Influence of growth rings position of wood on the determination of its shear strenght parallel to the fibers

Abstract Shear strength parallel to the fibers (f v0 ) is extremely important for the design of timber structures. Then, due to the lack of information related to a possible variation in the f v0 of hardwood species according to the load application plane in relation to its growth rings/rays, this work performed tests for the determination of f v0 according to NBR 7190-3 (ABNT, 2022b) varying load planes. Thereby, the load was applied on the longitudinal-tangential (LT) and longitudinal-radial (LR) planes of the species of caixeta (Simarouba amara) and roxinho (Peltogyne spp.). Through variance analysis (5% confidence), results did not point to statistical differences between f v0 values when the load plane was changed. Therefore, the f v0 of this species can be determined without significant risk of reduction according to ray/ring orientation. Furthermore, it was determined a ratio of f v0,k /f c0,k equal to 0.23 and 0.38 was determined for roxinho and caixeta, respectively. Thus, this result confirms the need for characterizing unfamiliar wood species when received on construction site, in order to save money and/or for safety reasons.

摘要：平行于纤维的抗剪强度（shear strength parallel to the fibers）对木结构工程的设计至关重要。鉴于当前缺乏阔叶树种的该强度值随荷载作用平面（相对于其生长年轮与木射线）变化的相关数据，本研究依据NBR 7190-3（ABNT，2022b）标准，针对荷载作用平面变量开展了该强度（f_v0）的测定试验。试验荷载分别施加于caixeta（Simarouba amara）和roxinho（Peltogyne spp.）的纵向-弦向（LT）与纵向-径向（LR）平面。通过置信水平为5%的方差分析，结果显示改变荷载作用平面时，两类树种的f_v0值未呈现统计学显著性差异。因此，无需考虑木射线与年轮取向，即可安全测定该类树种的f_v0值，不存在显著的强度折减风险。此外，本研究还测定得到：roxinho的特征平行纤维抗剪强度与特征平行纤维抗压强度的比值（f_v0,k /f_c0,k）为0.23，caixeta的该比值为0.38。综上，本研究结果证实：施工现场接收陌生木材树种时，需对其进行性能表征，这既是出于成本节约的考量，也是为了保障结构安全。