Theoretical Joist-Rupture Sequences in Wood-Floor System Model

Abstract

The mechanical behavior of wood is strongly dependent on factors such as species, grade, moisture content, and member size as well as on time effects such as duration of load and creep. Time-dependent phenomena, combined with the variability inherent in a biological material, make 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 viscoelastic stress-strain models have been used to account for time-dependent effects. Recent structural reliability studies on wood systems have used these types of models to include time-dependent phenomena in the assessment of reliability indices for various strength and serviceability limit states. Structural reliability studies produce a notional estimate of the expected frequency of exceedance for a particular limit state, but they do not reveal information on the process leading to that limit-state failure. In the present study, the performance of light-frame–dimension lumber wood-floor systems is investigated using a time-dependent Monte Carlo simulation for combined dead and occupancy live loads throughout a 50 year design lifetime. Particular attention is paid to the relative frequency and temporal characteristics of joist ruptures predicted by commonly accepted duration-of-load models. The results of the study provide insight into probable long-term wood-system behavior and can help to further the development of appropriate design, inspection, and maintenance procedures.