Explicit formulae for the flange efficiency of curved beams

Deformation of the cross-section of a curved beam of thin-walled open section, such as a channel-section formed from thin sheet material, leads to loss of stiffness due to reduced effectiveness of the flanges. Explicit formulae are derived for the flange efficiency of curved beams of channel, Z– and I–section, in which the geometric parameters on which loss of flange efficiency depends are easily identified. The formulae are readily adapted for curved beams of composite material, identifying also the particular properties of the laminate that relate to flange efficiency. The formulae are approximate, but nevertheless of good accuracy in the practical range of designs.