Research On Seismic Performance Of Concrete Filled Steel Tube Frame-RC Core Wall Composite Structure

Concrete filled steel tube(CFT)frame-reinforced concrete(RC)core wall structure is a composite structural system widely used in high-rise buildings in China in recent years.This structural system combines the advantages of the two structures of CFT frame and RC core wall,with significant economic benefits.At present,there is still a lack of research on the seismic performance of the CFT frame-RC core wall structure.There are disputes about the requirements of the frame shear force sharing ratio and the method of shear force adjustment in the frame-core wall structure system in chinese specifications.Therefore,in this paper,the frame shear sharing ratio was used as the key parameter.4structural models were established by adjusting the frame strength,frame stiffness and beam-column joints respectively.The influence of the frame shear sharing ratio on the seismic performance of the CFT frame-RC core tube structure was studied,and recommendations of seismic design were proposed according to the results.The main research contents are as follows:(1)Four CFT frame-RC core tube structure models were designed and established in SATWE as the research object of this paper.The basic model meets the specification requirements except for the shear sharing ratio.The other models were adjusted with the frame strength,frame stiffness,and beam-column joints to make the structure meet the requirements of the frame shear sharing ratio for the frame’s lateral bearing capacity and lateral stiffness in the code or become a single-impact lateral force system respectively.In order to consider the comprehensive performance of the structure,the effect of adjusting the shear sharing ratio on the economic benefit of the structure through different methods was studied.The study found that the structural economic benefits that meet the requirements of the standard frame shear sharing ratio by increasing the frame stiffness are the worst.(2)The finite element analysis models of four structures were established in MSC.MARC.The beam element based on the fiber model and the layered shell element were used to simulate the CFT frame and the RC core wall respectively.The validity of the models was verified,which laid the foundation for the subsequent analysis of the seismic performance of the structure.The pushover analysis of the four structure models was carried out with the inverted triangular distribution lateral loading mode.According to the analysis results,the plastic development law of the structure was explored,and the influence of the shear sharing ratio on the change mechanism of base shear of frame and core wall under lateral load was studied.The study found that the difference in base shear force for structures with different shear sharing ratios mainly comes from the frame,and the core tube is almost the same.(3)Four typical seismic waves were used to analyze the dynamic time-history of the structure under the three anti-seismic settings of frequent,design-based and rare earthquakes.The effect of the frame shear sharing ratio on the displacement variation of the structure was explored.The maximum inter-story drift ratio and plastic damage state of structures with different frame shear sharing ratios under three seismic settings were compared.The influence of the frame shear force sharing ratio on the base shear force of the frame and the core wall in the structure under earthquake action was studied.The study found that the nonlinear response of the structure is significantly affected by the seismic characteristics,and the plastic damage of the core wall near the floor with the variable cross section of the vertical load-bearing member and the bottom was the most serious.(4)Ten seismic waves were selected to analyze the seismic fragility of the structure based on incremental dynamic analysis.IDA curve clusters were plotted using spectral acceleration and maximum interlayer displacement angle as seismic wave strength index and structural damage index,respectively.Five performance levels and their quantitative indicators of the CFT frame-RC core tube structure are determined.Through the anticollapse reserve coefficient,the influence of the frame shear sharing ratio on the structural anti-collapse safety reserve by different methods.According to the comprehensive evaluation of the seismic performance of the structure,the seismic design recommendations for the CFT frame-RC core tube structure are proposed.The study showed that,the "hardening" phenomenon of the single lateral force structure system is weak and the safety reserve against collapse is low,relatively.Increasing the frame beam strength only by increasing the strength of the frame beam will reduce the structural collapse safety reserve.Increasing the stiffness of the frame can improve the safety reserve of the structure against collapse.