Civil Engineering Reference
In-Depth Information
appropriate). It can be expressed in the form
F
v
=
α
v
f
ub
A
(9.5)
inwhich
α
v
=
0.6generally(exceptGrade10.9boltswhentheshearplanepasses
through the threaded portion of the bolt, in which case
α
v
=
0.5). The factor
α
v
=
0.6 is close to the theoretical yield value of
τ
y
/
f
y
≈
0.577 (Section 1.3.1)
and the experimental value of 0.62 reported in [9].
EC3-1-8 [1] therefore requires the design shear force
F
v
,
Ed
to be limited by
F
v
,
Ed
≤
F
v
,
Rd
=
f
ub
γ
M
2
α
vn
A
n
,
(9.6)
n
where
γ
M
2
=
1.25isthepartialfactorfortheconnectorresistance(1.50forGrade
4.6 bolts),
n
is the number of shear planes,
A
n
and
α
vn
are the appropriate values
forthe
n
thshearplane.Itiscommonandconservativetodeterminethearea
A
n
at
a shear plane by substituting the tensile stress area
A
s
for the shank area
A
of the
bolt.
Forboltsinlongjointswithadistance
L
j
betweentheendboltsinthejoint,the
shear resistance of all bolts is reduced by using the factor
β
Lf
=
1
−
L
j
−
15
d
200
d
(9.7)
provided that 0.75
≤
β
Lf
≤
1, where
d
is the diameter of the bolt.
9.6.2 Bolts in tension
The resistance of a bolt in tension (Figure 9.1c) depends on the tensile strength
f
ub
of the bolt and the minimum cross-sectional area of the threaded length of the
bolt.The design force
F
t
,
Ed
is limited by EC3-1-8 [1] to
F
t
,
Ed
≤
F
t
,
Rd
=
0.9
f
ub
A
s
/γ
M
2
,
(9.8)
where
γ
M
2
=
1.25(1.50forGrade4.6bolts)and
A
s
isthetensilestressareaofthe
bolt. The use of 0.9
f
ub
for the limit state of bolt fracture in addition to the partial
factor
γ
M
2
for the connector resistance reflects the reduced ductility at tensile
fracture compared with shear failure.
If any of the connecting plates is sufficiently flexible, then additional prying
forcesmaybeinducedinthebolts,asinFigure9.13b.However,EC3-1-8doesnot
providespecificguidanceonhowtodeterminethepryingforceinthebolt,evenin
theT-stub component based method of design. Under some circumstances which
minimise plate flexure in a joint component so that the additional tensile forces
caused by prying are small, it has been suggested that the prying forces need not
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