Strain variation analysis of cross-laminated timber elements under cyclic moisture

Despite the growing use of cross-laminated timber (CLT) panels in the construction industry, their behaviours under weather conditions, especially cyclic moisture which generated additional strains, requires further investigation. To address this gap, an extensive experimental campaign was carried out to evaluate CLT elements, in which strains are measured, under cyclic moisture changes, using Digital Image Correlation (DIC). In this way, the effects of cyclic humidity changes on amplitude and distribution of strains on four different configurations of CLT panels, divided based on the free flow direction of moisture, are explained. Regarding RH cycle tests, CLT specimens were conditioned in climatic chambers for 324 days at constant temperature 20 (°C) with a humidity cycle varying every 21 days between 30% and 90%, getting constant at 65% after the first 142 days. Results show that, in the main face, drying periods present tensile strain while wetting periods present compressive strains in the longitudinal direction. But, in the tangential direction, restrained strains tend to reduce significantly from first to last drying cycles for all test configurations. Moreover, in the lateral face, drying periods present tensile strains while wetting periods present compressive strains in the tangential direction. Experimental results confirmed that the ratio between tangential and longitudinal directions tends to decrease with the number of RH cycles, and successive RH cycles do not cause cumulative strains on CLT panels.