Experimental investigation on mechanical properties of Chinese fir composites as cross-laminated timber

Abstract

Chinese fir (Cunninghamia lanceolata (Lamb.) Hook.) is a significant plantation species in South China. However, this plantation species is primarily utilized to produce low-value wood products. This study evaluated the feasibility of manufacturing cross-laminated timber using fast-grown small-diameter Chinese fir by investigating its bending performance and exploring the contribution of the lamination effect to the load capacity. Through bending tests and theoretical analysis, three different lay-ups with the same cross-laminated timber thickness (105 mm) but varying lamination thicknesses (35 mm, 21 mm, 15 mm) were examined. The results revealed that the 5-layer and 7-layer CLT, with the average bending strength of 37.4 MPa and 33.9 MPa, showed the significantly higher mean values than the 3-layer CLT (23.2 MPa). Moreover, the predicted ultimate loads and failure modes aligned with the experimental observations. Additionally, all mechanical criteria met the mechanical performance requirements for the 105 mm thick cross-laminated timber according to the ANSI/APA PRG 320 standard, except for bending stiffness. These findings provide valuable insights for improving the performance of Chinese fir cross-laminated timber made from small-diameter timber by optimizing lamination thickness and underscore the viability of producing cross-laminated timber using Chinese fir.