Welded flange-bolted web connection is one of the common joints in the steel structure,and the mechanical performance and failure mode of the joint is related to the collapse resistance of steel frame closely.To compare and analyze the failure mode,mechanical property and res-istance mechanism under the condition of progressive collapse,the beam-column substructures of three different span ratios(1:0.6,1:1.0, 1:1.4)with welded flange-bolted web connection in minor-axis direction were selected,which included three columns and two beams,to conduct monotonic static loading test by alternate load path method.The test results indicated that the fracture of specimens begins with the beam tension flange,and then part of the main internal force is transferred by the bolts on web,followed by buckling of the compression flange of the beam end.Finally,specimens are deactivated because of the shear failure on bolt holes or fracture of web and junction plate.The process of anti-collapse mechanism appears the flexure phase,flexure-catenary mixed phase and catenary phase.It could be found that joint with welded flange-bolted web connection possesses high redundancy,which has enough rotational capacity after the fracture of tension flange.The catenary could be developed and take the lead in the following great deformation in two factors,which are the magnitude of the axial tension generated in the beam-column members,and the sufficient rotation angle of the beam end.The deformation of the beam-column joint is beneficial for the beam-column substruc-ture to bear the load by collaboration between the beam and the column.For the unequal span specimens,the initial fracture of substructure is al-ways at the short-span beam with small span-depth ratio and the short beam has better catenary mechanism than the long one.%栓焊连接是钢结构建筑中常用的节点形式之一,该节点的受力性能和破坏方式与钢框架结构的抗倒塌性能密切相关.针对栓焊连接节点,采用备用荷载路径法,选择两跨三柱型梁柱子结构作为研究对象,对3个不同跨度比(1:0.6、1:1.0、1:1.4)的弱轴栓焊连接梁柱子结构试件进行单调静力加载试验,对比分析了连续倒塌条件下3个试件的破坏模式、力学性能和抗力机制.试验结果表明:3个试件的破坏过程均为梁端受拉翼缘先后发生断裂,进而断裂截面部分内力转由腹板螺栓传递,且梁端受压翼缘屈曲,最终由于梁柱节点处梁腹板螺栓孔发生剪切破坏或梁腹板、节点板断裂使试件丧失承载力.通过分析试件的失效机理可知,3个试件的抗力机制发展过程经历了梁机制阶段、梁机制向悬链线机制转变的过渡阶段、悬链线机制阶段.弱轴栓焊连接节点具有较高的冗余度,当受拉翼缘断裂后节点仍具有一定的转动能力,剩余结构通过梁柱之间可靠的拉结力及梁端产生的较大转角保证悬链线效应能够充分发挥,且在之后的大变形中起主导作用,而梁柱节点变形的快速增大有利于梁柱子结构通过梁柱构件间的协同工作继续承担荷载.对不等跨弱轴栓焊连接梁柱子结构试件,其初始断裂部位往往位于跨高比较小的短梁,且短梁相比长梁的悬链线效应更为显著.
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