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AD 423: Reduction in bending resistance due to high shear

When considering the resistance of cross sections under combined bending and high shear, (where the shear is equal to or exceeds half the plastic shear resistance), the resistance moment of the section should be reduced: see BS EN 1993-1-1 cl. 6.2.8(3). A reduced yield strength (1-ρ)fy where

should be used to calculate the contribution of the shear area to the resistance moment of the section. For an I section, the shear resistance is mainly provided by the web. In cl. 6.2.8(5) the alternative approach calculates the bending resistance by deducting ρ times the plastic modulus of the web from the full plastic modulus of the section, equivalent to using a reduced web thickness.

Similarly, a reduced yield strength (1-ρ)fy applied to the shear area should be used when considering combined bending, shear and axial force, when the design shear exceeds half the plastic shear resistance of the section. A reduced plate thickness for the relevant part of the cross section may be used as an alternative. Clause 6.2.10(3) of BS EN 1993-1-1 refers.

Contact: Richard Henderson
Tel: 01344 636555

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