Development of Design Guidelines for Steel Cantilever Beams in Canada

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The roofs of many light single-storey steel buildings in North America that are large in plan area, such as supermarkets or big box stores, are built using the "Gerber system" to resist gravity loads. The Gerber system consists of cantilever girders that are supported atop the columns and interstitial drop-in girder segments along the column line in one direction, typically with open-web steel joists constituting the secondary framing in the perpendicular direction. This system tends to reduce girder sizes by taking advantage of the negative moment capacity of the girders at the column supports, while maintaining a cost similar to that of a simply-supported frame structure. The design of girders in such systems is often governed by their stability. The current Canadian standard for design of steel buildings, CSA S16, provides very limited information related to the Gerber system and it is therefore the responsibility of the structural engineer to develop a rational design method. Remarkably, and of concern to several leading industry experts, widely-used textbooks and guidelines may not adequately describe the behaviour and resistance of such system. This research project aims to develop design methods for steel Gerber systems and has four specific objectives: 1) to identify the influential parameters pertaining to the stability of cantilever girders; 2) to assess, by means of numerical simulations and a full-scale experimental program, the stability response of such girders; 3) to develop design methods for Gerber systems and other cantilevers, and propose stability design requirements within the framework of the Canadian steel design standard; and 4) to perform a thorough reliability analysis. The research team will perform full-scale laboratory experiments and employ advanced numerical modelling techniques to achieve the objectives of this project. The results will provide improved design tools to structural engineers for use in day-to-day practice, resulting in safer structures while reducing construction costs. The data obtained from the experimental test program proposed here will supplement existing studies to instill greater confidence in the validity of the design equations prescribed for cantilever girders.