Seismic Evaluation Of CFRP-retrofitted Earthquake-damaged Non-ductile RC Frames

Part of the reinforced concrete(RC)frame structures were designed and built according to the previous seismic design code.Some of the structures did not consider the earthquake action during the engineering design,some of the structures were designed to meet outdated criterion for seismic precaution,which shows inadequate ductility under the earthquake action.This kind of structures is called the non-ductile RC frame in this paper.Based on the investigation of real earthquakes,it is generally reflected that the RC frames are mostly mild or moderate damage after the earthquake.Obviously,the demolition or reconstruction of these mild or moderately damaged houses will cause huge economic burden.The Carbon Fiber Reinforced Polymer(CFRP)retrofitting method has many advantages,but at present,in the research_es on the CFRP-retrofitted earthquake-damaged non-ductile RC frames,there are few literature concerning about the level and the magnitude of the seismic bearing capacity of each layer before and after the CFRP-retrofitted,and no conclusion is reach_ed wh_ether the interstory drift can meet the requirement of the current seismic design code of China.In view of the above problems,this paper is based on the scale test research,and it is utilized the finite element method to study the seismic performance of the full scale CFRP-retrofitted frame.The main contents are as follows:(1)A 1/2 scale,2-bay,2-story non-ductile RC frame substructure specimen was designed in this paper.The pseudo static test was simulated the earthquake to cause the damage,and the pseudo static test was carried out again after the CFRP-retrofitted.The hysteretic curves of the frame before and after reinforcement was obtained.The hysteretic curve of the CFRP-retrofitted frame is fuller,which indicates that CFRP can improve the energy dissipation capacity of the non-ductile RC frames.(2)Based on skeleton curve,the seismic performance of frame before and after reinforcement is analyzed,such as strength,stiffness,ductility and energy dissipation.The analysis results show that the maximum bearing capacity of the reinforcement is increased by 3.59%,indicating that the CFRP has limited effect on improving the bearing capacity of the structure;the minimum ductility coefficient of the 7 degree fortification requirement is 2.183 and the average displacement ductility coefficient of the CFRP-retrofitted specimen,(?)=2.81,which exceeds the minimum ductility factor of 28.90%,indicating that the ductility meets the requirement of criterion for seismic precaution;the limiting state equivalent viscous damping coefficient (?)=0.136 satisfies the requirement of general RC frame structure,and achieves the energy dissipation level of general RC frame structure.(3)Based on the constitutive models of damaged concrete and CFRP-retrofitted concrete,the finite element of nonlinear hysteretic behavior of CFRP-retrofitted non-ductile RC frame was simulated by using OpenSees,and the correctness of the model was verified by comparison with the experimental results.The Pushover analysis method was used to study the collapse failure mode of the five layer CFRP-retrofitted non-ductile RC frame(the arch_etype structure of the substructure).The first,second story beam ends and the third story beam ends were developed into plastic hinge,and then the bottom end of the two side columns was developed into plastic hinge.The,strong column and weak beam"of CFRP-retrofitted frame can improve ductility,and thus prevent the sudden collapse.(4)The seismic performance of the 5-story CFRP-retrofitted earthquake-damaged RC frame was quantitatively evaluated by the capacity spectrum method.Under the action of small earthquakes,moderate earthquakes and great earthquakes,the maximum interstorey displacement angles of the structures are 0.0007,0.002 and 0.01394,respectively,which satisfy the requirements of the 1/550(0.0018)of the elastic interstory drift,and the 1/50(0.02)of the elastic-plastic interstory drift.