Experimental and numerical analysis of hybrid cross-laminated timbers

This study aims to investigate the effects of various wood species and layer thicknesses on the structural performance of hybrid cross-laminated timber (CLT) panels through experimental and numerical methods. In the research, both homogeneous and hybrid CLT configurations were prepared using Uludağ fir, spruce, and poplar species. The mechanical properties of these panels were thoroughly analyzed. Within the scope of the experimental tests, critical parameters such as bending strength, modulus of elasticity, shear modulus, screw withdrawal resistance, rolling shear strength, compressive strength, and lap shear strength were measured. The results revealed that spruce exhibited superior performance, particularly in terms of bending strength, modulus of elasticity, compressive strength, and screw-holding capacity compared to the other species. Although fir and poplar presented lower density and mechanical properties, suitable combinations in hybrid panels allowed for significant improvements in mechanical performance. Layer thickness—especially that of the outer layers—played a decisive role in mechanical characteristics such as bending resistance and shear modulus. Panels with 20 mm outer layer thickness generally demonstrated higher mechanical strength and stiffness than those with 18 mm thickness. Furthermore, it was determined that hybrid layer configurations enabled optimization in terms of lightweight design and mechanical performance. The dynamic modulus of elasticity values obtained through non-destructive testing showed high agreement with static measurements in homogeneous panels, whereas in hybrid panels, the variation between measurement points significantly increased. This phenomenon is explained by the mechanical incompatibility of different wood species and the effect of interlayer transitions on wave propagation. Numerical analyses performed using the finite element method showed strong agreement with experimental results, particularly in homogeneous panels with 18-18-18 mm layer thickness. However, in asymmetric hybrid panels with thicknesses such as 20-14-20 mm, discrepancies between experimental and numerical results became more pronounced. This indicates that numerical models cannot fully reflect material heterogeneity, layer transitions, and structural asymmetries. The research emphasizes the importance of selecting appropriate wood species combinations and layer thicknesses to enhance the structural performance of hybrid CLT systems. Furthermore, it highlights the necessity of more detailed consideration of material and geometric heterogeneities in numerical modeling. In conclusion, hybrid CLT panels possess high potential for widespread application in the timber construction sector as sustainable and efficient structural materials.