Short-Term and Long-Term Deflections in Lightweight Wood Trusses

Wood structures exhibit a continuing deformation for more than one year after the application of the load. This may result in excessive deflections and can lead to serviceability problems such as cracking of plaster, etc. This study proposes to evaluate the current status of the knowledge, both analytical and experimental and the methods used by practicing engineers in the field to calculate short and long-term wood truss deflections. Three components of the deflection of wood trusses are discussed in this study: slip, elastic and inelastic deflections. The strength and stiffness performance of trussed rafters and trusses with different connection systems are discussed. Three methods of calculating deflections in wood trusses are presented; they are the energy methods, the graphical methods and the empirical formulae. Also a section is devoted to the computer programs available and widely used today in the analysis of wood trusses. A literature review on recent research on short-term and long-term studies and the results of a survey conducted to determine field practices in calculating truss deflections are presented in this thesis. Based on the findings of this study, a number of recommendations are suggested in order to improve the design and the analysis of wood trusses