THEORETICAL JOIST-RUPTURE SEQUENCES IN WOOD-FLOOR SYSTEM MODEL

The mechanical behavior of wood is strongly dependent on factors such as species, grade, moisture content, and member size as well as on tim e effects such as duration of load and creep. Time-dependent phenomena , combined with the variability inherent in a biological material, mak e it challenging to definitively evaluate the long-term performance of wood structures in general through experimental testing programs. In analytical studies of wood systems, damage accumulation and viscoelast ic stress-strain models have been used to account for time-dependent e ffects. Recent structural reliability studies on wood systems have use d these types of models to include time-dependent phenomena in the ass essment of reliability indices for various strength and serviceability limit states. Structural reliability studies produce a notional estim ate of the expected frequency of exceedance for a particular limit sta te, but they do not reveal information on the process leading to that limit-state failure. In the present study, the performance of light-fr ame-dimension lumber wood-floor systems is investigated using a time-d ependent Monte Carlo simulation for combined dead and occupancy live l oads throughout a 50 year design lifetime. Particular attention is pai d to the relative frequency and temporal characteristics of joist rupt ures predicted by commonly accepted duration-of-load models. The resul ts of the study provide insight into probable long-term wood-system be havior and can help to further the development of appropriate design, inspection, and maintenance procedures.