Timber Moisture Content Changes and Associated Stress Predictions on Structural Wood Screws
Wood is a hygroscopic material, and changes in moisture content can lead to swelling and shrinkage throughout the service life of a structural wood member. Moisture induced dimensional changes can lead to stresses (restrained or un-restrained) in both wood and the embedded fasteners that must be accounted for with special detailing early on in the design stage. This newsletter looks over some of the special considerations regarding moisture induced dimensional changes in wood and how these may be addressed when using modern self tapping screw connection systems. Special attention is paid to situations where restrained wood swelling is thought to develop tensile forces on fasteners, and a calculation method is presented for approximating these forces based on existing literature.