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Steel Designers' Manual - 6th Edition (2003)
492 Plate girders
f = 1
when £ 56
f = ≥ 156
115
f =
1 15 + 0 002( -56)
56 < < 156
1.15
l
1.35
when l
.
. . l
when l
The value of tl/ty is taken as the lower of tu/ty computed as above and 1.0.
The term mfw in the above equations is a non-dimensional representation of the
plastic moment resistance of the flange (taking the smaller value of the top and
bottom flanges, ignoring any concrete).
m
fw
Mp
=
dwet
s
s b f
=
2d
t s
2
w yw
yf fe f 2
Values of tl/ty versus l are plotted in Figures 11–17 of the Code corresponding to
various values of mfw and f. These can be used directly by designers.
The term bfe is the width of flange associated with the web and is limited to
Ê
bfe £ 10tfÁ
Ë s
2
we w yw
355 12
yf
ˆ
˜
¯
Where two flanges are unequal, the value of mfw is taken conservatively as the value
corresponding to the weaker flange. Moreover, only a section symmetric about the
mid-plane is taken as effective; any portion of the flange plate outside this plane
of symmetry is ignored so that complexities due to the torsion of the flange are
eliminated.
The above procedure has to be repeated for several values of q, and the highest
value of tu/ty is to be used. From parametric studies it has been established that q
is never less than (1/3)cot -1 f or more than (4/3)cot -1 f.
When tension field action is used, consideration must be given to the anchorage
of the tension field forces in the end panels, and special procedures must be adopted
for designing the end stiffener.
17.6.2.6 Combined bending and shear (clause 9.9.3 of the Code)
The Code has simplified the procedure for girders without longitudinal stiffeners
by allowing shear and bending resistance to be calculated independently and then
combined by employing an interaction relationship on the basis given below.
(a) The bending resistance of the whole section is determined with and without
contribution from the web (Ml and MR respectively).