竹集成材钉节点抗剪性能试验研究

Experimental Study on Shear Performance of Laminated Bamboo Lumber Nailed Connections

为研究铁钉直径和夹角对节点的破坏模式及承载力、滞回特性、刚度退化、耗能能力等性能的影响,对50个竹集成材(Laminated Bamboo Lumber,LBL)钉节点进行单调和低周反复荷载试验.结果表明:不同加载模式下的节点破坏模式存在明显区别.单调荷载作用下,节点的破坏模式主要表现为铁钉“双铰”模式和钉杆下部的纤维压碎破坏.而在低周反复荷载作用下大部分的铁钉发生了由于反复弯曲变形所致的疲劳断裂破坏,这种破坏现象却极少发生在振动台试验和实际的地震中.铁钉直径是影响钉节点受力性能的主要因素,节点的承载能力和刚度随铁钉直径的增加而显著提高,而夹角对节点的力学性能影响较小.LBL钉节点单调加载试件的承载力和刚度均比低周反复荷载加载试件高.加载初期试件的荷载-位移滞回曲线形状不饱满,具有明显的“捏缩”现象.试件的累积耗能随铁钉直径增大而增加,并随加载角度增大而减小.研究成果可为LBL钉节点的设计提供理论依据,并加速其在土木工程领域的应用.

In order to investigate the effect of the nail diameter and loading direction to the grain on the failure mode,load carrying capacity,hysteresis characteristics,stiffness degradation,and energy consumption capacity of the specimens,50 laminated bamboo lumber(LBL)nailed connections were tested under monotonic and cyclic loadings.It is found that the failure phenomenon of the nailed connections varies greatly between different loading methods.For the specimens loaded monotonically,two plastic hinges within the nail and fiber crushing beneath the nail shank were observed.However,most nails failed in low cycle fatigue fracture due to reversed bending in the reversed cyclic loading tests,which is seldom investigated during the shaking table tests and earthquake excitation.The nail diameter is the major factor that affects the mechanical performance of the nailed connections.The load carrying capacity and the stiffness of the specimens increase significantly with the increase of the nail diameter,while the effect of the loading direction to grain is small.The load carrying capacity and stiffness of the specimens under monotonic loading are higher than those subjected to reversed cyclic loading.The load-displacement hysteresis curves of the specimens are not in plump shapes and have significant pinch phenomena at the initial loading stage.The cumulative dissipated energy of the nailed connections increases with the increasing nail diameter and decreases with the increase of the loading direction to the grain.These findings obtained in this study can offer a theoretical reference for the design of the LBL nailed connections,and speed up its applications in the field of civil engineering.