Length effect in prefabricated wood I-joists

Length effect in structural wood members like traditional solid sawn lumber , glulam beams, and structural composite lumber, has been recognized for ma ny years. Length effect methodology for composite wood I-joists is not pres ently included in the American Society for Testing and Materials (ASTM) Sta ndard specification for establishing and monitoring structural capacities o f prefabricated wood I-joists (D 5055). These I-joists use either structura l composite lumber or solid sawn lumber for flange material. When necessary , flanges are finger-jointed to obtain long lengths. This paper proposes a methodology to compute the effect of length for composite I-joists using ei ther un-jointed or finger-jointed flange material. The theory is based on t he Weibull weak-link statistics. The effects are easily calculated and exam ples are presented. The theoretical results are compared to experimental da ta from two independent studies. The close agreement between theory and dat a is demonstrated. This methodology has been proposed for implementation in ASTM D 5055 and is currently being reviewed by committee.