Development of hybrid cross-laminated timber made of lumber and OSB

Abstract

Cross laminated timber (CLT) is a kind of prefabricated engineered wood product. However, it has been found that the relatively low rolling shear capacities of CLT could result in a noticeable amount of deflection in service and eventually failure. In the meantime, it has been discovered that the oriented strand board (OSB) shows good shear resistance. This study was aimed at developing a hybrid CLT made of spruce-pine-fir (SPF) lumber of a grade of #2 and OSB panel of a grade for wall sheathing to improve its out-of-plane bending properties. Two types of three-layer downsized CLT panels were designed and fabricated, namely hybrid CLT made of SPF lumbers as top and bottom layers in the major direction and OSB panel as transverse layer in the minor direction (the major direction of OSB panel was perpendicular to the major direction of CLT), and generic CLT made of all SPF lumbers that was used as control. The long-span bending, short-span bending, rolling shear and block shear tests were conducted to determine the flexural strength and stiffness, maximum shear strength, rolling shear strength and block shear strength of the specimens made in this study. It was found (1) The long-span bending test results showed that there was not a significant difference in the effective modulus of elasticity (MOE) between the hybrid and generic CLT in the both major direction and minor direction. What is more, hybrid CLT had an average effective MOR values of 26.85 MPa and 6.03 MPa in the major and minor directions, respectively, which were 42.4% and 38.0% lower than those of generic CLT. (2) The short-span bending test results showed that there was not a significant difference between generic CLT and hybrid CLT (4.10 MPa for generic CLT and 3.83MPa for hybrid CLT). However, in the minor direction, the maximum shear strength of hybrid CLT was 0.87 MPa, 44.1% lower than that of generic CLT (1.56MPa) (3) The rolling shear test results showed that the rolling shear strength of lumber was 1.31 MPa, which was 14.5% higher than that of OSB. (4) The internal bonding strength of OSB was 1.64kPa, lower than bonding strength of lumber-to-lumber (approximately 2.68 kPa) and lumber-to-OSB (approximately 2.70 kPa). It could be concluded that the hybrid CLT, with OSB as the transverse layer material (the major direction of OSB panel was perpendicular to the major direction of CLT), developed in this study couldn’t improve the overall properties of generic CLT noticeably. It could also be recommended that further research could focus on the orientation of OSB when used in the transverse layer in manufacturing of hybrid CLT by selecting OSB panels with higher grade. Keywords: Hybrid cross-laminated timber, dimension lumber, oriented strand board, effective modulus of elasticity, effective modulus of rupture, rolling shear strength and modulus, block shear strength.