Lateral Stability and Design of Gerber Systems

The present paper addresses the behaviour, resistance and design of steel beams with overhanging segments against Lateral Torsional Buckling -- so-called Gerber systems. This system has been used extensively in North America for the roof girders of single story buildings -- typically warehouses and commercial buildings. This system is quite rational and economic, and also requires simple fabrication and erection works. However, the design process deserves careful and specific attention with respect to (i) the L.T.B. check of the overhanging segment which cannot be assumed as a typical cantilever since the adjacent back-span cannot provide full fixity, (ii) the L.T.B. check of simply supported parts under realistic lateral restraints and (iii) the design of connections at vertical supports, namely with respect to bracing considerations. Research investigations aimed at understanding deeper the buckling behaviour of such systems, characterizing the key design parameters and developing an adequate design method were undertaken and are reported in the paper. Comprehensive F.E. studies on various major influences such as span ratios, lateral support conditions or the need for vertical stiffeners are detailed and analysed. Eventually, a devoted set of design rules and recommendations is proposed.

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