Load Sharing Effects in Light-Frame Wood-Truss Assemblies

Abstract

Load sharing among repetitive wood members interconnected by structural sheathing strengthens light-frame assemblies beyond that assumed in designing a single member. A repetitive member factor of 1.15 applied to bending resistance has been traditionally included in wood design standards to account for this effect. The focus of this study was to quantify load-sharing effects on members in metal-plate-connected wood trusses. This was accomplished using a detailed structural analysis model and statistical characterizations of lumber stiffness and strength properties. Monte Carlo simulations were conducted on six common truss configurations and one dimension lumber joist floor where wood member properties were randomly selected from distributions representing properties of the lumber grade. The assemblies were analyzed with and without attached sheathing to directly quantify the load-sharing effects in the system. The computed mean load-sharing factors ranged from 1.06 to 1.24 in the truss assemblies and from 1.17 to 1.19 for the joist assembly. The load-sharing factors were found to be applicable to wood truss members subject to tensile or compressive forces in addition to bending forces.