Behaviour of hybrid cross laminated timber in compression perpendicular to grain in different layup structure, support conditions, and loading configurations

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Cross laminated timber (CLT) is recognized as alternative to traditional construction materials. As a floor member, it causes the compressive deformation or even damage perpendicular to the grain of CLT due to vertical load imposed by the column or wall. The challenge is how to improve the compressive strength (fc,90) and elastic modulus (Ec,90) perpendicular to the grain under the high diversity of possible load configurations. Compared with normal CLT, hybrid CLT (HCLT) used structural composite materials (e.g. laminated strand lumber) instead of timber, which had more homogeneous mechanical properties. In this study, the spruce-pine-fir (SPF) and laminated strand lumber (LSL) were used to prepare HCLT. The full surface loading, point loading representing columns and line loading representing walls of HCLT in the perpendicular to grain direction were carried out. The results show that fc,90 increased with increasing thickness ratio of LSL in the total thickness of HCLT under full surface loading, the highest increase in strength of HCLT reached 35.71 %, data of Ec,90 had the opposite conclusion. In the case of point loading, the fc,90 and Ec,90 under discretely support was lower than those under successively support. Load configuration had significant influence on the fc,90 and Ec,90 including middle position (M), corner position (C), edge parallel (E) and edge vertical (V) to the grain of the outer layer. In the case of line loading, it was in good agreement with point loading results, and fc,90 and Ec,90 under line loading were lower than that under point loading. The failure modes were mainly the cracks along the wood ray direction of SPF material, while no obvious damage for LSL under full surface loading. In addition, the failure modes mainly of local loading included the shear failure for SPF material, fiber fracture failure of LSL material and the adhesive layer cracking in the non-directly compression zone.