Design of Diaphragm-Braced I-Beams

by David A. Nethercot, Lect. in Civ. and Struc. Engrg.; Univ. of Sheffield, Sheffield, United Kingdom,
Nicholas S. Trahair, (M.ASCE), Assoc. Prof. in Civ. Engrg.; Univ. of Sydney, Sydney, Australia,


Serial Information: Journal of the Structural Division, 1975, Vol. 101, Issue 10, Pg. 2045-2061


Document Type: Journal Paper

Discussion: Allen David (See full record)
Discussion: Subramanian Narayanan (See full record)
Discussion: Errera Samuel J. (See full record)
Discussion: Apparao Tamirisa V.S.R. (See full record)
Closure: (See full record)

Abstract: 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.

Subject Headings: I beams | Diaphragms (structural) | Shear strength | Bracing | Structural strength | Elastic analysis | Plastic design

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