Rate-of-Load and Duration-of-Load Effects for Wood Fasteners

Abstract

It has been suggested that duration-of-load (DOL) effects in connections differ substantially from those in wood members and that the factors developed using cumulative damage models based on tests of wood members in bending (i.e., creep rupture) are not appropriate for the design of connections. This paper presents the results from a test program that attempts to quantify rate-of-load and short-term DOL effects for wood fasteners (such as nails and screws) subject to withdrawal or lateral loads. The results from this preliminary study suggest that no obvious rate-of-loading effects exists for nailed connections subject to either lateral or withdrawal loading. This has particular significance, for example, in the design of roof sheathing systems and roof-to-wall connections to resist high-wind uplift loads. Although by no means a complete treatment of the topic of DOL (i.e., time) effects in fasteners, this study serves to highlight differences between connection and wood member time effects and both raises and answers some questions about the validity of adjustment factors for time effects for short-term loadings (i.e., wind and seismic) in wood connection design.