Experimental research on ultimate bearing capacity of N-joints of grouted square steel tube trusses

摘要

空钢管桁架N型节点易发生压陷破坏,为了使杆件破坏先于节点破坏而发生,提出了在弦杆内灌浆以提高节点压陷承载力的设想．进行了8个灌浆方钢管桁架N型节点的承载力试验．基于试验结果,进行了试件的几何参数分析,研究了套箍系数、支杆间隙和支主杆边长比等参数对节点性能的影响．基于试验结果和模拟分析结果,揭示了这类节点的受力机理与破坏模式,提出了对应于不同破坏模式的节点承载力计算公式：N型受压节点及受拉节点承载力分别按弦杆压陷破坏和冲剪破坏模式进行计算；弦杆的承载力要按弦杆直剪破坏模式进行校核．%Cave-in failure is apt to occur in joints of trusses made of square hollow sections. In order to turn the failure mode into a strength failure mode of joint members, the idea is proposed that the chord of the truss is grouted to increase the cave-in bearing capacity of a hollow tube chord. An experiment of eight specimens of N-joints made of grout-filled square steel tubes is performed. Based on the experimental study, the geometrical parameters of specimens are analyzed, and the effects of the confinement index ξ, the spacing between the two web members g and the ratio of side length of the vertical web member to that of the chord β on the behavior of specimens are investigated through simulation analysis by an ANSYS program. Based on the test results and simulation analyses, the mechanical properties and the failure modes of this kind of joints are analyzed and the formulae to predict the ultimate bearing capacities corresponding to different failure modes are developed. The ultimate bearing capacity of compressive N-joints is calculated in accordance with the cave-in failure mode of a chord member; the ultimate bearing capacity of tension N-joints is calculated in accordance with the punching-shear failure mode; the ultimate bearing capacity of a chord member is calculated in accordance with the shear failure mode in normal sections.