35 8118 :
BRITISH STANDARD
?art 1 : 1991
nccwpmting
Lmendment No. 1
Structural use of
aluminium
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Part 1: Code of practice fordesign
ICs 91.080.10
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Committees responsible for this
British Standard
The preparationof this British Standard was entrusted the
by Civil Engineering and
Building Structures StandardsPolicy Comnuttee(CSW-) to Technical Comnuttee
CSE936,upon whichthe following bodies were represented
Aluminium Federation
Association of Consulting Engineers
Institution of Civil Engineers
Institution of Structural Engineers
London Regional "ansport
Mirustry of Defence
Royal Institute of British Architects
Royal Institutionof Chartered Surveyors
Welding Institute
This British Standard, having
been prepared under the
direction of the Civil Engineering
and Building Structures
Standards Policy Committee, was
published under the authority of
the Standards Committee and
comes into effect on
31 March 1992
O BSI 07-1999
Amendments issued sincepublication
Amd. No.
Date
comment
10485
July 1999
Indicated by a side line
The followingBSI references
relate to the work on this
standard:
Committee reference CSEX36
Draft for comment W12254 DC
ISBN O 580 19209 1
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Contents
Foreword
Code of practice
Section 1. General
1.1
Scope
1.2
Definitions
1.3
m o r symbols
Section 2. Properties and selection of materials
Designation of materials
2.1
Permitted materials
2.2
2.2.1 Extrusions, sheet,plate, drawn tube, forgings and castings
Bolts and rivets
2.2.2
2.2.3 Filler metals
Strength, mechanical and physical properties
2.3
2.3.1 Strength and mechanical properties
25.2 Physical properties
Durability and corrosion protection
2.4
2.4.1 General
2.4.2 Durability of alloys
2.4.3 Corrosion protection
Fabridonand construction
2.5
2.5.1 General
2.5.2 Bending and forming
2.5.3 Welding
Selection of materials
2.6
Availability
2.7
2.7.1 General
structural sections
2.7.2
2.7.3 Tube
Sheet, strip and plate
2.7.4
2.7.5
Forgings
effects
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CaStings
2.7.6
Section 3. Design principles
3.1
Limit state design
3.2
Loading
3.2.1 General
3.2.2
Nominal l o a m
3.2.3
Factored loading
3.2.4
Dynamic
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page
h i d e front cover
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Committees responsible
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STD-BSI BS 8LL8: PART L-ENGL L992 m l b 2 V b b 9 079V532 Vb3 D
BS 8118 : Part 1 : 1991
3.3
3.3.1
3.3.2
3.3.3
3.4
3.4.1
3.4.2
3.4.3
3.5
3.6
3.6.1
3.6.2
3.6.3
3.7
3.8
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Static strength
General
Actioneffect under factored loading
Factored resistance
Deformation
Recoverable elastic deformation
Pernxment inelastic deformation
Distortion due to frequent assembly
Durability
Fatigue
General
Total collapse
Stable crack growth
Vibration
Testing
Section 4. Static designof members
4.1
Introduction
4.1.1 General
4.1.2
Linut state of static strength
4.1.3 Heat-affected zones W s )
4.1.4 Advanced design
4.2
Linuting stresses
4.3
Section classification and local buckling
4.3.1 General
4.3.2
Slenderness parameterß
4.3.3
Section classification
4.3.4
Local bucklung
4.4
HAZ softenmg macent to welds
4.4.1 General
4.4.2
Severity of softening
4.4.3
Extent of HAZ
4.5
B€!amS
4.5.1 Introduction
4.5.2 Uniaxial monlent resistance of the section
4.5.3
Shear force resistance
4.5.4
Combined moment and shear force
4.5.5
Web bearing
4.5.6
Lateral torsional buckling
4.6
Tension members
4.6.1 General
4.6.2 Tension resistance
4.6.3 Eccentrically connectedties
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Compression members
General
Section classification for axial compression
Resistance to overall buckling
Colunm bucklig
Torsional buckling
Strut curve selection
Local squashing
Hybrid sections
Certain casesof eccentrically connectedstruts
Battened struts
Bending with axial force and biaxial bending
General
Section classification and localb u c m under combined actions
Section check
Overall buckling check
Deformation (serviceabilitylimit state)
General
Recoverable elastic deflection
Section 5. Plates and plate girders
5.1
General
5.2
Unstiffened plates
5.2.1 General
5.2.2 Unstiffened plates under directstress
Unstiffened plates under in-plane moment
5.2.3
Longitudinal stress w e n t on unstiffened plates
5.2.4
UnstifTened plates in shear
5.2.5
5.2.6 Combined actions
Multi-stiffened plating
5.3
5.3.1 General
5.3.2 Multi-stiffened plating under uniform compression
5.3.3 Multi-stiffened plating under in-plane moment
5.3.4 Longitudinal stress gradlent on multi-stiffened plates
Multi-stiffened plating inshear
5.3.5
5.4
Plate girders
5.4.1 General
5.4.2
Moment resistance of transversely stiffened plate girders
Shear resistance of transversely stiffened plate girders
5.4.3
5.4.4
Longitudinally and transversely stiffened girders
Web stiffeners and tongueplates
5.4.5
5.4.6
Use of corrugated or closely stiffened webs
5.4.7
Girders under combined moment andshear
4.7
4.7.1
4.7.2
4.7.3
4.7.4
4.7.5
4.7.6
4.7.7
4.7.8
4.7.9
4.7.10
4.8
4.8.1
4.8.2
4.8.3
4.8.4
4.9
4.9.1
4.9.2
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STDaBSI BS ALLB: PART L-ENGL L99L
BS8118 : Part 1 : 1991
L b 2 4 b b 9 0794534 23b
Section 6. Static design of joints
General
Riveted and bolted joints: design considerations
General
Groups of fasteners
Effect of cross-sectional areas of plies
Long joints
Riveted and bolted joints: geometrical and other general considerations
Minimum spacing
Maximunl spacing
Edge distance
Hole clearance
Packing
Countersinking
Long grip rivets
Washers and loclung devices
Intersections
Factored resistance of individual rivets and b o l t s other than HSFG bolts
conlplying with British Standards
6.4.1 Linuting stresses
6.4.2 Shear
6.4.3 Axial tension
6.4.4 Bearing
6.4.5
Combined shear and tension
6.5
High strength friction grip(HSFG) bolts
6.5.1 General
6.5.2 Ultimate l i t state (static strength)
6.5.3 Friction capacity
6.5.4 Serviceability linutstate (defornaon)
6.5.5 Prestress
6.5.6 Slip factor
6.6
Pinned joints
6.6.1 General
6.6.2
Solid pins
6.6.3 Members connected by pins
6.7
Welded joints
6.7.1 General
6.7.2
Effect of welding on static strength
6.7.3
Effect of welding on fatigue strength
6.7.4 Corrosion
6.7.5
Edge preparations
6.7.6 Dístortion
6.7.7 Infonnation given to fabricator
6.7.8 Butt welds
6.7.9
F'illet welds
6.1
6.2
6.2.1
6.2.2
6.2.3
6.2.4
6.3
6.3.1
6.3.2
6.3.3
6.3.4
6.3.5
6.3.6
6.3.7
6.3.8
6.3.9
6.4
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resistance
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Design strengthof welded joints
6.8
6.8.1 General
Groups of welds
6.8.2
Linuting stress of weld metal
6.8.3
6.8.4 Limiting stress in the HAZ
Factored resistance of welds
6.9
6.9.1 Butt weld metal
6.9.2 Fillet weld metal
6.9.3 Heat-affected zones (HAZs)
Bonded joints
6.10
6.10.1 General
6.10.2 Factored
6.10.3 Tests
Section 7. Fatigue
Introduction
7.1
7.1.1 General
7.1.2 Influence of fatigue on design
7.1.3 Mechanism of failure
7.1.4 Potential sites for fatigue cracking
7.1.5 Conditions for fatigue susceptibility
Fatigue design criteria
7.2
7.2.1 Design philosophy
7.2.2 Fatigue failure criterion
Fatigue assessment procedure
7.3
Fatigue loading
7.4
Stresses
7.5
7.5.1 Derivation of stresses
7.5.2 Stress parameters
Derivation of stress spectra
7.6
7.6.1 Cycle counting
7.6.2 Derivation of stress spectrum
Classification of details
7.7
Fatigue strength data
7.8
7.8.1 Classified details
Unclassified details
7.8.2
7.8.3 Low endurance range
7.8.4 Improvenlent techniques
7.8.5
Workmanship
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fatigue
Section 8. Testing
113
8.1
General
113
8.2
Preparation
for test
113
8.3
Static tests
113
8.3.1 General
8.3.2 Application of loads
113
114
8.3.3 Acceptance
criteria
114
8.3.4 Retests
measurement
resistance
8.3.5 Ultimate
for
8.4
testingAcceptance
114
8.4.1 Objectives of test
114
8.4.2
Derivation
data
of loading
114
8.4.3 Derivation of stress data
115
8.4.4of Derivation endurance data
1l G
8.4.5
Acceptance
116
8.5
Reporting
117
Appendices
A
Nomenclature of aluminiun~products
118
B
F o m d statenlent of safety factor fommt adoptedin the code for static
123
design resistance calculations
124
m i c a l values of design life
C
124
Derivation of material limiting stresses for use in design
D
125
Elasto-plastic moment calculation
E
128
F
HAZs aqjacent to welds
General formulae forthe torsional propertiesof thin-walled open
G
133
sections
145
H
Lateral torsional bucklingof beams
Torsional buckling of struts: determinationof slenderness paranleter,1 147
J
151
K
Equations to design curves
strength
L
Fatigue
data
154
Thbles
2.1
Heat-treatable alloys
2.2
Non-heat-treatable alloys
Bolt and rivet material
2.3
Welding
filler metals
2.4
Physical properties
2.6
General corrosion protectionof alminium structures
2.6
2.7
Additional protectionat metal-to-metal contacts to combat crevice and
2.8
2.9
2.10
3.1
3.2
3.3
3.4
galvanic effects
Selection of filler wires and rods for inert-gas welding
Product form availability
F h g e of sizes for extruded section complying withBS 1161
Load factors (based on building structures)
Load factors for combinedloads
Material factors
Limiting deflections
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G
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O BSI 07-1999
~
~~
STD*BSI BS 8118: PART 1-ENGL 1991 m Lb24bb9 0794517 T q 5 m
BS 8118 : Part 1 : 1991
Limiting stresses, heat-treatable alloys
Linuthg stresses, non-heat-treatable alloys
Limiting values ofP
Curve selection for figure 4.5 (local buckling)
HAZ softening factor
Extent of HAZ, factor a
Lateral torsional bucklingof beams, coefficients X and Y
Effective length factor K for struts
Torsional buckling parameters forstruts
Choice of strut curve diagram
Limiting stress pf for alunkium fasteners
Limiting stresses of weld metal p ,
Limiting stress P, and p , in the HAZ
Type 1 classifications: non-welded details
Type 2 classifications: welded details on surface of member
Type 3 classifications: welded details at end connectionsof member
Values of Kz and m in figure 7.9
Fatigue test factorF
Nearest foreign equivalentsto designated wrought and cast alloys
complying with British Standards
Qpical values of design life
c.1
D.l
Limiting stress P, for weld metal
F. 1
Modified HAZ softening factor4
F.2
General deternkation of IC, and 4
Specimen calculation: monosynunetric shape
6.1
6.2
Specimen calculation: skew-symmetric shape
6.3
Specimen calculation: asymmetricshape
Effective length1 for beanls of length L
H. 1
Effective length I for cantileverof length L
H.2
K. 1
Eauations to desim curves
Figures
Qpes of flat element
4.1
Flat elements understress gradient, valueof g
4.2
B u c m modes for flat reinforced elements
4.3
Reinforced elements, value of h
4.4
4.5
Local buckling factor kL
4.6
Extent of HAZ, definition of z
4.7
Typical heat-path measurement
Lateral torsional buckling, equivalent
uniform moment M
4.8
4.9
Lateral torsional buckling of beams, bucklingstress p ,
4.10 Column buckling stress P, for struts
4.11
Torsional buckling of struts, interaction factor k
4.12
Torsional buckling stress P , for struts
5.1
Unstiffened plate
5.2
Multi-stiffened plate
5.3
Plate girder
4.1
4.2
4.3
4.4
4.5
4.6
4.7
4.8
4.9
4.10
6.1
6.2
6.3
7.1
7.2
7.3
7.4
8.1
A. 1
v
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STD-BSI BS 8118: PART L-ENGL 3991 m Lb24bb9 07911518 981 m
BS 8118 :Part i : 1991
page
ction
method
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es
8
Elastic criticalshear buckling factor v1
Basic tension fieldshear buckling factorv2
Flange assisted tension fieldshear buckling factor v3
Shear buckling factorml
Effective
Schematic
interaction
diagrams
girders
plate for
Effective butt weld throats
Effective fillet weld throats
Failure planes for static welded joint checks
Butt weld design
Fillet weld design
Effective length of longitudmal fillet welds
Thick adhered shear test
Thin sheet test specimens
Fatigue assessment procedure
Stress paranleter for parent nlaterial
Stresses in
throats
Stress in lapped joints
Stresses in root of fillet
Reservoir
Simplified stress spectrum
m i c a l &-N relationship
Designf,-N curves (for variable amplitudestress histories)
Method of identifkation of fatigue class of drawings
Ultinmte linut state criterion
E.l
Assunled elasteplastic stress patterns (non-hybrid)
F.1
Extent of HAZ, factor 9
F.2
Qpical hardness
plot
along
a heat
path
from
a weld
6.1 Torsion constant
coefficients
certain
forfillets
and
bulbs
6.2
Shear centre position(S) and warping factor(H) for certain thin-walled
sections
6.3
Monosynunetric section notation
6.4
Skew-synmetric section notation
notation
6.5
Aspmetric section
J.1
Sections which exhibit no interaction between the pure torsional and
flexural
5.2
Monosymmetric section
5.3
Asymmetric section
5.4
Nonlogranl for solving cubic equationa? + Ax - B = O
K.1
Buckling strength at high slenderness
L.l
Zone of greatest variation in effectivef,-N curves
5.4
5.5
5.6
5.7
5.8
stiffener
5.9
6.1
6.2
6.3
6.4
6.5
6.6
6.7
6.8
7.1
7.2
weld 7.3
7.4
7.5
counting
cycle
7.6
7.7
7.8
7.9
7.10
B.l
buckling
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0 BSI 07-1999
STD.BS1 BS B11B: PART It-ENGL 1971
l b 2 4 b b 9 0774539 B38 m
BS 8118 :Part 1 : 1991
Foreword
This Part of BS 8118 has been prepared underthe direction of the Civil Engineering
and Building Structures S t a n h d s Policy Committee.BS 8118 is a document
l nMunstructures
combining a code of practice to cover the design and testing ofau
(Part 1) and a specification for materials, fabrication and protection
(Part 2).
This Part of BS 8118 gives recomnlendations forthe design of the elenlents of framed,
alunmunl alloy.
lattice and stiffened plate structures, using wrought
Although BS 8118 is a revision of CP 118 it is written witha different design
so that a period
philosophy. Because ofthis CP 118 will not be withdrawn immediately
of overlap in designprocedures can be allowed.
It has been assumed inthe draftmg of this British Standardthat the execution of its
provisions is entrusted to appropriately qualified and experienced people and
that
construction and supervisionis carried out by capable and experienced organizations.
The full list of organizationsthat have taken partin the work of the Technical
Committee is given on the inside front cover. The Chairman
of the Technical
a particular
Committee is Dr P S Bulson CBE and the following people have made
contribution in the drafting of the code.
Mr R J Bartlett
Mr M J Bayley
Mr P G Buxton
Dr M S G Culliiore
MrJBDwight
Prof. H R Evans
Mr K Ewing
Mr W Ferguson
Mr R A Foulkes
Mr J H Howlett
M r D Knight
Mr W I Liddell
Prof. D A Nethercot
Dr M H Ogle
Mr J A Thornton
Mr P BTindall
Compliance with a British Standarddoes notof itself confer immunity
from legal obligations.
Summary of pages
This docunlent conlprisesa front cover, an inside front cover, pages to
1 156, an inside
back cover anda back cover.
this document indicates whenthe
The BSI copyright notice displayed throughout
document was last issued.
Sideliningin this document indicatesthe most recent changes
by amendment.
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9
BS 8118 :Part 1 : 1991
Section 1
Section 1. General
1.2.7 factored load
A nominal load multiplied by the relevant partial load
This Part of BS 8118 gives reconmendations for the
design of the elements of franled, lattice and stiffened factor.
plate structures, using wrought aluminiumalloy. Where 1.2.8 factored life
castings or forgings are used they should be
The design life multiplied bythe relevant partial life
manufactured and designedin accordance with the
factor.
appropriate British Standard and in close consultation
with the specific manufacturer.
1.2.9 factored resistance
The design reconmendations are for a variety of
The resistance of a member divided by the relevant
aluminium alloys suitable for structural use, and apply partial material factor.
to a range of structures subjected to normal
1.2.10 fail safe
atmospheric conditions such as bridges, buildings,
towers, road and rail vehicles, nlarine craft, cranes and The ability of a structure to continue to be serviceable
after the discovery and monitoring of fatigue cracks.
offshore topside structures.
The reconmendations do not cover aerospace alloys,
1.2.11 fatigue
the detail design of castings, curved shellstructures or The damage, by gradual cracking, to a structural
structures subjected to severe thermalor chenucal
member caused by repeated applications of a stress
conditions. They are not intended to be used for the
that is insufficient to cause failure by a single
design of containment vessels, pipework, airborne
application.
structures or naval vessels, or for any application for
1.2.12 fusion boundary
which specific alternative codes exist, e.g.BS 5500 for
pressure vesselsand BS 5649 for lighting columns.
The material in a heat-affected zone inmediately
NOTE. The titles of the publications referred to in this standard
a a c e n t to the leg of a weld.
1.1 scope
--`,,,,,,`,,,``,```,,`,````,``,-`-`,,`,,`,`,,`---
are listed on the inside of the back cover.
1.2 Definitions
For the purpose of this Part of BS 8118 the following
defintions apply.
1.2.1 compact cross-section
A cross-section that can develop the full plastic
capacity, either in compression or bending, with no
reduction due to localbucklii of thin-walled
elements.
1.2.2 design life
The period in which thestructure or component is
required to perform safely, withan acceptable
probability that it will not require repairor withdrawal
from service.
1.2.3 designspectrum
1.2.13 heat affected zone
A zone in which there is a reduction in strength of
material in the vicinity of welds in certain classes of
aluminium alloy.
1.2.14 imposed load
All loadmg on a structure other than dead or wind
loading.
1.2.15 instability
A loss of stiffness of a structure (usually sudden)that
limits its load-canying capability andin certain
instances can cause catastrophic failure.
1.2.16 lateral torsional buckling
The bucklmg of a beam accompanied by a
combination of lateral displacement and twisting.
stress ranges caused by loading events.
1.2.17 lateral restraint
Restraint that limits lateral movement of the
compression flangeof a beam.
1.2.4 detailclass
A rating given to a detail which indicates its levelof
fatigue resistance.
1.2.18 limit state
Condition beyond whicha structure is unfit for its
intended use.
1.2.5 edge distance
Distance from the centre of a fastener hole to the
nearest edgeof an element.
1.2.19 loading event
A defined loading cycle which, for design purposes,is
assumed to repeat a given number of times.
1.2.6 effectivelength
Length between pointsof effective restmint of a
member, multiplied by a factor to take account of end
conditions and loadmg.
1.2.20load spectrum
A tabulation showingthe relative frequenciesof
loading events of different intensities ona structure.
A tabulation of the numbers of occurrences of all the
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~~
STD-BSI BS ALLB: PART L-ENGL 1991 m l b 2 4 b b 9 07911521 117b m
BS 8118 :Part 1 : 1991
Section 1
1.2.21 local buckling
Buckling of the thin walls of a component in
compression, characterizedby the fomwtion of waves
or ripples alongthe member.
1.2.22Miner’ssummation
A cumulative fatigue danlagesumnution based on a
rule devised by Palmagren and Miner.
1.2.23nominalload
The load to which a structure may be expected to be
subjected during nomml service.
1.2.24 outstand element
The element of a section, composedof flat or curved
elements, which is supported along one longitudinal
edge, free along the other.
1.2.34 stress range
(1) The greatest algebraic difference betweenthe
principal stresses occurring on principal planes not
more than 45 O apart in any stress cycle on a plate or
element.
(2) The algebraicor vector difference between the
greatest and least vector sum of stresses in any one
stress cycle on a weld.
1.2.35 stress spectrum
A tabulation of the numbers of occurrences of all the
stress ranges of different magnitudes duringa loading
event.
1.2.36 torsional buckling
Buckling of a strut accompanied by tw-.
1.2.37 torsional/flexural buckling
1.2.25 reinforcedelement
Buckl~ngof a strut accompanied by overall flexureas
The element of a section which is stiffened by the
well as twisting.
introduction of longitudinal reinforcement, either along
1.2.38 ultimate limit states
the edge of the element, or within its width.
Those limit states which when exceeded can cause
1.2.26 resistance
collapse of part or whole of a structure
The strength of a member based on calculations,using NOTE. Specific terms relating to limit state principles are defined
acceptable maximum values for material strength.
in appendix B.
1.2.27 safe life
A design against fatiguein which the calculated life is
many times longer thanthe life required in service.
1.2.28 semi-compact cross-section
A cross-section of a beam in whichthe stress in the
extreme fibresis limited to the 0.2 % proof stress,
because local bucklingof the compression elements
would prevent developmentof the full plastic moment
capacity.
1.2.29 serviceability limit states
Those limit states which when exceeded can leadto
the structure being unfit for its intended use, even
though the structure has not collapsed.
1.2.30 slenderness
The effective length of a strut divided by the radius of
gyration.
1.2.31 stiffenedelements
The element of a section, composed of flat or curved
elements, which is supported along both longitudinal
edges.
1.2.32 stress cycle
A pattern of variation of stress at a point, whichis
normally in the form of two opposing half-waves.
1.2.33 stress history
A record showing howthe stress at a point varies
during loading.
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1.3 Major symbols
A
Area
or Durability rating
A,
Effective
section area
A,
Effective shear area
a
Spacing
of transverse
stiffeners
or Width of unstiffened plates
B
Overall
width of multi-stiffened
plate
orDurability rating
BRF Factoredresistance inbearing of a fastener
b
Width
of
flat
element
be
Effectivewidthof webplate (plate girder)
C
Durability rating
or Lip size
D
Diameterofround
tube to mid-metal
or Overall depth of web to outside flanges
d
Depth
of web
between
flanges
or Depth of unstiffened plates
&c
Nominal diameter of fastener or pin
E
Modulus
elasticity
of
F
Fatigue test factor
F
Fusionboundary of heataffected zone (HAZ)
F,
Frictioncapacity ofhigh strengthfrictiongrip
bolt (HSFG bolt)
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I
BS 8118 :Part 1 : 1991
Section 1
M R S ~ Factoreduniaxialmonlentresistanceabout
major axis (with allowance for shear)
foc
M R S ~ Factoreduniaxialmomentresistance about
fov
nlinor axis (with allowance for shear)
fr
Design stress range
Factored moment of resistance to lateral
torsional buckling
fu
Ultimatetensile stress (designated R, in
BS EN 10002-1)
M,
Semi-compact
value
of
MRS
f0,2
Minimum 0.2 % tensileproof stress (designated
M,
Uniaxialmoment about nqjor axis
Rp0.2 in BS EN 10002-1)
M,
Equivalentuniformmomentaboutmajor
axis
G
Shear
modulus
My
Uniaxialmoment about n k o r axis
g
Stress gradient
coefficient
My
Equivalent uniform monlent about n k o r axis
gt
Throatweld
of
M1
Maximum factored
monlent
g,
Leg length of weld
M2
Minin~unlfactored
nlonlent
H
Warping factor
m
Inverse
slope
off,
- N curve(fatigue)
h
Reinforced
elements
coefficient
ml, m2 Shear buckling factors (plate girders)
or Distance to a free edge
N
Number
of
webs
IS
Secondmomentof area of fullsection of
or Predicted cycles to failure (endurance)
effective stiffener (plategirder)
n
Equivalentnumberofcyclesof
stress range
ISU Secondmomentof area of one subunit of
(fatigue)
plating (multi-stiffened plates)
or Time in days between welding and loading
Iy
Secondmomentof
area aboutcentroid axis
P
Axialtensileorcompressiveforcedue
to
J
Torsion constant
factored
loading
K
Effectivelengthfactorfor
struts
or Protection
KI
Coefficientincalculationofresistanceofbolts
PC.
Elasticcriticalloadfortorsionalbuckling
Kz
Constant
in
fatigue
failure
criterion
P,
Proofloadfor
a bolt
kL
Local buckling
coefficient
PP
Prestress
load
k,
Reductionfactoronlongitudinalresistance
to
PR
Factored
axial resistancebasedonoverall
take account of high shear
colunm
or
torsional buckling
k,
Strengthfactorfor
HAZ material
PRB Factoredresistance of butt weld
Modified strength factor forHAZ material
k;
PRF Factoredresistance of filletweld
Length between supports
PRFB Factored resistance of HAZ adjacent to butt
Effective length between lateral supports
weld fusion boundary (direct normal tensile
force)
Effective length ofbutt weld
PRFF Factored resistance of HAZ adJacent to fillet
Effective length of fillet weld
weld fusion boundary (direct nomlal tensile
Moment under factored loading
force)
Equivalent uniform moment
PRG Factoredresistance of bondedjoint
Elastic critical uniform moment for lateral
PRS Factored axial resistance(tensile or
torsional buckling
compressive)
Fully compact valueof MRS
Mf
PRTB Factored resistance of HAZ adjacent to butt
weld toe (direct nomml tensileforce)
MRF Reduced value of MRS for flanges only
Factored moment resistanceof a section in the PRTF Factored resistance of HAZ adjacent to fillet
MRS
absence of shear
weld toe (direct nomml tensile force)
Reduced factored moment resistanceof a
Ph
Factored axial resistance to overallcolunm
section to allow for shear
buckling aboutn d o r axis
f
Reduction
factor
applied
Constant
amplitude
cut-off
Variable
amplitude
cut-off
to kZ
stress
stress
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STD.BSI BS 8118: PAKT 1-ENGL 17’91 D Lb211bbS 07911523 2119 D
BS 8118 : Part 1 : 1991
Section 1
Factored axial resistance to overall column
tC
buckling about minoraxis
Factored resistance of HAZ under direct
PRZ
te
loam
tf
Linuting stress for local capacity (tension and
Pa
t2
compression)
V
Linuting direct stress in HAZ
P,
VRFB
Linuting stress for solid rivets and bolts
Pf
Linuting stress for bending and overall yielding
Po
VRFF
Limiting stress for flange material
Pof
Limiting stress for web material
Pow
vRS
Limiting stress for overall buckling stability
PS
VRTB
OT Lateral torsional buckling stress
VRTF
or Buckling stress for web treated as a thin
column between flanges
PRY
Weld penetration
p,
Linuting stress in shear
p,
Linuting shear stress in HAZ
p,
Limiting stress ofweldmetal
pwl
Stressarising at extremeedge of webdue to
localized force
pw2
Stress arising at nud-point of webdueto
.localized force
pl
Stress axis value of p s in strut curve diagran~
or Value of po for unwelded fully compact section
Radius of curvature of curved internal
element, to nud-metal
Minor axis radius of gyration
Plastic section nlodulusof gross section,with
no reduction for HAZ, local buckling, or holes
Extemal loading actions under factored
loading
Plastic modulus of effective flange section
(plate girder)
Plastic modulus of net section
Plastic modulus of net effective section
Factor on pl to allow for strut not meeting
tolerances of straightness or twist
Toe of HAZ
Thickness
Lesser of 0 . 5 ( t ~+ k)and 1.5t~
Thickness of thinnest element connectedby
welding
Pt
VRW
VRZ
Vtf
V1
v2
v3
W
W
Y
yc
yo
Thickness of thickest elenlent connectedby
welding
Effective throat thickness
Flange thickness
Flange thickness
Shear force under factored loading
Factored shear resistance of HAZ adjacent to
butt weld fusion boundary
Factored shear resistance of HAZ adjacent to
fillet weld fusion boundary
Factored shear force resistance
Factored shear resistance of HAZ adjacent to
butt weld toe
Factored shear resistance of HAZ adjacent to
fillet weld toe
Reduced value of VRS
Factored resistance of HAZ in shear
Tension field factor (plate girders)
Elastic critical shear buckling factor
Basic tension field shear buckling factor
Flange assisted tension fieldshear buckling
factor
Weld metal
Pitch of stiffeners in multi-stiffened plate
Distance from centre of multi-stiffened plate to
centre of outermost stiffener
Distancefromneutral axis tomoreheavily
conlpressed edge
Distancefromneutral axis to less heavily
compressed edge, or edge in tension
Distancefromneutral axis to mostseverely
stressed fibres
y2
Distancefromneutral axis to the compression
flange element in a bean1
2,
Elastic
modulus
of
effective
section
Zn
Elasticnlodulus of netsection
Zn,
Elasticnlodulus of neteffectivesection
z
Distance the HAZ extends fromaweld
z,
Basic
value
of
2
(Y
Ratio of nlinimunl to nlaxinlunl shear stress in
web (elastic stress distribution)
ur Modlfylng factor for extent of HAZ to allow
for elevated tenlperature
‘YS
Coefficient in calculation of boltorrivet in
single shear
Y1
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13
ß
Slenderness
parameter
ßo
Senu-conlpact h i t i n g value of ß
fi1
Fully conlpact
linuting
value
ofß
Yc
Consequences of failure
factor
Yf
Overall
load
factor
y f l , ya Partial load factors
y~
Fatigue
life
factor
YS
Material factor
Fatigue
material
factor
Coefficient in calculation of frictioncapacity
&
constant (%)
Ym
ymf
250
A
‘T1
T1
72
--`,,,,,,`,,,``,```,,`,````,``,-`-`,,`,,`,`,,`---
PS
Slenderness parameter for colunm buckling,
torsional buckling, andlateral torsional
buckling
Slenderness ratioof strut about ninor axis
M0-g
factor for extentof HAZ to allow
for increased heat build-up
Elastic critical stress of element with
reinforcement
Elastic critical stress of element without
reinforcenlent
Normal stress on weld under factored loading
Shear stress perpendicular to weld axis
Shear stress parallel to weld axis
Slip factor
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Section 2
BS 8118 :Part 1 : 1991
Section 2. Properties and selection of materials
2.1 Designation of materials
The designation of wrought alunMum and aluminium
alloys for general engineering purposes used t
inhis
standard is in accordance with the international 4-digit
classification system. Detailsof this system are given in
appendix A. Table A l in appendix A shows by cross
reference the current and old British Standard
designations together withthe nearest equivalentIS0
and other foreign designations.
The designation for castings is in accordance with the
system used in BS 1490 for aluminium alloy castings.
The alloy temper designation used inthis standard is
generally in accordance withthe IS0 2107 ‘alternative’
temper designation system. Detailsof t
h system
together with the former systemstill used for some
alloys and forms of nlaterials are given in appendix A.
NOTE.To simplify the text and to avoid confusion, in sections
four, five and six the temper designations M,TB, TF and TH are
not used. The equivalent temper designations F, T4,T6 and T8
respectively are used.
2.2 Permitted materials
2.2.1 Extrusions, sheet, plate, drawn tube,
forgings and castings
--`,,,,,,`,,,``,```,,`,````,``,-`-`,,`,,`,`,,`---
2.2.1.1 Standard materials
2.2.1.1.1 G e n a l
This Part of BS 8118 covers the design of structures
fabricated from a rangeof aluniniun1alloys used in
conditions and tempers listed in tables2.1 and 2.2 and
commonly supplied to the specifications given in
BS 8118 : Part 2.
The alloysare in two categories, the first of
heat-treatable alloysgiven in table 2.1 and described
in 2.2.1.1.2 and the second of non-heat-treatable alloys
in table 2.2 and described in2.2.1.1.3.
Castings should only be usedin load bearing structures
after both adequate testing and the setting of
upquality
control procedures for productionof the castings has
been performed to the approval of the engineer. The
to
design rules of this standard should not be applied
castings without close consultation withthe
nmufacturers thereof.
2.2.1.1.2 Heat-treatable alloys
The following alloys derive strength from heat
treatment.
(a) Alloy 6082. The commonestof these alloys is
the medium strength alloy, 6082,(Al SilMgMn) of
durability ratingB (see 2.4.2) used usually in the
fully heat-treated condition, i.e.6082-T6, and used in
welded and non-welded structures.
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The choice of this alloy is based on a conlbination
of good physical properties anda good degree of
resistance to corrosion. It is available in most fornq
solid and hollow extrusions, plates,sheets, tubes and
forgings. Care should be taken in designto account
for loss of strength in welded joints in the
heat-affected zone (HAZ).
@) AUoy 6061. An alternative alloy to 6082 is 6061,
(Al MglSiCu) of durability ratingB which has very
similar properties with slight inlprovenlent
in
forndility and surface finish.It is available in
extruded tabular form and mainly used for
structures.
(c) AUoy 6063. In applications where strength is not
of paramount importance andhas to be
compromised with appearance,the alloy 6063
(Al MgO,7Si) of durability ratingB is preferred,
because it combines moderate strength with
good
durability and surface finish. Itis particularly
responsive to anodizing and sinlilar patented
finishing processes.Alloy 6063 has a lower strength
than 6082, and like the latter there is a loss of
strength in welded joints inthe HAZ. It is available
in extrusions, tubes and forgings andis particularly
suitable for thin-walled and intricate extruded
sections. Itis used nlainly for architectural
applications such as curtain walling and window
frames.
(d) AUoy 7020.A further alloy whichis readily
weldable (although not restrictedto welded
series
structures) is the medium strength 7
alloy 7020 (Al Zn4,5Mgl) of durability rating C. It has
better post-weld strength than the 6
series
due to its natural agem property. This material and
others in the 7
series of alloys are however
sensitive to environmental conditionsand its
satisfactory performanceis as dependent on correct
methods of manufacture and fabrication as on
control of composition and tensile properties.If
material in the T6 condition is subjected to any
operations which induce cold work,such as
bending, shearing, punching, etc.the alloy may be
made susceptible to stress corrosion cracking; it is
essential therefore that there be drect collaboration
between the engineer and the nmufacturer on the
intended use and the likely service conditions.This
alloy is available normally onlyin rolled forms and
simple extruded solid and hollow sections, though
forgings can sometimes be madeto special order.
(e) AUoy LM25 Alloy LM25 (Al Si7Mg) of durability
rating B is a casting alloy with good foundry
characteristics, corrosion resistance and nlechanical
properties. It is available in four conditions of heat
treatment in both sand and chill castings, and is
mainly used for architectural and food
nmnufacturing installations.
***
* *
***
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-
STD.BSI BS 8LLE: PART L-ENGL J751 D 1 b 2 4 b b 7 077452b T58 m
BS 8118 :Part 1 : 1991
Section 2
***
2.2.1.1.3 Non-heat-treatablealloys.
The strongest 5
series alloy which offers
inmunity
to
stress
corrosion
when exposed to
The following alloys derive enhanced strength only by
elevated
temperature
is
5454.
The 5
series
strain hardening. Theyare normally produced in sheet
alloys with greater than3 % Mg may be rendered
and plate forms and occasionally
in some sinlple
susceptible to stress corrosion when exposed to
extruded foms.
elevated tenlperatures.
(a) AUoy 1200.The alloy 1200 (Al99,O)of durability
(jjAlloy 5251 : in seam welded tube. Sean1 welded
rating A is ‘conunercially pure’aluminium with high
tubes are produced from 5251 strip (Al M@) giving a
ductility and a very good corrosion resistance. It is
durability rating B to the tube, which has been
used for architectural work where components
are
further
strengthened by work hardening through
not highly stressed and is available insheet only.
forming and finishing rolls.Its n& uses are in
(3)AUoy 3103.The alloy3103 (Al Ml) of durability
general engineering such as garden furniture,
rating A is stronger and harder than‘commercially
handrails and ladders.
pure’ a
u
ln
M
u
m but with the same high ductility and
(g) AUoy W 5 .Alloy LM5 (AlMg5Sil) of durability
very good corrosion resistance, andis used
raking A is a medium strength casting alloy
extensively for building sheet and vehicle panelling.
possessing excellent finishing properties where it
It is available in sheet form.
maintains a surface of high polish, but is only
(c) AUoy 3105.The alloy 3105(Al Mn0,5Mg0.5) of
suitable for simple shapes. Itis mainly used for sand
durability ratingA is becoming more prevalent in the
castings for architectural and decorativepurposes
profied buildmg sheet market dueto its superior
and where anodizingis required.
properties over3103 in hardness and strength.It also
(h) AUoy LM6. Alloy L M G (Al Sil2) of durability
has an economic advantage. Availableform are
rating B is a further mediuni strength casting alloy
linuted to sheet.
which has excellent foundrychmcteristics, high
(d) A h y 5083.The alloy 5083 (Al Mg4,5Mn0.7) of
ductility and impact strength, together with good
durability ratingA is used for weldedstructures,
corrosion resistance. It is suitable for both sand and
plating and tank work, because it welds readily
chill castings and for a wide range of uses in
without sigruficant loss of strength andhas high
general, marine and electrical applications and in
ductility. The tensile strengthof 5083 in the O and F
castings of above avemge complexity and size.
conditions is lower than 6082-T6 but sigrufcantly
higher if the latter is welded. However, subjectionto 2.2.1.2 Materials in other thicknesses and allogs
long exposure at temperatures above65 “C, it can
with other standard and non-standard properties
result in grain-boundary precipitationof
The alloys listed in tables 2.1 and 2.2 are sonletimes
nmgnesiunl/alunlinium intermetallic compounds
used in other thicknesses andin other standard and
.which corrode preferentiallyin sonle adverse
non-standard tempers and conditions. Guaranteed
environments. This effect is aggravated if the alloy is nlininlunl properties for such materials may be used if
subjected to subsequent cold working operations. It agreed between designer and client.
is available in plate, sheet, simple extruded sections,
drawn tube and forging. Apart from its easy welding 2.2.1.3 Other allous
and good formability properties, italso exhibits very Other alloys are available which offer higher strengths,
good durability, especially in nlarine environments.
e.g. 2014A andor better post-weld strengths, e.g.7019,
but these strengths nlay be achievedto the detriment
(e) AUoys 5251, 5154A
a.& 5454. Alloys 5251
of other properties. The engineeris therefore, advised
(Al M@), 5154A (Al Mg3,5(A)) and 5454 (Al Mg3Mn)
all of durability ratingA are available in sheet, plate against using anyof these alloys without careful
a reputable
consideration, and in full consultation with
and simple extrusions.5154A and 5251 are also
nmufacturer. Properties to be considered include
available as forgings. Magnesium is the main
durability, weldability, resistanceto crack propagation,
addition and as a result the alloys are ductile in the
soft condition, but work harden rapidly. They have and behaviour in service. Other alloysin the 7
series having higher proof strengths suchas 7019 will
good weldability and very good resistanceto
corrosive attack, especially in a marine atmosphere. require particular control onnmufach~ringprocesses,
for example control of micro structure, residual stress
For this reason theyare used in panelling and
and cold working, see 2.2.1.1.1 (d).
structures exposed to marine atmospheres. 5154A
and 5454 are stronger than 5251..
2.2.2 Bolts and rivets
Bolt and rivet materials togetherwith their durability
ratings are given in table 2.3. Guidance on the selection
of bolt and rivet materialsis given in 2.4.3.2.
***
***
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Section 2
C
Y
s
W
3
l b
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Bs 8118 : Part 1 : 1991
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O
1
Section 2
O B S I 07-1mcJ
I
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I
4
S!
B
1
t
a
lm
19
Ia
BS 8118 : Part 1 : 1991
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I
1
L
Section 2
~
n
m
n
m
4
~~
n
Z Z
z z z
VI dl VI
N
ck VI VI
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m m
VI
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21
BS 8118 :Part 1 : 1991
STD-BSI BS BLLB: PART L-ENGL L99L m L b 2 9 b b 9 07q9529 7b7 m
E
O BSI 07-1999
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These materials mayalso be used for special
proprietary rivet and bolt products, including thread
inserts.
Special head shapes may be necessary for the larger
diameter rivets, see BS 1974l).
2.2.3 Filler metals
Filler metals for tungsten inert-gas (TIG) welding and
metal inert-gas(MIG) welding, are given in table 2.4
on the
together with their durability ratings. Guidance
selection of filler metalsis given in 2.5.3.2.
2 3 Strength, mechanical and physical
properties
2.3.1 Strength and mechanical properties
The range of the standard alloys togetherwith their
available fornw, temper conditions and mechanical
properties are shown in tables 2.1 and 2.2.
The mechanical properties for wrought materials for
the tempers and conditionsof the alloys given in
tables 2.1 and2.2 have been used to determine the
limiting stresses given in table 4.1. Where alloys are
welded the approximate percentage reductionin
strength of the alloy is given for each temper. These
strengths in the HAZ may not be achieved until after a
period of natural or artficial ageing, see notes to
table 2.1for details.
The strength of bolt and rivetmaterial is given in
table 2.3.
I lbble 2.4 Weldingfiller metals
Filler
metal
group
BS alloy
IS0 alloy
designation?)
Qpe 1
1080A
1050A
3103
Al99,8
Al99,5
Al Mn1
Al Si5 (A)
Al Si12
(A)
Al Mg5
Al Mg5Cr(A)
Al Mg5,BMnCr
Al Mg4,5Mn
Qpe 3
1 me 1
Qpe 5
4047A3)
4043A
505GA
5356
5556A
5183
I
DurabilitJ
rating
designation')
A
A
IB
A
l) See BS 2901 : Part 4 for chemical composition.
?) Or nearest equivalent.
3, 4047A is specifically used to prevent weld metal cracking in
joining involving high dilution and high restraint. In most cases
4043A is refera able.
The mechanical propertiesof the alloys vary with
temperatwe and those given in tables 2.1, 2.2 and 2.3
should be applied to the design of structures over a
temperature range -50 "C to 70 "C except for 5083
(see 2.2.1.1.3 (d)). The 0.2 % proof stress and tensile
strength improveat lower temperatures,but at higher
tenlperatures are reduced. For properties outside the
temperature range given, the manufacturer shouldbe
consulted. The alloywill melt withinthe range 550 "C
to 660 "C, with the precise range dependenton the
alloy.
2.3.2 Physical properties
The physical propertiesfor the standard alloys
although varying slightlymay be taken as constant and
are listed in table2.5. In critical structures the engineer
nlay wish to use the exact value which should be
obtained froma reputable nlanufacturer.
'Igble 2.5 Physical properties
Property
I Value
Density
Modulus of elasticity
Modulus of rigidity
Coefficient of thermal
expansion
2.4 Durability and corrosion protection
2.4.1 General
In many instances the standard nmterials listedin
tables 2.1 to 2.4 can be used in the ndl-finish, as
extruded or as welded condition withoutthe need for
surface protection.
The good corrosion resistanceof aluminium and its
alloys is attributable to the protective oxide film which
forms on the surface of the metal inunediatelyon
exposure to air. This film is normally invisible,
relatively inert andas it forms naturally on exposure to
air or oxygen, and in many complex environments
containing oxygen;the protective film is thw
self-sealing.
In mdd environnlents an alunWum surface will retain
its original appearance for years, and no protection is
needed for most alloys. In moderate industrial
environments there will be a darkening and roughening
of the surface. As the atmosphere becomes more
aggressive such as in certain strongly acidicor strongly
alkaline environments,the surface discoloration and
roughening will worsen with visible white powdery
surface oxides andthe oxide film may itself be soluble.
The metal ceasesto be fully protected and added
protection is necessary. These conditions mayalso
occur in crevices due to high local acid or alkaline
conditions, but agentshaving this extreme effectare
relatively fewin number.
')Obsolescent standard
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2 710 kg/m3
70 O00 N/nun2
2G GOO N/nun2
23 X
per "C
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BS 8118 :Part 1 : 1991
Section 2
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In coastal and marine environments
the surface will
2.4.3 Corrosion protection
roughen and acquire agrey, stonelike, appearance, and
2.4.3.1 Overall corrosion protection
protection of some alloysis necessary. Where
The need to provide overall corrosion protectionto
aluninhm is immersed in water special precautions
structures constructed from the alloys or conlbination
may be necessary.
Where surface attack does occur corrosionhime curves of alloys listed in tables2.1, 2.2, 2.3 and 2.4 when
for aluninium and aluminium alloys usually follow an exposed to different environments (seePD 6484)is
given in table 2.6. The methods of providing corrosion
exponential form, with a fairly rapid initial loss of
protection
in these environments are detailed in
this there is
reflectivity after slight weathering. After
BS
8112
: Part 2.
very little further change over very extensive periods.
In selecting the appropriate colunm of table 2.6 for an
On atmospheric exposure,the initial stage may be a
atmospheric environment there maybe localities
few months or 2 to 3 years, followed by little,if any)
further change over periodsof 10,30 or even 80 years. within a region that have ‘nucroclinlates’ vastly
different fromthe environmental characteristicsof the
Such behaviouris consistent forall external freely
region as a whole. A region designated ‘rural‘may have
exposed conditions and for all intemal or shielded
local environments more closely resenlblingan
conditions, except where extremesof acidity or
industrial atmosphere at sites close to and down wind
alkalinity can develop. Tropical environmentsare in
general no more harmfulto aluminium than temperate of factories. Siilarly, a site near the sea but close to
environments, although certain alloys (seeBS 5500) are shore installations may, with the appropriate prevailing
winds, have the characteristics of an industrial, rather
affected by long exposure to high ambient
than marine, atmosphere. The environmentis not
~
e
temperatures, particularly whenin a n
necessarily the sanle fora structure inside a building
environment.
as for one outside.
2.4.2 Durability of alloys
Because of these factors, localized conditionsof
The alloys listed in tables 2.1, 2.2, 2.3 and 2.4 are
increased severitymay result. It is advisable to study
categorized intothree durability ratings A, B and C in
the precise conditions prevailingat the actual site
descending order of durability. These ratings are used
before deciding on the appropriate environment
to determine the need and degree of protection
column of table 2.6.
required. In constructions employing morethan one
alloy, including filler metalsin welded construction, the Where hollow sections are employed consideration
should be given to the need to protect the internal void
protection should bein accordance with the lowest of
to
prevent corrosion arising from
the ingress of
their durability ratings.
corrosive agents. Becauseof the difficulty of painting
such sections, chemical conversion coatings
may be
beneficial. Where the internal void is sealed effectively,
internal protectionis not necessary.
~~_____
I
rable 2.6 General corrosion protection of aluminium structures
I
~1
~_____
Material
durability thickness
ratmg
mm
h o y
I
I Protection needed according- to environment
~~
Rural
IndustriaUurban
Moderate Severe
Marine
NonModerate
industrial
I None
I None
P
P
P
P
None None
P
P
IA
I All
I None
I None
B
<3
23
None
C
All
None
P
P
P
None None
P’)
P
IP
P
I
1 Immersed
Atmospheric
Fresh water
Sea water
I None
I None
P
P
PZ)
P
P
Severe
IP
I
NR
Ke?l
P Protection needed (see BS 81 18: Part 2).
P’)Requires only local corrosion protection to weld and HAZ in urban non-industrial environments.
P?) Protection not recommended if of welded construction.
NR Immersion in sea water is not recommended.
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23
S T S O B S 1 BS 8118: PART L-ENGL
1591 m 1 b 2 4 b b 7 0 7 7 4 5 3 2 2 5 1 m
BS 8118 :Part 1 : 1991
Section 2
2.4.3.3.3 Contact with timber
Consideration shouldalso be given to contacting
In an industrial, dampor nlarine environment the
surfaces in crevices and contact with certain metalsor timber should be primed and painted inaccordance
washings from certain metals which nlay cause
with good practice.
electrochemical attack.of alunlinium (see PD 6484).
Some wood preservatives nlay be harnuûlto
Such condtions can occur within a structure at joints. aluminiun~As a general guidethe following
Contact surfaces andjoints of alunlinium to a l u n ~ i u m preservatives have been agreed betweenthe
or to other metals and contact surfacesin bolted,
AlunIMun~Federation, the British Wood Preserving
riveted, welded and high strength friction grip(HSFG)
Association
and Danlp-proofing Associationto be safe
bolted joints should be given additional protection to
aluminiun~without special precautions:
for
use
with
that required by table 2.6 as defined in table 2.7. Details
a) coal tar creosote;
of the corrosion protection procedure required are
given in BS 8118 : Part 2.
b) coal tar oil;
c) chlorinated napthalenes;
2.4.3.3 Contact with othernon-metallic materials
d) zinc naphnates;
2.4.3.3.1 Contact with concrete, masonry W plaster
e) pentachlorophenol;
Aluminium in contact with dense compact concrete,
f)
organo-tin oxides;
masonry or plaster in a dry unpolluted or nuld
environment should be coated on the contacting
g) orthophenylphenol.
surface with a coat of bituminous paint,
Where timber, treated withthe following preservatives,
see BS 8118 : Part 2. In an industrial or marine
is used in damp situationsthe aluni ni un^ surface in
environment the contacting surfaceof the alununiunl
contact with the treated timber should havea
should be coated withat least two coats of heavy duty substantial applicationof sealant:
bituminous paint;the surface of the contacting material
1) copper napthanate;
should preferablybe similarly painted. Submerged
2) copperchrome-menate;
contact between aluminiun~and such nlaterials is not
reconunended, but if unavoidable separation ofthe
3) bom-boric acid.
materials is reconunended by the use of a suitable
Other preservatives should not be used in association
mastic or a heavy duty damp course layer.
with alminiunl.
Lightweight concrete and similar products require
Reference may be made to CP 143 : Part 15.
additional consideration when wateror rising danlp
Oak, chestnut and western red cedar, unless well
can extract a steady supplyof aggressive alkali from
seasoned, are likely to be h a r n ~to
l alunIMun~.
the cement. The alkali water can thenattack
aluminium surfaces other than the direct contact
2.4.3.3.4 Contact with soils
surfaces.
The surface of the metal in contact with soil shouldbe
protected with a least two coats of bituminous paint,
2.4.3.3.2 Embedment in concrete
The dunMun~
surfaces before embedmentin concrete hot bitumen, or plasticized coal-tar pitch,see BS 8118 :
Part 2. Additional wrapping-tapes nlay be usedto
should be protected with at leasttwo coats of
prevent
mechanical danmge to the coating.
bituminous paint or hot bitumen, see BS 8118 : Part 2,
and the coats should extend at least 75 nun above the 2.4.3.3.5 Immersion in water
concrete surface after embedment.
Where au
l nMun parts are inunersed in freshwater or
Where the concrete contains chloridese.g. as additives sea water including contanûnated water,the aluni ni un^
or due to the use of sea-dredged aggregate, at least
should preferably be of durability rating A, with
two coats of plasticized coal-tar pitch should be
fastenings of alunIMun~or corrosion-resisting steelor
applied in accordance with BS 8118 : Part 2 and the
fastened by welding. Tables 2.6 and 2.7 give the
finished assembly should be overpainted locally with
protection neededfor fresh water andsea water
the Same material, after the concrete has fully set, to
inunelsion.
seal the surface. Care shouldbe taken where metallic
In addition the engineer should obtain competent
contact occurs betweenthe embedded alun Mun^ parts advice on the oxygen content, pH number, chenucal or
and any steel reinforcement.
metallic, particularly copper, content andthe amount
of nlovenlent of the water as these factors nlay affect
the degree of protection required.
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2.4.3.2 Metal-to-metal contactsincluding joints
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m
m
m
M
m
dr
M
4
4
4
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25
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--`,,,,,,`,,,``,```,,`,````,``,-`-`,,`,,`,`,,`---
2.4.3.3.6 Contact with chemicals used in the
building industry
Fungicides and mould repellents may contain metal
compounds based on copper, mercury, tin and lead
which, under wet or danlp conditions could cause
corrosion of the alunMun1. The harmful effects may
be countered by protecting the contacting surfaces
whch may be subject to washmg or seepage from the
chemicals.
Some cleaning materials can affectthe surface of the
alunMum. Where such chemicals are used to clean
aluminium or other materials in the structure, care
should be taken to ensure that the effects will not be
detrimental to the aluminium. Often quick and
adequate water rinsing will suffice, while inother
situations temporary measuresmay be necessary to
protect the aluni ni un^ from contact with the cleaners.
Particular attention is drawn to the susceptibility
of 6082,6063,6061 and5251 alloys to cracking during
solidification when weldsare made under constraint.
This may be avoided bythe use of the filler nmterials
and welding techniques recommended (seeBS 8118 :
Part 2 : 1990). This will ensure a suitable combination
of filler material in the actual weld.
2.5.3.2 Filler metals.
The filler wirefor use in welded construction should
be chosen in accordance with table2.8.
2.6 Selection of materials
The choice of an alloy or alloys for any structure is
determined by a combination of a number of factors:
strength, see 2.3; durability, see 2.4; physical properties,
see 2.3; weldability, see 2.5; formability, see 2.5 and
availability, see 2.7 in both the particular fornl and
2.4.3.3.7 Contact with insulating materials used in
alloy required. The standard nlaterials given in
thÆ building industry
tables 2.1 and 2.2 are described in terns of the above
Products such as glass fibre, polyurethane and various factors in 2.2.1.1.2 and 2.2.1.1.3.
insulation products may contain corrosive agents
which can be extracted under moist conditionsto the
.
nlaterials should 2.7 Availability
detriment of the a l u m i n i u n ~ Insulating
be tested for compatibility with alunlinium under damp 2.7.1 General
and saline conditions. Where thereis doubt, a sealant
The range of alloys given in tables 2.1 and 2.2 are not
as described in BS 8118 : Part 2 should be appliedto
available
in all product forms. Table 2.9 indicates
the
the associated aluni ni un^ surfaces.
alloys available in particular product
f o m and where
nlaterials may be stocked in liuted quantities. Product
2.5 Fabrication and construction
and alloy combinations notnorndly manufactured but
which may be manufactured by special arrangement
2.5.1 General
are indicated, design in thesenlaterials should only be
The fabrication and construction requirementsto be
attempted after confurnationof their availabilitywith
detailed are included in the relevant design clauses.
the materials supplier.
BS 8118 : Part 2 specifiesthe methods of fabrication to
2.7.2 Structural sections
be followed. In addition 2.5.2 and 2.5.3 should be
considered by the engineer.
A number of structural extruded sections cornplying
with BS 1161 and some other structural sections are
2.5.2 Bending and forming
available in 6082-T6 or 6063-T6 from stock, but in most
Alunwunl alloys are available in a wide range of
instances they will need to be produced to order,
tempers which affect their formability. Where bending see table 2.9. Table 2.10 gives the range of sizes of
or forming is required the engineer should consultthe
sections given in BS 1161. Other sizes may be obtained
manufacturer for guidance on the choice of alloy,
from existingor new dies by arrangement with the
temper and any subsequent heat treatmentthat may be manufacturer. Where sectionsare produced to order,
required.
minimm1 order quantities may be applied. Special new
extruded
sections are normally nude to order and the
2.5.3 Welding
low cost of simple dies gives great flexibilityin this
2.5.3.1 General
design. The engineer should consultthe manufacturer
at an early stageto verify the shape, thickness, size
The loss of strength that can occur in the vicinity of
and feasibility of the design of a new section and
the weld with some alloys and tempers should be
delivery of both the new die and the extruded section.
considered by the engineer in the choice of the alloy
Some sections or products are nmle by drawing,
or alloys to be used in welded construction. The
engineer shouldsatisfy himself that the combination of forming or roll forming, these operations nlay require
special tooling.
parent and fillermaterials is suitable in regard to
strength and durabilityfor the service conditions of the
shucture.
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~
~~
~~
STD-BSI BS BLLB: PART L-ENGL L771 m L b 2 4 b b 9 0794535 Tb0 W
Section 2
BS 8118 :Part 1 : 1991
hble 2.8 Selection of filler wires and rods for inert-gas welding
'arent metal combination')
T
~
L200
7020
6061
6063
6082
5556A
Type 5
me 5
Type 5
5
Type 5
Type 5
Type 4 5
Type 4
Type 4
i083
m 5
5556A
il54A
i251
-5
1454
6082
}
7020
me
m 5
Type 5
m 5
5
m 5
5556A
me
m
m
i083
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~~
.st part
5
5
1200
1
3103
3
105
LM6
LM25
Castings
LM5
Castings
***
l ) Filler metals for parent combination to be welded are shown in one box, which is located at the intersection of the relevant parent.
and 7020
metal row and column. In each box, the filler metal for maximum strength is shown in the top line; in the cm? of G
alloys, this will be below the fully heat-treated parent metal strength. The filler metal for maximum resistance to corrosion is shown
in the middle line. The filler metal for freedom from persistent weld cracking is shown in the bottom line.
1' NR = Not recommended. The welding of alloys containing approximately 2 % or more ofMg with AI-Si (5% to 12 % Si) filler metal
(and vice versa) is not recommended because sufficient MgxSi precipitate is formed at the fusion boundary to embrittle the joint.
3, The corrosion behaviour of weld metal is likely to be bett,er if its alloy content is close to that of the parent metal and not markedly
higher. Thus for service in potentially corrosive environments it is preferable to weld 5154A with 5154A filler metal or 5454 with 5554
filler metal. However, in some cases this may only be possible at the expense of weld soundness, so that a compromise will be
necessary.
'1 If higher strength and/or better crack resistance is essential, type 4 filler metal can be used.
NOTE 1. Table derived from BS 3019 : Part 1 and BS 3571 : Part 1.
NOTE 2. For paflicular filler metal alloys in each alloy type see table 2.4.
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28
u
Y
--`,,,,,,`,,,``,```,,`,````,``,-`-`,,`,,`,`,,`---
E
-1
'T
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STDOBSI B S 8238: PART I-ENGL 2991,
lb211bb9 07911537 833 M
Section 2
BS 8118 :Part 1 : 1991
Table 2.10 Range of sizes for extruded sections
comDlsing- with BS 1161
"
Section type
Range of size
nun
Equal angles
Unequal angles
Channels
Tee-sections
I-sections
Equal bulb angles
Unequal bulb angles
Lipped channels
Bulb teesections
30x30 to 120x120
50x38 to 140x105
60x30 to 240X 100
50x38 to 120x90
60x30 to 160x80
50x50 to 120X 120
50X37.5 to 140x105
80x40 to 140x70
90x75 to 180x150
2.7.3 lbbe
Tube may be produced by extrusion, by drawing or
seam welding. Tubeis available from stock in someof
these forms in a linuting range of sizes but generally it
will be made to order, see table 2.9.
2.7.5 Forgings
Forgings are supplied to order as hand forgings or die
forgings, the former nornwlly requiring all over
machining to acheve the finished dinlensions whilst
the latter are produced to the frnished dinlensions.
Dies for forgingsare relatively expensive and costs
should include at least one forging nmde andcut up to
check grain flow to prove the die for forgings usedin
structural applications.
2.7.6 Castings
Castings are supplied to order as sand casting or chill
castings. Sand castingsare produced from patterns
made at moderate cost and are used nornlally for s n ~ l
quantity production. Chill castingsare generally used
for larger quantity production and where greater
production rates are required, where greater
dimensional accuracy and good surface finish is
required. The cost of tooling may be high, especially
for pressure die castings.
2.7.4 Sheet, strip and plate
A wide nnge of sheet, strip and plateis normally
2.9). Some
stocked in the standard alloys (see table
alloys are available as patterned sheet and as
treadplatè. There is a wide range of standard rolled
roofing and cladding products, someof which are
available in moderate quantities from stockin both mill
finish and painted, but mostare generally produced to
order.
--`,,,,,,`,,,``,```,,`,````,``,-`-`,,`,,`,`,,`---
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29
Section 3. Design principles
Structures should be designedby considering the linut
states at which they become unft for their intended
use. Considemtion should always be given
to the
following linut states:
(a) static strength (ultimate linutstate) (see 3.3);
@) defornmtion (serviceability linut state) (see 3.4);
(c) durability (see3.5).
In certain structures it will be necessary to consider
one or both of the following:
(1) fatigue (see 3.6);
(2) vibration (see 3.7).
Design will nomlally be carried out by calculation
using the guidance given in sections 4 to 7 and
appendices B to L. It is permissible, however,to ver@
a proposed design by testing (see section8).
3.2 Loading
Where possible they shouldbe detemined from the
relevant British Standard. For dead and imposed
loading refer to BS 6399 : Part 1. For wind loadiig on
buildings refer to CP 3 : Chapter V: Part 2. British
Standards also exist for nominal loads on cranes and
lifts (including dynamic effects). Whereno relevant
British Standard exists nonlinal loads should
be
decided by the designer and the client. A method of
assessing loads using a statistical and probability basis
is given in appendix B.
When the imposed load consistsof soil or other filling,
considemtion should be givento the material
becoming saturated. In assessing temperature effects it
nmy be assumed that in the UK, in the absence of local
i n f o d o n , the average internal temperatureof the
structure varies between -5 "C and +35 "C. The effect
of the colour of extemal sheeting on intemal
tenlperature shouldalso be considered.
3.2.3 Factored loading
Factored loads are used for checkingthe linut state of
static strength.They are the nominal loads multiplied
by the overall load factor, yf, which provides an
allowance for variability in loadmg, accidental
overload, etc. yf is defined as follows:
3.2.1 General
A structure or structural component should be
designed to resist all loads and actionsto which,
within reason, it can be subjected. These
are classihl
Yf = YflYa
as follows.
where
(a) Dead load. Self-weight of the structure and of
yf1 and
are the partialloadfactors.
any permanently attached item it supports.
yfl is governed by the type of load, and y f allows
~
@) Imposed bad. Any statically or dynamically
some relaxation whena conlbination of imposed
applied load other than dead or wind loading.
andor wind loads is applied to the structure. As a
(c) Wind loud. Dynamic loading due to wind g u s t s .
guide, tables 3.1 and 3.2 give valus of yfl and y f ~based
(d) Tempemture eflect. Temperature fluctuations
on building structures, but different valuesnmy be
leading to forces in a structural component.
used by agreement betweenthe designer and the
client. If different valuesare chosen by referenceto
All relevant loads shouldbe considered separately or
in such realistic combinationsas to conlprise the most other British Standards,c m should be taken to ensure
that y f l does not includea factor to allow for
critical effects onthe elements and the shvcture as a
variability of material strength. For initial designof
whole. The magnitude and frequency of fluctuating
simple structuresy f ~may be conservatively taken
loads should also be considered. Particular attention
should be givento loading conditions during assembly, as 1.0 for all imposed or wind loads.
and the settlementof supporting structures may need
Table 3.1 Load factors (based onbuilding
to be taken into account. The possibility
of loads due
structures)
to seismic forces, fire, explosion and vehicular impact
should be considered.
Type of load
Yfl
3.2.2 Nominal loading
Nominal loads are defined as those to which the
structure may be reasonably expected to be carrying
during normal service. Theyare used for checking the
limit m e s of deformation, fatigue and vibration.
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Dead load
Direct effect
Countering overturningor uplift
Imposed load (not including wind loads)
Wind load
Forces due to temperature effects
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1.2
0.8
1.33
1.2
1.0
O BSI 07-1999
--`,,,,,,`,,,``,```,,`,````,``,-`-`,,`,,`,`,,`---
3.1 Limit state design
~~
~~
~
STDmBSI BS 8118: PART 1-ENGL L991 D '1b211bb7 0794539 bob D
Section 3
BS 8118 :Part 1 : 1991
Table 3.2 Load factors for combined loads
Load combination
Yk-2
1.0
Dead load
Imposed or wind load giving most severe
1.0
loading action onthe conlponent
Imposed or wind load giving second nlost
0.8
severe loading actionon the component
Inlposed or wind load giving third most severe 0.6
loading action of the component
Imposed or wind load giving fourth nlost
0.4
severe loading action onthe component
NOTE. In sonle structures the wind load could be the most
severe applied load, in others the wind load could produce load
effects less severe than those due to the mJor imposed loads.
I
3.2.4 Dynamic effects
In order to determine the nominal loading ona
structure under dynamic conditions, reference should
be nlade if possible to an appropriate British Standard.
Forces from dynanuc effectsare treated as imposed
loads in table 3.1.
In other cases, should a 'dynamic magnification factor'
be used, the designer should be aware that this might
be a dangerous procedureif the response of the
structure is not taken into account.This applies
particularly to aluminium structures of high flexibility
that have a natural periodof vibration similar in
magnitude to that of the imposed load.
If initial calculations showthat a problem exists, a
more detailed computation based onthe equations of
motion should be carried out. The need to provide
artificial damping shouldbe examined, and tests on
prototype componentsmay also be necessary.
3.3.3 Factored resistance
This is the calculated resistance dividedby the nlaterial
factor ym. The calculated resistance is the actual
capacity of the component in relationto the
actioneffect being considered (axial load, bending
moment or shear force), basedon recognized
structural analysis and assuming satisfactory
manufacture.
The material factor, ym, takes account of differences
between the strengths of material test specimens and
the strength of the actual material in the structure as
nmufactured, and reflects possible doubtas to the
soundnes of the component as built. ym should
normally be taken from table 3.3, but different values
may be used by agreement betweenthe designer and
the client.
Tbble 3.3 Material factors
5 p e of construction
Riveted and bolted
I Welded
Bonded
I ym
Members
Joints
1.2
1.2
I 1.3l)
3.0
I 1.2
I 1.2
1
For welding procedures which do not comply with BS 4870 :
Part 2. Y, should be increased to 1.6.
Rules for establishingthe calculated resistance are
given in sections four andfive (members) and section
six (joints). A method of assessing the calculated
resistance or the basis of statistics and probability is
given in appendix B.
NOTE. In certain structures it is necessary to check that failure
will not occur by overturning or sway failure.
3.4 Deformation
3.3 Static strength
3.3.1 General
A component is acceptable in terms of static strength
if the following is satisfied
3.4.1 Recoverable elastic deformation
A structure is acceptable in terms of deformation if the
following is satisfied
elastic deflection under
nominal loading
Actioneffect under factored resistance
factored loa(see appendixB)
3.3.2 Action-effect under factored loading
This is the axial force, bending momentor shear force
arising in a component due to the application of
factored loading, foundby using accepted structural
analysis. The factored loadingis found by taking the
nominal loads and multiplying each by the appropriate
load factor.
limiting
deflection
It is permissible, when different combinationsof
imposed loading are possible, to assume a reduced
loading equal to ya X nominal loads, whereyn is given
in table 3.2.
The calculation of elastic deflection should generally
be based on the properties of the gross cross-section.
However, for slender sections itmay be necessary to
take reduced section propertiesto allow for local
buckling (see section4).
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-~
~~
31
STD-BSI BS ALLB: P A R T L-ENGL 1771 W 1b2qhb7 07745'iO 328 m
BS 8118 :Part 1 : 1991
Section 3
'hble 3.4 Limiting deflections
Element
1
Recommended
deflection limit
(see note)
LI180
Cantilevers carrymgfloors
Beams carrying plasteror other LB60
brittle finish
Purlins and sheetingrails:
LBO0
(a) under dead load only
(b) under worst combination LI100
of dead, imposed, wind and
snow loads
Curtain wall mullions and
transoms:
LI175
(a) single glazed
LI250
(b) double glazed
LI300
Tops of columns: horizontal
deflection
NOTE. L is the length between SUDDOT~S.
3.4.2 Permanent inelastic deformation
It may be generally assumed that components, whose
static strengthhas been calculated in accordance with
section four,will not suffer sigruficant permanent
deformation under actionof nominal loading. This
applies to all alloy groups.
3.4.3 Distortion due to frequent assembly
In certain structures which have to be assembled and
disassembled frequently, itis necessary to consider the
possibility of changes in major dimensionsof the
coupling system, leadingto the gradual build-up of
unacceptable errors in the assembled shape.
3.5 Durability
The durability rating of alloy groups is given in
tables 2.1 to 2.4. If a structure is designed in a durable
alloy and protected in accordance with
BS 8118 :
Part 2, it w
l
i be deemed &factory. The degree of
exposure and the design l i e should be taken into
consideration.
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3.6 Fatigue
3.6.1 General
Any structure or structural conlponent which is subject
to signifcant variations in load should be checked for
fatigue. In general two possible linlit states should be
considered:
a) total collapse;
b) stable crack growth (danlage tolerant).
In both cases the design load spectrum (unfactored)is
assunled to act.
3.6.2 Total collapse
The procedure for considering this limit state is to
determine the predicted life in accordance with section
seven, and checkthat this is not less than the design
life. In certain circunlstancesthe designer may wish to
increase the nonunal design lifeby nwltiplying by a
factor (the fatigue life factor) y~ (>1). The choice of n,
could be influenced by the following:
(a) the possibility of increasing crack growth during
the later stages of the life of the detail;
(b) the accuracy of the assunled loading spectrum;
(c) whether records of loading will be kept during
the life of the detail;
(d) the possibdity of a change of use of the structure
in mid-life.
The designer mayalso wish to apply a fatigue material
factor, ymf, to the design stress range given in
figure 7.9. The stress range would be divided by ynlf
(> l ) ,and the choice of ymf could be influenced by the
following
( 1 ) the need for the detail to exist in a very hostile
environment;
(2) whether failure of the detail will result in failure
of the entire structure, or whether alternative load
paths exist.
3.6.3 Stable crack growth
Damage to a structure under fatigue conditionsis
assessed by monitoring the rate of growth of fatigue
cracks by inspection at regular intervals. Methods of
inspection, allowable limiting crack lengths, allowable
rates of crack growth, andthe tinle between
inspections should be agreed betweenthe client and
the designer. Crack growth is stable when the
allowable rate of crack growth does not suddenly
increase between inspections.
NOTE. Methods for calculating crack growth and limiting crack
length are outside the scope of this code, but the ease with which
a detail can be inspected for cracks can influence the choice of
ymf (see 3.6.2).
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--`,,,,,,`,,,``,```,,`,````,``,-`-`,,`,,`,`,,`---
The linuting deflection should be based on the relevant
British Standard, or agreed between the designer and
the client. In the absence of such information table3.4
gives suggested values for certain typesof structure. In
setting linuting deflections it is important to realise that
dunmum is three times as flexible as steel, so unduly
s n d limiting deflections should be avoided.
3.7 Vibration
3.8 Testing
For certain structures the possibility of undesirable
vibration under nornd service conditions should be
considered. In checking for the inconlpatibility of
vibration amplitudes nominal loads should beused. If
vibration is thought to be a potential problem, the
possibility of fatigue failure shouldalso be checked
(see 3.6).
Structural conlponents designedin accordance with
sections 4 to 7 and the appropriate appendicesare
acceptable without testing. Conlponents designed using
other calculation nlethods, and conlponents not
amenable to calculation, are acceptable only if their
resistance has been verified by testing. Such testing
should be carried out in accordance with section 8.
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33
Section 4. Static design of members
4.1 Introduction
4.1.4 Advanced design
4.1.1 General
All members should satisfy the linut states of static
strength and of deformation. Deformationis covered
in 4.9.
Where reference is made to design curves, itis
Members can be safely designed usingthe
recommendations of this section andthe appropriate
appendices. Other appendices providea fuller
treatment of certain specificaspects of member
behaviour, and their use may leadto lighter designs.
in 4.3.
4.1.3 Heat-affected zones ( W s )
Structural aluminium materialg e n e d y becomes
weakened in the heat-affected zone (HAZ) adjacent to
welds, and this should be allowedfor in the design.
This does not apply when the parent material is in
the O or T4 condition; or when it is in the F condition
and design is based on O-condition properties.
Rules for estinlatingthe severity and extentof HAZ
softening are given in 4.4. Subsequent clauses then
show how to allow for the effect of this softening on
member resistance.
It is important to realize that a small weld, as used for
example in connectmg a small attachment,may
considerably reducethe resistance of a member, due to
softening of part of the crosssection. In beams it is
often beneficial to locate welds in low-stressareas,
i.e. near the neutral axis or away from the region of
peak monlent.
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4.2 Limiting stresses
Resistance calculationsfor members are made using
assumed linuting stresses as follows:
P,
pa
pv
P,
is the linutmg stress for bending and overall
yielding;
is the linuting stress for local capacity of the
section in tension or compression;
is thelinuting stress in shear;
is the linuting stress for overall buckling
staJ3ility.
Values of po,pa and pv depend on the material
properties and should be takenas in table 4.1 or 4.2.
For materials not covered in these tables referto
appendix D.
Values of P, should be determined in accordance
with 4.5.6.5 or 4.7.6.
4.3 Section classification and local
buckling
4.3.1 General
4.3.1.1 Section classmeation
Resistance of members under momentor axial
compression may become reduced by local buckling, if
the slenderness of their component elementsis high.
The first step in checking such members is to establish
the section classification, i.e.the susceptibility to local
buckling. In order to do this, and also to allow for the
effect of local buckling (when necessary),the designer
should considerthe slenderness of the individual
elements comprising the section.
4.3.1.2 mpes of element
The following basic typesof thin-walled elementare
identified in these rules:
(a) flat outstand element;
@) flat internal element;
(c) curved internal element.
These are often unreinforced, i.e. not longitudinally
stiffened (see figure4.1 (a)). The stabilityof flat
elements can be greatly improved
by the provision of
longitudinal stiffening ribsor lips, see figure 4.1 (b), in
which case the elements are referred to as reinforced.
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--`,,,,,,`,,,``,```,,`,````,``,-`-`,,`,,`,`,,`---
pernwible instead for the designer to use formulae
from which the curves are derived (see appendixK).
Members are usually formed of extrusions, plate,sheet,
tube or a combination of these. The rules belowdo not
apply to castings, and designers wishingto employ
castings should do so in close consultation withthe
manufacturers thereof.
4.1.2 Limit state of static strength
The factored resistanceof a member to a specific
actioneffect should not be lessthan the magnitude of
that actioneffect arising under factored loading.
Rules for obtaining resistanceto different actions are
given as follows:
(a) for bema (resistance to moment and shear
force) (see4.5);
(b) for ties (resistance to axial tension) (see 4.6);
(c) for struts (resistance to axial compression)
(see 4.7).
The procedure for calculatingthe interaction between
moment and axial load in members subject to
combined actions is given in 4.8.
The formulae given contain limiting
stresses (po, pa,
h)related to material properties, which should be
taken in accordance with4.2. They also contain the
material factory,,, which should be read from table3.3.
The resistance of a member may be reduced as a
result of local buckling, dependingon the slenderness
of its cross section. A proposed design is checked
(except for a member under axial tension)by
c l a s s i i g the section in terms of its susceptibility to
this type of failure. A method for checking the local
buckling, including sectionclassikation, is given
~~
~
STDmBSI BS 8118: PART 1-ENGL 1991 m l b 2 q b b 9 079q5q3 03'7
Section 4
BS 8118 :Part 1 : 1991
1 ' 1 rable 4.1 Limiting stresses, heat-treatable alloys
dloy
Condition
'roduct
I lLimiting stress
TThickness
Up to and
DO
0,
Dl,
mm
NhUn2
N/nun2
150
6
10
150
10
150
25
150
10
150
150
3
25
10
150
20
150
3
25
G
10
120
25
25
25
25
140
240
225
65
35
50
110
160
180
160
115
115
105
105
115
255
270
255
240
255
240
255
185
160
280
270
260
N/nun2
145
145
135
40
60
including
--`,,,,,,`,,,``,```,,`,````,``,-`-`,,`,,`,`,,`---
i082
7020
T6
TG
Extrusion
Drawn tube
T4
T4
T4
T5
T6
T6
T6
T4
T4
T4
T4
T4
T6
Extrusion
Drawn tube
T6
T6
Sheet
Plate
TG
Drawn tube
T6
T4
T4
T6
T6
Forgings
Extrusion
Sheet, plate
Extrusion
Sheet, plate
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Forgings
Extrusion
Extrusion
Drawn tube
Forgings
Extrusion
Sheet
Plate
Drawn tube
Forgings
Extrusion
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265
260
35
120
100
130
175
190
170
145
145
140
140
145
275
290
275
265
280
275
275
230
205
310
295
50
G5
95
110
95
70
70
65
65
70
155
160
155
145
155
145
155
110
95
170
160
35
~
Alloy
Condition
Product
IS
7Thickness
"
T
Over
Pa
including
1200
3103
3105
5083
H14
H14
H18
H14
H16
H18
o, F
O
O
F
H22
H22
5154A
5251
5454
o, F
O
O
H22
H24
H24
F
H22
H24
o, F
O
H22
H24
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36
Sheet
Sheet
Sheet
Sheet
Sheet
Sheet
Extrusion
Sheet, plate
Drawn tube
Sheet, plate
Sheet, plate
Drawn tube
Extrusion
Sheet, plate
D r a m tube
Sheet, plate
Sheet, plate
Drawn tube
Welded tube
Sheet, plate
Sheet, plate
Extrusion
Sheet, plate
Sheet
Sheet
nun
0.2
0.2
0.2
0.2
0.2
0.2
0.2
3
0.2
-
0.2
0.2
0.2
-
312*5
3
3
3
150
80
10
25
6
10
150
G
10
G
6
10
0.8
0.2
0.2
1.0
3
-
150
3
0.2
3.2
3.2
5
3
3
i7
r.
"
I :i
N/mnl2
95
120
150
N/n&
55
G5
90
145
170
190
105
105
105
130
235
235
G5
65
G5
160
225
200
150
175
200
150
150
150
170
270
270
100
100
100
200
250
220
220
125
175
65
60
180
200
230
155
200
85
100
115
G5
G5
G5
75
140
140
40
40
40
85
135
180
130
75
105
100
10
j5
!15
!35
35
110
120
I
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--`,,,,,,`,,,``,```,,`,````,``,-`-`,,`,,`,`,,`---
~~~
Table 4.2 Limiting stresses, non-heat-treatable all
Section 4
BS 8118 : Part 1 : 1991
--`,,,,,,`,,,``,```,,`,````,``,-`-`,,`,,`,`,,`---
I
I
Key
o : outstand
1 : internal
(a) Unreinforced
@) Reinforced
Figure 4.1 mpes of flat element
4.3.1.3 Shear webs
The buckling of shear webs is treated separately
(see 4.5.3.3 and also section 5).
from the elastic neutral axis, although in checking
whether a section is fully compact it is pernlissible to
use the plastic neutral axis.
4.3.2 Slenderness parameter ß
4.3.2.3 Reirtforcedjlat elements
4.3.2.1 General
The susceptibilityto local buckling of an element in a
bean1 (nlonlent resistance)or in a strut (axial force
resistance) depends onthe paranleter ß as defined
in 4.3.2.2 to 4.3.2.5.
4.3.2.2 Unreidorcedjlat elements
The paranleter ß depends onb/t or U t for the element
concerned, where t is the elenlent thickness, b the
width of an element generally, andd the depth of a
web element in a beam. b and d should be taken as
the flat elenlent width, measured where relevantto the
springing of a fillet or to the toe of a weld.
ß is defined as follows:
(a) elenlentunder uniforn~conlpression:
/3 = b/t;
@) elenlent understress gmdient:
I
(I) internalelementwith
a stress
ß = 0.wt
gradient that results in a neutral axis at or
the centre:
0.4b/t
(2) forany other stress gradients
/3 = gb/t or
gdt
BSI 07-1999
ß = hb/t
where
b and t
where g is the stress gradient coefficient and is read
from figure 4.2. In figure 4.2 yc and yo are the distances
from the neutral axis of the gross sectionto the more
heavily conlpressed edge and the other edge
respectively of the element, taken positive towardsthe
conlpression side.They should generally be measured
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W o possible buckling modes should be considered as
follows (see figure4.3, and separate ß values found for
each
(a) mode 1 : the reinforced element buckles as a unit
talang the reinforcement with it;
(b) mode 2 : the sub-elenlents comprisingthe
reinforced elenlent thenlselves buckle as individual
elenlents the junctions between themstaymg
straight.
For mode 2 buckhg ß is found separately foreach
sub-elenlent in accordance with 4.3.2.2. For mode 1 it
is generally determinedas follows (but see the note
to 4.5.2.1, concerning outstand elenlents in beanls).
(a) Mode 1, umform conlpression.
(1) Standard reinforcement, defined as
reinforcenlent consisting of single-sided rib or lip
of thickness equalto the element thckness t,
located as in figure 4.4 :
h
are defined as in 4.3.2.2
is read
from
figure
4.4 (a), (b) or
(c) as appropriate.
For figure 4.4, c should be takenas the clear
depth of the rib or lip measured to the surface of
the plate
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37
~
STD-BSI BS 8118: PART L-ENGL 1991 D Bb24bb9 079454b 8llb
BS 8118 : Part 1 : 1991
Section 4
(2) Non-standard reinforcenlent.With any other
shape of reinforcenlent ß should be foundby
replacing it withan equivalent rib or lip of the
standard form and proceeding as in (1). The value
of c for the equivalent rib or lip is chosen so that
its second moment of area about the nud-planeof
the plate is the sanle as that for the true
reinforcement.
(3) General method. For cases not covered by (1)
or (2) ß nlay be taken as follows:
P = WO(~cdacr>o’4
where
are the elastic
critical stresses,
acr
and
assunling
simple
edge
support,
with
acro
and
without the reinforcement.
(b) Mode 1, stress-gradient.
ß should be foundusing the expression in (a) (3)
where acrand acronow relate to the stress at the
more heavily conlpressed edge of the elenlent.
4.3.2.4 Curved internal elements
For a shadow curved element underuniform
compression, ß should be determinedas follows:
b/t
= [ 1 + (0.006b4/RZi2]
where
R is the radius of curvature to nud-nlew
b is the developed width of element at nud-metal
t is the thickness
For shallow curved elements undera stress gradient, a
more favourable valueof ß may be taken, obtained by
factoring the above value byg as found from figure 4.2.
The above treatmentis valid, providedR/b is not less
tha O.lb/t. Sections containing more deeply curved
elements require special study.
1 .o
9
0.5
I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I
I
I
I
I
I
I
-2
-1.5
-1
-0.5
O
0.5
1 .o
Yo /Y,
NOTE.For internal elements or outstands (peak compression at root) use curve A.
For outstands beak compression at toe)use line B.
Figure 4.2 Flat elements under stress gradient, value of g
@I
Figure 4.3 Buckling modes for flat reinforced elements
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STDmBSI BS 8118: PART 1-ENGL 1 9 9 1 m Lb24bb90794547 782 9
Section 4
BS 8118 :Part 1 : 1991
O
c
O
c
--`,,,,,,`,,,``,```,,`,````,``,-`-`,,`,,`,`,,`---
u)
EII'
O
c:
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39
STD*BSI BS BLLB: PART L-ENGL L931
BS 8118 : Part 1 : 1991
--`,,,,,,`,,,``,```,,`,````,``,-`-`,,`,,`,`,,`---
4.3.2.5 Round tubes
ß should be found as follows, with no distinction
between axial compression and bending:
ß=3 (m)%
where
D is the dianleter to nud-metal;
t is the thickness.
4.3.3 Section classification
4.3.3.1 General
The procedure is to classe the individual elements
comprising the section, exceptfor any element
stressed wholly in tension. The classification ofthe
section is then taken as that for the least favourable
element. Individual elementsare classified in
accordance with4.3.3.4 or 4.3.3.5.
4.3.3.2 Sections: beams and struts
For the section of a beam (moment resistance)or of a
strut (axialforce resistance) the following
classications apply.
(a) Moment resistance:
(1) fully compact local buckling can be ignored;
(2) senu-conlpact: the section can develop a
moment equal to po times the elastic section
modulus;
(3) slender: the moment resistance is reduced by
premature local bucklingat an extreme fibre
stress below P,.
(b) Axial compression resistance:
(1) compact: local bucklingcan be ignored
(2) slender: local buckhg lowers the resistance.
L b 2 4 b b 9 079q548 b19
Section 4
Table 4.3 Limiting values ofß
Elements
ßo
Unwelded Welded
P1
Welded
Outstand
7E
GE
GE
5E
elements
Internal
22E
I&
1 8 ~
15 E
elements
NOTE 1. The quantity E should generally be taken as follows
(except for certain flange elements in beams, see 4.3.3.5):
E = (250/p0)"
where
po is the liniiting stress (in N/mm2) (see tables 4.1 and 4.2).
NOTE 2. An element is considered as welded if it contains
welding at an edge or at any point in its width. When the
stability of a particular cross-section of a meniber is evaluated,
however, it is permissible to consider an elenlent as unweldcd if
it contains no welding at that section, even though it is welded
elsewhere along its length.
NOTE 3. In a welded element the classification is independent of
the extent of the HAZ.
4.3.3.5 Understressedjlange elements
A more favourable classification mayif desired be
taken for flange elements in members under bending,
or bending with axial force,that are both:
a) parallel to the axis of bending; and
b) less highly stressed than the most severely
stressed fibresin the section.
For these itis permissible, in using table 4.3, to take a
modified value of E as follows:
E = (2501Jdp&
Ih
where y1 and y2 are the distances from the neutral
axis of the gross section to the most severely stressed
fibres and to the element respectively. They should
generally be measured from the elastic neutral axis,
4.3.3.3 Sections subject to combined actions
although in checking whethera section is fully
compact it is pernksible to use the plastic one.
For the classification of sections requiredto carry
biaxial bending, or simultaneous bendmg with axial
4.3.4 Local buckling
force, see 4.8.2.1.
4.3.4.1 General
4.3.3.4 Element classtfication
The possibility of local buckling in members classified
The classificationof an individual element depends on as slender is generally allowed for by replacingthe
true section by an effective one. The effective section
the value ofß (see 4.3.2) as follows:
is obtained by employing a local buckling coefficient
(a) elements in beams (moment resistance):
k~ to factor down the thickness, this being applied to
any uniform thickness slender elementthat is wholly
fully compact
ß 5 P1
or partly in compression. Elementsthat are not
uniform in thickness require special study.
ßI < ß 5 ßo senu-conlpact
slender
4.3.4.2 Determination of kL
ß>ßo
The coefficient kL, which is found separatelyfor
@) elements in struts (axial resistance):
different elementsof the section, is read from the
appropriate
curvein figure4.5 selected in accordance
ß 5 ßo compact
with
table
4
.
4
.In order to select the correct curve the
ß > bo slender
value of ß/E should be determinedas follows:
where ßo and ßI are as given in table 4.3.
ß
is found as in 4.3.2;
E
= ( 2 5 0 / ~generally
~)~
(but see note 3 of 4.5.2.3
for bean1 con7pression &anges);
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Unwelded
~
STD-BSI BS BLLB: PART L-ENGL L771 D fb2qbb7 O794549 555 m
Section 4
BS 8118 :Part 1 : 1991
--`,,,,,,`,,,``,```,,`,````,``,-`-`,,`,,`,`,,`---
where
po is the linuting stress for material ( i N/nun2),
regardless of HAZ effects.
I a b l e 4.4 Curve selection for figure 4.5 (local
This applies when the resistanceof a member is
governed by pa or P , rather than P,. To find k, for
nuterials not covered in table 4.5 see appendix F'.
4.4.2.2 7020 material
The alternative IC, values given in table 4.5 for 7020
material should normally be applied as follows,
Elements
Unwelded
I Welded
according to the nature of the stress acting on the HAZ
curve B
Flat outstand
curve A
nuterial:
elenlents
(a) value (A): tensile stress acting transversely to the
curve D
curve C
axis of a butt or fillet weld;
Internal elements
(flat or curved)
(b) value (B): any other stress condition, i.e.
longitudinal stress, transverse conlpression, shear.
Lower of
Round tubes
Lower of
curves C and curves D and
It is sometinles pernkible to increase value (A) to a
E
E
figure above that in the table, depending on the degree
I NOTE. &e note 3 to table 4.3
I of themlal control exercised during fabrication (see
appendix F').
In order to decide whether an element should countas
4.4.2.3 Recovery time for heat-treated alloys
unwelded or welded in table 4.4,refer to note 2 to
table 4.3.
The k, values given in table 4.5are valid from the
following times after welding, provided
the material
In the case of reinforced flat elements it is important
has been held at a tenlperature not less than15 "C:
to consider both possible modes
of buckling (see
figure 4.3) and take the more critical. In the case of
(a) 6
*series alloys
3 days;
mode 1 buckling the factor k~ should be applied to the
area of the reinforcement as well as to the basic plate
(b) 7
*series alloys
30 days.
thickness.
In d e t e r n m g the resistance of components that are
4.3.4.3 Sections subject to combined actions
to be loaded sooner than this, but not less than 24 h
For the determinationof k~ in sections required to
after welding, the value of k, should be reduced by a
carry biaxial bending, or simultaneous bending with
factorf found as follows:
axial force,see 4.8.2.2.
(1) G
f = 0.9 + 0.1 ((71 - 1)/2]"'
series alloys
4.4 HAZ softening adjacent to welds
(2) 7
f = 0.8 + 0.2 ( ( n- 1)/29]"
series
alloys
~
~
~design nto allow~for the ~softening~ that i
n
usually occurs in the vicinity of welds. The region
worst affected extends inmediately around the weld, where
n is the t h e (in days) between welding and loading.
beyond which the material properties rapidly improve
to their M1 parent values. The softening affects the
If the material is held at a temperature below15 "C
0.2 % proof stress more severely than the tensile
after welding, the recovery time will be prolonged and
strength.
advice should be sought.
For design purposes itis acceptable to approximateto 4.4.3 Extent of HAZ
the true con&tion by a s s u n ~ gthat around each weld
there is a zone, the HAZ, in which strength properties 4.4.3.1 Definition of z
are reduced by a constant factor&. Outside this zone
The HAZ is assunled to extend a distance z in any
it is assunled that the full parent propertiesapply. The
direction from a weld, measured as follows:
severity of the softening in theHAZ, as defined by h,
(1) transversely from the centre-line of an in-line
is covered in 4.4.2. The extent of the HAZ, defined by
butt weld (see figure 4.G(a));
a distance z from the weld, is considered in4.4.3.
(2) at fillet welds, transversely from the point of
It is sonletinles possibleto nutigate the effectsof HAZ
intersection
of the welded surfaces (see
softening by means of artificial ageing applied after
figures 4.G(e),O,(g) and0));
welding (see appendixF').
(3) at butt welds used in corner,tee or cruciforn~
4.4.2 Severity of softening
joints, transversely from the point of intersection
4.4.2.1 HAZ soflening factor
of the welded surfaces (see figures4.6(b), (c) and
(dl);
The factor kLshould nornlally be taken from table 4.5.
For certain calculations it is pemussible instead to use
(4) in any radial direction from the end of a weld
a more favourable valueas explained in appendixF.
(see figures4.G(i) and o)).
buckling)
**
**
I
***
***
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41
1.0
--`,,,,,,`,,,``,```,,`,````,``,-`-`,,`,,`,`,,`---
kL
0.5
Curve A outstands, unwdded.
Curve B outstands, welded.
(a) For flat outstand elements
Figure 4.6 Local buckling factor k~
The HAZ boundaries should generallybe taken as
straight lines normalto the metal surface,as shown in
figure 4.6 However, it is permissible instead to asume
a curved boundaryof radius z as shown at B (in place
of A) in figure4.G(i). This w
litend to be advantageous
when surface welding is applied to thick material.
4.4.3.2 Basic formulafor z
The following expression should generallybe used for
estimating z:
z = (Yrlz,
(Y
and v
***
(i
20
)
= 3tA
@) All other types of butt weld and all types of fillet
weld
where
20
(a) in-line butt welds:
(1) 7
series alloys:
(i) zo = 30 + tA/2
(ii)zo = 4.5t*
(2) other alloys:
(i) zo = 20 + tA/3
is the
basic
value
(see
4.4.3.3);
are rn-g
factors, which may be
found from4.4.3.4 and 4.4.3.5, or
alternatively using appendixE
***
(1) 7
series alloys:
(i) z, = 30 + t,&
(i) zo = 4.5tB2/tA
(2) other alloys:
(i) zo = 20 + t A B
The use of appendix F wil tend to be favourable when
(i)20 = 3tB2/tA
the interpass temperature during fabrication
is held
where
below the normal value requiredin BS 8118 : Part 2.
4.4.3.3 Determination of zo
tA
is the lesser of 0.5(t~+ LC) and 1.5t~;
The basic valuezo, which would relate to an isolated
$, tC are the thickness of the thinnest and
weld laid on unheated material with conlplete
thickest elements connected by welding
interpass cooling, should be taken as the lower of the
respectively.
two values given by (i) and (ii) (in mm) (depending on
the parent material) as follows:
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BS 8118 :Part 1 : 1991
Section 4
1.0
kL
0.5
Curve C: internal elements, unwelded
Curve D: internal elements, welded
Curve E: round tubes
NOTE. See note 3 to table 4.3
@) For internal elements and round tubes
Figure 4.5 Local buckling factor k, (cmZuded)
4.4.3.4 Determination of a
Thefactor CY in 4.4.3.2 providesfor the possibilityofwhere
the material at the start of deposition of a weld pass
being at an elevated
temperature,
due
either
to
preheat, or to the layingof apreviouspass or weld in
the sanle joint. Its value may be taken from table4.6,
which is valid provided fabrication complies with
BS 8118 : Part 2 (alternatively see appendix F).
4.4.3.5 Determination of 8
The factor 8 in 4.4.3.2 covers the possibility of
increased heat build-up dueto the following:
(a) proximity of a free edge or edges; or
(b) other welding in the sanle vicinity.
The value of 8 may be found as in (1) or (2) as
follows, provided fabrication satisfiesBS 8118 : Part 2.
Alternatively refer to appendix F.
(1) For a joint away from which there
are at least
two valid heat-paths:
q=l
a valid
heat-path
being
which
for
one
h
hl
h 2 hl.
is the distance to a free edge, or half the
distance to a nearbyweld(seenote);
4 . 5 for
~ 7~
series alloys, or
= 3 w o for other alloys.
***
When a weld is located too close to the free edge
of an outstand, suchthat h < hl, it should be
assumed that the entire width of the outstand is
subject to the factor kZ.
NOTE. The distance h, should be measured from the point of
reference in the weld considered (see figure 4.6) and along
the relevant heat-path through the metal at mid-thickness.
The heat-path follows the profile of the section and need not
necessarily be straight (sec figure 4.7).
(2) For a joint from whichthere is only one valid
heat-path:
tc 5 25
= 1.50
tc > 25
8 = 1.33
--`,,,,,,`,,,``,```,,`,````,``,-`-`,,`,,`,`,,`---
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43
lhble 4.5 HAZ softening factor IC,
ì
Condition
Alloy
kz
Non-heat treatable
H14
H14
H18
H14
H16
H18
1200
3103
3105
O. 13
O. 18
O. 13
O. 17
O. 15
O. 13
"
o, F
5083
1.00
0.45
-_
1.00
0.40
0.29
0.20
1.00
0.35
0.24
1.00
0.35
0.30
H22
o, F
5154A
H22
H24
F
F
H22
H24
5251
"
o, F
5454
H22
H24
Heat-treatable
0.50
1.00
O.65
0.80
O.75
0.50
0.45
1.00
0.50
0.80(A) l.OO(B)
O.GO(A) 0.80@)
(see note 2)
T6
T4
T4
T4
T5
T6
T6
T4
T6
T4
T6
6061
6063
6082
7020
I
____~
I
NOTE 1. In the product column, E, S, P, DT,WT and F refer respectively to extrusion, she< plate, dr&n tube, welded tube and
forgings.
NOTE 2. For 7020 material refer to 4.4.2.2, for the applicability of the A and B values.
--`,,,,,,`,,,``,```,,`,````,``,-`-`,,`,,`,`,,`---
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(h)
--`,,,,,,`,,,``,```,,`,````,``,-`-`,,`,,`,`,,`---
Figure 4.6 Extent of H A Z , definition of z
1 Table 4.6 Extent of H A Z , factor a
Case
Value of a
Joint configuration
i, S 25 mm
P
Q
Substantially straight continuous weld figure (see
figures 4,6(a), (c),
(e)
1.0
total deposit area d 50 nun2
1.5
total deDosit area > 50 nun2
1.5
Substantially straight continuous joint containing
two or more
adjacent welds (see figures4.6 @), (d), (0 and (h))
1.5
2.0
1.5
2.0
~
R
S
~~
Localized irregular joint
(a) member-twnenlber jointsin trusses;
(b) welds connecting transverse stiffenersin beanls and
plate-girdvrs;
(c) welds used to connect lugs and other attachments.
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2.0
45
4.5.1.4 Biaxid bending
--`,,,,,,`,,,``,```,,`,````,``,-`-`,,`,,`,`,,`---
I
Beanw subjectedto simultaneous bending about both
principal axes shouldalso be checked using 4.8.
4.5.2 Uniaxial moment resistance of the section
Figure 4.7 Qpical heat-path
measurement
4.4.3.6 Overlapping HAZs
When two joints are located so that their respective
HAZs (deternined as in 4.4.3) overlap, it may be
assunled that the extent of the HAZ on the outer side
of each jointis unaltered by the proximity.
In calculating whetherW s overlap, the possibility of
elevated tenlperatures shouldbe taken into accountby
using the formula for x from 4.4.3.2.
4.4.3.7 Experimental determination of z
As an alternative to estimating the extent of the HAZ
by calculation, it is pernutted instead to determine it
experimentally. This may be done by conducting a
hardness survey ona representative specimen (see
appendix F).
4.5 Beams
4.5.1 Introduction
4.5.1.1 General
I
4.5.2.1 Section class@cation for moment
resistance
It is f M necessary to classa the section as fully
compact, senucompact, or slender, the classifcation
being based on that of the least favourable of its
component elements.This should be carried out in
accordance with 4.3.3.
In the case of a reinforced outstand elenlent,fornpart or all of the compression flange,the presence of
reinforcenlent inthe form of an outwardly facing lip
should be ignored inclassifying the section.
4.5.2.2 Basic calculation
The factored moment resistanceM m at a given
section, in the absence of shear should generally be
found as follows:
(a) unwelded, fully compact
@) unwelded, semi-conpact
(c) welded, fully compact
(d) welded, senu-compact
(e) unwelded, slender
MB = poS,/ym;
M m = pOz,/ym;
MRS = PoSndYm;
MB = P J n d Y m ;
MRS = Po&hn or
p,,Zn/ym whichever is
the snnller;
MB = P J & m or
PJndYm whichever is
the smaller;
(0 welded,
slender
The following checks should generally
be carried out
on all bean= (including plate girders).
(a) Moment check. At any cross-section the
moment M under factored loading should not exceed where
the factored moment resistanceMB of that section,
Snand Zn are the plastic moduli respectively of
as found from 4.5.2 (or alternatively appendixE).
the net section;
MRS should be suitably reduced to allow for
coincident shear when necessasy (see4.5.4).
Sne and Zn, are the plastic and elastic moduli
respectively for the net effective section;
@) Shear check. At any cross-section the shear
the
force V under factored loading should not exceed
ze
is the elastic
nlodulus of effective
factored shear force resistanceV= (see 4.5.3).
section;
For some cases it is also necessary to make one or
Po
is the linuting stress (see
tables 4.1
both of the following checks:
and 4.2);
(1) web bearing check (see4.5.5);
Ym
is the nlaterial
factor (see table 3.3).
(2) lateral torsional buckling check (see4.5.6).
4.5.1.2 Plate ginlers
Plate girders having slender stiffened webs should
preferably be designed using5.4. It is permissible to
design then1as beams, but with probable lossof
economy.
NOTE. For semi-compact and slender sections it is permissible, if
found favourable, to take a moment resistance based on an
elasto-plastic stress pattern as set out in appendix E, instead of
using the expressions in 4.5.2.2. When this is done, note 5
to 4.6.2.3 is invalid.
4.5.1.3 Bending with axial load
For the design of beam required to carry load, in
addition to moment, reference should bemade to 4.8.
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--`,,,,,,`,,,``,```,,`,````,``,-`-`,,`,,`,`,,`---
4.5.2.3 Assumed section
(a) Each elenlentis classified according to its
particular valueof pw
The terminology used in4.5.2.2 is as follows:
(a) net section includesthe deduction for holes only; (b) For a fully compact sectionMRS is found using
conventional plastic bending theory, allowing for the
(b) net effective section includesthe reduced
value
of po in each element, and again using the net
thickness taken in the vicinity of welds, to allow for
effective sectionin the case of welded members.
HAZ softening, together with deduction for holes;
(c) For other sectionsMRS is found from
(c) effective section includesthe reduced
expression (b), (d) or (e) in 4.5.2.2 as appropriate,
thicknesses takento allow for HAZ softening and
basing p o and 2 on the point in the section giving
local buckling,but with no deduction for holes.
the lowest valuesof MRS.
In itenls (b) and (c) the reduced thicknesses should
4.5.2.5 Semi-compact sections
generally be taken as follows for different elementsin
a section (but see notes 1 to 5).
For these it is permitted, if desired, to take an
improved value ofM m which may be obtained by
(1) Slender elenlentfree of HAZ effects. A
interpolation as follows:
thickness k ~ ist taken for the whole element,
where kL is found as in 4.3.4.
= h& + ßo-ß (Mf - M,)
(2) Non-slender elements subject to HAZ effects. A
ßo -P1
thickness of kt is taken in the softened parts of
where:
the element, where & and the extent of the
Mf and M, are the fully compact
softening are as given in 4.4.2 and 4.4.3.
and senu-compact valuesof
(3) Slender element withHAZ effects. The reduced
MRS
found from4.5.2.2;
thickness is taken as the lesser of kt and k ~ int
the softenedpart, and as kLt in the rest of the
ß
is the valueof ß for the mostcritical
element in the section;
element.
NOTE 1. When a hole is located in a reduced thickness region, the
81 and ßo are the fully and senu-compact
deduction for that hole may be based on the reduced thickness.
linuting values of ß for that Sanle
NOTE 2. In the case of reinforced elements kL should be applied
table element (see table 4.3).
to the area of the reinforcement as well as to the basic plate
thickness.
NOTE 3. In considering a slender flange element that lies nearer
to the neutral axis than does the extreme fibre tensile material, it
is permissible to take a more favourable value for k,,. This is done
by using a modified value of E in figure 4.5 (instead of the normal
value, see 4.3.4.2) as follows:
& = (25O~l/p&)”’
where y1 and are the distances from the elastic neutral axis of
the gross section to the extreme fibres and to the element
considered, respectively. This relaxation only applies if the
element is substantially parallel to the axis of bending.
NOTE 4. For a reinforced element forming part or all of the
compression flange of a slender section, in which the
reinforcement takes the form of an outwardly facing lip, the
presence of the lip should be ignored in determining the moment
resistance.
NOTE 6 . For a welded element in a semicompact or slender
section a more favourable assumed thickness may be taken as
follows:
(a) HAZ softening is ignored in any material less than k$l from
the elastic neutral axis of the gross section, where y1 is the
distance therefrom to the furthest extreme fibres of the section.
@) For HAZ material, at a distance y ( > k g y ,from
)
the neutral
axis, kZ may be replaced by a value kzy determined as follows:
kzy = k, + 1 - u/ul
4.5.2.4 Hubrid sections
The moment capacityof a hybrid section, containing
parent materials of different strengths,may be safely
based on the lowest value of po within the section.
Alternatively, the following more advantageous
procedure may be used.
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4.5.3 Shear force resistance
4.5.3.1 Section classGfication
It is first necessary to classm the section as conlpact
or slender in terms of its resistance to shear force as
follows:
(a) a compact section is unaffected by buckhng;
(b) a slender section shouldbe checked for
buckling.
The sections are classified as follows:
(1) sections containing shear webs orientated in
the plane of loadiig, without tongue-plates:
Ut I4 9 ~compact
Ut > 4 9 ~ slender
where
is the clear
depth of
web
between
flanges (measured on the slope in the
case of inclined webs);
t
is the web
thickness;
E
= (250/p0)“ m (150/”,)”;
po and pv are the linuting stress (in N/nun2)
(see tables4.1 and 4.2);
d
(2) sections as in (l), but with tongue-plates:
see 4.5.3.5;
(3) solid bar compact;
(4) round tube: same classlfication as for axial
compression (see 4.3.2.5 and 4.3.3.4(b)).
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47
~
STD-BSI BS 8118: PART 1-ENGL 1991 D lb211bb9 0791155b 795 D
BS 8118 :Part 1 : 1991
Section 4
I
The factored shear force resistance VRS at a section, in
the absence of moment, may be found using the
following equation:
v, = P d v ~ Y n l
where
p , is the limiting stress (see tables4.1 and 4.2);
A, is the effective shear area;
Ym is the material factor (see table3.3).
The effective shear area is as follows.
(a) For sections containingshear webs without
tongue- plates, that are free from HAZ softening,A,
is determined fromthe following equation:
Av = 0.8 NDt
where:
D is the overall depth of web measured to outer
surface of flanges;
t is the web thickness;
N is the number of webs.
The presence of small holes may be ignored,
provided in total they do not occupy more than 20 %
of the clear web depth, between flanges.
(b) For sectionsas in (a), but with webs affectedby
HAZ softening A, is deternined from the following
equation:
A, = N(0.8Dt - ‘(1- &)&t)
where
d,
is the total depth of HAZ material occurring
Ir,
within the clear depth of the web between
flanges (see 4.4.3);
is the softening factor (see 4.4.2).
For a web welded over its full depth, or
continuously welded longitudinallyat any point in its
depth, V, should be taken as Ir, tinles the unwelded
value.
(c) For a solid bar,A, = 0.8A or O.Me.
(d) For a compact round tube,A, = 0.64 or 0.64,
where
A
4
is the section area ( i the absence of HAZ
softening);
is the effective section area (when HAZ
softening is present), foundby taking an
effective thicknessof Ir, times the true
thickness forHAZ nlaterial.
In the case of sections containing shear webs, the
methods providedfor the calculation of V, for plate
@ers may be used (see 5.4.3.2 and 5.4.3.5).
4.5.3.3 Slender sections
The factored shear force resistance V, in the absence
of moment for sections containing slendershear webs
without tongue-plates, orientatedin the plane of
loading, should be taken as the lesser of the two
values obtained from(a) and (b) as follows:
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(a) Yielding check. The resistance is calculated as
for a conlpact section,using 4.5.3.2 (a) or @) as
appropriate.
(b) Buckling check. VRS, in kN, is obtained from the
following expression:
v, = 340Nt3/dym
where
d is the clear depth of web between flanges (nun);
t is the web thickness (nun);
N is the number of webs;
ym is the material factor (see table 3.3).
4.5.3.4 Inclined shear webs
The expressions covering compact sections
in 4.5.3.2 (a) and (b) renlain valid for inclined webs,
provided D is still measured normalto the neutral axis.
But in checking slender inclined webs (see4.5.3.3) the
expression in (b) should be factored by cos 8, where 8
is the angle between the web and the plane of the
applied l o w .
4.5.3.5 Use of tongue-plates
The shear force resistanceof sections containing shear
webs with tongue-plates may safely be found generally
using the treatment given in 5.4.3.1 to 5.4.3.5, but with
the v-factors takenas follows:
v1
qf
is the elasticcritical shear buckling factor
and is determined as given in 5.4.3.3;
is the tensionfieldfactorand is equal to
zero.
This treatment is valid only if the tongue-plates comply
with 5.4.5.
4.5.4 Combined moment and shear force
4.5.4.1 Moment with low shear
At any section it may be assunled that the factored
moment resistanceMRS is unaffected by a coincident
shear force V (under factored loading) lessthan half
the factored shear force resistance V, found
in 4.5.3.3.
4.5.4.2 Moment with high shear
If V exceeds 0.5 V,, a reduced value forthe factored
monlent resistance MRSO should be found as follows:
(a) For sections with shear webs, connected to
flanges at both longitudinal edges:
MRN =
(I+(1 - U)(O.6 - 1.2 VNRS)]
(b) For other sections:
MRN = MRS(1.6 - 1.2vfl,)
where
k
?
,
M,
ci
is the factoredmomentresistance of the
section in the absence of shear
(see 4.5.2);
is the ratio ofminimunl to nmximunl
shear stress in the web, assuning an
e W c stress distribution.
For sections classifiedas slender for bending,or
affected by HAZ softening, (Y should be based on the
assumed section used in the determination of MRS
(see 4.5.2.3).
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I
I
--`,,,,,,`,,,``,```,,`,````,``,-`-`,,`,,`,`,,`---
4.5.3.2 Compact sections
4.5.5 Web bearing
4.5.6 Lateral torsional buckling
4.5.5.1 General
4.5.6.1 General
A beam, other than those allowed exemption
in 4.5.6.2, should be checked against possible failure
by lateral torsional bucklingin accordance with4.5.6.3
to 4.5.6.8.
4.5.5.2 Unstwened web
When the web itself is required to carry the localized
force, without the provisionof a bearing stiffener,as
for example undera rolling load, both the following
should be met:
(a) Pwl SPalY, or k&a/Yrn;
0P W ~ ~ P J Y ~ ;
where
Pwl and Pw2 are stresses arising at its extreme
edge and mid-point respectively,
assuming a 45 O dispersion angle
either sideof a localized force;
is the linuting stres (see tables 4.1
Pa
and 4.2);
is the buckliig stress for the web
PS
treated as a thin colunm between
the flanges;
is the softening factor forHAZ
material (see Appendix F, table F1
and 4.4.2);
is the material factor (see table3.3).
Ym
In (a) the second expression should be used whenthe
web is welded to the flange andHAZ softening occurs.
Otherwise the first expression is valid.
p, should be determined as given in 4.7.4.1 selecting
the curve in figure 4.10(a) that intercepts the stress-&
at a value po (see tables4.1 and 4.2). The slenderness
parameter A to be used to select the curve should
allow for possible relative lateral movement
of the
flanges as the web buckles. Assuminga web fixity
intemediate between full fUrty and sinlple support,the
value of A is given by 2 . W t .
4.5.5.3 Web with tongue-plate
When a tongueplate is provided, 4.5.5.2(a) should be
satisfied both at the top edge of the tongueplate, and
at the upper edgeof the thin web.
4.5.5.4 Stwened web
A bearing stiffener,if fitted, should beof compact
section. It may be conservatively designed on the
assumption that it resists the entire bearing force,
unaided by the web, the stiffener being checkedas a
strut (see 4.7) for out-of-plane column bucklig and
if
local squashing, with bending effects allowed for
necessary (see 4.8). Alternatively, a more econonucal
stiffener may be designed by referringto the plate
grder stiffener clause (see5.4.5).
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4.5.6.2 Exemptions
The possibility of premature failureby lateral torsional
buckling may be ignored in any of the following cases:
(a) bending aboutthe minor axis;
(b) beam supported against lateral movement
throughout its length;
(c) lateral supportsto compression flange provided
at spacing not greaterthan 4Ocry,
where
Y
r
E
Po
I
is the minor axis radius of
gyration
of
the section:
= (250/p0)N;
is the linuting stress ( i N/nuu2) of
compression flange material(see
tables 4.1 and 4.2).
4.5.6.3 Basic condition
The beam should be checked for possible lateral
torsional bucklig in every unsupported bay between
points of lateral support.In each of these the following
condition shouldbe satisfied
M 5 MRx
where
--`,,,,,,`,,,``,```,,`,````,``,-`-`,,`,,`,`,,`---
This c l a w concerns the design of webs subjected to
localized forces causedby concentrated loadsor
reactions appliedto a beam.
M
is the moment arising under factored
MRX
is the factored momentof resistance to
lateral torsionalbucklig, and is equal to
PsS/y,;
S
is the plastic section modulus of gross
section, without reduction forHAZ
softening, local bucklingor holes;
is the material factor (see table3.3);
is the buckling stress (see 4.5.6.5).
loa- in
Ym
PS
the length considered;
4.5.6.4 Allowance for moment variation
The value ofM in 4.5.6.3 may be safely takenas the
maximum value arising inthe bay considered.
Alternatively, it ispernutted totake M as the equivalent
unifom.1 moment M. For the case of simple moment_
gradient in the length considered (linear variation)M
may be taken as follows:
(a) for 1.0 > MdMl 2 -0.5 2 = O.Wl + 0.m~;
@) for M2/M1 < -0.5
2 = 0.Ml;
where M1 and M2 are respectively the n~aximun.1 and
minimum moments arising (see figure4.8). For other
cases of moment variation refer to appendix H.
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~
~~
~~
~~
STD-BSI BS 8118: PART L-ENGL 1991 W Lb2Vbb9 079V558 5b8 D
BS 8118 :Part 1 : 1991
Section 4
Figure 4.8 Lateral torsional buckling,
equivalent uniform momentEi
4.5.6.5 Buckling stress
--`,,,,,,`,,,``,```,,`,````,``,-`-`,,`,,`,`,,`---
The lateral torsional bucklingstressp, should be read
from figure4.9 using the curve which interceptsthe
stress axis at a stress pl found as follows:
(a) For unwelded fully compact section
P l =Po;
@) For other sections, including hybrid
PI = Y n f l R d S
where
po
MRS
S
ym
is the limiting stress (seetables 4.1 and 4.2);
is the factoredmonlent resismce of the
section;
is the plasticsectionmodulus of gross
section;
is the materialfactor (seetable 3.3).
For the following cases, however, appendixH should
be used to find the effective length of the bean1 (1):
(1) cantilever b e a m s ;
(2) bean- subject to destabilizing loads,
i.e. loading between points of lateral support, that
effectively acts at a point in the section on the
compression side ofthe neutral axis;
(3) beams subjectto normal loads whenthe
compression flangeis laterally unrestrained, both
flanges are free to rotate in plan, and torsional
restraint is provided only by the bearing of the
bottom flange on the supports.
For all other types of support 1 may be safely taken
as the distance between pointsof lateral support.
Alternatively a more favourable value for certain
restraint conditions may be found using H.l.
@) General expression:L = 1r(Es/2M,~)”
where
E
is the modulus of elasticity;
S
is the plastic section modulus of gross section;
Mc, is the elastic critical uniforn~moment
(see H.2).
(c) Channel and I-section members coveredby
table 4.7 : parameter A may be taken as follows, but
should not exceedthe value given by (a):
XI,,
where:
M m should be found generally in accordance
with 4.5.2, allowing for local buckling and HAZ
softening, but with no deductionfor holes.
D
is the overall
section
deptly
tZ
NOTE. For beams of high slenderness ( A > 130) it will be
necessary to refer to the appropriate nondimensional curve in
appendix K to find P,.
is the flange
thickness;
X and Y
are the coeffkients to be found
using table 4.7 or they may be
conservatively takenas X = 1.0,
Y = 0.05.
4.5.6.6 Slenderness parameter
The lateral torsional buckling slenderness parameter
I,
needed for figure 4.9, may be obtained using any of the
following expressions(a) to (c).
(a) Conservative value:A = I , = Ur,
where
is the effective length for lateral torsional
buckling;
r, is the minor axis I‘ddius of w o n for gross
section.
1
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NOTE. When the flange reinforcement to an I-beam or channel
member is not of the precise form shown in table 4.7 (simple lips),
it is still permissible to obtain I using the expression in (c) above.
In so doing, X and Y should be taken as for an equivalent simple
lip having the same internal depth C, while A, is calculated for the
section with its actual reinforcement.
4.5.6.7 Wective lateral restraints
Bracing systems providing lateral restmint shouldbe
designed on the assumption that the total lateralforce
exerted by a compression flange, under factored
loading, shared between the points of restraint in any
one span,is 3 % of the compression inthat flange.
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~
~~~
~
~~
STD.BSI BS 8118: PART L-ENGL L99L D 1b24bb9 0794559 4 T 4 D
BS 8118 : Part 1 : 1991
Section 4
300
200
N
E
E
z
P"
100
O
50
100
A
NOTE. To find ps at A > 130 refer to figure K1.
Figure 4.9 Lateral torsional buckling of beams, buckling stress P,
Where a series of two or more parallel bean- require
lateral restraint, itis not adequate merely to tie the
compression flanges togetherso that they become
mutually dependent. Adequate restraintwill be
provided only by anchoringthe ties to an independent
robust support, or by providing a triangulated bracing
system. If the number of parallel beams exceed three,
it is sufficient for the restmint system to be designed
to resist the sum of the lateral forces derived fromthe
three largest compressive forces only.
However, when HAZ softening occurs at the ends of
the bay only,its presence may be ignored in
considering lateral torsionalbucklig, provided that
such softening does not extenda distance along the
member, at each end of the bay, greater than the width
of the section.
4.5.6.8 Beams containing localized welds
The value of MRS in 4.5.6.5 for a beam, subjectto HAZ
softening, should generally referto the most
unfavourable section in the bay considered, even when
such softening occurs only locally alongthe length.
"he tension P arising under factoredloadiig of axially
loaded tension membem (ties) should not exceed the
factored tension resistancePR^ of the section
4.6 Tension members
4.6.1 General
(see 4.6.2).
For tension members having eccentric end connections
it is generally necessary to refer to 4.8 to allow for
interaction between axial load andthe moments
introduced. However, in certain cases (see 4.6.3) it is
permissible to use a simplified procedure.
--`,,,,,,`,,,``,```,,`,````,``,-`-`,,`,,`,`,,`---
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51
I a b l e 4.7 Lateral torsional buckling of beams, coefficients X and Y
I
1Coefficients
I Beam section
t2
X = 0.90 - 0.03 D
- + 0.04 -
B
Y = 0.05 - 0.010
tl
{%
--- 1
)}%
"1
0.03 - 0.07B
1, = t2
-
C
0.3 B
C
Y = 0.05 - 0.06 -
o
D
rD
t2
X = 0.95 - 0.03-B + 0.06 11
Y = 0.07 - 0.014
{ %$ 1)}
-
- 0.06-
B
?
C
B
- 0.3 -
C
Y = 0.07 - 0.10 D
I
NOTE 1. The expmions for X and Yare valid.for 1.5 5 D l 3 5 4.5,
5 0.5
NOTE 2. For the specific shape of lipped channel standardized in BS 1161 : X = 0.95, Y = 0.071.
--`,,,,,,`,,,``,```,,`,````,``,-`-`,,`,,`,`,,`--~~
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4.6.2 Tension resistance
4.6.2.4 Staggered holes
Where staggered holes occur, alternative values forA,
or An, should be calculatedas in (a) and (b) as
The factored tension resistancePS should be takenas
follows,
and the lower value then usedin 4.6.2.3.
the lesser of two values Corresponding respectively to:
(a)
An or A,, is taken at the least favourable
(a) general yielding alongthe member (see 4.6.2.2);
cross-section.
(b) local failure at a critical section (see4.6.2.3).
@) A dlagonal or zig-% section is considered, with
4.6.2.2 General yielding
An or A,, found as follows.
The value PB is based on the generalcrosssection of
A, = A - H or A,, =A, - H
the member along its length, ignoringthe effect of end
where
connections, occasional holesor localized HAZ regions
H = XAh as follows.
(a) For a member free fromHAZ softening, or only
x and y
are the longitudinalandtransverse
thus affected at localized positions along its length:
pitch of holes respectively;
PRS = P&Ym
t
is the plate
thickness
or effective
(b) For a member in whichthe section contains
plate
thickness;
HAZ material generally along the length, as with
is the sun1 of hole areas on the
longitudinal welds.
diagonal or zig-zag section
&S = P 4 J Y r n
considered.
where
P , is the linuting stress (see tables4.1 and 4.2);
4.6.2.5 Hubrid sections
A is the goss section area;
The tension capacity of a hybrid section, containing
material of different strengths should be foundby
A, is the effective section area;
adding togetherthe resistances of the various parts,
ym is the nmterial factor (see table3.3).
obtained in 4.6.2.3.
A, is found by taking a reduced area equal to k,
4.6.3 Eccentrically connected ties
tinles the true area for a softened zone,k, being
taken as in 4.4.2, and the extent of the zone as
Eccentrically connected ties include the following:
in 4.4.3.
(a) angles connected through one leg;
4.6.2.3 Local failure
(b) web-connected channels;
The value of PRS is based on the most critical section
(c) flange connected tees.
as follows:
Singlebay tension membersof these three types may
(a) For a section free fromHAZ softening:
be designed as axially loaded and the variation in
stress in the outstanding leg or legs ignored, provided
PRS= P & n h
that, in deternmng the area An or A,, needed for the
(b) For a section containing HAZ material:
local check (see4.6.2.3), part of the outstanding leg
PRS= PdndYn,
area is deducted from the gross area, as well as any
deduction for holesor HAZ effects. The amount of
where
outstanding leg to be deducted is as follows:
pa is the linuting stress (see tables 4.1 and 4.2);
(1) single
componentconnectedoneside
0.U"
An is the net section area, with deduction for
of a gusset
holes;
(2) double
conlponent
synuuetrically
0.2.4,
An, is the net effective section area;
connected either sideof gusset
ym is the nlaterial factor (see table 3.3).
where A, is the effective area of the outstanding leg or
legs lying clear of the connected element,but ignoring
The value of An, is found in the sanleway as A,
any fillet.
(see 4.6.2.2), but with suitable deduction for holesif
necessary. The deductionfor holes in HAZ regions may When such members are continuous over several bays,
it is only necessary to apply the above treatment at the
be based on the reduced thickness&t.
outer ends of the end bays. Elsewhere the local
tension resistance may be found as in 4.6.2.3, without
any outstanding leg deduction.
The general yielding check shouldbe performed as
given in 4.6.2.2.
--`,,,,,,`,,,``,```,,`,````,``,-`-`,,`,,`,`,,`---
4.6.2.1 General
X$%&/
CA
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53
~~~
~
~~
~~
~
~
~
STD-BSI BS 8118: PART 1-ENGL L991 D l b 2 4 b b 9 07945b2 T99 m
BS 8118 :Part 1 : 1991
Section 4
4.7 Compression members
4.7.4 Column buckling
4.7.1 General
4.7.4.1 Buckling stress
The value of ps for colunm buckling shouldbe read
4.7.1.1 Three checks are generally needed for axially
--`,,,,,,`,,,``,```,,`,````,``,-`-`,,`,,`,`,,`---
loaded conlpression members(struts) as follows:
(a) column, i.e. f l e d , buckling check (see 4.7.3
and 4.7.4) (refers to overall buckling of the member
as a whole);
(b) torsional buckling check (see4.7.3 and 4.7.5)
(refers to overall buckling of the member as a
whole);
(c) local squashmg check(see 4.7.7) (relates to the
weakest cross-section downits length).
Check (a) should always be made. Check(b) is
generally required, but nlay be waived in some cases.
Check (c) is only needed for struts having low
slenderness ratiosthat are sigruficantly weakened
locally by holes or welding.
4.7.1.2 To take account of interaction between axial
load and bending itis generally necessary to refer
to 4.8. However, for struts having eccentric
endconnections it is in certain cases permissibleto
use a simplified procedure (see4.7.9) to allow for the
moments introduced.
4.7.2 Section classification for axial
compression
Before nuking any of the three checks given in 4.7.1 it
is first necessary to class@ the cross-section as
compact or slender. The classication is based on that
of the least favourableof its component elements,in
accordance with4.3.3.
4.7.3 Resistance to overall buckling
With both checks (a) and @) the axial thrust P under
factored loading should not exceedthe factored axial
resistance PR based on overall buckling, given by the
following:
h =PSAlYm
where
A
PS
ym
is the gross area,withoutreduction for HAZ
softening, local bucklingor holes;
is the buckling stress inflexural or torsional
buckling;
is the material factor (see table 3.3).
In finding p, for column buckling, failure about both
principal axes should be considered and the lower
value taken.
NOTE. For a strut of high slenderness (1 z 130) it will be
necessary to refer to appendix K to find P,.
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from the appropriate curvein figure 4.10, selected in
accordance with4.7.6.
4.7.4.2 Slenderness parameter
The colunm buckling slenderness parameterA needed
for figure 4.10 is defined as follows:
A = Ur
where
I is the effective length;
r is the d
u
s of gyration;
both appropriateto the direction of buckling
considered.
The effective length1 should be taken as KL, where L
is the length between pointsof lateral support; or for a
cantilever strut, its length. The valueof K,the effective
length factorfor struts should be assessed froma
knowledge of the end conditions; table4.8 gives
guidance.
The value ofr should be based on the gross section for
all members.
NOTE. When the cross-section is wholly or substantially affected
by HAZ softening at a directionally restrained end ofa member,
such restraint should be ignored in arriving at a suitable value
for K. Thus for case 1 in table 4.8 K should be taken as 1.0 if the
section is fully softened at each end.
mble 4.8 Effective length factorK for struts
End conditions
K
1 Effectively held in position and
0.7
restrained in direction at both ends
2 Effectively held in position at both
0.85
ends and restrained in direction at one
end
3 Effectively held in positionat both
1.0
ends, but not restrained in direction
4 Effectively held in positionat one
1.25
end, and restrained in directionat both
ends
5 Effectively held in position and
1.5
restrained in direction at one end, and
partially restrained in direction but not
held in position at the other end
6 Effectively held in position and
2.0
restrained in directionat one end, but
not held in positionor restrained at the
other end
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i
STDaBSI BS 8118: PART L-ENGL 1991 W LbZqbb9 079q5b3 9 2 5 m
Section 4
BS 8118 :Part 1 : 1991
300
--`,,,,,,`,,,``,```,,`,````,``,-`-`,,`,,`,`,,`---
I
200
N
E
E
z
am
100
O
50
100
A
(a>
NOTE. To find p , at d > 130 refer to figure K.l.
Figure 4.10 Column buckling stress P, for struts
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55
300
A
@>
NOTE. To find p , at 1 > 130 refer to figure K.l.
Figure 4.10 Column buckling stress P, for struts (continued)
--`,,,,,,`,,,``,```,,`,````,``,-`-`,,`,,`,`,,`---
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300
200
N
E
E
\
æ
Q.*
100
--`,,,,,,`,,,``,```,,`,````,``,-`-`,,`,,`,`,,`---
Figure 4.10 Column buckling stress P, for struts (conclwled)
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4.7.5 Torsional buckling
4.7.5.1 Exemptions
The possibility of torsional bucklingmay be ignored
for the following:
(a) closed hollow sections;
(b) doubly symmetrical I-sections;
(c) sections composed entirelyof radiamg
outstands, e.g. angles,tees, cruciform, that are
classified as compact in accordance with4.3.3.
4.7.5.2 Slenderness parameter
The torsional buckling slenderness parameter1 may be
obtained using either (a) or (b) below, or else by
referring to appendix J. It should alwaysbe based on
the gross area of the section as follows.
(a) General formula I = n(EAPCr)”
where
4.7.6.2 Determination of p l
The value ofpl should g e n e d y be found as follows
(but refer to 4.7.6.4 for sections composed of radiating
outstands):
(a) compactsection,with no HAZ
effects
(b) other sections,
generally
where
A
A,
p,
pl = P ,
Pl = (AeWPo
is the gross area of section;
is the area of effective section
(see 4.7.6.3);
is the limiting stress for the
material (see tables 4.1
and 4.2).
is the gross section area, withoutreduction
for local buckling, HAZ softening or holes;
E
is the modulus of elasticity;
PCr is the elastic critical load for torsional
buckling, allowing for interaction with
column buckling when necessary.
Curve selection on this basis is valid, providedthe
member meetsthe tolerances of straightness and twist
laid down for extruded material (seeBS 8118 : Part 2).
When there is a possibility that a fabricated strut will
fail to meet these tolerances,p l should be takenas
S times the value given by4.7.6.2 (a) or (b) above,
where
S = 0.6 + O.Eiexp(- 0.021) (but not exceeding 1.0).
(b) Sections as given in table 4.9
4.7.6.3 w e c t i v e section
A
Effective section appliesto strut sections that are as
follows:
where
(a) classified as slender;
k
is readfromfigure 4.11.
(b) affected by HAZ softenkg
At
is found as fOllOWS:
(c) both (a) and (b).
(1) for angles, tees, cruciforms It = 1,
The effective sectionmay be obtained by talung
reduced thicknesses, withno deduction for holes as
(2) for channels, t o p ”
follows, andmay be based on the least favourable
cross section (but see 4.7.6.5 for welded members).
1 10
- [ 1 + (YA,W,”))
(1) Slender section,free from HAZ softening. The
thickness
of any element is taken as kL tinles its
W l e 4.9 contains expressions for1, and y and
t, where kL is found as in 4.3.4. In
true
thickness
also for S and X (needed for figure 4.11).
the case of reinforced elementskL should be
In (2) the quantity Ax should be taken as the
applied to the area of the reinforcement as well as
effective slendernessfor column buckling about
to the basic thicknessof the plate.
axis xx (asdefined in table 4.9).
(2) Compact section, withHAZ softening. The
4.7.5.3 Buckling stress
thickness of any softened zone shouldbe reduced
so as to give it an assumedarea equal to k, times
The value of p , for torsional buckling should be read
its true area. The extent of such a zone should be
from the appropriate curvein figure 4.12, selected in
found from4.4.3, and the value of & from 4.4.2.
accordance with4.7.6.
(3) Slender section, withHAZ softening. For
4.7.6 Strut curve selection
slender elementsfree from HAZ effects the
4.7.6.1 Basic procedure
reduced thicknessis found as in (1); and for HAZ
regions not located in slender elementsit is taken
The overall bucklingStressp, should be read from the
as in (2). If an element is both slender and
appropriate strut curve diagram in figure 4.10 (for
affected byHAZ softening, the reduced thickness
column buckling)or fgwe 4.12 (for torsional
is taken as the lesser of kLt and &t in the softened
buckling). Choice of diagm should be in accordance
part and as k ~ elsewhere
t
in it.
with table 4.10. In any given diagram the appropriate
c w e is that meeting the stress axis at a stress p l , to
Sections composedof radiating outstands are treated
be determined as in 4.7.6.2.
specially (see4.7.6.4).
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--`,,,,,,`,,,``,```,,`,````,``,-`-`,,`,,`,`,,`---
1 = k1t
Table 4.9 Torsional buckling parameters for struts
1
i = I&,
Y = 0.6
lo = 11 - ( ~ - 1 ) ( 2 ( ~ - 1-)1.5~)
~
2
5 = I&,
Y = 0.6
--`,,,,,,`,,,``,```,,`,````,``,-`-`,,`,,`,`,,`---
l o = 66
(:see note1
3
S = Iu/Io
Equal
X = 0.61
U
4
p 5 5
A, = (D/t)(4.2 + 0.8
0.5 IBAI I1.0
S = ~4 = (1
- O . G P ~ .(Oh)"
~
+ 6(1 - BAI)2)(Iu/10)
X = X , = 0.6 - 0.4(1 -
5
p55
I , = A4 + 1.5p(url) - 2 ( ~ - 1 ) ~
0.5 IBA9 I1.0
S = S4
1 IW I2.5
x = x4
I , = 57
[see note 1)
6
S = 1.4(Iu110)
x = 0.60
p I3.5
7
I, = 5.Wt -
(Bk)%
x =1
2
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59
BS 8118 :Part 1 : 1991
Section 4
--`,,,,,,`,,,``,```,,`,````,``,-`-`,,`,,`,`,,`---
a b l e 4.9 Torsional buckling parameters for struts (continued)
8
Y
9
P55
,Y
0.5 5 D B 5 2.0
1 5 W 5 2.5
10
(see note 1)
Ao = 70
,Y
S = Ay/Ao
x = 0.83
‘Y
11
[see note 1)
1, = GO
,Y
5 = AylAo
Y = 0.76
Y
12
[see note 1)
I , = 63
IY
i = “/Ao
Y = 0.89
13
1.5 S D B 5 2.0
1, = (D/t( 1.4 + 1.5(BD) +
+ l.l(D/!) -
3 I3.5
(D/t)”
: = )Ly/Ao
= 1.3- 0.8DB + 0.2(DB)2
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~~
S T D - B S IB S
Section 4
'
B 1 L B : PART L-ENGL 1991, m Lb24bbS D7795b7 3 4 3
BS 8118 :Part 1 : 1991
I Table 4.9 Torsional buckling parameters for struts (continued)
Lo = 65
see note 1)
T
~
= Iy/Io
I:= 0.78
lO=(B/t2)(7+ 1.5(D/B)(t2/tl))
; = &/It
Y = 0.38 DI3 - 0.04
Y = 0.14 - O. W / B - 0.02tzItl
1 5 D/B 5 3
I , = (B/t)(7 + 1.5D/B + 5C/B)
C/B 5 0.4
5 = &/It
Unifoml thickness
Y = 0.38D/B - 0.04(D/B)2 - 0.25C/B
Y = 0.12 - O.O2D/B + (O.G(C/B)'/(D/B - 0.5))
1 zs D/B 5 3
Lo = (B/t)(7 + 1.5D/B + 5CB)
C/B 5 0.4
S = Ax/&
Unifoml thiclaess
X = 0.38D/B - 0.04(D/B)"
Y = 0.12 - 0.20B - (O.O5(C//BY(DB- 0.5)}
[see note 1)
I , = 126
S = &/At
X = 0.59
Y = 0.104
--`,,,,,,`,,,``,```,,`,````,``,-`-`,,`,,`,`,,`---
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61
lhble 4.9 Torsional buckling parameters for struts (concluded)
NOTE 1. Shapes of reinforced section complying with BS llGl
NOTE 2. The sections are generally of uniform thickness t , except cases 14 and 15.
NOTE 3. i,,,,L,, L, is the slenderness parameter (//Y) for flexural buckling about the u, x or y axis.
NOTE 4. p is a factor depending on the amount of fillet material at the root of the section as follows:
Radiused fillets p = R4
45’ fillets
p = 1.6F/’t
r
NOTE 5. The values given for L,, X and Yare only valid within the linlits shown. In the case of back-to-back angles (cases 8 to 12) the
expressions cease to apply if the gap between the angles exceeds 2t.
’hble 4.10 Choice of strut curve diagram
Unwelded strut
Q p e of buckling
Welded strut
Column buckling:
synmetric or nddly asymmetric section Figure 4.10@) Figure 4.10(a)
section
asymmetric
severely
Figure 4.10(b) Figure 4.10(c)
Torsional buckling:
Figure 4.12(a)
generally
section
composed of radiating
outstands (see 4.7.6.4)
Figure
4.12@)
I
I
NOTE 1. A strut should generally be regarded as welded, for the purpose of this table, if it contains welds on a length greater than the
‘argest dimension of the section. This is regardless of whether or not there are HAZ effects.
VOTE 2. A mildly asymmetric section is one for which y1/y2 I1.5 where .y1 and g2 are the distances from the buckling axis to the
Further and nearer extreme fibres, respectively. Otherwise, the section should be treated as severely asymmetric.
4.7.6.4 Sections composed of radiating outstands
For sections suchas angles, tees and cruciforms,
composed entirely of radiating outstands, local and
torsional bucklingare closely related. For suchstruts
the procedure should beas follows:
(a) Section containing only unreinforced outstands.
(1) In considering torsional buckling figure
4.12 (b)
may be used for findingps, instead of
figure 4.12 (a). (The relevant diagram for column
buckling is unaltered).
(2) In determining p l , needed for selecting the
appropriate curve in figures 4.10 and 4.12
(see 4.7.6.2), the area A, should be based onan
effective sectionin which the nomml reduction is
made for zones affected byHAZ softening, but
with no reduction for local buckhng,
i.e. take ICL = 1. Thus for such a section free of
HAZ effects: p l = po.
62
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@) Section containing outstands with tip
reinforcement. If the reinforced outstands are such
that mode 1 would be critical in terms of local
buckling (see4.3.2.3), the same procedureis
followed as in (a). But if mode 2 is critical,
figure 4.12 (a) should be employedand the effective
section foundas in 4.7.6.3.
4.7.6.5 Struts containing localized welds
Strut curve selectionfor a member affected byHAZ
softening should generally be based on
a value of p l
obtained for the most unfavourable section, even when
such softening occurs only locally along the length.
This includes HAZ effects due to the welding on of
tempomy attachments.
However, when such HAZ softening has a certain
specified location along the length,its presence may be
ignored in considering overall buckling, providedthe
softening does not extend longitudinallya distance
greater than the least overall widthof the member, The
location of the HAZ softening, forthis relaxation to be
allowed, is the position of zero or near-zero curvature
in the buckled form of the strut.
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--`,,,,,,`,,,``,```,,`,````,``,-`-`,,`,,`,`,,`---
“c
--`,,,,,,`,,,``,```,,`,````,``,-`-`,,`,,`,`,,`---
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300
200
N
E
E
z
P"
100
--`,,,,,,`,,,``,```,,`,````,``,-`-`,,`,,`,`,,`---
(al
NOTE. To find p , at L > 130 refer to figure K.l
Figure 4.12 Torsional buckling stress P, for struts
Thus for a strut held in position at its ends (see
table 4.8, case 3) it may be assumed that the overall
buckling resistanceis unaffected by the presence of
localized softened zones,if these are located at the
ends. (In such a case it will be importantto nmke the
local squashing check).
4.7.7 Local squashing
The axial thrustP under factored loading should not
exceed the factored resistance Pm of the most
unfavourable section alongthe length of a strut,
detemked as follows:
(a) compact section, free from HAZ . pRs =pdn/ym;
effects
@) other sections, generally
PRS= PaPnJYnl;
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64
where
pa is the liiting stress (see tables 4.1 and 4.2);
An is the net section area, with deduction for
unfilled holes;
An, is the net effective section area;
ym is the nuterial factor (see table 3.3).
The area A,, should be taken as A, less deductionfor
unfilled holes, whereA, is the effective area used in
the considemtion of overall buckling (colunm or
torsional), see 4.7.6.3 and 4.7.6.4. For holes locatedin
reduced thickness regions the deduction nlay
be based
on the reduced thickness, insteadof the full thickness.
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~
STD-BSI BS 6118: PART 1-ENGL 3773 W 1 b 2 4 b b 7 0774573 674 W
Section 4
BS 8118 :Part 1 : 1991
300
200
N
-E
E
z
P”
100
@>
Figure 4.12 Torsional bucklingstress P, for struts (concluded)
I
of the connected element, andif no deliberate bending
4.7.8 Hybrid sections
is applied
In struts containing parent materialsof different
strengths each element should be classified according (a) single angle connected through one legonly;
to its particular value of P,.
@) back-teback angles connected oneside of a
The resistance PR to overall colunm or torsional
gusset;
buckling nlay be found assunkg a uniform value of P,,
(c) single channel connected by its web only;
equal to the weighted averageof the P, values for the
single tee connected by its table only.
various parts (weighted accordingto the gross areas
For
these itis pernussible, in makingthe check for
thereof).
colunm
buckling out of the plane of the attached
The resistance PRSto local squashingmay be found by
element
or elements, to ignore the eccentricity of
sunming the resistance of the various parts.
loading, and instead take a reduced axial conlpression
4.7.9 Certain cases of eccentrically connected
resistance equalto 40 % of the value that would be
struts
obtained for centroidal loading usingthe radius of
gyration about the axis parallel to the gusset. The
4.7.9.1 Single-bay struts
torsional buckling resistance is assunled unaffected by
The following typesof eccentrically connectedstrut
the eccentricity.
may be treated using a simple method, insteadof the
interaction procedure given in 4.8, provided the
attachment is sufficient to prevent rotation in the plane
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G5
4.7.9.2 Struts of two components back-to-back
a
Such struts of double angle, channelor tee
construction, connected either sideof end-gussets, may
be designed as nlonolithic centroidally loaded
members providedthat the following occur
(a) the two components are securely connected
together at their ends; and
(b) they are connected alsoat the third points, using
spacers equal to the gusset thickness.
4.7.10 Battened struts
which should bethe subject of special study. However,
if a battened strut complies with4.7.10.2, it is
pernksible to regard it as monolithic and obtain its
resistance in the nornml way.
4.7.10.2 To be treated as a monolithic member a
battened strut should satisfy the following.
(a) It should be axially loaded.
(b) It should comprise two main components joined
by equally spaced battens, the cross-section being
symmetrical about an axis n o m d to the battens.
(c) Battens should generallybe in pairs. However, if
the main components are toe-to-toe tees or angles,
single battens are allowed.
(d) A2 5 0.8A1
where
are the Slendernessparametersfor
column buckling of the complete
member about axes parallel to and
normal to the battens, respectively.
(e) A3 I0.7 A2
where
In designing the battens it is important to consider the
possible weakening effects of local buckling and HAZ
softening (if welded).
4.8 Bending with axial force and biaxial
bending
4.7.10.1 The general rules for struts given in 4.7.3
to 4.7.7 do not generally applyto battened members,
AI and A2
N
is thespacing of main components
measured to the centroids of the
connections to each batten;
is the number of battens at each position
(1 or 2).
4.8.1 General
4.8.1.1 This clause gives interaction formulae for
checking members subjectedto the following cases of
combined action effect:
(a) caseA, major axis bending with axial force
o;
(My +o;
(Mx +
(b) case B, minor axis bending with axial force
(c) caseC , biaxial bending (Mx+ My);
(d) caseD, biaxial bending withaxial force
(Mx +My + P )
where
P
Mxand My
is the axial
force
a x i s i i under
factored loadmg;
are the miaxial moments about nwjor
and minor axes respectively arising
under factored loading.
4.8.1.2 %o checks are in general needed, as follows:
(a) section check (see4.8.3);
o>)overall buckling check (see 4.8.4).
The section checkis always needed. The overall
buckling check may be waived for the following
buckling of one main component
circumstances:
between battens, based on column
(1) in case A, when P is tensile and also the
or torsional buckling whicheveris
member is exempt from lateral torsional buckling
the more critical.
(see 4.5.6.2);
(2) in case B, when P is tensile.
(f) The batten system should be designedto resist a
total shear force V in the plane of the battens, taken In malong the section checkthe values taken for Pm,
as 2.5 % of the axial force inthe whole member
Mmx and Mmy should take due accountof the
under factored l o a m .
presence of holes and of HAZ softening
(g) The connection of each batten to each main
where
component should be designed to transmit the
following sinlultaneous actions under factored
pR!3
is the factored axial resistance of
loading:
the cross-section, see 4.6.2 (tension)
or 4.7.7 (compression);
(1) longitudinal shear of VdNa.
M s x and Mmy me the factored uniaxial moment
(2) moment of VdLW acting in the plane of the
resistances of the cross-section
batten;
(see 4.5.2), @usted to allow for
where:
coincident shear if necessary
(see 4.5.4), about major and minor
d
is the longitudinalspacingbetweencentres
axes respectively.
of battens;
A3
is the slenderness
parameter
for
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~
STD=BSI BS 8 f i L B : PART 1-ENGL 199L m l b Z V b b 9 079V575 b V 7 m
Section 4
BS 8118 :Part 1 : 1991
MR, is the factored moment resistance to lateral
torsional buckling (see4.5.6.3).
4.8.2 Section classification and local buckling
under combined actions
4.8.2.1 Section classification
P
M,
-+-+-"51.0
M
PRS MRSx MRSy
When the axial force,P, is tensile, the factored axial
resistance, PRS,should be found from clause4.6.2.3
(local
4.8.3.2 Other cases
For casesA, B or C (see 4.8.1.1) the fornwla given
in 4.8.3.1 should be used,with the appropriate
numerator quantity put equalto zero.
4.8.4 Overall buckling check
4.8.4.1 General
For members subjectto axial tension combinedwith
bending the presence of the axial force shouldbe
ignored in checking against overall buckling. For
members subject to axial compression with bending,or
to biaxial bending, the appropriate interaction fornwlae
(see 4.8.4.2 to 4.8.4.5) should be satisfied on any
unsupported length liableto buckle.
All quantities in the interaction fornwlae shouldbe
taken as positive.
4.8.4.2 Case A (mqjor axis bending with axial
compression)
For caseA both conditions (a) and (b) as follows
should be satisfied
(a) prevention of nlajor axis buckling:
The section should be givena single classification
(fully compact, senu-compactor slender) generally in
accordance with4.3.3.2 and 4.3.3.4 (a).
h so doing, the value of j? for any given element
should be based on a value of g (see figure4.2)
Corresponding to the stress pattern produced in that
element when all the actions M,, My)are applied
sinlultaneously. The quantitiesyo and yc, needed for
figure 4.2, should generally be found using the elastic
neutral axis of the gross section underthe combined
actions, although in checking whether a section is fully
compact it is permitted to use the plastic one. Note
that it is possible for the elastic neutral axis to lie
@) prevention of nunor axis buckling:
outside the section, in which case go and yc will be of
P
the same sign. The method given in4.3.3.5 for
+ -51.0
MRx
determining a more favourable classlfication for underwhere
stressed flange elements, is still valid provided yo and
gc again relate to the stress pattern under the
MX
is the equivalent
unifoml
moment,
combined actions.
about the major axis obtained as
Any section found to be fully compact or
in 4.5.6.4
senucompact under the above procedureis counted as
P h and PR^
are the factored axial resistances to
compact when obtainingthe axial resistance,no
overall column buckling, about
reduction being made for local buckling.
major and nxinor axes respectively,
4.8.2.2 Eflectiue section
see 4.7.3 and 4.7.4.
For a member classed as slender (see4.8.2.1) each
individual resistance should be found using an effective If the axial forceP causes torsional buckling(see
section that relates specificallyto the action concerned 4.7.5), the factored axial resistances to torsional
buckling should be used in (a) and @).
(c M, or My), this being generally different for the
different actions. Thus when obtainingaxial resistance, 4.8.4.3 Case B (minor axis bending with axial
the factor k~ (see figure4.5) for each elementis based compression)
on a P value for that element correspondingto uniform For case B following single condition should be
stress (g = 1). While for fmdmg moment resistance, a P satisfied (preventionof minor axis buckling):
value is taken that relates to the stress pattern in the
element when the section is under pure bending.
(e
6
a,
4.8.3 Section check
4.8.3.1 General formula (case D)
The cross-section is adequate if the followingis
where
satisfied at every position alongthe length, all six
quantities being takenas positive:
Xiy
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is the equivalent ~ n i f o r nmoment
~
about the
minor axis obtained as in 4.5.6.4
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I
--`,,,,,,`,,,``,```,,`,````,``,-`-`,,`,,`,`,,`---
In making the overall buckling check the values of
MRS, and M R should
~ ~ generally refer to the most
unfavourable section inthe bay considered, taldng
account of local buckling and HAZ softening, but
ignoring holes. HAZ softening
failure). may be ignored when it
occurs at the extreme ends of a spanning,
i.e. non-cantilever, bay.
For sections exempt from lateral torsional buckling
(see 4.5.6.2),
shouldbetakenequal to M a x
where
G7
~~~~~
~
~~
STD-BSI BS ALLA: PART L-ENGL 1 9 9 1 E Lb24bb9079457b 583 E
BS8118 :Part 1 : 1991
Section 4
4.8.4.4 Case C (biaxial bending)
For case C the following single condition should be
satisfied (preventionof minor axis buckling):
4.8.4.5 Case D (biaxial bending with axial force)
For caseD the condition shouldbe satisfied
where
M R ~is the valueof
that wouldbeacceptablein
conlbination with4 but in the absence of
minor axis bending, as given in 4.8.4.3 (lesser
value);
MRQ is the similar value for By,in the absence of
major axis bending, as given in 4.8.4.4.
4.9 Deformation (serviceability limit
State)
4.9.1 General
4.9.2 Recoverable elastic deflection
4.9.2.1 Compact sections
The elastic deflection of these nlay be calculated using
gross section properties, ignoring holesor HAZ effects.
For beams this applies both to fully and to compact
sections and senu-compact sections.
4.9.2.2 Slender sections
Deflection calculations should generally
be perfomled
using section properties calculated foran effective
section that allows for localbucklig, but ignores any
effects of HAZ softening or holes. The assumed
effective section maybe conservatively basedon
reduced thicknessesas given in 4.5.2.3(1) for bending,
or 4.7.6.3(1) for axial conlpression, or the following
more favourable procedure may be adopted.
(a) Reclasse and slender elenlent usinga nlodified
value for E in 4.3.3.4, obtained by taking P, equal to
two-thirds of the nornlal value given in tables4.1
and 4.2.
(b) If the section is then found to be no longer
slender, the gross section propertiesare taken.
(c) If as reclassified, it is still slender,a new
effective sectionis assunled, basedon k~ values
found by using the nlodified value of E from (a) for
figure 4.5.
The recoverable elastic deflection (see 4.9.2) under
nominal loading (unfactored) should not exceedthe
limiting value (see3.4).
If the ultimate l i t state (static strength)has been
satisfied, using4.2 to 4.8, it may be assumed that
pemment inelastic deformationin service will be
negligible. No separate check for this is generally
needed.
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O BSI 07-1999
STD*BSI BS B1L8: PART L-ENGL 1991 9 l b 2 9 b b 9 079VS77 lr1T m
Section 5
BS 8118 :Part 1 : 1991
Section 5. Plates and plate girders
5.1 General
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This section coversthe static strength (ultimatelimit
state) of the following structural components:
(a) unstiffened plates (see5.2 and figure 5.1);
@) multi-stiffened plating (see5.3 and figure5.2);
(c) plate-girders (see 5.4 and figure5.3).
For (a) and (c) the resistance obtained will tend to be
more favourable thanthat based on the simpler rules
of section 4,especially when considering slender plates
or webs of low aspect ratio ( d d ) . Multi-stiffened
plating is not covered in section4.
B
m
P”--+
Figure 5.2 Multi-stiffened plate
L
d
c
œ
Figure 5.1 Unstiffened
plate
5 2 Unstiffened plates
5.2.1 General
Unstif‘fened plates subjectto direct stress may be
designed in accordance with 5.2.2 to 5.2.4, and those
loaded in shear in accordance with5.2.5. Lnteraction
effects are covered in 5.2.6.
The plate tluckness is denoted by t throughout.
1
I
c
i [ End
-n
U
c
W
t
panel
Figure 5.3 Plate girder
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69
5.2.2 Unstiffened plates under direct stress
5.2.2.1 General
(2) Column treatment. k~ is taken equal to the
ratiopdp,, where p , is the column bucklingstress
read from figure4.10 (a). The appropriate curve to
use is that intersecting the stress axis at a value
po. The slenderness parameterA should normally
be taken as follows:
A = 3.5 d t
corresponding to simple support, although a lower
value may be taken if this can be justified.
The resistance of a plate to uniform in-plane
conlpression,.F: acting in the direction shown in
figure 5.1 is described in 5.2.2.2 to 5.2.2.4.
5.2.2.2 Classtfication
The plate should be classifiedas follows:
( 4 ß 5 P1
fully-conlpact;
senucompact;
slender
@Iß1<ß‘ßo
(c) ß ß o
5.2.3 Unstiffened plates under in-plane moment
5.2.3.1 General
The resistance of a plate to pure in-plane moment
acting on the sides of width d (see figure 5.1) is
described in 5.2.3.2 to 5.2.3.4. If the moment varies in
the direction parallelto dinlension a, see also 5.2.4.
where
ß = ut;
ßo and ßI are as given in table 4.3.
5.2.3.2 Classification
5.2.2.3 Fullg and semi-compactplates
The factored axial resistancePRSto uniform
compression should be based onthe least favourable
cross-section as follows:
(a) full~conl~act PRS= PrtAndYm
@) semi-compact
PRS=
Ym
is the neteffective area for allowingfor
holes, and takinga reduced thicknesskt
in any region affected byHAZ softening
(see 4.4.4 and 4.4.3);
is the nlaterialfactor(seetable
3.3).
5.2.2.4 Slender plates
A yielding check and a buckling check should be
perfomled, taking valuesas follows for the factored
axial resistancepRs.
(a) Yielding check. Pm is obtained as in 5.2.2.3 for a
senucompact plate, ignoring buckling.
(b) Buckling check. Pm = P&&,,
where
po
A,
(a>ß 5 P1
fully compact;
(b)ßl<ßSßO
semi-compact;
slender;
(c) ß > ß o
where
pa and P, are linuting stresses (see tables 4.1
and 4.2);
Arie
The plate should be classifiedas follows:
is the limiting stress (seetables 4.1 and 4.2);
is the effectivearea,obtainedby
taking
reduced thicknessto allow for bucklingas
well as HAZ softening, but with holes
ignored.
In @) the effective area should generally be based on
the least favourable cross-section,taking a thickness
equal to the lesser of kt and kLt in HAZ regions, and
kLt elsewhere. However, HAZ softening due to welds at
the loaded edges may be ignored in this check.
The factor kL may be determined by the more
favourable of the treatments (1) and (2) as follows.
(1) Plate treatment. k~ is read from curve C or D
in figure 4.5, taliing P = d/t and E = (250/p0)”.
where
ß = 0.3WG
ß o and P1 are as given in table 4.3.
5.2.3.3 FullIl and semi-compactplates
The factored moment resistanceMB should be based
on the least favourable cross-section, using
the relevant
expression in 4.5.2.2 (a) to (d), and taking anassumed
section as defined in4.5.2.3 (a) or @).
5.2.3.4 Slender plates
The factored moment resistance shouldbe taken as
the lesser of two values foundas in (a) and (b) as
follows.
(a) Yielding check. MB is obtained as in 5.2.3.3 for
a semicompact plate ignoring buckling.
(b) Buckling check.Mm if found as follows:
MRS= P$&m
where
2,
is the elastic modulus of the effective section.
The calculation in @) should generally be based on the
effective sectionat the least favourable position, with
no deduction for holes, takinga thickness equal to the
lesser of kt and kLt in HAZ regions, and kLt elsewhere.
However, HAZ softening due to welds at the loaded
edges may be ignored in this check.
The factor kL should be read from curveC or D in
fim4.5, takingß = 0 . W t and E = (250/’0)’.
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O BSI 07-1999
STD=BSI BS ALLB: PART L-ENGL 1791 D l b 2 V b b 7 07911577 292 m
Section 5
BS 8118 : Part 1 : 1991
5.2.4 Longitudinal stress gradient on unstiffened
plates
5.2.4.1 General
Cases wherethe applied actionP or M on an
W f e n e d plate varies longitudinally inthe direction
shown in figure 5.1,are given in 5.2.4.2 and 5.2.4.3.
5.2.4.2 Fullg and semi-compact plates
The factored resistanceat any cross-section should not
be less than the action arisiig at that section under
factored loading.
5.2.4.3 Slender plates
The yielding check shouldagain be satisfied at every
cross-section. But for the buckling check it is sufficient
to compare the factored resistancewith the action
arising at a distance x from the more heavily loaded
end of the panel, wherex is 0.4 times the elastic plate
buckling half-wavelength.
(b) Buckling check. The resistancemay be safely
found as in 4.5.3.3 (b). Alternatively the following
expression may be used, which is more favourable
when a is less than 2.M:
v,
= vlPvd%ll
I
where v1 is the elastic critical shear buckling factor
read from figure 5.4taking E = (150/pv)
The expression in 4.5.3.3 @) still fails to take
advantage of tension field action. If it is believed that
the edge conditionsare such that a tension field is
sustainable, the designer nmy refer to the even more
favourable treatment available for type1 panels in
plate girder webs (see5.4.3.4).
5.2.6 Combined actions
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5.2.6.1 Classification
A plate, subjected to combined axial force P and
a
moment M under factored loading should be given
single classification (fully compact, semi-conlpactor
5.2.5 Unstiffened plates in shear
slender) generally in accordancewith 4.8.2.1. In so
doing, the value taken for
fi should be based on the
5.2.5.1 General
stress pattern produced in the plate whenP and M act
Unstiffened plates undershear should be classified as
together, based on an appropriate valueof g (see
compact or slender, as in 4.5.3.1.
figure 4.2).
The presence of small holesnmy be ignored when
Where the plate is classed as slender, each individual
finding the shear resistance, provided they do not
resistance (PRSand MRS) should be based on the
occupy morethan 20 % of the crosssection area on the specific type of action considered,as in 4.8.2.2.
width d.
5.2.6.2 Axial force with moment
5.2.5.2 Compact shear web
The following condition should be satisfiedfor a plate
The factored shear force resistance VRS should be
subjected to axial force withmoment
found as follows:
VRS = P d d h
P
M
-5 1.0
PRS 'MRS
where
p , is the linuting stress (see tables 4.1 and 4.2);
ym is the material factor (see table3.3).
Av is the effective shear area, taken as follows;
where:
(a) for unwelded platesA, = dt;
@) for plates fully welded along one or more
edges Av = k d t ;
(c) for partially welded plates,A, is the effective
area on the width d, found by taking a reduced
thickness kt in softened zones (see4.4.2
and 4.4.3).
5.2.5.3 Slender shear web
The factored shear force resistance V= should be
taken as the lesser of the two values obtained from(a)
and @) as follows.
(a) Yielding check. The resistance is found as for a
compact plate, using5.2.5.2.
P and M
are the axialforceandin-plane
moment respectivelyW i g under
factored loading.
PRSand MRS are the factored resistancesto axial
force and in-plane moment
respectively, each reducedto allow for
coincident high shear if necessary
(see 5.2.6.4).
5.2.6.3 Direct stress with low shear
It may be assumed that a coincident shear force V
(under factored loading) has no effect onthe
longitudinal resistanceof a plate, provided V does not
exceed half its factored shear force resistance VRS.
5.2.6.4 Direct stress with high shear
If V exceeds 0.5VRS, the longitudinal resistance (axial
force, moment) should be reduced by a factor k,
where:
k, = 1.6 - 1.2 VWRS
~
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71
~~
~
~~~
~
STD.BS1 BS B L L B : PART L-ENGL 3991, m L b 2 4 b b 9 0774580 T04 m
BS 8118 :Part 1 : 1991
Section 5
The stressp, should be read from the appropriate
curve in figure 4.10 relevant to colunm bucklingof the
5.3.1 General
subunit as a simple strut out of the plane of the
The following rules concern plating, supported on all plating.
four edges (see figure5.2), that is reinforced with three The slenderness parameterA needed for figure4.10
or more equally spaced longitudinal stiffeners
or
may be based on an effective lengthI equal to the
corrugations. Thesemay be unsupported on their
lesser of (a) and (b) as follows:
whole length or else be continuous over intemlediate
(a) the distance between positionsof effective lateral
tranmerse stiffeners. The dinlensionL should be taken
support, such as end supports or effective transverse
as the spacing of the supports when fitted. An essential
stiffeners;
feature of the design is that the longitudmal
(b) the elastic orthotropic buckling half-wavelength.
reinforcement, but not transverse stiffening,is
'subcritical', i.e. it can deform withthe plating in an
The part of figure 4.10 (a), @) or (c) used depends on
the section shape of the subunit and whether it
overall buckling mode.
contains longitudinal welding (see table 4.10),the
The resistance of such plating to longitudinal direct
actual curve beingthat which intercepts the stress axis
stress in the direction of the reinforcement is given
at a value pl as defined in 4.7.6.2.The following
in 5.3.2 to 5.3.4, and to shear in 5.3.5. Interaction
should
be noted when deternining the effective
between different effects maybe allowed for in the
area
A,
(needed for findingpl).
same way as for unstiffened plates (see5.2.6).
(1)
The value of I ~ Lfor elements such as E in
The treatments given become invalidif the
figure
5.2 should be basedon their full
cross-section contains any outstand elementsthat are
dimensions,
even though theyare cut in two for
classified as slender.
the formation of sub-units.
When the construction consistsof flat plating with
(2) HAZ softening due to welds at the loaded
applied stiffeners,the resistance to transverse direct
edges
or at transverse stiffenersmay be ignored in
stress may be taken the Same as for an unstiffened
finding
A,.
plate. With corrugated construction itis negligible.
5.3.3 Multi-stiffened plating under in-plane
5.3.2 Multi-stiffened plating under uniform
moment
compression
5.3.3.1 General
5.3.2.1 General
Two checks should be performed, a yielding check
' h o checks should be performed,a yielding check
(see 5.3.3.3) and a colunm check (see5.3.3.4).
(see 5.3.2.2) and a colunm check (see5.3.2.3). The
crosssection should be classied as compact or
5.3.3.2 Section classification and local buckling
slender in accordance with4.3.3, considering all the
The cross-section should be classified as compact or
component elements before carryingout either check.
slender
(see4.3.3) when carrying out either check.
Slender outstand elementsare not permitted.
For the purpose of classifymg individual elements, and
5.3.2.2 Yielding check
also when determiningI ~ Lfor slender elements, itmay
The entire section shouldbe checked for local
generally be assumed that each element is under
squashing in the sanle way as for a strut (see 4.7.7).
uniform compression takingg = 1 in 4.3.2.2. However,
in the case of the yielding check only, it is permissible
The resistance qls should be based on the least
favourable cross-section, taking accountof local
to base g on the actual stress pattern in elements
conlprising the outermost region of the plating, and to
buckling andHAZ softening if necessary, andalso any
unfilled holes.
repeat ths value for the corresponding elements
further in. This may be favourable whenthe number of
5.3.2.3 Column check
stiffeners or corrugations is small. Slender outstand
The plating is regarded as an assemblage of identical
elements should not be allowed.
column subunits, each containing one centrally
located stiffeneror corrugation and witha width equal 5.3.3.3 yielding check
to the pitch W.The factored axial resistancePm is then The entire cross-sectionof the plating should be
taken as:
treated as a beam under in-plane bending (see
4.5.2.2).
The factored moment resistanceMm should be based
PRS = P&Y,
on the least favourable cross-section, taking accountof
where
local buckling and HAZ softening if necessaty, and also
any holes.
P,
is the buckhg stress for a colunm s u b unit;
A
is the gross area of the entire cross section of
the plating;
ym nlateriaJ factor (see table 3.3).
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--`,,,,,,`,,,``,```,,`,````,``,-`-`,,`,,`,`,,`---
5.3 Multi-stiffened plating
STDOBSI BS BLLB: PART L-ENGL 1991 m L b 2 q b b S 079qSBL 940 m
Section 5
BS 8118 :Part 1 : 1991
5.3.3.4 Column check
The platmg is regarded as an assemblage of colunu
subunits in the sanle general way as for axial
compression (see 5.3.2.3), the factored moment
resistance MRS being taken as follows:
MRS= PszB/2yYm
where.
P,
2
B
y
Ym
is the buckling stress for columnsub-unit;
is the elastic section modulus of the full cross
section of the plating for in-plane bending;
is the overallwidthofplating;
is the distance from centre ofplating to centre
of outermost stiffener,
is the material factor (see table 3.3).
5.3.5.2 Yielding check
The factored shear force resistance VRS is taken as the
same as that for a flat unstiffened plateof the sanle
overall aspect (LB) and the same general thickness t,
found in accordance with5.2.5.2.
5.3.5.3 Buckling check
The factored shear force resistance is found from the
following:
VFS vlPvBt/y,
where
pv
is the limiting stress (see tables 4.1 and 4.2);
B
t
is the widthofplating (seefigure5.2);
is the generalplatethickness;
is the material factor (see table 3.3);
is theelasticcritical shear bucklingfactor
(see figure 5.4).
ym
v1
The stress P, should be read from figure4.10 in the
same way as for uniform compression (see5.3.2.3).
In order to calculate v1 the following values should be
used
5.3.4 Longitudinal stress gradient on
multi-stiffened plates
5.3.4.1 General
Cases wherethe applied action P or M on a
multi-stiffened plate varies in
the direction of the
stiffeners or corrugations are described in 5.3.4.2
and 5.3.4.3.
5.3.4.2 Yielding check
The factored resistance at anycrosssection should be
not less than the action a r i s i i at that section under
factored loading.
5.3.4.3 Column check
a
=B ,
d
1
= o.(jl(wt3/Is~)0~~7~;
is the effective length of plating;
W
is the pitch of stiffeners or corrugations;
Is11 is the second moment of area of one sub-unit
of the plating (asdefined in 5.3.2.3) about a
centroidal axis parallelto the plane of the
plating;
= (150/p,) y2.
E
The effective length1 may be safely taken as the
unsupported lengthL (see figure 5.2). WhenL greatly
exceedsB, a more favourable result may be obtained
by putting 1 equal to the elastic orthotropic shear
buckling half-wavelength.
No allowance for HAZ softening need be made in
performing the buckling check.
For the column check itis sufficient to compare the
factored resistance withthe action arising ata
distance x from the more heavily loaded endof a
panel, wherex is 0.4t h e s the effective buckling
length l.
5.3.5 Multi-stiffened plating in shear
5.3.5.1 General
A yielding check (see 5.3.5.2) and a buckling check
(see 5.3.5.3) should be performed. The methods given
in 5.3.5.2 to 5.3.5.3 are valid provided the following
5.4 Plate girders
5.4.1 General
A plate girder is a fabricated bean1 comprising tension
occur.
h g e , compression flange and web plate. The webis
typically of slender proportions and reinforced
(a) The pitch W of the stiffeners or corrugations
transversely with bearing and intermediate stiffeners
does not exceed 0.3L (see figure 5.2).
@) Any outstand elementof the section is classified (see figure5.3). It may have longitudinal stiffeners too.
as compact in terms of axial resistance (see4.3.3.4). A basic feature is that the web stiffenersare designed
to provide supported edges forthe panels of the web,
(c) Any internal elementis classified as compact in
staying essentially straightas buckling proceeds.
terms of shear resistance' (see4.5.3.1).
The moment and shear resistances of plate girders
(d) Stiffeners or corrugations, as well as the actual
having transversely stiffened webs are covered in 5.4.2
plating, are as follows:
and 5.4.3, while 5.4.4 gives the modifications needed
(1) effectively connectedto the transverse framing when longitudinal stiffenersare added. In considering
at either end;
moment resistance it is pemussible to follow
appendix
E instead of 5.4.2, if desired, and economies
(2) continuous at any transverse stiffener position.
nlay result.
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73
~~
STD-BSI BS 8118: P A R T 1-ENGL 1991 m bb2qbb7 077q582 8 8 7 D
BS 8118 :Part 1 : 1991
Section 5
The methods given in 5.4.2, 5.4.3 and 5.4.4 are valid
provided the following occur.
(a) The stiffeners comply with5.4.5.
(b) The spacing a of transverse stiffeners is not less
than half the clear depth of the web between flange
plates @ut see 5.4.6 for corrugated or closely
stiffened webs).
It may be beneficial to provide a tongueplate, to one
or both flanges. To be effective this should conlply
with 5.4.5.8.
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Interaction between moment andshear is dealt with
in 5.4.7.
If web bearing or lateral torsional bucklingis thought
to be a factor, the designer should referto 4.5.5
or 4.5.6. For girders subject to axial load, as well as
bending, 4.8 is relevant.
The treatment of plate girders given in5.4.2 to 5.4.7 is
also generally applicableto box section girders
provided the webs are sindar in foml.
5.4.2 Moment resistance of transversely
stiffened plate girders
5.4.2.1 General
In order to determine the factored moment resistance
a yielding check (see 5.4.2.2) and a buckling check
(see 5.4.2.3) should be performed.
For hybrid girders, with differing flange and web
material, the designer should referalso to 4.5.2.4.
5.4.2.2 Yielding check
The moment arisingat any cross-section under
factored load should not exceedthe factored moment
resistance MRS that would apply if the section were
treated as senu-compact. Thevalue of Mm is obtained
from 4.5.2.2 @) or (d) as appropriate, taking account
of any holes or HAZ effects, but ignoring local
buckling.
It may be assumed that any tongue-plate, if fitted,
provides effective edge support to the slender web
plate to which it is joined, provided it complies
with 5.4.5.8. Thus to find k~ for the web plate from
figure 4.5 (b), P may be based on a value of d measured
to the tip of the tongue or tongues.
5.4.2.4 Alternative treatment of web buckling
If the neutral axis is located so that it is nearer to the
edge of the web in compression than itis to the one in
tension, it is permissible to treat the web as composed
of two zones with differing values
of k~ obtained as
follows.
(a) Zone 1, extending a distance y1 either side of
neutral axis. k~ is read from figure 4.5 @) talnng
/3=0.7gl/t where y1 is the distance from the gross
neutral axis to the compressed edge.
@) Zone 2, occupying the rest of the web: k~ = 1.0.
5.4.3 Shear resistance of transversely stiffened
plate girders
5.4.3.1 General
A yielding check (see5.4.3.2) and a buckling check
( s e e 5.4.3.3) should be carried out. For webs with
continuous longitudinal welds itis also necessary to
carry out a HAZ check (see 5.4.3.5). The presence of
small holes in the web platemay be ignored for either
check, provided they donot occupy more than 20 % of
its section area
5.4.3.2 Yielding check
At any cross-section the shear force Varking under
factored load should not exceeda value VRS found as
follows:
(a) no tongueplate
(b) with tongueplate or
plates
v,
= h AweIYm;
V, = (pvwAwe +
5.4.2.3 Buckling check
+ hAte)Ym;
where
The following treatment appliesto plate girders with
transverse stiffeners,but no longitudinal stiffeners.
P,, and p f i
are limiting stresses for the weband
tongueplate materials respectively
For each bay of the girder between transverse
(equivalent to pv in tables 4.1
stiffeners the moment arising under factored load,at a
and 4.2);
distance O.& from its more heavily stressed end,
should not exceed the factored moment resistanceMRS
Awe
is the effective
section area of web
for that bay based onultimate failure by buckling. The
plate between flanges,or to
value of MRs is obtained in accordance with4.5.2.2 (e),
tongueplate tips;
allowing for local buckling andHAZ softening, but
Ate
is the effective
section
area of
ignoring holes. However,it is permissible for the
tongueplate, or total area for two
purpose of this check to ignore HAZ effects caused by
Such;
the welding on of transverse stiffeners.
Ym
is the material
factor
(seetable 3.3).
In considering web bucklig, the effective thickness
factor k~ should generallybe found in accordance
The effective areas are obtained takmg reduced
with 4.3.4, talung P as in 4.3.2.2. However, if the
thicknesses equal to times the true thickness in any
compressed edge of the web is nearer to the neutral
HAZ
region (see 4.4.2 and 4.4.3).
axis than is the edge in tension, it is permissible
instead to proceed as in 5.4.2.4, which wil tend to be
more favourable.
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~~
~
~
~~
1971 m 1b211bb7 07711583 713
S T D = B S I BS 811B: PART1-ENGL
Section 5
BS 8118 : Part 1 : 1991
5.4.3.3 Buckling check
5.4.3.4 Tensionfield action
In any bay between transverse stiffeners theshear
' h o types of web panel are identified as follows
(a) ?sTpe 1: Panels able to sustain a tension field,
force Vaxising under factored loading should not
exceed the limiting value V= for that bay, based on
ultinmte failure by buckling. The value of VRS should
be found using the appropriate expression(a) or (b) as
follows, which take due advantage of post-buckled
behaviour
I tongueplate
(a) no
I tongueplate
@>with
or
plates
--`,,,,,,`,,,``,```,,`,````,``,-`-`,,`,,`,`,,`---
where
d
is the depth of webmeasuredbetweenflanges,
or to tongue-plate tips;
t
is the unreducedthickness ofweb plate;
v1
is the initial shear bucklig factor read from
figure 5.4 taking E = (1501'p~)~;
vtf is the tension field factor (see 5.4.3.4).
namely:
(1) an internal panel;
(2) a panel in an end-bay provided with an
adequate end-post conlplying with5.4.5.6.
(b) 'Qpe 2 a panel in an end-bay lacking an
adequate end-post.
There is negligible tension field action intype 2 panels,
and for these vtf in 5.4.3.3 should be taken as zero.
m e 1 panels are generally ableto develop further
shear resistance after the initial onset of buckling, due
to tension field action. For these vtf should be taken as
follows:
Vtf = v2 + mv3;
(i) unwelded
panel
(i)panelwithedgewelds
vtf = k;
+
where m is the lesser of ml and q
The other quantities are as defined in 5.4.3.2.
1.0
o. 9
0.8
O .7
0.6
"I
O. 5
0.4
O.3
o. 2
o. I
O
O
40
80
120
160
200
240
280
d/t&
NOTE. For longitudinally stiffened panels d should be taken as the depth of the largest sub-panel.
Figure 5.4 Elastic critical shear buckling factor v1
1
I
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75
should be suitably sharedin obtaining Sf for each web.
where
5.4.3.5 HAZ check
Pi?
is the shear buckling
factor,
v3
is the shear buckling
factor,
determined from figure5.6;
is the HAZ softering factor (see4.4.2);
determined from figure5.5;
ml and
are shear buckling
factors
where
ml is the determined from figure5.7;
where
m2 = (4PofSf~P0wd2~>
%
where
I
is the second moment of area of the gross
cross section;
p0f and P,,
are linuting stresses po for flange
and web material (see figure 4.1);
Sf
is the plastic
modulus
of effective
flange section about its own equal
area axis, in the plane of the web
(the lower value is taken if the
flanges are different).
is the first moment of gross excluded area
outside the weld
where
is the section area
is the distance of the centroid of the neutral
axis to this area
and /c;, pm and y,, are as defined in 5.4.3.2
and 5.4.3.4.
In deteminhg Sf the section considered should
if
include the flange plate together with tongue plate
present, with suitable thickness reductionto allow for
local buckling and HAZ softening (see 4.5.2.3), but
with no deduction for holes. If the girder has two or
more webs, the plastic modulus of the whole flange
a/d
"2
0.50
O. 4
0.75
1.0
0.3
1.5
0.2
2.0
22.5
0.1
O
40
80
120
160
200
240
280 d/ts
NOTE. The figure should not be used for panels with longitudinal stiffeners.
Figure 5.5 Basic tension field shear buckling factor
76
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--`,,,,,,`,,,``,```,,`,````,``,-`-`,,`,,`,`,,`---
k;
For webs with longitudinal weldsthe shear force T/:
arising under factored load, should not exceedthe
factored shear force resistance VRS at any such weld,
where VRS is given as follows:
STD.BSI BS 8118: PART L-ENGL 1991 m L b 2 4 b b 9 0799585 59b W
Section 5
BS 8118 :Part 1 : 1991
“J
2.0
1.8
1.6
1.4
1.2
1.0
0.8
0.6
0.4
0.2
O
40
80
120
160
200
240
280 d / t &
NOTE. This figure should not be used for panels with longitudinal stiffeners
Figure 5.6 Flange assisted tension field shear buckling factor v3
m,
a/d
0.7
22.5
2.0
1.5
0.6
0.5
1.0
0.4
0.75
0.3
0.50
0.2
0.1
O
40
80
120
160
200
240
280 d / t &
NOTE. This figure should not be used for panels with longitudinal st,iffeners.
Figure 5.7 Shear buckling factor ml
--`,,,,,,`,,,``,```,,`,````,``,-`-`,,`,,`,`,,`---
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77
NOTE. Figures 5.5 to 5.7 should not be used for web panels
with longitudinal stiffeners.
(3) m2 is calculated as in 5.4.3.4, taking d as
defined in 5.4.3.3.
5.4.5 Web stiffeners and tongue-plates
5.4.5.1 General
The following types of web stiffener are considered
(see figure 5.3). They may be single- or double-sided
(a) type A, intermediate stiffener transverse stiffener
other than that covered by type B;
@) type B, bearing stiffener: transverse stiffenerat
point of concentrated load or reaction;
(c) type C, longitudinal stiffener spanning
longitudinally between transverse stiffeners.
In order that predicted resistancesmay be achieved, it
is genemlly necessary that web stiffeners comply with
the following:
(1) types A,B,C: compactness (see5.4.5.2);
(2) types A,B,C: s m e s s (see 5.4.5.4);
(3) types A,B only: stability (see 5.4.5.5).
A transverse stiffener should extend without break
from flange to flange, even when tongue, platesare
fitted. Where a bearing stiffener, proper provision
should be madeat the flange for transferringthe
applied force intothe stiffener. It is not essential for
the stiffener to be connected to the flanges.
Where possible longitudinal stiffeners should be made
continuous from one web bayto the next. Where this
is not possible, the separate lengths shouldabut on to
the transverse stiffener dividing them.
5.4.5.2 Compactness
All stiffeners should beof compact section in temw of
resistance to axial compression (see 4.3.3.4).
5.4.5.3 Eflective stwener section
The effective stiffener section is used in checking the
stiffness and stability requirements. It consists
of the
actual stiffener,or pair of stiffeners if double-sided,
together with an effective widthbe of web plate (see
figure 5.8). The latter extends a distance bl either side
of the stiffener attachmentor attachments as shown,
and is given generally by the following:
(a) for a transverse
stiffener,
bl = lesser of 0.1% and
15ct
NOTE. For a transverse stiffener located at an end of the girder
the value of b, on the outboard side (only) should be taken as
follows, instead of the value given in(a):
b , = lesser of a, and 7 ~ t
where a, is the distance from the stiffener to the fret? edge of
the web plate.
@) For a longitudinal
stiffener,
bl = lesser of 0.13davand
15~t
Figure 5.8 Effective stiffener section
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--`,,,,,,`,,,``,```,,`,````,``,-`-`,,`,,`,`,,`---
5.4.4 Longitudinally and transversely stiffened
girders
5.4.4.1 Moment resistance
The procedure for determiningthe moment resistance
is basically as for girders having transverse stiffeners
only, and involvesa yielding check anda buckling
check. The yielding check is as given in 5.4.2.2.
In making the buckling check (see5.4.2.3) it is
assumed that each longitudinal stiffener providesa line
of support to the web, thus dividing it into separate
sub-panels fromthe point of view of local buckling. In
determining the effective section of the girder,
improved values of kL may be used for the sub-panels.
These are obtained by taking the correct width and
stress pattern for each sub-panel in d e t e r n m g its
value.
5.4.4.2 Shear resistance
The yielding check (see 5.4.3.2) and the HAZ check
(see 5.4.3.5) are unaffected by the presence of
longitudinal stiffeners.
The buckling check shouldbe carried out genemlly in
accordance with 5.4.3.3, but with v1 and VE found as
follows:
(a) the value of vl is deternmed from figure 5.4,
taking d equal to the depth of the largest sub-panel
(instead of the full web depth);
@) the value of vtf is calculated using equation(i) or
(ii) in 5.4.3.4 as appropriate, with factors %, v3 and
m obtained as follows:
(1) the value of m is taken as the lesser of ml and
mz;
(2) the values 3, v3 and ml are calculated using
the formulae in appendix K that relate to
figures 5.5 to 5.7 respectively, takingd as the full
depth as defined in 5.4.3.3, and v1 as the value
found in (a) above.
where
E
pv
dav
= (150/Pv)”;
is the linuting stress for webmaterial(see
tables 4.1 and 4.2);
is the averagedepth of the twosub-panels
lying either side of the longitudinal stiffener.
It is inlportant to allow for the bending effects that will
be introduced, if there is eccentricity between the l i e
of action of P and the centroidal axis of the effective
section. This nmy be undertaken usingthe interaction
formulae given in 4.8.3 and 4.8.4.4 where My is the
moment due to the action and Mx = O. Such
eccentricity occurs especially when single-sided
stiffeners are used.
5.4.5.6 End posts required to resist tension field
When
detemthe shear force resistanceof an end
For the panel proportionsgiven, the second moment of
o
f
a
plate
@er,
it is only pernutted to take
bay
area I , of the full section of the effective stiffener
advantage
of
tension
field actionif an adequate
(see 5.4.5.3) about a centroidal axis pasallel to the web
is
provided
at
the outer end of the web panel.
end-post
should satisfy the following:
This should be designed to perfornl two functions as
follows, although interaction between the two effects
(a) for a transverse
I, 2 d t 3 ( ~ d / ,- 0.7);
may be ignored:
stiffener ( d d I2.5),
(a) to act as a bearing stiffener, resistingthe reaction
(b) for a longitudinal
1, 2 Ug(2ddav - 0.7).
at the girder support;
stiffener (da& 5 2.!5),
@) to act as a short beam spanning betweenthe
girder
flanges, resistingthe tension field inthe plane
The stiffness conditionnlay be waived when the panel
of the web.
proportions lie outside the range indicated.
An end-post may be either of the following forms, in
5.4.5.5 Stability (Dansverse stmeners onlu)
either case securely connected
to both of the girder
The effective stiffener section (see5.4.5.3) is
flanges.
considered as a strut carrying a thrust P under
(1) It may conlprise two double-sided transverse
factored loading given by the following:
stiffeners, formingthe flanges of the short beam,
together with a strip of web plate between them.
(a) for a intermediate P = VB,
One of the transverse stiffeners shouldbe suitably
stiffener,
located so as to fulfil the bearing role.
@) for a bearing
P=P1 + V A
(2) It may be in the foml of inserted material,
stiffener,
connected to the end of the web plate.
In
performing
function @), the end-post has to resist a
where
shear force Vep together with a moment M, acting in
the plane of the web plate (under factoredLading),
V
is the averagevalue of the shear force
given by the following:
arising in the web panels either sideof the
stiffener considered
P1
is the concentratedload or reactionacting
at stiffener.
Mep = 0.1 dVq
axial
The value of P should not exceed the factored
where
resistance of the strut, as determined from 4.7 taking
account of column buckling (out of the plane of the
9
is the mean shear stress arismg in
endweb) and local squashing, but ignoring torsional
panel of web under factored loading,
buckling. In considering column bucklingan effective
based on unreduced thickness;
strut length 1 should be taken as follows:
Pv
is the limiting stress for webmaterial(see
(1) for d d 2 1.5,
tables 4.1 and 4.2);
I = d;
1 = d(1.6 - 0.4 dd)%
(2) for d d < 1.5,
v1 and 212 are factors relating to end-panels found
from figures 5.4 and 5.5, or from 5.4.4.3
When the panel dimension a is different on opposite
( i longitudinally stiffened).
sides of the stiffener, an average value should be taken
In calculating q it is pemkssible to assume that part of
for it in the expressions in (1) and (2). For any end
stiffener 1 = d.
the shear force on the girder is carried by the
tongueplates, if fitted.
5.4.5.4 Stmness
--`,,,,,,`,,,``,```,,`,````,``,-`-`,,`,,`,`,,`---
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79
5.4.6 Use of corrugated or closely stiffened
5.4.5.7 End-posts required to resist torsion
If an end-post is the sole means of providing resistance webs
against twist at the end of a girder, the following
should be met:
where
lep
d
tr
R
W
is the secondnloment of area of the
end-post section aboutthe centre-line of the
web;
is the depth ofweb measuredbetween
flanges, or to tongue-plate tips;
is the flangethickness(taken
as the
nwximunl value whenthe thickness varies
along the girder);
is the reaction at the end of the girder
considered, under factored loading;
is the total factoredloadingon the adjacent
span.
5.4.5.8 lbngue-plates
A tongueplate comprises nlaterial extending in froma
flange to form a thickened outer part to the web. To be
effective its dinlensions should be suchthat it is
conlpact when consideredas a plain outstand in axial
conlpression (see4.3.3).
When a tongue is of t w or~ three-ply construction,
comprising the web-plate connected to an element or
elements integral with the flange, the thickness t
reqyired for checlungits compactness nmy be taken as
the total thickness. However, in rivetedor bolted
construction, itis also necessary to check that any
outstand beyond the last line of rivets or bolts is in
itself compact.
5.4.6.1 General
Girders having transverse web reinforcement in
the
form of cormgations or closely-spaced stiffeners,at a
pitch less than 0.3 times the depth between flanges, i.e.
failing to satisfy 5.4.l(b), are described in 5.4.6.2
and 5.4.6.3.
This transverse reinforcement is treated as subcritical,
in that it may deform with the web in an overall
buckling mode and hence not necessarily
satisfy 5.4.5.4 and 5.4.5.5.
5.4.6.2 Moment resistance
When the web consists of a flat plate with applied
stiffeners, the moment resistance should be foundas
in 5.4.2. But with a corrugated web it shouldbe
assunled that the web contributionis zero, the moment
resistance being provided solelyby the flanges.
5.4.6.3 Shear force resistance
The factored shear force resistance VRS should be
determined as in 5.3.5 for multi-stiffened plating in
shear.
5.4.7 Girders under combined moment and shear
Rgures 5.9(a) and (b) show schenlatically the form of
the nlonlent-shear interaction diagramfor plate
girders, covering:
(a) bays unable to sustain a tension field;
(b) bays with tension field action.
Such a diagram may be constructed, for any given bay
between transverse stiffeners,in order to determine
the factored nloment resistanceMRSO in the presence
of a coincident shear force V (arising under factored
loading). The notation is as follows:
MRS is the factored nlonlent resistance inthe
absence of shear (see 5.4.2 and 5.4.4.2);
MRFis the reduced value of MRS for the flanges on
their own, with web onutted
V m is the factored shear force resistance (see5.4.3
and 5.4.4.3);
VRWis the reduced value forVm obtained by
putting m = O (see 5.4.3.4, and 5.4.4.3).
--`,,,,,,`,,,``,```,,`,````,``,-`-`,,`,,`,`,,`---
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STD.BSI BS 8118: PART L-ENGL 1991
Section 5
Lb2qbb7 077ri589 131 m
BS 8118 :Part 1 : 1991
O
(a)field
No tension
@) With
fieldtension
Figure 5.9 Schematic interaction diagrams for plate girders
--`,,,,,,`,,,``,```,,`,````,``,-`-`,,`,,`,`,,`---
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81
~~
STD-BSI BS ALLA: PART L-ENGL 1791 D L b 2 4 b b 9 079q590 9 5 3 D
BS 8118 : Part 1 : 1991
Section 6
Section 6.Static design of joints
6.1 General
--`,,,,,,`,,,``,```,,`,````,``,-`-`,,`,,`,`,,`---
This section deals with the design of
joints made by
u
s
q fasteners, adhesives, or by welding. The
following typesof fastener are discussed: rivets, black
bolts, close tolerance bolts, high strength friction grip
bolts (HSFG bolts), special fasteners and pins. For
joints made by welding,the design resistance of butt
and fillet welds is defined. The design of joints
between cast or forged elements should be carried out
in conjunction with the manufacturers.
The following types of connectionare called joints:
(a) connections between structural members,e.g.
bean1 to column;
(b) connections betweenthe elements of a ‘built-up’
member, e.g. webs to flanges, splices;
(c) connections between localized details and
structural members, e.g. bracketto beam, lug and
clevis in a tension member.
All types of connection should be designedto meet the
h u t states of static strength and fatigue.No checks for
serviceability h u t states are required, except for pin
joints in structures that are frequently assembled and
disassenlbled, forjoints where deflections are critical
is to be
or, for friction grip bolted joints, where slip
prevented. The factored loadmg ona joint should be
calculated using the load factors given in section
3.
Fasteners subjectto reversal of load should be either
close toleranceor turned barrel bolts, solid rivets,
HSFG bolts, or special fastenersthat prevent
nlovement.
Hollow rivets and other special fasteners which
do not
comply with British Standardsmay be used provided
their performance has been demonstmted to the
satisfaction of the designer by testingor other means.
They should be spaced and designedby liaison
between the designer and the manufacturer. In
demountable joints with steel fasteners threadinserts
should be used in any threaded aluminium elementof
the joint. Their performance should be demonstrated
to the satisfaction of the designer by testing or other
means.
6.2 Riveted and boltedjoints design
considerations
6.2.1 General
Joints using rivets or bolts should be designedso that
under the factored load the loading actionat any
fastener positiondoes not exceed the factored
resistance of the fastener there.
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6.2.2 Groups of fasteners
Groups of rivets, boltsor special fasteners, known
collectively as ‘fasteners’,f o r n ~ ag connection, should
be designed on the basis of a realistic assumption of
the distribution of internal forces, having regard to
relative stiffness. Itis essential that equilibrium with
the external factored loadsbe maintained.
6.2.3 Effect of cross-sectional areasof plies
The design of the plies at sections containing holesfor
fasteners should be based on
ninhunl net areas,
except for rivets in compression. In certain friction
grip boltedjoints the linut state is met by the friction
capacity of the joint, and in these circumstancesthe
design should be based on minimum gross areas.
6.2.4 Long joints
When the length of a joint, measured between centres
of end fasteners in the direction of transmission of the
load, is more than 15&(where G$ is the nonlinal
dianleter of the fastener), or when the number of
fasteners in this dn-ection exceeds five, the designer
should take account of the reduction in the average
strength of individual fasteners due to uneven
distribution of the load between them.
6.3 Riveted and boltedjoints: geometrical
and other general considerations
6.3.1 Minimum spacing
The spacing betweencentres of bolts and rivets should
be not less than 2.5 times the bolt or rivet dianleter.
Closer spacingis permitted for HSFG bolts, limited by
the size of the washer, bolt headsor spanners, and the
need to meet the linut states.
6.3.2 Maximum spacing
In tension membersthe spacing of a x e n t bolts or
rivets on a line in the direction of stress should not
exceed 16t or 200 nun, where t is the thickness of the
thinnest outside ply. In conlpression or shear nlenlbers
it should not exceedSt, or 200 nun. In addition, the
spacing of Nacent bolts or rivets on a line macent
and parallelto an edge of an outsideply should not
exceed St or 100 mm. Where rivets and bolts are
staggered on adjacentlines, and the lines are not more
than 75 mm apart, the above limits may be increased
by 50 O h
In any event, the spacing of d a c e n t rivets and bolts,
whether staggeredor not, should not exceed32t
or 300 mm in tension membels, and20t or 300 nun in
compression andshear memberrs.
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These reconmendations apply only to lap and cover
6.3.7 Long grip rivets
plate joints between flat plates. The spacing
of bolts
The grip length of rivets should not exceed five times
and rivets in spigot joints, joints between tubular
the hole dianleter.
nlenlbers and between parts of very disshular
6.3.8 Washers and locking devices
thicknesses should bedeternined from consideration
of the local geometry and the loading on the joint.
Washers should beused in accordance with 2.3 of
6.3.3 Edge distance
BS 8118 : Part 2 : 1991. Locking devices approved by
the engineer should be usedon nuts liable to work
The edge distance, measured from the centreof the
rivet or bolt, for extruded, rolled or nmchined edges, loose because of vibration or stress fluctuation.
should be not less than 1.5 t h e s the rivet or bolt
6.3.9 Intersections
dianleter. If, on the bearing side, the edge distance is
Members meeting at a joint should norndly be
less than twicethe diameter, the bearing capacity
arranged with their centroidalaxes meeting at a point.
should be reduced (see 6.4.4). If the edges are
In the case of bolted framing of angles and tees, the
sheared, the above linuts should be increased
by
setting out linesof the bolts may be used instead of
3 nun.
the centroidal axis.
6.3.4 Hole clearance
The hole clearance can be slightly greater than allowed
in table 3.1 of BS 8118 : Part 2 : 1991. A clearance of
6.4 Factored resistanceof individual
1.6 null is allowable. Bolts that transnut fluctuating
rivets
and bolts other than HSFG bolts
loads, other than wind loads, should be close-fitting,or
complying with British Standards
HSFG.
6.3.5 Packing
6.4.1 Limiting stresses
Where fasteners are carrying shear through a packhg,
The linutingstress pf for solid rivets and boltsis
a reduction of the factored design resistance should be defined as follows.
taken into accountif the thickness of packing exceeds
(a) Steel fasteners:pf is the guaranteed minimum
25 % of the fastener diameter,or 50 % of the ply
yield
stress for the bolt or rivet stock.
thickness.
(b) Stainless steel bolts and stainless steel rivets:
6.3.6 Countersinking
pf
is the lesser of O. 5v0.2 + fJ and 1. 2f0.2.
Onehalf of the depth of any countersinking of a rivet
(c)
AlunWun~bolts and rivets: valuesof pf for the
or bolt should be neglected when calculating its length
aluminiunl alloys in table 2.3 are given in table 6. 1.
in bearing. No reduction is necefor rivets or bolts
Where the shear strength value is available, derived
in shear. The factored design resistancein axial tension
from tests on the bolt or on the rivet in the as-dnven
of a countersunk rivet or bolt should be takenas
condition (see BS 1974l) for large dmleter rivets),
twc+third.s of that of a plain rivet or bolt of the sanle
this nmy be used. In this case, as,in the expression
dianleter. The depth of countersinking should not
exceed the thickness of the countersunk part
for VRS in 6.4.2 should be reduced from 0.6 to 0.33.
less 4 nun, otherwise performance should be
demonstrated by testing.
I Table 6.1 Limiting stress pf for aluminium fasteners
Fastener type
Bolts
Rivets
Alloy
Condition supplied Method of driving
6082
T6
6061
5056A
5154A
5154A
6082
6082
5056A
5056A
T8
H24
Diameter
null
56
6 to 12
5 12
5 12
Cold or hot
Cold
Cold
Cold
Cold or hot
Cold
P,
N/rnl2
165
175
175
175
120
140
110
165
145
155
')Obsolescent standard.
--`,,,,,,`,,,``,```,,`,````,``,-`-`,,`,,`,`,,`---
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83
6.4.2 Shear
The factored resistance(V,)
in single shear is taken as:
VRS = asPde&Ym
where
The bearing capacity of the connected ply is given by
either of the following, whicheveris the lesser:
of a single rivet or bolt
where
is as defined in 6.4.1;
= 0.6 for aluminium bolts or rivets;
= 0.7 for steel bolts or rivets;
is the material factor, and is equal to 1.2 for all
bolts and rivets, i.e. aluminiun~,steel and
stainles steel (see table3.3).
pf
a,
ym
For bolts:
A,, = Ath, the stress area of the threaded part of the
bolt, when the shear plane passes throughthat area;
or
A,, = ASH,the area of the shank, when the shear
plane pases through the shank.
= Ah, the area of the hole;
KI = 1.0 forrivets;
= 0.96 for close tolerance bolts;
--`,,,,,,`,,,``,```,,`,````,``,-`-`,,`,,`,`,,`---
The factored resistance, PRT, for a single fastener in
axial tension is taken as
&r = aPf A t d h
where
a
.-
t
pf
ym
is the n o n W dianleter of fastener;
is the thickness of connected ply;
is defined for steel and alunIMun~fasteners in
6.4.1;
is the materid factor (see table 3.3).
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84
When bolts or rivets (exceptau
l nmun~rivets see
6.4.3) are subjected to both shear and tension the
.
are as definedin.6.4.1 and 6.4.2;
= 1.0 for steel and stainlesssteel
bolts and rivets;
= O. G for aluminium bolts.
The use of aluminium rivets in tension is not
recommended.
6.4.4 h
a
r
i
n
g
The effective factored resisbnce in bearing for a rivet
or bolt is the lesser of the factored resistance in
bearing of the single fastenerBRFand the bearing
capacity of the connected ply BRF
The fsctored mistance in bearing, BRRfor a single
fastener is taken as
BRF= dr &PUYnl
where
df
6.4.5 Combined shear and tension
V
6.4.3 Axial tension
a
P,
P
= 0.85 for n a m d clearance bolts.
pr, Atb and ym
c
is the distance from centre of hole to the
aaacent edge in the direction the fastener bears;
= 2 when df/t 10;
= 2Wdf when 10 df/t < 13;
= 1.5 when &/t < 13;
for the material of the connected ply is the lesser
of 0.5(f0.2 +fJand 1.2fo.z (see tables 4.1 and
4.2).
following condition should be satisfied (
iaddition to
6.4.2 and 6.4.3):
(PPE# + (V/vRS)25 1
where
For rivets:
A,,
e
V,
is the axial tensile load arising under factored
loading;
is the shear load arising under factored loading;
is the factored resistance in axial tension;
is the factored resistance in shear.
6.5 High strength friction grip (HSFG)
6.5.1 General
Only pre-loaded general grade HSFG bolts in
accordance with BS 4395 : Part 1 should be used for
alunwun~structures. Design nmy be based on
calculations forjoints where the proof strength of the
nwerial of the connected parts exceeds 230 N/nm2.
For connected parts manufactured from nlaterial with
a proof strength lessthan 230 N/nmi2, the strength of
joints using general grade HSFG bolts should be
proved to the satisfaction of the engineer by testing. In
alunIMm structures the relaxation of bolt preload
due to tension in the joined nlaterial cannot be
ignored.
The themul expansion of dunmum exceeds that of
steel andthe variation in bolt tension due to change of
tenlperature cannot be ignored. Reducedtenlpemre
reduces friction capacity and increased temperature
increases the tensile stress in the bolt and the bearing
stress under the washers. These effectsare only
significant for extremesof temperature change and
long grip lengths.
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6.5.2 Ultimate limit state (static strength)
6.6 Pinned joints
For HSFG bolts in n o d clearance holes, as specified
in table 3.1 of BS 8118 : Part 2 : 1991, the ultimate
capacity is the lesser of the shear capacity as
determined in 6.4.2 or the bearing capacityas
determined in 6.4.4.
6.5.3 Friction capacity
The factored resistance in shear depends on the
friction capacity of an HSFG bolt, where the friction
capacity (Fc,) is given by the following:
Fc = Pp PS NFh m
where
ps
is the slipfactor (see 6.5.6);
Ym
= 1.33 if the value of ps is taken as 0.33,
Ym
= 1. 1 if the value of ps is foundfromtests;
NF
is the number of frictioninterfaces.
6.5.4 Serviceability limit state (deformation)
The serviceability limitstate for a connection nmde
with HSFG bolts is reached when the shear load
applied to any bolt equals its friction capacity,
determined from 6.5.3. For the serviceability limitstate
check
= 1.2.
6.5.5 Prestress
The prestress load for a HSFG bolt should be taken as
follows:
PP = P,- 0.9s,,
where
s,b
BS 4395 : Part 1 : 1969);
is the appliedexternaltensileload in the
axial direction of the bolt (if any).
of
O. GpfIy”,;
where
pa
yn,
is defined for steel and alununiwu pins in
6.4.1;
is the material factor (see table 3.3).
6.6.3 Members connected by pins
Where all the connected parts are of aluninium alloy
and the friction interfaceshave been treated to ensure
consistent friction propertiesby blastmg with
alunwium oxide G38 grit complying with BS 2451, a
value of ps = 0.33 nmy be assumed provided thetotal
thickness of the connected parts exceeds the bolt
diameter, and the gross area stress in the parts does
not exceed O.Gf0.2, (wherefo.2 is the 0.2 % tensile proof
strength of the plate material).
If one or more of the above conditionsare not
complied with pusshould be deternwed from tests in
accordance with BS 4GO4 :“Part1.
The number of bolts needed to obtain the friction
capacity to satisfy 6.5.4, when talung ps = 0.33,may be
greater than the number needed to satisfy the ultimate
limit state (see 6.5.2). In such cases it may be
advantageous to develop a surface treatment forthe
interfaces which will increasethe slip factor.
O BSI 07-19N
(a) mean shear stress inpin:
(b) bending stresspin:
1.2PdYm;
in
If the pin is in a pernment installation, a fully plastic
distribution of bending stress may be assumed at the
factored design load.
6.5.6 Slip factor
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Consideration should be givento bending stresses in
pins, and forthis purpose the effective span is taken as
the distance between centres of bearings. However,if
the bearing plates havea thickness greater thanhalf
the pin dianleter, consideration may be givento the
variation of bearing pressureacross the plate thickness
when determining the effective span.
If the pin is to be removed to dismantle the structure,
and reinserted to reassemble the structure, the
cross-section of the pin should be checked for a
serviceability limit associated withthe linut of elastic
behaviour. The followingstresses should not be
exceeded under the factored load:
--`,,,,,,`,,,``,```,,`,````,``,-`-`,,`,,`,`,,`---
(see 6.5.5);
is the prestressload
is the proofload of the bolt(seetable4
In a pinned joint the parts are connected by a single
pin, which allows rotation. There is no axial load in
the pin, and therefore no clamping action onthe parts
to be connected. pins may not be loadedin single
shear, so one of the nlenlbem to be joined should have
a fork end, or clevis. The pin retaining system, e.g. a
spring clip, shouldbe designed to withstand a lateral
load equal to 10 % of the total shear load on the pin.
6.6.2 Solid pins
PP
P,,
6.6.1 General
The following rules should not be used whenthe line
of action of the load is in a direction other than the
dlrection of the grain flow in the connected parts.
The net areaacross the pin hole, nornd to the axis of
a pin-connected tension member should be at least
1.33pYm/”al and the thickness of the connected
member should be at least pY,,,Il.Gp,df for permanent
installations or pYmIl.4p& for demountable ones,
where
P
pa
df
ym
is the axial factoredload;
is defined in 4.2 for the material of the
connected member;
is the pindianleter;
is the nmterial factor (see table 3.3).
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E5
~~~
STDmBSI BS 8114: PART I-ENGL 1771 m lb21ibb9 0791i571i 5T9 D
BS 811s : Part 1 : 1991
Section G
The n e t nl-t3a o f m y stwion 0 1 1 t9tht.r side of the axis
o f the nltmbcr, nwnsnrt~dn t :u1 mglr of 43" or less to
the asis o f the men1ber. sllould br at lrast 0.9Pym/pi,.
Thr net n-idth of tlw bearing plate a t tlw pin hole,
measul-rd no11nal to the axis of the member, should
not escerd eight times the tldchess of the bearing
plate.
The diameter of the pin hole should not exceed the pin
diameter by more t l m 5 "O.
P111 plates. and any connections between them and the
menlber. should be designed to cany a share of the
total axial load in proportion to the plate's shxe of the
total beaing xea of the pin.
I
6.7 Welded joints
6.7.1 General
Tlus reconuuendation includes welded attachments,
whether or llot they are required to transnut load from
the menlber.
6.7.3 Effect of welding on fatigue strength
The fatigue strength of a joint. depends onthe severity
of the stress concentration, which can arise fromthe
overall geometry of the joint as well as the local
geometry of the weld. Fatigue classifkations of
conmlonly used joint detailsare referred to in 7.3. The
fatigue classificationmay be used to select the detail
appropriate to the application that gives the best
fatigue resistance.
6.7.4 Corrosion
--`,,,,,,`,,,``,```,,`,````,``,-`-`,,`,,`,`,,`---
Joints should be detailedso that inaccessible pockets
or crevices capableof retaining moistureor dirt are
avoided. Where cavitiesare unavoidable, they should
be sealed by weldingor protective compounds, or
made accessible for inspection and maintenance.
The design guidance given here applies onlyto welds
made in accordance with 3.9 of BS 8118 : Part 2 : 1991
6.7.5 Edge preparations
using the reconmended combinations of parent and
fdler matelial given in table 2.8 of this Part.
Edge preparations forwelded joints, includingbutt and
fillet
welds, includingthe use of permanent or
The \-elsath& of welding enables joints between
menlbels to be made in different ways. In selecting the tempomy backing bars, are given in BS 3019 : Part 1
type of joint to be used. the designer should consider and BS 3571 : Part 1. The actual preparation shouldbe
approved as part of the welding procedure. Welding
the follo\ving:
positions are defined in BS 499 : Part 1.
(a) the effect of the joint on the static strength of
the member (see 4.4);
6.7.6 Distortion
(b) the effect of the joint on the fatigue strength of
Every weld causes shrinkage and distortion, andthe
the member (see section 7);
effects are more marked in aluminium construction
(c) the reduction of stress concentration by suitable than in steel. Shrinkage and distortion should be
compensated or balanced so as to nlaintain the desired
choice of detail;
shape
and dinlension of the finished structure.The
(d) the choice of detail that enables good welds to
designer
should consultthe fabricator in the early
be made and properly inspected;
stages of design about weldmg method, distortion and
(e) the choice of detail that avoids general corrosion, related aspects such as welding sequences andthe use
and local corrosion due to crevices (see 4.3 of
of jigs.
BS 8118 : Part 2 : 1991);
6.7.7 Information given to fabricator
(0 the effects of welding distortion.
Drawings and specifications shouldbe provided, giving
6.7.2 Effect of welding on static strength
the followmg infommtion about everyweld
Welding can affect the strengthof the parent metal in
(a) parent and filler material;
the vicinity of the weld, as described in detail in
(b) dimensions of weld (see BS 499 : Part 2 for
section 4.For non-heat-treatable alloysin the O or F
correct
use of symbols);
condition the softening effectis insigrufcant and HAZ
(c) edge preparation andweldmg position;
effects can be ignored. The jointis therefore as strong
as the unwelded parent metal.In heat-treatable alloys
(d) welding process;
in most heat-treated conditions (6 * :i*: and 7 * *
(e) special requirements, suchas smoothness of
series), and in non-heat-treatable alloysin any
weld profde, and the preheat and interpass
work-hardened condition (5 :k 'k series), welding
temperature;
reduces strength. For exceptionsto this general rule
(f) quality control requkments (seeBS 8118 : Part 2)
see table 4.5, & = 1
for
In members made from materialthat suffers strength
(1) weld procedure approv&
reduction, the weld should prefembly be parallel
to the
(2) welder approv&
direction of the applied load; welds transverseto the
applied load should be avoided if possible, or
(3) weld quality class (see notes 1 to 3);
positioned in regions of low stress.
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(4) levels of inspection of welded joints;
(5) acceptance levels for weld quality;
(G) weld repair procedure.
NOTE 1 Where a weld quality class is not specified on the
drawing ‘normal’ weld qualityis assumed.
NOTE 2. Where the actions under factored loading do not exceed
one-third of the factored resistance of the member or joint, e.g.
stiffness may dictate, a lower quality and degree of inspection is
acceptable. This should apply to both static and fatigue resistance.
In this case ‘minimum’ quality level may be specified.
NOTE 3. Where joints are designed on fatigue strength
requirements, refer to 7.8.5.
6.7.8 Butt welds
--`,,,,,,`,,,``,```,,`,````,``,-`-`,,`,,`,`,,`---
Single-sided partial penetration and intermittent butt
welds should notbe used to transmit tensile forces,
nor to transmit a bending monlent aboutthe
longitudinal axis of the weld.
The effectivethroat thickness of a partial penetration
butt weld (see figures GA@) and (c)) should be taken
as:
(a) the depth of weld preparation wherethis is of
the J or U type;
(b) the depth of weld preparation minus 3 mm or
25 Yó, whichever is the less, where this is of the V or
bevel type.
It is also possible to detemke throat thickness by
procedure trials. If this is done the throat thickness
should not be takenas more than the penetration
consistently achieved, ignoring weld reinforcement.
N1 penetration may be assumed in a singlesided butt
weld if a backing plate is used. In a teejoint a
superimposed fillet weldmay be taken into account.
In a line of intemuttent welds there shouldbe a weld
at each end of the part connected.
The design resistanceof a fillet welded jointis
given in 6.9.2.
A fillet weld should be continued aroundthe corner at
the end or side of a part, for a length beyond the
corner of not less than twice the leg length of the
weld. See 4.4.3.6 for the effect of overlapping H A Z S .
If two longitudinal fillet welds aloneare used in a
lapjointed end connection, the length of each should
be not lessthan the distance between them.
The throat of a fillet weld a t ) , see figure 6.2 (a), is the
height of a triangle that can be inscribed within the
weld and measured perpendicularto its outer side.
Exceptionally a fillet weld throat can be takento
include any specified penetration,Pt, provided
procedure trials show to the satisfaction of the
engineer that this penetration can be consistently
achieved. A large throat nmy be assunled if procedure
trials show that the necessary penetration beyondthe
nominal root can be consistently achieved,
by
automatic welding, for example (seefigure 6.2@)).
The effective area of a fillet weld is its throat
dimension @t> multiplied by its effective length, except
that, for fillet welds in holes or slots, the effective area
should not be greaterthan the area of the hole or slot.
Effective length is defined in 6.9.2.
6.8 Design strength of welded joints
6.8.1 General
In the design of welded joints consideration shouldbe
given
both to the strength of the weld metal andto the
6.7.9 Fillet welds
strength of the material in the HAZ adjacent to the
Single-sided fillet welds should not be usedto transmit weld fusion boundary (see 4.4 and figure 6.3). Limiting
moments about their own axes. Intermittent fillet
stresses for the material in the HAZ are referred to in
welds may only be used if the distance between the
6.9. The deformation capacityof the joint is improved
ends of aaacent welds, whether in line or staggered on when the factored resistanceof the weld is greater
alternative sides of the part, does not exceed the lesser than that of the agjacent materialin the HAZ.
of the following:
(a) 10 times the thickness of the thinner parent
nmterial or 300 nun, if it is in compression or shew,
(b) 24 times that thickness or 300 mm, if it is in
tension.
\
Root bead
(4
(b)
Figure 6.1 Effective butt weld throats
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87
_ _ _ _ _ _ _ ~~ ~ ~ ~ _ _ _ _ _ _ _ _ _ _ _ _ ~ ~
STD.BS1 BS 8118: PART L-ENGL 1991 m 1b2rlbbS 079rl59b 3 7 1
BS 8118 :Part 1 : 1991
Section 6
@>
(a)
gris the throat length of weld
g, is the leg length of weld
p , is the penetration
6.8.2 Groups of welds
A welded joint consisting of a group of welds should
be designed on the basis of a realistic distribution of
forces amongstthe welds having regardto their
reMve stiffnesses. It is essential that equilibrium with
the external factored loads is maintained.
6.8.3 Limiting stress of weld metal
The filler wirefor use in welded construction should
be chosen in accordance with 2.5.3.2 and table 2.8.
Values of the linuting stress of the weld metalpw( i
N / m z ) for the pernutted conlbinationsof filler and
parent nmterials, shown in table2.8, are shown in
table 6.2.
Higher values of limitingstress may be needed for
particular filler materials by reference to appendix D.
6.8.4 Limiting stress in the HAZ
Linuting stresses p , and P, for the material in the
HAZ are given in table 6.3, where P, and pw, are the
linuting direct and shear stress respectively.
6.9 Factored resistance of welds
6.9.1 Butt weld metal
A butt weld subjected to shear and axial loading
should be proportional such
that the following applies:
( a l 2 + 3 Q 2 ) l n 5 pw/ynl
where
is the nornd stress perpendicular to the throat
section under factoredl o w ;
52
is the shear stress acting on the throat section
parallel to the axis of the weld under factored
loading;
pw is the linuting stress for the weld metal
(see 6.8.3);
ynl is the nmterial factor for the weld metal
(see table 3.3).
For a butt weld with an oblique tensile load
(see figure 6.4) the factored resistance PRBis given by
the following:
pwzete(l+ 2 cos%) -'h
PRB =
Ym
where
le
is the effectivelength of the weld.
NOTE 1. The effective length of the weld is the total
weld length when end imperfections are avoided by the
use of run-on and run-off plates. Otherwise it is the total
length minus twice the weld width (see figure 6.4);
te
8
is the effectivethroatthickness of the weld
(see 6.7.8);
is the anglebetween the line of the buttweld
and the line of action of the external load (see
figure 6.4).
NOTE 2. The design stress for the weld metal in conlpression nlay
be taken equal to that in tension, except where buckling can
occur.
NOTE 3. Where the parent metal is different in thickness on each
side of the weld, the possibility of a stress concentration effect
should be investigated.
NOTE 4. Where the weld is subjected to in-plane bending the
factored resistance per unit length can be found by omitting I , in
the expression for PRB.
For a joint with no external shear forces and the line
of the butt weld perpendicular to the line of action of
the external load, 6 = go", 52 = O and the factored
resistance is as follows:
o
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For an externalshear load, parallelto the line of the
butt weld, the factored resistanceis as follows:
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O BSI 07-19W
--`,,,,,,`,,,``,```,,`,````,``,-`-`,,`,,`,`,,`---
Figure 6.2 Effective fillet weld throats
STD-BSI BS 8118: PART 1-ENGL 1991
Section 6
1b29bb9
079q597
208
BS 8118 :Part 1 : 1991
I Table 6.2 Limiting stresses of weld metal P,
Parent metal
alloys
I Non-heat-treatable
6464A
1200
3106
N/m2
55
alloys
I Heat-treatable
6261
3103
6464
6061
I
60637 0 2 06083
~~
6082
N/m2
N/nun2 N/nun2
N / m 2N/nun2N/nuu2
N/nm2
N/nu$
190 150 245
255 210 190 200
NOTE.When using dissimilar parent metals the lower of the two limiting stresses for the weld metal should be taken. When welds are
made on parent metals not included in table 6.2 or appendix D the value of the limiting stress for the weld metal should be obtained
experimentally.
a b l e 6.3 Limiting stresses P, and pvzin the HAZ
I
Heat-treatable alloys
Parent alloy
Parent alloy
Condition
supplied
6061
GO63
T6
T4
T5
TG
T4
TG
T4
T4
TG
TG
1200
3103
3015
5083
5154A
5251
5454
PaZ
Pvz
N h 2
N/nun2
15
20
25
90
60
40
55
25
35
40
150
100
70
95
6082
7020
P,
Pvz
N/nun2
145
85
95
95
140
150
170(A)
N/nd
85
50
55
55
85
90
210(B)
180(A)
125
110
145
240(B)
(see note 2)
NOTE 1. All conditions are supplied (see table 4.5).
NOTE 2. For 7020 material refer to 4.4.2.2.for the annlicabilitv of the A and B values.
6.9.2 Fillet weld metal
A fillet weld should be proportioned suchthat the
following expressionis satisfied
(al2+ 3 ( q 2 + q 2 ) ” S 0.85pw/ym
where
P , 01, 72 and ym are as defined in 6.9.1;
r1 is the shear stress acting on the throat section
perpendicular to the axis of the weld.
The relationship between 01, r1 and r2 is governed by
the direction of the external loading action,S, at the
weld (see figure 6.5).
For a simple transversefiiet weld (load applied
perpendicular to the length of the weld) 01 = rl,
r2 = O and the factored resistance is as follows:
where le is the effective length of the weld (asfor butt
welds).
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100
I
For a simple longitudinal fillet weld (load applied
parallel to the length of the weld) 01 = r1 = O and the
factored resistance depends only on r2 as follows:
0.85-PdffJt
pRF =
--`,,,,,,`,,,``,```,,`,````,``,-`-`,,`,,`,`,,`---
Non-heat-treatable alloys (see note 1)
3%ym
where If is the effective length of the fillet weld. The
value of l f is influenced by the total length of the weld,
as indicated in figure 6.6, which provides a guide to
the variation of If with L, where L is the total weld
length. Figure 6.6 is based on the results of a small
number of tests.
When the stress distribution along the weld
corresponds to that in the adjacent parent materialas,
for example, in the case of a weld connecting the
flange and web of a plate girder, the effective lengthis
as for butt welds.If the weld is subjected to in-plane
bending the factored resistance per unit length can be
found by onuttingle, or If in the expression forPKF.
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89
T
a) In-line butt
@) Fillet welded lap
T
T
T
2 ) Tee butt
T
(d) Tee fillet
P
"L
Ii
I
l
pa
I
I
I
T
T
T
I
T
:) Tee butt and tee fillet
Key (see figures 6.1 and 6.2)
W: weld metal (see 6.9.1 and 6.9.2)
F heat-affected zone (fusion boundary)
T: heat-affected zone (
t
o
e
)
for fillets the width of the zone is t
is the failure plane
butts: plane is equal to the plate thickness
fillets: plane width is the width of the leg
length of the weld
The shaded area is the heat affected zone
"
"
J
I-
) Potential failure lines shown on a plan view at the joint end
'igure6.3 Failure planes for static welded joint checks
--`,,,,,,`,,,``,```,,`,````,``,-`-`,,`,,`,`,,`---
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S
E x terna1 loading action
in plane o f plates
Figure 6.4 Butt weld design
action
loading
External
I
--`,,,,,,`,,,``,```,,`,````,``,-`-`,,`,,`,`,,`---
TZ
Weld throat
Effet t i v
cross-sectional
ar ea
Figure 6.5 Fillet weld design
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91
(b) Shear forcein failure plane:
1. o
(1) butts:
VRFB= pvzLt
-(at the fusion boundary)
Ym
'
vRTB = P
f
-
S(
atthe toe, see figure 6.3)
where
L
0.5
Ym
VRFB are the factored shear
andresistances
of a HAZ adjacent
VRTB to a butt weld.
o
10
L
-
50
9,
(2) fillets:
VRFF=
Ym
NOTE. This figure only applies if Wgt < 50.
Figure 6.6 Effective length of
longitudinal fillet welds
(atthe fusion
boundary)
PVZLt
VRTF = Ym
(
a
tthe toe, see figure 6.3 and 6.9.3(d))
where
--`,,,,,,`,,,``,```,,`,````,``,-`-`,,`,,`,`,,`---
6.9.3 Heat-affected zones ( W S )
The factored resistanceof a HAZ adjacent to a weld
(see figures6.1, 6.2 and 6.3) is given by the following.
(a) Direct tensile force normalto the failure plane
(see figure 6.3):
(1) butts:
PRFB=
PRTB
=
Ym
(at the fusion
boundary)
ym (atthe toe, see figure 6.3)
where
are the factoreddirect
andresistances
of a HAZ a a c e n t
~ R T B to a butt weld
P,
is the limiting direct stress in the HAZ;
L
is the total weld
length.
~RFB
(2) fillets
h F F*= P
I'RTF
(atthe fusion boundary)
(
a
tthe toe, see figure 6.3
and 6.9.3(d))
where
pRm
are the factoreddirect
and
resistances of a HAZ ascent
PRTF to a filletweld.
~
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VRFF are the factored shear
of a HAZ adjacent
andresistances
VRTF to a filletweld.
(c) When there is a combined shear and direct force
on the H A Z , these forces should be linutedin
accordance with the following equation:
(~!&/pRz)~i(SflRZ)'
5 1
where
S, and S b
are the extemal loading actions
under factored loading onthe HAZ
in the direct loading and shear;
PRZand VRZ are the factored resistances of the
HAZ in direct loading and shear.
(d) When checking the factored resistanceof a fillet
weld at its toe, note that for thicker sectionsthe
HAZ does not extendthe full thickness and a
snlituer valueof t should be taken (see figure4.6(i)
and 4.4.3.1).
(e) Where the failure planeis subjected to in-plane
bending, the factored resistance canbe expressed in
ternu of resistance per unit length by onuttingL
from the above equations.
(0 Where the failure planeis subjected to in-plane
bending and shear, the factored resistanceper unit
length should be reduced to allow for the combined
effects of shear and direct stress (see 6.9.3(c)).
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6.10 Bonded joints
6.10.1 General
establish the mean and standard deviationof the failing
loads. The factored resistance of a bonded joint, PRG,
is then given by
PRG= (R, - 2SdYnv
where
--`,,,,,,`,,,``,```,,`,````,``,-`-`,,`,,`,`,,`---
Structuraljoints in aluminium may be made by
bonding with adhesive. Bonding needs an expert
technique and should be used with great care
(see BS 8118 : Part 2).
R,
is the mean of the failingloads;
Bonded joints are suitable for carryingshear loads, but
sd
is the standarddeviation of the failingloads;
should not be used in tension or where the loadiig
ym
is the nlaterialfactorforbonded joints (see
causes peehg or other forces tending to open the
table 3.3) and is equal to 3.0.
joint.
Loads should be carried over as large an area as
The ym factor should be increased in relationto the
possible. Increasing the width of joints usually
increases the strength pro rata Increasing the length is loss of performance of adhesive at extremes of
operating temperature and environment.
beneficial only for veryshort overlaps.
6.10.3 Tests
The performance of large bondedjoints can be
improved by reducing peel and cleavage stresses, and
Manufacturer's test data may be used as the most
reducing stress concentrations at the end of laps. It is
optimistic values for initial design. Thesedata are
helpful to taper off the ends of laps and introduce
generally given for thick adherendshear test samples
conlpensation pieces.
as shown in figure 6.7. When only mean strengths are
Bonded joints need to be supported after assembly for quoted, s d should be taken as O.LR,, (see appendix B).
the period necessary to allow the optimum bond
strength of the adhesive to be developed. Entrained air
pockets shouldbe avoided.
Many different adhesivesare available each, generally,
being suitable fora specified range of applications and
service conditions only. The suitabilityof the adhesive
in all resIjects for useon, and for the life of, a
particular structure, should be demonstmtedto the
satisfaction of the designer, who should obtain
specialist advice at all stages of the design and
construction.
A specified jointing system, comprising preparation
of
the adherend surfaces,the adhesive, bondmg and
as
curing processes, should be strictly followed
variation of any step can severely affectthe
performance of the joint.
6.10.2 Factored resistance
The factored resistanceof a bonded joint is influenced
by the following factors:
(a) the surface preparation procedures before
bonding;
(b) the direction of stresses in the joint;
All dimensions are in
millimetres.
(c) the size and shapeof the components to be
joined;
Figure 6.7 Thick
adhered shear test
(d) the thickness of the glue line;
(e) the assenlbly and curing procedures;
(0 the service tenpxahre and environment;
Thin sheet lap tests (see BS 5350 : Part C5) may be
(g) design life.
used for conlparative purposes, durability studies,
surface treatment assessment, curing conditions, etc.
Unless validated test data äre available the strength of
Strength valueswill be low due to the tendency of this
the joint should be establishedby testing. Generally,
joint to peel and will be conservative if used for
sanlple joints should be made at full scale, using the
structural design calculations (see figure 6.8).
sanle manufacturing procedureas for production
joints. These should be tested with sinular joint
construction and loadingto that occurring in the actual
of five tests should be made to
structure. A minin~un~
~
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93
STD-BSI BS 8118: PART 1-ENGL 1991 D Lb2qbb9 079qb02 4T5 I
Section 6
BS 8118 :Part 1 : 1991
I
I
O
--`,,,,,,`,,,``,```,,`,````,``,-`-`,,`,,`,`,,`---
O
@) double overlap joint
(a) single overlap joint
82.53
(c) position of pin hole in joint specimens
All dimensions are in millinletres
Figure 6.8 Thin sheet test specimens
94
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STD-BSI BS 8118: PART 1-ENGL 1991 m LbZ'ibb9 079qb03 331 D
Section 7
BS 8118 :Part 1 : 1991
Section 7.Fatigue
7.1.4 Potential sites for fatigue cracking
Most common initiation sites for fatigue cracks are as
follows:
(a) toes and roots of fusion welds;
(b) machined comers and drilled holes;
(c) surfaces under high contact pressure (fretting);
(d) roots of fastener threads.
7.1 Introduction
7.1.1 General
This section contains ternw specificto fatigue
assessment which are defined in 1.2. The data given in
this section applies to elements formed from
extrusions, plates,sheet and strip. The data should not
be used for castingsor forgings. Designers wishingto
employ castingsor forgings under fatigue conditions
7.1.5 Conditions for fatigue susceptibility
should consultthe nmufacturers.
The
n& conditions affecting fatigueperfornmce are
This section gives recommendations for assessment by
as follows:
calculation alone. Thedata provided may not be
adequate for all applications. In this case additional
(a) High ratio of dyzumic to static load. Moving or
data may be obtained from test. Guidance onthis is
structures, suchas land or sea transport
given in section 8. Test data obtained in accordance
vehicles, cranes, etc.are more likely to be prone to
with section8 may be used as a substitute forthe
fatigue problenlsthan fured structures, unless the
design data given in section 7.
latter are predonlinantly carrying movingloads, as in
the
case of bridges.
7.1.2 Influence of fatigue on design
(b) FFI.equent applications of load. This results in a
Structures subjectedto fluctuating service loadsmay
high
nunlber of cycles inthe design life. Slender
be liable to fail by fatigue. The degree of compliance
structures
or members with lownatural frequencies
with the static limit state criteria given in sections 3
are
particularly
prone to resonance and hence
and 4 nmy not selve as any useful guideto the risk of
magrufication
of
dynanuc stress, even though the
fatigue failure.
static design stresses are low. Structures subjected
It is necessary to establish as early as possible the
predonmtly to fluid loading, such as wind and
extent to which fatigue is likely to control the design.
structures supporthg nlachinery, should be carefully
In doing this the following factors are important.
checked for resonant effects.
(a) An accurate prediction of the full complete
(c) Use of welding. Some commonly used welded
service loading sequence throughout the design life
details have low fatigue strength.This applies not
should be available.
only to joints between members, butalso to any
@) The elastic response of the structure under these
attachment to a loaded member, whetheror not the
loads should be accurately assessed.
resulting connectionis considered to be 'structural'.
(c) Detail design, methods of manufacture and
(d) Complexit3 ofjoint d e t a i l . Complex joints
degree of quality control can havea major influence
frequently result in high stress concentrations due to
on fatigue strength, and should be defined more
local variationsin stiffness of the load path. Whilst
precisely than for statically controlled members.This
these may have little effecton the ultimate static
can have a sigrufcant influenceon design and
capacity of the joint they can havea severe effect on
construction cost.
the member
fatigue resistance. If fatigue is don-t
cross-sectional shape should be selected to ensure
7.1.3 Mechanism of failure
smoothness and simplicityof joint design, so that
Fatigue failure usually initiatesat a point of high stress
stresses can be calculated and adequate standards of
concentration, particularlyif sharp crack-like
fabrication and inspection can be assured.
discontinuities exist there. Fatigue cracks will extend
(e) Enwimment. In certain thermal and chemical
incrementally underthe action of cyclic stress change.
environments
fatigue strength may be reduced.
They normally remain stable under constant load.
Ultimate failure occurs whenthe remaining
cross-section is insufficient to carry the peak tensile
load applied throughout.
Fatigue cracks propagate approximatelyat right angles
to the direction of rnaximum principal stress range.
The rate of propagation is proportional to at least the
third power of the product of the stress range and the
square root of the total crack length. Forthis reason
crack growth is slow in the early stages, and fatigue
cracks tend to be inconspicuous for the major partof
their life. This may give rise to problems of detection
in senice.
7.2 Fatigue design criteria
7.2.1 Design philosophy
It is reconunended that, wherever possible, aluminium
structures are designed on the basis of providing a safe
life. The assessment methodin this section is designed
to ensure that the probability of failure by fatigue
during the structure's life is comparable with that for
other ultimate h u t state modes of failure.
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95
There may be circumstances wherethe severity of
loading, degree of reduhdancy andthe ease of
inspection and repairare such that a fail safe or
damage tolerant approachmay be justified in
economic terms. In this case the safety margins nmy
be reduced from those required fora safe life design.
Guidance on this is given in section 3.
7.2.2 Fatigue failure criterion
The basis of fatigue design used hereis that the
required life will be achieved provided that
frmN 5 K2
where
N
K2
fr
m
is the predictednumber ofcycles to failure
of a stress range fr;
is a constantdependmgon the class of
detail, and ensuresa high probability of
survival (see 7.8.1);
is the principal stress rangeat the detailand
is constant for all cycles;
is the inverseslope of the& - N curvesand
is a constant for most detail classes.
For most practical purposes structural details do not
experience constant amplitude stress histories. The
treatment for general loadingis given in 7.3.
The method of deriving the appropriate stress range@)
fr is given in 7.4 and 7.6. Classifications for more
conmonly used detail types are given in 7.7. Values of
K2 and m are given in 7.8.
Provided that the fatigue strengthdata in 7.8, and the
loading, complies with 7.4, then the overall load factor
yf should be takento be unity.
7.3 Fatigue assessment procedure
A structural member may containa number of
potential fatigue crack initiafion sites. Regions
of the
structure containingthe highest stress fluctuations
and/or the severest stress concentrations would
nomdly be checked first. The basic procedure is as
follows (see figure 7.1).
(a) Obtain an upper bound estimateof the service
loadmg sequence forthe structure’s design life (see
7.4 and appendix C).
@) Estinlate the resulting stress history at the detail
being checked (see 7.5).
(c) Reduce the stress hist~ryto an equivalent
number of cycles (TZ)of different stress rangesf,
using a cycle counting technique(see 7.6.1).
(d) Rank the cycles in descending order of
an@ittlde,frl,fa ... to form a
spectrum
(see 7.6.2).
(e) Classify the detail in accordance with tables 7.1
to 7.3, and 7.7. For the appropriate classifcationand
design stress range (&I, etc.), find the pem-ible
stre=
endurance (NI,etc.) from 7.8.1. Where it has been
decided to use a value of yn,f other than unity, this
should be taken into accountin setting the values of
the design stress ranges (see 3.6.2).
(f) Sum the total danwe for all cycles using Miner’s
summation:
factored design life
The estimated life =
vn
If
:x
-&N
exceeds unity either the stress ranges should
be reduced at that point or the detal should be
changed to a higher class (see 7.7).
7.4 Fatigue loading
All sources of fluctuating stress in the structure should
be identified. Thesenmy arise as a result of the
following:
(a) superimposed moving loads, including vibrations
from machinery in stationary structures;
@) environmental loadssuch as wind, waves, etc.;
(c) acceleration forces in moving structures;
(d) temperature changes.
Loading for fatigue is normally described in tem- of
a design load spectrum, which definesa range of
intensities of a specific live load event and the
number of times that each intensity levelis applied
during the structure’s design life.If two or more
independent live load events are likely to occur then
it will be necessary to specify the phasing between
them.
Guidance on loading specificallyfor fatigue
assessment may be obtained fromBS 2573 (cranes),
BS 5400 : Part 10 Wghway and railway bridges) and
BS 8100 (lattice towers).
Reahtic assessment of the fatigue loading is crucial
to the calculation of the life of the structure. Where
no published data for live loading exist,resort may
have to be n ~ to eobtaining data from existing
structures subjectedto sinular effects. By recording
continuous strain or deflection measurenlents overa
suitable sanlplig period, loading data nmy be
inferred by subsequent analysis of the ,response.
Particular care should be takento assess dynanuc
nmgnifkation effects where loading frequenciesare
close to one of the natural frequenciesof the
structure. Further guidance is given in 8.4.2.
The design load spectrum should be selectedon the
basis that it is an upper bound estimate of the
accumulated service conditions overthe full design
life of the structure. Account should be takenof all
likely operational and environmental effects arising
from the foreseeable usage of the structure during
that period. The confidence linut on the design load
spectrum should be based on mean plus 2 standard
deviation linuts on both amplitude and frequency.
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I
:
-!J"y
Typical load cycle [repeated n times
Loadindesignlife
I
5
PA
pe
Detail X-X
Time
t
Time
(a) Loading sequence
@) Stress history at X-X
\
\
\
'"
'""
(reservoir method I
(c) Cycle counting
..
--`,,,,,,`,,,``,```,,`,````,``,-`-`,,`,,`,`,,`---
I
I c 2
I
1I f r 3
1
fr,
Total cycles i n
factored Life
(d) Stress spectrum
fr
(f) Damage summation
(Palmagren-Miner rule)
fr 1
fr2
fr 3
fr I
N,
Cycles
N2 N, N,
(e) C,ycles to failure
Figure 7.1 Fatigue assessment procedure
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7.5 Stresses
7.5.1 Derivation of stresses
Where the stress response is to be calculated from
specified load events, elastic theory should be usedto
model the structure. Section properties should not be
reduced for HAZ or local buckling effects, butsee
7.5.2(a)(4). Modelling of the elastic stiftñessesof
nlenlbers and joints should be accurate and should
include the effects of any permanent non-structural
material which may mod@ the stiffness. No plastic
redtstribution of stresses should be allowed.
Where stress response data are to be obtained from
strain measurements ona sinular structure, care
should be taken in siting strain transducers to ensure
that the correct stress paranleter is being measured
(see 7.5.2). Further guidance on the measurement of
strain data is given in 8.4.
(5) shear lag, distortion and warping in wide
plated or hollow menlbem;
(6) non-linear out-of-plane bending effects in
slender componentssuch as flat plates wherethe
static stress is close to the elastic critical stress,
e.g. tension field in webs.
The presence of residual stresses may be ignored for
welded joints as these are already included in the
fr - N data. In mechanical joints, provided any
tensile residual stresses are allowed for,that part of
the stress range which is in overall compressionnny
be reduced by 40 %.
FiUet and partid p m t m t i o n butt welds. Cracks
initiating from weldroots and propagating through
the weld throat should be assessed usingthe vector
sum of the shear stresses in the weld metal basedon
an effective throat dimension (see figure7.3).
In lapped joints in one planethe stress per unit
length of weld may be calculated onthe basis of the
average area for axial forcesand an elastic polar
modulus of the weld group for in-plane moments
(see figure 7.4).
In tee-joints any effect of different axial stiffness
along the joint should be taken into account.
Where single filletsor incompletely penetmted butt
welds are subjected to out-of-plane bending
moments the stresses at the root should be
calculated using a linear stress distribution through
the throat (see figure 7.5).
No allowance should berime for bearing contact
on the root face in partially penetrated welded
joints.
(c) Threaded fasteners under axid load. Cracks
initiating at thread roots should be assessed using
the mean axial stress on the core area of the thread.
Where bending is also present the peak stress should
be used, calculated onthe elastic modulus of the
core.
m)
7.5.2 Stress parameters
The stresses to be used in the fatigue assessment
procedures in 7.3 depend on the crack initiation site
and propagation path, as follows.
(a) Parent materid a n d f u u penetration butt welds.
Cracks initiating from weldtoes, fastener holes,
faying surfaces, etc. and propagating through parent
material or fully penetrated weld metal should be
assessed using the nominal principalstress range in
the member at that point.
The local stress concentration effectsof weld profde,
bolt and rivet holes, etc. shouldbe ignored as these
are taken into accountin the& - N strength data for
the appropriate detail class.They do not therefore
need to be calculated (see tables 7.1to 7.3). If
detailed finte element modelsof joints are
calculated the mesh should notbe so fine that local
stresses are used (see also 8.4.4.1).
Other larger geometrical effects which may give
rise
to the non-linear stress distributions in certain
circumstances should be taken into account (see
figure 7.2). Examples of these are as follows:
7.6 Derivation of stress spectra
(1) gross changes in crosssection shape, e.g. at
cut-outs;
7.6.1 Cycle counting
(2) gross changes in crosssection stifmess, e.g. at Cycle countingis a procedure for breaking down a
angled junctions betweenthin wall members;
complex stress history into a convenient spectrum of
cycles in terms of amplitudef, and frequencyn (see
(3) changes in direction or alignment beyond
figure 7.1). There are various methods inuse. For short
those pernutted in tables 7.1 to 7.3;
stress
histories where simpleloadmg events are
(4) secondary bendingstresses arising from joint
a number of times, the reservoir method is
repeated
fMty in lattice structures;
reconunended. It is easy to visualize and simpleto use
(see figure 7.6). Where long stress histories haveto be
used, such as those obtained from measuredstrains in
actual structures (see 8.4) the &-flow method is
reconunended. Both methodsare suitable for computer
analysis.
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O BSI 07-1999
Bs 8118 : part 1 : 1991
Section 7
"
heMioImlmq"
fmm
Away
all structural conne&om or parts
On a member
At
of
any external or internal edge
constant or smoothly
varying cross-section
No holes or
Any apertUre or reemant comer
- ."-
rornem
-Tpenhmnt
""
"
At a lapped or spliced connection
fastened
At a small hole (may Friction grip bolts
Rivets
contain bolt for minor
with:
Bearing bolts
m-)
Hole diameter r3t
z6
I
I
I
All surfaces rolled, extruded or machined to Surfaces machined or Holes drilled or removed
a smooth finish in direction of fr
@undindirection
lbrqued to proof load Cold driven
off,
of bolt
Nuts secured
mechanically or by
Net cross-sectional area
Use stress concentmtion factor for apertures
or reentrant comem
"
M
"
"
bnn=Lmr
1.1
1.2
-panriMdelu
80
Bo
11.3
160
1.4
1.5
1.6
1.7
3s
29
29
17
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STD-BSI BS BLLB: P A R T L-ENGL 1991
l b 2 9 b b 9 0794b08 913 D
I
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--`,,,,,,`,,,``,```,,`,````,``,-`-`,,`,,`,`,,`---
fr = P + M
-Design stress range
A
P - M c
] M
T
-P
Linear stress distribution
assumed.
Weld toe stress concentration
factor not calculated
Crack initiation site
(a) Local stress concentrator
Meannet stress, C
I-LZI
attachment
Non-linear stress
distribution
Design stress atinitiation site,)(
Large aperture or
re -entrant corner
--
@) Large stress concentrator (large opening)
Figure 7.2 Stress parameter for parent material
A
P, and H, a r e forces per unit length
Vector stress
4 4
H,l29,
Figure 7.3 Stresses in weld throats
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105
9
Stressdistribution
due to direct load P
--`,,,,,,`,,,``,```,,`,````,``,-`-`,,`,,`,`,,`---
Lapped a r e a
Stress distribution
due to moment M
NOTE. Maximum shear flux along welds = M a I o
where
Io
d
is polar second moment of area about centroid of weld
group;
is the maximum distance of a point in the weld group from
the centroid
Figure 7.4 Stress in lapped joints
7.7 Classification of details
M
n
The fatigue strengthof a detail is always dependent on
the following factors:
(a) the direction of the fluctuating stress relative to
the detail;
@) the location of the initiating crack in the detal;
(c) the geonletrical arrangement and relative
proportion of the detail.
It may also depend on the following:
(1) the product fornl;
(2) the nlaterial (unless welded);
Figure 7.5 Stresses in root of
(3) the method of fabrication;
fillet
(4) the degree of inspection after fabrication.
Tables 7.1 to 7.3 show the classifications for more
7.6.2 Derivation of stress spectrum
commonly used details. For convenience they have
The listing of cycles in descending order of amplitude
been divided into three basic groups, namely:
fr results in a stress spectrum. For ease of calculation
(i) type 1, non-welded details, see table 7.1;
it may be required to simplify the spectrum into fewer
(ii)type 2, welded details on surface of loaded
bands. A conservative methodis to group bands
member,
see table 7.2;
together into larger groups containingthe same total
number of cycles, but whose amplitudeis equal to that
(iii) type 3, welded details at end connections,see
table 7.3.
of the highest band in the group. More accurately, the
weighted average of all the bands in one group can be The tables are used by identlfylngthe detail in the
calculated usingthe power m, where m is the inverse
figure closest to the one in the structure being
slope of the& - N curve most likelyto be used (see
assessed. The classes forthe particular crack initiation
figure 7.7). The use of an arithmetic mean value w
l
i
sites associated with thatare then checked in the
always be unconservative.
relevant table. In sonle cases particular nwufacturing
or inspection operations nlaybe needed which are
outside those required in BS 8118 : Part 2.
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-
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B
I
Step 1. Determine stress history for
loading event. Identify peak (B)
A
V
-L7 -
Time
Step 2. Move stress history on left of
peak to right
step 3. Fill resulting ‘reservoir’ with
‘water’. Greatest. dept,h is major
cycle
Step 4. Drain at greatest depth. Find
new maximum depth. This is second
largest cycle
Step 5 onwards. Repeat until all
‘water’ drained. Sum of all cycles is
stress spectrum for above history
~
I I I
Cycles
Figure 7.6 Reservoir cycle counting method
--`,,,,,,`,,,``,```,,`,````,``,-`-`,,`,,`,`,,`---
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107
~~
STD*BSI BS 81LB: PART L-ENGL 1991 D lb2'4bb9 0794bL2 3'44 M
BS 8118 :Part 1 : 1991
Section 7
r
r1
"_-
lo-Peak(conservative)
.""_
m = Inverse slope o f
thelog f , l l o g N
Recorded spectrum
curve
spectrumSimplified
(see 7.2.2 and
figure 7.8 or 7.9 1
Original-,
bands
Simplified
ba n-d
I
L
I
I
I
i-q
H
'
I l i
"1 "2
.
II
I
1
I
"3%
Cumulativefrequency
n
Figure 7.7 Simplified stress spectrum
L
7.8 Fatigue strength data
7.8.1 Classified details
The generalized formof the& - N relationship is
shown in figure 7.8, plotted on logarithmic scales. The
design curve represents meanminus 2 standard
deviation level belowthe mean line through
experimental data.
The constant amplitude cut-off stress,&, occurs at
lo7 cycles, below which constant amplitudestress
cycles are assumed to be nondartuging. However,
even if occasional cycles occur abovethis level, they
will cause propagation which,as the crack extends,
will cause lower amplitude cyclesto beconle
damgmg. For this reason the slope of the& - N
m e s ( s e e figure 7.8) is changed to l/(m + 2) between
5 x 106 and 108 cycles for general spectrum loading
conditions.
r'Igble 7.4 Values of K2 and m in figure 7.9
Detail
class
60
50
42
35
29
24
20
17
14
m,
4.5
4
3.5
3.25
3
3
3
3
3
foc
fov
N/mm2
42.0
33.4
26.5
21.3
17.0
14.0
11.7
Nhm2
30.9
24.1
18.7
9.9
6.9
8.2
5.7
2.01 X 1014
1.25 X 1013
9.60 x 10"
2.09 x 10"
4.88 x 1010
2.76 X 1O'O
1.60 x 10'0
9.83 x 109
5.49 x 109
14.9
11.7
9.7
8.1
--`,,,,,,`,,,``,```,,`,````,``,-`-`,,`,,`,`,,`---
NOTE. fr applies to all types of stress range, including fluctuating
compressive stresses.
Any stress cycles below the variable amplitude cut-off
stressfov, which occurs at 10s cycles, are assumed to
be nondamaghg.
It should be noted that the use of the V(m + 2) slope
may be conservativefor some spectra. Where a design
is critically dependent onthis region and where
nlitximum economy is sought it may be appropriate to
consider using component testing (see8.4.4.1) or
applying fracture mechanics analysis. The values of K2
and m are given in table 7.4 for each detail class.
Designf, - N curves are given in figure 7.9.
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.~~
~
STD-BSI BS 8118: PART 1-ENGL 1991
1b24bb7 0 7 7 4 b L 3 200
Section 7
BS 8118 :Part 1 : 1991
7.8.2 Unclassified details
Details not fully covered by tables 7.1to 7.3 should be
assessed by reference to published data where
available. Alternatively fatigue acceptancetests may be
carried out in accordance with 8.4.4.1.
Guidance on the derivation off, - N data, and on
conditions where higher strengths
might be expected,
is given in appendix L.
7.8.5 Workmanship
The maximum pernutted class for classified details in
tables 7.1 to 7.3 represents the maximum fatigue
strength pernuttedby this code forthe detail in
question without further substantiationby test (see
section 8). Where the fatigue stressingat a classified
detail is significantly belowthat pernutied the required
libe less than the maximum pernutted class.
class w
This will always occur when high class details itre
located close to low class details where bothare
experiencing similar stress fluctuations.
The higher class details often require additional
inspection and denmd higher worknxinshipstandards
(see 3.9.9.3 and appendixB of BS 8118 : Part 2 : 1991).
It is important to the economy of manufacture that
inspection and workmsurshipstandards are not
7.8.4 Improvement techniques
dictated by the nlaxinlum pernutted classof every
The fatigue strengthof certain detailtypes shown in
detail, but by the required class. The required class at a
tables 7.1 to 7.3 may be improved by the application of detail is obtained by determining the lowestf, - N
special manufacturing techniques. Theseare generally
curve fromfigure 7.9 where Miner’s sumnmtion is less
expensive to apply and present quality control
than unity (see 7.3(f)). Where stress fluctuations occur
difficulties. They should not be relied upon for general in more than one directionat a detail different class
is particularly criticalto requirements may be found for each directionh order
design purposes, unless fatigue
the overall economy of the structure, in which case
that inspection can be particularly concentrated on
specialist advice shouldbe sought. They are more
those parts of the structure which are critical for
commonly used to overconle existing design
fatigue the following actions should be taken.
deficiencies.
(a) Determine by calculationthose regions of the
The following techniques have been used on
structure where the class requirement exceeds
au
lnmum alloys and are most effective for high cycle
class 20.
applications.
@) Indicate on the detailed drawings at all detailsin
(a) Introduction of compressive residualstresses at
these regions the required class and the direction of
the location of crack initiation. This may be carried
stress fluctuation as shown in figure 7.10.
out at transverse weld toes by peening. At bolt holes
(c) Any drawing which contains a detail with a
the cold expansion methodmay be used.
required fatigue class greaterthan 20 should have
(b) Reduction of stress concentration effect at the
the following general note added
location of crack initiation. This may be carried out
‘Details requiring quality above normalare indicated
by grinding transverse weldtoes to a smooth profile.
with a Fat number and an arrow(see appendix B of
BS 8118 : Part 2 : 1991).’
7.8.3 Low endurance range
In the e n d m c e range between 10-3and 1@a check
should be made that the design stress range from
figure 7.9 does not resultin a maximum tensile stress
that exceeds the static design stress for the detail. This
possibility is indicated by a note on figure7.9.
--`,,,,,,`,,,``,```,,`,````,``,-`-`,,`,,`,`,,`---
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109
~~
~~
~
~~
STD-BSI BS BLLB: PART II-ENGL 3 7 9 1 W IIb2qbb7 07711bL4 L17 m
BS 8118 :Part 1 : 1991
Section 7
+ratter in test data
-o
\
O
U
VI
m
O
*
-IReference strength
I
r'
al
cn
r
C
O
CI C
-----.
L
VI
VI
al
L
ov
c
VI
lo4
zX10
6
sX1o6
10'
Endurance N (cycles 1
10
1 log scale 1
NOTE.
foc
fov
is the constant amplitude cut-off stress;
is the variable amplitude cut-off stress.
Figure 7.8 '1[srpicalf, - N relationship
--`,,,,,,`,,,``,```,,`,````,``,-`-`,,`,,`,`,,`---
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STD-BSI BS 8118: PART L-ENGL 1771 W L b 2 4 b b 9 077qbL5 053 II
Section 7
BS 8118 :Part 1 : 1991
H
W
d
U
h
U
-a
0,
X
N
c
Q
N
E
E
z
c
._
c
c
m
c
E
c
m
al
W
c
W
c
al
'c
W
c
II
m
H
Q
--`,,,,,,`,,,``,```,,`,````,``,-`-`,,`,,`,`,,`---
-
U
111
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1-
Fat 29
I
Fat 24
Fat 24
View X - X
X
Figure 7.10 Method of identification of required fatigue class on
drawings
--`,,,,,,`,,,``,```,,`,````,``,-`-`,,`,,`,`,,`---
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BS 8118 :Part 1 : 1991
Section 8
Section 8. Testing
8.1 General
Where the tests are to be applied to a sinlulation of the
actual structure or to a component the sample should
--`,,,,,,`,,,``,```,,`,````,``,-`-`,,`,,`,`,,`---
A structure or structural conlponent designedin
be mounted in such a way that it will experience the
accordance with sections 2 to 7 of this code need not
normal
restmints to the effects of the conlbination of
be verified by testing but nlay beso verified at the
applied
loads.
nmufacturer’s discretion. Such testing nlay be under
In the circunutances where the combination of applied
static loading (see 8.3), fatigue loading (see 8.4), or
loads, their directions,and orientation of the sample
both.
can produce permutationsof the resistance of the
Verification by testing is appropriate wherethe
that combination whichis expected to give the
sample,
following occur
lowest resistance should be used.
(a) the structure or component is not amenable to
verifcation by analysis or such a procedure is
8.3 Static tests
deemed to be impracticable;
@) materials or design procedures otherthan those
8.3.1 General
referred to in sections 2 to 7 were used;
Static tests are intended to show whether the structure
(c) there is doubt or dmgreement about the validity or conlponent can carrythe unfactored loads (known
of the design method,the quality of nmterial or the
as the nominal loads, see 3.2.2) without exceeding the
quality of the workmanship.
serviceability limitstate, and also whether it can cany
the factored loads(see 3.2.3) without exceeding the
The nlethod and extentof testing shouldbe agreed
ultimate limit state. It is sonletinles appropriateto
between the designer (supplier), andthe engineer
cany out an ultinmte mistance test (see 8.3.5).
responsible for acceptance (purchaser).The methodof
testing should be consistent with the service conditions 8.3.2 Application of loads
for the structure or component and may comprise a
statically or dynanucally loaded resistance test and/or a Loading should be by means of dead weights, force
generating devices,or Wlacement generating devices.
fatigue resistancetest. Tests should be conducted at a
The
method should include force nleasuring devices of
competent facility acceptableto both supplier and
known
accuracy,
purchaser.
Prior to the application of each combination of
The number of samples to be tested should be agreed
nominal loads the sample nmy be loaded and unloaded
between purchaser and supplier
having regard to the
once. The loadingto be applied for this optional
numbers of components to be nmnufactured. Where
‘settling down’ cycle should not exceedthe nonlinal
the number of samples to be tested is to be large a
loads
or such other lower level of loading relatingto a
sufficient numberof samples should be testedto
limiting deformation criterionfor acceptance. The
pernut statistical analysisof the mean resistance and
loading should be nxtintainedfor at least 15 min. It is
standard deviation for each conditionof loading.
recommended that displacements be measured during
Where acceptance of the design depends upon
the settling down cycle. Reloading should not occur
verifcation by testing the purchaser or his agent
within 15 min of removal of the settlung load.
should be afforded the facility of witnessing every test. Anchorages should be checkedfor tightness before
Where verification of the design depends upon testing proceeding with the main test.
a report should be issued describing
in detail (or by
Loading up to the nominal loads should proceed infive
reference to the appropriate British Standard)the
approximately equal increments. Each increnlent
method of testing andgiving all the measured
should be maintained whilst deflection and/orstrain
resistances in the form of a type test certificate
readings are obtained and the sample is examined for
containing at least the information listed in 8.5.
signs of distress. At the fiRh increment (serviceability
h u t ) the deflection(s) andor strajns should be
recorded imnlediakly after application
of the load(s)
8.2 Preparation for test
and again afterthis load level has been maintained for
The sample to be tested, if not the actual structure or
15 min.
component to be destined for service, should represent
The nominal loads should be removed and the
as accurately as possible the design in t e r m of
structure inspected before the application of factored
material properties, dimensions, methods
of jointing,
loads. Loading should thenbe applied incrementally up
and finishes wherethe latter may be sensitive to the
to
the factored load (sometiriles referred
to as the
effects of strain.
’proof
load),
recordhg
deflections
and
behaviour
as
The test sample should beset up in a normal attitude
before. The increase from nominalto factored load
so that the dead loads due to self-weight are operating should be made in at least five increments. The
normally. Where this is not possible the effectsof dead factored load should be maintainedfor 15 nin during
load may be represented by equivalent imposed loads.
which tinle the deflection(s) should be monitored and
the sanlple examined for signsof distress.
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In this condition the consequence for personnelof a
sudden failure shouldbe taken into account and
suitable precautions taken.
The factored loading should be removed after 15 nun
and the residual deflection recorded after a
further 15 nin.
Deflection shouldbe measured by instruments or
recorded autonmtically by systenw of known accuracy.
Load deflection curves should be plotted.
8.4 Acceptance testing for fatigue
8.4.1 Objectives of test
Where there are insufficient data for verification of a
design by calculation alone in accordance with
section 7, supplenlentary evidencenmy be provided by
a specific testing progranune. Testdata nmy be
required for one or more of the following additional
reasons.
(a) The applied loading history or spectrum, for
8.3.3 Acceptance criteria
either single or multiple loads,is not available and is
beyond practical methodsof theoretical calculations
The structure nlay be deemed to meet the
(see 7.4). This may apply particularlyto moving or
serviceability and ultimate l i t state reconmendations
fluid loaded structures where dynanucor resonance
if all the following conditionsare met:
effects can occur. Guidance on methodsof test is
(a) the deflections recorded under the influence of
given in 8.4.2.
the noninal loads should not exceed those
(b) The geometry of the structure is sufficiently
pernutted at the limit of serviceability;
conlplex
that estinutes of member forces or local
(b) there should be no visible evidenceof nonelastic
stress fields are beyond practical methods of
defornlation, instability,or other distress underthe
calculations (see 7.5). Guidance on methods of test
influence of the noninal loads;
is given in 8.4.3.
(c) under the factored loadsthe sample should not
(c) The materials, dimensional details, or methods of
show excessive defornmtion, instabilityor signs of
manufacture of members or joints are different from
inuninent collapse;
those given in tables ‘7.1 to ‘7.3. Guidance on
(d) the residual deflection(s) measured 15 nin after
methods of test is given in 8.4.4.
renlod of all loads should not exceed5 % of the
Testing nlay be canled out on conlplete prototype or
deflection(s) under load.
production structures or on component parts of those
8.3.4 Retest
structures. The degree to which the test stmcture
should nlatch the nlatellals. dimensional details and
Where the tested sample fails to meet the criterion of
8.3.3(d) the test nlay be repeated. If, after a nuximum methods of nmufacture of the fulal production
of 10 applications of the factored load the criterion has structure will depend on the infomation being derived
from the test (see 8.4.2 to 8.4.4).
not been met, the sample should be rejected and the
rejection recorded inthe report with any observations 8.4.2 Derivation of loading data
on the cause of rejection.
The method of obtaining loading data will dependon
8.3.6 Ultimate resistance measurement
the type of structure. Three basic typesare as follows.
The ultimate resistance test is appropriate for type
(a) Fixed structures subject to mechanical loading,
testing when large numbers of sinular structures are
e.g. bridges, crane girclers and machinely supports.
built. It is not part of an acceptance test procedure.
Existing sinular structures subject to the Sanle
loading sources nlay be used to obtain the
Where the test sample is expendable the ultimate
amplitude, phasing and frequency ofthe applied
resistance nmy be obtained by reapplying the factored
loads. Strain, deflectionor accelemtion timsducers
loads in a single increment and then gmdually
fured to selected conlponents which have been
increasing all the imposed loads proportionally until
calibrated under known applied loads can record the
the sanlple is incapable of supporting further load.
force
pattern overa typical working peliodof the
The ultimate load(s) and mode of failure should be
structure,
using analog or digital data acquisition
recorded,
equipment. The conlponents should be selected in
The dtinlate resistance value measured inthe test
such a way that the nuin loading components can
should be aausted t.0 take into account the difference
be independently deduced usingthe influence
between the nlechanical properties and geometryof
coefficients obtained from the calibration loadings.
the test specimen and the ninimunl specified
Alternatively
load cells can be mounted at the
properties and nonunal geonletry. The results should
interfaces
between
the applied load and the
be aausted using the appropriate linutstate fornula in
structure
and
a
continuous
record obtained using
sections 4, 5 and G for the particular failure modein
the
sanle
equipnlent.
question.
The ultimate resistance should not be less than y*,
times the factored load. The value of y,, should be the
value relating to that element of the structure where
failure first. occurs.
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~
~~~
STD.BS1 BS B 1 1 b : PART 1-ENGL L991
Section 8
7T9 M
BS 8118 :Part 1 : 1991
1b24bb9
0794b19
--`,,,,,,`,,,``,```,,`,````,``,-`-`,,`,,`,`,,`---
The n w , stiffness and logarithmic decrementof the 8.4.3 Derivation of stress data
test structure should be within30 % of that in the
8.4.3.1 Component test data
fmal design and the natural frequencyof the modes
Where simple menlbers occursuch that the main force
giving rise to the greatest strain fluctuations should
conlponents in the nlenlber can be calculated or
be within 10 %. If ths is not the case the loading
nleasured easily it will be suitableto test conlponents
response should be subsequently verified ona
containing the joint or detail to be analysed.
structure made to the final design.
A suitable specimen of identical dinlensions to that
The frequency component of the load spectrum
used in the final design should be gauged usinga
obtained from the working period should be
convenient method suchas electric resistancestrain
nlultiplied by the ratio of the design life to the
gauges, moiré fringe pattern or thermal elastic
working period to obtain the fínal design spectrum.
techniques. The ends of the conjponent shouldbe
Allowance for growth in anlplitude or frequency
sufficiently f a r from the local asea of interest that the
during the design life should also be made as
local effectsat the point of application of the applied
required.
loads do not affect the distribution of stress at the
o>) Fixed structures subject to environmental
point. The force components andthe stress gradients
loading, e.g. nlasts, chinmeys and offshore topside
in the region of interest should be identicalto that in
structures.
the
whole structure.
The methods of derivation of loading spectrum are
Influence coefficients can be obtained from statically
basically the sanle as in 8.4.2(a) except that the
working period will generally needto be longer due applied loads which will enablethe stress pattern to be
detemmed for any desired combination of load
to the need to obtain a representative spectrum of
component. If required the Coefficients can be obtained
environmental loads suchas wind and wave loads.
from scaled down specinlens providedthe whole
The fatigue damage tendsto be confined to a
specific band inthe overall loading spectrum dueto conlponent is scaled equally.
effects of fluid flow induced resonance.This tends
8.4.3.2 Structure test data
to be very specific to direction, frequency and
damping. Forthis reason greater precisionis needed In certain types of structure such as shell stmctures
the continuity of the structural materialmay make it
in simulating both the structural properties( n w ,
stiffness and damping) and aerodynamic properties impracticable to isolate conlponents with simple
applied forces. In this case stress data should be
(cross-sectional geometry).
obtained from prototypesor production structures.
It is reconmended that the loading is subsequently
Similar methods for nleasurement maybe used as for
verified on a structure to the final design if the
component testing. Formost general use it is
original loading data is obtained from structures
with a natural frequencyor danlping differing by
reconmended that static loadsare applied as
more than 10 %, or if the cross-sectional shapeis not independent conlponents so that the stresses can be
identical.
combined using the individual influence coefficients for
the
point of interest. The loading should go througha
A final design spectrumcan be obtained in tern^ of
shakedown cycle before obtainingthe influence
direction, amplitude and frequencyof loading,
coefficient data.
suitably modified by conlparing the loading data
during the data collection period with the
8.4.3.3 Verification of stress historu
meteorological records obtained over a typical
The sanle method as described in 8.4.3.2 may be used
design life of the structure.
to
venfy the stress history at a point during prototype
(c) Moving structures, e.g. road and rail vehicles, and
testing
under a specified loading.In this case data
boats.
acquisition equipmentas used in 8.4.2(a) should be
In these types of structure the geometry of the riding used to record either the full stress history or to
surface should be adequately defined
in term of
perform a cycle counting operation. Thelatter can be
shape and amplitude of undulations and frequency, used to prehct life once the appropriate& - N curve
as this will have a sigruficant effect on the dynandc has been chosen.
loading on the structure. Other loading effects such
A further option, which nlay be usedin the case of
as cargo on and off loading can be measured using
uncertain load histories, is to keep the cycle counting
the principles outlined in 8.4.2(a).
device permanently attachedto the structure in
Riding surfaces such as purpose-built test tracksmay service.
be used to obtain load histories for prototype
designs. Load data from previous structures should
be used with caution, as snlall differences,
particularly in bogie design for example, can
substantially alter the dynanlic response. Itis
reconmended that loading is verified on the final
design if full scale fatigue testingis not to be
adopted (see 8.4.4).
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8.4.4 Derivation of endurance data
8.4.4.1 Component testing
Whenever force spectra or stress history data are
known conlponent testing can be done to ver@the
design of critical parts of the structure. The conlponent
to be tested shouldbe nmufactured to exactly the
sanle dimensions and proceduresas are intended to be
used in the final design.All these aspects should be
fully documented before nunufacture of the test
conlponent is carried out. In addition any method of
non-destructive testing andthe acceptance criteria
should be documented, together withthe inspector’s
report on the quality of the joints to be tested.
The test specinlens should be loadedin a sinular
manner to that described in 8.4.2(a). Strain gauges
should be used to verify that the stress fluctuations are
as required. The sitingof strain gauges should be such
that they are recording the correct stress parameter
(see 7.5). If the nonlinal stress is being recordedthe
gauge should beat least 10 null from any weld toe.
Where the stress gradient is steep three gauges should
be used to enable interpolation to be carried out.
In order to obtain anfr - N curire for design purposes
a minin~un~
of eight identical specimens should be
tested to give endurances in the range 103 to l@
cycles. Testing should be carried out with reference to
the appropriate proceduresin BS 3518. A mean curve
should be calculated and a design curve obtained
which is parallel to the mean curve but not less than
two standard deviations awaynor greater than 80 % of
the strength value, whicheveris the lower. This allows
for wider variationsin production than is normally
expected in a single set of fatigue specimens.
For danmge tolerance designsa record of fatigue crack
growth with cycles should be obtained.
Alternatively, if the design stress history is known and
a variable amplitude facilityis available the specimen
nlay be tested underthe unfactored stress history.
8.4.4.2 Full scale testing
Full scale testing may be carried out under actual
opemting conditions,or in a testing facility with the
test load conlponents appliedby hydraulic or other
methods of control.
The conditions for nmwfacturing the structure should
be as for component testingin 8.4.4.1.
The loads applied should not exceed the nominal
loads.
Where the service loads vary in a random n w e r
between limits they should be represented by an
equivalent seriesof loads agreed betweenthe supplier
and the purchaser.
Alternatively, the test load(s) should equalthe
unfactored load(s)
The application of loads to the sample should
reproduce exactly the application conditions expected
for the structure or conlponent in service.
Testing should continue until fracture occurs or until
the sample is incapable of reacting to the full test load
because of damage sustajned.
The number of applications of test load(s) to failure
should be accurately counted and recorded with
observations of the progressive developnlent of
defects.
8.4.5 Acceptance
The criterion for acceptance depends upon whether
the structure is required to give a safe life performance
as
(see (a)), or damage tolerant perfomlance (see
follows.
(a) In a safe life design the d e t e m w g linut state is
that defined in 3.6.2. For acceptancethe life to
failure determinedby test, @usted to take account
of the number of test results available, should notbe
less than the factored design lifeas defined in 3.6.2,
as follows:
Na L factored design life
F
where
m))
N,
F
is the logmeanlife to failure;
is a factordependentupon the effective
number of test results available, as
defined in table 8.1.
(b) In a damage tolerant designthe deternlining limit
state is that defined in 3.6.3. Acceptance is
dependent upon the lifeof a crack reaching a size
which could be detected bya method of inspection
which can be applied in service. It also depends on
the rate of growth of the crack, critical crack length
considerations, andthe implications forthe residual
safety of the structure and the costs of repair.
Criteria for factoring the measured life and for
acceptance will vary from one applicationto another
and should be agreed with the engineer responsible
for acceptance.
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~
Lb24bb9 079Vb21 357 D
STD-BSI BS B11B: PART 1-ENGL 1991
BS 8118 :Part 1 : 1991
Section 8
Table 8.1 Fatigue test factor F
Number of samples tested
L
2
Identical samples all tested to failure. All
3.80
sanlples failed, factors on log meanassunkg
population standard deviationas log 0.176
Identical samples all tested sinwltaneously. 3.80
First sample to fail with population standard
deviation assunledas log 0.176
3.12
2.67
9
10
2.55 2.73
2.48
2.44
2.40
1.75
1.54
1.54
8
1.60
'Fi
(h) m m w of loads and defornmtions andE;tress at
At the conclusion of any testing performedin
accordance withthis section a type test certificate
should be compiled containingthe following
information:
(a) name and addressof the test house;
(b) accreditation referenceof the test facility (where
appropriate);
(c) date of test;
(d) name@)of witnesses;
(e) description of sanlples tested by:
(1) reference to serial number where appropriate;
or
(2) reference to drawing nunIber(s) where
appropriate; or
(3) description with sketches or diagranw; or
(4) photographs;
(f) description of load systenls applied including
references to other British Standards where
appropriate;
(g) record of load applications and measured
reactions to loading, i.e. deflection, strain, life;
O BSI 07-1990
2.01
6
-
8.5 Reporting
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citica~acceptance points, correspondingto the
acceptance criteriaas defined in 8.3.3
(i) record of ultinmte load and nlode of failure;
record of locations of observations by reference
t.4) (e)(2),(ex31 or (eI(4);
(k) notes of any observed behaviour relevantto the
safety or serviceability of the object under test, e.g.
nature and locationof cracking in fatigue test;
(l) record of environmental conditionsat time of
testing where relevant;
(m) statenlent of validation authority for all
measuring equipment used;
(n) definition of purpose or objectives of test;
(o) statenlent of compliance or non-conlpliance with
relevant acceptance criteriaas appropriate;
(P) record of names and status of persons
responsible for testmg and issuing of report;
(Cr>
report serial number and dateof issue.
a)
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Results of test
117
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STD=BSI BS BLLB: PART L-ENGL L991 m Lb2rlbbS 0794b22 293
BS 8118 :Part 1 : 1991
Appendix A
Appendices
A.2.4 National variations
National variations of wrought alunmun~and wrought
aluminium alloys registered byanother country are
A.l Introduction
identified by a serial letter afterthe numerical
designation. The serial letters are assigned in
Complete information on the nomenclature of
alphabetical sequence startingwith A for the first
structural wrought aluminium productsis to be found
I, O and Q.
in the British Standards for wrought aluminium alloys national variation registered, but omitting
for general engineering purposes. The nomenclature A.3 Temper or condition
for casting alloysdoes not follow the same
A.3.1 General
nomenclature systemas wrought alloys and reference
should be made to BS 1490. The following notes,
The designation for the temper or condition of the
however, serveas a general guidefor wrought alloys.
aluminium or aluminium alloy is indicated by a letter
which may be followed bya number or numbers. This
A.2 Alloys groups
part of the designation followsthe alloy group
A.2-1 General
designation andis separated by a hyphen.
The first part of an alloy designation indicatingthe
A.3.2 Non-heat-treatable allogs
alloy group consists of four digits as follows:
The non-heat-treatable alloys (e.g.5083) are those for
strain
which strength can be increased only by
(a) A l u n ~ u m99.00 % (dm)
l***
hardening. This s
t
&hardening may be deliberate, as
n m u m and greater
in the stretch straightening of an extrusion, or due to
@) Aluminium alloys groups by mqor
forming or other cold working of a finished product.
alloying elements
The tempers of non-heat-treatableproducts are
identified by the following suffiï letters and symbols:
2
*
*
*
(1) Copper
(2) Manganese
3***
F As fabricated. Thistemperdesignation
(3) Silicon
4***
applies to material which acquires some
(4)Magnesium
5***
temper
from shaping processes in which
(5) Magnesium ‘and silicon
6***
there is no special control over thernd
(6) Zinc
7***
treatment or amount of strain hardening. For
( 7 ) Other element
B***
wrought products there are no mechanical
(S) Unused series
properly huts.
9***
Appendix A. Nomenclature of aluminium
products
O Annealed. T ~ temper
N
designationapplies to
A.2.2 11 S 1 group
material which is fully annealed to obtain the
In the l*
group for minimum purities of
lowest strength condition.
a
u
ln
M
u
n
lof 99.00 % ( d m )and greater,the last two
of the four digits inthe designation indicatethe
H Strain-hardened. This temperdesignation
minimum aluminium percentage. These digitsare the
applies to nlaterial subjected to the
sanle as the two digits to the nght of the decimal point
application of cold work and partial
in the minimum aluminium percentage when itis
annealing (or hot forming),or to a
expressed to the nearest 0.01% ( d m ) .
combination of cold work and partial
annealing or stabilizing, in order to achieve
The second digit in the designation indicates
the specified mechanical properties. TheH is
modifications in impurity limits or alloying elements. If
always followed by two or more digits
the second digit in the designation is zero, it indicates
indicating the fmal degree of strain-hardening.
unalloyed aluminium having natural impurity linlits:
integers 1 to 9, which are assigned consecutively as
needed, indicate special control of one or more
The first digit following the H indicates the specific
individual impurities or alloying elements.
combination of basic operationsas follows:
A.2.3 2 b 1 1to 8
groups
H l Strain-hardened only. This temper
Inthe2*fc*toS8**~upsthelasttwoofthe
designation appliesto material subjectedto
four digits in the designation haveno special
the application of cold work after annealing
sigruficance but serve onlyto identify the different
or hot forming.
aluminium alloys inthe group. The second digitin the
If the
alloy designation indicates alloy modifications.
H2 Stmin-harde)2ed and partially annealed. This
second digit inthe design is zero, it indicatesthe
temper designation appliesto achieve the
origml alloy. Integers 1 to 9, whch are assigned
specified mechanical properties.
consecutively, indicate alloy modifications.
H3 Strain-hardenedandstabilized.
**
***
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The second digit (2,4,6 or 8) following the Hl or H2
designation indicates the degreeof strain-hardening in
ascending order of temper.
The effect of heating these nmterialsis to reduce their
strength. Strength can only be recovered by further
strain-hardening.
A.5 Temper nomenclature for alloys in
standards which have not adopted the IS0 2107
alternative temper designation system
A.5.1 General
Those alloys covered by British Standards which have
not adopted the IS0 2107 alternative temper
designation system use the following existing British
Standard temper designation system.
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A.3.3 Heat-treatable alloys
The heat-treatable alloys(e.g. 6082) derive enhanced
strength from either oneor two stages of heat
A.5.2 Non-heat-treatable alloys
treatment. The first stage, solution heat treatment,
The temper of non-heat-treatable products are
consists of heatmg the material thoroughly to a
identified by the following suffm letters and symbols:
prescribed high tenlperature and then quenching in
it
cold water, the quench increasesthe strength
O
annealed
Softest,
i.e.
considerably fromthat of the hot, annealed condition.
The second stage, precipitation heat treatment,or
M
As manufactured,
i.e.
partly
hardened
ageing, when the material is kept for a prescribed time
in
the
0rduw-y
course
of manufacture
at a prescribed moderate tenlperature, producesa
further increase in strength. With some alloys ageing
H2 to H8 Progressivedegrees of hardness
occurs naturally after somedays or weeks at room
temperature, so that the second fornml heat treatment
A.5.3 Heat-treatable alloys
may be discarded. The conditionof a heat-treatable
product is identified by the following suffii letters and The condition of heat-treatable productis identified by
symbols. For full details andother subdivisions see
one or two suffiw letters as follows:
BS 1470 and BS 1474.
O
Annealed
F
As fabricated,with no fornd heat treatment
T4Solutionheat-treatedandnaturallyaged
Cooled from an elevated tenlperature shaping
process and then artificially aged
TG
Solutionheat-treatedandthenartificially
aged
T8
Solution heat-treated, cold worked and then
artificially aged.
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M
As manufactured,withnofornlalheat
treatment
heat-treated
to
(TB7 solution heat-treated and stabilized, applies
Castings)
TF N l y , i.e. two stage, heat-treated
TE Artificially aged without prior solution heat
treatment
A.4 Examples of alloy and temper nomenclature
Examples of alloy and temper nonlenclature are as
follows:
@) GO82-TG
Annealed
TBSolution
T5
(a) 5154A-H24
O
Indicates the non-heat-treatable
nugnesiunl bearing rough alloy
5154 with a national variation,
which has been strain-hardened
and partially annealedto achieve
the specified mechanical
properties fora temper half way
between the annealed and fully
hardened tenlper condition.
Indicates the heat
treatable
magnesium-silicon wrought alloy
6082, in the fully heat-treated
foml.
TH Solution heat-treated, cold worked and then
artificially aged
A.5.4 Examples of alloy and temper
nomenclature
Examples of alloy and temper nomenclature are as
follows:
(a) LM25-lX
Indicatestheheat-treatable
magnesium-silicon casting alloy
LM25 with precipitation heat
treatment only.
@) 7020-TF
Indicates the heat-treatable zinc
bearing wrought alloy7020 in the
fully heat-treated fornl.
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119
~~
~~
~
~~~
STD.BSI BS 8118: PART 1-ENGL L771 m 1b2rlbb9 077qb24 Obb m
BS 8118 :Part 1 : 1991
Appendix A
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A.6 Foreign equivalents to British Standard
alloys
Table A.l lists the nearest foreign equivalentsof the
British Standard wrought andcast alloys referred to in
tables 2.1 and 2.2. They are not necessarily exact
equivalents, and for detailedinformation on their
conlpositions and properties reference should be nlade
to the relevant national standards. The formerBritish
Standard designations forthe alloys listedin tables 2.1
and 2.2 are also given.
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Appendix A
h
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3103
AlMnl
3106
AlMn0,5M@,5
5083
AlMg4,5MnO,7
5154A AlMg3,XA)
5251
AlMg2
6454 Al Mg3Mn
6061
AlMglSiCu
Bs 8118 : Ihrt 1 : 1-1
N3
N31
NB
N5
N4
N51
6063
AlMg0,751
H20
H9
WS2
AlSilMgbfn
AlZn4.5Mgl
AlMg6Sil
H30
H17
LM6
7020
LM6
3103
AlMn
3106
5083
ALMg4,5Mn
5154A
5251
54546061
-
-
-
6063-
6082-
-
AlMIll
P-AlMn1.2
iuMno,5M@,5
AMg4,5Mn
P-AlMg4,5
-
5083
5154
5251
5083
5454
8081
5454
6061
3106
6083
5154
U51
5454
6061
-
BOB2
7020
Albl@il
GS40
AG6
GAI&@
P-AlblgZbín
P-AlM@,"n
P-AlMglsKxl
P-Al Si0.5Mg
P-AISilMgMn
P-AIZn4,5Mg
GAlMlg
SUN
A413
GALS112
GAlSi13
6063
8082
7020
514.1
AIZn4,SMgl 7020
GAM@
S
G
W
A4132
GAlSi
SG AlSi12
-
-
-
356.2
-
357.1
SG AlSi7Mg
A3105
AMY13
A5154
Ab@Mn0,3
AIMg2,7Mn
ALMglSiCu
-
DG ALSll2Fe
A356.2
-
Sc 70N A-S7G
GAISI7Mg
S 7 0 A-S7009
A-S7GO6
GAlSI'IMgW,
A5464
A6061
A6063
-
Am01
ADcGClAV
FIAS AG7A
D N DIS
A D c l c3Av
c3As Ac3A
C4CVC4CS
AoIcAC4CH
oIcIK3
L-38111Al-IMn
L383l/Al-O,5"g
L332UAI4,5Mg
LrnAI-3,5Mg
L33611Al-ZMg
L3391/Al-3Mgbln
L342WAl-lMgSicu
L-3441/AI-O,7M@i
L3453IAl-Isi"n
L37411AI-4ZnlMg
L2331
GAISil3
A4132
I
GAlSi7m
A367.2
I21
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Appendix B. Formal statement of safety
factor format adopted in the code for
static design resistance calculations
where
R, is the mean resistance based on calculations
using the arithmetic meanof material
strength test results;
B.l Nominal load
v
is the relativemeanquadraticdeviation of
The nonWal load, or characteristic action(Fk) is that
the distribution of material strength found by
value of the applied load whichhas an expected return
tests, or the coefficient of variation of the
period of not less thanthe specified design life of the
distribution function;
structure, (often obtained from loading specifications).
k
is a coefficientdepending on the probability
B.2 Factored load
distribution function.
The factored load,or design action P d ) is deternwed
B.5
Factored
resistance
from the nominal load bythe following relationship:
The factored resistanceor design resistance@d ) is
F d = Yf F
K
determined fromthe relationship:
where
y
is the load factorfor the load in question.
Rk
Rd = ym
B.3 Action-effect under factored loading
where
The acticn-effect under factoredloading, or design
Ym
is the nlaterial strength factor.
actim-effect(sd) is the effect of the factored load,or
B.6
Verification
of structural adequacy
combination of factored loads onthe structural
For a satisfactory design,the following relationship
member (forces, moments, etc.)
should be satisfied:
B.4 Nominal resistance
Rd >
(see
figure B.l)
The n o n w resistance, or characteristic resistance
where
(Rd is defined by the relationship:
yc is the factor for consequences of failure
(taken as unity for nornlal applications).
Rk = &n (1 - h),
Action - effect
under factored load
I
I
Nominalresistance
Resistance R
Figure B.l Ultimate limit state criterion
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Factoredresistance
123
Appendix C. m i c a l values of design life
D.2 Limiting stress for weld metal
The fatigue assessment procedure (see7.3) requires a
design l i e for the structure. When this Me is not
specified by the client, the designer may use the typical
values @ven in table
C.l
D.2.1 Enhanced values of p ,
The values forthe weld metal limitingstress P, in
table 6.2 are based on test results for butt-welded
specimens. With certain of the permitted filler alloys it
is found that higher weld strengthsthan those given in
table 6.2 apply. In order to take advantage of this in
design it is permissible to take P, from table D.l,
instead of table 6.2.
It is emphasized that these higher valuesare only valid
if every precautionis taken to avoid cracking.
rlhble C.l Qpical values of design life
Structure
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Highway bridges
Flood protection works
Buildings, prinwy structure
Breakwaters
Lattice towers and nlasts
Tall towers
Railway vehicles
Building cladding
Boats
Cranes
Containers
Vehicle bodies
Scaffolding
1
Design life
Years
120
100
100
GO
50
50
35
30
30
20
15
10
10
Appendix D. Derivation of material
limiting stresses for use in design
D.l Limiting stresses for parent metal
D.2.2 Determination of p , for other material
When welds are made on parent alloys not covered in
table D.l, the limiting weld metalstress P, should be
obtained experinlentally.
D.3 Limiting stress for H A Z material
D.3.1 Basic expressions
The limiting stresses P, and pw for HAZ material used
in the design of welded joints, as listed in table 6.3, are
based on the relevant expression fromthe following.
These expressions may be employedfor materials not
covered in that table.
(a) Heat-treatable material:
P, = kz'Pa
P, = 0.GPa.Z
where
P,
given by table 4.1or by D.l;
NOTE. See sections 4 and 5.
The linutingstresses P,, pa and pv used in the design
of menlbers, as listed in tables 4.1 and 4.2, are based
on the following expressions. These expressions nlay
be employed to obtain po, Pa and p, for nlaterials not
covered in tables4.1 and 4.2.
is the linuting stress for parent metal, as
is the modified softening factor found
k'
from F.2.
@) Non-heat-treatable material:
P, = L2fm
P, = 0 . G h
where
f02
wherefo.2 andf, itre nomdly taken as the guaranteed
mininlunl tensile 0.2 % proof stress and tensile strength
of the material respectively. When no guaranteed value
is quoted for one or both, assumed valuesmay be used
for& and fu as follows:
(1) values equalto 80 % of the typical values given
by the nmufacturers; or
(2) the values for the sune nlaterial in the
O condition.
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is the guaranteed minimum 0.2 % proof
stress for the parent metal concerned,if
it is in the annealed O condition. When
only a typical value of f0.2 is available, a
figure equalto 80 % of this should be
used in the expression forP,.
D.3.2 7% *seriesmaterial
The alternative valuesA and B for P, and P, are
obtained by using the relevant value of k; in D.3.l(a).
The value of k; is normally as given in F.2. When
finding valueA, however, it is sometimes possible to
take a more favourable valueof Ici This applies when
either of the following occur
(a) a single pass weld is laid in isolation; or
@) stricter thermal controlis exercised than that
normally called for in BS 8118 : Part 2.
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1
a b l e D.1 Limiting stress pwfor weld metal
Filler
Parent metal
I Heat-treatable
Non-heat treatable
31031200
5251
6454
5164A
3106
1080A
5083
I
6063
6061
6082
1
MOA
215
190
190
205
215
220
5056A
5556A
55541)
210
l) These alloys should be used in conditions where corrosion is likely to be a problem.
NOTE. When using dissimilar parent metals the lower value of the two limiting stresses for the weld metal should be given.
I
E.2 Elasto-plastic stress pattern
Appendix E. Elasto-plastic moment
calculation
An idealized elasaplastic stress pattern is constructed,
based on an assumed nlaterial with sudden yield atpo
E.2.1 Rules for constructing stress pattern.
--`,,,,,,`,,,``,```,,`,````,``,-`-`,,`,,`,`,,`---
Refer to F.2.3, cases 1 and 2.
(instead of the true st-strain
curve). w i c a l
E.l General
examples appear in figure E.l. The rules for
This appendix gives an alternative method for
constructing such a pattern are as follows.
obtaining the factored moment resistanceMm of
(a) Calculations shouldbe made using a net section,
slender and senu-compact beam sections, which
nmy
with deductions for holes, but with no reductionin
be used instead of 4.6.2 or 5.4.2.
thickness to allow for HAZ or local bucklig effects.
The elasto-pla&c method presented will prove
(b) Elements are classified in accordance
advantageous for sectionsin which a critical element
with 4.3.3.4 (but see note).
for local buckling, havinga pvalue roughly in the
(c) The limiting compressivestress P , in a slender
(see table4.3),contains compressed
region of
element is found thus:
material that lies nearerthe neutral axis than do the
outermost tension fibresof the section. m i c a l
Pm = ~ L P O
examples are sections in which
where
(a) the extreme compression material, incorporating
P, is the limiting s
t
r
e
s for material (see tables 4.1
a critical flange element, lies nearerto the neutral
and 4.2);
axis than does the extreme tension nlaterial (see
kL is the local buckling factor foundas in 4.3.4.2
figure E.l(a)): or
(but see note).
(b) a critical web element terminates some distance
For a longitudwy stiffened web different valuesof
in from the extreme compression face, dueto the
P m will in general be thus obtained forthe various
presence of a tongue-plate (see figureE.l@)).
sub-panels, based on their differingk~ values
NOTE. The use of this appendix may prove disadvantageous when
(see 5.4.4.2).
applied to sections in which the critical element is very slender
(d) The stress pattern should be such that the total
Co * ßo).
force in compression balances that in tension.
3
/,
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125
~~~
~
STD-BSI BS 8118: PART J-ENGL 1991
BS 8118 :Part 1 : 1991
(e) On the tension side the extreme fibrestress
should not exceedP,. It is pernissible for plasticity
to spread in from this face.
(f) On the conlpression sidethe stress in any
element should not exceeda limiting valuep as
follows:
(1) fully compact or semi-compact element,p = po;
(2) slender element, p = Pm.
(g) It is permissible for plasticity to spread in from
the compression faceof the section, only if the
compression flangeis fully compact.
(h) For a section witha fully compact compression
flange, and witha tongue-plate ascent to the
compression edgeof a semi-compact or slender web
(see figure E.l(b)), the distance that plasticity may
spread in from the compression face is limited as
follows:
(1) senucompact web: plasticity to to extend
beyond the compression edge of the web.
(2) slender web: rule f(2) to be satisfied for the
web.
In any HAZ region the stress should be reduced
to Mo,if this is less than the general stress level
therein. It is not pernutted to use
u)
u.
NOTE. In applying rules @) and (c) the value E should always be
determined using the expression in note 1 of table 4.3. The
modified E value given in 4.3.3.5 or note 3 of 4.5.2.3 is not valid
for use with this appendix.
E.2.2 Hgbrid sections
In applying E.2.1 to a hybrid section, fabricated from
components of differing strength, itis helpful to
Emember that the strain distribution will be linear
right across the section. This has the following
implications forthe assumed stress pattern.
(a) In the elastic zone the stress varies linearly either
side of the neutral axis, without steps.
(b) In any plastic zonethere will be a stepchange in
stress between nlaterials of different P,.
(c) At the junction betweenthe elastic and plastic
zones there will also be a step, if this junction
coincides with a change in nuterial.
~~
~
ItbZ'ibb9 0794bZ9 b'i8 W
Appendix E
E.3 Calculation of moment resistance
E.3.1 General
The factored moment resistanceMB is found as
follows:
MRS= M u h m
where
Mu is the ultinlate moment found from E.3.2 or
E.3.3;
y,,,
is the material factor (see table 3.3).
E.3.2 Slender sections
Mu is taken as the moment correspondingto the
adopted stress-pattern (see E.2).
E.3.3 Semi-compact sections
Mu is found by interpolation as follows:
MU=M,+"-
ßo -
ß o - P1
(Md - IVus)
where
Mus
Muf
ß
ß1 and ßo
is the moment
corresponding to the
adopted stress pattern (see E.2.1);
is the moment
value
obtained
if the
section is treated as fully compact;
is the value o f ß for the critical
element;
are the fully compact and
semi-compact limiting values of ß for
that element (see table4.3).
NOTE. The limitations on the spreading in of plasticity from the
compression face of the section, contained in E.2.1 (rules (8)
and (h)), relate to the determination of M
,
. When the ultimate
moment Mu acts, there will generally be an increased spread of
plasticity.
--`,,,,,,`,,,``,```,,`,````,``,-`-`,,`,,`,`,,`---
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I
~~
STD-BSI BS 8118: PART 1-ENGL 1991
Appendix E
l b 2 4 b b 7 0774b30 3bT
BS 8118 :Part 1 : 1991
Critical element
e-f
neutral
--`,,,,,,`,,,``,```,,`,````,``,-`-`,,`,,`,`,,`---
Elastic
Compression
P
Criticalelement
@I
Line 1: critical element is semicompact.
Line 2: critical element is slender.
Figure E.l. Assumed elasto-plastic stress patterns (non-hybrid)
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127
--`,,,,,,`,,,``,```,,`,````,``,-`-`,,`,,`,`,,`---
F.2.2 k,for other materials
The softening factor(IC,or k$) may be found using
F.1 Introduction
El.
table F2 for materials not covered in tables 4.5 and
F.l.l General
F.2.3
7*
*series
material
The methods provided in 4.4 for estinming the severity
At welds in such alloys with tensile stress acting
and extent of HAZ softening adjacentto welds will
sonletimes tend to be pessimistic. This appendix gives transverse to the weld axis, the softening factor
alternative treatments for such cases, which produce
(k,=k$)should be taken as value A. For other stress
more favourable valuesof k, (severity, see F.2) and z
conditions valueB may be used.
(extent, see F.3).
Value A should nornmlly be takenas in the relevant
The possible benefits of post-weld artificial ageing
are
table (table4.5 or table El). However, a more
considered in F.4.
favourable valueis allowed in the following cases:
As an altemativeto calculation it is pemuible to find
(a) Case 1. Isolated straight singlepass weld without
the extent of the HAZ experimentally by means of a
preheat: valueA nlay be takenthe sanle as value B,
hardness survey. Guidance for so doing is given in F.5.
nanlely 1.0 for the T4 condition and 0.8 for the TG
condition.
F.1.2 Thermal control
(b) Case 2. Other welds, withstricter thermal control
The extent of HAZ softening, and sonletinlesits
exercised than that nornmlly called for in BS 8118 :
severity, depend on the inter-pass temperatureT,, i.e.
Part 2: value A may be taken as follows:
the temperature of the adjacent parent metal atthe
(1) for 40 "C < T, I 80 "C
start of laying any weld pass. The following factors
tend to elevate T,:
for T4 condition
1.2 - 0.005T0
for TG condition
1.0 - 0.005To
(a) deposition of previous passes in a multi-pass
(2) for T, 5 40"C
joint;
for T4 condition
1.0
(b) previous weldingof a nearby joint;
for
T
G
condition
0.8
(c) use of preheat.
Appendix F. HAZs adjacent to welds
*
where
Excessive build-up of.tenlperaturecan be prevented by
To is the interpass temperature,to be stated in the
exercising thermal control during fabrication,that is by
contract specification.
letting the metal cool down adequately between
F.3 Extent of H A Z
passes. The methods in4.4.2 and 4.4.3 for estimating
HAZ effects are valid if the thermal control satisfies
F.3.1 General
BS 8118 : Part 2, nanlely:
The methods given in 4.4.3, for obtaining the
z, may lead to an overestimate of the extent
dinlension
T, 5 80 "C;
(a) 7
series alloys
of
the
H
A
Z
.
The following sections give alternative
T,
5,
100
"C.
(b) other alloys
treatments, which can be used to obtain more
It is often possibleto reduce the extent of the HAZ
favourable estimates in some cases.
softening, and sometimes its severity, by exercising
F.3.2 Modtifiedformula for
z
stricter themml controlthan this, i.e. by specifymg a
It
is
pemlissible
to
use
the
following
expression forx ,
lower value for To.In order to take advantage of such
instead
of
that
given
i
n
4.4.3.2:
improvement, the designer should state in the
z = 6aqzo
specification that tighter control is to apply, and give
where
the reduced value to which T, should now be linuted.
a and q
are modifyq factors (see 4.4.3.4
More favourable HAZ rules are provided in F.2.3, F.3.3
and 4.4.3.5);
and F.3.4, which may be used when such a practice is
adopted.
X0
is the basic
value
of z.
The extra factor6 would normally be taken as 1.0, but
F.2 Softening factor k,
in the following cases (a) and (b) a lower value is
F.2.1 Modified values of k,
allowed.
When the resistance is governed by pa or P , rather
(a) For a joint away from whichthere are three or
than P,, it is pernkible to take a modified valuek;
more
valid heat-paths
for the softening factoras given in table El, instead of
6
=
0.75
the nomml value k, from table4.5. T ~ I applies
S
for the
A valid heat-path beingas defined in 4.4.3.5.
following:
@) For a straight jointof length L less the 5z0:
(a) shear in beanls (see4.5.3);
6 = (1.5 + 1.%/~,)/(3+ Uzo)
(b) local failurein tension members (see4.6.2.3);
(c) local squashingin struts (see 4.7.7).
When a joint comes into both these categories,
6
The use of the nlodified value k$ for these is
should be takenas the lower of the values given by (a)
favowable for most(but not all) n~aterials.
and (b) respectively.
***
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I
STDOBSI BS BLLB: PART 1-ENGL 1991 m LbZ'ibb9 079qb32 132
Appendix F
BS 8118 :Part 1 : 1991
~
~~
lbble F.1 Modified H A Z softening factor
4noy
Condition
G.
TG, TF
T4
T4
T4
T5
TG
T6
T4
T6
T4
TG
0.55
H14
H14
H18
H14
H1G
0.25
Heat-treatable
GOG1
6063
6082
7020
1.00
0.70
0.80
0.75
0.55
0.50
1.00
0.55
O.SO(A), 1.00(B)
O.GO(A), 0.80@)
(see note 2)
Non-heat treatable
3103
3105
0.30
0.24
0.28
0.24
0.21
H18
5083
5 154A
5251
5454
o, F
1.o0
H22
O,F
H22
H24
F
F
H22
H24
o, F
H22
H24
0.55
1.00
0.50
0.40
0.30
1.o0
--`,,,,,,`,,,``,```,,`,````,``,-`-`,,`,,`,`,,`---
1200
0.45
0.35
1.00
0.45
0.40
NOTE 1. In the product column E, , P, DT,WT and F refer respectively to extrusion, sheet, plate, drawn tube, welded tubeand forgings.
NOTE 2. For 7020 material refer to 4.4.2.2, for the applicability of the A and B values.
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129
'Pdble F.2 General determination of k, and k;
Alloy series
Condition
k, (see notes 1 and 2)
o, F
T4
T5
TG
Other (see note 3)
1.00
1.00
O.75
0.50
Heat-treatable
7***
O,F
T4
0.50 P o d P o
1.00
0.80(A)
TG
1.00(B)
O.GO(A)
0.80(B)
Other
(see note3)
0*6POdPO(A)
0.8POdPO@)
o, F
1.00
Other (see note 3)
PodPo
--`,,,,,,`,,,``,```,,`,````,``,-`-`,,`,,`,`,,`---
G***
Non-heat-treatable
1***,3***or5***
NOTE 1. k, is the normal value.
12;is a modified value for use in certain cases (see F.2.1).
NOTE 2. Notation is as follows:
p o and pa are the limiting stress for parent material in the condition used (se tables 4.1 and 4.2);
poGand paGare the limiting stresses for the parent materials in the TG - condition.
poo and pao are the limiting stresses for the parent materials in the O - condition.
NOTE 3. The value taken should never exceed 1.0.
E3.3 Alternative determinationof (Y
It is pernwible to take a lower value of (Y for cases Q
and R in table 4.G for a joint to which either (a) or @)
applies as follows.
(a) Nornd thernd control is exercised (ascalled
for in BS 8118 : Part Z), tc does not exceed 25 nun
and the total area A (in nun2) of all weld deposits in
the joint is known:
(Y
50 A I150
O! =
0.75 + 0.005A
A > 150
01 =
1.5
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= 1.0
A 5 50
@) Stricter thermal controlis exercised than that
called for in BS 8118 : Part 2
IC S 25 mm tC > 25 mm
0.5Tl 5 To < T1
= 0.5 +
+TV1
(Y = 1.0
(Y
01 =
2TJTl
To 5
(Y = 1.0
where
To is the reduced interpass temperature (to be
stated in specification);
T1 is the normal interpass t e m p e m e in
accordance withBS 8118 : Part 2,
= 80 "C for 7
series alloys;
= 100 "C for other alloys;
tc is the thickness of thickest part joined.
***
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O E S 1 07-1999
STD-BSI BS 8118: PART 2-ENGL 199L W L b 2 4 b b 9 0794b34 T 0 5 W
Appendix F
BS 8118 :Part 1 : 1991
F.3.4 Alternative determinationof q
F.5.2 Experimental method
When stricter thernlal control is specified than that
The preferred method employsthe Vickers Diamond
required by BS 8118 : Patt 2, it is pernutted to read q
technique. This may be applied to an actual prototype,
from figure El instead of finding it from 4.4.3.5. The
or to a trial fabrication representing partof an overall
quantities needed forthe figure should be taken as
structure. The procedure is to take a series of hardness
follows:
readings at varying distances fromthe weld, and hence
deternine atwhat point the full parent properties are
(a) To, Tl and tc are as defined in F.3.3;
regained. Preferably,the specimen should be sectioned
(b) h and hl are as defined in 4.4.3.5;
perpendicular to the weld, and readings taken at
(c) denotes sunmation for all heat-paths from the nud-thickness on the cut face (after suitable surface
joint.
Preparation). However it nlaybe possible to take the
r e a h g s directly on to the surface of the conlponent.
NOTE. When t C > 25 mm and preheat is used, no improvenlent in
1
q is permitted. In such cases the full value q = 1.33 should be
E5.3 Interpretation method 1
There are two pernutted methodsfor interpreting the
F.4 Post-weld artificial ageing
results, of which the following (method1) is
With the G
and 7
series heat-treatable
preferable.
alloys it is sonletinles beneficialto apply heat
treatment in the form of artificial ageing after welding. A typical hardness plotis of the form shown in
figure F.2, on which it is usually possibleto distinguish
This involves heating the welded conlponent toa
tenlperature in the range 100 "C to 180 "C for a t h e of two points A and B as shown. The dimensionz, used
in design to define the distance that the assunled HAZ
up to 24 h. The exact procedure dependson the alloy.
extends
from the weld, should be takenas follows:
The following benefits nlay be obtained by such
z = 0.5 (X, + X B )
treatment.
where
(a) The thne to reach stable nmhanical properties is
reduced to a value belowthat indicated in 4.4.2.3.
X, and X B are the distances of points A and B
(b) The strength of parts of the HAZ, but not
from the centre-line of a butt weld or
necessarily the whole, is raised. In design this nxty
the root of a fillet weld.
be assunled to effectively reduce the extent of the
HAZ.
F.5.4 Interpretation method 2
(c) Sonle improvement will occur in the strength of
This nlay have to be used if only point B can be
the weld metal.
distinguished on the plot, i.e. the point at which parent
In order to quantify these benefits itis necessary to
hardness is effectively regained, pointA being difficult
carry out tests, using representative specimens
to locate. In this case z should be taken as follows:
(see F.5). These should accuratelysindate the true
(a) for 5
series alloys z = 0.65X~;
situation in terns of: metal thickness, geometry, filler
(b) for 6
series alloys z = 0.75X~;
metal and welding paranleters,as well as the exact
post-weld treatment enlployed.
(c) for 7
series alloys z = o.go&.
F.5 Hardness surveys
used.
**
***
--`,,,,,,`,,,``,```,,`,````,``,-`-`,,`,,`,`,,`---
***
***
***
F.5.1 General
It is pernutted to detemine the extent of the HAZ
experinlentally (see4.4.3.7), the most usual procedure
is to conduct a hardness survey.
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131
1.5
1
1.o
/
4
1.5
l
i
.2
rl
1
i
.4
/ 1.0
1.2
t p 2 5 mm
1.4
I
I
1.6
~
1.8
1.0 -L
1 .o
O
0.5
1.0 TOIT
I
O
I
1.0 TOI6
0.5
@>
(a>
Figure F.l Extent of HAZ, factor
B
0 0 0 0 0 0 0 0 0 0 0
O
E
O
O
S
O
O
L
I
O
4
x
o A
O o o o o
u
n
5
c
Y)
'P
L
t
QI
v1
O
I
Figure F.2 Qpical hardness plot along a heat path from a weld
--`,,,,,,`,,,``,```,,`,````,``,-`-`,,`,,`,`,,`---
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Appendix G. General formulae for the
torsional properties of thin-walled open
sections
6.1 General
This appendix shows howto detemme certain section
properties, neededin buckling calculations that involve
torsion (see appendicesH and J). The section
properties are as follows:
(a) torsion constantJ (see 6.2);
(b) polar second momentof area about shear centre,
Zp (see6.3);
6.2 Torsion constant
The torsional stiffnessof a member having a
thin-walled cross-sectionis given by the product of GJ,
where G is the shear modulus of the nuterial and J is
the torsion constant of the cross-section. For
thin-walled open sections without pronounced
dations of thickness, suchas fillets or bulbs, J is
given by the following:
J!!?!3
O
where
t
is the thickness;
is measuredalong the nuddlelineof
S
profile;
is the totallength of thenuddleline.
the
For a section composed solelyof flat plate elements,
each of uniform thickness, this equation reduces to the
following:
J = -1C b $ ,
3
where b is the width of an element, measuredat the
mid-thickness of the profile.When such a section is
reinforced with fillets and/or bulbs,the following
expression may be used
J = C ( 0 3 + qN)tI4 + $bt3
where
t
N
Pandq
The position of S may be found as follows:
(a) for bisymnletric or skewsynunetric sections, S
coincides with G
(b) for sections composed entirely
of radiating
outstands (such as angles, tees or cruciforms), S lies
at the point of intersection of the component
elements;
(c) for certain specific typesof section, see
figure G.2;
(d) for monosynmetric sections composedof flat
elements, generally,see 6.5;
(e) for asynmetric sections composed of flat
elements, generally,see 6.7.
6.4 Warping factor
The warping factorH may be found as follows:
(a) for sections composed entirelyof radiating
outstands (such as angles, tees or crucifomB), H
may be conservatively assunledto be zero;
@) for certain specific typesof section, see
figure G.2;
(c) for monosymmetric sections composedof flat
elements, see 6.5;
(d) for skewsymnletric sections composed of flat
elements, see 6.6;
(e) for asymmetric sections composedof flat
elements, see 6.7.
is the thickness of adjacent flat
material;
is the fillet or bulb
dimension, as
defrned in figure G.1;
are coefficients to be readfrom
figure G.1.
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A
9
are secondmoments of area about
centroidal axes;
is the section are%
is the distance
between
centroid
G
and shear centre S.
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133
--`,,,,,,`,,,``,```,,`,````,``,-`-`,,`,,`,`,,`---
Z, and Zy
For sections not coveredby the procedures given in
this appendix, refer to the l i t e m e .
S
6.3 Polar second moment of area about shear
centre
The polar second momentof area about the shear
centre, Zp,is given by the following:
Zp = Zx + Zy + Ag2
where
(c) warping factorH (see 6.4).
J =
The first sunmation is extended to every filletor bulb
region within the section (see figureG.l).
In nmking the sheared sununation forthe flat elements,
the width of any element abuttingon a fillet or bulb
should now be measuredto the edge of the shaded
area shown in figure G.l.
~~
STD-BSI BS 8118: PART L-ENGL 1991 U Lb2qbb9 079qb37 7Lq W
BS 8118 : Part 1 : 1991
--`,,,,,,`,,,``,```,,`,````,``,-`-`,,`,,`,`,,`---
Appendix G
26
S1
?+P
Figure G.l Torsion constant coefficients forcertain fillets and bulbs
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3b
e=-
1 c
e = a'b't
-+"
I , (4 2b
F+6
3a2b
b2t
H = - (46 +
+ 3a2c
6
+ a") - $1,
--`,,,,,,`,,,``,```,,`,````,``,-`-`,,`,,`,`,,`---
E
U
+ a2b)
4I-t
IV
e = 3111 - 3212
Y'
X H = a2l1I,
Y'
where I, and I' are the
~
IY
- a"l,
- 4
+
C"',(a2 + ")3
respective second moments
of area of the flanges about
the W axis
H=
b%
12(2b +a + 2c)
X (a2(b'
+ 26a. + 4bc + 6ac) +
+ 4c2(3ba + 3a' + 4bc + 2ac + C')}
Figure 6.2 Shear centre position (S) and warping factor (H) for certain thin-walled sections
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135
G.5 Monosymmetric sections composed of flat
elements
6.5.1 Notation and signConvention
The section is broken down into2V flat elements,
numbered 1 to Von each sideof the axis of
symmetry AA, counting outwards fromthe point B
where the cross-section intersectsAA (see figure G.3).
The following notation relatesto the Rth element in
the upper half of the section:
b
is the elementwidth;
t
is the elementthickness;
a
is the perpendiculardistancefromnudpoint
of the element to AA;
is the projected width of the elenlent on an
axis perpendicular to A A ,
is the perpendicular distance from B to the
centre-line of the element;
c
d
6.5.3 Specimen calculation
Table G.l gives a specimen calculation fora
nlonosymmetric section. The elements taken into
consideration in this calculation are the numbers
within trianglesin the diagram in table G.l.
6.6 Skew-symmetric section composed of flat
elements
G.6.1 Notation and signconvention
The section is broken down into2V flat elements,
numbered from 1 to Von each side of the point of
synmetry G, counting towards G (see figure G.4). The
following notation relates to the Rth element inthe
upper half of the section:
b
t
d
is the elenlent
width;
is the element
thickness;
is the perpendiculardistancefrom
the centre-line of the elenlent;
is the total
section
area;
R
P=Ybd
Y
A
G to
2
6.5.2 Formulae
The distance e by which the shear centre liesto the
left of B is given by:
R
P = cbd
2
The sununation forP extends only to the upper half of
the section. It begins with the second element, since
there is no contribution fromthe first element (for
which d = O). The sign conventionis as follows:
(a) b, t are always positive;
(b) d is taken as positive if the elenlent produced in
the sense towardsG has G on its left, and negative if
G is on its right.
6.6.2 Formula
The warping factorH is given by the following
1
where
I u is the second moment of area of the whole
section aboutAA.
The warping factorH is then given by:
b2d211
(P+K)(P+K-M)+3
where
NOTE. This t,reatment only C O V ~ ~aS section that can be developed
from a single piece of sheet (possibly varying in thickness). For
sections that bifurcate, refer to the literature.
NOTE. This treatment only covers sections that can be developed
from a single piece. of sheet (possible varying h thickness). For
sections that bifurcate it is necessary to refer to the literature.
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6.6.3 Specimen calculation
Table G.2 gives a specimen calculationfor a
skew-synmetric section.The elements taken into
consideration in this calculation are the numbers
within trianglesin the diagram in table G.2.
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--`,,,,,,`,,,``,```,,`,````,``,-`-`,,`,,`,`,,`---
The sunmation for P extends only to the half of the
section aboveAA. It begins with the second element,
since there is no contribution from the first elenlent
(for which d = O).
The sign convention.is as follows:
(a) u,b, t are always positive;
(b) c is taken as positive if the element considered
in the sense towards B is convergent withAA, and
negative if divergent;
(c) d is taken as positive if the element produced in
the sem towards B has B on its left; and negative if
B is on its right.
~
1
-
STD=BSI BS 8118: PART 1-ENGL 1991 m 1b24bb9 0794b40 207 m
Appendix G
BS 8118 :Part 1 : 1991
Rth element
t
O
I s t element
S
-
A
A
Figure 6.3 Monosymmetric section notation.
--`,,,,,,`,,,``,```,,`,````,``,-`-`,,`,,`,`,,`---
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137
a b l e G.l Specimen calculation: monosymmetric shape
A-
!
U1 dimensions are in millimetres.
2
R=
4
3
128
30
5
5
100
60
U
80
O
c
60
28
d
3.58 X 103
1.80 X 1@
bd
1.80 X 1@
5.40 X 103
P
1.08 X lo6
2.16 X loi
2aP
1.08 X lo5
3.10 X lo5
5d(a - c/G)
1.08 X 105
7.70 X l@
BaP - bd(a - c/G)
4.93 x los
1.62 X 107
bt(2aP- bd (a - &)J
Sunmution of last line = 1.05 X 109 mm"
(obtained by calculation not shown) = 2.35 X lo7 m m 4
X 109 = 45 nun
Shear-centre positione = 1.05
.35 X 107
PZ
3.24 X 106
3.24 X 106
3dP
!9d"l.3
1.08 X lo6
1.08 x 106
Pz - bdP + @&/3
1.62 X 10s
it (P2- bclP + b2d2/3)
hmmation of last line = 2.80 X 10'0 mm6
Narping factor H = (2 x 2.80 X lolo) - (452 X 2.35 x lo7)
b
t
32
8
127
-25
189
6.05 X 103
1.14 X 104
2.90 x 106
7.94 x 105
2.11 x 106
5.40 X 10s
--`,,,,,,`,,,``,```,,`,````,``,-`-`,,`,,`,`,,`---
1.30 X los
6.90 X lo7
1.22 X 107
7.32 X 107
1.87 X 1O'O
= 8.41 X lo9m m G
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O ßSI 07-1999
V t h element
1
1 s t element
Centroid andshear-centre
both lie at the point o f
symmetry G
r=
Mid - thickness L ¡ne
Figure 6.4 Skew-symmetric section notation
6 . 7 Asymmetric section composed of flat
elements
1’
P=Cbd
1
6.7.1 Notation and signconvention
The section is broken down into n flat elements,
numbered from 1to n starting from an edgeE of the
section (see figureG.5).
The following notation relates to the r&element:
b is the element width;
t is the element thickness;
a, and a, are the co-ordinates of the nudpoint R of
the element with respect to u,v (the principal axes
of the section);
c, and c, are the projected widths of element on G,
and G, respectively;
d is the perpendicular distance fromG (the centroid
of the section);
d’ is the perpendicular distancefrom S (the shear
centre) to be located. U and Vare the co-ordinates
of s.
1‘
P =zbd’
1
The sign convention is as follows:
(a) b and t are always positive;
(b) a, and a, are the actual co-ordinates of R, which
nmy be positive or negative dependingon the
quadrant within whichR lies;
(c) c, and C, are positive if u (or v ) increases
within the element in the sense away from the
previous (r-1)th element; and negative if u (or u)
decreases;
(d) d and d’ are positive if the element producedin
the sense away fromthe (r-1)th element has an
anticlockwise monlent aboutG (or S); and negative
if clockwise.
--`,,,,,,`,,,``,```,,`,````,``,-`-`,,`,,`,`,,`---
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139
6.7.2 Formulae
warping
factor
The
H is then given by the following:
The cclordinates of the shear centre S are given by the
following:
(P' - K')(P' - R - bd') +
1
y]]
where
1
bd'
Kt=z~bt(P"--)
2
1
A is the section area.
area Of the
6.7.3 Specimen calculation
Table G.3 gives a specimen calculation foran
asynmetric section. The elements taken into
consideration in this calculation are the menibers
within trianglesin the diagram in table G.3.
--`,,,,,,`,,,``,```,,`,````,``,-`-`,,`,,`,`,,`---
where
W
'
arethe ='OOfnd
section about Guand G,.
NOTE. This treatment only covers sections that can be developtd
from a single piece of she& (possibly varying in thickness). F&
sections
that bifurcate it is necessary to refer to the literature.
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BS 8118 :Part 1 : 1991
Appendix G
nth element
7
r th element
Figure 6.5 Asymmetric section notation
O BSI 07-19!39
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--`,,,,,,`,,,``,```,,`,````,``,-`-`,,`,,`,`,,`---
STD=BSI BS ALLA: PART 1-ENGL 1991 m Lb24bb9 0 7 7 4 b 4 4 954 W
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141
Table 6.2 Specimen calculation: skew-symmetric shapes
t
Centroid and shear-centre
both lie at point of symmetry G
R=
1
2
3
50
40
20
2
3
3
O
40
-70
bd
1600
-1400
P
1600
200
bt(P - bdn)
96 O00
%
o
0
0
--`,,,,,,`,,,``,```,,`,````,``,-`-`,,`,,`,`,,`---
Dinlensions are in millinietres unless otherwise indicated.
Sunmmtion of last line = 150 O00 nun4
(P + k)(P + k - bd)
287 X 103
-570 X 103
- 357 X 103
b2d2/3
O
853 X 103
653 X 103
&[((P + @(P + K - b d ) ] +
+ (b2&ß)]
28.7 X 106
34.0 x 106
17.8 X 106
Sununation of last line = 80.5+ 106 mm6
Warping factor H = 2 x 80.5 x 106 = 161 x 106m m 6
142
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. .
4.0
36.I
I
p
--(G++ rw + -op V)fi
I..
d'
I
64.5 mm
17.67 X 16m
- M 7
P
W€" - "n)
x:[b#p- w'n)l-
-4647
-0.384 x 106
-
- M')
- 66.0
-31.0
28.4
13.8
32.8
3717
-12.8
- 1056
106
i:::
178.8
-9aa
- lsss
-1.893 x 1 6
-0.463 x I06
20.6
1649
-317
-0.913 x 106
- ]S1
-a
-
2.594 x 106
4.605 x 106
1366 x 106
-5.186 x 106
7.198 x 1
6
bt[[(P- ITXP - IT - M'))+ 342 x 106
w2/9
-0.088 x 106
0.368 x 106
83 x 106
t (b%%3)]
X~~.a"dw~=1211x10Dmms
143
--`,,,,,,`,,,``,```,,`,````,``,-`-`,,`,,`,`,,`---
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10.0
62.5
4
- 184.3
M'
(P- ITXP - K
-67.3
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- 0.913 x 1 0 6
0.806 x 106
595 x 106
.-
. * "".--"
".
l
"
Appendix H
BS 8118 :Part 1 : 1991
Appendix H. Lateral torsional buckling of
beams
For a unifornl section synunetrical aboutthe n k o r
axis only, M,, is given by the following:
H.l Effective lengths of beams
H.l.l Beams supported at both ends
The effective length1 of a beanl for use in4.5.6.6.
should be obtained from tableH.l for beanw with
effective lateral restraintsat their ends only.
For beanw with effective lateral restraintsat intervals
within their length,the value of 1 should be taken as
the length between restraints.
+
Xßx
21
y)"}
GJ
where
H.1.2 Destabilizing loads
Destabilizing load conditions exist whena load is
applied to the top flange of a beam and boththe load
and the flange are free to deflect laterally relative to
the centroid of the beanl. In such cases the increased
effective lengtksof table H.l should be used.
For beanw carrying destabilizing loads with effective
lateral restraints at intervals within their lengths,the
value of 1 should be taken as 1.2 tinles the length
between restraints.
IX
is the second
moment
of area
around the major centroid axis
YO
is the
distance
between
centroid
and
shear centre;
A
is the cross-sectional area of the
H. 1.3 Cantilevers
cantilever
For cantilevers with no internlediate restraints and no
x and y
are the CO - ordinates of the element
moment applied at the tip, the effective length 1 should
respect to the
of area dA with
be obtained from tableR2.
CO - ordinate axes through
the
If internlediate restraintsare provided, the values of 1
centroid.
I
for the lengths between restraints should be obtained
from H.l.l or H.1.2.
In both cases referencemay be made to published
For cantilevers subjectedto a moment at the tip, 1
literature for solutions forMc, relating to loading
should be obtained from H.l.l or H.1.2.
arrangements other than unifornl monleAt. When such
H.2 Determination of I
allowances are made in d e t e m w g L,M in 4.5.6.4
should be taken as the maxinlunl value in the beam.
The lateral torsional buckling slenderness paranleterL
is obtained from the following (see4.5.6.6@)):
H.3 Beams of varying section throughout their
A = R(ES/Mcr)
length
where
When the section of a doubly symmetrical bean1 varies
along its length between restraint points,the buckling
stress P, should be deternined using the properties of
Mcr
is the elastic
critical uniform monlent
E and S are as defined in 4.5.6.6.
the section at the point of maxinlunl moment. This
value of p , then applies throughoutthe length between
For a doubly symmetricaluniform section, M,, is given restraint points andno further allowances forthe
pattern of moments should be made.
by the following:
Provided that Rfis not less than 0.2, the value of L
Mc, = (EIyGJ) (1 + n2 EHl12GJ)
based on the cross-section at the point of nmximum
moment should be multiplied by
where
(1.5 - 0.5Rf) 2 1.0
where Rf is the ratio of flange area at the point of
IY
issecond
themoment
of area
about the centroid axis,
minimum moment to that ai the point of maxin~unl
G, J and H
are as defined in 1.3.
moment between adjacent restraint points.
Rfrefers eitherto the ratio of total area of both
flanges or to the area of the conlpression flange only,
whichever givesthe smaller valueof Rf.Values of Rf
less than 0.2 represent an extreme degree of flange
taper which is not covered by this clause.
'
3
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--`,,,,,,`,,,``,```,,`,````,``,-`-`,,`,,`,`,,`---
I
~~
BS 8118 :Part 1 : 1991
Appendix H
'bble H.1 Effective length 1 for beams of length L
ILoading conditions
Conditions of restraint at supports
t Normal
Compression flange laterally
Both flanges fully restrainedagainst
rotation on plan
restrained
Bean1 fully restrained against torsion Both flanges partially restrained against 0.85L
rotation on plan
Both flanges freeto rotate on plan
1.OL
Compression flange laterally
Restraint against torsion provided only 1.OL + W
unrestrained.
by positive connection of bottom flange
Both flanges free to rotate on plan
to supports
Restraint against torsion provided only 1.2L + W
by dead bearing of bottonl flange on
supports
Destabilizing
0.85L
1.OL
1.25
1.z+ 20
1.4+W
I
kble H.2 Effective length 1 for cantilever of length L
T Loading conditions
Restraint conditions
i t support
At tip
2ontinuous with lateral restraint only Free
Laterally restrainedon top flange only
Torsionally restrained only
Laterally and torsionally restrained
2ontinuous with lateral and torsional Free
Pstraint
Lateral restraint on top flange only
Torsionally restrained only
Laterally and torsionally restrained
Free
Built-in laterally&d torsionally
Lateral restraint on top flange only
Torsionally restrained only
LateraUy and torsionally restrained
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1
Normal
Destabilizing
3.0L
2.7L
2.4L
2. lL
1.OL
0.9L
0.W
0.7L
O.%
O. 7L
0.GL
0.5L
7.5L
7.5L
4.5L
3.m
2.5L
2.5L
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1.5L
1.2L
1.U
1.4
0.GL
0.5L
--`,,,,,,`,,,``,```,,`,````,``,-`-`,,`,,`,`,,`---
~~~
NOTE. D is the depth of beam. L is the bean enpth.
~~
~
~
STD-BSI BS 8118: PART 1-ENGL 1991
Appendix J
--`,,,,,,`,,,``,```,,`,````,``,-`-`,,`,,`,`,,`---
Appendix J. 'Ilmional buckling of struts:
determination of slenderness parameter A
5.1 General
In strut design, the rigorous determination ofthe
slenderness parameter1for torsional buckling tendsto
be laborious. A sinlplified procedure is provided
in 4.7.5.2@) using empirical fomwlae(see table 4.9),
but this only covers a limited range of section shapes.
The purpose of this appendix is to present a general
procedure, that enables J. to be found for any section.
This more rigorous procedure may of course be
applied to the sections in table 4.9 if desired and
economies may result.
The treatment involvesthe use of the following
properties of the section which nlay be found using
appendix G
(a) J is the torsion constane
(b) Ip is the polar second monlentof area about
shear centre;
(c) H is the warping factor.
5.2 Buckling modes
There are three fundamental modes forthe overall
bucklmg of a strut, as follows, where uu and W are the
principal axes of the section
Pure torsional bucklingis defined as a bodily rotation
of the section aboutits shear centre, over the central
part of the length of the member. In practice this pure
torsional buckling is only observed for certain shapes
of section. For the majority of shapes it is found that
interaction takes place between pure torsion and
flexure, with the centre of rotation moving away from
the shear centre. The resulting decreasein resistance
to torsional bucklmg should be taken into account
in
design.
(a) Bisymmetric
m
BS 8118 : Part 1 : 1991
The required quantityfor the slenderness paranleterJ.
allowing for flexural interactionis obtained from the
following:
J. = kJ.t
where
k
At
is the interactionfactor(see 5.4);
is the slenderness p m l e t e r that
corresponds to torsional buckling (see5.3).
5.3 Determination of At
The general expressionfor the slenderness At,
correspondmg to pure torsional buckling,is as follows:
10
" = (1 + 26H/J12) %
where
Io
1
= 5.14 (Ida%;
is the effectivebucklinglength;
It should be noted that sections conlposed of radiating
outstands do not warp when theytwist (H = O), giving
At = 1,. Examples of such shapes are angles, tees and
crucifornls.
5.4.1 Section free from flexural interaction
It is found that the three fundanlental modes of overall
buckling (see 5.2) do not interact with one another,
when the sectionis of either of the following types
(see figure J.1):
(a) bisynnetric;
@) skew-synmetric.
For such sections k = 1, or in other words A = L,.
In calculating At, 1 should be taken the sanle as for
colunm buckliig about the nlqjor principal axis
(see 4.7.4.2).
@) Skew-symmetric
Figure J.l Sections which exhibit no interaction between thepure
torsional and flexural buckling modes
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Lb2libbS
075libli9
li3b
5.4 Determination of k
(a) pure colunm, i.e. flexural,
bucklig about W;
(b) pure colunm buckling about uu;
(c) pure torsional buckling.
I
~
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147
5.4.3 Asgmmetric sections
For sections having a singleaxis of synmetry ss (see
figure J.2), the pure torsional mode interactswith
colunm bucklingabout ss giving the following:
When the section has no axis of synmletry, as in
figure 5.3 the three fundanlental modesall interact,
leading to an equation for I as follows:
A = (&/.")It
where
I = kAt
where
k is read from figure 4.11 taking S and X as follows:
S = Is/&;
= IglIp;
where
x
I,
It
Ig
Ip
is the slenderness paranleter for pure column
buckling about SS;
is the slendernessparanleterforpure
torsional buckling;
is the polar second nlonlent of area.about
centroid G;
is the second monlent of area about shear
centre S.
The effective length 1 to be used in finding I , and It
should be found in accordance with 4.7.4.2, based on
colunm buckling aboutSS.
Q
= Sv(3x/(C+ sv2))";
X
= IglIp;
SV
= A&;
1,
is the slenderness paranleter for pure
C
rP
Uand V
X
NOTE. For such sections column buckling about the axis
perpendicular to SS occurs independently, without interaction.
colunm buckling aboutW;
is the slenderness paranleter for pure
torsional buckling;
= (1 - u%pz) + y( 1 - v2/Yp2);
is the polar radius of gyration of
section about shear centre S
are the coordinates of shear centre
(see figure5.3);
is the lowest root of the following
cubic equation:
$-@++-B=O
where
NOTE. The pure torsional buckling mode interacts with flexure
about SS.
27@Y+
B = (C + $33
where
y = Iu/Iv
I" and I, are the second monlentsof area about use
and W, the principal axes of section
The cubic nlay be solved withthe aid of the
nomogram illustrated in figure5.4
Figure 5.2 Monosymmetric section
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--`,,,,,,`,,,``,```,,`,````,``,-`-`,,`,,`,`,,`---
5.4.2 Monosgmmetric sections
~
~
STD-BSI BS BLLB: PART L-ENGL 1993
Appendix J
L b 2 q b b l 077qb51 094
BS 8118 :Part 1 : 1991
U
--`,,,,,,`,,,``,```,,`,````,``,-`-`,,`,,`,`,,`---
NOTE.The three fundamental buckling modes (pure torsion,
flexure about uu, flexure about W) all interact
Figure 5.3 A symmetric section
~~~
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149
BS 8118 :Part 1 : 1991
Amendix .J
3.0 -
2.6 -
- 0.1 o
2.5 -
- 0.1 2
-
--`,,,,,,`,,,``,```,,`,````,``,-`-`,,`,,`,`,,`---
- 0.1 4
-
- 0.1 6
-
- 0.1 8
-
- 0.20
- 0.22
- 0.24
-
- 0.26
- 0.28
r2.4
- 0.30
- 0.32
-
- 0.34
- 0.36
- 0.38
3.6
1.1
-
1.0
- 0.40
- 0.42
0.9
0.44
0.46
O.#
0.50
NOTE. The figure is taken from R. Kappus. ""sting
failure of centrally loaded open section
columns in the elastic range". NACA Technical Memorandum No.851,193.
Figure 5.4 Nomogram for solving cubic equation x3 -
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+ Ax - B = O
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~
STD-BSI BS ALLB: PART It-ENGL 1991 H l b 2 4 b b 9 0794b53 9b7 m
Appendix K
BS 8118 : Part 1 : 1991
0.3
0.2
PS
4
0.1
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O
100
120
140
160
180
200
P, is the buckling stress; P, is as defined in 4.7.6.2 or 4.7.6.4
Figure K.l. Buckling strength at high slenderness
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151
L b 2 9 b b S 0794b59 B T 3 M
Appendix K
STD.BSI BS BLbLB: PART 1-ENGL 1993
BS 8118 :Part 1 : 1991
a b l e K . l Equations to design curves
Figure
Curve
Formula
4.2
B
A
4.5
A
g=l
g = 0.70 + 0.30
g = 0.801(1 - Y&),
h = ( 1 + 0.1 (Cl¿ - 1)2]-E
h = [ 1 + 2.5 ( C l t -1)2/(blt)]h = [ 1 + 4.5 (ch - 1)2)l(b/t)}kL = l l h - 28h2
kL = 1 0 5 1 ~ ~
kL = 1OIX - 24x2
kL = 10.51~~
kL = 3Ux - 2 2 0 1 ~ ~
kL = 2 9 1 ~ 198/x2
B
C
D
E
Range
7 < x I12.1
x 5 12.1
6 < x 5 12.9
x 2 12.9
x > 22
x > 18
kL = 1OWX2
where x = ßh
2x9
4.11
=[ 1+sz {(1+
-
s2)2 - 4Xs2)"
I"
Buckling curves:
--`,,,,,,`,,,``,```,,`,````,``,-`-`,,`,,`,`,,`---
PS = NP1
where
4.9
4.10 (a)
(b)
(c)
L12 (a)
(b>
A1
c
0.G
0.2
0.2
0.10
0.20
0.45
0.80 0.2
0.35
0.4
0.6
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0.20
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BS 8118 :Part 1 : 1991
Appendix K
1
I 'Igble K.l Equation to design curves (concluded)
Figure
:tuve
5.4
Formula
v1 = (5.35 + 4
lange
6)
2 4 3 0
!.5 2 a > 1.0
d
5.5
5.6
5.7
e = 2-3 tan1 (au)
v1 is as found from figure 5.4
E1
tr I25
9 = 1.0
= 1.0
TO
"> 1
Tl
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153
BS 8118 :Part 1 : 1991
Appendix L
L.2 Conditions when higher fatigue strengths
may occur
L.l Derivation of fr - N data
In some designs where fatigue doninates and where
The designf, - N curves in figure 7.9 are obtained from the achievement of nlinimum mass or mininun initial
constant amplitude test data with endurances generally cost is of particular economic importance,the option
in the regionof
to 2 X 106 cycles.Themajority of
of obtaining specific fatigue strength
data may be
data have been obtained from narrow plate specimens resorted to (see 8.4.4). In order to make a decision
in the region of 6 mm to 12 mm thick. More recently a whether or not to obtain further databy testing, the
database of some 120fr - N curves for both extruded following factors may be taken into account.
and fabricated I-beams in thicknesses inthe range
(a) Benefits may result where residual stresses are
8 mm to 15 mm has also been included. Materials cover kept low or conlpressive in the direction of stress
the more commonlyused 5
and 6
series
fluctuation eitherby a carefuuy controlled
alloys and 7020.
fabrication sequence (particularly welding)or by
The design curves representa survival probability of at
subsequent mechanical improvement techniques, e.g.
least 97.5 % for the classified details tested, whenall
hole expansion or weld toe peening. The nlain
the relevant tests data for each detail typeare analysed
benefits are likely to occur wherethe damage arises
together. 'lJqically the mean fatiguestrength& - N
mainly from high endurance stress ranges in the
curve forthe data within any one detail typeis 30 % to
spectrum (see figureL.l)
50 % m e r than the design curve.
@) Higher fatigue strengthsmay occur where the
The curves are considered to be safe for any condition
scale of the component is small. This may apply
of mean stress up to the tensile proof stress. No
when thicknesses and weld sizesare lower than
relaxation is recommended for applied lower mean
e mm.
stresses as the actual mean stress local to positions of
(c) If there is a stress gradient with a rapid
potential fatigue crack initiation may be high even
reduction of stress away from the initiation site,
though the nominal stress is not. This applies
hgher fatigue strengthsmay occur, for exampleat a
particularly to welded structures and complex
transverse welded attachmentor a plate in bending.
structures where weld shrinkage and lackof fit
(d) If the spectrunl shape is fairly flat with a large
stresses can occur respectively,
number of cycles at or below the constant amplitude
The new curve prodùcedby the change in slopeof the
non-propagating stress level, the effective slope
design curve beyond 5 X 106 cycles has been chosento
beyond 5 X 106 cycles may be significantly flatter
be a lower bound to take account of danmge due to a
(see figure L. 1).
high stress range in the spectrum. A high stress range
If
testing
is resorted to and a higher strength obtained,
can allow stress ranges below the initial
it
is
important
that the conditions for fabrication are
non-propagating stress level to add to crack growth
in
any
way during production.This applies
not
varied
damage. In the absence of variable amplitudetest data
to detail geometry, sequence (including jigging and
the lower slope of m + 2 has been found by fracture
welding), weld quality, surface preparation (including
mechanics to be safe for most commonly used
maclurung, hole drilling and cleaning).
spectrum shapes.
Appendix L. Fatigue strength data
***
,
***
~
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STDOBSI BS 8118: PART 1-ENGL L991 m 1b2'IbbS 0 7 9 q b 5 7 502 W
Appendix L
BS 8118 :Part 1 : 1991
I
I
io5
5 x106
Endurance N (cycles)
Figure L . l Zone of greatest variation in effective& - N curves
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155
STD=BSI BS 8118: PART 1-ENGL 1991
BS 8118 : Part 1 : 1991
1b24bb9 0794b58 gq9
"
Publications referred to
BS 499
BS 729
BS llGl
BS 1470
BS 1471
BS 1472
BS 1473
BS 1474
BS 1490
--`,,,,,,`,,,``,```,,`,````,``,-`-`,,`,,`,`,,`---
BS 1974
BS 2451
BS 2573
BS 2901
BS 3019
BS 3518
BS 3571
BS 4300
BS 4395
BS 4604
BS 4870
BS 5350
BS 5400
BS 5500
BS 5G49
156
Welding terms and symbols
Part 1 Glossary f o r welding, brazing and thermal cutting
Part 2 Specification f o r s p b o l s for welding
Specification for hot dip galvanized coatings on ironand steel articles
Specification for aluminiumaUoy sections for structural purposes
Specvication for wroughtaluminium and aluminium alloys f o r general engineering purposes:
plate, sheet and strip
Specification f o r wrought aluminiumand aluminium alloys f o r general engineering purposes
- drawn tube
Specification f o r wrought aluminium and aluminium alloys f o r g&
engineering purposes
-forging stock and forgings
Specvication f o r wrought aluminium and aluminium aUoys f o r general engineering purposes
- rivet, bolt and screw stock
Specification f o r wrought aluminium and aluminium alloys f o r general engineering purposes
- bars, extruded round tubes and sections
Specification f o r aluminium and aluminium aUoy ingots and castingsf o r general engineering
purposes
SpecZfication for large aluminium aUoy rivets (Yi in. to 1 in. nominal diameters)
Specification f o r chided iron shot and grit
Rules f w the design of manes
F i k rods and wires for gas-shielded arc welding
Part 4 Specificationf o r aluminium and aluminium alloys and magnesium alloys
TIG welding
Part 1 Specification f o r TIG welding of aluminium, magnesium and theira h y s
Methods of fatigue testing
MIG welding
Part 1 Specification f o r MIG welding of aluminium and aluminium alloys
Wrought aluminium and aluminium alloys f o r general engineering purposes
(supplementayy series)
Part 1 Aluminium ahoy longitudinally welded tube
Part 12 5454 Bars, extruded round tube and sections
Part 14 7020 Plate, sheet and strip
Part 15 7020 Bar, extruded round tube and sections
Specification for high strength f i c t i o n grip bolts and associated nuts and washersfor
structural engineering
Part 1 G e n e m l grade
Spec$ficationfor the use of high strengthfmction grip bolts in structural steelwork. Metric series
Part 1 General grade
Speafication f o r approval testing of welding procedures
Part 2 TIG or MIG of aluminium and its alloys
Methods of test for adhesives
Part C5 Determination of bond strength in longitudinal shear
Steel, concrete and composite bridges
Part 10 Code of practice for fatigue
Specification for unfired fusion welded pressure vessels
Lighting columns
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S T D = B S I BS 8118: PART 3-ENGL 1991
BS 6105
BS 6399
BS 8100
BS 8118
CP 3
CP 143
PD 6484
Is0 209
IS0 2107
1b2qbb9 079qb59 385 m
BS 8118 : Part 1 : 1991
Specification f o r corrosion-resistant stainlesssteel fasteners
Loading for buildings
Part 1 Code of practice for dead and imposed loads
Lattice towers and masts
Structurai useof aluminium
Part 2 Specification for materials, workmanship and protection
Code of basic data f o r the design of buildings
Chapter V Loading
Part 2 Wind loads
Code of practice for sheet roof and W& coverings
Part 15 Aluminium. Metric units
Commentary on corrosion at bimetaUic contacts and its aUeviation
Wrought aluminium and aluminium aUoys - Chernical composition and forms of products
Part 1 Chemical composition
Aluminium, magnesium and their &YS - Temper designations
R. Kappus, Twisting failureof centra& loaded open section columns in elastic range'. NACA Technical
Memorandum No. 851, 1938.
BS EN 10002 Tensile testing of metuUic materials
Part 1 Method of test at ambient temperature
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BS 8118 :
Part 1 : 1991
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