The effects of densification on rolling shear performance of southern yellow pine cross-laminated timber

Abstract

This study evaluated the improvement in the shear performance of cross-laminated timber (CLT) through the densification of the transverse layers. Loblolly pine (Pinus taeda L., one of ten species known as Southern Yellow Pine (SYP)) lumber was used to fabricate CLT rolling shear specimens. Considering the compression ratio, thickness reduction to the initial thickness, lumber with an average density of 641.23 kg/m3 was compressed to three different levels: 16.67%, 33.33%, and 50.00%. For this compression, a thermomechanical densification technique was employed, in which lumber was softened by soaking in boiling water for 10 min and then hot-pressed at 140 °C to the target thicknesses. To differentiate the improvement in the shear performance due to the increased density from that of the aspect ratio, non-densified lumbers with the same aspect ratio as densified specimens were also used to fabricate CLT rolling shear specimens. The rolling shear performance of CLT specimens was evaluated using modified planar shear testing. The rolling shear strength increased by about 108% when the transverse layer was compressed for 50%. Likewise, it was found that there is a linear relationship between the percentage of increase in rolling shear strength and the compression ratio. Although the increased aspect ratio improves the rolling shear strength, results revealed that specimens with densified transverse layers outperformed those with non-densified specimens at the same aspect ratio.