Study On The Seismic Performance Of RC Frame Structures With Added Steel Story

Non-renewable land resources make urban building land increasingly depleted,and effectively improving the utilization rate of existing buildings has become the focus of many scholars.Because the added layer of steel structure has the advantages of light weight,little influence on the bearing capacity of the original building,fast construction speed almost does not affect the normal use of the original building,and can be recycled and save resources after demolition,it has become one of the effective ways to alleviate the shortage of land.But most of the domestic scholars’ research only focused on the top added steel stories,and there are few research results on other forms of story adding,leading to the lack of reasonable design reference for actual engineering.Based on an engineering example of a four-story frame structure in Xi’an,this paper uses ETABS software to model the frame structures before and after story adding,and to analyze the seismic performance.The main work of this paper is as follows.1.This paper summarizes the structural seismic analysis method and damping theory,and combines the characteristics of the engineering example to determine the structural seismic analysis method and the overall damping ratio of the structures before and after story adding.Aiming at the problem of insufficient bearing capacity of the concrete beams and columns of the original structure after the adding of stories,determined economical and suitable strengthening methods.2.The modal analysis results of the structures before and after story adding show that the added top steel story makes the overall structural less stiff,and the period of the structure becomes longer.The added interior steel story makes the overall structure stiffer,and the period of the structure becomes shorter.3.The results of the response spectrum analysis and the elastoplastic time history analysis of the structures before and after story adding show that the added top steel story makes the maximum story displacement and the maximum inter-story displacement angle larger,the added interior steel story makes the maximum story displacement and the maximum inter-story displacement angle smaller,and those stories closer to the story added are more affected by it.The added top story and the interior one both make the maximum shear force larger.4.Under rare earthquakes,the development of plastic hinges of the structure before and after story adding show that the added steel stories make the plastic hinges in the structure appear earlier and more in number.The third story of the original frame structure is the weak one of the structure,then the added top steel story makes the top story of the original structure a new weak story.At the end of the earthquake,plastic hinges appear only in the beams but not the columns,indicating that the structure meets the requirement of "strong column and weak beam" for seismic design.