Civil Engineering Reference
In-Depth Information
Worked examples of checking the moment resistance are given in
Sections 5.12.15 and 4.9.2-4.9.4, and a worked example of using the moment
resistance check to design a suitable section is given in Section 5.12.16.
5.6.1.4 Checking the lateral bracing
Beams with insufficient lateral bracing must also be designed to resist lateral
buckling.ThedesignofbeamsagainstlateralbucklingisdiscussedinSection6.9.
It is assumed in this chapter that there is sufficient bracing to prevent lateral
buckling. While the adequacy of bracing for this purpose may be checked by
determining the lateral buckling moment resistance as in Section 6.9, EC3 also
givessimpler(andoftenconservative)rulesforthispurpose.Forexample,lateral
buckling may be assumed to be prevented if the geometrical slenderness of each
segment between restraints satisfies
i
f
,
z
≤
37.56
L
c
M
c
,
Rd
M
y
,
Ed
235
f
y
(5.42)
k
c
inwhich
i
f
,
z
istheradiusofgyrationaboutthe
z
axisofanequivalentcompression
flange,
k
c
isacorrectionfactorwhichallowsforthemomentdistribution,
M
c
,
Rd
is
thedesignresistanceofafullybracedsegment,and
M
y
,
Ed
isthemaximumdesign
moment in the segment.
Aworked example of checking the lateral bracing is given in Section 5.12.15.
5.6.1.5 Checking the shear resistance
For the shear resistance check, the inequality
V
Ed
≤
V
c
,
Rd
(5.43)
must be satisfied, in which
V
Ed
is the maximum design shear force, and
V
c
,
Rd
the
design shear resistance.
For a stocky web with
d
w
/
t
w
≤
72
√
(
235
/
f
y
)
and for which the elastic shear
stress distribution is approximately uniform (as in the case of an equal flanged
I-section), the uniform shear resistance
V
c
,
Rd
is usually given by
V
c
,
Rd
=
A
v
(
f
y
/
√
3
)
(5.44)
inwhich
f
y
/
√
3istheshearyieldstress
τ
y
(Section1.3.1)and
A
v
isthesheararea
of the web defined in Clause 6.2.6(2) of EC3. All the webs of UB's and UC's
in S275 steel satisfy
d
w
/
t
w
≤
72
√
(
235
/
f
y
)
. A worked example of checking the
uniform shear capacity of a compact web is given in Section 5.12.15.
Search WWH ::
Custom Search