## 1 Introduction  
Wood, a natural orthotropic material, has unique properties in different grain directions of the three mutually perpendicular axes: longitudinal, radial, and tangential (as shown in Figure 1). The longitudinal axis L is parallel to the grain, the radial axis R is normal to the growth rings (perpendicular to the grain in the radial direction), and the tangential axis T is perpendicular to the grain but tangent to the growth rings. The strength and stiffness properties of wood in the grain direction are much higher than the strength and stiffness properties perpendicular to the grain direction. In addition to the mechanical properties, given its hygroscopic nature, wood dimensional changes (i.e., the shrinkage and swelling) occur in each direction and vary with moisture content (MC%). This property of wood is referred to as dimensional stability. The dimensional stability affects how a final timber product will distort in service. The percent shrinkage and swelling of wood are greatest in the tangential direction, less in the radial direction, and least in the longitudinal direction; the latter changes are mostly negligible. The natural properties of wood have been the basis for innovations in mass timber products such as Glued-laminated Timber (GLT) and Cross-laminated Timber (CLT). GLT includes layers of timber boards glued together parallel in one major load-bearing direction (0\({}^{\circ}\)); CLT consists of crosswise orientated layers, where the layers are orientated perpendicular to each other, providing one major (0\({}^{\circ}\)) and one minor (90\({}^{\circ}\)) load-bearing direction for out-of-plane bending [1]. The cross layers of CLT help to minimize the overall shrinkage and swelling of the structural panel. Thus, CLT panels show higher dimensional stability compared to GLT beams. For bending out-of-plane, CLT's cross layers are responsible for the panel's bidirectional strength and work to distribute the load in the minor direction as well. However, the cross layers have lower stiffness and strength (in the major axis direction), leading to a greater panel deflection than with GLT. Recognizing these relative advantages and limitations of GLT and CLT, an optimized/modified orientation of the inner layers in a diagonal direction could be developed to improve the out-of-plane bending stiffness while maintaining structural and dimensional stability. The product created with inner layers at varying angles is called Diagonal-Cross-laminated Timber (DCLT). DCLT can be seen as a standard counterpart to CLT, offering improved mechanical properties using the same panel thicknesses while using less fiber, resulting in lower fabrication and material cost. CLT is a balanced and symmetric laminate since the material properties, the thickness of its layers, and the orientation of its plies are symmetric about the midplane [2]. However, DCLT can be introduced as a balanced and antisymmetric laminate to improve the overall stiffness. This means that in DCLT panels, the plies with the same thickness are a mirror image of the geometrical midplane. Therefore, for each +\(\alpha\) angle-ply laminate in the panel, there is an equally thick \(-\alpha\) angle-ply laminate as well. Figure 2 illustrates the configurations of GLT, DCLT, and CLT to show how DCLT lay-up can be orientated compared to GLT and CLT products. Several studies have been conducted to study the potential relationship between the grain orientation of DCLT's inner lamina and the panel's bending and shear stiffness  
Figure 1: Three perpendicular axes of wood grain orientation. Figure 2: GLT, DCLT, and CLT lay-up configurations [3]. properties. [PERSON] et al. [4] investigated the difference between bending stiffness in conventional CLT panels and DCLT panels with inner layers of 45\({}^{\circ}\) grain orientation.