Numerical Model for Creep Behavior of Axially Loaded CLT Panels

Abstract

The performance of post-tensioned rocking cross-laminated timber (CLT) panels depends on the ability to maintain the post-tensioned force in the strand. This post-tensioned force may change over time due to the creep behavior of wood, which, in turn, is a function of time and moisture content in the CLT panels. In this study, a numerical moisture content diffusion model was developed to predict moisture content migration through CLT panels when the ambient relative humidity changes. Fick’s second law and the moisture content diffusion coefficients were applied to derive the differential diffusion equation for use in a numerical model. A four-element creep model was included to estimate the creep deformation of CLT panels over time under an axial load with changing environmental conditions. Data from a series of moisture content and creep tests under different configurations and environmental conditions were used to calibrate the proposed moisture content diffusion and creep model for CLT panels. The moisture content diffusion model was calibrated for two relative humidity steps, 50%–70% and 70%–90%. Then, a new creep model at material level that considers the change of moisture content in CLT panels was introduced. The viscoelastic parameters and mechano-sorptive constants were recommended for the creep model based on creep test data. Axial strain in CLT panels varied under 2% when ambient relative humidity switched between 50% and 70%. The axial strains in CLT panels with three layers were more sensitive to variations in surrounding relative humidity than those of CLT panels with five layers.