Limit State Probabilities for Wood Structural Members

Abstract

Estimates of the limit state probability for wood members, where the limit state is failure by creep rupture, must be based on analyses that take into account the temporal characteristics of the applied loads. These estimates require: (1) construction of appropriate load process models; (2) a probabilistic description of wood member strength; and (3) a cumulative damage analysis. Reliability analyses of beams subjected to dead, snow, and live loads were performed to evaluate the effects of using different load duration models and different parameters in the snow and live load process models. It was found that the most important factor determining failure is the duration and magnitude of the extreme load pulses. The choice of load duration model, in contrast, was relatively unimportant. Reliabilities associated with existing design criteria were evaluated, and resistance factors for use in a proposed load and resistance factor design format were determined, using glulam beams in bending as an example.