization temperature range; however, with modern steel making plant, carbon levels in austenitic stainless steels are generally low, 0.05% or less, and sensitization due to welding is rarely encountered when proper advi ce fr om the steel supplier is obtained and followed. The low carbon ‘L’ grade versions of austenitic stainless steels are limited to 0.03% carbon maximum, and are even less susceptible to sensitization. They are used where plate thicknesses of about 6 mm or greater give thermal conditions during welding, which induce sensitization. Prolonged holding times at elevated temperatures can eventually lead to sensitization in ‘L’ grades. Thus, these grades should not be used continuously at temperatures greater than about 425°C if full corrosion resistance is to be retained. Intergranular corrosion (sensitizaton) is a complex subject, and a specialist’s advice should be sought regarding stabilization and sensitization issues, as they affect both austenitic and non-austenitic stainless steels. C7.3.6

Galvanic corrosion

When two dissimilar metals are in contact and are connected by an electrolyte, i.e. an electrically conducting liquid such as water, rain or condensation, a current flows from the anodic metal to the cathodic or nobler metal through the electrolyte. As a result, the less noble metal corrodes.

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This form of corrosion may occur when stainless steel is joined to carbon or low alloy steels. It may also occur, though to a much smaller degree, between different types of stainless steel. For welded joints, it is important to select welding consumables to give weld metal that is at least as noble as the parent material. In corrosive environments such as heavy industrial atmospheres, marine atmospheres, and where immersion in brackish or sea water may occur, martensitic and ferritic bolts should be avoided for joining austenitic stainless steels unless suitably insulated. Galvanic corrosion need not be a problem with stainless steels, though sometimes its prevention can require precauti ons which at first sight might seem surprising. Galvanic corrosion can be avoided by preventing current flow by —


(a)

insulating dissimilar metals, i.e. breaking the metallic path; or

(b)

preventing electrolyte bridging, i.e. breaking the electrolytic path by paint or other coating.

The risk of corrosion attack is greatest if the area of the more noble metal, e.g. stainless steel, is large compared with the area of the less noble metal, e.g. carbon steel. Special attention should be paid to the use of paints or other coatings on the carbon steel. If there are any small pores or pinholes in the coating, the small area of bare carbon steel will provide a very large cathode/anode area ratio, and severe pitting of the carbon steel may occur. This will be most severe under immersed conditions. For this reason, it is preferable to paint the stainless steel; any pores will lead to small area ratios. In practice, it is normal to paint the carbon steel for protection from general corrosion, and to continue the paint over the weld metal and a strip of stainless steel to prevent galvanic corrosion. In some industries, e.g. petrochemical industries, all parts of the structure may need to be earthed to inhibit spark formation. Necessarily, there can be no electrical isolation at the earthing connection. If galvanic corrosion is a potential problem, i.e. if long periods of wetness or immersion are envisaged, consideration may be given to special thickening of the carbon steel to allow for galvanic corrosion in the vicinity of the earthing connection. Solutions containing dissolved copper salts, such as copper corrosion products, should not be allowed to contact stai nless steel, as they will tend to auto -plate copper ont o the surface, occluding the self-repair of the passive film. C7.3.7

Stress corrosion cracking

Stress corrosion cracking (SCC) results from the joint action of tensile stresses in the steel and a specific corrosive environment, in conditions where neither singly would cause cracking. The stresses may be applied or they may be internal or residual, and they need not be high in relation to the proof stress. Internal stresses may result from cold working, welding or thermal gradients in service. They may also arise from the wedging action of corrosion products growing in a crack. SCC is a delayed failure process, in which cracking initiates after an incubation time. Propagation of the cracks is fast. SCC is rarely encountered at room temperature for austenitic stainless steels, but may occur at temperatures above about 60 oC in environments having high chloride concentrations. Nevertheless, SCC has been known to occur at temperatures below 60oC, e.g. in swimming pool atmospheres. SCC can be caused by concentration due to evaporation of solutions with low chloride concentrations, which, hence, may occur at the liquid/air interface; however, SCC is unlikely to be significant in many structural applications. In most media, the resistance to SCC of duplex stainless steels is superior to austenitic stainless steels of about the same alloy content, e.g. expressed as PRE. This relative immunity is due to the mixture of austenite and ferrite in the microstructure. Ferrite is much less susceptible to SCC than austenite. Careful selection of consumables and welding procedures is needed to ensure the appropriate microstructural mix in the weld metal for retention of SCC resistance. COPYRIGHT

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Shot peening, which imparts residual compressive stresses in the surface layer of the steel, is beneficial in reducing or preventing SCC. Clearly, any subsequent process that relieves these residual compressive surface stresses will remove the benefit. Note that shotcontaining iron or steel should be avoided, to prevent surface contamination and subsequent corrosion of the stainless steel. Resistance to SCC is of particular interest in the selection of high-strength stainless steels for fasteners. SCC should be considered when quench-hardened martensitic stainless steels or precipitation-hardening stainless steels are used in marine or industrial locations in which chlorides are present. The martensitic steels are liable to stress corrosion failure in a wide variety of corrosive media if heat treated to strengths greater than about 1050 MPa. Below this strength level, they are very resistant to cracking. Ferritic stainless steels have good resistance to stress corrosion cracking but are not immune. C7.3.8


Effect of welding on corrosion resistance

Welding and other fabrication processes can have adverse effects on the corrosion resistance of stainless steels, through mechanisms such as pitting, sensitization, galvanic action, stress corrosion cracking and the like. Specialist advice should be sought regarding the effects of fabrication processes on corrosion resistance for specific applications. C7.4 C7.4.1

Corrosion in selected environments

Air

The effects of atmospheres on stainless steels vary. Rural atmospheres, uncontaminated by industrial fumes or coastal salt, are very mildly corrosive to stainl ess steels, even in areas of high humidity. Industrial and marine atmospheres are considerably more severe. Ambient temperatures also have a very strong effect. Table C3 gives the most common structural grades of stainless steel, 304(L), 316(L) and S31803, used in atmospheric service environments. The most common causes of atmospheric corrosion are particles of metallic iron or steel contamination, arising from fabrication and transport operations, and chlorides originating from the sea, from industrial processes or from calcium chloride in cement. Deposited particles, alth ough inert, may absorb weak acid solutions of sulf ur dioxide from the atmosphere, which may locally break down the passive film, or may occlude the surface, preventing self-repair of the passive layer. The general appearance of exposed stainless steel is affected by surface finish, the smoother the better, and whether or not regular washing down is carried out, either intentionally or by rain. It is commonly assumed that stainless steels will not corrode in atmospheric conditions, and the occurrence of corrosion is taken to indicate imminent failure; however, the general atmospheric corrosion rates of the 18% chromium grades are at least one thousand times slower than for carbon steels, so the useful properties of the stainless are maintained for an extended period, albeit with an impaired appearance. Even in aggressive marine and industrial conditions, where pitting corrosion of stainless steels but not of carbon steels takes place, the life of membranes (roofs, gutters) of stainless steel is several times that of carbon steel of the same thickness.

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TABLE C3 A PRACTICAL GUIDE TO SELECTING GRADES OF STAINLESS STEEL Location

Rural

Urban

Industrial

Seaside

Grade

I

L

M

H

I

L

M

H

I

L

M

H

I

L

M

H

430

O

∆

∆

∆

O

X

X

X

∆

X

X

X

∆

X

X

X

304(L)

O

O

O

O

O

O

O

∆

O

∆

∆

O

∆

316(L)

O

O

O

O

O

O

O

O

O

O

O

∆ ∆

O

O

∆ ∆

∆ ∆

S31803

O

O

O

O

O

O

O

O

O

O

O

O

O

O

O

O

NOTES:


1

I: Indoors.

2

L: Least corrosive conditions within each location (low temperature, low humidity).

3

M: Medium, typical of each location.

4

H: Highly corrosive conditions within each location (high temperature, high humidity, air pollution).

5

O: Suitable.

6

∆: Unsuitable; however, usable if a smooth surface finish material is used and washed frequently.

7

X: Unsuitable.

C7.4.2

Sea water

Sea water, including brackish water, contains high levels of chloride and may be very corrosive. In particular, pitting corrosion of grade 304(L) may occur under particles deposited in pipes, which obstruct the maintenance of the passive surface layer. This may occur in stagnant conditions, or when stream velocities are below about 1.5 m/s. Grades 304(L) and 316(L) can also suffer attack at crevices, whether resulting from design details or from fouling organisms such as barnacles. Satisfactory performance may be obtained from a grade of lesser resistance, for example, by draining a pipeline while not o perating. Salt spray may be more aggressive than immersion, as high chloride concentrations may develop by evaporation. Since sea water is highly conductive, galvanic corrosion should be considered if stainless steel is used with other metals in sea water. C7.4.3

Other waters

The austenitic stainless steels usually perform satisfactorily in distilled, potable or boiled water. Where acidity is high 316(L) may be required, otherwise 304(L) is usually sufficient. 316(L) may also be more suitable where there are minor amounts of chloride present, to avoid possible pitting and crevice corrosion problems. River water needs special consideration; biological and microbiological activity can cause pitting in austenitic stainless steels within a comparatively short time, particularly where anaerobic bacteria metabolize sulfur species to produce the reducing sulfuric and sulfurous acids. The possibility of erosion-corrosion should be considered for waters containing abrasive part icles. C7.4.4

Chemical environments

The range of application of stainless steel in chemical environments is wide and it is not appropriate to grade selection in this St andard. The advice of a specialist corrosion engineer should be sought. Charts published by manufacturers showing results of corrosion tests in various chemicals should be used with caution. Although giving a guide to the resistance of a particular grade, service conditions such as temperatures, pressures, concentrations, and the like, vary and will generally differ from the test conditions. Impurities, temperature fluctuations and the COPYRIGHT

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degree of aeration can have a marked effect on results. It is also essential to consider all part s of the operational cycle, incl uding cleanin g practices and downtimes in selecting grades for severe corrosion service. C7.5

Design for corrosion control

Careful attention to detailing is also important for realizing the full serviceability of stainless steels. Anti-corrosion requirements should be considered in planning and in design. The following check list should be considered: (a)


Avoid dirt entrapment by (see Figure C4) — (i)

orienting angle and channel profiles to minimize dirt retention;

(ii)

providi ng drainage holes, sufficientl y large to prevent blockages;

(iii)

avoiding horizontal surfaces;

(iv)

specifying a small slope on nominally horizontal gusset stiffeners;

(v)

using tubular and bar sections;

(vi)

sealing tubes with dry gas or air where harmful condensates may form; and

(vii) specifying smooth finishes. (b)

(c)

(d)

Avoid crevices by (see Figure C4) — (i)

using welded rather than bolted connections;

(ii)

using full penetration welds;

(iii)

using closing welds or mastic fillers;

(iv)

dressing/profiling welds to a smooth finish; and

(v)

preventing biofouling.

Reduce the likelihood of stress corrosion cracking in those specific environments (where it could occur) by — (i)

minimizing fabrication stresses by careful choice of welding sequence; and

(ii)

inducing compressive surface stresses by shot or bead peening (avoiding the use of iron/steel shot).

Reduce likelihood of pitting by — (i)

removing weld spatter and associated surface oxide;

(ii)

pickling welds to remove high temperature oxides by using a pickling bath or paste, cont aining a mi xture of nitric and hydrofluoric acids; NOT E: Welds that are not cleaned up will have i nferior c orrosion res ist ance.

(e)

(iii)

avoiding pick-up of carbon steel particles (e.g. use workshop areas and tools dedicated to stainless steel, protect from carbon steel lifting gear, jigs and fixtures); and

(iv)

following a suitable surface maintenance/cleaning program.

Reduce the likelihood of galvanic corrosion by (see Figure C5) — (i)

electrically insulating unlike metals from each other;

(ii)

using paints appropriately—the more active metal and the joint with the more noble metal should be painted;

(iii)

minimizing periods of wetness; and

(iv)

using metals that are close to each other in electrical potential. COPYRIGHT

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Not all items on the check list will give the best detail from a structural strength point of view, and neither are the items intended to be applied to all environments. In particular, in environments of low corrosivity or where regular maintenance is carried out, many will not be required .


FIGURE C4

DESIGN DETAILS TO AVOID DIRT ENTRAPMENT AND CREVICES

NOTE : The i nsul ating material ch osen for the washer, bush and gaske t shoul d be stru cturall y ad equat e to c arry the design loads and should be non-porous.

FIGURE C5

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C8 GRADE SELECTION C8.1 Introduction

The selection of the correct grade of stainless steel should take into account the environment of the application, the fabrication route, surface finish and the maintenance of the structure. The maintenance is usually minimal, and no more onerous than for other metals in decorative applications; merely washing down the stainless steel, even naturally by rain, will markedly assist in extending t he servi ce life. The first step is to characterize the service environment, including reasonably anticipated deviations from the main design conditions. In categorizing atmospheric environments, special attention should be given to highly localized conditions such as proximity to chimneys venting corrosive fumes. Possible future developments or change of use should also be considered. The surface condition of the steel and the temperature, and the anticipated stress, could also be i mportant parameters. Candidate grades can then be chosen to give satisfactory corrosion resistance in the environment.


The selection process should consider which possible forms of corrosion might be significant in the operating environment in accordance with Paragraph C6, which outlines the broad principles underlying the corrosion of stainless steels, and indicates conditions where the use of stainless steels should be free of undue risk and complication. It is also intended to illustrate general points of good practice, as well as the circumstances where stainless steels may have to be used with caution. In these latter conditions, specialist advice should be sought. In many cases, the steels can still be successfully used. The suitability of grades is best evaluated from experience of stainless steels in similar applications and environments, and scrutiny of structures on neighbouring sites is warranted. Caution should be exercised when considering the use of ‘free-machining’ stainless steels for fasteners. The addition of sulfur in the composition of these steels, commonly designated 303 in the austenitic class, reduces their corrosion resistance, especially in industrial and marine environments. This applies particularly to fasteners specified in ISO 3506, grade A1 materials (see Appendix D). C8.2

Grade selection

There are many grades of stainless steel. Paragraphs C8.2.1 to C8.2.8 refer to some of the more common grades, which are readily available in some product forms, particularly the flat products from which cold-formed products are usually made. Further information on other grades is available from the references listed in Paragraph C9, or from steel suppliers. Because of the range of factors that can affect grade selection, specialist advice should always be obtained for specific applications and fabrication processes. C8.2.1

Ferritic grade 409

Ferritic grade 409 is suitable for use in mildly corrosive environments, where some staining and thickness loss due to corrosion can be tolerated. It is generally not available in thicknesses greater than 2 mm, and is not weldable for structural purposes. The main use of this grade is in automotive exhaust systems and in i ndustrial equipment. C8.2.2

Ferritic grade EN 10088 1.4003

Ferritic grade EN 10088 1.4003 is widely available, and can be used in mildly corrosive environments, where some staining due to corrosion can be tolerated. It is available in a range of thicknesses, and is weldable for structural purposes where proper procedures are followed.

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C8.2.3

100

Ferritic grade 430

Ferritic grade 430 is widely available, and is used primarily for decorative purposes in dry, indoor environments, and in white goods. It cannot be welded reliably for structural purposes, and is only availabl e in thinner gauges, up to about 1.6 mm, and usually in BA or No. 4 finish. C8.2.4

Austenitic grade 304

Austenitic grade 304 is the most widely used stainless steel, giving the best combination of strength, corrosion resistance, ductility, fabricability and cost. It is the most widely available in different product forms. This grade can be used in most atmospheric locations (see Table C2), and i n many applications with water of chloride content up to about 200 ppm. It may be susceptible to SCC in the presence of chloride at temperatures in excess of about 60oC. Grade 304 is readily weldable, requiring no preheat, postheat or post-weld heat treatment. The lower carbon grade 304L may be preferred where sensitization issues are of concern. C8.2.5



Austenitic grade 316 is also widely available, and is used where the corrosion resistance of grade 304 is inadequate, particularly in the presence of chloride. The molybdenum content improves resistance to pitting and crevice corrosion, but the SCC performance of grade 316 is similar to that of grade 304. The lo wer carbon grade 316L may be preferred where sensitization issues are of concern. C8.2.6


Austenitic grade 301 is a slightly leaner austenitic grade, which can be temper rolled to high strengths. It is used particularly in transport applications, and in wear applications where a combination of high strength and ductility gives good resistance to abrasive wear. The higher strength tempers are available only in limited thicknesses, and generally on mill enquiry only. C8.2.7

Martensitic grade 420C

Martensitic grade 420C is used for wear components, as it can be heat-treated to very high hardness and strength. It is difficult to weld, and is rarely welded structurally. C8.2.8

Duplex grade S31803

Duplex grade S31803 is the most corrosion resistant of the commonly used grades, due to the high chromium (22%) and molybdenum (3%) contents. It is also significantly higher in strength than the austenitic grades in the annealed condition, and may be used in lighter sections, to offset the higher cost. This grade is especially useful in higher chloride, high stress environments where there is a risk of SCC with the austenitic grades, and where there is a risk of pitting and crevice corrosion. The grade is widely available, although mainly in flat products. C9 REFERENCES

1

Properties and selection, Irons, steels and hi gh-performance alloys, Metals Handbook , 10th Edition, Volume 1, American Society for Metals, Ohio, 1990.

2

Australian stainless reference manual , 3rd Edition, Australian Stainless Steel Development Association, Brisbane, 1998.

3

WTIA Technical Note 13—Stainless steels for corrosive environments, WTIA, Sydney, 1983.

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APPENDIX D

STAINLESS STEEL FASTENERS (Informative) D1 INTRODUCTION

Fasteners are available in a wide range of forms, meeting several Australian and overseas Standards. The most widely available fasteners meet ISO 3506, designated A2 and A4, which corresponds to grades 304 and 316 respectively. Care should be exercised in the use of grade A1(303) as it has markedly inferior corrosion resistance compared to grade A2(304). Other grades available include the following:


(a)

SS2343

Known as ‘Moly plus’ in Europe. This grade has high strength, greater than 800 MPa tensile strength, with greater than 2.5% molybdenum and less than 0.03% carbon.

(b)

3 10

Used parti cularl y in hi gh-t emperat ure appl icati ons , such as furnaces.

(c)

3 21

So me si zes of imperi al co nt inuousl y t hreaded rod ar e avai lable, as wel l as some imperial sizes of bolts.

(d)

301,431,420 Commonly used for smaller items where spring strength is required, e.g. circlips, crinkle washers, rolled spring pins and spiral pins.

Fasteners have also been made to order in other grades, but are generally not stocked. D2 IDENTIFYING STAINLESS STEEL FASTENERS D2.1 General

Metric and imperial sizes that are made to different standards and identification marks for these fasteners, while sometimes similar, may not be the same. Most fasteners available include the manufacturer’s identification mark and the steel grade. Metric fasteners are usually identified in accordance with ISO 3506, including steel grade, propert y class and manufacturer’s identification mark; however, this is a European specification and should be used as a guide only, as it does not describe all fasteners. Most imperial fasteners are made for the large American market and carry a manufacturer’s identification and the AISI steel grade, e.g. 304 or 316. A recent common practice is to use the UNS number instead of the AISI, e.g. S31600 or S30400. Markings generally occur only on hexagon bolts, set screws, socket cap screws and hexagonal nuts of M5 diameter and greater. Fasteners without markings should not immediately be dismissed as unsuitable. Standards may not require such stringent controls or the supplier may be able to furnish a manufacturer’s certificate with the goods to indicate their grade and authenticity. In most cases, it is sufficient only to specify the grade of stainless steels; however, for critical applications, a compliance certificate or letter of conformance is recommended. Full chemical and mechanical certificates are available from reputable suppliers; however, there may be an extra charge associated with these more detailed reports. Certificates should be requested at the point of inquiry and stated on the purchase order. It is normal practice to provide goods without certi ficates or letters of conf ormance.

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D2.2

Identifying stainless steel fasteners to ISO 3506

Hexagon bolts and screws, and hexagon socket head cap screws of size M5 and greater, shall be marked with steel grade, property class and manufacturer’s identification. Hexagon nuts of size M5 or greater shall be marked with steel grade and property class if necessary, and with the manufacturer’s identification where possible. Fasteners not marked or marked only with the stainless steel grade are assumed to correspond with the lowest stainless steel property class. For example, screws marked A2-70 have a tensile strength of 700 MPa. Unmarked screws or those marked A2 or A4 are assumed to be class A2-50 having a tensile strength of 500 MPa (see Figures D1 and D2). The selection of the steels is at the manufacturer’s discretion, provided the steels used correspond with the permitted composition and guarantee — (a)

the required physical and mechanical properties; and

(b)

an equivalent corrosion resistance.

Alloys specified in ISO 3506 and their equivalent common grade designations are given in Table D1. ) d e t n i r p n e h w d e e t n a r a u g t o n y c n e r r u c t n e m u c o D ( 7 1 0 2 v o N 4 1 n o D N A L S N E E U Q N R E H T U O S F O Y T I S R E V I N U y b d e s s e c c A

FIGURE D1

FIGURE D2

MARKING OF BOLTS AND SCREWS

MARKING OF NUTS AND ALTERNATIVE MARKING PRACTICE COPYRIGHT

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TABLE D1 EQUIVALENT ALLOYS Stainless steel grades

Equivalent alloys

Approximate composition

A1

303

18% Cr, 8% Ni, 0.25% S

A2

302, 304,304L, 321, 347

18% Cr, 8% Ni

A4

316, 316L, 317, 317L

18% Cr, 8% Ni, 2-3% Mo

C1

410, 420

12% Cr

C3

431

16% Cr, 1.5% Ni

C4

416

12% Cr, 0.12% C

F1

430

17% Cr

The flow chart shows stainless steel grades suitable for use in accordance with ISO 3506. The manufacturer, however, has the option to use other stainless steels provided they meet the requirements of ISO 3506.


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APPENDIX E

FLEXURAL MEMBERS SUBJECTED TO POSITIVE AND NEGATIVE BENDING (Informative) E1 GENERAL

If the geometrical properties of flexural members are based on the effective design width accounting for flange curling and such a member is subjected to positive and negative bending moments, e.g. in the case of a continuous beam or a rigid frame, Paragraphs E2 and E3 may apply, subject to the limitations specified in Paragraph E4. E2 LOAD-CARRYING CAPACITY [STRENGTH]


The bending moments and the support reactions may be determined assuming constant section beams or frames, provided that the ratio of section moduli for positive and negative bending moments does not exceed the values specifi ed in Paragraph E4. The maximum design bending moments ( M *) so determined should not exceed the nominal member moment capacity ( M b) times φ b calculated in accordance with Paragraph E1 for positive or negative bending moment, as appropriate. E3 DEFLECTIONS

Deflections may be determined assuming constant section beams or frames, and are based on a mean second moment of area, provided that the ratio of second moments of area for posi tive and negative bending moment does not exceed t he value specified in Paragraph E4. E4 LIMITATIONS

For the purpose of Paragraphs E2 and E3, the ratios of geometrical properties of a member for positive and negative bending moments, determined in accordance with this Standard, should not exceed the following: (a)

(b)

Section moduli: (i)

Continuous beams.....................................................................................1.35.

(ii)

Rigid frames .............................................................................................1.25.

Second moment of area: (i)

Continuous beams.....................................................................................1.20.

(ii)

Rigid frames .............................................................................................1.16.

For the purpose of this Paragraph, the section property with the greater value should be taken as the numerator of the ratio. For members with ratios outside the limits specified in this Paragraph, a rational analysis approach may be developed based on testing.

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APPENDIX F

FATIGUE (Informative) F1 GENERAL

The information in this Appendix pertains to the high cycle fatigue properties of structural stainless steel used at or near room temperature, and not in a corrosive environment. It only applies to grades of stainless steel listed in Clause 1.5.2.1.


Euro Inox Design Manual (Ref. 1) and Eurocode 3 (Ref. 2) are two Standards which make recommendations for the fatigue of stainless steel. Euro Inox Design Manual and Eurocode 3 utilize well established fatigue rules for carbon steels and apply them, with some restrictions, to stainless steels. The fatigue provisions of Euro Inox Design Manual, and in particular Eurocode 3 are similar to AS 4100 (Ref. 3) or NZS 3404 (Ref. 14). It is, therefore, recommended that AS 4100 be used for the fatigue design of st ainless steel structures, within the limits of appli cability specified in Paragraphs F2, F3, F4 and F5. F2 WELD FATIGUE

Fatigue is the process by which cracks are initiated and propagate through a structure under cyclical loading until failure. Failure may occur through the component becoming unserviceable because of the size of the resulting fatigue cracks, or alternatively because the component catastrophically fails, i.e. fractures. Fatigue failures may occur without warning and may seriously compromise the capacity of a structure to carry its design load. A further consideration is that fatigue failure will initiate from seemingly minor details in the component. Consequently design and construction to withstand fatigue l oadings requires control of all aspects of the design, fabrication and use of a structure throughout its service life. Generally, fatigue failure of structural steelwork does not occur since the loadings are largely static. Usually the dead load of a structure is large relative to its live load and so the normal strength design is governed by this dead load. In this case the cycling live load stresses would be small and fatigue failure probably would not occur. It is important for the designer to identify when significant cyclical loading are applied to the structure and design for fatigue accordingly. Significant cyclical loadings may be applied to members supporting lifting appliances, rolling loads or vibrating machinery, or for wind-induced oscillations (Ref. 1). Fatigue is normally broken into two regimes depending on the magnitude of the applied stresses. Structural steelwork is normally fatigue loaded in the high cycle regime, whereby the applied stresses are low, and the life of the structure is greater than about 10 4 stress cycles. This is the regime covered by Euro Inox Design Manual and Eurocode 3, as well as AS 4100. In the high cycle regime, the bulk of the structure behaves elastically, and the fatigue design is carried out with references to a stress-life diagram (S-N diagram). At higher stresses there is significant plasticity adjacent to the crack or stress concentration and the strain-life diagram ( ε-N diagram) provides a more discriminating measure of the fatigue history of a structure. Low cycle fatigue is not normally relevant to structural steel work and is not considered in Euro Inox Design Manual, Eurocode 3 and AS 4100. For high cycle fatigue in an unwelded component, cracks are usually initiated at stress concentrations. The magnitude of the stress concentrations in an unwelded component are usually such that this crack initiation phase occupies a large fraction of the component’s life. The fatigue life of an unwelded component depends on the applied maximum principal COPYRIGHT

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stress range, the magnitude and orientation of the stress concentrating feature, thickness, material, material strength, and the presence and sign (tension or compression) of any mean stress. The compressive part of any applied stress state (mean plus applied range) is not damaging in unwelded components and is ignored in a fatigue assessment. Fatigue of welded components differs fundamentally from fatigue of unwelded components (Ref. 4). The differences can be attributed to the following: (a)

The presence of a high tensile residual stress state (high mean stress), typically of yield magnitude in the welded component.

(b)

The high stress concentration factor adjacent to the weld.

(c)

The presence of weld defects.

(d)

The insensitivity of crack propagation rate on mean stress for structural steels.

Unless special precautions are taken to reduce the high stress concentration around the weld in a welded component, the initiation phase of crack growth is typically short. There also may be pre-existing crack like weld defects in the structure. Normally the bulk of the fatigue life of a welded component is spent on pr opagating a crack to failure. ) d e t n i r p n e h w d e e t n a r a u g t o n y c n e r r u c t n e m u c o D ( 7 1 0 2 v o N 4 1 n o D N A L S N E E U Q N R E H T U O S F O Y T I S R E V I N U y b d e s s e c c A

The presence of the high tensile residual stresses of yield magnitude means that when a load is superimposed, the stress range seen by the component effectively cycles from the yield stress downwards by an amount equal to the applied stress range. This means t hat any mean component of an applied stress range may be ignored, and that even fully compressive stress ranges are as damaging as the equivalent fully tensile stress ranges. A further factor is that the crack propagation rate is largely insensitive to the applied mean stress. Another consideration is that in high cycle fatigue of welded structures, the strength of the material is largely irrelevant. Ref. 4 indicates that the S-N curves of welded components up to around 800 MPa UTS are similar. This is in direct contrast to the situation in an unwelded component, where the fatigue life improves with increasing strength. Most structural fatigue Standards contain provisions for fatigue of components with specified yield strengths up to about 700 MPa. The relevant carbon steel high cycle fatigue Standards such as Euro Inox Design Manual, Eurocode 3 and AS 4100 take the above into account when formulating their recommendations. Design for fatigue using these Standards requires identification of the relevant fatigue detail classification. Various types of welded joints are classified into groups according to their capability of resisting fatigue loads. Each of these groups are assigned a unique S-N curve, and this then becomes the fatigue detail classification for the detail or group of details. These detail classifications have been selected based on a large number of fatigue tests on typical welded details. Since this is the case, the fatigue detail classifications typically include the following effects: (i)

Local stress concentration.

(ii)

Typical defects present.

(iii) Metallurgical effects such as weld metal composition and parent plate composition. (iv)

Direction of applied loadings.

( v)

Failure locati on.

(vi)

Residual stress effects.

(vii) Joint preparation and some joint fabrication qualit y issues. Typically the relevant fatigue Standards also provide guidance on the following: (A)

Reduction in fatigue strength due to plate thickness effects.

(B)

Treatment of variable amplitude cycles (Miner’s rule). COPYRIGHT

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(C)

Endurance (constant amplitude) limit.

(D)

Limitations or restrictions on fatigue in corrosive environments.

(E)

Limitations or restrictions on fatigue at high or low service temperatures.

(F)

Maximum material strength limitations.

(G)

Fatigue strength enhancement (if any) due to stress relief.

(H)

Definition of failure and relevant safety factors.

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The relevant high cycle fatigue Standards also specify that the fatigue stress analysis should be elastic onl y, with no allowance made for load redistribution effects through yielding. Other effects that cause load redistribution are usually taken into account, (e.g. shear lag). It should be noted that the highest fatigue strengths, or the highest fatigue detail classifications, are obtained when the effects of stress concentrations and weld defects are minimized. It is instructive to consider potential crack initiation sites and whether the applied loading would open a crack that initiates. A further consideration is that the fatigue life is a strong function of the applied loading. A small reduction in stress range will result in a large increase in fatigue life. ) d e t n i r p n e h w d e e t n a r a u g t o n y c n e r r u c t n e m u c o D ( 7 1 0 2 v o N 4 1 n o D N A L S N E E U Q N R E H T U O S F O Y T I S R E V I N U y b d e s s e c c A

Given the large numbers of variables that are taken into account when testing for and formulating fatigue recommendations for carbon steel structures, it is surprising that Euro Inox Design Manual and Eurocode 3 treat stainless steel high cycle fatigue in a similar manner, and utilize similar S-N curves to carbon steels. Communication with research groups in Europe has indicated that stainless steel fatigue research is ongoing and more extensive fatigue data for stainless steel should be available shortly. Controlling fatigue failure requires control of all details of design, fabrication and use of a component, and even seemingly minor details may act as crack initiation sites causing fatigue failure. In this context it should be noted that stainless steel structures are sometimes fabricated differently to carbon steel structures. The low thermal conductivity and high coefficient of thermal expansion of austenitic stainless steels, compared with carbon steels, results in differing welding techniques to control distortion, compared with the equivalent carbon steel fabrication. Often much more attention is paid to minimizing the amount of welding by using discontinuous welds, which may mean a differing fatigue detail classification for a stainless steel weldment compared with the equivalent carbon steel component. Stainless steels are often utilized for corrosive conditions, while carbon steel fatigue Standards exclude fatigue assessment in corrosive conditions, or alternatively severely derate the fatigue detail classification. Fatigue assessment of stainless steel structures in corrosive conditions is precluded from Euro Inox Design Manual, Eurocode 3 and AS 4100. F3 FATIGUE DESIGN IN ACCORDANCE WITH EURO INOX

The Euro Inox Design Manual stainless steel fatigue recommendations (Ref. 1) are based o n a limited range of stainless steel fatigue tests which were then compared with carbon steel curves from BS 5400 (Ref. 6), and the Offshore Installations Guide (Ref. 7). This comparison indicated that some joints in stainless steel were inferior in fatigue to a similar joint in carbon steel. The recommendation of Euro Inox Design Manual was then that all details in stainless steel be derated one fatigue detail classification from the equivalent detail in carbon steel. Communication with European fatigue researchers indicates that the current perception is that the fatigue properties of stainless steel are not inferior to carbon steel. For this reason Eurocode 3 does not derate the stainless steel fatigue detail classification. Euro Inox Design Manual also contains data on crack propagation rates in stainless steels. It is noted that the crack propagation rates in stainless steels are similar to crack propagation rates in carbon steels. COPYRIGHT

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F4 FATIGUE DESIGN IN ACCORDANCE WITH EUROCODE 3

Eurocode 3 (Ref. 2) uses carbon steel fatigue curves from Eurocode 3 Part 1-1 (Ref. 8), but does not derate the fatigue detail classification when transitioning from a carbon steel joint to a stainless steel joint. Eurocode 3’s fatigue recommendations are based on the ECCS fatigue Standard (Ref. 5). The ECCS’s fatigue requirements are also the basis for the fatigue requirements of AS 4100. In general, the fatigue pro visions of AS 4100 and Eurocode 3 are similar.


The major difference between AS 4100 and Eurocode 3 is that Eurocode 3 gives more extensive guidance on selection of safety factors for fatigue loading. AS 4100 nominates capacity factors for redundant and non-redundant structural elements based on the probability of global structural collaps e because of failure of the weld in question. The capacity factors specified in AS 4100 are also used to account for variations in in-service inspection procedures as well as highly variable loading histories, i.e., where Miner’s Rule may not apply. Eurocode 3 uses ‘partial safety factors’ on the loading and fatigue strength to account for the same variables that AS 4100 specifies. The relevant partial safety factors are the inverse of the equivalent capacity factor. The partial safety factors for fatigue strength used in Eurocode 3 are contained in Table F1. The partial safety factors for the applied fatigue loads are set to 1.0, i .e., no factor is applied to the loading. National Application Documents (NADs) are the mechanism whereby various member countries of the Eurocode organization convert Eurocodes back into national Standards. The Eurocode 3 NAD for Finland (Ref. 12) utilizes the above partial safety factors for fatigue of stainless steels with the following conditions: (a)

Building structures must not use partial safety factors from the ‘fail-safe component’ column.

(b)

Where no periodic inspections are carried out, the appropriate partial safety factor is 1.6.

TABLE F1 PARTIAL SAFETY FACTORS FOR FATIGUE STRENGTH IN ACCORDANCE WITH EUROCODE 3 ‘Fail-safe’

Non ‘fail-safe’

components

components

Periodic inspection and maintenance. Accessible joint d etai l

1.00

1.25

Periodic inspection and maintenance. Poor accessibility

1.15

1.35

Inspection and access

F5 FATIGUE IN ACCORDANCE WITH AS 4100 WITH APPLICATION TO STAINLESS STEEL

The fatigue design of stainless steel structures should comply with the provisions of AS 4100 (Ref. 3). All limitations that are specified in AS 4100 or AS 4100 Supp. 1 (Ref. 11) are to be foll owed. When designing for fatigue of stainless steel structures in accordance with AS 4100, the following are to be considered: (a)

No corrosion or immersion The fatigue recommendations of AS 4100 are restricted to mildly corrosive conditions, where ‘mildly corrosive’ is defined as equivalent to COPYRIGHT

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protected steelwork in a normal atmospheric envi ronment. Since stai nless steel is typically used unprotected, this requirement should be modified. The design of stainless steel in fatigue-loaded applications is restricted to grades of stainless steel appropriate to withstand the corrosive conditions. Note that AS 4100 does not apply to stress corrosion cracking.


(b)

High cycle fatigue only AS 4100 does not apply for stress cycles less than 10 5 cycles, or stress ranges greater than 1.5 σ y. The maximum design stress is limited to σ y. Note that the stress evaluation must be based on elastic analysis or on measured load histories.

(c)

Thermal fatigue AS 4100 only applies to structures that operate at temperatures lower than 150° C.

(d)

Welding AS 4100 requires that detail categories 112 and lower be performed to AS/NZS 1554.1 (Ref. 9), category SP. For detail category 125, AS 4100 requires welding to AS/NZS 1554.5 (Ref. 10). AS/NZS 1554, Parts 1 and 5 are carbon steel welding Standards. Fatigue design of stainless steel structures in accordance with AS 4100 should have equivalent weld defect acceptance and weld inspection criteria as specified in AS/NZS 1554, Parts 1 and 5. Accordingly, in dynamic load situations where AS 1400 requires detail category 112 or l ower, weld imperfections should meet the requirements of category 1B in accordance with AS/NZS 1554.6. Where detail categories greater than 112 are applicable, weld surface imperfections should meet the requirements of Class A in accordance with AS/NZS 1554.6 and weld internal imperfections should meet the requirements of AS/NZS 1554.5. In some circumstances, it may be appropriate or necessary to carry out a fracture mechanics assessment in accordance with BS 7910, provided any defects present do not adversely affect the corrosion resistance of the structure, or conflict with the surface finish requirements of the component.

(e)

Capacity [strength reduction] factor for the weld fatigue The capacity factor in AS 4100 for the weld fatigue strength equals 1.0 assuming the following criteria are met: (i)

The detail is located on a redundant load path, in a position where failure at that point alone will not lead to overall collaps e of the structure.

(ii)

The stress history is estimated by conventional methods.

(ii)

The load cycles are not highly irregular.

(iii)

The detail is accessible for, and subject to, regular inspection.

The capacity factor is reduced if any of Items (e)(i) to (iii) do not apply. A capacity factor of 0.7 or lower is nominated if the detail is located on a non-redundant load path. Further guid ance on the selectio n of capacity factors lower than 0.7, given the above criteria, may be made with reference to the partial safety factors of Eurocode 3 and the relevant NAD’s (e.g. Ref. 12). (f)

Thickness correction for plates thicker than 25 mm ECCS (Ref. 5) recommends caution when applying the fatigue rules to plates thicker than 25 mm, since at the time of publication of ECCS, only a limited range of fatigue tests had taken place on plates thi cker than 25 mm. These tests were limited to transversely welded details in joi nts between equal thickness plates. ECCS gives guidance on the applicability of fracture mechanics for resolving such situations.

It may be that there are some situations where the use of the standard S-N curve approach to fatigue is not adequate, and a fracture mechanics approach may be more applicable. In this situation the requirements from ECCS (Ref. 5) may be followed.

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Situations that may require consideration of fracture mechanics include the following (Ref. 5): (i)

When the remaining fatigue life of a cracked structure is assessed.

(ii)

When fitness for purpose is assessed.

(iii)

When plate thicknesses is greater than 25 mm and there is doubt as to the applicability of the fatigue curves.

(iv)

When the effect of varying one or more geometry or stress parameters is being considered for a given detail.

(v)

When in-service inspection intervals are being fixed.

(vi)

When an unusual stress direction, not comparable with any detail category, is being assessed.

F6 REFERENCES


1

Euro Inox Design Manual for Structural Stainless Steel , Nickel Development Institute, 1994.

2

Eurocode 3: Design of Steel Structures, Part 1-4: General rules — Supplementary rules for stai nless st eels, CEN, 1996.

3

AS 4100—1998, Steel Structures, Standards Australia, 1998.

4

Gurney T. R., Fati gue of Welded Structures, Cambridge University Press, 1978.

5

Recommendations for the Fatigue Design of Steel Structures, ECCS — Technical Committee 6 — Fatigue, European Convention for Constructional Steelwork, 1985.

6

BS 5400, Part 10:, ‘Steel, concrete and composite bridges, Part 10: Code of practice for fatigue’, British Standards Institution, 1980.

7

Offshore Installations: Guidance on design, construction and certification, Health and Safety Executive, 4 th Edition, 1990.

8

Eurocode 3: Design of Steel Structures, Part 1-1: General rules and rules for buildings, CEN, 1992.

9

AS/NZS 1554.1: Structural steel welding , Part 1: Welding Standards Australia/Standards New Zealand, 2000.

10

AS/NZS 1554.5: Structural Steel Welding , Part 5: Welding of steel structures subject to high levels of fatigue loading , Australian Standards/Standards New Zealand, 1995.

11

AS/NZS 1554.6: Structural steel welding , Part 6: Welding stainless structural purp oses, Standards Australia/Standards New Zealand, 1994.

12

AS 4100: Steel structures, Standards Australia, 1998.

13

AS 4100 Supplement 1 — 1999, Steel Structures — Commentary, Standards Australia, 1999.

14

NZS 3404.1: Steel structures Standard , Part 1: Steel structures Standard , Standards New Zealand, 1997.

15

NZS 3404.2: Steel structures Standard , Part 2: Commentary to the Steel Structures Standard , Standards New Zealand, 1997.

16

Draft National Application Document for prestandard Eurocode 3: Design of steel structures, Part 1-4: General rules — Supplementary rules of stainless steels, National Building Code of Finland, 1998.

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APPENDIX G

FIRE (Informative) G1 GENERAL

At this stage, Standards Australia/Standards New Zealand is not in a position to provide design rules for determination of the period of structural adequacy (PSA) for stainless steel structures. This Appendix outlines the approach to the design of steel building elements required to have a fire resistance level (FRL), currently adopted by some overseas Standards. G2 PROPERTIES OF STAINLESS STEELS


It has long been recognized that some stainless steels retain their mechanical properties, e.g. stiffness and strength, at elevated temperatures better than carbon steels. For this reason, stainless steel elements in buildings may be able to achieve a required FRL with less fire protection than would be required for the equivalent carbon steel element, or in some cases with no fire protection. Fire tests may be used to determine the PSA for a specific element, provided the test accurately reflects the conditions in the actual structure; however, fire tests are expensive and hence may only be feasible for large projects. The use of calculation methods to determine the PSA for carbon steel elements is well established in several Standards, such as AS 4100 and Eurocode 3; however, this is not the case in relation to stainless steels, in that the advantages of stainless steel are not yet formally recognized in Standards such as Eurocode 3. Research in Finland and the UK has focused on the fire performance of some of the more commonly used austenitic stainless steels. The results of this research has resulted in recommendations for the fire design of stainless steel elements in the current draft of the Finnish national application document for Eurocode 3 and is expected to be more formally incorporated into the relevant section of Eurocode 3 when it is upgraded from a preStandard (ENV) to a Standard ( EN). G3 OTHER STANDARDS

This Standard has been mainly based on ANSI/ASCE-8-90, Specification for the Design of Cold-Formed Stainless Steel Structural Members, which contains no guidance on the fire design of stainless steel members. ENV 1993-1-4: Eurocode 3: Design of steel structures, Part 1-4: General rules— Supplementary rules for stainless steel states that for structural fire design, reference should be made to ENV 1993-1-2, which is Eurocode 3— Design of steel structures, Part 1-2: General rules, Structural fire design. However, this Part of Eurocode 3 applies to the fire design of carbon steel. Reference is also made in ENV 1993-1-4 to EN 10088 Stainless steels, which is the stainless steel materials Standard, for information on the properties of stainless steels at elevated temperat ures. The current draft of the National Application Document for Finland, for use in conjunction with Eurocode 3, contains specific data for the reduction factors for stainless steels at elevated temperatures, for a range of austenitic stainless steels. This data, in conjunction with ENV 199-1-2, enables the relevant calculations for the fire design of stainless steel members to be carried out. COPYRIGHT

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Pending the release of EN 1993-1-4 , the Draf t National Appl ication Document for prestandard SFS-ENV 1993-1-4, forming part of the National Building Code of Finland, used in conjunction with ENV 199-1-2, appears at this stage to contain the most specific guidance on the fire design of stainless steel members manufactured from certain specific grades of austenitic stainless steel. G4 POST-FIRE PERFORMANCE

Where temperatures in the range of 350 to 850°C are experienced, various precipitates may form, which may adversely affect corrosion resistance, i.e. sensitization or toughness, due to embrittlement.


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APPENDIX H

SECTION PROPERTIES (Normative) H1 SHEAR CENTRE DISTANCE ( m), TORSION CONSTANT ( J ) AND WARPING CONSTANT ( I w)

Values of m, J and I w for certain sections are shown in Fi gure H1. For I w of sections other than those given in Figure H1, I w shall be taken as zero for box sections. H2 MONOSYMMETRY SECTION CONSTANTS

Monosymmetry section constants are calculated as follows:


β

=

β y

=

x

l I x

l I y

(∫

A x

(∫

A xy

2

yd A +

2

d A +

∫

A

y 3 d A

∫ x A

3

) − 2 y

d A

. . . H2(1)

o

)− 2 x

o

. . . H2(2)

Where the x-axis is the axis of symmetry (see Table H1) —

β x

=0

β y

=

β w

. . . H2(3)

+ β f + β L I y

− 2 xo

. . . H2(4)

NOT ES: 1

For doubly symmetric sections, β x = 0 and β y = 0.

2

In the calculation of β y using the value of x o , determined from Table H1, x o and x- are to be taken as negative.

Where the y-axis is the axis of symmetry, interchange x and y in the equations for the x-axis of symmetry and Table H1.

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AS/NZS 4673:2001


FIGURE H1

114

SHEAR CENTRE DISTANCE, TORSION CONSTANT AND WARPING CONSTANT FOR CERTAIN SECTIONS

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NOTES TO FIGURE H1: 3

∑ bt

1

For all open section: J =

2

For members cold-formed from a single steel sheet of uniform thickness: J =

3

.

the flat sheet. 3

For the box and rectangle sections, I w is negligibly small in comparison to J .


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wf t 3 where wf is the feed width of 3


TABLE H1 CERTAIN MONOSYMMETRIC SECTIONS—CENTROID AND SHEAR-CENTRE DISTANCES AND MONOSYMMETRY SECTION CONSTANTS Section

– x

x o

β β w

β β f

β β L

( + x)4 − ( x)4  +   2 2 l 2  a t (b + x ) − ( x )  4  

0

l 2

b a + 2b

C O P Y R I G H T

b ( b + 2c) a + 2b + 2c

2

2

1

3b b + a + 2b 6b + a

bt (b + 2c ) A

+

12

t x a3 + t ( x )3 a

12

l

bt 1

12 I x

12

(6 ca2 + 3ba2 − 8 c3 )

t x a3 + t ( x )3 a

2 l 4

 

t (b + x )4

( 

LEGEND: s.c. = shear centre c.g. = centre of gravity

b (b + 2c)

bt (b + 2c) A

(6 ca

2

+

bt

1

12 I x

12

2

+ 3 ba − 8 c

3

)

t x a3 + t ( x )3 a

12 l 4

( 

t  b + x

( 

(

4 − ( x )  + 

a 2 t  b + x

l a + 2b + 2c

t  b

2 ct x + b

)2 − ( x)2  

)4 − ( x)4  +

a 2 t  b + x

)2 − ( x)2  

)3 + 23 t ( x + b)

1 1 6

 a  3  a  3   + c  −     2   2  

(

2 ct x + b

)3 + 23 t ( x + b)

 a  3  a  3    −  − c    2   2  

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APPENDIX I

UNSTIFFENED ELEMENTS WITH STRESS GRADIENT (Normative) TABLE I1 PLATE BUCKLING COEFFICIENTS ( k ) AND EFFECTIVE WIDTHS ( be) Stress distribution

Effective width ( be )

(compressive positive)

For 1 > ψ ≥ 0:

b e = ρ b ) d e t n i r p n e h w d e e t n a r a u g t o n y c n e r r u c t n e m u c o D ( 7 1 0 2 v o N 4 1 n o D N A L S N E E U Q N R E H T U O S F O Y T I S R E V I N U y b d e s s e c c A

For ψ < 0:

be

ψ = f 2* / f 1* Plate buckling coefficient ( k )

= ρ bc =

ρ b 1 − ψ

+1

0

−1

0.43

0.57

0.85

+1

≥ ψ ≥ − 1

0.57 – 0.21 ψ + 0.07 ψ 2

For 1 > ψ ≥0:

be = ρ b

For ψ < 0:

be

ψ = f 2* / f 1* Plate buckling coefficient ( k )

= ρ bc =

+1

1 > ψ > 0

0

0.43

0.578

1.70

ρ b 1 − ψ

0 > ψ >

1.70 − 5 ψ + 17.1 ψ 2

ψ + 0.34 NOTE :

f 1* and f 2* are web stresses calculated on the basis of the full section.

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−1 23.8

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APPENDIX J

HOLLOW SECTION LATTICE GIRDER CONNECTIONS (Normative) J1 GENERAL

This Appendix provides rules to determine the static design capacity of uniplanar joints in lattice structures composed of rectangular, square or circular hollow sections, or combinations of these hollow sections with open sections. The static design capacities of the joints are expressed in terms of maximum design axial resistances for the brace members. This Appendix applies to both, hot-rolled and col d-formed hollow sections.


The welds shall be designed to have sufficient capacity and ductility to allow redistribution of non-uniform stress distributions and to allow redistribution of secondary bending moments. The nominal wall thickness of hollow sections shall be greater than or equal to 2.5 mm but less than or equal to 25 mm, unless special measures have been taken to ensure that the through thickness properties of the material will be adequate. The joint capacity [strength reduction] factor ( φ ) shall be taken as 0.9. J2 DEFINITIONS

The definitions below apply to this Appendix. J2.1

Gap ( g )

The distance measured along the length of the connecting face of the chord, between the toes of the adjacent members (see Figure J1). J2.2

Uniplanar joint

A connection between members that are situated in a single plane and which transmit primarily axial f orces. J2.3

Overlap (λ ov )

λ ov

 q  =    × 100% p  

(see Figure J1)

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FIGURE J1


AS/NZS 4673:2001

GAP AND OVERLAP JOINTS

J3 FIELD OF APPLICATION

This Appendix may be used only where all of the followin g conditions are satisfied: (a)

Members shall have compact cross-sections as specified in Clauses 3.6.2 and 3.6.3 for rectangular and circular hollow sections respectively.

(b)

The angles between the chords and the brace members, and between adjacent brace members shall not be less than 30 ° .

(c)

Moments resulting from eccentricities may be neglected in calculating the resistance of the joint, pr ovided that the eccentricities are within the following li mits:

− 0.55d o ≤ e ≤ 0.25d o − 0.55ho ≤ e ≤ 0.25ho

(i) (ii) where e

d o ho

= = =

eccentricity as shown in Figure J2 diameter of the chord depth of the chord, in th e plane of the lattice girder

(d)

Members at a joint shall have their ends prepared in such a way that their cross-sectional shape is not modified.

(e)

In gap-type joints, the gap between the brace members shall not be less than ( t 1 to ensure that the clearance is adequate to form satisfactory welds.

(f)

In overlap joints, the overlap shall be sufficient to ensure that the interconnection of the brace members is adequate for satisfactory shear transfer from one brace to the other.

(g)

Where overlapping brace members have different thicknesses, the thinner member shall overlap the thicker member.

(h)

Where overlapping brace members are of different strength grades, the member with the lower yield stress shall overlap the member with the hi gher yield stress.

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FIGURE J2

ECCENTRICITY OF JOINTS

J4 ANALYSIS

The axial force distribution in a lattice girder may be determined on the assumption that the members are connected by pinned joints. Secondary moments in the joints caused by the actual bending stiff ness of the j oints may be neglected, provided that — (a)

the joint geometry is within the range of validity given in Tables J6.1, J7.1 or Table J8.1, as appropriate; and

(b)

the ratio of the length of the system to the depth of the members in the plane of the girder is not less than — (i)

12 for chord members; and

(ii)

24 for chord members.

Eccentricities that are within the limits specified in Paragraph J3 may be neglected. The joints are predominantly statically loaded. J5 WELDS

In welded connections, the connection shall be established around the entire perimeter of the hollow section by means of butt or fillet welding, or combinations of both. In partially overlapping joints, the hidden part of the connection need not be welded. The design resistance of the weld per unit length of the perimeter shall not be less than the design tensile resistance of the cross-section of the member per unit length of the perimeter. For Class B fillet weld, this requirement can be met provided the t hroat thickness (t t) satisfies the following: t t t 1

 f  ≥ 1.875 y    f uw 

. . . J5(1)

The requirement of this Paragraph may be waived where smaller weld sizes can be justified with regard to the resistance and to the deformation capacity or rotation capacity, or both. COPYRIGHT

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J6 WELDED JOINTS BETWEEN CIRCULAR HOLLOW SECTIONS

The design internal axial forces, in both the brace members and in the chords, shall not be greater than the design resistances of the members determined in accordance with Section 3. In addition, for brace members, the design internal axial forces shall not be greater than the resistances of the joints. Provided that the geometry of the joints is within the range of validity given in Table J6.1, the design resistances of the joints shall be determined using the equations given in Table J6.2. For joints outside the range of validity given in Table J6.1, a detailed analysis shall be made. This analysis shall take account of the secondary moments in the joints caused by the bending stiffness of the joints.

TABLE J6.1 RANGE OF VALIDITY FOR WELDED JOINTS BETWEEN CIRCULAR HOLLOW SECTIONS ) d e t n i r p n e h w d e e t n a r a u g t o n y c n e r r u c t n e m u c o D ( 7 1 0 2 v o N 4 1 n o D N A L S N E E U Q N R E H T U O S F O Y T I S R E V I N U y b d e s s e c c A

≤ d i/d o ≤ 1.0 5 ≤ d i/2t I ≤ 25 5 ≤ d o /2t o ≤ 25 5 ≤ d o /2t o ≤ 20

0.2

(for X-joints)

λ ov ≥ 25% g

≥ t 1 + t 2

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TABLE J6.2 DESIGN RESISTANCES OF WELDED JOINTS BETWEEN CIRCULAR HOLLOW SECTIONS Design resistance

Type of joint

( i = 1 or 2)

Chord plastification

ϕ N l n

=

f yot o2 sinθ 1

ϕ  ( 2.8 + 14.2β 2 )γ 0.2k p   0.9 







ϕ N l n

=

f yot o2

 5.2   ϕ    k p   sinθ 1  (1 − 0.81β )    0.9 


ϕ N l n ϕ N 2 n

T, Y and X joints, and K, N and KT joints with a gap When d i

≤ d o − 2t o

   ϕ  1.8 + 10.2   k pk g   d 1     sinθ 1  0.9    d o     sinθ 1   =   N 1n  sinθ 2 

=

f yot o2

Punching shear

ϕ N l n

 1 + sinθ i   ϕ   f    =  yo  π t d  o i  2sin 2θ   0.9  3     i 

where for n p ≤ 0 (tension)

k p = 1.0 k p

= 1 − 0.3 n p 1 + n p

for n p ≤ 0 (compression)

For k p ≤ 1.0 k g

= γ

0.2

  0.024 γ 1.2 1 +   exp (0.5g / t o ) − 1.33) + 1 

(see Figure J3)

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FIGURE J3

AS/NZS 4673:2001

VALUES OF FACTOR ( k g )

J7 WELDED JOINTS BETWEEN HOLLOW SECTION BRACE MEMBERS AND SQUARE/RECTANGULAR HOLLOW SECTION CHORDS J7.1 General

The design internal axial forces, in both the brace members and in the chords, shall not be greater than the design resistances of the members determined in accordance with Section 3. In addition, for brace members, the design internal axial forces shall not be greater than the resistances of the joints. J7.2

Square or circular brace members and square chords

Provided that the geometry of the joints is within the range of validity given in Table J7.1, the design resistances of the joints shall be determined using the equations given in Table J7.2. For joints outside the range of validit y given in Table J7.1, see Paragraph J7.3. J7.3

Rectangular sections

The design capacities of joints between rectangular hollow sections, and of joints between square hollow sections outside the range of validity given in Table J7.1, shall be based on the following criteria, as applicable: (a)

Plastic failure of the chord face or the chord cross-section.

(b)

Crack initiation leading to rupture of the bracings from the chord (punching shear).

(c)

Cracking in the welds or in the bracings (effective widths).

(d)

Chord wall bearing of local bucklin g under the compression bracing.

(e)

Local buckling in the compressive areas of the members.

(f)

Shear failure of the chord.

The modes of failure relevant to Items (a) to (f) are given in Figure J4. COPYRIGHT


TABLE J7.1 RANGE OF VALIDITY FOR WELDED JOINTS BETWEEN SQUARE OR CIRCULAR HOLLOW SECTION B RACE MEMBERS AND SQUARE HOLLOW SECTION CHORDS

A S / N Z S 4 6 7 3 : 2 0 0 1

Joint parameters ( i = 1 or 2, and j = overlapped brace)

bi

Type of joint

or

t i

bi or d i bo

b1 + b2

d i t i

Compression

0.25 ≤

K gap joint

C O P Y R I G

bi bo

N gap j oint

H T

bi bo

10 ≤ bi t i

≤ 1.25

bi

bi

t i

≥ 0.35

t o

≤ 35

≤ 35

bi bo

≥ 0.25

bi t i

≤ 1.1

0.4 ≤

d i bo

≤ 0.8

d i t i

≤ 1.5

— g

15 ≤ bi t i

≤ 35

bo t o

≤ 35

0.6 ≤

b1 + b2

E o

bo

F χ i

t o

E o

d i

F χ i

t i

≤ 50

2b1

bo

≤ 1.3

≥ 0.5 (1 − β )

but

g bo

≤ 40

t j bi

+ t 2

≤ 1.0 25%

≤ λ ov ≤ 100%

≥ 0.75

As above but replace b 1 with d 1

NOTE : Outside thes e parame ter rang es, the resi stance of the join t may be deter mined as for a joint with a r ectan gular chord sect ion (see Pa ragr aph F7. 3).

124

≥ 1.5 (1 − β )

and g ≥ t 1

b j Circular brace member

Gap or overlap

—

t i K overlap joint N overl ap j oint

t i t j

F χ i

and

and bo

E o

bo

or

and

b j

Tension

≤ 0.85

  b   ≥ 0.1 + 0.1 + 0.01 o    a  t o   

bi

t o

bo

T, Y or X joint

2b1

bo

1 2 4

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TABLE J7.2 DESIGN RESISTANCES OF WELDED JOINTS BETWEEN SQUARE OR CIRCULAR HOLLOW SECTION BRACE MEMBERS AND SQUARE HOLLOW SECTION CHORDS Design resistance

Type of joint

( i = 1 or 2, j = overlapped brace)

β ≤ 0.85

Chord face yielding

ϕ N ln

=

f yo t o2

(1 − β )sinθ i

 2 β  ϕ  0.5   sinθ + 4 (1 − β )  k n  0.9   1   

β ≤ 1. 0

Chord face yielding ) d e t n i r p n e h w d e e t n a r a u g t o n y c n e r r u c t n e m u c o D ( 7 1 0 2 v o N 4 1 n o D N A L S N E E U Q N R E H T U O S F O Y T I S R E V I N U y b d e s s e c c A

ϕ N ln

=

8.9 f yo t o2 sinθ i

 b1 − b2  0.5  ϕ   2b  γ k n  0.9    o  

Effective width

ϕ N ln

25%

λ ϕ  = f yi t i  ov (2hi − 4t i ) + beff + be.ov      50   0.9 

Effective width

ϕ N ln

50%

Circular braces

≤ λ ov < 80 %

ϕ  = f yi t i [2hi − 4t i + beff + be.ov ]     0.9 

λ ov ≥ 80%

Effective width

ϕ N ln

≤ λ ov < 50 %

ϕ  = f yi t i [2hi − 4t i + bi + be.ov ]     0.9 

— Multiple the above design resistances by π /4. — Repla ce b 1 and h 1 with d 1. — Repla ce b 2 and h 2 with d 2. Functions

For n ≤ 0 (tension): k n = 1.0

  10    f yo t o  bi but beff ≤ bi    bo t o   f yit i  

beff = 

For n ≥ 0 (compressi on): k n

beff

= 1.3 -

0.4n

β

but k n

≤ 1.0

 10   f yi t j     = ≤  b j t j   f yit i  bi but be.ov bi    

NOTE : Only the over lapping brac e needs to be checked. The brace member effi ciency, i.e. the desi gn resi stan ce of the joint divided by the design plastic resistance of the brace, for the overlapped brace should be taken as less than or equal to the o verlapping brace.

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FIGURE J4

MODES OF FAILURE — RECTANGULAR HOLLOW SECTIONS

J8 WELDED JOINTS BETWEEN BETWEEN HOLLOW SECTION BRACE MEMBERS MEMBERS AND I-SECTION CHORDS

The design internal axial forces in the brace members and in the chords shall not be greater than the design capacity of the members determined in accordance with Section 3. In addition, the design internal axial forces in the brace members shall also not be greater than the design capacities of the joints. In gap-type joints, the tensile design capacities ( φ N t to to ) of the chords allowing for shear force transferred between the brace members by the chords and neglecting the relevant secondary moments shall be determined as follows: (a)

For

V o*

≤ 0.5 :

. . . J8(1)

N to

= f yo Aoφ t

. . . J8(2)

ϕ t

= 0.85

ϕ vV vo

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(b)

For 0.5 <

V o*

ϕ uV no

≤ 1.0 :

. . . J8(3)

2   2V *    − 1 N to = f yo  Ao − Avo   φ V   v v  

ϕ t

AS/NZS 4673:2001

. . . J8(4)

= 0.85

where φv and V v shall be determined in accordance with Clause 3.3.4 and Avo is the web area of the chord transferring the shear force. Provided that the geometry of the joints is within the range of the validity given in Table J8.1, the design capacities of the joints shall be determined using the equations given in Table J8.2. For joints outside the range of validity given in Table J8.1, a detailed analysis shall be made. This analysis shall take account of the secondary moments in the joints caused by the bendin bend ing g stiff st iffness ness of the joint jo ints. s. ) d e t n i r p n e h w d e e t n a r a u g t o n y c n e r r u c t n e m u c o D ( 7 1 0 2 v o N 4 1 n o D N A L S N E E U Q N R E H T U O S F O Y T I S R E V I N U y b d e s s e c c A

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Accessed by UNIVERSITY OF SOUTHERN QUEENSLAND on 14 Nov 2017 (Document currency not guaranteed when printed) A S / N Z S 4 6 7 3 : 2 0 0 1

TABLE J8.1 RANGE OF VALIDITY FOR WELDED JOINTS B ETWEEN HOLLOW SECTION BRACE MEMBERS AND I-SECTION CHORDS Joint parameter ( i = = 1 or 2 and j = = overlapped brace) Type of joint

hi

b j

d w

bo

bi

bi

t w

t o

bi t i C o mp r e s s i o n

d w X joint C O P Y R I G H T

0.5 ≤

hi bi

≤ 2.0

—

t w

≤ 1.2

hi

≤ 400 mm

t i

T joint

bo hi

t o

K gap joint

bi

= 1.0

—

t w

N ga p join j ointt K overlap joint N o verlap verl ap j oint oin t

≤ 1.5

E o f yo

and 0.5 ≤

hi bi

≤ 2.0

bd bi

≥ 0.75

d w

t i

,

d i t i Te nsi on

f yo

Y joint

d w

hi

E o

and d w

,

≤ 400 mm

≤ 0.75

E o

bi

f yo

t i d i t i

≤ 1.1

E o f y1

hi t i

≤ 1.1

E o

bi

f y1

t i

≤ 1.6

E o f y1

d i t i

≤ 35 ≤ 35 ≤ 50

1 2 8

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TABLE J8.2 DESIGN RESISTANCES OF WELDED JOINTS BETWEEN HOLLOW SECTION BRACE MEMBERS AND I-SECTION CHORDS Design resistance ( i = 1 or 2 and j = overlapped brace)

Type of joint

Chord web yielding

ϕ N 1n

=

f yo t w bw sin θ 1

 ϕ     0.9 

Effective width

ϕ N 1n

ϕ  = 2 f y1 t 1beff     0.9 

Chord web stability f yo t w bw  ϕ  ϕ N 1n =   sin θ 1  0.9 


Effective width

ϕ N 1n

ϕ  = 2 f y1 t 1beff     0.9 

Effective width check not required if — g

(a)

t f

≥ (20 − 28β ) ;

(b)

β ≤ (1.0 − 0.03γ ) ;

(c)

0.75 ≤

(d)

0.75 ≤

d 1 d 2 b1 b2

≤ 1.33 for CHS; and ≤ 1.33 for RHS.

Chord shear

ϕ N 1n

=

f yo A v 3

 ϕ    sin θ 1  0.9  25% ≤ λ ov < 50%

Effective width

ϕ N 1n

 λ  ϕ  = f yit i  ov (2hi − 4t i ) + beff + be.ov      50   0.9  50% ≤ λ ov < 80%

Effective width

ϕ N 1n

ϕ  = f yit i [2hi − 4t i + bi + be.ov ]     0.9  λ ov ≥ 80%

Effective width

ϕ N 1n

ϕ  = f yit i [2hi − 4t i + bi + be.ov ]     0.9 

Functions For RHS: hi

(a)

bw

=

(b)

bw

≤ 2t i + 10 (t f + r )

sin θ 1

+ 5 (t f + r )

Av

= Ao − (2 − a ) bot f + (t w + 2r ) t f

For RHS brace:

a

 1 = 1 + ( 4 g 2

For CHS brace:

a

=0

 0.5  3t f 2 ) 

For CHS: d i

(a)

bw

=

(b)

bw

≤ 2t i + 10 (t f + r )

beff

sin θ 1

+ 5 (t f + r )

 f  = t w + 2r + 7  yo   t f but beff ≤ bi  f yi 

be.ov

 10   f yjt j     bi but be.ov ≤ bi =     b t f t  j j   yi i 

NOTE : Only the over lapping brace needs to be checked. The brac e membe r effi cien cy, i.e. the design resi stan ce of the joint divided by the design plastic resistance of the brace, for the overlapped brace should not be greater than the overlapping brac e. COPYRIGHT

130

AS/NZS 4673:2001

APPENDIX K

DETERMINATION OF THE CAPACITY [STRENGTH REDUCTION] FACTOR (Normative) This Appendix applies to situations where statistical data is available for the mean ( M m) and coefficient of variation (V M) of the ratio of measured yield stress to nominal yield stress. It provides the reducti on in capacity [strength redu ctio n] factor (φ ), which shall be applied when the design is based on the measured yield stress. Where the design shall be based on the mean value of measured yield stress, M m shall be taken as unity. Where applied to the production of cold-formed members, where the yield stress is enhanced by the forming process and the nominal yield stress of the finished product shall be used for desi gn, M m and V M are the mean and coefficient of variation of the ratio of measured yield stress to nominal yield stress of the finished product respectively. ) d e t n i r p n e h w d e e t n a r a u g t o n y c n e r r u c t n e m u c o D ( 7 1 0 2 v o N 4 1 n o D N A L S N E E U Q N R E H T U O S F O Y T I S R E V I N U y b d e s s e c c A

When V M is less than or equal to 0.15, the reduced capacity [strength reduction] factor shall be determined by substituting the stat istical values of M m and V M into —

φ

=

M m M mo

(1 + cV Mo2 )(1 − cV M2 ) φ o ≤ φ o

. . . K1(1)

where φ o is the capacity [strength reduction] factor given in thi s Standard, and— M mo V Mo c c

= = = =

1.1 0.1 5.0 for members 6.5 for fasteners

The capacity [strength reduction] factor ( φ ) shall not be greater than the reference value (φ o). When V m is greater than 0.15, the reduced capacity [strength reduction] factor shall be determined by substituting the statistical values of M m and V M into —

φ

=

M m M mo

2 exp  β   V Mo

 

+ V Fo2 + V Po2 + V Qo2 −

V M2

+ V Fo2 + V Po2 + V Qo2   φ o ≤ φ o  

. . . K1(2)

φo is the capacity [strength reduction] factor, and — M mo = 1.1 V Mo = 0.1 F mo = 1.0 V Fo = 0.05 V Po = 0.15 V Qo = 0.21 β = 3.0 for members β = 4.5 for fasteners

where

The capacity [strength reduction] factor shall not be greater than the reference value ( φ o).

COPYRIGHT

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As 4673 - 2001 Cold Formed Stainless Steel Structures Unlocked

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