Investigation On Collapse Resistance Capacity Of In-service Low-ductile RC Frame Structures

Recently,large earthquakes frequently struck the whole world,causing serious damage to various building structures.Previous earthquake damage and experimental studies have shown that,most of the severely damaged or destroyed buildings are low-ductile R.C.frame structures with poor seismic fortification level,insufficient seismic fortification measures and long service ages under earthquake.And these structures have different seismic capabilities in different times.Therefore,it has practical significance to investigate the global collapse resistance capacity of low-ductile R.C.frame structures.In this paper,the influence factors of ductility are compared.And the ability of collapse resistance capacity and the ability of dispersion are studied,the main research word is as follows:(1)The research of RC frame structures' ductility and the collapse of structures under earthquakes is reviewed.And this paper introduces the factors that influence the structures' ductility and the analysis methods of anti-seismic performance of structures.This paper introduces research theories of RC frame structure under earthquakes and criteria for judging the collapse of RC frame structures.(2)The numerical analysis models,with an active reinforced concrete frame structure as the prototype,were established separately by Open Sees considering stirrup arrangement,space,diameter,and concrete strength.The sensitive factors affecting structural ductility were acquired by static pushover analysis.The influence of stirrup arrangement,space and diameter to ductility is basically same.And concrete strength is proved the minimal influence to ductility.(3)And then,two R.C.frame structures(low-ductile and newly-built structures)of the same dimension and reinforcement ratio but different ductility are modeled for incremental dynamic analysis in Open Sees based on results of pushover analysis.The IDA of 25 ground motions recorded is comparied by the two structures.Global collapse resistance capacity of different ductility structures is investigated by Sa(T1,5%),the index of collapse resistance capacity with 50% collapse probability.The collapse resistance capacity of newly-built structures is better than that of low-ductile R.C.frame structures.(4)The residual drift of the two structures is studied based on the maximum inter-storey drift ratio of 0.02 and 0.05,the maximum residual inter-storey drift ratio of R.C.frame structures increases greatly when the maximum inter-storey drift ratio is more than 0.02.And the maximum residual inter-storey drift ratio of low-ductile structures increases fastert than that of newly-built structures.In short,based on the research on the ductility of R.C.frame structures at home and abroad,some sensitive factors affecting the ductility of R.C.frame structures are summarized.The collapse resistance capacity of newly-built structures is better than that of low-ductile R.C.frame structures by comparison with two structures.And the maximum residual inter-storey drift ratio of low-ductile structures increases fastert than that of newly-built structures.