IRC Wall Bracing: Combined Wind Uplift and Shear Load Path
As part of a comprehensive update of the 2009 International Residential Code (IRC) wall bracing provisions, a new requirement was introduced that braced wall panels must be presumed to resist combined (simultaneous) uplift and shear loads, unless an independent continuous uplift load path is provided using hurricane ties and metal straps. This change represents a significant shift in the prescriptive wall bracing provisions, with potential impacts on prescriptive braced wall amounts, performance of conventional braced wall methods, braced wall panel connection requirements, and development of alternative bracing solutions.
The combined uplift and shear load path, however, is not well understood, particularly at the whole-house level. Existing results of whole-house tests under pure shear loading (without the uplift loading) indicate significant system effects relative to building code design calculations. Considerations for the whole-house response under combined loading include load sharing, redistribution of forces through diaphragms, contribution of finishes, and contribution of those walls and partitions not designated as braced walls. Because the wind pressures vary substantially across the building’s surfaces, loading considerations are also highly important to understanding the realistic force distribution between braced walls in a building.
An expert meeting was held on July 26th, 2010 in Leesburg, VA in an effort to gather input from industry experts on issues related to the combined uplift and shear load path requirements in the IRC wind wall bracing provisions, with particular regard to immediate research needs, testing and setup requirements, and directions for future building code development that would facilitate increased construction and design efficiency while also simplifying prescriptive provisions.
This paper summarizes the findings of that meeting. First, a brief background literature review of previous combined uplift and shear load research is presented. This background review is followed by a synopsis of the presentations on ongoing research and analysis made at the expert meeting by University of Western Ontario, American Wood Council, Simpson Strong-Tie, APA – The Engineered Wood Association, and others. Finally, a summary of the experts’ opinions and suggestions for future research needs is presented. It is envisioned that this paper will provide the basis for development of future detailed research agendas and specific test plans.
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