Multiple-member wood structural systems are designed using the current National Design Specification with an increase in allowable bending stress of 15% to account for load sharing and partially composite action. Efforts are underway to develop Load and Resistance Factor Design (LRFD) procedures for engineered wood construction to enable design of wood structures to be performed in a similar fashion as design of steel or reinforced concrete structures. The proposed LRFD methodology includes a system factor derived by probabilistic analysis to account explicitly for load sharing among members in a wood structural system. Available statistical data on mechanical properties of individual pieces of lumber along with structural system and stochastic damage accumulation models can be utilized to evaluate system reliability and to develop LRFD design criteria that are consistent with a desired reliability
