Advancing Design Provisions for Lateral Stability of Wood Built-up Beams

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The proposed research project will address a long-standing technical issue related to the stability of built-up beams in wood construction. Built-up beams are formed by connecting two or more pieces of lumber vertically through mechanical fasteners (e.g., nails, screws, etc.). Research efforts are needed to address the design challenges and uncertainties associated with built-up beams. The lateral stability of a built-up beam is largely affected by the slip between individual plies. The design standard in Canada specifies the requirement for the design of built-up beams, however the effect of the connection slip between the lamination is not quantified. This could lead to either and overly conservative or unsafe design. The proposed research project aims to provide specific guidance on the lateral stability of built-up beams in the CSA O86 Standard by investigating the composite action of fasteners. This includes establishing design criteria under which full composite action is achieved, and formulating expressions that would reduce the critical moment capacity when only partial composite action is attained. After the completion of the project, the research outcome will be disseminated to the education, design and construction communities through publications and outreach programs. The project is expected to have a significant impact on the wood industry in that the research results, once successfully adopted by the CSA O86 Standard, would streamline the design process by reducing the uncertainties currently experienced by engineers when specifying built-up beams. By addressing the aspects related to design, cost and safety, built-up beams would become more reliable and economical for use in wood construction. Since built-up beams can be sourced from either traditional sawn lumber or new materials such as structural composite lumber, advancement in built-up beams would have the potential to benefit a large portion of the wood industry.