竹集成材钉节点力学性能的试验研究

为研究现代竹构建筑中钉节点的受力性能和变形性能，对85个竹集成材钉连接节点试件进行单调加载试验，研究不同钉子端距、中距、边距、行距对钉节点的承载性能、变形特性和破坏机理的影响。试验结果表明，节点的力学性能主要取决于端距和中距，而边距和行距的影响较小。加载初期的钉孔间隙导致节点初期的刚度较低。当端距和中距小于6D（D为钉子直径）时，节点的承载力随着端距和中距的增加而呈增大趋势，当端距和中距大于等于6D时，节点的承载力将不再增大。钉节点的破坏形态与钉子的布置密切相关。当端距或中距小于6D时，分别以端部剪切破坏和纵向劈裂破坏为主；当边距小于4D或行距小于3D时，分别以劈裂和块剪破坏为主。当钉子的端距、中距、边距和行距布置满足最小容许要求时，钉节点以销槽承压破坏模式为主，表现出较好的延性特征。试验结果的回归分析表明，Folz模型能较好地反映钉节点在各个受力阶段的荷载-位移本构关系，而基于Foschi和Hassanieh模型预测的弹塑性阶段的钉节点荷载-本构关系结果偏于保守，但明显高估了破坏阶段的受力变形性能。研究结果可为竹集成材钉节点的设计与应用提供参考。

Experimental study on mechanical performance of laminated bamboo lumber nailed connections

In recent years, the building industry of China has expanded rapidly, however, construction materials such as the steel and cement are extensive used, which leads to serious environmental issues and energy consumption. As one of the fast-growing plants in the world, bamboo has been applied in civil engineering field for thousands of years. However, some disadvantages are exposed during the practice, such as thin-walled hollow and the diameter of bamboo culm decreases from the bottom to top. More importantly, the service life of bamboo structures generally does not exceed 3 years when the untreated bamboo exposure to natural environment. Recently, more and more attention are paid on the laminated bamboo lumber (LBL), which is considered as an alternative to wood because of its advantage of higher ration of strength to weight. Dowel connections including bolt, nail, screw and dowel are common types of connections in timber engineering for a large range of structural applications. Among them, nail connection is simple to produce and can be used for small as well as for large forces. Over the last decade, the use of LBL for modern bamboo structure has become increasing popular in China. LBL nailed connection which consisted of one middle member and two side members were introduced. A total of 85 specimens were tested in order to investigate the effect of parameters on capacity, deformation and failure modes of nailed connections, including end distance (e1), center-to-center distance (s), row spacing (r) and edge distance (e2). It was found that the mechanical performance of nailed connections was mainly determined by the end distance and center-to-center distance of nails, and the influence of row spacing and edge distance was relative small. The initial gap between the lead hole and nails tended to result in lower stiffness. Four failure modes were recorded, including compression failure at the nail hole, splitting, shear failure at the end and block shear. For e1 or s less than 6 times the diameter of nails (D), the nailed connections failed in shear failure at the end and splitting, respectively. For r less than 3D or e2 less than 4D, the connections failed in splitting and block shear, respectively. When nail spacing meet the minimum structural requirement, the nailed connections failed in compression failure of nail holes in the middle or side members, showing good ductile behavior. The ultimate load and yield load of specimens increased with the increase of nail spacing and kept constant as the nails spacing satisfied the minimum structural requirement. Many models had been proposed to quantify the load-displacement relationship of wood nailed connections, such as Folz''s, Foschi''s and Hassanieh''s model. Using the regression analysis for comparing the three theoretical models, it was found that the Folz''s model was more objectively reflected the load- displacement relationship of LBL nailed connections loaded parallel to grain. A good agreement could be observed between the Foschi''s or Hassanieh''s model and experimental results in the elastic stage, but great deviation of the theoretical results in the post-yielding stage increased gradually. The results provided useful information for modeling various bamboo structures containing LBL nailed connections.