Electronic Thesis and Dissertation Repository

Degree

Doctor of Philosophy

Program

Civil and Environmental Engineering

Supervisor(s)

Dr. F. Michael Bartlett

Abstract

Gypsum board is the most commonly used sheathing material in Canadian residential construction. Current Canadian standards recognize the role of gypsum-board sheathing in bracing studs to prevent weak-axis buckling and in resisting in-plane shear, but do not recognize its potential contribution to axial compressive resistance of a sheathed wall. The research in this thesis, therefore, investigates this contribution for light-frame wood stud walls sheathed with gypsum-board on both sides of the stud. The axial compressive resistance of bare and gypsum-board sheathed studs were computed using new finite element models that account for the nonlinear wood stress-strain relationship and nonlinear shear load-slip response of gypsum-board-to-stud fastener connections. These models were validated using full-scale test data for 100 bare and 19 sheathed studs, and with an idealized responses of fastener connections derived using test data from 283 monotonic and 15 load-reversal tests. The strength distributions of the axial capacities of bare and sheathed studs were quantified by conducting Monte Carlo simulations using these models. As a result, it was determined that gypsum-board sheathing increases the axial compressive resistance of wood studs by a factor of 1.05 to 1.56, depending on the stud size, stud length, gypsum-board thickness, and fastener spacing. A modification factor that conforms to the current CAN/CSA-086-09 equations (CWC, 2009) to account for the strength increment provided by the gypsum-board sheathing was then derived as a function modulus of elasticity of the wood for various stud sizes and lengths, gypsum-board thicknesses, and fastener spacings. The revised equation was used to compute the factored axial compressive resistance of 2400 and 3600 mm long gypsum-board-sheathed 38x89 and 38x140 mm wood studs. A total of 15 additional stud designs are recommended to be included in Part 9 “Housing and Small Buildings” of National Building Code of Canada (NRC, 2010) when the extra strength provided by 12.7 mm or 15.9 mm gypsum-board sheathing, with a maximum fastener spacing of 300 mm, is accounted for.


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