| The specially shaped column is widely used because it produces no exposed corner in interior and meets people’s higher demands of buildings such as practicability of interior space.However,the traditional reinforced concrete(RC)specially shaped column has many defects,limiting the wider development of the specially shaped column structure.Of late years,the researches of concrete filled steel tube(CFT)show that its’ performance is excellent.Therefore,scholars at home and abroad put forward CFT specially shaped column,and have conducted many researches of it.However,there are few researches on CFT specially shaped column frame structure system.Based on the existing research results,this paper makes a series of seismic analysis of the threedimensional finite element model of CFT specially shaped column frame structure system,in order to provide a reference for perfecting the theoretical system of CFT specially shaped column.The maincontents are as follows:(1)Based on the finite element software MSC.Marc and user subroutins,according to the existing test research of CFT specially shaped column frame,the fiber model of CFT specially shaped column frame is established.The hysteresis and peak bearing capacity of the finite element analysis under the cycle reciprocating load are in good agreement with the test results.It identifies the rationality of the modeling tools and methods and lays a foundation for the establishment of a rational fiber model of the frame structures composed of H steel beams and CFT specially shaped columns.(2)The researches mainly set out from three aspects,the comparison of seismic performance between CFT specially shaped column frame and CFT column frame,length to thickness ratio of column in CFT specially shaped column frame,and maximum height of this kand of frame.The rational comparison models are designed by ETABS firstly.Then,the rational fiber models are established.Next,earthquake records with appropriate characteristics and number are selected.Finally,time history analyses of frames are conducted under all three earthquake standards.Based on the analyses results,top displacement,base shear,story drift,and plastic development regularity of frames are analyzed and summarized.(3)Based on the above-mentioned fiber models and earthquake records,seismic collapse vulnerability analysis based on incremental dynamic analysis(IDA)is conducted,and the collapse margin ratio(CMR)of frames is obtained.Based on these results,not only the seismic performance but also the collapse resistance of comparison frames can be made a more comprehensive and quantitative evaluation.The main conclusions are as follows:(1)CFT specially shaped column frame structure with conventional heigh is similar to CFT column frame structure system in seismic performance and collapse resistance.Therefore,the design of CFT specially shaped column frame structure with conventional heigh can refer to the relevant regulations for rectangular CFT column structure system in Technical Code for Concrete Filled Steel Tubular Structures.However,the CFT specilly shaped columns should be strengthened propertly,so that beams will first be in plastic state,and the proportion of columns in plastic state and the degree of plastic development of columns will be reduced.(2)Increasing the length to thickness ratio of CFT specially shaped column from 4to 5 can not significantly improve the seismic response and collapse resistance of the structure.Then increasing the height of the structure,the maximum story drifts under frequently occurring earthquake and collapse probalilites under rarely earthquake are outof-codes,and the seismic response is greatly magnified and collapse margin is greatly reduced.So it is not recommended to increase the length to thickness ratio of CFT specially shaped column to 5.(3)When the height of the frame structure with CFT specially shaped columns slightly exceeds the limit height of 60 m or 50 m at 7(0.1g)or 8(0.2g)seismic intensity protection,the seismic response under all three earthquake standards and collapse resistance of CFT specially shaped column frame structures are similar to those of CFT column frame structures.But the former’s components in plastic state are mainly columns.Therefore,the maximum height of CFT specially shaped column frame structure system can refer to the relevant regulations in Technical Code for Concrete Filled Steel Tubular Structures.However,because CFT specially shaped column is easier to be in plastic state,it should be strengthed propertly in the structural design. |
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