Creep Behavior Model for Structural Lumber

Abstract

An existing four‐element viscoelastic model is used to model the creep response of lumber as a function of load and is modified to account for thermal and moisture effects, including mechanosorptive effects (i.e., the nonlinear interaction between applied stress and changing moisture content reflected in the creep response of wood). Creep data from a large population of Douglas fir nominal 2‐in.‐by‐4‐in. (38.1‐mm‐by‐88.9‐mm) lumber are used to calibrate the model. The lumber is actually tested to failure as part of a parent load‐duration (creep‐rupture) study, but the time‐dependent deflections are also monitored. The purpose for monitoring and evaluating the creep behavior of the lumber is to provide insight into the long‐term behavior of lumber and develop a general creep model that accounts for load and hygrothermal effects.