Combined Loads on Sheathing to Framing Fasteners in Wood Construction

Abstract

The design of mechanical fasteners such as nails and screws used in light-frame construction typically is based on a single assumed loading mechanism or failure limit state, either withdrawal load or lateral load. Observations of failed structures, both in the field and in the laboratory, have confirmed that simple mechanical fasteners in light-frame construction often exhibit combined (lateral and withdrawal) failure modes. In recognizing the potential for combined loads, the 1997 National Design Specification and the new LRFD Standard for Wood Construction both provide some guidance for considering combined loads on fasteners. To better understand the interaction of lateral and withdrawal loads on a variety of wood connections, including both mechanical fasteners and adhesives, a test program was conducted with some of the results reported here. In addition to a description of the test program and findings, a comparison is made with the two empirical code equations and suggestions are made for possible modifications. The results of this research indicate that the combined load interaction for mechanical connectors and adhesives are different and in fact are more critical for typical attachment of roof sheathing using mechanical connectors.