System Factors for Light-Frame Wood Truss Assemblies
Publication: Journal of Structural Engineering
Volume 121, Issue 2
Abstract
Light-frame wood roof assemblies may be stronger than what the current single member design approach suggests because of repetitive member load sharing and partial composite action. These strengthening effects are partially addressed in the National Design Specification for Wood Construction through a repetitive use factor of 1.15, applied to the allowable bending stress for repetitive wood members. This paper examines the effect of load sharing and composite action on wood pitched-roof assemblies through a new analysis model. Individual truss and roof assembly strength distributions were computed using the new model. The results show that slope, span, and other truss characteristics cause significant changes in the system factor for a given roof structure configuration. Computed system factors are presented in terms suitable for working stress and reliability-based design methodologies. Computed working stress design system factors vary from 1.15 to over 1.50 for the roof structures studied, suggesting that the current 1.15 factor may be conservative for many roof structures. This conservatism must be retained until more sophisticated analysis models, such as the one proposed herein, are fully verified and accepted for design.
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Information & Authors
Information
Published In
Journal of Structural Engineering
Volume 121 • Issue 2 • February 1995
Pages: 290 - 300
Copyright
Copyright © 1995 American Society of Civil Engineers.
History
Published online: Feb 1, 1995
Published in print: Feb 1995
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