Evaluation of bending performance in full-scale cross-laminated timber made from trembling aspen lumber

Abstract

Cross-laminated timber (CLT) is an innovative engineered wood product with excellent stiffness and strength in two directions, typically made from combination species of Spruce-Pine-Fir or Douglas Fir-Larch in North America. Trembling aspen (Populus tremuloides), a widely distributed species in North America, exhibits a great potential for producing CLT due to its outstanding rolling shear properties and relatively low raw material cost. This study was aimed at evaluating the bending properties of full-scale CLT panel and specimen manufactured from trembling aspen lumber sourced in Alberta, Canada. The longitudinal stress wave (LSW) method was employed for sorting lumber based on the modulus of elasticity (MOE). Three- and five-layer CLT panels in two strength directions were constructed, measuring 2.7 m in length and 1.2 m in width. Static third-point bending tests were conducted for CLT panels and specimens. It was found that (1) The mean effective bending stiffnesses ((EI)_eff,f,0 and (EI)_eff,f,90) of three-layer CLT panels in the major- and minor-strength directions were 32.1% and 44.8% higher, respectively, than the values calculated using the shear analogy method. Similarly, for five-layer CLT panels, (EI)_eff,f,0 increased by 46.6% and (EI)_eff,f,90 by 43.3%; (2) For five-layer CLT specimens, the mean (EI)_eff,f,0 and (EI)_eff,f,90 were 19.2% and 30.3% higher, respectively, than grade E1 requirements specified in the standard ANSI/APA PRG-320, and the mean (EI)_eff,f,0 and (EI)_eff,f,90 of three-layer CLT specimens increased by 1.5% and 40.7% compared to those of grade E1, respectively; (3) The mean bending moment resistance ((F_bS)_eff,f,0) for five-layer CLT specimens in the major-strength direction was approximately 5.0% lower than that of CLT made with western hemlock, and the mean (F_bS)_eff,f,0 of three-layer CLT specimens was about 25.3% lower than that of CLT made with black spruce; (4) The rolling shear failure was observed to be the predominant failure mode in the major-strength groups, occurring approximately 50% in both three- and five-layer CLT specimens. For the minor-strength group, the tension failure was observed as primary failure mode, accounting for 50% as well. (5) The mean absolute percentage errors forecast for the mean (EI)_eff of three-layer CLT panels and specimens in the major-strength was 8.47% and 10.10%, respectively.