Design of Diaphragm-Braced I-Beams

Previous studies of the effectiveness of corrugated steel sheeting acting as shear diaphragms in stabilising slender I-beams have been reviewed in addition to the two criteria that govern the effectiveness of such bracing; diaphragm stiffness, which controls beam strength, and diaphragm strength have been identified. While an existing method of calculating the elastic critical moment of a diaphragm-braced beam is satisfactory, the calculations required in the subsequent check of the diaphragm strength are too involved for routine design. A new method, requiring far simpler calculations, has been derived. The whole process of beam and bracing design has then been cast in a form that is in keeping with accepted design methods for unbraced beams. Inspection of the bracing requirements of hot-rolled sections together with the results of shear tests on diaphragm assemblies suggests that in many cases lateral buckling will be prevented, in which case the beam may be designed elastically for its full in-plane capacity.