Evaluation of out-of-plane bending performance of cross-laminated timber (CLT) with various layups made from Japanese cedar (Cryptomeria japonica)

Abstract This study assesses the out-of-plane bending performance of cross-laminated timber (CLT) panels made from Japanese cedar to determine the bending modulus of elasticity ( E ) and shear modulus ( G ) through both dynamic and static testing methods. Six CLT layups, as defined by the Japanese Agricultural Standard (JAS) 3079, were tested in both major and minor strength directions. The findings reveal that E values obtained from the Timoshenko–Goens–Hearmon (TGH) method, the variable span method, and the shear-free (local) values of the out-of-plane bending test were generally consistent. However, the values derived from the transformed section method were generally lower, especially in the minor strength direction. The TGH method consistently yielded higher G values compared to the variable span method, which exhibited irregular patterns in minor strength direction layups with fewer layers. The E / G ratios from the variable span method reached approximately 80 for certain layups in the major strength direction, surpassing the default value of 50 used in JAS 3079. This indicates the need for an adjustment factor near 0.85, rather than the default 0.9 specified in JAS 3079. While the 0.9 adjustment factor is appropriate for most CLT layups, it can underestimate deformation in those susceptible to rolling shear. In addition, out-of-plane bending test results show that the 0.65 reduction factor from the Notification of the Ministry of Land, Infrastructure, Transport and Tourism is suitable for the major strength direction but may be too conservative for layups in the minor strength direction.