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The structural performance of tall wood-frame walls under axial and transversal loads Leonard, Daniel

Abstract

Tall wood-frame walls have emerged as a viable alternative to steel, concrete, and masonry in the construction of large industrial, commercial, and institutional buildings in North America. The construction of tall wood-frame walls incorporates the advantages of typical residential wood-frame platform construction, which include fast construction times and the use of relatively unskilled labour to deliver lightweight buildings proven to be durable over many years of usage. Some of the restrictions placed on the construction of residential wood-frame walls by applicable building codes are also currently placed on the construction of tall wood-frame walls. This study focused on the response of tall wood-frame walls under axial and transversal, or out-of- plane, loading with particular emphasis on addressing the appropriateness of certain current code restrictions on this type of construction. The axial loads represented the loads applied to the walls from the roof structure including the loads from snow, rain, and wind. The loads in the transversal direction represented either compression or suction to the face of the wall due to wind pressure. Because of the inherent variability and non-linear behaviour of wood, many of the components of tall wood-frame walls were tested separately prior to testing the full-scale wall specimens. These component tests were used to determine the bending stiffness of each material component individually. In addition to the lateral and withdrawal stiffness of nailed connections, the bending stiffness of composite studs with sheathing, and the response of sheathing panels under racking loads with varied stud spacing was investigated. The tests of the sheathing panels showed that the current limit on stud spacing in the Canadian Wood Design Code is not appropriate for this type of wall construction. Because these types of walls are designed using an equivalent static wind pressure rather than a true representation of the dynamic characteristics of wind, monotonic tests were primarily conducted on all of the components and the full-scale walls. The experimental results from the component tests were used to verify linear analytical models representing the load-deformation behaviour of composite T-beams, consisting of a stud connected to a tributary width of sheathing, under transversal loads. These models were then used to verify more sophisticated linear models representing the load-deformation behaviour of full-scale walls under axial and transversal loads. Non-linear finite element models of full-scale walls were also verified using the results from the component tests. Design equations were presented that accurately account for the composite action that exists between the sheathing and the studs. Finally, some design and construction recommendations are discussed regarding several aspects o f tall wood-frame walls based on the results of the full-scale wall tests.

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