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 纤维平行剪切强度（f_v0）对木结构设计具有至关重要的工程意义。鉴于当前尚缺乏阔叶树种纤维平行剪切强度（f_v0）随荷载作用平面相对于生长年轮与木射线的变化规律相关研究数据，本研究依据NBR 7190-3（ABNT，2022b）标准，通过改变荷载作用平面开展f_v0测定试验。试验分别针对卡谢塔木（Simarouba amara）与罗辛霍木（Peltogyne spp.），在其纵向-切向（LT）与纵向-径向（LR）平面施加荷载。经置信度为5%的方差分析，结果表明：改变荷载作用平面时，两种木材的f_v0值未呈现统计学显著性差异。因此，测定该类树种的f_v0时，无需考虑木射线与年轮取向，不存在显著的强度折减风险。此外，本研究测得罗辛霍木与卡谢塔木的特征纤维平行剪切强度与特征顺纹抗压强度比值（f_v0,k/f_c0,k）分别为0.23与0.38。综上，该结果证实：为控制成本或保障结构安全，对施工现场接收的陌生木材树种进行性能表征是十分必要的。