Model validation and 2-D hygrothermal simulations of wetting and drying behavior of cross-laminated timber

Abstract

Cross-laminated timber (CLT) is one of the most important mass timber materials that are commonly used in mid-rise or even high-rise timber buildings. However, exposure to moisture during construction may increase the moisture damage risks, and impact the durability performance of CLT buildings. To investigate potential solutions for avoiding wetting of CLT components during construction, CLT specimens having different moisture protection measures were tested in the damp and mild wintertime climate in Vancouver. This follow-up work focuses on two-dimensional (2-D) hygrothermal modeling of the wetting and drying behavior of bare CLT (without any protection) and the validation with measurements from the field exposure test, emphasizing the influence of material properties. The hygrothermal models are firstly calibrated for two CLT specimens positioned horizontally, with and without a butt joint, by using material properties from different laboratory tests, and assuming different rain penetration paths. The calibrated models are then applied to simulate CLT specimens positioned vertically, which have end grain directly exposed to rain or damp concrete in the test. The work reveals that the moisture storage function above RH 95%, which includes the saturation water content reported in different literature, has a significant influence on the hygrothermal simulation results; meanwhile, assigning different water absorption coefficients for the transverse and longitudinal directions of wood significantly improves the accuracy of the hygrothermal model created for simulating rainwater penetration into the CLT panel. This paper provides a recommendation on how to properly model the CLT panels exposed to rainwater, which often occurs during construction.