The Design of Modern Steel Bridges - TEDI
The Design of Modern Steel Bridges - TEDI
The Design of Modern Steel Bridges - TEDI
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152 <strong>The</strong> <strong>Design</strong> <strong>of</strong> <strong>Modern</strong> <strong>Steel</strong> <strong>Bridges</strong><br />
or<br />
syfBT 2 f<br />
syb 2 t<br />
1:25<br />
5<br />
p2 s2<br />
sy<br />
For S 4 1.0, s2 is zero and hence any web panel adjacent to a flange and with<br />
slenderness ratio S 4 1.0 may be taken as restrained irrespective <strong>of</strong> the size <strong>of</strong><br />
the girder flange. For web panels with S 5 3.6, s2 ¼ 0.5 sy, and hence such a<br />
panel adjacent to a flange can be considered restrained only if the following<br />
condition is satisfied for the size <strong>of</strong> the flange<br />
syfBT 2 f<br />
syb 2 t 50:0625<br />
s 2 yf<br />
s 2 yf<br />
s 2 yf<br />
s 2 yf<br />
s2 f<br />
s2 f<br />
!<br />
!<br />
ð5:49Þ<br />
For a web panel adjacent to a flange and with slenderness ratio 1.0 < S < 3.6,<br />
the flange size has to satisfy the following condition for the panel to be<br />
considered restrained<br />
i.e.<br />
5.7.2 Plates under shear<br />
syfBT 2 f<br />
syb 2 t<br />
1:25<br />
5 0:192ðS 1Þ<br />
p2 5 0:024ðS 1Þ<br />
s 2 yf<br />
s 2 yf<br />
s 2 yf<br />
s2 f<br />
s 2 yf<br />
!<br />
s2 f<br />
!<br />
ð5:50Þ<br />
In Section 5.4.5 the tension-field strength <strong>of</strong> a plate subjected to shear was<br />
shown to depend upon a flange stiffness parameter m given by<br />
m ¼ Mp<br />
b 2 tsy<br />
This parameter is one-quarter <strong>of</strong> the ratio <strong>of</strong> the plastic moduli <strong>of</strong> the flange<br />
plate and the web plate about their respective horizontal centroidal axes, which<br />
has been used in the section above for determining the flange stiffness required<br />
to achieve restrained plate capacity under compressive applied loading. <strong>The</strong><br />
minimum values <strong>of</strong> m required to achieve in the tension field mechanism the<br />
levels <strong>of</strong> shear capacities represented by the restrained plate capacities in shear<br />
may be obtained from the expression for tension field strength for different<br />
aspect ratios <strong>of</strong> the plate. <strong>The</strong>se minimum values should, however, be increased<br />
by a safety margin, since the tension field mechanism is attained with deformations<br />
in the plate, and in the flange member, <strong>of</strong> a much larger magnitude<br />
than is associated with the ultimate strength <strong>of</strong> orthogonally stiffened plates.<br />
By this method, the following stiffness requirement for the flange member has