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Steel Designers' Manual - 6th Edition (2003)
472 Plate girders
Table 17.1 Recommended span-to-depth ratios for plate girders used in buildings
Applications Span-to-depth ratio
(1) Constant-depth beams used in simply-supported composite girders, and 12 to 20
for simply-supported non-composite girders, with concrete decking
(2) Constant-depth beams used in continuous non-composite girders using 15 to 20
concrete decking (NB continuous composite girders are rare in buildings)
(3) Simply-supported crane girders (non-composite construction is usual) 10 to 15
3.5 of the Code), even though more slender cross-sections are permitted.The choice
of plate thickness is related to buckling. If the plates are too thin they may require
stiffening to restore adequate stiffness and strength, and the extra workmanship
required is expensive.
In view of the above the maximum depth-to-thickness ratio (d/t) of the webs of
plate girders in buildings is usually limited to
Ê
dt<
120 e = 120Á Ë p
where pyw is the design strength of the web plate. The outstand width-to-thickness
ratio of the compression flange (b/T) is usually limited to
Ê
bT£
13 e = 13Á Ë p
where pyf is the design strength of the compression flange.
Changes in flange size along the girder are not usually worthwhile in buildings.
For non-composite girders the flange width is usually within the range 0.3–0.5 times
the depth of the section (0.4 is most common). For simply-supported composite
girders these guidelines can still be employed for preliminary sizing of compression
flanges. The width of tension flanges can be increased by 30%.
17.3.3 Stiffeners
275 12
275 12
yf
yw
ˆ
˜
¯
ˆ
˜
¯
Horizontal web stiffeners are not usually required for plate girders used in buildings.Vertical
web stiffeners may be provided to enhance the resistance to shear near
the supports. Intermediate stiffening at locations far away from supports will, in
general, be unnecessary due to reduced shear.
The provision of vertical or transverse web stiffeners increases both the critical
shear strength qcr (initial buckling strength) and the shear buckling strength qw
(post-buckling strength) of web panels. The critical shear strength is increased by
a reduction in the web panel aspect ratio a/d (width/depth). Shear buckling strength
is increased by enhanced tension field action, whereby diagonal tensile membrane