竹集成材-定向刨花板钉连接力学性能

Mechanical performance of nailed connections between laminated bamboo lumber and oriented strand board

竹木组合剪力墙是一种以竹集成材(laminated bamboo lumber, LBL)为墙骨柱、定向刨花板(oriented strand board, OSB)为覆面板,两者通过铁钉连接而成的抗侧力构件。风荷载和地震作用下竹木剪力墙的破坏往往始于LBL与OSB间的钉节点失效。以钉直径d、OSB钉边距a、LBL钉边距b和加载方向为参数,制作并测试了6组共150个LBL-OSB钉节点试件,研究其破坏模式、承载力和变形性能。结果表明:破坏模式与OSB钉边距和LBL钉边距密切相关,主要表现为OSB面板边缘撕裂破坏、钉子“单铰”弯曲破坏、钉子穿透面板和LBL端部剪切破坏。当OSB钉边距或LBL钉边距不满足构造要求时,试件容易发生过早的脆性破坏。OSB和LBL的钉边距最小值为15 mm。极限荷载随着钉直径的增大而增大,横纹试件的承载能力略低于顺纹试件。试件的荷载-位移曲线可大致划分为弹性阶段、弹塑性阶段和下降阶段,Folz提出的本构模型可以很好地模拟LBL-OSB钉节点的荷载-滑移本构关系。研究成果可为竹木结构剪力墙的设计和有限元分析提供参考。

Bamboo culm is usually used to build houses and bridges in many countries, but bamboo culm diameter tapers from bottom to top with different bamboo species. More importantly, the service life of bamboo structures would be reduced significantly due to the improper handling. A series of engineered bamboo products, such as laminated bamboo lumber(LBL), bamboo scrimber and oriented bamboo strand board has been developed in recent years. Shear walls in low-rise bamboo-frame structures are often designed to withstand lateral load induced by wind and earthquake loadings. A typical LBL frame shear wall consists of 1 220 or 2 440 mm long frame structure, with 40 mm×90 mm studs typically spaced 405 mm on centers, double end studs, and 40 mm×90 mm single plates at the top and bottom of the wall. Usually, the oriented strand boards(OSB) are used as sheathing material and connected to the LBL frame using smooth shanked nails. The existing studies have shown that the sheathing-framing connections govern the behavior of the shear walls. The effect of parameters including nail diameter d, the distance of nail to the edge of OSB a, the distance of nail to the edge of LBL b, and the loading direction on the mechanical performance of the LBL-OSB connections were investigated. It was found that the failure modes of the nailed connections were closely related to the distance of nail to the edge of OSB, the distance of nail to the edge of LBL, and the loading direction, but not related to the nail diameter. Four failure modes were recorded, including nail tears sheathing panel, nail pull through sheathing, single plastic hinge within the nail, and splitting failure of LBL members. When the distance of the nail to the edge of OSB and LBL did not meet the minimum construction requirements, the nailed connections were prone to be damaged prematurely. As expected, the maximum load of specimens increased with the increase of the nail diameter, and the load carrying capacity of the parallel-to-grain specimens was lower than those of specimens loaded perpendicular to the grain. All LBL-OSB connections exhibited similar load-slip response, and the failure process of connections could be classified into three phases. The theoretical model developed by Folz was capable to simulate the load-slip relationship of connections loaded parallel to the grain and perpendicular to the grain. The research results obtained can provide reference for the application and finite element analysis of LBL structures containing LBL-OSB connections.