Effect of transverse-layer edge gaps on damage accumulation and long-term duration-of-load bending behavior of fast-growing fir cross-laminated timber

This study investigated fast-growing fir CLT specimens with 0 and 6 mm transverse-layer edge gaps through short-term bending and duration-of-load (DOL) tests. Based on experimental results, DOL factors were further predicted, and survival analysis was conducted.

Short-term tests showed that edge gaps slightly reduced bending performance, with the average modulus of elasticity, ultimate capacity, and bending strength decreasing by 5.2%, 5.0%, and 4.8%, respectively. Compared with short-term tests, DOL tests produced more severe crack propagation and damage accumulation. At identical load levels, gap-free specimens showed 15.7–40.9 times longer failure time than specimens with 6 mm gaps, resulting in a DOL factor over 14.3% higher after 50 years.