I ::= 0

BS 8118: Part 1 1991 Section 2

These materials may also be used for special The mechanical properties of the alloys Valll with
proprietary livet and bolt products, including temperature and those given in tables 2.1, 2.2
thread inserts. and 2.:3 should be applied to the design of
Special head shapes may be necessary for the structures over a temperature range 50 to
larger diameter rivets, see BS 1974 L) 70 "C except for 5083 (see 2.2.1.1.3(d)). The 0.2 %
proof stress and tensile strength improve at lower
2.2.;) Filler metals temperatures, but at higher temperatures are
Filler metals for tungsten inert-gas welding (TIG) reduced. For properties outside the temperature
and metal welding (1IIG) are given in range given, the manufacturer should be consulted.
table 2.4 together with their durability ratings. The alloys will melt within the range 550°C
Guidanee on the selection of filler metals is to 660 with the range dependent on
in 2.5.3.2. the alloy.
2.3.2 Physical properties
2.3 Strength, mechanical and physical The physical properties for the standard alloys
although varying slightly may be taken as constant
properties and are listed in table 2.:). In critical structures ~he
2.3.1 Strength and mechanical properties engineer may wish to use the E'xaCt value which
The range of the standard alloys together with should be obtained from a repurable manufacturer.
their ilvailable forms, temper conditions and
mechanical properties are shown in tables 2.1
and 2.2.
The mechanical properties for wrought materials Density
for the ternpers and conditions of the alloys Modulus of elasticity
in tables :2.1 and 2.2 have been used to determine
Modulus of rigidity ~6 600 \;/mm2
the limiting stresses in table 4.1. Where
alloys are welded the approximate percentage Coefficient of thermal 23 10- () per
reduction in strength of the alloy is given for each expansion
tClnper. These strengths in the HAZ may not be
achieved until after a period of natural or artificial 2.4 Durability and corrosion protection
ageing, see notes to table 2.1 for details.
2.4.1 General
The strength of bolt and rivet material is given in
table 2 In many instances the standard materials ~isted in
tables 2.1 to 2,-} can be used 111 the mill-finish, as
. Thble 2.4 '\Velding filler metals extruded or as welded conciitio!1 O,Vl1hout the need
for surface protection.
: Filler BS alloy : ISO a.lloy
: metal designa:tion ~) , designatiOlr n The good corrosion resistance of aluminium and its
alloys is attributable to the pmtecrive ()xide film.
which forms on the surface of the merai
1080A /\189.8 immediately on (~xposure to air. Tnis film is
1050A normally invisible, relatively inert and ~s it forms
naturally on exposure to air or oxygen. and tn
3103
many complex environments containing oxygen. it
is self-sealing.
· Al Sil2(A) In mild environments an aluminium surface will
retain its original appearance for years. and no
5056A · AllIg6 protection is needed for most alloys. In moderate
.'):356 A111g5Cr(:\) iA industrial environments there will be a darkening
555fLA. · Al 2lV1nCr and roughening of the suIi'ace. A.s the atmosphere
becomes more aggressive. such as in certain
Al .'Ifg4)5Mn strongly acidic or alkaline environments,
the surface discoloraLion and roughening will
: lr !",nrpst equlvalen\. 'Norsen with visible white powdery surface oxides.
The oxide film may Itself he soluble. The metal
;1 c~n,~7 ::;ppcifically u~ed pre'\.~pnt \,\~()id ('r;lckint~
involving high dilution :lnd lligh restraint. In nloSt ,,-(1::;12:3
,:eases ro be protected and 'ldded orotection is
l~ preferable. necessary. These (;onditions may aiso oc'cur 10
,:re':ices due to Lligh local ;)1' ~11kaline
conditions. but agents having this extreme effect
:lrE' l'elath'ely fe\v in number:
, BS 8118 : Part 1 : 1991 Section 3

Section 3. Design principles

3.1 Limit state design determined from the relevant British Standard. For
dead and imposed loading refer to BS 6399 :
Structures should be designed by considering the Part 1. For 'wind loading on buildings refer to
limit states at which they become unfit for their CP 3 : Chapter V : Part 2. British Standards also
intended use. Consideration should always be given exist for nominal loads on cranes and lifts
to the following limit states: (including dynamic effects). Where no relevant
(a) static strength (ultimate limit state) (see 3.3); British Standard exists nominal loads should be
(b) deformation (serviceability limit state)
decided by the designer and the client. A method
(see 3.4);
of assessing loads using a statistical and probability
(c) durability (see a.5). basis is given in appendix B.
In certain structures it will be necessary to When the imposed load consists of soil or other
consider one or both of the following: filling, consideration should be given to the
material becoming saturated. In assessing
(1) fatigue (see 3.6); temperature effects it may be assumed that in the
(2) vibration (see 3.7). UK, in the absence of local information, the
D~sign will normally be carried out by calculation average internal temperature of the structure
using the guidance given in sections 4 to 7 and varies between 5 °C and + 35°C. The effect of
appendices B to L. It is permissible, however, to the colour of external sheeting on internal
verify a proposed design by testing (see section 8). temperature should also be considered.
3.2.3 Factored loading
3.2 Loading Factored loads are used for checking the limit state
of static strength. They are the nominal loads
3.2.1 General multiplied by the overall load factor, 'Yf, which
A :structure or structural component should be provides an allowance for variability in loading,
designed to resist all loads and actions to which, accidental overload, etc. 'Yf is defined as follows:
within reason, it can be subjected. These are
'Yf 'Yfl'Yf2
classified as follows.
where
ea) Dead load. Self-weight of the structure and of
any permanently attached item it supports. 'Yfl and 'Yf2 are the partial load factors.

(b) [mposed load. Any statically or dynamically 'Yfl is governed by the type of load, and 'Yf2 allows
applied load other than dead or wind loading. some relaxation when a combination of imposed
and/or wind loads is applied to the structure. As a
(c) Wi'nd load. Dynamic loading due to \vind
guide, tables 3.1 and 3.2 give values of i'fl and 1I2
gusts.
based on building structures, but different values
(d) Temperature effect. Temperature fluctuations may be used by agreement between the designer
leading to forces in a structural component. and the client. If different values are chosen bv
All relevant loads should be considered separately reference to other British Standards, care sho~ld
or in such realistic combinations as to comprise the be taken to ensure that 'Yfl does not include a
most critical effects on the elements and the factor to allow for variability of material strength.
structure as a whole. The magnitude and frequency For the initi-al design of simple structures'Yf2 may
of fluctuating loads should also be considered. be conservatively taken as 1.0 for all imposed or
Particular attention should be given to loading wind loads.
conditions during assembly, and the settlement of
supporting structures may need to be taken into Table 3.1 Load factors (based on building
account. The possibility of loads due to seismic
forces, fire, explosion and vehicular impact should
be considered.
:3.2.2 Nominal loading
Direct effect
)Iominalloads are defined as rhose to which the
strucmre may be reasonably expected to be Countering overturning or uplift

carrying during 110ITnai ~ervice. They are used for Impused load (not including wind loads)

checking the limit states of deformation, fatigue Wind !uad

and \'ibration. Where possible they should be

Forces due to effects

.~~------

;30

 Section 6 BS 8118 : Part 1 : 1991

These recommendations apply only to lap and 6.3.7 Long grip rivets
cover plate joints between flat plates. The spacing The grip length of rivets should not exceed five
of bolts and rivets in spigot joints, joints between times the hole diameter.
tubular members and between parts of very
dissimilar thicknesses should be determined from 6.3.8 Washers and locking devices
consideration of the local geometry and the loading Wa.'lhers should be used in accordance with 2.3 of
on the joint. BS 8118 : Part 2 : 1991. Locking devices approved
by the engineer should be used on nuts liable to
6.3.3 Edge distance
work loose because of vibration or stress
The edge distance, measured from the centre of fluctuation.
the rivet or bolt, for extruded, rolled or machined
edges, should be not less than 1.5 times the rivet 6.3.9 Intersections
or bolt diameter. If, on the bearing side, the edge Members meeting at a joint should nonnally be
distance is less than twice the diameter, the arranged with their centrodial axes meeting at a
bearing capacity should be reduced 6.4.4). If point. In the case of bolted framing of angles and
the edges are sheared, the above limits should be tees, the setting out lines of the bolts may be used
increased by 3 mm. instead of the centroidal axis.
6.3.4 Hole dearance
The hole clearance should be in accordance with 6.4 Factored resistance of individual
table 3.1 of BS 8118 : Part 2 : 1991. Bolts that
transmit fluctuating loads, other than wind loads,
rivets and bolts other than HSFG bolts
should be close-fitting, or HSFG. complying with British Standards
6.3.5 Packing 6.4.1 Limiting stresses
Where fasteners are carrying shear through a The limiting stress Pf for solid rivets and bolts is
packing, a reduction of the factored design defined as follows.
resistance should be taken into account if the (a) Steel fasteners: Pr is the gua.rameed minimum
thickness of packing exceeds 25 % of the fa.'itener yield stress for the bolt or rivet stock.
diameter, or 50 % of the ply thickness.
(b) Stainless steel bolts and stainless steel rivets:
6.3.6 Countersinking
Pf is the lesser of 0.5([0,2 ftJ and 1.2/0.2.
One-half of the depth of any countersinking of a
rivet or bolt should be neglected when calculating (c) Aluminium bolts and rivets: values of Pf for
its length in bearing. ~o reduction is necessary for the aluminium alloys in table 2.3 are given in
rivets or bolts in shear. The factored design table 6.1. Where the shear strength value is
resistance in axial tension of a countersunk rivet or available, derived from tests on the bolt or on
bolt should be taken as t'No-thirds of that of a plain the rivet in the as-driven condition (see
rivet or bolt of the same diameter. The depth of BS 1974 1) for large diameter rivets), this may be
countersinking should not exceed the thickness of used. In this case, as in the expression for VHS
the countersunk part less 4 mm, othenvise in 6.4.2 should be reduced from 0.6 to 0.33.
perfonnance should be demonstrated by testing.

Bolts s6
6 to 12 175
s12 175
175
Rivets
; 5154A • 140
6082 110
6082 s 25 165
.6056A s 25 145
H22 s 25 . 155

1) Obsolescent smndard.

83

 BS 8118 : Part 1 : 1991 Section 6

6.4.2 Shear The bearing capacity of the connected ply is given

The factored resistance (VRS) of a single rivet or
by either of the following, whichever is the lesser:
bolt in single shear is taken as:
BRP = edt tPahm; or
VRS = Cl'sPfAesKlhm
BRP = etPa/l'm
where
where
Pf is as defined in 6.4.1;
e is the distance from centre of hole to the
Cl's 0.6 for aluminium bolts or rivets;
adjacent edge in the direction the fastener
bears;
Cl's = 0.7 for steel bolts or rivets;

I'm i<; the material factor, and is equal to 1.2 for

c 2 when dtlt < 10;

all bolts and rivets, Le. aluminium, steel and 20tldr: when 10 < dtlt < 13;
stainless steel (see table 3.3). 1.5 when dtlt > 13;
For bolts: Pa for the material of the connected ply is the
"4es = Atb, the stress area of the threaded part of lesser of 0.5Cto.::! + f;) and 1.2fo.2 (see
the bolt, when the shear plane passes through tables 4.1 and 4.2). ;: l:1o..f..,t Got;)/ rs
that area; or
6.4.5 Combined shear and tension
Aes = ASH) the area of the shank, when the

shear plane passes through the shank.

When bolts or rivets (except aluminium rivets
see 6.4.3) are subjected to both shear and tension
the following condition should be satisfied (in
For rivets: addition to 6.4.2 and 6.4.3):
the area of the hole;
44es = A h , (P/PRT) 2 (V/VRS )2:::; 1
KI = 1.0 for rivets; where
0.95 for close tolerance bolts;
P is the axial tensile load arising under

0.85 for normal clearance bolts. factored loading;

6.4.3 Axial tension V is the shear load arising under factored

The factored resistance, PRT) for a single fastener loading;
in axial tension is taken as PRT is the factored resistance in axial tension;
PRT = apf Atbi'Ym VRS is the factored resistance in shear.
where
Pt, Atb and 1m are as defined in 6.4.1 and 6.4.2; 6.5 HSFG bolts
a 1.0 for steel and stainless steel 6.5.1 General
bolts and rivets; Only pre-loaded general grade HSFG bolts in
a = 0.6 for aluminium bolts. accordance with BS 4395 : Part 1 should be used
for aluminium structures. Design may be based on
The use of aluminium rivets in tension is not calculations for joints where the proof strength of
recommended. the material of the connected parts exceeds
6.4.4 Bearing 230 N/mm 2 . For connected parts manufactured
from material with a proof strength less than
The effective factored resistance in bearing for a
230 N/mm2, the strength of joints using general
rivet or bolt is the lesser of the factored resistance
grade HSFG bolts should be proved to the
in bearing of the single fastener BRF and the
satisfaction of the engineer by testing. In
bearing capacity of the connected ply BRP.
aluminium structures the relaxation of bolt
The factored resistance in bearing, BRF. for :l single pre-load due to tension in the joined material
fastener is taken as cannot be ignored.
BRF = dr: t2pf/lm The thermal expansion of aluminium exceeds that
where of steel and the variation in bolt tension due to
change of temperature cannot be ignored. Reduced
df is the nominal diameter of fastener;
temperature reduces friction capacity' and
t is the thickness of connected ply:
increased temperature increases the stress
in the bolt and the bearing suess under the
Pf is defined for steel and aluminium fasteners
washers. These effects are only significant for
in 6.4.1;
extremes of temperature change and long grip
1m is the material factor (see rable :3.:3). ,enJrths,

84

!'?l
"'j .£ Section 3 BS 8118 : Part 1 : 1991
1
t
fj
·"f

.:'.L USE

: Thble 3.2 Load factors for combined loads 3.3.3 Factored resistance
Load I 'Yf2 This is the calculated resistance divided by the
material factor 'Ym. The calculated resistance is the
Dead load : 1.0 actual capacity of the component in relation to the
Imposed or wind load giving most severe 11.0 I action-effect being considered (axial load, bending
loading action on the component i moment or shear force), based on recognized
structural analysis and assuming satisfactory
Imposed or wind load giving second most 08
manufacture.
1 . .
severe loading action on the component
The material factor, 'Ym, takes account of
Unposed or wind load giving third most 06 differences between the strengths of material test
severe loading action of the component 1 .
specimens and the strength of the actual material
i ~ • in the structure as manufactured, and reflects
1,severe loading action on the component possible doubt as to the soundness of the
component as built. 'Ym should normally be taken
NOTE. In some structures the wind load-could be the most

severe applied load; in others the wind load could produce

from table 3.3, but different values may be used by
load effects less severe than those due-ttl the major imposed
agreement between the designer and the client.
loads.

~----------------------------------------------~/
'Thble 3.3 Material factors
3.2.4 Dynamic effects Type of construction : 'Ym
In order to determine the nominal loading on a
structure under dynamic conditions, reference I I Members I Joints
should be made if possible to an appropriate British : Riveted and bolted 1.2 11.2
Standard. Forces from dynamic effects are treated
as imposed loads in table 3.1.
In other cases, should the designer use a 'dyllamic
magnification factor' he should beware that this i l
) For welding procedures which do not comply with BS 4870 : !

might be a dangerous procedure if the response of I Part 2, "fm should be increa5ed to 1.6.
--------------------~
the structure is not taken into account. This
applies particularly to aluminium structures of high Rules for establishing rhe calculated resistance are
flexibility that have a natural period of vibration given in sections 4 and 5 (members) and section
similar in magnitude to that of the imposed load. 6 (joints). A method of assessing the calculated
resistance on the basis of statistics and probability
If initial calculations show that a problem exists, a is given in appendix B.

more detailed computation based on the equations

)l0TE. In certain structures it is necessary to check that failure

of motion should be carried out. The need to will not occur by overturning or sway failure.

provide artificial damping should be examined, and

tests on prototype components may also be
necessary. 3.4 Deformation
3.4.1 Recoverable elastic deformation
3.3 Static strength A structure is acceptable in terms of deformation if
the following is satisfied:
3.3.1 General
A component is acceptable in terms of static elastic deflection under < limiting
strength if the following is satisfied: nominal loading deflection
Action-effect under ..- factored resistance
It is permissible, when different combinations of
factored loading ... appendix B)
imposed loading are possible, to assume a reduced
loading equal to 'Yf2 x nominal loads, where 'Yf2 is
:3.3.2 Action-effect under factored loading given in table :3,2.
This is the axial force, bending moment or shear The calculation of elastic deflection should
force ariSing in a component due to the application generally be based on the properties of the gross
of factored loading, found by using accepted cross section. However, for slender sections it may
stmctural anaiysis. 1ne factored loading is found be necessary to take reduced section properties to
by taking the nominal loads and multiplying each allow for local buckling (see section 4),
by the appropriate load factor.

31
 t

BS 8118 : Part 1 : 1991 Section 4

Section 4. Static design of members

4.1 Introduction 4.1.4 Advanced design

4.1.1 General Members can be safely designed using the

All members should satisfy the limit states of static recommendations of this section and certain

strength and of deformation. Deformation is appropriate appendices. Other appendices provide

covered in 4.9. a fuller treatment of certain specific aspects of

member behaviour, and their use may lead to

Where reference is made to design curves, it is

permissible instead for the designer to use formulae lighter designs.

from which the curves are derived (see

appendix K).
4.2 Limiting stresses
Members are usually formed of extrusions, plate,
Resistance calculations for members are made using
sheet, tube or a combination of these. The rules
assumed limiting stresses as follows:
below do not apply to castings, and designers

wishing to employ castings should do so in Close

Po is the limiting stress for bending and overall

consultation with the manufacturers thereof.

yielding;
4. 1. 2 IJmit state of static strength
Pa 1s the limiting stress for local capacity of the
The factored resistance of a member to a specific
section in tension or compression;
action-effect should not be less than the magnitude
of that action-effect arising under factored loading. Pv is the limiting stress in shear;
Rules for obtaining resistance to different actions Ps is the limiting stress for overall buckling

are given as follows: stability.

(a) for beams (resistance to moment and shear

force) (see 4.5); Values of Po, Pa and Pv depend on the material
(b) for ties (resistance to axial tension) (see 4.6); properties and should be taken as in table 4.1 or
(c) for struts (resistance to axial compression) 4.2. For materials not covered in these tables refer

(see 4.7). to appendix D.

The procedure for calculating the interaction Values of Ps should be determined in accordance

between moment and axial load in members \vith 4.5.6.5 or 4.7.6.

su~ject to combined actions is given in 4.8.

The formulae given contain limiting stresses (Po,
Pa, Pv) related to material properties, which should 4.3 Section classification and local
be taken in accordance with 4.2. They also contain buckling
the material factor rm which should be read from
4.3.1 General
table 3.3.
The resistance of a member may be reduced as a 4.3.1.1 Section classification
result of local buckling, depending on the Resistance of members under moment or axial
slenderness of its cross section. A proposed design compression may become reduced by local
is checked (except for a member under axial buckling, if the slenderness of their component
tension) by classifying the section in terms of its elements is high. The first step in checking such
susceptibility to this type of failure. A method for members is to establish the section classification,
checking the local buckling, including section i.e. the susceptibility to local buckling. In order to
classification, is given in 4.3. do this, and also to allow for the effect of local
i.1.3 Heat-affected zones (HAZs) buckling (when necessary), the designer should
Structural aluminium material generally becomes consider the slenderness of the individual elements
weakened in the heat-affected zone (HAZ) adjacent comprising the section.
to welds, and this should be allowed for in the
design. This does not apply when the parent 4.3.1.2 Types of ele",;ent
material is in the 0 or T4 condition; or when it is The follOwing basic types of thin-walled element
in the F condition and design is based on are identified in these rules:
O-condition properties. (a) flat outstand element;
Rules for estimating the severity and extent of HAZ (b) flat internal element;
softening are given in 4.4. Subsequent clauses then
show how to allow for the effect of this softening (c) curved internal element.
on member resistance. These are often unreinforced, Le. not
It is important to realize that a small weld, as used longitudinally stiffened (see figure 4.1(a)). The
for example in connecting a small attachment, may stability of flat elements can be greatly improved
considerably reduce the resistance of a member, by the provision of longitudinal stiffening ribs or
due to softening of part of the cross section. In lips. see figure 4.1(b), in which case the elements
beams it is often beneficial to locate welds in are referred to as reinforced.
'o'v-stress ;:reas, i.2. !"lear the :ieut::.:tl ilxis or away
from the region of peak moment.
Section 4 BS 8118 : Part 1 : 1991

Thble 4.1 Limiting stresses, heat-treatable alloys

Alloy I Condition : Product : TIrlckness : Limiting stress

, , ,
o
lu
,
d
~ I

!
Imm nun Nimm2 'N/mm2 1 N/mm2
6061 T6 Extrusion - 150 240 260 145
T6 Drawn tube 6 240 265 145
6 1
10 225 260 1
135
6063 T4 Extrusion - 150 65 85 40
T4 Drawn tube 1­ 10 95 120 60
I

T4 f::Forgings - 150 80 100 50

T5 . Extrusion - 25 110 130 65
T6 Extrusion 150 160 175 95
T6 Drawn tube
,'",,, 10 180 190 ! 110
I T6 - : 150 160
l Forgings 170 195
16082 T4 I Extrusion - 150 115 145 70
T4 I Sheet 0.2 3 115 145 70
I T4 Plate 3 25 105 140 65
T4 Drawn tube 10 105 140 65
T4 Forgings - 150 115 145 70
T6 Extrusion - 20 255 275 155
20 150 270 290 160
T6 Sheet 0.2 3 255 275 155
T6 Plate 3 25 240 265 145
T6 Drawn tube - 6 255 280 155
6 10 240 275 145
T6 Forgings - 120 255 i
275 155 I
7020 T4 n.
Dx~r U"lV>I - 25 ! 185 :230 110
I

T4 Sheet, plate 0.2 25 160 205 95

T6 Extrusion - 25 280 310 170
T6 Sheet, plate 0.2 25 270 295 160

35
 . -~:. _>.ic:.,s,ii;:;',;;";;,,w,31·· :_. ~t

BS 8118 : Part 1 : 1991 Section 4

Thble 4.2 Limiting stresses, non-heat-treatable alloys

Alloy I Condition ! Product

Thickness Limiting stress
lOver Up to and Po I P,. Pv
II I I including

I~
I
I mm N/mm2 N/mm2 N/mm2
1200 I H14 Sheet 12.5 90 95 55
1
. 3103 H14 Sheet 10.2 12.5 110 1120 '65
,
H18 Sheet 10.2 3 150 1150 190
3105 H14 Sheet : 0.2 3 I 145 150 ! 85
H16 Sheet ' 0.2 3 175 100
<. /170
H18 Sheet 0.2 3 190 200 115 I
5083 0, F I Extrusion - '- ! 150 '105 150 65
0 Sheet, plate 0.2" 80 105 150 65
0 Drawn tube - 10 105 150 65
F Sheet, plate 3 25 130 170 75
H22 Sheet, plate 0.2 6 235 270 140
I, H22 I Drawn tube 10 ,235 270 1
140
1 5154A 10, F Extrusion - 1150 1
65 100 40
0 Sheet, plate 0.2 6 65 I
100 40
0 Drawn tube - 10 65 100 •40
I
I
H22 Sheet, plate 0.2 6 160 200 95
I H24 Sheet, plate 0.2 6 225 250 135 I
H24 I Drawn tube I
10 1200 1220 1180
I
'F I Welded tube 0.8 : 2.0 ! 220
/230 I 130
I H22 i Sheet, plate 0.2 6 I 125 155
175
I H24 I Sheet, plate

l
1
0.2 16 175 : 200 105
5454 '0, F
o
j Extrusion
Sheet, ;;>late
1- [0.2
150 /' 65
60
: 100
95 J L 5
: 40

H22 Sheet 0.2 3 180 215 110

.1 0-,2 .~.. 12.Qg_~3i.
I i

H24 Sheet 3 __ 120

:36

 BS 8118 : Part 1 : 1991

""'''''-..-~~-- ___ ~ ____ ~_h_,,?>_

'f" tt t.'die- "'wcZ:hiit!ti$$tef(­

Section 4
,~f
••
.-.-;~-
-, -~,
.

4.7 Compression members 4.7.4 Column buckling

4.7.1 General 4.7.4.1 Buckling stress
The value of Ps for column buckling should be read
4.7.1.1 Three checks are generally needed fOf·
from the appropriate curve in figure 4.10, selected
axially loaded compression members (struts) as in accordance with 4.7.6.
follows:
Ca) column, Le. flexural, buckling check 4.7.4.2 Slenderness parameter
(see 4.7.3 and 4.7.4) (refers to overall buckling The column buckling slenderness parameter A
of the member as a whole); needed for figure 4.10 is defined as follows:
(b) torsional buckling check (see 4.7.3 and 4.7.5) A = lIr
(refers to overall buckling of the member as a where
whole);
I is the effective length;
ec) local squashing check (see 4.7.7) (relitles to
r is the radius of gyration;
the weakest cross section down its lengtk).
Check (a) should always be made. Check (b) is both, appropriate to the direction of buckling
generally required, but may be waived in some conSidered.
cases. Check Cc) is only needed for struts having The effective length l should be taken as KL,
low slenderness ratios that are significantly where L is the length between points of lateral
weakened locally by holes or welding. support; or for a cantilever strut, its length. The
value of K, the effective length factor for struts
4.7.1.2 Th take account of interaction between should be assessed from a knowledge of the end
axial load and bending it is generally necessary to conditions; table 4.8 gives guidance.
refer to 4.8. However, for struts having eccentric
end connections it is in certain cases permissible to The value of r should be based on the gross section
use a simplified procedure (see 4.7.9) to allow for for all members.
the moments introduced. NarE. VVnen the cross section is wholly or substantially affected
by HAZ softening at a directionally restrained end of a member,
4.7.2 Section classification for axial such restraint should be ignored in arriving at a suitable value
for K. Thus Jor case 1 in table 4.8 K should be taken as L 0 if
compression the section is fully softened at each end.
Before making any of the three checks given
in 4.7.1 it is first necessary to classify the
cross-section as compact or slender. The
classification is based on that of the least
favourable of its component elements, in 1 Effectively held in position and
accordance with 4.3.3. restrained in direction at both ends
4.7.3 Resistance to overall buckling 2 Effectively held in position at both i 0.85
ends and restrained in direction at
With both checks Ca) and (b) the axial thrust P one end
under factored loading should not exceed the
factored axial resistance P R based on overall 3 Effectively held in position at both I 1.0
buckling, given by the following: ends, but not restrained in direction
PR psAh'm 4 Effectively held in position at one i 1.25
where end, and restrained in direction at
both ends
A is the gross area, without reduction for HAZ 5 Effectively held in position and I 1. ,5
softening, local buckling or holes; restrained in direction at one end,
Ps is the buckling stress in flexural or torsional and partially restrained in direction
buckling; I but not held in position at the other
1m is the material factor (see table ;3.3).
end
6 Effectively held in position and I :2,0
In finding Ps for column buckling, failure about restrained in direction at one end,
both principal axes should be considered and the but not held in position or restrained
lower value taken. : at the other end
"iCITE..For a strut of high slenderness (t. > 130) it will be
necessary to refer to appendix K to find Ps'

34
~
_-"f"

Section 4 BS 8118 : Part 1 : 1991

i"-... l\. 1\ I i 1
i
I" ~ .\ . ! I
i ' '\. \1\ • i !
-r
300 " \. 1\ 1\
" '\\ \\'
\\
I
"- r-.. \ \\' !

.\' l\
I ...... k.. ."t--...
.\l\ I I

i
"
1 ........ '{ 1\ ~\\I\
k...
i""\ 1\ ~\\
l\' ,\
1

I
I
i t---.. i'- \ .\' ~\\
N I"\. \. ~\~I\ I !
200 1'-....... '\. \'\ ,\
. 'I-:: f.,1 ~ I
!

r- l- I i ' [\~I\
e
e

--z .
!--h....
1"---
"
J'...
l'\ 1\
.\ ~[\
~\
~ -.. r-.
i'- "-
........
"N.\ ~~ i
I
i
~ "- ~~ 1
!
t--r- ....... I" ~ ~ 11 i i i
I I !-- h... 1':R ~~ i I i
100 I "i- f-- ~ r.... "-R'~ I
I • I
, . I
1 I N- ~ ~ '"

I
i
i
!

T i
. !

,
I
i
"
i'-
i
~~~
i

"'r-:::::: ~ ~
r.::::;; ~ --.-...
: 1
!
j i
I ! ~~~
I I -r=:
I
I ' I
• i • i ! I
I I I I I I : I
a 50 100
A
(a)

NOTE. To find Ps at A > 130 refer to figure K. L

Figure 4.10 Column buckling stress Ps for struts

55
~_•._._.~","" .. "~n."" __._ _._~'"~.,,_~_.- '__.«~_ _ • ''1'' ""'9¥ifw1" >be ""'~t"~;'.f?i'*ff ri@" J......... ....:_ "-~:Wj'i'ii> 7:1 ."""$=;-77
C

BS 8118: Part 1 : 1991 Section 4

t.1 I
\l \1\ \J i I
~

b. 1\ }'\l'S
1'\..1 "i. '{ \h.\
h.L\J.....1l1\
T"J l\.~ i

'"E 200
--
E
:z
111.11111 1111111111
i"'-l N \)'\'t\~ \ 1
1

t:::I.'" b:L 1 'h N'\~~

i """" ~r\\~[\f
i I' "k ""1'\ ~&. I

't--J "":\:~ ,\
I ----....... f""­ I""~ ~l\. I I I I I i I
• j ~ i"'-"~ 0' i I I I I l I
100 -r­ r--.. r--.. ""'~ 2S i I I I ! I I I
i'r­ r--. ' 0 ~ ~ i
r--.. r--.::--;: ~ . . . ~ I I I I j
I r-...

a 50 100
A
(b)

:"farE. Th find Ps at A > 130 refer to figure K.l.

Figure 4.10 Column buclding stress Ps for struts (continued)

56
 Section 4 BS 8118 : Part 1 : 1991

t;L

200
~

II -..
z
~'"
t

i
t
100
It

I
,
I

a 50 100
A
(c)

Figure 4.10 Column buckling stress Ps for struts (concluded)

57
BS 8118 : Part 1 : 1991 Section 4

4.7.5 Torsional buckling 4.7.6.2 Determination of PI

4.7.5.1 Exemptions The value of PI should generally be found as
follows (but refer to 4.7.6.4 for sections composed
The possibility of torsional buckling may be ignored
of radiating outstands):
for the following:
(a) closed hollow sections; (a) compact section, with no PI = Po
(b) doubly symmetrical I-sections; HAZ effects
(c) sections composed entirely of radiating (b) other sections, generally PI = (AeIA)po
outstands, e.g. angles, tees, cruciforms, that are where
classified as compact in accordance with 4.3.3.
A is the gross area of section;
4.7.5.2 Slenderness parameter
Ae is the area of effective section (see 4.7.6.3);
The torsional buckling slenderness parameter A
may be obtained using either (a) or (b) below, or Po is the limiting stress for the material (see
else by referring to appendix J. It shoul:& always be tables 4.1 and 4.2).
based on the gross area of the section as follows.
Curve selection on this basis is valid, provided the
member meets the tolerances of straightness and
(a) General formula A = 1l"(EAJPer )V,
twist laid down for extruded material (see
where BS 8118 : Part 2). When there is a possibility that a
A is the gross section area, without reduction fabricated strut will fail to meet these tolerances,
for local buckling, HAZ softening or holes; PI should be taken as s times the value given
by 4.7.6.2(a) or (b) above, where:
E is the modulus of elasticity;
s = 0.6 + 0.5exp( -0.02A) (but not
Per is the elastic critical load for torsional exceeding l.0).
buckling, allowing for interaction with
column buckling when necessary. 4.7.6.3 Effective section
(b) Sections as given in table 4.9
Effective section applies to strut sections that are
as follows:
A kAt

(a) classified as slender;

where

(b) affected by HAZ softening;

k is read from figure 4.11

(c) both (a) and (b).

At is found as follows:

The effective section may be obtained by taking

(1) for angles, tees, cruciforms At = Ao reduced thicknesses, with no deduction for holes as
(2) for channels, top-hats
follows, and may be based on the least favourable
cross section (but see 4.7.6.5 for welded members).
AO

At = ""'[1:--+--::-(:::-:YA=-oZ"""/::-"A-'/"')"'""r'"'"Vz (1) Slender section, free from HAZ softening.

The thickness of any element is taken as kL times
Thble 4.9 contains expressions for Ao and Y; its true thickness t, where kL is found as .
and also for s and X (needed for figure 4.11). in 4.3.4. In the case of reinforced elements kL
In (2) the quantity Ax should be taken as the should be applied to the area of the
effective slenderness for column buckling reinforcement as well as to the basic thickness of
about axis xx (as defined in table 4.9). the plate.
(2) Compact section, with HAZ softening. The
4.7.5.3 Buckling stress thickness of any softened zone should be reduced
The value of Ps for torsional buckling should be so as to give it an assumed area equal to k z times
read from the appropriate curve in figure 4.12, its true area. The-extent of such a zone should
selected in accordance with 4.7.6. be found from 4.4.3, and the value of kz
from 4.4.2.
4.7.6 Strut curve selection
(3) Slender section, with HAZ softening. For
4.7.6.1 Basic procedure slender elements free from HAZ effects the
The overall buckling stress Ps should be read from reduced thickness is found as in (1); and for HAZ
the appropriate strut curve diagram in figure 4.10 regions not located in slender elements it is taken
(for column buckling) or figure 4.12 (for torsional as in (2). If an element is both slender and
buckling). Choice of diagram should be in affected by HAZ softening, the reduced thickness
accordance with table 4.10. In any given diagram is taken as the lesser of kLt and kzt in the
the appropriate curve is that meeting the stress softened part and as kLt elsewhere in it.
axis at a stress Pit to be determined as in 4.7.6.2. Sections composed of radiating outstands are
treated specially (see 4. 7.o.,~).

58
 BS 8118 : Part 1 ! 1991 Section 6

Section 6. Static design of joints

6.1 General
6.2.2 Groups of fasteners
This section deals with the design of joints made by
Groups of rivets, bolts or special fasteners, known
using fasteners, adhesives, or by welding. The
collectively as 'fasteners', forming a connection,
follOwing types of fastener are discussed: rivets,
should be designed on the basis of a realistic
black bolts, close tolerance bolts, high strength
assumption of the distribution of internal forces,
friction grip bolts (HSFG bolts), special fasteners
having regard to relative stiffness. It is essential
and pins. For joints made by welding the design
that equilibrium with the external factored loads

resistance of butt and fillet welds is defined. The

be maintained.

design of joints between cast or forged elements

6.2.3 Effect of cross-sectional areas of plies
should be carried out in conjunction with the

manufacturers.
The design of the plies at sections containing holes
for fasteners should be based on minimum net
The following types of connection are called joints:
areas, except for rivets in compression, In certain
(a) connections between structural members, friction grip bolted joints the limit state is met by
e.g. beam to column; '!:' the friction capacity of the joint, and in these
(b) connections between the element~;of a circumstances the design should be based on
'built-up' member, e.g. webs to flanges, splices; ~um gross areas.

(c) connections between localized details and 6.2.4 Long joints

structural members, e.g. brac~{et to beam, lug When the length of a joint, measured between
and clevis in a tension member. centres of end fasteners in the direction of
All types of connection should be designed to meet transmission of the load, is more than 15df (where
the limit states of static strength and fatigue. No dr is the nominal diameter of the fastener), or
checks for serviceability limit states are required, when the number of fasteners in this direction
except for pin joints in structures that are exceeds five, the designer should take account of
frequently assembled and disassembled, for joints the reduction in the average strength of individual
where deflections are critical or, for friction grip fasteners due to uneven distribution of the load
bolted joints, where slip is to be prevented. The between them.
factored loading on a joint should be calculated
using the load factors given in section 3. Fasteners
subject to reversal of load should be either close' 6.3 Riveted and bolted joints:
tolerance or turned barrel bolts, solid rivets, HSFG geometrical and other general
bolts, or special fasteners that prevent movement. considerations
Hollow rivets and other special fasteners which do 6.3.1 Minimum spacing
not comply with British Standards may be used
provided their performance has been demonstrated The spacing between centres of bolts and rivets
to the satisfaction of the designer by testing or should be not less than 2.5 times the bolt or rivet
other means. They should be spaced and designed diameter. Closer spacing is permitted for HSFG
by liaison between the designer and the bolts, limited by the size of the washer, bolt heads
manufacturer. In demountable joints with steel or spanners, and the need to meet the limit states.
fasteners thread inserts should be used in any 6.3.2 Maximum spacing
threaded aluminium element of the joint. Their
In tension members the spacing of adjacent bolts or
,per.fonuance. should be .demonstrated to the
rivets on a line in the direction of stress should not
satisfaction of the designer by testing or other
exceed 16t or 200 mm, where t is the thickness of
means.
the thinnest outside ply. In compression or shear
members it should not exceed 8t, or 200 mm. In
6.2 Riveted and bolted joints: design
addition. the spacing of adjacent bolts or rivets on
considerations
a line adjacent am:} parallel to an edge of an
outside ply should not exceed 8t or 100 mm. Where
6.2.1 General
rivets and bolts are staggered on adjacent lines.
Joints using rivets or bolts should be designed so
and the lines are not more than 75 mm apart, the
that under the factored load the loading action at
above limits may be increased by 50 %.
any fastener position does not exceed the factored
In any event, the spacing of adjacent rivets and
resistance of the fastener there.
bolts, whether staggered or not, should not exceed
32t or 300 mm in tension members. and 20t or
:300 mm in compression and shear members.

82
 Section 6 BS 8118 = Part 1 : 1991

At U t;;·l:'
tIV'~ ..

These recommendations apply only to lap and 6.3.7 Long grip rivets
cover plate joints between flat plates. The spacing The grip length of rivets should not exceed five
of bolts and rivets in spigot joints, joints between times the hole diameter.
tubular members and between parts of very
dissimilar thicknesses should be determined from 6.3.8 Washers and locking devices
consideration of the local geometry and the loading Washers should be used in accordance with 2.3 of
on the joint. BS 8118 : Part 2 : 1991. Locking devices approved
6.3.3 Edge distance by the engineer should be used on nuts liable to
work loose because of vibration or stress
The edge distance, measured from the centre of fluctuation.
the rivet or bolt, for extruded, rolled or machined
edges, should be not less than 1.5 times the rivet 6.3.9 Intersections
or bolt diameter. If, on the bearing side, the edge Members meeting at a joint should normally be
distance is less than twice the diameter, the arranged with their centrodial axes meeting at a
bearing capacity should be reduced (see 6.4.4). If point. In the case of bolted framing of angles and
the edges are sheared, the above limits should be tees, the setting out lines of the bolts may be used
increased by 3 mm. v ..
instead of the centroidal axis.
6.3.4 Hole c l e a r a n c e ; · 1
The hole clearance should be in accordance with 6.4 Factored resistance of individual
table 3.1·of BS 8118 : Part 2 : 1991. Bolts that
transmit fluctuating loads, other than wind loads, rivets and bolts other than HSFG bolts
should be close-fitting, or HSFG. complying with British Standards
6.3.5 Packing 6.4.1 Limiting stresses
Where fasteners are carrying shear through a The limiting stress Pr for solid rivets and bolts is
packing, a reduction of the factored design defined as follows.
resistance should be taken into account if the (a) Steel fasteners: Pr is the guaranteed minimum
thickness of packing exceeds 25 % of the fastener yield stress for the bolt or rivet stock.
diameter, or 50 % of the ply thickness.
(b) Stainless steel bolts and stainless steel rivets:
6.3.6 Countersinking
Pr is the lesser of 0.5([0,2 . ;. iu) and 1.2io.2.
One-half of the depth of any countersinking of a
rivet or bolt should be neglected when calculating (c) Aluminium bolts and rivets: values of Pr for
its length in bearing. No reduction is necessary for the aluminium alloys in table 2.3 are given in
rivets or bolts in shear. The factored design table 6.1. Where the shear strength value is
resistance in axial tension of a countersunk rivet or available, derived from tests on the bolt or on
bolt should be taken as two-thirds of that of a plain the rivet in the as-driven condition (see
rivet or bolt of the same diameter. The depth of BS 1974 1) for large diameter rivets), this may be
countersinking should not exceed the thickness of used. In this case, as in the expression for VRS
the countersunk part less 4 mm, otherwise in 6.4.2 should be reduced from 0.6 to 0.33.
performance should be demonstrated by testing.

r Thble 6.1 L:iIititing stress Pr for aluminium fasteners

: Fastener type : Alloy I Condition 'supplied ! Method of driving I Diameter I Pf
mm I N/mm2
Bolts 6082 T6 :::;6 165
6 to 12 175

6082
6082
5056A
5056A

1) Obsolescent standard.

83
 .:;

DS 8118 : Part 1 : 1991 Section 6

6.4.2 Shear The bearing capacity of the connected ply is given

The factored resistance (VRS) of a single rivet or by either of the following, whichever is the lesser:
bolt in single shear is taken as: BRP = cdr tPa/Ym; or
VRS asPrAesKlhm BRP = etPai-Ym
where where
is as defined in 6.4.1;

Pr e is the distance from centre of hole to the

as = 0.6 for aluminium bolts or rivets;
adjacent edge in the direction the fastener
as 0.7 for steel bolts or rivets;
bears;
c = 2 when drlt < 10;
fm is the material factor, and is equal to 1.2 for

all bolts and rivets, i.e. aluminium, steel and = 20tldr when 10 < drlt < 13;
stainless steel (see table 3.3). = 1.5 when drlt > 13;
For bolts: Pa for the material of the connected ply is the
Aes = Atb, the stress area of the threaded part of lesser of 0.5([0'2 + fu) and 1.2fo.2 (see
the bolt, when the shear plane passes through ." tables 4.1 and 4.2).
that area; or
Aes = ASH, the area of the shank, when the
6.4.5 Combined shear and tension
shear plane passes through the shank.
When bolts or rivets (except aluminium rivets
see 6.4.3) are subjected to both shear and tension
the following condition should be satisfied (in
For rivets: addition to 6.4.2 and 6.4.3):
~4es = Ah, the area of the hole; (PIPRT)2 + (VIVRS)2 :5 1
Kl = 1.0 for rivets;
where
= 0.95 for dose tolerance bolts;

P is the axial tensile load arising under

= 0.85 for normal clearance bolts.
factored loading;
6.4.3 Axial tension V is the shear load arising under factored
The factored resistance, PRT, for a single fastener loading;
in axial tension is taken as PRT is the factored resistance in axial tension;
PfIT = apf Atbhm VRs is the factored resistance in shear.
where
Atb and fm are as defined in 6.4.1 and 6.4.2;
Pf, 6.5 HSFG bolts
a = 1.0 for steel and stainless steel 6.5.1 General
bolts and rivets; Only pre-loaded general grade HSFG bolts in
a = 0.6 for aluminium bolts. accordance with BS 4395 : Part 1 should be used
for aluminium structures. Design may be based on
The use of aluminium rivets in tension is not calculations for joints where the proof strength of
recommended. the material of the connected parts exceeds
6.4.4 Bearing 230 N/mm 2 . For connected parts manufactured
from material with a proof strength less than
The effective factored resistance in bearing for a
230 N/mm2, the strength of joints using general
rivet or bolt is the lesser of the factored resistance
grade HSFG bolts should be proved to the
in bearing of the single fastener BRF and the
satisfaction of the engineer by testing. In
bearing capacity of the connected ply BRP.
aluminium structures the relaxation of bolt
The factored resistance in bearing, BRF, for a single pre-load due to tension in the joined material
fastener is taken as cannot be ignored.
BRF = dr t2pf/rm The thermal expansion of aluminium exceeds that
where of steel and the variation in bolt tension due to
change of temperature cannot be ignored. Reduced
(ir is the nominal diameter of fastener; temperature reduces friction capacity and
is the thickness of connected ply; increased temperature increases the tensile stress
in the bolt and the bearing stress under the
Pf is defined for steel and aluminium fasteners
washers. These effects are only significant for
in 6.4.1; extremes of temperature change and long grip
Ym is the material factor (see table 3.3). lemnhs.

84