旧面板对轻型木结构钉节点力学性能的影响

Influence of old panel on the mechanical properties of nailed joints in light wood frame structure

旨在通过新、旧定向刨花板(OSB)面板钉节点的对比研究,探究面板自然劣化对钉节点连接性能的影响,为今后的木结构设计和用材作参考。选取云杉-松木-冷杉规格材(SPF)、不同厚度的新旧OSB和国产麻花钉,将麻花钉垂直钉入OSB和SPF之间,依据荷载垂直于木材纹理和平行于木材纹理两种方向,共制作72个钉节点连接试件。试验参考ASTM D1761-12,对试件进行单调加载,研究不同厚度自然劣化后的旧OSB面板在横纹和顺纹连接情况下对轻型木结构钉节点力学性能的影响。结果表明:新旧OSB连接对比,除延性系数外,旧OSB面板与SPF连接的钉节点试件的荷载、刚度、耗能能力等都呈下降趋势;厚度不同的OSB连接对比,12. 0mm厚度的OSB面板连接的钉节点的荷载、刚度、延性系数、耗能能力都大于9.5 mm的OSB面板连接的试件,且12.0 mm旧板连接的力学性能下降幅度小于9.5 mm;在荷载、初始刚度、延性方面,旧板横纹连接小于顺纹连接的下降幅度;在耗能上,旧板横纹连接与顺纹连接区别不明显。试验中多发生钉子一铰弯曲和OSB、SPF破坏的试验现象,符合欧洲木结构设计规范中的破坏模式,因此可用欧洲规范计算本研究中钉连接节点最大荷载。

Light wood frame structure consists of wood frame shear wall,floor and roof system.As a main bearing system,the wall can not only withstand vertical loads and transmit the loads to the foundation,but also resist the horizontal effects caused by earthquakes or wind.The shear wall is mainly connected by nails.The performance of nailed joints directly affects the lateral stiffness and horizontal bearing capacity.Current studies focus on the influence of the panel type,thickness and the contact area on the mechanical properties of the nailed joints,in which,all the panels used were new materials and no study discussed the effects of old OSB(oriented strand board) on the mechanical property of nailed joints.By comparing the new and old OSB connected to the SPF lumber,this paper aimed at investigating the changing rules of the mechanical performance of nailed joints due to the natural aging OSB panels and then made reference to the design and material selection.The old OSB involved in the research was removed from existed buildings after 6 years service.Seventy-two nailed joints specimens were made with SPF lumber,the new and old OSB and the domestic twist nails.The nails were driven vertically between the OSB and the SPF lumber according to the directions of perpendicular-to-grain and parallel-to-grain.Monotonic loading test was applied based on ASTM D1761-12 to explore the influence of the new and old OSB panels with different thicknesses using the perpendicular-to-grain connection and parallel-to-grain connection on the mechanical properties.Test results showed that,when comparing old and new OSB connections,the load-withstanding,stiffness,and energy dissipation capacity of the nailed joints specimens connected with old OSB had a decreased trend except the ductility factor.The decrease of all mechanical properties for 12.0 mm thick old OSB was smaller than that of the 9.5 mm thick OSB.In the comparison of different thicknesses of OSB,the nailed joints specimens connected with 12.0 mm thick OSB showed better load-withstanding,stiffness,ductility coefficient,energy dissipation capacity than that of the 9.5 mm thick OSB.For the load-withstanding,stiffness,ductility factor,the decrease of perpendicular-to-grain connection of the old OSB was smaller than the parallel-to-grain connection.For the energy dissipation capacity,there was no obvious difference between the parallel-to-grain connection and the perpendicular-to-grain.The fracture modes of nailed joints were typically the OSB and SPF lumber cracking and rods bending,which consisted of the destructive pattern in the European Wood Design Code.The maximum load of the nailed joints can be calculated by the European Wood Design Code.The theoretical calculated values were in good agreement with the experimental values.The maximum load fitting results of the 9.5 mm thick new OSB board connected to the SPF lumber were better than that of the 12.0 mm thick OSB.