火灾下拉剪组合作用对高强螺栓节点性能影响的试验研究

火灾中节点的承载力随着温度的升高而降低,高温下梁的悬链线效应在梁内产生较大的拉力,高强螺栓连接节点通常在拉剪共同作用下发生破坏。采用自定义双线性炉温控制曲线,进行两类共8组高强螺栓连接节点的恒载升温试验,分析了端板式连接和腹板双角钢连接两类节点在高温以及拉剪共同作用下的变形发展及破坏规律。试验结果表明:高强螺栓连接节点区的梁端板、连接角钢、柱上翼缘及高强螺栓的温度接近,且较梁柱构件温度低50℃左右;节点刚度随着温度的升高而降低,且大约在节点温度达到500℃后刚度下降速度明显加快;火灾下8mm端板节点的变形集中于拉力较大侧端板及螺栓,16mm端板节点的变形则集中于拉力较大侧螺栓及柱上翼缘;腹板双角钢连接节点主要是角钢产生较大变形;两类节点失效温度随拉力或剪力的增加而减小,且同类节点在不同拉剪组合作用下的残余变形模态类似。

EXPERIMENTAL RESEARCH ON THE BEHAVIOR OF HIGH-STRENGTH BOLTED CONNECTIONS UNDER COMBINED TENSION AND SHEAR IN FIRE

During a fire, the fire resistance of steel connections decreases as temperature increases, and large deformation of beams leads to huge catenary forces within beams. As a result, connections are generally loaded to failure under combined tension and shear forces. Transient fire tests were conducted on eight specimens of two connection types to study their fire-resistance when subjected to different combinations of tension and shear, in which furnace temperature was increased according to a specified bilinear curve. The experimental results indicate that the temperatures of beam endplates, cleat connections, column top flanges and high-strength bolts in the panel zone of high-strength bolted connections were similar, and were about 50℃ lower than that of beams and columns. The stiffness of the connections decreased continuously during the heating, and dropped sharply when the connection temperature exceeded 500℃. The deformation of the 8mm thick flush endplate connection was mainly observed in the endplates and the bolts. When the endplate thickness was 16mm, significant deformations were observed in the column top flanges and the bolts. The double web cleat connections failed because of the excessive deformation of the angles. For all the connections, fire-resistance decreases with an increase in either tension or shear, but the residual deformations were similar among the different connections under a series of tension and shear actions.