SABS 0162-2 Part II-Limit-states Design of Cold Formed
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UDC 693.814 ISBN 0-626-09270-1 SABS 0162=2:1993 Code of practice The structural use of steel Part 2: Limit-states design of cold-formed steelwork Published by THE COUNCIL OF THE SOUTH AFRICAN BUREAU OF STANDARDS Gr 14
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SABS 0162 IS SOUTH AFRICAN CODE
Transcript of SABS 0162-2 Part II-Limit-states Design of Cold Formed
UDC 693.814 ISBN 0-626-09270-1 SABS
0162=2:1993
Code of practice
The structural use of steel
Part 2: Limit-states design of cold-formed steelwork
Published by THE COUNCIL OF THE SOUTH AFRICAN BUREAU OF STANDARDS Gr 14
SABS 0 162-2: 1993
Amdt No. Amendments issued since publication
Date Text affected
UDC 693.814 SABS 01 62-2: 1993
SOUTH AFRICAN BUREAU OF STANDARDS
CODE OF PRACTICE
THE STRUCTURAL USE OF STEEL
PART 2: LIMIT-STATES DESIGN OF COLD-ROLLED STEELWORK
Obtainable from the
South African Bureau of Standards Private Bag XI91 Pretoria Republic of South Africa 0001
Telephone : (012) 428-791 1
E-mail : [email protected] Website : http://www.sabs.co.za
Fax : (012) 344-1568
COPYRIGHT RESERVED
Printed in the Republic of South Africa by the South African Bureau of Standards
SABS 01 62-2: 1993
Acknowledgement
The South African Bureau of Standards wishes to acknowledge the valuable assistance of the South African Institute of Steel Construction in the preparation of this part of SABS 0162, which is based on the Canadian Standards Association standard CAN/CSA-S136-M89, Cold formed steel structural members.
Notice
This part of SABS 0162 was approved by the Council of the South African Bureau of Standards on 25 February 1993.
NOTES
1 In terms of the regulations promulgated under the Standards Act, 1982 (Act 30 of 1982), it is a punishable offence for any person to falsely claim compliance with the provisions of a code of practice published by the South African Bureau of Standards.
2 Authorities who wish to incorporate any part of this code of practice into any legislation in the manner intended by section 33 of the Act should consult the South African Bureau of Standards regarding the implications.
This part of SABS 0162 will be revised when necessary in order to keep abreast of progress. Comment will be welcomed and will be considered when this part of SABS 0162 is revised.
Foreword
The technical committee responsible for this part of SABS 0162 decided that it should be based on the Canadian standard CAN/CSA-S136-M89.
This part of SABS 0162 is compatible with section 4 of SABS 0160, The general procedures and loadings to be adopted in the design of buildings.
SABS 0162 consists of the following parts’), under the general title The structural use of steel:
- Part 1: Limit-states design of hot-rolled steelwork.
- Part 2: Limit-states design of cold-formed steelwork.
1) SABS 0162:1984, as amended, has, for practical purposes, been renumbered SABS 0162-3 but is expected to fall away sometime in the future.
ISBN 0-626-09270-1
ii
SABS 01 62-2: 1993
Contents
Acknowledgement ...............................................................................................................
Notice ............................................................................................................................
Foreword ............................................................................................................................
Committee ............................................................................................................................
Scope and application ...................................................................................................
1.1 Scope .................................................................................................................. 1.2 Application ..........................................................................................................
Definitions. symbols and units .......................................................................................
2.1 Definitions .......................................................................................................... 2.2 Symbols ............................................................................................................. 2.3 Units ................................................................................................................... 2.4 Normative references .........................................................................................
Materials .........................................................................................................................
3.1 Standard steels ................................................................................................... 3.2 Other steels ....................................................................................................... 3.3 Physical properties ............................................................................................
Loads and limit-state criterion ........................................................................................
4.1 Loads ................................................................................................................. 4.2 Limit-states criterion ..........................................................................................
General design considerations ......................................................................................
5.1 5.2 5.2.1 5.2.2 5.2.3 5.3 5.4 5.5 5.6 5.6.1 5.6.2 5.6.3 5.6.4
General .............................................................................................................. Coldwork of forming .......................................................................................... Application ......................................................................................................... Fully effective elements ..................................................................................... Elements not fully effective Maximum effective slenderness ratio for members in compression Maximum flat width ratios for elements in compression Maximum section depths ................................................................................... Properties of sections ......................................................................................... General ............................................................................................................... Effective design width of elements in compression ........................................... Shear lag effects ................................................................................................. Curling of flanges ...............................................................................................
.......... , .................................................................... ................
...................................
Page
II
ii
II
vii
1
1 1
1
1 4
10 11
12
12 12 13
13
13 13
13
13 13 13 14 14 15 15 15 16 16 16 26 27
iii
SABS 0162-2:1993
Contents (continued)
Page
6 Member resistance ........................................................................................................
6.1 General ................................................. ................................................ 6.2 Resistance factors for strength analysis ... ..................... .... ............................... 6.3 Members in tension ........................................................................................... 6.4 Members in bending ....... ............................................................................. 6.4.1 General ................ 6.4.2 Laterally supported 6.4.3 Laterally unsupported mem ............................................... 6.4.4 Channels and Z-shaped members with unsti 6.4.5 Shear in webs .................................................... .................................. 6.4.6 Combined bending and shear in webs ............................................................. 6.4.7 Web crippling ............................ .............................................................. 6.4.8 Combined web crippling and be ................ ............................ 6.5 Transverse stiffeners for beam webs .................................... .................... 6.5.1 Bearing stiffeners .......... ............................................... 6.5.2 Intermediate stiffeners ................... ....... 6.5.3 Integral stiffeners ................................... ................................................ 6.6 Members in compression (concentricall . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6.6.1 General ................................................ ............................ 6.6.2 Sections not subject to torsional-flexural ............................ 6.6.3 Singly-symmetric sections .... . . .. . .. .. .. .. . . .. . . .. . .. .. . . .. .. .. . ... . . . . . .. ........... . . ............. ....... 6.6.4 Point-symmetric sections .... ...... 6.6.5 Circular hollow sections ............................ ..... ........ ............................................ 6.6.6 Other sections .................................................... .................................. 6.6.7 Built-up members .......... ............................................................................ 6.7 Combined axial load and ..................................................... 6.7.1 Doubly-symmetric sections (in r hollow sections) ........ ................ 6.7.2 Singly-symmetric sections .................................................................................. 6.7.3 Coefficients of equivalent uniform bending ............... .... .... ................................. 6.7.4 Single angles loaded through one leg ...................................... 6.8 Wall studs ........ ....................................................................................... 6.8.1 General .......... .................................................... 6.8.2 Studs in compr .... ......................................... . ...... 6.8.3 Studs subject to combined axial load and bending ...........................................
............ ........................... ..................
7 Connections ....... .... ..... .................................. ............................................... ... .............
7.1 General .............................................................................................................. 7.1.1 Design .................................................................... .................................. 7.1.2 Connections subject to force reversal .................... ..................................... 7.1.3 Fastening methods .................................. ............................................... 7.1.4 Resistance factor ..___....... ..................... .. .......................................... 7.2 Welded connections ..... .......................................... 7.2.1 Qualification .. .............................. 7.2.2 Arc welds ............................................................................................................ 7.2.3 Resistance welds .....
. . , . . . . .
........................................................................ ...
28
28 28 28 29 29 30 31 34 35 36 36 39 39 39 40 41 41 41 42 42 44 44 44 44 45 45 46 48
49 49 49 53
54
54 54 54 54 54 54 54 54 57
48
iv
SABS 01 62-2: 1993
Con tents (continued)
Page
7.3 Mechanical fasteners (bolts. rivets i3nd screws) ................................................ 7.3.1 General ............................................................................................................... 7.3.2 Factored shear resistance .................................................................................. 7.3.3 Factored tensile resistance (bolts) ..................................................................... 7.3.4 Factored combined shear and tensile resistance (bolts) ................................... 7.3.5 Factored bearing resistance (single fasteners) .................................................. 7.3.6 Factored bearing resistance (groups of fasteners) ............................................ 7.3.7 Dimensions of fastener holes ............................................................................. 7.3.8 7.4 Connections in built-up members ...................................................................... 7.5 Spacing of fasteners in compressive elements .................................................
Minimum edge distance and spacing .................................................................
8 Bracing .........................................................................................................................
8.1 General .............................................................................................................. 8.2 Sections that are symmetric relative to the plane of loading ............................ 8.2.1 General ..............................................................................................................
8.2.3 Bracing by deck. slab or sheathing ................................................................... 8.3 Channel and Z-shaped members in bending ................................................... 8.3.1 General ............................................................................................................... 8.3.2 Discrete bracing .................................................................................................. 8.3.3 One flange braced by deck. slab or sheathing .................................................. 8.3.4 Both flanges braced by deck. slab or sheathing ................................................
8.2.2 Discrete bracing .................................................................................................
9 Testing ..........................................................................................................................
9.1 General ............................................................................................................... 9.2 Types of test ......................................................................................................
9.3.1 Type A - Virgin steel properties ........................................................................
9.3.3 Type C - Performance tests .............................................................................
9.3 Test procedures .................................................................................................
9.3.2 Type B - Cold-formed steel propellties .............................................................
9.3.4 Type D - Confirmatory tests ..............................................................................
10 Fabrication ....................................................................................................................
10.1 General .............................................................................................................. 10.2 Maximum slenderness ratios ............................................................................ 10.3 Fastenings ......................................................................................................... 10.4 Straightening and flattening ............................................................................... 10.5 Provision for expansion and contraction ............................................................ 10.6 Tolerances .........................................................................................................
57 57 60 60 60 60 62 63 63 63 64
64
64 65 65 65 65 65 65 65 66 66
66
66 67 67 67 67 68 69
69
69 69 69 70 70 70
SABS 0162-2~1993
Contents (continued, Page
11 Erection ............................................................................................................................
.............. 11 . I Handling requirements ................................................................... 11.2 Temporary loads during erection .............. ...................................... 11.3 Marking of members .................................. .......................................... 11.4 Setting out and erection .... .... ..... .... ........... ..................................................... 11.5 Tolerances ........... ......... .... ......... ............. ........... ..............................
12 Cleaning, surface preparation and protective treatment .... .... .... ............................ .... ......
12.1 Storage and handling ............................................................................................ 12.2 Surface preparation and protective treatment ............ ..................................... .....
70
70 70 70 70 70
71
71 71
vi
SABS 01 62-2: 1993
Committee
South African Bureau of Standards ................................................................ VJ Woodlock (Chairman) I Jablonski (Standards writer) E Coetzee (Committee clerk)
Benard & Partners Incorporated ......................................................................... ED Benard J Main
BKS Inc ............................................................................................................... AG Ballack NW Dekker
Department of Public Works ............................................................................... MG Knoetze
Engineering Management Services Tvl (Pty) Ltd ...... ....................................... C Lilley HP Wilson
lscor Limited ....................................................................................................... J Barnard JL Meyer
Provincial Administration of Natal Chief Directorate: Works .................................................................................. D le Voy
N Mann
Provincial Administration of the Orange Free State ........................................... B Keyter
South African Fire Services Institute .................................................................. CH de Bruyn J Jakobsen
The South African Institute of Steel Construction .............................................. J Duncan KO Horngren
Transnet Limited ................................................................................................. J Geldenhuys SFL Visser
University of Pretoria ........................................................................................... WMG Burdzik SWJ van Rensburg
University of the Witwatersrand .......................................................................... AR Kemp S Krige
vi i
SABS 0162-2:1993
Blank
viii
CODE OF PRACTICE SABS 0162-2~1993
The structural use of steel
Part 2: Limit-states design of cold-formed steelwork
1 Scope and application
1.1 Scope
This part of SABS 0162 applies to the design, based on limit states, of structural members cold-formed to shape, from carbon or low-alloy steel sheet, strip or plate of thickness up to 25 mm and intended for load-carrying purposes in buildings. For applications other than in buildings, supplementary codes of practice may have to be used to take account of different structural loads and effects, environments or service conditions.
1.2 Application
Where a structure consists of cold-formed steel structural members, provision shall be made to ensure adequate stability of the structure as a whole and adequate lateral, torsional and local stability of all structural parts individually, so as to ensure resistance to widespread collapse following a local failure. Supplementary provisions may be required for structures where accidental loads, for example vehicle impact or explosion, may occur. When members designed in accordance with this part of SABS 0162 are intended for use in structures where other recognized codes of practice apply, this part of SABS 01 62 shall supplement such codes as applicable. The resistance factors adopted in this part of SABS 0162 are correlated with the loads and load factors for buildings as specified in SABS 0160. (See also clause 4.)
Where this part of SABS 01 62 does not provide design expressions or dimensional limitations that are directly applicable to a specific situation, a rational design, if based on appropriate theory, analysis, test results or engineering judgment, may be used.
2 Definitions, symbols and units
2.1 Definitions
For the purposes of this part of SABS 0162, the following definitions apply:
2.1 .I asymmetric section: A section that is not symmetric about either an axis or a point.
1
SABS 01 62-21 1993
2.1.2 cold-forming: The shaping of flat rolled steel at ambient temperature to produce a formed section or profile.
2.1.3 cross-sectional areas
2.1.3.1 effective cross-sectional area A,: The cross-sectional area calculated using the effective widths of compressive elements in accordance with 5.6.2. It can be an effective gross cross-sectional area, or an effective net cross-sectional area, as applicable.
2.1.3.2 full cross-sectional area A: The cross-sectional area for which the effective width of cornpressive elements, determined in accordance with 5.6.2, is equal to or less than the limiting flat width and which is therefore equal to either the gross or the net cross-sectional area, as applicable. In clause 6, the full cross-sectional area is equal to either the gross or the net cross-sectional area, as applicable.
2.1.3.3 gross cross-sectional area A,: The cross-sectional area without deductions for holes, openings and other cut-outs. Effective widths are not considered.
2.1.3.4 net cross-sectional area A,: The gross cross-sectional area less the area of holes, openings and other cut-outs. Effective widths are not considered.
2.1.4 doubly-symmetric section: A section that is symmetric about two orthogonal axes through its centroid.
2.1.5 effective slenderness ratio KLlr of a compressive member: The ratio of the effective length KL to the radius of gyration r of the full cross-section.
2.1.6 effective width b: The dimension substituted for the flat width of an element when the flat width is reduced for design purposes.
NOTE - Effective width is determined in accordance with 5.6.2.
2.1.7 effective width ratio B (= blt) : The ratio of the effective width b to the thickness t of an element, determined in accordance with 5.6.2.
2.1.8 Engineer: The person responsible for the design and satisfactory completion of a structure in accordance with the provisions of this part of SABS 0162.
2.1.9 factored resistance: The product of a nominal resistance R and the appropriate resistance factor di
2.1.10 flange of a section in bending: The flat width, including any intermediate stiffeners plus the adjoining corners.
2.1 .I 1 flat width w: The width of an element, excluding rounded corners.
2.1 .I 2 flat width ratio W (= wlt): The ratio of the flat width w to the thickness t of the element.
2.1.13 limit states: Those conditions in which a structural member ceases to fulfil the function for which it was designed. The states concerning safety are called the ultimate limit states and include exceeding of load-carrying capacity, overturning, uplift, sliding, fracture and fatigue failure. The states that restrict the intended use and occupancy of a structure are called serviceability limit states and include excessive deflection, vibration and permanent deformation.
2
SABS 01 62-2: 1993
2.1 . I 4 multiple-stiffened element: An element that is stiffened at both edges and is also stiffened by means of intermediate stiffeners that are parallel to the direction of stress and is such that it complies with 5.6.2.5.
2.1.15 nominal loads: The nominal loads specified in SABS 0160.
2.1 . I6 point-symmetric section: A section that is symmetric about its centroid.
2.1.17 resistance R: The resistance of a member, connection or structure, as calculated in accordance with this part of SABS 0162, based on the specified material properties and nominal dimensions.
2.1.18 resistance factor 6: A factor, given in the appropriate clauses of this part of SABS 0162, applied to a specific material property or to the iresistance of a member, connection or structure that, for the limit state under consideration, takes into account the variability of material properties, dimensions, workmanship, type of failure and uncertainty in the prediction of member resistance.
To maintain simplicity of design formulae in this part of SABS 0162, the type of failure and the uncertainty in prediction of member resistance have been incorporated in the expressions for member resistance.
2.1 . I 9 serviceability load: The design load or action effect pertaining to the serviceability limit state (see 4.4.2 of SABS 0160).
2.1.20 singly-symmetric section: A section that is symmetric about one axis through its centroid.
2.1.21 stiffened element: A flat element both) edges of which parallel to the direction of stress are supported by stiffeners that comply with 5.6.2.
2.1.22 structural quality steel: Steel produced to a recognized standard or other published specification that specifies mechanical properties and chemical composition.
2.1.23 subelement of a multiple-stiffened element: The portion of a multiple-stiffened element between adjacent intermediate stiffeners, between web and intermediate stiffener, or between edge and intermediate stiffener.
2.1.24 thickness t : The base steel thickness, exclusive of coatings.
2.1.25 torsional-flexural buckling: A mode of buckling in which compressive members bend and twist simultaneously.
2.1.26 ultimate load: The design load or action effect pertaining to the ultimate limit state (see 4.4.2 of SABS 0160).
2.1.27 unstiffened element: A flat element with one longitudinal free edge.
2.1.28 virgin steel: Steel in the condition prio8r to cold forming.
2.1.29 wall stud: A vertical steel member supporting the sheathing in drywall construction.
2.1.30 web of a section in bending: The portion that joins two flanges or is joined to only one flange (provided that it crosses the centroidal axis and transmits shear); taken as the flat length, measured in the plane of the web, excluding the corners.
3
SABS 0162-2:1993
2.2 Symbols
The following symbols are used throughout this part of SABS 0162: (Deviations from them and additional nomenclature are noted where they appear.)
full cross-sectional area of a member
area term used in calculating resistance of bearing stiffeners; cross-sectional area of a fastener, based on its nominal diameter
area term used in calculating resistance of bearing stiffeners
effective cross-sectional area of a member in compression or bending
effective cross-sectional area of a stiffener
full cross-sectional area of a stiffener section, excluding any portion of adjacent elements
gross cross-sectional area of a member
net cross-sectional area of a member
area term used in calculating the resistance of circular hollow section compressive members, when considering local buckling
reduced effective cross-sectional area of a stiffener
gross cross-sectional area of transverse or intermediate stiffeners
cross-sectional area of a web
fastener edge distance; length of a bracing interval; distance between web centrelines of a closed box section; effective throat thickness of a fillet weld; effective throat thickness of a flare-bevel groove weld
distance between the shear centre of a channel and the mid-plane of the web
effective width ratio of an element in compression (blt); wall stud spacing
reduced effective width ratio; the factored bearing resistance of a sheet
effective design width; width of the outstanding leg of an angle or the flange of a channel; distance between flange centrelines for closed box section; width of an arc seam weld
effective widths (see figures 2, 6(a) and 6(b))
bending coefficient
Euler elastic buckling load (= 7c2€Z/(KL)')
initial wall stud imperfection in the direction parallel to a wall
limiting flat width ratio
4
SABS 01 62-2: 1993
c, =
c, =
c, =
cy =
- - C
Do =
d =
de =
d,, =
di =
d, =
d, =
E =
E, =
e
f -
- - -
- - fa
fa" - -
factored compressive resistance of a concentrically loaded member; factored compressive resistance of a transverse stiffener
axial compression in member or component due to ultimate loads
warping torsional constant
factor used in inelastic resistance calculations
distance from the centroid of a member to its extreme compressive fibre; permissible curling displacement
initial wall stud imperfection in the direction perpendicular to a wall
diameter of a fastener; outside diameter of a circular hollow section; flat width of a lip stiffener
effective width of a lip stiffener (see figure 2)
diameter of a fastener hole
overall depth of a lip stiffener (see figure 2)
reduced effective width of a lip stiffener (see figure 2)
minimum overall depth of a simple lip stiffener bent at right angles
elastic modulus of steel
initial twist of wall stud from ideal configuration (rad)
eccentricity
calculated stress in an element
compressive limit stress under concentric loading
calculated average flange stress, i.e. maximum flange stress multiplied by the ratio of effective design width to actual width
bending stress
elastic buckling stress
compressive limit stress in a single-,web beam, circular hollow section beam or box beam
Euler elastic buckling stress
elastic buckling stress about the strong axis
elastic buckling stress about the xy axis
elastic buckling stress about the weak axis
5
SABS 0162-2:1993
fP = critical elastic buckling stress
fS = Euler elastic buckling stress about the axis of symmetry for singly-symmetric sections
fSt = elastic torsional-flexural buckling stress
ft = elastic torsional buckling stress
f" = tensile strength of virgin steel, determined in accordance with 3.2; tensile strength of
fastener
f" = limit stress in shear
fY = tensile yield stress of virgin steel
ffi = tensile yield stress of flats
fY ' = average tensile yield stress that incorporates the effects of coldwork of forming
f,, f2 = calculated stresses (see figures 6(a) and 6(b))
f3 = calculated stress (see figure 2)
G = shear modulus of steel (assumed to be 80 x 103 MPa)
g = distance from a fastener to flanges that are tending to close in a built-up member; spacing of rows of fasteners, measured perpendicular to the direction of force
H = web slenderness ratio (= h,lt)
h = overall depth of section
h, = clear distance between flats of flanges, measured in the plane of the web
h, = clear perpendicular distance between the flats of flanges
h, = flat dimension of a web, measured in the plane of the web
1, = required moment of inertia for an adequate stiffener that allows an adjacent compressive element to behave as a fully stiffened element (applies to edge and intermediate stiffeners)
IS = moment of inertia of the full cross-sectional area of a stiffener, about its own centroidal
axis parallel to the element to be stiffened; moment of inertia of a pair of attached intermediate stiffeners or of a single intermediate stiffener, with reference to an axis in the plane of the web
Is, = moment of inertia of the full cross-sectional area of a multiple-stiffened element, including intermediate stiffeners, about its own centroidal axis
1, = moment of inertia of the full cross-sectional area about its major centroidal axis
1 Y = moment of inertia of the full cross-sectional area about its centroidal axis parallel to the web(s)
6
SABS 0 1 62-2: 1 993
product of inertia of the full cross-sectional area
moment of inertia of the compressive portion of a full cross-sectional area about the centroidal axis of the entire section parallel to the web(s)
St Venant torsion constant
effective length factor
effective length
effective length factor for torsional buckling
buckling coefficient for compressive elements
shear buckling coefficient
unbraced length of a member; span of a beam; length of a weld; length of a wall stud
total length of a transverse stiffener
length of a member unsupported against twisting
bearing length
factored moment resistance
factored moment resistances with the possibility of lateral instability excluded
moment in a member or component due to ultimate loads
moments at the point under consideration due to ultimate loads when used in conjunction with 6.7.1 (a); maximum calculated moments due to ultimate loads occurring either at or between braced points when used in conjunction with 6.7.l(b); moment due to ultimate loads when used in conjunction with 6.8.3
ultimate moment causing a maximum compressive strain of Cyey
moment causing a maximum strain of ey
smaller end moment
larger end moment
distance between the shear centre of a channel and the mid-plane of the web; number of holes across a connected leg or web of a tensile member; number of fasteners in the first row parallel to the edge
ratio of the bearing length to the web thickness (= l,,lf)
7
number of rows of fasteners
number of 90" corners in the flange of a section in bending or in the entire cross-section of a compressive or tensile member. If angles other than 90" are used, n, is the sum of the bend angles divided by 90"
number of fasteners across a connected leg or web
number of holes across the connected leg or web of a tensile member
lateral force due to the ultimate loads used to design a bracing
factored web-crippling resistance of a member in bending
concentrated load or reaction due to ultimate loads
perimeter length of a multiple-stiffened element between the webs or from a web to an edge stiffener; the ultimate load per unit length of a beam
limit shear rigidity, with sheathing on both sides of the wall studs
If1 I' If2 I limit shear rigidity per unit length of the stud spacing, with sheathing on both sides of the studs, based on the actual fastener spacing
limit shear rigidity per unit length of the stud spacing, with sheathing on both sides of the studs, based on a 300 mm fastener spacing
ratio of the inside bend radius to the thickness (= r/t ); the resistance
tested serviceability limit state
tested strength limit state
radius of gyration of the full cross-sectional area: inside bend radius
polar radius of gyration of the full cross-sectional area about the shear centre
least radius of gyration of the full cross-sectional area
radii of gyration of the full cross-sectional area about the centroidal principal axes
radius of gyration of the full cross-sectional area of an individual section in a built-up member
spacing between fasteners; spacing between rows of fasteners measured parallel to the direction of force; distance between transverse stiffeners
factored tensile resistance
base steel thickness; thickness of a/the thinner connected sheet; thickness of a cover plate or sheet
SABS 01 62-2: 1993
ws
W*
W
wln
ws
W'
= equivalent thickness of replaced intermediate stiffeners (see figure 4)
= thickness of the thickest connected sheet in a simple lap joint; thickness of flange in closed box members
= thickness of a web in a closed box member
= locally applied ultimate load on a beam
= factored shear resistance of a web or fastener
= shear force in a member or component due to ultimate loads
= flat width ratio (= wlf)
= ratio of the width of a flange projecting beyond the web or half the distance between webs for box or U-type sections, to the thickness of the flange (= w'lt)
= limiting flat width ratio for fully effective compressive elements
= flat width ratio of a multiple-stiffened flange element between webs or from the web to an edge stiffener (= wJtJ
= flat width ratio of a flange element stiffened by webs with one intermediate stiffener (= WJt)
= ratio of the centreline length of a flange cross section of a member in bending, or of the entire cross-section of a tensile or compressive member, to the thickness
= flat width
= flat width between webs or from the web to an edge stiffener of a multiple-stiffened flange element (see figure 4)
= flat width of a stiffened flange element with one intermediate stiffener (see figure 3)
= width of a flange projection beyond the web for an I-beam and similar sections; half the distance between webs for box or U-type sections
= distance from a concentrated load point to a brace
= distance from a shear centre to the centroid of the section
= compressive section modulus based on the moment of inertia of the effective cross- sectional area, calculated in acclordance with 5.6.2, divided by the distance from the centroidal axis to the extreme cornpressive fibre
= compressive section modulus based on the moment of inertia of the full cross-sectional area (gross or net) divided by the distance from the centroidal axis to the extreme compressive fibre
= tensile section modulus based on the moment of inertia of the effective gross cross- sectional area, calculated in accordance with 5.6.2, divided by the distance from the centroidal axis to the extreme tensile fibre
9
SABS 01 62-21 1993
tensile section modulus based on the moment of inertia of the effective net cross-sectional area, calculated in accordance with 5.6.2, divided by the distance from the centroidal axis to the extreme tensile fibre
compressive section modulus of the full cross-sectional area about the centroidal x-axis perpendicular to the web, i.e. I, divided by the distance from the centroidal axis to the extreme compressive fibre
compressive section modulus of the full cross-sectional area about the centroidal y-axis parallel to the web, i.e. Iy divided by the distance from the centroidal axis to the extreme compressive fibre
load factor
amplification factors
shear strain in the sheathing of wall studs
limit shear strain in the sheathing of wall studs under ultimate loads
yield strain (= ClE)
angle between the plane of a web and the plane of a bearing surface (degrees); angle made by the end edge with the direction of load (degrees)
Poisson's ratio (= 0,30)
resistance factor for tension, bending and shear
resistance factor for axial compression
resistance factor for connections
resistance factor for web crippling in beams having other than a single unreinforced web
resistance factor for web crippling in beams having a single unreinforced web
resistance factor for other strength limit states as determined by the tensile strength of the material
coefficients used to determine the equivalent uniform bending stress
2.3 Units
Equations and expressions used in this part of SABS 0162 are compatible with the following SI (metric) units:
- force: newtons (N)
- length: millimetres (mm)
- moment: newton-millimetres (N.mm)
- strength and stress: megapascals (MPa)
10
SABS 01 62-2: 1993
2.4 Normative references
The following standards contain provisions which, through reference in this text, constitute provisions of this part of SABS 0162. All standards are subject to revision and, since any reference to a standard is deemed to be a reference to the latest edition of that standard, parties to agreements based on this part of SABS 0162 are encouraged to take steps to ensure the use of the most recent editions of the standards indicated below. Information on currently valid national and international standards may be obtained from the South African Bureau of Standards.
AWS D 1 . I , Structural welding code - Steel.
BS 1449-1.4, Steel plate, sheet and strip - Parl' 1: Carbon and carbon-manganese plate, sheet and strip - Section 1.4: Specification for hot-rolled wide material based on specified minimum strength.
BS 1449-1.5, Steel plate, sheet and strip - Pan' 1: Carbon and carbon-manganese plate, sheet and strip - Section 1.5: Specification for cold-rolled wide material based on specified minimum strength.
BS 1449-1.10, Steel plate, sheet and strip - Part 1: Carbon and carbon-manganese plate, sheet and strip - Section 1.70: Specification for hot-rolled narrow strip based on specified minimum strength.
BS 1449-1 .I 1, Steel plate, sheet and strip - Part 1: Carbon and carbon-manganese plate, sheet and strip - Section 1.17: Specification for cold-rolled narrow strip based on specified minimum strength.
BS 4360, Weldable structural steels.
BS 4848-2, Hot-rolled structural steel sections -- Part 2: Specification for hot-finished hollow sections.
Euronorm 149, Flat products of steels with a high yield strength for cold-working; wide flats, sheets and strip.
IS0 657-1 4, Hot-rolled steel sections - Part 14: Hot-finished structural hollow sections - Dimensions and sectional properties.
SABS 657-1, Steel tubes for non-pressure purposes - Part 1: Steel tubes for scaffolding and for structural and general engineering purposes.
SABS 1 200-HI Standardized specifications for civil engineering construction - H: Structural steelwork.
SABS 1431, Weldable structural steels.
SABS 044, Welding.
SABS 054, Tensile testing of metallic materials.
SABS 01 60, The general procedures and loadings to be adopted in the design of buildings.
SABS 0 162- 1, The structural use of steel - Part 1: Limit-states design of hot-rolled steelwork.
11
SABS 0162-2:1993
3 Materials
3.1 Standard steels
Steel for the manufacture of structural members in accordance with this part of SABS 0162 shall comply with one of the following standards, except as provided for in 3.2:
SABS 1431
BS 1449-1 : section 1.4
BS 1449-1 : section 1.5
BS 1449-1 : section 1.10
BS 1449-1 : section 1.1 1
Euronorm 149
BS 4360
For the steels listed above, fy and fu shall have the specified values as given in the relevant standard.
3.2 Other steels
3.2.1 Other structural quality steels
For structural quality steels not listed in 3.1, fy and fu shall have the specified minimum values given in the relevant standard or published material specification. These steels shall comply with the requirements of 3.2.3.
3.2.2 Commercial quality steels and steels of unknown origin
For steels not covered by 3.1 or 3.2.1, tensile tests shall be carried out in accordance with 9.3.1. The design values fy and fu shall be 0,8 times the yield strength and 0,8 times the tensile strength determined from the tests. These steels shall comply with the requirements of 3.2.3.
3.2.3 Ductility requirements
Steels conforming to 3.2.1 and 3.2.2 shall have a tensile-strength-to-yield-strength ratio of at least 1,08. Total elongation shall be at least 10 % for a 50 mm gauge length or at least 7 % for a 200 mm gauge length standard specimen tested in accordance with SABS 054.
Steels that do not comply with the ductility requirements given above may be used in particular applications, provided the following conditions are met:
a) the yield strength for design fy shall not exceed the lesser of 0,75 of the specified yield strength and 360 MPa, and the tensile strength for design fu shall not exceed 0,75 of the specified minimum tensile strength, when clauses 5 to 8 of this part of SABS 0162 are being used;
b) the suitability of such steelsfor the application (including connections) shall be determined by load tests in accordance with clause 9; and
12
SABS 01 62-2: 1993
c) for applications with established performance, no load testing is required, but loads shall not exceed those calculated when clauses 5 to 8 together with clause 9 are being used.
3.3 Physical properties
The values of physical properties of steel used for design purposes shall be:
- Elastic modulus (E) : 203 000 MPa
-Shear modulus (G) : 78 000 MPa
- Poisson's ratio (p)
- Mass density
: 0,3
: 7 850 kg/m3
- Coefficient of linear thermal expansion : 1 1,7 x 1 O-6/oC
4 Loads and limit-states criterion
4.1 Loads
Nominal loads and other influences to be considered in the design of cold-formed steel structural members shall be adopted in accordance with sections 1 to 5 of SABS 0160.
4.2 Limit-states criterion
The criterion for avoiding failure at ultimate limit states or avoiding unfitness for purpose at serviceability limit states of a structure or part thereof is:
Design resistance 1. Effect of ultimate or serviceability loads,
where the design resistance is determined in accordance with this part of SABS 0162, and the effect of the ultimate or serviceability loads is determined in accordance with this part of SABS 0162, using the ultimate or serviceability loads defined in sections 4 and 5 of SABS 0160.
5 General design considerations
5.1 General
Unless otherwise specified, all calculations for loads, forces, deflections and other effects shall be in accordance with conventional methods of structural analysis. Design shall be made with reference to the load factors and strength criteria given in this part of SABS 0162.
5.2 Coldwork of forming
5.2.1 Application
5.2.1.1 The use of coldwork of forming is optional. If used, it shall be confined to members designed in accordance with 5.2.2 and with the following subclauses:
13
SABS 0162-2:1993
a) 6.3: members in tension;
b) 6.4.1, 6.4.2 (except 6.4.2.2) and 6.4.3 (except 6.4.3.5): members in bending;
c) 6.6 (except 6.6.5): members in compression (concentrically loaded);
d) 6.7: combined axial load and bending; and
e) 6.8: wall studs.
5.2.1.2 When coldwork of forming is being used, fy shall be replaced by fy'.
5.2.1.3 The increase in yield stress due to coldwork of forming shall not be used for members that are welded, annealed, galvanized (after forming), or subject (after forming) to heat treatment that may soften the steel in critical areas.
5.2.2 Fully effective elements
For axially loaded tensile members, tensile flanges of members in bending, axially loaded compressive members with fully effective area, and compressive flanges of members in bending the elements of which are not subject to a reduction in effective area as required by 5.6.2, the yield stress fy' shall be determined by one of the following methods:
a) from full-section tensile or compressive tests in accordance with 9.3.2; or
b) by calculation, as follows:
f;' = f; + 5nc (f"-fy) / w
where
fy' is the calculated average tensile yield stress over the full cold-formed section of a tensile or compressive member, or over the full flange of a member in bending;
fy, fu are the specified minimum tensile yield stress and tensile strength, respectively, of the virgin steel established in accordance with clause 3;
nc is the number of 90" corners in the flange of a member in bending or in the entire cross- section of a compressive or tensile member. If angles other than 90" are used, n, is the sum of the bend angles divided by 90"; and
W is the ratio of the centreline length of a flange cross-section of a member in bending, or of the entire cross-section of a tensile or compressive member, to the thickness.
5.2.3 Elements not fully effective
For axially loaded compressive members and the compressive flanges of members in bending that do not comply with 5.2.2, the yield stress fy' shall be taken as the lesser of
a) the specified minimum tensile yield stress of the virgin steel established in accordance with clause 3; and
b) the tensile yield stress of the flats ffl determined in accordance with 9.3.2.
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SABS 01 62-2: 1993
5.3 Maximum effective slenderness ratio for members in compression
The effective slenderness ratio KUr of members in compression shall not exceed 200. The value of the effective length factor K to be used in the design of members in compression shall be at least that given in 9.3 (or in appendix B) of SABS 0162-1.
5.4 Maximum flat width ratios for elements in compression
The flat width ratio W, disregarding intermediate stiffeners, shall not exceed:
a) for stiffened compressive elements that have one longitudinal edge connected to a web or flange element and the other stiffened by
1) a simple lip : 60
2) any other kind of stiffener : when I, < I, : 60
when I, > I , : 90
b) for stiffened compressive elements with both longitudinal edges connected to a web or other stiffened element : 500
c) for unstiffened compressive elements : 60
NOTES
1 Unstiffened compressive elements (see (c) above) that have flat width ratios exceeding approximately 30 and stiffened compressive elements (see (b) above) that have flat width ratios exceeding approximately 250 are likely to develop noticeable deformation under nominal load without detriment to the load-carrying ability.
2 Compressive elements that have flat width ratios exceeding the limits specified above may be used to support loads, but substantial deformation of such elements under load may occur and may invalidate the design formulae of this part of SABS 0162.
3 Additional flat width limits may be specified in certain clauses.
5.5 Maximum section depths
5.5.1 The web slenderness ratio H of members in bending shall not exceed:
a) for sections with unreinforced webs : 200
b) for sections with webs provided with transverse stiffeners and complying with 6.5
1) with bearing stiffeners only : 260
2) with bearing stiffeners and intermediate stiffeners : 300
15
SABS 0162-2~1993
H being calculated as follows:
H = h,/t
where:
h, is the flat dimension of the web, measured in the plane of the web; and
t is the web thickness.
5.5.2 Where a web consists of two or more sheets, the slenderness ratio H shall be calculated for each individual sheet.
5.6 Properties of sections
5.6.1 General
Properties of sections, including cross-sectional area, moment of inertia, section modulus and radius of gyration, shall be determined in accordance with conventional methods. Properties shall be based on the gross cross-sectional area (or net cross-sectional area where applicable), except where the substitution of effective width for the flat width is required by 5.6.2.
5.6.2 Effective design width of elements in compression
5.6.2.1 General
When the flat width ratio W for elements in compression exceeds wim , the flat width w shall be replaced by an effective width b . The effective width is a function of the effective width ratio B, and is defined in 5.6.2.2 to 5.6.2.8.
NOTE - For shear lag effects, see 5.6.3 and for curling of flanges, see 5.6.4.
For strength calculations, ultimate loads are used; for serviceability calculations, serviceability loads are used.
The effective width ratio B shall be determined as follows:
Case 1: W z LWlm
B = W
Case 2: W > ylm
B = 0,95 m [ 1 ~ m] where, for cases 1 and 2,
W,, = 0,644 w f ;
k and Ware as defined in 5.6.2.2 to 5.6.2.8; and
16
SABS 0162-2:1993
a) for strength determination:
f is the calculated stress in the compressive element (I fJ, using ultimate loads and effective section properties;
b) for serviceability determination:
f is the calculated stress in the compressive element, using serviceability loads and effective section properties.
5.6.2.2 Elements under uniform stress stiffened on each edge by a web or flange
5.6.2.2.1 The effective design width b = Bt for strength and serviceability shall be determined in accordance with 5.6.2.1, with k = 4 and W = w/t . See figure 1.
5.6.2.2.2 For the special case of serviceability determination of stiffened elements of multiple-web profiles, an alternative method of calculating the effective width is given by the following:
Case 1: W < Wim
B = W
Case 2: Qim < W I CO,
0 438 W
B = 0,95 m f 1,358 - - 44 5 W
Case 3: W > CO,
B = 0,95 @f [,,,I + 0 , 5 9 m f ~ - 0;9 wj5 w
where, for cases 1,2 and 3,
W,, = 0,644 @f ;
w = w/ t :
0,256 m f c o w =
1,052 fi - 0,328 w f ’
k =4; and
f is the calculated stress in the clDmpressive element, using serviceability loads and effective section properties.
17
SABS 0162-211993
f (compression)
I SABS 0162-2 Drg12836-ec/00-05
Figure 1 - Example of stiffened flange element subject to uniform compressive stress
5.6.2.3 Elements under uniform stress stiffened on one edge by a web or flange and on the other by an edge stiffener
The effective widths b, and b, , the reduced effective width d, and the reduced effective area A, for strength and serviceability shall be determined in accordance with the following (see figure 2):
Case 1: W z w,m, (no edge stiffener required)
b, = b, = w12
d, = d, for simple lip stiffener
A, = A,, for other stiffener shapes
Case 2: W,,,,,, < W c wlm2 b, = I,Bt/2 5 Btl2
b, = Bt - b,
d, = d, I , 5 d, for simple lip stiffener
A, = A,, I , 5 A,, for other stiffener shapes
where I , = Islla
I, = 400f4 1 WIW,im2 ~ I’ = 400t4(W1W,im2 - 0,328)’
Case 3: W > \n/lim2
b, , b,, dr, A,, I, are as defined in case 2, with
18
SABS 0162-2~1993
where, for cases 1, 2, and 3,
b, , b,
W i m l = 0,644 mf with k = 0,4.3;
Y i m 2 = 0,644 mf with k = 4;
W = wl t ;
d , w , di are dimensions illustrated in figure 2;
are the effective widths illustrated in figure 2;
is the effective width of the stiffener illustrated in figure 2 and calculated in accordance with 5.6.2.7, with W = dlt and f = f3 ;
are the calculated stresses in the compressive element, using ultimate loads and effective section properties for strength determination, and serviceability loads and effective section properties for serviceability determination (see figure 2);
is the reduced effective width of the stiffener illustrated in figure 2 to be used in calculating overall effective section properties;
is the effective area of the stiffener, based on the local buckling effective widths of the individual plate elements;
is the reduced effective area of the stiffener to be used in calculating overall effective section properties; the centroid of the stiffener is considered to be located at the centroid of the full area of the stiffener, and the moment of inertia of the stiffener about its own centroidal axis shall be that of the full section of the stiffener;
is the required moment of inertia for an adequate stiffener that allows the adjacent compressive element to behave as a fully stiffened element;
is the moment of inertia of full cross-sectional area of a stiffener, about its own centroidal axis parallel to the element to be stiffened (for edge stiffeners, the radius between the stiffener and the element to be stiffened shall not be considered as part of the stiffener); for the edge stiffener shown in figure 2,
Z, = fd 3sin2 /12; and
is calculated in accordance with 5.6.2.1, with k for simple lip stiffeners as given in table 1, while for other stiffener shapes,
k = 3,57(Zr)" + 0,43 5 4;
n = 030 for case 2;
n = 0,33 for case 3.
19
SABS 0162-2:1993
0,25 c d,lw 5 0,8
k = 5,25 ~ 5(d, /w)
k = [4,82 - 5(d, / w ) ] ( I ~ ) ~ ' ~ + 0,43
~ k = 525 - 5(d, IW) I
1 k = [4,82 - 5(d, /W)](Z,)O'~~ + 0,43
Table 1 - Buckling coefficients for elements in compression under uniform stress with a simple lip stiffener
(as shown in figure 2)
1 2
NOTE - d/t 5 14.
3
d,lw 5 0,25
k = 4
k = 3,57 ([,)Of5 + 0,43
k = 4
k = 3,57 (Zr)0,33 + 0,43
4
f (compression)
Figure 2 - Example of edge-stiffened flange element subject to uniform compressive stress
5.6.2.4 Elements under uniform stress with one intermediate stiffener and stiffened on each edge by a web or flange
The effective width b = Bt for strength and serviceability shall be determined in accordance with the following (see figure 3):
Case 1: W, 5 qim (no intermediate stiffener required)
b = w
b = Bt
where B is calculated in accordance with 5.6.2.1, with W = w/t , and k is defined as follows:
20
SABS 01 62-2: 1993
k = 3(Zr)03 + 1 5 4
I, = &/Ia
i, = 50y"WS/W,,, - I ]
Ar = A e J r 5 Aes
Case 3: W, > 3 4 ,
b = Bt
where B is calculated in accordance with 5.6.2.1, with W = wlt , and k is defined as follows:
k = 3(Ir)033 + 1 5 4
I, = IJIa
I, = P[128(Ws/W,im) - 2851
where, for cases 1 , 2 and 3,
yi, = 0,644 @% with k = 4;
f is the calculated stress in the compressive element, using ultimate loads and effective section properties for strength determination, and serviceability loads and effective section properties for serviceability determination (see figure 3);
W, = wJt, where w, is as illustrated in figure 3;
A,, is the effective cross-sectional area of the stiffener, based on the effective width of the individual plate elements;
A, is the reduced effective cross-sectional area of the stiffener to be used in calculating overall effective section properties; the centroid of the stiffener is considered to be located at the centroid of the full area of the stiffener, and the moment of inertia of the stiffener about its own centroidal axis shall be that of the full section of the stiffener:
i, is the required moment of inertia for an adequate stiffener that allows the adjacent compressive element to behave as ia fully stiffened element; and
I, is the moment of inertia of the full cross-sectional area of the stiffener, about its own centroidal axis parallel to the element to be stiffened.
21
SABS 0162-2:1993
f (compression)
mmmr IIrr ----lmmm _ _ _ _
SABS 0162-2 r Drg.12835-ec/00-05
Figure 3 - Example of stiffened flange element with one intermediate stiffener, subject to uniform compressive stress
5.6.2.5 Elements under uniform stress with multiple stiffeners
For a flat compressive element to be considered a multiple stiffened element, it shall either be stiffened between webs with two or more intermediate stiffeners or be stiffened between a web and an edge stiffener with one or more intermediate stiffeners (see figure 4).
The intermediate stiffener(s) shall be disregarded, unless, for each stiffener,
where
I , = (4W- 26)t 2 18t4 ;
I , is the moment of inertia of the full cross-sectional area of the stiffener, about its own centroidal axis parallel to the element to be stiffened; and
I , is the required moment of inertia for an adequate stiffener.
The following limitations shall also apply:
a) if the spacing of the stiffeners between two webs is such that the flat width ratio W of any of the subelements between the stiffeners is larger than Yim, only two intermediate stiffeners (those nearest each web) shall be considered effective;
b) if the spacing of the stiffeners between a web and an edge stiffener is such that the flat width ratio W of any of the subelements between the stiffeners is larger than Yim, only the intermediate stiffener nearest the web shall be considered effective;
c) the effective width b of the subelements in (a) and (b) above shall be based on the reduced effective width ratio B, , with b = B,t
22
SABS 0162-2:1993
where
B, = B when W I 60; and
B, = B - 0, l W + 6 when W > 60;
where B is calculated in accordance with 5.6.2.1, with k = 4 and W = w/t ;
d) when the effective structural properties of a section are being calculated, the area of edge and intermediate stiffeners in (a) and (b) above shall be replaced by a reduced effective area A,
4 = A, when WI 60;
A, = (3 - 2B, /W + B, 130 - W/30)A,
Ar = (Br IWA,
when 60 < W I 90; and
when W > 90;
where
wim = 0,644 mf with k = 4;
f is the calculated stress in the compressive element, using ultimate loads and effective section properties for strength determination, and serviceability loads and effective section properties for serviceability determination (see figure 4);
w = wlt ;
A, is the reduced effective area of stiffener to be used in calculating overall effective section properties; the centroid of the stiffener is considered to be located at the centroid of the full area of the stiffener, and the moment of inertia of the stiffener about its own centroidal axis is that of the full section of the stiffener: and
A, is the full cross-sectional area of stiffener; and
e) if the intermediate stiffeners are spaced so closely that the flat width ratio Wof all the subelements between stiffeners does not exceed W,,, , all the stiffeners may be considered effective. In the calculation of the flat width ratio W , and the effective width ratio B of the entire multiple stiffened element, such element shall be considered as replaced by an element without intermediate stiffeners whose width w, is the flat width between webs or from web to edge stiffener, and whose equivalent thickness t, is determined as follows:
where
I,, is the moment of inertia of full cross-sectional area of the multiple stiffened element, including intermediate stiffeners, abcrut its own centroidal axis;
is the perimeter length of the multiple stiffened element, between webs or from web to edge stiffener, as illustrated in figure 4;
p
t is the base steel thickness;
w, is the flat width between webs or from web to edge stiffener, as illustrated in figure 4; and
w, = WJt,
23
SABS 01 62-2: 1993
The effective width ratio B of the multiple stiffened element including stiffeners is calculated using W = W, , and the effective area of this element, used to calculate section properties, is Btst .
The moment of inertia of the entire section shall be calculated assuming the "equivalent element" to be located at the centroidal axis of the multiple stiffened element, including intermediate stiffeners. The actual extreme fibre distance shall be used in calculating the section modulus.
ession)
dashed l ine element
Figure 4 - Example of multiple stiffened flange element subject to uniform compressive stress
5.6.2.6 Unstiffened elements under uniform stress
The effective width b = Bt for strength and serviceability shall be determined in accordance with 5.6.2.1, with k = 0,43 and W = w/t (see figure 5).
f (compression)
f- I SABS 0162-2 I Org.12837-ec/00-05
Figure 5 - Example of unstiffened flange element subject to uniform compressive stress
24
SABS 01 62-2: 1993
f r
5.6.2.7 Unstiffened elements and edge stiffeners under a stress gradient
The effective width d, = Bt shall be determined by calculating B in accordance with 5.6.2.1, with k = 0,43 , f = f3 , and W = d/t. For strength determination, f3 is calculated using ultimate loads and effective section properties; for serviceability determination, f3 is calculated using serviceability loads and effective section properties (see figure 2).
5.6.2.8 Webs and stiffened elements under stress gradient
When W > w,,,, , the effective widths b, and b:, for strength and serviceability shall be determined in accordance with the following:
a) for webs (f, in compression and f, in tension - see figure 6(a)):
b, = Bt/(3 + 9); and
b, = Bt/(l + q) - b,;
where B is calculated in accordance with 5.621, with f = f, , and k is calculated as follows:
k = 4 + 2 ( 1 + q ) 3 + 2 ( l +q) whenO< q < 1;and
k = 6(1 + 9)' when 1 c q < 3;
f1 (compression)
f2 (t
\t' // I / Centroidal axis
'ens
Figure 6(a) - Example of stiffened web element subject to stress gradient (compression and tension)
b) for other stiffened elements (6 and f2 in compression - see figure 6(b)):
b, = Bt/(3 - 9); and
where B is calculated in accordance with 5.6.2.1, with f = f, , and k is calculated as follows:
k = 4 + 2 ( 1 -q)3+2(1 -q);
25
SABS 0162-2:1993
where, for both cases (a) and (b) above,
b,, b, are the effective widths illustrated in figures 6(a) and 6(b);
w = wlt;
w is the flat width illustrated in figures 6(a) and 6(b);
f,, f, are the calculated stresses shown in figures 6(a) and 6(b).
In figure 6(a), f, is in compression and fz in tension. In figure 6(b), f, and f, are both in compression, with f, > fz . For strength determination, f, and f, are calculated using ultimate loads and effective section properties; for serviceability determination, f, and f, are calculated using serviceability loads and effective section properties.
f i (compression1
. zh f7 (compression)
I/ I I Centroidal axis I I
A-J I
Figure 6(b) - Example of stiffened flange element subject to stress gradient (compression both ends)
5.6.3 Shear lag effects
Where the span of a member in bending is less than 30w‘ (with w’ as defined in table 2) and the member carries a single concentrated load, or several such loads spaced farther apart than 2w’, the effective width of any flange b , whether in tension or in compression, shall also be limited by the ratio given in table 2. Flanges in compression shall also be limited by the effective width provisions of 5.6.2.
26
SABS 01 62-2: 1993
1 2 3 4 5 6 7 Span L 30w' 25w' 2Ow' 18w' 16w' 14w'
Ratioblw 1.00 0,96 0,91 0,89 0,86 0.82
Table 2 - Short wide flanges (maximum allowable ratio of effective width to actual width)
8 9 10 11 12w' I O W ' 8w' 6w' 0,78 0,73 0,67 0,55
NOTES
L is the full span for simple beams, or the distance between inflection points for continuous beams, or twice the length of cantilever beams;
is the width of flange projecting beyond the web for I-beam and similar sections, or half the distance between webs for box or U-shaped sections. For flanges of I-beams and similar sections stiffened by lips at the outer edges, w' shall be taken as the sum of the flange projection beyond the web plus the depth of the lip;
is the effective width of flange; and
w'
b
5.6.4 Curling of flanges
Where a flange of a member in bending is unusually wide and it is desired to limit the amount of curling or movement of the flange towards the centroidal axis, the gross width ratio W, of either stiffened or unstiffened compressive and tensile flanges shall not exceed the value Wmax, as follows:
where
w, W'
t
h2
C
fa"
= w'lt ;
is the width of flange projecting beyond the web for I-beams and similar sections, or half the distance between webs for box or U-type sections;
is the thickness of flange;
is the clear perpendicular distance between flats of flanges;
is the permissible curling displacement; and
is the average flange stress, which equals the maximum flange stress multiplied by the ratio of the effective design width to the actual width calculated at nominal loads.
NOTE - The allowable amount of curling will vary witl-i different kinds of sections and should be established by the Engineer. An amount of curling displacement in the order of 5 % of the depth of the section is usually not considered excessive.
27
SABS 0162-2~1993
6 Member resistance
6.1 General
All factored resistances determined in accordance with this clause shall exceed or be equal to the effect of the ultimate loads determined in accordance with 4.2.
6.2 Resistance factors for strength analysis
Unless otherwise specified, the value of the resistance factor when member resistance is being determined shall be taken as follows:
a) for axial tension, bending and shear: @ = 0,90;
b) for axial compression:
1) doubly symmetric sections; double-angle sections restrained against torsional-flexural buckling; and circular hollow sections: @a = 0,90;
2) singly symmetric, point-symmetric and asymmetric sections; single angles and double-angle sections not restrained against torsional-flexural buckling; and bearing stiffeners: = 0,75;
c) for web crippling in beams:
1) single unreinforced webs and deck sections: @s = 0,80;
2) other webs: a0 = 0,67;
d) for connections: aC = 0,67; and
e) for limit states determined by the tensile strength of the material: @, = 0,75.
6.3 Members in tension
6.3.1 The factored tensile resistance T, of a concentrically loaded member shall be the lesser of
a) Try = @A,fy ; and
b) Tr, = @UA”fU ’
6.3.2 Except as provided in 6.3.3, the factored tensile resistance T, of eccentrically-loaded tensile members shall be the lesser of
@U fu
(I/A,, + e/Z,,,) and Tru = Try = @fY
(I/Ag + e/Z,)
where
Z, is the tensile section modulus based on the moment of inertia of the effective gross cross- sectional area, calculated in accordance with 5.6.2, divided by the distance from the centroidal axis to the extreme tensile fibre; and
28
SABS 0162-2:1993
Ztn is the tensile section modulus based on the moment of inertia of the effective net cross-sectional area, calculated in accordance with 5.6.2, divided by the distance from the centroidal axis to the extreme tensile fibre.
6.3.3 The factored tensile resistance Tr of single angles with unstiffened legs connected by fasteners in one leg, and single channels with unstiffenetl flanges connected by fasteners in the web, shall be the lesser of
a) for angles, Tr, = @,, [Ag - (0,7b + mdh)t]fU ; and
T,= @Agf,
b) for channels, Tr, = [Ag - ( b + rnd,$ If" ;
T, = @Agfy
where
b is the width of outstanding leg of an angle or flange of a channel;
dh is the diameter of fastener hole;
rn is the number of holes across the connected leg or web; and
t is the base steel thickness.
6.4 Members in bending
6.4.1 General
6.4.1.1 The factored moment resistance of a rnember in bending shall be the least of
M, = @Zxcfc (applies to 6.4.3.5 only)
where
fc is the compressive limit stress calculated in accordance with either 6.4.2 or 6.4.3;
Zc is the compressive section modulus based on the moment of inertia of the effective cross- sectional area, calculated in accordance with 5.6.2, divided by the distance from the centroidal axis to the extreme compressive fibre;
Z, is the tensile section modulus based Ion the moment of inertia of the effective gross cross- sectional area, calculated in accordance with 5.6.2, divided by the distance from the centroidal axis to the extreme tensile fibre;
29
SABS 0162-211993
Z,, is the tensile section modulus based on the moment of inertia of the effective net cross- sectional area, calculated in accordance with 5.6.2, divided by the distance from the centroidal axis to the extreme tensile fibre; and
Z,, is the compressive section modulus of the full cross-sectional area about the centroidal axis perpendicular to the web 1, divided by the distance from the centroidal axis to the extreme compressive fibre.
6.4.1.2 The following exceptions, additions and modifications to 6.4.1 .I shall apply:
a) for channels and Z-shaped members with unstiffened flanges, see also 6.4.4;
b for closed box members, see 6.4.3.4;
c) for circular hollow sections, see 6.4.3.5;
d) the factored moment resistance AAr of a member classified as a structural hollow section manufactured in accordance with SABS 657-1 (cold-formed non-stress-relieved), or in accordance with BS 4848-2 or IS0 657-1 4 (hot-formed or cold-formed stress-relieved), and complying with clause 1 1 of SABS 0162-1 for sections of class 1, 2 or 3, shall be calculated in accordance with that standard.
e) in addition to 6.4.1 .I, 6.4.6 and 6.4.8 shall be considered.
6.4.2 Laterally supported members
f, shall be calculated in accordance with either 6.4.2.1 or 6.4.2.2. Lateral support may be provided by continuous or discrete bracing members. For discrete bracing, 6.4.2 only applies when f,, , as calculated in accordance with 6.4.3, is equal to or exceeds fy .
6.4.2.1 Based on initiation of yielding
fc = fy .
6.4.2.2 Based on inelastic reserve capacity
NOTE -This subclause does not apply to cylindrical hollow members (see 6.4.3.5).
6.4.2.2.1 The inelastic reserve capacity may be used when all of the following conditions are met:
a) the member is not subject to twisting or to lateral, torsional or torsional-flexural buckling;
b) the effect, if any, of coldwork of forming is disregarded;
c) the ratio of the depth of the compressive portion of the web to its thickness does not exceed
1 , l l R ;
d) the depth-to-thickness ratio h,lt does not exceed 3 , 7 3 R ;
e) the shear force due to ultimate loads V, does not exceed 0,64 Awfy ; and
f) the bend angle between web and flange is between 70" and 1 IO"(inc1usive).
SABS 01 62-2: 1993
6.4.2.2.2
where
Z, is defined in clause 6.4.1.1 ;
My is the moment causing a maximum strain of ey , where ey = fy /E ;
M; is the ultimate moment causing a maximum compressive strain of CYc,
(no limit is placed on the maximum tensile strain); and
is a factor determined as follows:
shall not exceed 1,25 My /Z, or M M; IZ,
Cy
a) for stiffened compressive elements without intermediate stiffeners,
1) when W 5 1 , I l a :
cy = 3;
2) when 1 , l I a c W I 1,28dE'fy :
C, = 3 - 11,8 W f l € - 1 , l l ;
3) when W > 1 , 2 8 m
cy= 1;
b) for unstiffened compressive elements, coinpressive elements with edge stiffeners, compressive elements with one intermediate stiffener and multiple stiffened compressive elements,
cy= 1.
6.4.2.2.3 Where applicable, effective design widths shall be used in calculating section properties.
M; shall be calculated considering equilibrium of stresses, assuming
a) an ideally elastic-plastic stress-strain curve that is the same in tension as in compression;
b) small deformations; and
c) plane sections before bending remain plane during bending.
6.4.3 Laterally unsupported members
6.4.3.1 General
For symmetric I-shaped, Z-shaped, or singly-symmetric single-web members, fc shall be calculated as follows:
a) when fb > f'l2 :
f c = f ' - - (f32 I fy 4fb
f ' = 1,11 f y ;
31
SABS 0162-2:1993
b) when fb I f l 2 :
fc = fb ;
where fb shall be calculated in accordance with 6.4.3.2, 6.4.3.3 or 6.4.3.4, as applicable.
6.4.3.2 Bending about a centroidal axis perpendicular to the web
fb shall be calculated as follows:
a) for doubly-symmetric I-sections,
fb = 0,833 cbfbe ;
b) for singly-symmetric sections such as channels,
fb = ~ CbroA ,&-( ; ZXC
c) for point-symmetric Z-sections,
fb = - Cbr,A 2ZXC
6.4.3.3 Bending about a centroidal axis parallel to the web of singly-symmetric sections, such as channels
fb shall be calculated as follows:
where, for clauses 6.4.3.1, 6.4.3.2 and 6.4.3.3,
h
L
I Y C
ZYC
z x c
A
32
is the overall depth of section;
is the unbraced length of member;
is the moment of inertia of the compressive portion of the full cross-sectional area about the centroidal axis of the entire section parallel to the web(s);
is the compressive section modulus of the full cross-sectional area about the centroidal y-axis parallel to the web (Iy divided by the distance from the centroidal axis to the extreme compressive fibre);
is the compressive section modulus of the full cross-sectional area about the centroidal x-axis perpendicular to the web (Ix divided by the distance from the centroidal axis to the extreme compressive fibre);
is the full cross-sectional area of member; and
SABS 01 62-2: 1993
C, = Vw is the bending coefficient and can be taken conservatively as unity; or shall not exceed 2,5 when w is calculated as
w
w
= 0,6 + 0,4 Ml/M2 for me'mbers bent in single curvature, or
= 0,6 - 0,4 Ml/M2 for members bent in double curvature,
where M,/M2 is the moment ratio of smaller to larger moment at opposite ends of the unbraced length, in the plane of bending.
When the bending moment at any point within ;an unbraced length is larger than that at either end of this length, the bending coefficient C, shall be taken as unity. Also, for members subject to combined axial and bending forces (see 6.7), C, shall be taken as unity.
Furthermore,
C, = +I for bending causing compression on the shear-centre side of the centroid;
C, = -1 for bending causing tension on the shear-centre side of the centroid; and
ro = ,/- ;
where
rxl 'y
K,, K,, Kt
L,, L,, L,
xo
J
c*
are the radii of gyration of the full cross section about the centroidal principal axes;
are the effective length factors for bending about the x-axis and y-axis, and for twisting;
are the unbraced length of member for bending about the x-axis and y-axis, and for twisting;
is the distance from shear centre to centroid of section;
is the St. Venant torsion const.ant for open sections;
is the warping constant of torsion; and
i I
x3dA + J n x y 2 d A ] t I X , ~ . = - [,A 21,
6.4.3.4 Closed box members
When bending is about the major axis of the section, fc is determined in accordance with 6.4.3.1, with fb defined as follows:
where
is the moment of inertia of the full cross-sectional area about the centroidal axis parallel to the web(s);
is the unbraced length of the member;
1,
L
33
SABS 0162-2:1993
Z,, is the compressive section modulus of the full cross-sectional area about the centroidal axis perpendicular to the web, i.e. 1,divided by the distance from the centroidal axis to the extreme compressive fibre; and
J = 2(ab)2 for closed members. alt, + d/t2
where
a is the distance between web centrelines;
b is the distance between flange centrelines;
t,
t2
is the thickness of the flanges; and
is the thickness of the webs.
6.4.3.5 Circular hollow sections
For outside-diameter-to-wall-thickness ratios dlt not exceeding 0,441 Elf, , the compressive stress fc on the full cross-sectional area shall be calculated as follows:
a) when dlt 5 0,07 Elf,:
fc = 1,25 fy ;
b) when 0,07 Elfy < dlt 5 0,319 Elfy
0,965 + 0,02 - " 1 fy ; and E
dlt
c) when 0,319 Elfy < dlt I 0,441 Elfy :
0,328E dl t
f c = - .
6.4.3.6 Other sections
For singly-symmetric I-sections and for asymmetric sections whose cross-sections do not have any symmetry, either about an axis or a point, the factored moment resistance shall be determined by rational analysis. Alternatively, members subject to bending that are composed of such sections may be tested in accordance with 9.3.3.
6.4.4 Channels and 2-shaped members with unstiffened flanges
For channels and Z-shaped members with unstiffened flanges and fc < fy , the factored moment resistance shall be further limited as follows:
4kn2 EZ, M, =
12(1 - p2)W2
where
k = 0,43;
34
SABS 01 62-2: 1993
Z, is the compressive section modulus based on the moment of inertia of the full cross- sectional area (gross or net), divided by the distance from the centroidal axis to the extreme compressive fibre; and
is the flat width ratio of the unstiffened flange (wlt). W
6.4.5 Shear in webs
The factored shear resistance V, of a web shall1 be determined by
vr = W w f v
where f, is determined as follows:
a) when H 5 ,/q :
f, = 0,64 fy
b) when /w < H I 1,41,/= :
0,641 K€ H
f; =
c) when H > 1,41 /wi : n2Ekv
fv = 12(1 - jL2)H2
where
A,
fv
fy
H = h3/f ;
is the area of the web;
is the limiting shear stress;
is the yield stress of the web material;
h, is the flat dimension of the web measured in the plane of web; and
k, is the shear buckling coefficient determined as follows:
1) for unreinforced webs, k, = 5,34;
2) for beam webs with transverse stiffeners satisfying the requirements of 6.5,
5 34 kv = 4 + -, when s/h3 I 1; (s1h3l2
k, = 5,34 + - , when slh, > 1; (s/h3)2
where s is the distance between transverse stiffeners.
Where the web consists of two or more sheets, each sheet shall be considered as a separate member carrying its share of the shear.
35
SABS 0162-2~1993
6.4.6 Combined bending and shear in webs
For webs subject to both bending and shear stresses, the member shall be so proportioned that the following limit is observed:
[ $I2 + [ + ) 2 5 1
For beam webs with both bearing and intermediate transverse stiffeners satisfying the requirements of 6.5, the member may be so proportioned that the following limits are observed:
MU
Mr
a) - I 1;
VU vr
b) - 5 1; and
VU M u vu Mr Vr Mr Vr
Mu c) 0,6 - + - 5 1,3 when - z 0,5 and - > 0,7 ;
where
Mu is the moment due to ultimate loads;
V, is the shear stress due to ultimate loads;
M,
V,
is defined in 6.4.1; and
is the factored shear resistance from 6.4.5 but without the limit of 0,64 fy on fv .
6.4.7 Web crippling
To avoid crippling of an unreinforced web of a member subject to bending, whose slenderness ratio H is equal to or less than 200, concentrated loads and reactions P, shall not exceed the values of Pr given in table 3 ,4 or 5. Webs of members in bending for which H exceeds 200 shall be provided with adequate means of transmitting concentrated loads or reactions directly into the web(s).
In tables 3, 4 and 5, P, represents the load or reaction for one solid web connecting top and bottom flanges. For webs consisting of two or more such sheets, P, shall be calculated for each individual sheet and the results added to obtain the limiting load or reaction for the full section.
One-flange loading or reaction occurs when the clear distance between the bearing edges of adjacent opposite concentrated loads or reactions exceeds 1 3 h, .
Two-flange loading or reaction occurs when the clear distance between the bearing edges of adjacent opposite concentrated loads or reactions is equal to or less than 1,5 h, .
End loading or reaction occurs when the distance from the edge of the bearing to the end of the member is equal to or less than 1 3 h, .
Interior loading or reaction occurs when the distance from the edge of the bearing to the end of the member exceeds 1 3 h, .
36
SABS 01 62-2: 1993
Table 3 - Values of f , for built-up sections
One-flange loading or reaction
P,= @,t2fyC2(10+ 125 0) t- Interior
I P, = @,t2fYC, (0,88 + 0,063f) (15 + 3,25 o ) I
Two-flange loading or reaction
F::C4 (0,64 + 0,16t) (10 + 1 3 0 )
@,t2fyC, (0,82 + 0,079t) (15 + 3,25 fl ) R 4, N .c 200 and I , Ih, < 1.
NOTE -This table applies to I-beams made of two channels connected back-to-back by a line of connectors near each flange or to similar sections that provide a high degree of restraint against rotation of the web, such as I-sections made by welding two angles to a channel.
Table 4 -Values for f , for sections having single webs
1
One-flange loading or reaction
Two-flange loading or reaction
2
End
For sections having stiffened flanges P, = 10t2fy (1,33 - 0,33k)(1,15 - 0,15R)(1 + O,OIN)(I - 0,0018H)
For sections having unstiffened flanges 7
interior**)
P,= @,6,6t2fy (1,33-0,33k)(1,15-0,15R)(1 + O,OIN)(l -0,0013H)
P,= @, 16t2fy (1,22 - 0,22k)(1,06 - 0,06R)(1 + 0,07N)(1 - 0,0014H)
End P, = as7,4t2f, (1,33 - 0,33k)(1,15 - 0,15R)(1 + O,OIN)(l - 0,0023H)
Interior P, = @, 16t2fy (1,22 - 0,22k)(1,06 - 0,06R)(1 + O,OlN)(l - 0,0029H)
*) When N > 60, the factor (1 + 0,Ol N) may be increased to (0,71 + 0,015 N). **) When N > 60, the factor (1 + 0,007 N) may be increased to (0,75 + 0,011 N).
NOTE - The above equations apply when R < 4, N < 200 and I , lh, 5 1.
NOTE -This table applies to single-web sections such as channels and 2-shaped sections.
37
SABS 0162-2:1993
r
Table 5 -Values of P, for deck sections (multiple webs)
2
End
P, = as 10 t2 fy (sin 8) (1 - 0 , l k) (1 - 0,l @ ) ( I + 0,005 N)(1 - 0,002 H )
Interior
P, = as 18 t2 fy (sin 8) (1 - 0,l k) (1 - 0,075 fi ) ( I + 0,005 N)(1 - 0,001 H )
End
P,= ~ s 1 0 f 2 f y ( s i n 8 ) ( l - 0 , l k)(1 - 0 , l ,&)(1+0,01N)(1-0,002H)
Interior
P, = as 18 t2 t; (sin 8)(l - 0,2 k) (1 - 0,03 ,& )(I + 0,ol N)(1 - 0,0015 H )
1
One-flange loading or reaction
Two-flange loading or reaction
NOTES
1 The above equations apply when R < 10, N 4 200, I , Ih, 4 2, and the cell spacing of the sections does not exceed 200 mm.
2 For single-hat sections, both webs shall be fastened to prevent spreading.
In tables 3, 4 and 5:
P, is the factored web crippling resistance;
C, = (1,49 - 0,53k) 1. 0,6;
C, = 1 + H/750 5 1,2;
C, = l / k when H 5 66,5;
C, = (1,l - H/665)/k when H > 66,5;
C, = (0,98 - H/865)/k ;
H = h,/t ;
h, is the flat dimension of the web measured in the plane of the web;
k = 883fjE ;
I, is the bearing length;
N = L,/t ;
R = r/t ;
r is the inside bend radius;
t is the web thickness; and
8 is the angle between the plane of the web and the plane of the bearing surface, 45" < 8 < 90" .
3%
SABS 0162-2~1993
6.4.8 Combined web crippling and bending
Except where otherwise noted, unreinforced flat webs of sections subject to a combination of bending and web crippling shall be designed to comply with the following requirements:
P" M" - + - 5 1,3 Pr Mr
where
P,
P,
is the concentrated load or reaction due to ultimate loads;
is the factored web-crippling resistance in accordance with 6.4.7;
Mu is the bending moment due to ultimate loads at the point of application of the concentrated load or reaction: and
M, is the factored moment resistance in accordance with 6.4.1 and 6.4.2.
Combined web crippling and bending does not need to be checked for multiple-web deck sections except where Mr has been calculated in accordance with 6.4.2.2.
6.5 Transverse stiffeners for beam webs
6.5.1 Bearing stiffeners
Transverse stiffeners attached to beam webs at points of concentrated loads or reactions shall be designed as compressive 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 load bearing into the end of the stiffener. Means for shear transfer between the stiffener and the web shall be provided in accordance with clause 7. The factored compressive resistance C, of the stiffener shall be the lesser of
where
A, = b,t + A, for transverse stiffeners at interior supports and under a concentrated load;
A,
A,
A,
A,
b,
b,
= b,t + A, for transverse stiffeners at an end support;
= 18t * + A, for transverse stiffeners at an interior support and under a concentrated load;
= 10t * + A, for transverse stiffeners at an end support;
is the gross cross-sectional area of a transverse stiffener;
= 25t [0,0024(LSt lt ) + 0,721 5 25t ;
= 12t [0,0044(L, l t ) + 0,831 5 12t;
39
SABS 0162-2:1993
fa is the compressive limit stress determined in accordance with 6.6 when the web stiffener section having a cross-sectional area A, is designed as an axially-loaded compressive member with K = 1 ;
fy
L,,
is the lower value of the yield stress of the beam web or the stiffener section;
is the total length of the transverse stiffener; and
t is the thickness of the beam web.
The flat width ratio Wof stiffened and unstiffened elements of cold-formed steel transverse stiffeners shall not exceed Vk,,,, as defined in 5.6.2, with f = fy , the yield stress of the stiffener steel.
6.5.2 Intermediate stiffeners
Where intermediate stiffeners are required, the spacing shall be such that the web shear V, does not exceed the value of V, permitted by 6.4.5, and the ratio slh, does not exceed (260/H)' or 3,O.
The moment of inertia of a pair of attached intermediate stiffeners or of a single intermediate stiffener, with reference to an axis in the plane of the web, shall be at least
I S = 5h,t3 [h3/s - 0,7~1h,] 2 (h3/50)4 .
The gross cross-sectional area of intermediate stiffeners shall be at least
YDH,t A, = ~ 1 ~ c, b3- (s/h3)2
2 s/h, + (1 + (S/h3)' )Ot5
where 310 OOOk,
H ' fy c, = when C, I 0,8 , and
c, = 500 - H
when 0,8 < C, I 1,0 ;
k, = 5,34 + - 4100 when slh, > 1,0 , and (S/hJ2
k, = 4,OO + - 5'34 when slh, I 1,0 : (s/h3)2
s is the distance between transverse stiffeners:
fv of web steel
fy of stiffener steel ' Y =
D = 1 ,O for stiffeners in pairs,
= 1,8 for single-angle stiffeners,
= 2,4 for single-plate stiffeners;
H = hJt;
40
h,
t is the web thickness.
is the flat dimension of the web measured in the plane of the web; and
6.5.3 Integral stiffeners
The factored resistance of members with integral stiffeners that do not comply with either 6.5.1 or 6.5.2, such as stamped or embedded transverse, inclined or longitudinal stiffeners, shall be determined by tests in accordance with 9.3.3.
6.6 Members in compression (concentrically loaded)
6.6.1 General
6.6.1.1 Except as provided in 6.6.1.2, 6.6 applies to members subject to compression in which the resultant of all loads and moments acting on the member is equivalent to a single force acting through the centroid of the full cross-sectional area in the direction of the longitudinal axis of the member. For such members, the compressive resistance C:, shall be determined in accordance with 6.6.1.3 and subsequent subclauses, as applicable.
6.6.1.2 The following exceptions, additions and modifications to 6.6.1 .I shall apply, as relevant:
a) members for which the loading criterion stated in 6.6.1.1 does not apply shall be designed in accordance with 6.7;
b) members classified as structural hollow sections and manufactured in accordance with SABS 657-1 (cold-formed non-stress-relieved) or in accordance with BS 4848-2 or IS0 657-14 (hot-formed or cold-formed stress-relieved), and complying with clause 11 of SABS 0162-1 for sections of class 1, 2 or 3, shall be designed in accordance with that standard;
c) members other than those referred to in (b) above that are cold-formed from material of thickness exceeding 4 3 mm shall be designed as follows:
1) the area of the member shall be the effective cross-sectional area calculated on the basis of the effective width provisions of 5.6.;!; and
2) the effective width shall be determined with the value of f set equal to the axial compressive stress given by the applicable expression in SABS 0162-1, taking the radius of gyration as that of the full cross-section of the member; and
d) additional requirements for members corisisting of channels, Z-shapes, or single angles with unstiffened flanges are given in 6.6.3.2.
6.6.1.3 Except as noted in 6.6.5, in the case of members in which the maximum flat width ratio of stiffened compressive elements does not exceed 200 and for which the maximum flat width ratio of unstiffened compressive elements does not exceed 60, the compressive resistance C, shall be determined by
where the compressive limit stress fa is determined as follows:
41
SABS 01 62-2: 1993
a) when fp > fy12,
f 2 f = f -2 a 4fp
b) when fp 5 fy/2,
fa = fp
where
A, is the effective cross-sectional area, determined in accordance with 5.6.2 or 6.6.5, as applicable, with f = fa ; and
is the critical elastic buckling stress, being the least of the stresses for Euler-flexural, torsional or torsional-flexural elastic buckling, multiplied by the coefficient 0,833, determined in accordance with 6.6.2, 6.6.3, 6.6.4 or 6.6.5.
fp
6.6.2 Sections not subject to torsional-flexural buckling
For I-sections, closed cross-sections and any other sections that can be shown to be not critical in torsional buckling or not subject to torsional-flexural buckling, fp is given by
fD = 0,833 fe
where
f, = x2E/(KL/r)'
KLIr is the the greater of the effective slenderness ratios about the principal axes;
K is the effective length factor (see 5.3);
L is the unbraced length of member; and
r is the radius of gyration of the full cross-sectional area.
6.6.3 Singly-symmetric sections
6.6.3.1 For singly-symmetric open sections, such as plain and lipped channels and single or double plain and lipped angles, that may be subject to torsional-flexural buckling, fp is given by
fp = 0,833 fst or 0,833 fe, whichever is less
where
f, is as defined in 6.6.2 or 6.6.7.1, as applicable, and
1 fst = - fs + ft - J( fs + f t ) 2 - 4Pfsf, 28 * [
fs = x2E/(KL/r)'
42
SABS 01 62-2: 1993
p = 1 - (xo/r0)’
A
r , = /- r, ,ry are the radii of gyration of the full cross-sectional area about the centroidal principal axes;
4
is the full cross-sectional area of the member;
is the effective length factor for torsional buckling;
L,
x,
KLIr is the effective slenderness ratio associated with bending about the axis of symmetry of the
is the length of a member unsupported against twisting;
is the distance from the shear centre ,to the centroid of the section;
full cross-sectional area; and
J is the St. Venant torsion constant for open sections
= 0,33 ( I , t , 3 + I, t Z 3 + ... t- I , t n 3 )
where
f,, f2, f,, are the steel thicknesses of the member segments; and
I,, 12, I,, are the middle line lengths of the member segments.
6.6.3.2 For channels, Z-shaped sections, and single-angle sections with unstiffened flanges, the factored compressive resistance shall be further limited as follows:
+akrc2EA c, = 12(1 - &w2
where
@a = 0,90;
k = 0,43;
A is the full cross-sectional area of member; and
W is the flat width ratio of unstiffened flange element.
This additional limit shall be waived if the channel or Z-shaped sections are fully restrained with respect to torsion and flexural buckling about the asyrrimetric axis.
43
SABS 0162-2:1993
6.6.4 Point-symmetric sections
For point-symmetric open sections, such as cruciform and Z-shaped sections, or such built-up sections that may be subject to torsional buckling and that are not braced against twisting, 6.6.1 shall be used to obtain the factored resistance, with fp equal to the lesser of 0,833 fe (from 6.6.2) and 0,833 ( (from 6.6.3).
6.6.5 Circular hollow sections
The outside-diameter-to-wall thickness ratio dlt shall not exceed 0,441 €If, . The compressive resistance shall be calculated in accordance with 6.6.1.3, with A, determined as follows:
a) when fp s f,l2:
A, = A
b) when fp > f,l2 and dlt s 0,113 Elf,:
A, = A
c) when fp > f,l2 and 0,113 Elf, < dlt s 0,441 Elf,:
where
+ 0,666 A ; 1 0,03 7 Elf,,
= [ d/t
fe = n2N(KLlr)2 ; and
fp = 0,833 f,.
6.6.6 Other sections
For asymmetric sections whose cross-sections do not have any symmetry either about an axis or a point, and for sections formed with any stiffened element whose flat width ratio exceeds 200 or any unstiffened elements whose flat width ratio exceeds 60, the factored compressive resistance shall be determined by rational analysis. Alternatively, compressive members composed of such sections may be tested in accordance with 9.3.3.
6.6.7 Built-up members
6.6.7.1 For compressive members composed of two or more sections connected together at discrete points, such as double angles and battened channels, thefactored compressive resistancefor buckling about the built-up member axis shall be given by 6.6.1, using
fD = 0,833 fe
where - X2E - fe
(KL I r)2 + ( s I r,)* ’
44
SABS 01 62-2: 1993
KUr is the overall slenderness ratio of the entire section about the built-up member axis;
s
r1
is the fastener spacing; and
is the radius of gyration of the full cross-sectional area of an individual section in a built-up member.
6.6.7.2 Each discrete connection shall be c,apable of transmitting a longitudinal shear force of 0,05 times the force in one section of a built-up member.
6.6.7.3 For torsional-flexural buckling of singly-symmetric sections, 6.6.1 shall be used to obtain the factored compressive resistance, except that in 6.6.3, fe shall be as determined in 6.6.7.1, and this fe
replaces 5 in the expression for ct . 6.7 Combined axial load and bending
6.7.1 Doubly-symmetric sections (including circular hollow sections)
When subject to both axial compression and bending, members shall be proportioned to comply with the following:
where
C, is the axial force in the member due to ultimate loads;
Cr = @,A& ;
A, is the effective cross-sectional area determined in accordance with 5.6.2, with f = fy ;
Mr is the factored moment resistance calculated in accordance with 6.4.1; and
Mu is the factored moment at the point under consideration;
is as defined in 6.6;
are the factored moment resistances determined in accordance with 6.4.1 and 6.4.3, with C, = 1;
are the maximum calculated moments due to ultimate loads occurring either at or between braced points;
are the coefficients used to determine equivalent uniform bending stress defined in 6.7.3:
are the amplification factors, equal to 1 - Cu/Ce;
45
SABS 0162-2:1993
CU
Ce
is the axial compressive force in the member due to ultimate loads; and
= Afe , where fe is as defined in 6.6.2, with KL/r being the slenderness ratio in the plane of bending for which is calculated (i.e. x-axis or y-axis) and A being the full cross-sectional area.
6.7.2 Singly-symmetric sections
When subject to both axial compression and bending, members shall be proportioned to comply with the following:
M + 3 1. l ,o c u Mux
Cr M r x M V
a) - + -
where C,, Cr, M,, My, Mu, and Muy are as defined in 6.7.1 (a);
where
CU is the axial compressive force due to ultimate loads;
C, is as defined in 6.6;
Mu,, Mu, are the maximum calculated moments due to ultimate loads occurring either at or between braced points;
w, , w, , a,, ay
Mrx
are as defined in 6.7.l(b);
is the lesser of @Z,fy or aUZtnfu , as defined in 6.4.1, and @Zcfb,,, where Z, is the compressive section modulus based on the moment of inertia of the effective cross-sectional area about the axis of symmetry, calculated in accordance with 5.6.2, divided by the distance from the centroidal axis to the extreme compressive fibre and fbx is determined as follows:
-when fcr > f42 ,
fy” fbx = fy ~ - 4 fcr
- when fcrs f42,
fbx = fcr
where 0,833cro A a
I X
fcr =
46
SABS 01 62-2: 1993
6 is as defined in 6.6.3.1;
I, is the moment of inertia of the full (cross-sectional area about the axis of symmetry;
c is the distance from the centroidal x-axis to the fibre with maximum compressive stress;
A is the full cross-sectional area of the member;
r., = ,/- ; and
KyLy is the effective length of the member about the y-axis.
Mry is the lesser of $Ztfy and QUZtnfu , as defined in 6.4.1, and @Zcfby, where fby is determined as follows:
- when fcr > fJ2 ,
-when fcr 5 f42 ,
fby = fcr
where
fc, = 0,833 fbc for bending causing compression on the shear-centre side of the centroid;
cr = 0,833 fbt for bending causing tension on the shear-centre side of the centroid;
fbt = - Mt = maximum compressive! bending stress caused by M, ; I Y
M c c I ,
fbc = - = maximum compressive bending stress caused by M, ;
A, r,, x,, 6 and are as defined in 6.6.3.1 ;
Iy is the moment of inertia of the full cross-sectional area about the asymmetric axis; and
c is the distance from the centroidal y-axis to the fibre with maximum compressive stress.
47
SABS 0162-2:1993
6.7.3 Coefficients of equivalent uniform bending
6.7.3.1 General
The coefficients of equivalent uniform bending w, and w, shall be determined by analysis, or the values specified in 6.7.3.2 and 6.7.3.3 may be used. The symbol w refers to either w, or w, .
6.7.3.2 Members not subject to transverse loads between supports
6.7.3.2.1 For compressive members in frames that depend on their own flexural stiffness to prevent sidesway in the direction being considered:
w = 0,85 for members bent in double curvature or subject to moment at one end only; and
w = 1 ,O for members bent in single curvature due to moments at both ends.
6.7.3.2.2 For compressive members in frames that are braced against joint translation in the direction being considered:
w = 0,6 + 0,4 M,lM, for members bent in single curvature; and
w = 0,6 - 0,4 Ml/M, for members bent in double curvature, but not less than 0,4
where Ml/M2 is the ratio of smaller to larger moment at opposite ends of the unbraced length in the plane of bending considered.
6.7.3.3 Members subject to transverse loads between supports
For compressive members in frames braced againstjoint translation in the plane of loading and subject to transverse loading between their supports, the value of w may be determined by rational analysis. However, in lieu of such analysis, the following values may be used:
w = 0,85 for members whose ends are restrained; and
w = 1,OO for members whose ends are unrestrained.
6.7.4 Single angles loaded through one leg
For single angles loaded at each end through the same leg by bolts or welds, the factored compressive resistance shall be given by 6.6.1.3, using fp = 0,833 fe , but shall not exceed 0,5 AfY for members loaded through a single bolt, or 0,67 Af, for members loaded through welds or multiple bolts,
where
L is the unbraced length of member;
r, is the least radius of gyration of the full cross-sectional area;
h is the larger leg width;
f is the leg thickness; and
48
SABS 01 62-2: 1993
K is the effective length factor = 0,8 for 1:ranslation-fixed connections using a single bolt and 0,7 for translation-fixed connections using welds or two or more bolts.
6.8 Wall studs
6.8.1 General
The factored compressive resistance of a stud may be calculated in accordance with 6.6 (disregarding sheathing) or on the assumption that the sheathing attached to both flanges of the stud furnishes adequate lateral and rotational support to the stud in the plane of the wall, provided that the stud, sheathing and attachments comply with the following requirements:
both ends of the stud are braced against rotation about the stud axis and against horizontal displacement perpendicular to the stud axis; however, the ends may or may not be free to rotate about the axes perpendicular to the stud axis;
sheathing is connected to the top and blottom members of the wall assembly to enhance the restraint provided to the stud and to stabilize the overall assembly;
sheathing retains adequate strength and stiffness for the expected service life of the wall;
steel bracing is installed as required for adequate structural integrity during construction and in the completed structure; and
steel studs do not exceed 152 mm in depth, 1,91 mm in base steel thickness, 5 m in length, and 345 MPa in yield stress, and the stud spacing is not less than 300 mm and not more than 600 mm.
6.8.2 Studs in compression
6.8.2.1 For studs that have identical sheathing material (having limit shear rigidity 6 ) attached to both flanges, and where any rotational restraint provided by the sheathing is ignored, the factored compressive resistance shall be determined Iby
C, = w,A,fa
where
A, is the effective cross-sectional area determined in accordance with 5.6.2, with f = fa ; and
fa is the least of the values for the following three provisions:
Provision 1
To preclude column buckling between fasteners in the plane of the wall, fa is determined as in 6.6.1, with KL equal to twice the distance between fasteners.
Provision 2
To preclude flexural or torsional overall column buckling, or both, fa is determined as follows:
a) when fp > f42,
( fJ2 f a = f - - 4fp
49
SABS 0162-2~1993
b) when fp 5 fJ2,
fa = fD
where
fp
1)
is the critical elastic buckling stress under concentric loading, which shall be taken as specified below for each section type:
for singly-symmetric channels, fp is the lesser of
fp = 0,833 (fey + 6,) and
2) for Z-shaped sections, fp is the lesser of
fp = 0,833 (< + 6,) and
3) for doubly-symmetric I-shaped sections, fp is the lesser of
fp = 0,833 (fey + 6,) and
fp = 0,833 fex
where, for items (I), (2) and (3) ,
fey = n2 E/(L/r,)*
fex = n2 E/(L/r,)’
fexy = n2 ElwlAL2
- - Q = gB is the limit shear rigidity with sheathing on both flanges of the studs;
- - q = g o ( 2 - ~1300) is the limit shear rigidity per unit length of stud spacing, with sheathing
on both flanges of studs, based on the actual fastener spacing (see table 6);
B is the stud spacing; - Q Q, = -; A
-
A is the full cross-sectional area of a stud;
50
SABS 01 62-2: 1993
p = 1 - (x,/r,)* ;
x, is the distance from the shear centre to the centroid of the section (absolute value);
2 2 2 ro = rx t ry t x,
r,, ry are the radii of gyration of the lull cross-sectional area about the centroidal principal
h
J
C,
L
Zv
axes;
is the overall depth of the sectiomn;
is the St. Venant torsion constant;
is the warping constant of torsio'n;
is the length of a stud; and
is the product of inertia of the full cross-sectional area
Provision 3
To preclude shear failure of the sheathing, fa shall also not exceed 0, where a is determined (by iteration), to satisfy the requirement that y, the shear strain in the sheathing corresponding to 0, does not exceed the limit shear strain of the sheathing 7 given in table 6. To initiate the iterative calculations required to establish the strain compatibility of ,y and 7 , 0 can initially be taken as the lesser value of fa as calculated in provisions 1 and 2 of this subclause. The shear strain y shall be determined as follows:
where C, and E, are the absolute values of C, and E, specified for each of the following types:
a) singly-symmetric channels
- c, = (Jco fey - (J + Q a
b) Z-shaped sections
51
SABS 0162-211993
c) I-shaped sections
E, = 0
where, for items (a), (b) and (c),
fex, fey, fexy, ftQ, 0 , ro and xo are as defined in provision 2 of this subclause;
CO, E, and Do are initial column imperfections, which shall be assumed to be at least as follows:
CO = L/350, in a direction parallel to the wall;
Do = L/700, in a direction perpendicular to the wall, and
15, = L/10 000 h, a measure of the initial twist of the stud from the ideal configuration.
If U > fy/2, then in the definitions for fey , fex , fexy and fta , the parameters E and G shall be replaced by E' and G', respectively, given by
E' = 4E a (fy - a )/f: and
G' = G(E '/a. For types of sheathing other than those given in table 6, 4, and 7 may be determined conservatively from representative small-scale tests as described by published, documented methods.
Sheathing parameter values 9, and 7 , determined from representative full-scale tests described by published, documented methods may also be used instead of the small-scale test values given in table 6.
52
SABS 01 62-21 1993
93 Lignocellulosic to 15 mm thick board gypsum board
Fibreboard (regular or impregnated) Fibreboard (heavy, impregnated)
Table 6 - Sheathing parameters’)
0,008
0,007 31 5 0,010
1 0,009
Sheathing material’)
- Limit shear rigidity 9 Limit shear strain y
mmlmm - 3 ’ I Nlmm
6.8.2.2 Studs with sheathing on one flange only, non-identical sheathing, or when the rotational restraint is included, or any combination of the above, shall be designed in accordance with the same basic principles of analysis used in deriving the provisions in 6.8.2.1.
6.8.3 Studs subject to combined axial load and bending
The factored resistance of studs subject to (combined axial compression and bending shall be determined by
When % 5 1 ,O , the following formula may be used in lieu of the above: C,
where
C,, is the axial compressive load in the stud due to ultimate loads;
C, is the factored compressive resistanc:e under concentric loading in accordance with 6.8.2;
Mu, is the maximum calculated moment about the x-axis due to ultimate loads;
Mm is the factored moment resistance calculated in accordance with 6.4.1 and 6.4.2;
53
SABS 0162-2:1993
C, =AY,,;
A is the full cross-sectional area of member;
L is the length of the wall stud; and
r, is the radius of gyration of the full cross-sectional area about the x-axis.
7 Connections
7.1 General
7.1.1 Design
Connections shall be designed to transmit the effects of ultimate loads in connected members with due regard for eccentricity.
7.1.2 Connections subject to force reversal
Connections subject to sudden reversal of force due to moving loads, other than loads caused by wind or earthquake, shall be proportioned for a force reversal equal to the sum of the forces of each sign.
7.1.3 Fastening methods
Any suitable mechanical fastener, weldment, special device or other effective means may be used to join component parts together, provided that the fastening method is compatible with the service conditions. Fastening methods that are not covered by requirements in clause 7 shall be subject to evidence of suitability prior to use.
7.1.4 Resistance factor
The value of the resistance factor I$ c , when connection resistance is being determined, shall be taken as 0,67.
7.2 Welded connections
7.2.1 Qualification
Arc welding shall be performed by a fabricator or erector qualified in accordance with AWS D1.l.
Resistance welding shall be performed by a fabricator or erector qualified in accordance with AWS D1.l.
7.2.2 Arc welds
7.2.2.1 Thickness limitations
7.2.2.1.1 Thicknesses exceeding 3 3 mm
Where each connected part exceeds 3,5 mm in thickness, welding shall comply with the provisions of SABS 044.
54
SABS 01 62-2: 1993
7.2.2.1.2 Thickness from 0,7 mm to 3 3 mm
Where at least one of the connected parts is between 0,7 mm and 3,5 mm in thickness, welding shall conform to the requirements contained in this p,art of SABS 0162 and shall be performed in accordance with the applicable requirements of AWS D1 .I.
7.2.2.1.3 Thickness less than 0,7 mm
Where at least one of the connected parts is less than 0,7 mm in thickness, welds shall be considered to have no structural value unless a value is substantiated by appropriate tests.
7.2.2.2 Butt welds
The resistance of butt welds in tension or in cornpression shall be the same as prescribed for the lower strength of the parent metal being joined. The butt weld shall fully penetrate the joint.
7.2.2.3 Arc spot and seam welds
7.2.2.3.1 General
Arc spot welds (circular in shape) and arc seam welds (oval in shape) covered by this part of SABS 0162 are for welding steel sheet to thicker supporting members in the flat position. The weld is formed by melting through the steel sheet to fuse with the underlying supporting member, whose thickness at the weld location shall be at least 2,5 times the steel sheet thickness (aggregate sheet thickness in the case of multiple plies). The materials to be joined shall be of weldable quality and the electrodes to be used shall be suited to the materials, the welding method, and the ambient conditions during welding.
7.2.2.3.2 Maximum and minimum sheet thickness
For arc spot and seam welds:
a) the maximum single sheet thickness shall 15e 2,O mm;
b) the minimum sheet thickness shall be 0,7 mm; and
c) the maximum aggregate sheet thickness of double sheets shall be 2,5 mm.
7.2.2.3.3 Minimum weld size
The minimum surface diameter of an arc spot weld shall be 12 mm and the minimum surface width and length of an arc seam weld shall be 10 mm and 25 mm, respectively.
7.2.2.3.4 Minimum distance to end of sheet
The distance from the centreline of the weld to the end or boundary of the connected sheet shall be at least 25 mm.
7.2.2.3.5 Factored resistances
The factored resistances shall be determined by
a) for an arc spot weld,
55
SABS 0162-2:1993
Tr =@,0,67t(d - t)fu ;
where
V,
T,
fu
fuw
f
d
d,
If
is the factored shear resistance;
is the factored tensile resistance;
is the specified minimum tensile strength of sheet;
is the specified minimum ultimate strength of the welding electrode;
is the thickness of the sheet; one sheet thickness in the case of multiple plies;
is the surface width (diameter) of the weld; not to be taken as greater than 20 mm;
is the effective width of the weld = 0,7d - 1 3 If ; and
is the total sheet thickness to be fused to the supporting member.
b) for an arc seam weld
V, = @,2,10t[0,25L +
Tr = @, 0,70t [ 0,25L
where
0,96(d- f)fu 5 4, [ : (de)2 + Ld, 0,75f,, 1 + 0,96(d - t ) ] f
U
L is the length of the seam weld excluding the circular ends (but which shall not exceed 3d ); and
d is the surface width (diameter) of the weld (but which shall not exceed 16 mm).
7.2.2.4 Fillet welds
Fillet welds covered by this part of SABS 0162 apply to the welding of joints in any position, either sheet-to-sheet or sheet-to-thicker-steel-member.
The factored shear resistance V, of a fillet weld in lap and T-joints shall be determined as follows:
a) for welds parallel to the direction of loading,
when Llt 525:
v, = @,fL( l - 0,OI)) f"
when Llt > 25:
V, = @,0,75tLfu
b) for welds perpendicular to the direction of loading,
v, = ac fLf,
where
L is the length of the fillet weld;
56
SABS 0162-2:1993
t is the thickness of the thinner sheet; ancl
fu is the tensile strength of the thinner sheet.
7.2.2.5 Flare-bevel groove welds
Flare-bevel groove welds covered by this pait of SABS 0162 apply to the welding of joints in any position, i.e. sheet-to-sheet for f1are-V groove welds, and sheet-to-sheet or sheet-to-thicker-steel- member for flare-bevel groove welds.
The factored shear resistance of the welds V, shall be governed by the thickness t of the steel sheet adjacent to the welds and shall be determined by
a) for flare-bevel groove welds perpendicular to direction of loading (see figure 7(a))
where
L is the length of the weld;
fu is the specified minimum tensile strength of the thinner sheet; and
t is the thickness of the thinner sheet,
b) for flare-bevel groove welds parallel to the direction of loading (see figures 7(b) and 7(c)), if the effective throat t , is equal to or exceeds t but is less than 2t, or if the lip height d is less than the weld length L, then
V, = @,0,75tLfu
If t, is equal to or greater than 2t and the lip height is equal to or greater than L, then
where t, is the effective throat of the flare-bevel groove weld as shown in figure 7(c).
7.2.3 Resistance welds
For sheets joined by spot welding, the factored shear resistance per spot weld in newtons shall be determined by
V, = @,4000t1*5
where t is expressed in millimetres.
This equation applies to welds in sheets of thickness between 0,7 mm and 6 mm (inclusive).
7.3 Mechanical fasteners (bolts, rivets and screws)
7.3.1 General
7.3.1 .I The following requirements apply where the thickness of the thinnest connected part does not exceed 4 3 mm, where there are no gaps between the connected parts, and where fasteners are installed with sufficient tightness to achieve satisfactory performance of the connection under expected
57
SABS 0 1 62-2: 1 993
service conditions. The design of mechanically fastened connections in which the thickness of all connected parts exceeds 43 mm shall be in accordance with SABS 01 62-1.
7.3.1.2 For screws and special fasteners not covered by 7.3.2,7.3.3 and 7.3.4, the factored resistance shall be taken as 0,75@, times the average ultimate resistance considered, as determined by the manufacturer.
50
SABS 01 62-2: 1993
Org.12840-ec/00-05 NOTE - t , = Lesser O F t, and t2
Figure 7 - Flare-bevel groove welds
59
SABS 0162-2:1993
7.3.2 Factored shear resistance
For bolts and solid rivets, the factored shear resistance V, of the fastener is given by
v, = @,0,6A,f”
where
A, is the cross sectional area of fastener based on nominal diameter; and
fu is the specified minimum tensile strength of fastener.
If bolt threads are in a shear plane, the afore-mentioned value of V, shall be multiplied by 0,75.
7.3.3 Factored tensile resistance (bolts)
The factored tensile resistance T, of a bolt is given by
A, is the cross sectional area of bolt based on nominal diameter; and
f, is the specified minimum tensile strength of bolt.
NOTE - The pullover strength of the connected sheet at the bolt head, nut, or washer shall be considered where bolt tension is involved.
7.3.4 Factored combined shear and tensile resistance (bolts)
For bolts subject to both shear and tension (exclusive of tension due to tightening), the reduced factored tensile resistance T,’ is given by
T,’ = 1,25 T, - kV, 5 T,
where
T, is the factored tensile resistance given in 7.3.3;
V, is the shear force on bolt due to ultimate load; and
k = 1,8, except that where bolt threads are excluded from each shear plane, k may be taken as 1,40.
7.3.5 Factored bearing resistance (single fasteners)
7.3.5.1 The factored bearing resistance of the connected part for each loaded fastener shall be determined from
60
SABS 01 62-2: 1993
10 < dlt 5 15
where
t is the thickness of the part;
d is the nominal diameter of the fastener;
fu is the specified minimum tensile strength c the connected part;
a is the distance from the hole centre to the edge towards which the force is directed; and
C is the the appropriate value from table 7.
Although a washer should be used under the element of the fastener (i.e. head or nut) that is turned during installation, the values of table 7 shall be applied whether or not washers are used.
Bearing resistance is independent of any tension in the fastener, or of whether the thread or the shank bears on the connected part.
Table 7 - Factor C for bearing resistance of fasteners
30 tld
Ratio of fastener diameter to thickness
of part dlt dlt 5 10
61
SABS 0162-2:1993
7.3.6 Factored bearing resistance (groups of fasteners)
7.3.6.1 Where the force is directed away from the edge of the connected part or the group of fasteners is remote from an edge, the bearing resistance of a group of fasteners in which the centre-to-centre distance between fasteners is at least Cd shall be equal to the sum of the individual resistances.
If the spacing is less than Cd but not less than 2,5d, the resistance shall be reduced proportionately.
7.3.6.2 For fastener groups where the force is directed towards an edge, the factored resistance shall be the lesser of that given by 7.3.6.1 and that given by
a) for rectangular groups as shown in figure 8(a):
B, act [(rn - l)(g ~ d h ) + (n - l ) (S - dh) + e] fu
b) for staggered groups as shown in figure 8(b):
B, = act [2(m ~ l ) (g ~ d , + $149) + e] fu
where
g, s are the spacings of rows of fasteners measured normal and parallel to the direction of force, respectively;
rn is the number of fasteners in the first row parallel to the edge;
n is the number of rows of fasteners:
e is the edge distance of the first row; if e =- Cd, e should be replaced by Cd in the equation;
d ,
C
is the diameter of a fastener hole;
is the appropriate value from table 7;
t is the thickness of the connected part; and
fu is the specified minimum tensile strength of the connected part.
The above equations represent the force required to tear out the portion bounded by the failure planes ABCD indicated in figure 8. For other fastener patterns, the tear-out resistance shall be shown to be adequate.
62
SABS 01 62-2: 1993
s e - I T 1 -
la)
A
D
- - s e
( b )
Figure 8 - Tear-out of bolt groups
7.3.7 Dimensions of fastener holes
Unless otherwise specified, circular holes for bolts shall not exceed nominal bolt diameter dplus 1 mm for bolt sizes up to 13 mm, and plus 2 mm for bolt sizes over 13 mm.
7.3.8 Minimum edge distance and spacing
The centre-to-centre distance between fasteners shall be at least 2,5d, and the distance from the centre of a fastener to an edge shall be at least 1,5d, where d is the nominal diameter of fastener.
7.4 Connections in built-up members
7.4.1 The number of fasteners joining components together to form a beam or column shall be sufficient to transfer the shear forces developed, and the fastener spacing shall be such that the calculated resistance is not invalidated by the buckling of the members between fasteners.
7.4.2 In columns composed of two or more sections, 6.6.7 shall apply.
7.4.3 In built-up beams, the fasteners shall be capable of transferring any force applied to one element only, at the point of application of the force.
In double-channel beams at points of load application, the connection shall be capable of resisting a force Vm/2g tending to separate the flanges,
where
V is the locally applied ultimate load on the beam;
rn is the distance between the shear centre of the channel and the mid-plane of the web; and
g is the distance from the fastener to flanges that are tending to close.
63
SABS 0162-2:1993
In the case of uniformly distributed loading, the value of Vshall be given by V= 3sp
where
s is the fastener spacing along the beam; and
p is the ultimate load per unit length of the beam.
The beam shall be fastened at spacings not greater than L/4.
7.5 Spacing of fasteners in compressive elements
The spacing sin the line of force of welds, rivets or bolts connecting a compressive cover plate or sheet to a non-integral stiffener or other element shall not exceed the lesser of s, and s, for stiffened elements, or the least of s,, s, and s, for unstiffened elements, where
a) s, is the spacing required to transmit the shear between the connected parts on the basis of the specified design strength per connection;
b) s b = 1,5t J E I f
where
f is the thickness of the cover plate or sheet; and
f is the compressive stress in the cover plate or sheet calculated using ultimate loads and effective section properties;
c) s , is the greater of 3w and 1,37t ,/E / fy
where
w is the flat width of the narrowest unstiffened compressive element in the portion of the cover plate or sheet that is tributary to the connections; and
f , is the yield stress of the cover plate or sheet.
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 13 mm. In all other cases, the spacing shall be taken as the centre-to-centre distance between connectors.
The above does not apply to cover sheets that act only as sheathing material and are not considered as load-carrying elements.
8 Bracing
8.1 General
8.1.1 Structural members and assemblies shall be adequately braced to prevent collapse and to maintain integrity during the expected service life of the structure. Care shall be taken to ensure that the bracing of entire structural systems is complete, particularly when there is interdependence between walls, floors, or roofs acting as diaphragms.
64
SABS 01 62-2: 1993
8.1.2 Design drawings shall show the details of the essential bracing requirements, including any details necessary to assure the effectiveness of the bracing or bracing system.
8.1.3 The spacing of braces shall not exceed the unbraced length assumed in the design of the member or component being braced.
8.2 Sections that are symmetric relative to the plane of loading
8.2.1 General
The provisions of 8.2 apply to members subject to compression and members subject to bending and that consist of symmetric sections in which the applied load does not induce twist.
8.2.2 Discrete bracing
The factored resistance of braces shall be at least 0,02 times the ultimate compressive force in the member subject to compression at the braced location or at least 0,02 times the ultimate compressive force in the compressive flange of the member subject to bending. When more than one brace acts at a common location and the nature of the braces is such that combined action is possible, the bracing force may be shared proportionately. The slenderness ratio of compressive braces shall not exceed 200.
8.2.3 Bracing by deck, slab or sheathing
The factored resistance of the attachments along the entire length of the braced member shall be at least 0,05 times the ultimate maximum compressive force in the member subject to compression or at least 0,05 times the ultimate maximum compressive force in the compressive flange of the member subject to bending.
8.3 Channel and 2-shaped members in bending
8.3.1 General
The provisions of 8.3 apply to members subject to compression and members subject to bending in which the applied load in the plane of the web induces twist. Braces shall be designed to avoid local crippling at the points of attachment to the member.
8.3.2 Discrete bracing
8.3.2.1 Braces shall be so connected as to effectively restrain both flanges of the sections at the ends and at intervals not exceeding one-quarter of the span length and in such a manner as to prevent tipping at the ends and lateral deflection of either flange in either direction at intermediate braces. Fewer braces may be used if this approach can be shown to be acceptable by rational analysis or by testing, taking into account the effects of both lateral and torsional displacements.
8.3.2.2 If fewer braces are used (when shown to be acceptable by rational analysis or by testing) for those sections used as purlins with "floating" type roof sheeting that allows for expansion and contraction independent of the purlins, the number of braces per bay shall be at least one for spans up to 7,O m and at least two for spans exceeding 7,O m.
8.3.2.3 If one-third or more of the total load on a beam is concentrated over a length of one-twelfth or less of the span of the beam, an additional brace shall be placed at or near the centre of this loaded length.
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8.3.2.4 Braces to restrain flanges shall be designed to resist a lateral force PL, determined as follows:
a) for a uniformly loaded beam, fL = 1,5K' times the load within a distance of 0,5a on each side of the brace: and
b) for concentrated loads, PL = K'times the concentrated load P within a distance of 0,3a on each side of the brace, plus 1,5(1 - x/a)PK'for each such concentrated load P, located further than 0,3a, but not further than the distance a, from the brace,
where
x is the distance from the concentrated load P, to the brace; and
a is the length of the bracing interval.
For channels, K' = m/h
where
rn is the distance between the shear centre and the mid-plane of web; and
h is the depth of the channel.
For Z-shaped members, K' = ZJIX
where
Ixy is the product of inertia of full cross-sectional area; and
1, is the moment of inertia of full cross-sectional area about the centroidal axis.
8.3.3 One flange braced by deck, slab or sheathing
8.3.3.1 The factored resistance of the attachment of a continuous deck, slab or sheathing shall be in accordance with 8.2.3.
8.3.3.2 Discrete bracing shall be provided to restrain the flange that is not braced by the deck, slab or sheathing.
8.3.3.3 The spacing of discrete bracing shall be in accordance with 8.3.2.1
8.3.4 Both flanges braced by deck, slab or sheathing
The factored resistance of the attachment shall be in accordance with 8.2.3.
9 Testing
9.1 General
9.1 . I Testing facilities shall be suitable for the type of test required (see 9.2). Tests may be made at a manufacturer's or an independent testing facility.
9.1 -2 Test results and reports for types C and D tests shall be certified by a Professional Engineer.
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9.1.3 The provisions of clause 9 do not apply to steel deck diaphragms, composite steel components or composite steel assemblies.
9.2 Types of tests
9.2.1 Type A tests are tensile tests to determine the mechanical properties of virgin steel.
9.2.2 Type B tests are tests to determine the modified mechanical properties of steel after cold forming for use of the change in strength that is permitted in 5.2.2(a) and 5.2.3.
9.2.3 Type C tests are structural performance tests to establish the limit states of structural elements or assemblies for which the composition or configuration is such that the calculation of their factored resistance or deformation cannot be made in accordance with the provisions of this part of SABS 0162.
9.2.4 Type D tests are confirmatory tests to verify the resistance to the specified ultimate loads of structural elements or assemblies designed in accordance with the provisions of this part of SABS 0162. These tests shall not be used to establish resistances exceeding those calculated in accordance with the provisions of this part of SABS 0162.
9.3 Test procedures
9.3.1 Type A - Virgin steel properties
Tensile testing procedures shall comply with the provisions of SABS 054. Two test specimens for tensile tests shall be taken from each coil of steel. A test specimen shall be taken longitudinally from each quarter point of the width near the outer end of the coil. The yield stress fy and the tensile strength fu shall be taken as the average of the test values. For the determination of fy and fu for use in design, see 3.2.
9.3.2 Type B - Cold-formed steel properties
9.3.2.1 Tensile testing procedures shall comply with the provisions of SABS 054. The yield stress of the material shall be adjusted by multiplying the test values by the ratio of the design yield stress fy (see 3.2) to the actual virgin yield stress.
9.3.2.2 The yield stress ffl of flat elements in a formed section to be used in 5.2.3 shall be established by means of a weighted average of the yield stresses of standard tensile samples taken longitudinally from the flat portions of a cold-formed member. The weighted average shall be the sum of the products of the average yield stress for each flat portion times its cross-sectional area, divided by the total area of flats in the cross-section. The exact number of such samples will depend on the shape of the member, i.e. on the number of flats in the cross-section. At least one tensile sample shall be taken from the middle of each flat. The actual virgin yield stress of the flat shall be determined in accordance with 9.3.2.1.
9.3.2.3 Compressive yield stress determinations shall be made by means of compression tests of short specimens of the full section. The compressive yield stress shall be taken as the smaller value of either the maximum compressive strength of the section divided by the gross cross-sectional area and the stress defined by one of the following methods:
a) for sharp yielding steel, the yield stress shall be determined by the autographic diagram method or by the total-strain-under-load method. When the total-strain-under-load method is used, there shall be evidence that the yield stress so determined agrees within 5 % with the yield stress that would be determined by the 0,2 % offset methods; and
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b) or gradual yielding steel, the yield stress shall be determined by the total-strain-under-load method or by the 0,2 % offset method. When the total-strain-under-load method is used, there shall be evidence that the yield stress so determined agrees within 5 % with the yield stress that would be determined by the 0,2 % offset method.
9.3.2.4 Where the principal effect of the loading to which the member will be subject in service will be to produce bending stresses, the yield stress shall be determined for the flanges only. In the determining of such yield stresses, tests shall be made on specimens cut from the section. Each such specimen shall consist of one complete flange plus a portion of the web such that the specimen is fully effective.
9.3.2.5 For acceptance and control purposes of full sections to be used with 5.2.2, two full-section tests shall be made from each lot of not more than 50 000 kg and not less than 30 000 kg of each section, or one test from each lot of less than 30 000 kg of each section. For this purpose, a lot may be defined as that quantity of one section that is formed in a single production run of material from one heat or cast.
9.3.2.6 At the option of the manufacturer, either tension or compression tests may be used for routine acceptance and control purposes, provided the manufacturer demonstrates that such tests reliably indicate the yield stress of the section when it is subjected to the kind of stress under which the member is to be used.
9.3.3 Type C - Performance tests
9.3.3.1 Procedures for testing shall be established with due consideration given to the loading and boundary conditions in which the elements or assemblies are intended to be used. Tensile testing procedures shall be in accordance with the provisions of SABS 054.
9.3.3.2 The factored resistance shall be taken as
where
at is the resistance factor corresponding to the appropriate limit state given in 6.2; and
R , is the tested strength limit state.
The virgin yield stress shall be determined. The performance test results shall be adjusted to the design yield stress fy (see 3.2) of the steel that the manufacturer intends to use. The test results shall not be adjusted upward if the yield stress of the test specimen is less than fy . Similar adjustments shall be made on the basis of tensile strength instead of yield stress where tensile strength is the critical factor.
Consideration shall also be given to any variation or difference that may exist between the design thickness and the actual thickness of the specimens used in the tests.
The tested serviceability limit state R, is equal to Rt .
9.3.3.3 The tested strength limit state Rt shall be established based on the mean values resulting from tests of not fewer than three identical specimens, provided that the deviation of any individual test result from the mean value obtained from all tests does not exceed 10 %. If such deviation from the mean exceeds 10 %, at least three more tests of the same kind shall be made. The average of the lowest three values of all tests made shall then be regarded as the tested strength limit-state value Rt.
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9.3.4 Type D - Confirmatory tests
9.3.4.1 Procedures for testing shall be established with due consideration given to the loading and boundary conditions in which the elements or assemblies are intended to be used.
9.3.4.2 The test shall be considered successful if the following conditions are met:
a) for strength determination,
atRt 2 effect of ultimate loads;
b) for deformation determination,
R, 2 effect of serviceability loads;
where for (a) and (b) above,
R, and at are as defined in 9.3.3.2; and
R, is the tested serviceability limit-state value.
9.3.4.3 The tested strength limit state Rt shall be established based on the mean values resulting from tests of not fewer than three identical specimens, provided that the deviation of any individual test result from the mean value obtained from all tests does not exceed 10 %. If such deviation from the mean exceeds 10 %, at least three more tests of the same kind shall be made. The average of the lowest three values of all tests made shall then be regarded as the tested strength limit-state value Rt.
10 Fabrication
10.1 General
All aspects of fabrication, both in the workshop and on site, shall comply with the provisions of 5.2 and 5.3 of SABS 1200-H, insofar as they are applicable to cold-formed structural members, and the provisions of the following subclauses. Where the provisions of the following subclauses differ from those of 5.2 and 5.3 of SABS 1200-H, the following subclauses shall govern.
10.2 Forming, cutting, punching and drilling
Members shall be formed at ambient temperature by a method that does not result in work-hardening to an extent that would limit the intended service and, where applicable, that does not result in damage to protective coatings that have been applied to the unformed material. Care shall be taken not to stretch, bend or otherwise distort parts of cold-formed members except as a necessary feature of the cold-forming operation. Components may be cut by splitting, shearing, sawing, flame or laser cutting or by friction disc. Holes and openings may be punched or drilled.
10.3 Fastenings
Steel components may be assembled by welds, mechanical fasteners (such as bolts, rivets or screws) or a combination of these. Assembly by other means (such as metal stitching and clinching) may also be used where suitable. The strength offastenings shall be established by test in accordance with 9.3.3, unless values are specified elsewhere in this part of SABS 0162.
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Where dissimilar metals are in contact, attention should be paid to insulation of the metals and the selection of suitable fasteners in order to inhibit galvanic corrosion.
10.4 Straightening and flattening
If straightening or flattening of material, members or parts is necessary, it shall be done by a process and in a manner that will not damage the material, including protective coatings, if present.
10.5 Provision for expansion and contraction
Where thermal expansion and contraction of cold-formed steel components in an assembly will adversely affect the structural safety or serviceability of that assembly, provision shall be made in the assembly to accommodate the anticipated range of thermal expansion and contraction.
10.6 Tolerances
Structural sections, deck, cladding and other load-carrying members shall be to the full dimensions claimed by the manufacturer. Fabrication tolerances shall be in accordance with established practice (see SABS 1200-H) unless more stringent requirements are specified. In no case shall tolerances exceed those necessary to ensure the specified strength and serviceability requirements of a member or assembly.
11 Erection
11 . I Handling requirements
Attention shall be paid to the handling of cold-formed members so as not to nick, gouge or dent the material, or damage the protective coating. Adequate precautions shall be taken when loading, unloading and handling long, slender members.
11.2 Temporary loads during erection
Erection and installation procedures shall be such as to avoid excessive temporary loads and deformations.
11.3 Marking of members
Tags, paint, ink marks or other suitable means shall be used to identify members of unassembled components or parts. Erection marks that damage the material or finished surfaces exposed to view shall not be used.
11.4 Setting out and erection
Setting out and erection of steelwork and grouting of supports shall comply with the provisions of 5.4, 5.5 and 5.6 of SABS 1200-H.
11.5 Tolerances
Tolerances on accuracy of erection of steelwork shall be as given in the relevant parts of clause 6 of SABS 1200-H.
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12 Cleaning, surface preparation and protective treatment
12.1 Storage and handling
All uncoated stock shall be stored in a dry place before being processed and, except for weathering grades, shall be protected by a rust-inhibitive coating immediately after having been processed.
12.2 Surface preparation and protective treatment
Members and components, other than those made of weathering grades of steel, shall be protected against corrosion by means of paint, zinc, aluminium, porcelain, enamel or other effective means, either singly or in combination.
Cleaning, surface preparation and protective treatment of steelwork shall comply with the provisions of SABS 1200-H. Paints and protective coatings shall comply with the same specification. Careful consideration shall be given to the selection cif coating systems to ensure that all procedures are compatible and will be such as to ensure adequate adhesion of the coating film.
sabs pta
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