In this paper, the three-layer Canadian hemlock CLT panel was designed to test the elastic modulus and bending strength of CLT specimens by four-point bending method. The interlaminar shear of CLT specimens was tested by short-span three-point bending method. Strength, the shear strength and wood breaking rate of the CLT specimens were tested by the stair shear method. At the same time, the failure mode of the CLT board was analyzed. The main conclusions indicate that the test values of bending and shear performance of Hemlock CLT can meet the relevant grade requirements of standard ANSI APA PRG320: 2012. During the bending process, the CLT specimen firstly exhibits a rolling shear failure of vertical layer after reaching the non-elastic deformation phase. After that, the damage extends gradually to the interface layer. The final failure mode is shear failure of interface layer or tensile failure of parallel layer. The interlaminar shear performance is partly relevant to the converted timber performance of parallel layer of CLT under the short-span three-point bending test conditions. The position of interlaminar shear failures is concentrated near support points of specimens and the position is generally located at the interface between parallel and vertical layers, inclining to the parallel ones. CLT at Grade 1 has significantly higher interlaminar shear strength than CLT at Grade 2. There is a certain variability in the test results of wood failure rate of CLT. The overall mechanical properties of the hemlock specification material and the hemlock CLT can meet the relevant grade requirements of Standard ANSI APA PRG320: 2012. The above can provide reference for the optimization design and application work of CLT heavy-duty timber structure.
Author: Zizhen Gao
Nanjing Forestry University, China