CFRP加固火灾后RC梁柱节点抗震性能试验

Experiment on seismic behavior of RC beam-column joints after fire and strengthened with CFRP

为评估折线形粘贴碳纤维增强复合材料(CFRP)布加固火灾后钢筋混凝土梁柱节点抗震性能的效果,分别进行未受火、火灾后和CFRP布加固火灾后带正交梁和楼板翼缘的钢筋混凝土梁柱中节点抗震性能的拟静力试验。火灾试验时采用ISO 834标准升温曲线、梁柱节点的受火方式为楼板下方受火,拟静力试验时柱子的轴压比为0.25。基于试验结果,考察火灾高温后CFRP布加固对混凝土梁柱节点的破坏形态、滞回曲线、骨架曲线、承载力、延性、刚度及滞回耗能的影响。研究结果表明:梁柱节点核心区均发生了剪切破坏;未受火和受火后梁柱节点分别在3/100和4/100位移角时达到最大承载力,该位移角下节点核心区可见最大斜裂缝宽度分别达到2.0、1.9mm;未受火梁柱节点和CFRP布加固后梁柱节点核心区箍筋发生屈服,90min的火灾高温作用会显著降低梁柱节点的抗震性能,受火后梁柱节点的开裂荷载、屈服荷载、极限荷载和延性系数分别降低了41.3%、18.5%、15.8%和14.8%;节点区折线形粘贴CFRP布加固对受火后混凝土梁柱节点抗震性能的提高有限,加固后梁柱节点的承载力未能恢复至未受火时情况;CFRP布加固火灾后梁柱节点开裂荷载、屈服荷载和极限荷载分别比火灾后未加固梁柱节点提高了16.5%、4.0%和3.4%,比未受火梁柱节点的降低了31.6%、15.2%和12.9%。火灾后钢筋混凝土梁柱节点抗震加固方案及其设计方法还有待进一步深入研究。

This paper presents an experimental study of the seismic behavior of reinforced concrete(RC)beam column joints after fire and strengthening with fold-line CFRP sheets.Pseudo-static loading was applied to RC beam column joints with orthogonal beams and floor flanges.Experimental tests were conducted on three specimens:one with no fire,one subjected to fire,and one subjected to both fire and strengthening with CFRP sheets.The ISO 834 standard temperature rise curve was used for the fire test,and the part beneath the floor of the joint was subjected to fire.The axial compression ratio of the column was maintained at 0.25.The effects of high temperature(due to the fire)and CFRP strengthening on the failure mode,hystereticcurve,skeleton curve,load bearing capacity,ductility,stiffness,and hysteretic energy of the joints were investigated.The results show that shear failure occurred in the core area of each joint.The maximum bearing capacities of the joint without fire and the joint subjected to fire are achieved at the displacement angles of 3/100 and 4/100,respectively.The corresponding maximum widths of the inclined cracks are 2.0 and 1.9 mm,respectively,in the core area of the joints under the displacement angles.The stirrups in the core area of the joint which is not subjected to fire,and that of the joint after fire and with CFRP reinforcement are founded to have yielded.The seismic performance of the joint is significantly reduced after a fire lasting 90 min.Specifically,the cracking load,yield load,ultimate load,and ductility coefficient of the joint are reduced by 41.3%,18.5%,15.8%,and 14.8%,respectively.Furthermore,strengthening the joint that is subjected to fire with CFRP sheets provided only limited improvements in the seismic performance of the joint,and this strengthening could not restore the bearing capacity to the same level as that of the specimen that is not subjected to fire.The cracking load,yield load,and ultimate load of the joint subjected to both fire and strengthening with CFRP are,respectively,16.5%,4.0%,and 3.4% higher than those of the joint that is subjected to fire but not strengthened.These parameters are 31.6%,15.2%,and 12.9%lower than those of the joint that is subjected to fire,respectively.The study concluded that further investigation is needed on the seismic strengthening scheme and design method for RC beam column joints subjected to fire.