Seismic Performance Of Angel Steel-CFRP Composite Retrofitting For Damaged Frame After Main Quake

Unscientifically designed column-beam joint and plastic hinge region of frame are usually damaged after main quake.Seismic retrofitting is needed to meet the capacity and deformability requirement for being put into use,and it's the same with undamaged structure where seismic fortification intensity improves.CFRP provides passive constraint and is weak in improving section bearing capacity and rigidity,thus a composite retrofitting method is proposed including repairing damaged concrete in plastic hinge region and joint,CFRP constraining repaired concrete ensuring that concrete could effectively work together,stainless angle steels with high ductility are placed at the bottom of columns to recover bearing capacity of column root section and to improve rotation ability of plastic hinge,in order to solve the problem that original reinforcement bars failed and no longer make contrbutions to resistance.Therefore,after simulating earthquake damage to frames by quasi-static test and retrofitting by composite method,the quasi-static test is carried again and seismic performance was evaluated.Aiming at influence on seismic perforcemence of angle steel with high ductility,with different axial load ratio levels(0.5,0.65,0.75),restoration and reinforcement of 5 frames are finished,and quasi-static test is carried,and the whole process of experiement was recorded,including concrete cracked,CFRP cracked,angel steel yielded,concrete failed and peeled,CFRP pulled off and so on.Compared and analysed failture mode of frame,angel steel and CFRP before and after retrofitting.After retrofitting by composite method,damage degree of columns decreases significantly,damage focused on ends of beam and joint core not damaged.The main failure mode of CFRP is tensile failure.Angel steel yielded by compression and left residual deformation.By comparing seismic performance index including hysteresis loop,horizontal bearing capacity,skeleton curve,displacement ductility,stiffness degradation,resistance attenuation,single cycle energy dissipation,cumulative energy dissipation,equivalent viscous damping coefficient of 5frames before and after retrofitting,the influence rule of factors including angle steel with high ductility,axial load ratio of columns,degree of damage etc.o n seismic performance of strengthening structures was revealed.The advantages and disadvantages of frames retrofitting by angle steel with high ductility-CFRP composite method under low-cycle reverse loading test.Two indexes,self relative single cycle energy ratio and self relative stiffness ratio are proposed to directly show reinforcemnet effect on energy consumption and stiffness.Range and growing rule of stain of angel-steel and CFRP were analysed.Actual working condition and effiency of reinforcing materials in different positions and with different consumption were concluded.Utilization factor of angel steel was proposed,and calculation formula between utilization factor of angel steel and self relative single cycle energy ratio as well as self relative stiffness ratio was fitted.Take use of utilization factor of angel steel and damage coefficient of original longitudinal reinforcement to consider the facts that angel steel and CFRP aren't able to be fully uesd,some failed reinforcement bars,which may experieced plastic deformation and strain softening or even pulled off,existed in damaged columns.Based on experiement results and current standards,meanwhile refering to existing research results,analysed the root section of column and stiffn ess changing section at the upper edge of vertical limb of angel steel after angel steel with high ductility-CFRP composite retrifitting method.Proposed suggested calculation formula of normal section bearing capacity and inclined section bearing capacity,which provides reference for design and calculation of angel steel with high ductility-CFRP composite retrifitting method in practical engineering.Focusing on materials,choice of retrofitting method,capacity calculation and horizontal displacelment checking,seismic design suggestions of AS-CFRP composite retrofitting method were provided.