## 1 Introduction
They tested two groups of 20 five-layered panels, with orientations of 0\({}^{\circ}\)-90\({}^{\circ}\)-0\({}^{\circ}\)-90\({}^{\circ}\)-0\({}^{\circ}\) and 0\({}^{\circ}\)-45\({}^{\circ}\)-0\({}^{\circ}\)-45\({}^{\circ}\)-0\({}^{\circ}\) under four-point bending in the main load-carrying direction in a flat-wise panel lay-up. Their evaluated results confirmed that the DCLT \(\pm\) 45\({}^{\circ}\) bending strength and the apparent stiffness (\(\text{El}_{\text{app}}\)) increased, respectively, by 35% and 15% over the conventional CLT panels with 90\({}^{\circ}\) layers. \(\text{El}_{\text{app}}\) is defined as the apparent bending stiffness of the panel in the span direction including both bending and shear deformation, while the \(\text{El}_{\text{eff}}\) of the panel refers to the effective bending stiffness in the span direction. In another study, these researchers [5] investigated the mechanics of the diagonally and conventionally layered CLT by a digital image correlation (DIC) technique and a destructive four-point bending test on samples with the conventional 90\({}^{\circ}\) and \(\pm\)45\({}^{\circ}\) alternating inner layers. DIC evaluations of 100 CLT panel layers showed that a considerable part of the stiffness of conventional CLT is reduced by the shear resistance of transverse layers. The overall experimental results showed the shear strain in CLT \(\pm\) 45\({}^{\circ}\) to be 60% lower than in CLT 90\({}^{\circ}\). The reduced strain in the transverse layers contributes to a stiffer panel and therefore suggests the use of CLT panels with a \(\pm\)45\({}^{\circ}\) layered configuration to be a more efficient material to use for timber engineering construction. Their results also showed that utilizing the lower-grade material for the transverse diagonal layers increased the yield values due to the increased stiffness properties of the overall product. Other researchers have shown interest in studying both the shear and bending performance of DCLT panels with different angle-ply orientations. [PERSON] et al. [6] performed research on three-ply DCLT panels fabricated from eastern hemlock. The inner layer had grain orientations of 30\({}^{\circ}\), 45\({}^{\circ}\), 60\({}^{\circ}\), and CLT (90\({}^{\circ}\)) relative to the main load-bearing direction. Their results of the short-span three-point bending test showed higher shear and bending properties for the DCLT 30\({}^{\circ}\) panels, followed by successively lower values for the DCLT 45\({}^{\circ}\), 60\({}^{\circ}\), and CLT (90\({}^{\circ}\)) panels. The \(\text{El}_{\text{app}}\) from their experimental short-span three-point bending results showed an increase of 174%, 112%, and 61%, respectively, for DCLT 30\({}^{\circ}\), DCLT 45\({}^{\circ}\), and DCLT 60\({}^{\circ}\), compared to CLT 90\({}^{\circ}\). Also, [PERSON] et al. [2] investigated the load-bearing behavior and efficiency of DCLT under a biaxial bending configuration experimentally and theoretically. They tested seven replicas of CLT and DCLT \(\pm\) 30\({}^{\circ}\) and \(\pm\)45\({}^{\circ}\) panels with different thicknesses. Their evaluation included an evaluation of the increase in the torsional stiffness of DCLT panels compared to conventional CLT panels. They tested an applied parametric numerical model to evaluate the influence of the layer arrangement as well as the width and thickness of the laminations on the torsional stiffness. They also designed an analytical model for finding the torsional stiffness of the panels using two methods: the Kirchhoff-Love and Reissner-Mindlin equations. Their results showed a considerable increase in the torsional stiffness of DCLT panels compared to conventional Cross-laminated Timber panels. Their results confirmed that DCLT could improve biaxial bending stiffness. Therefore, it could be an alternative option to CLT for floor systems governed by serviceability limit states such as deflections or vibrations. To determine wood properties at an angle to one of the principal axes, [PERSON]'s criterion is the most common method.