Reliability of Wood Joist Floor Systems with Creep

Abstract

Light-frame wood floors are constructed from a number of parallel flexural members (joists), which provide the primary structural support. Sheathing material is attached across the top edges of these joists to form the floor surface. Because the joists are connected in this manner, load sharing occurs, which enhances the performance of the system as a whole. Current design procedures focus on the behavior of single members with only limited provisions that account for the improved performance of systems. In this study, the reliability of wood joist floors is investigated considering both strength and serviceability limit states. The objective of the system reliability analyses is to determine appropriate system factors for use in single member load and resistance factor design checking equations. These factors are included to account for the beneficial effects associated with systems of parallel members. This study considers factors such as lumber species and grade, floor size, and the effects of creep deformations. A stochastic viscoelastic stress-strain relationship is used to model the time-dependent behavior of wood, and stochastic pulse process models are used to account for the temporal variability of the loads. Cumulative damage analysis using two common damage accumulation models is used to account for the time-dependent strength of wood flexural members.