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Steel Designers' Manual - 6th Edition (2003)
where py is the design strength of the steel and S is the plastic modulus. For class 3
semi-compact cross-sections:
Mc = pyZ
where Z is the elastic section modulus. For class 4 slender cross-sections:
Mc = pyZeff
where Zeff is the effective section modulus determined in accordance with clause
3.6.2 of the Code.
(2) High shear flanges-only method
If Fv > 0.6 Vw but the web is designed for shear only, provided that the flanges are
not class 4, a conservative value Mf for the moment resistance may be obtained by
assuming that the moment is resisted by the flanges only. Hence:
Mf = pyfSf
Design of plate girders used in buildings to BS 5950: Part 1: 2000 475
where Sf is the plastic modulus of the flanges only.
(3) High shear general method
If Fv > 0.6 Vw and the applied moment does not exceed the low shear value given
by (1), the web should be designed using Annex H.3 of the Code for the applied
shear combined with any additional moment beyond the flanges-only moment
resistance Mf given by (2).
17.4.4 Shear resistance
17.4.4.1 Web not susceptible to shear buckling
If the web depth to thickness ratio d/t £ 62e it is not susceptible to shear buckling
and the shear resistance Pv should be determined in accordance with clause 4.2.3 of
the Code, i.e.
Pv = 0.6pywAv = 0.6pywtd
where Av = td is the shear area.
17.4.4.2 Web susceptible to shear buckling
If d/t > 62e the shear buckling resistance of the web should be determined in accordance
with clause 4.4.5 of the Code.