Study On Seismic Performance Of High-rise Steel Frame With Mixed Braces Under Strong Earthquake

The Buckling-Restrained Braces(BRB)was proposed in order to avoid the premature buckling of ordinary supports during earthquakes,BRB is the first to yield and not buckle under the action of strong earthquakes,which can preferentially resist most of the seismic energy for the structure,so as to achieve the purpose of energy dissipation and shock absorption.According to the specific engineering project and the principle of BRB layout,three kinds of BRB layout schemes are designed,the reasonable BRB layout scheme is determined through the mode decomposition response spectrum method and the analysis of frequent earthquake time history response.Considering the economy of the structure,three hybrid brace layout schemes are designed based on the BRB layout scheme.Through numerical simulation research,finite element models of steel frames under different hybrid brace layout schemes were established,Push-over analysis was used to obtain the development law of plastic hinge and structural performance points,and the time-history analysis of the rarely occurred earthquake was carried out to obtain the seismic performance comparison of structures under different hybrid brace schemes.The main work carried out is as follows:(1)Taking pure steel frame,steel frame with mixed bracing based on engineering drawings and steel frames with three BRB layout schemes as the research object,the natural vibration characteristics and torsional effects of the structure were studied through dynamic characteristic analysis and response spectrum analysis of mode decomposition.The periodic ratio,torsional displacement ratio and displacement response of each structure were discussed,and the rationality of each structure was verified;The periodic ratio,torsional displacement ratio and displacement response of each structure were discussed,the rationality of each structure was verified,and the influence law of different BRB layout scheme on structure stiffness was obtained.(2)In order to reveal the seismic performance of the structure,the appropriate ground motion records were selected to carry out time history analysis of the structure under the frequently occurred earthquake.The displacement response of the structure under the frequently occurred earthquake was systematically analyzed,including the seismic characteristics of the inter-story displacement angle and the maximum horizontal displacement,as well as the floor shear and shear weight ratio,so as to determine a more reasonable BRB layout scheme.(3)Based on the known ratio of side stiffness,the cross sections of BRB and ordinary brace were determined.Taking BRB steel frame,ordinary braced steel frame and three kinds of mixed braced steel frame as the research object,the mechanical properties and safety properties of the structure were evaluated by Push-over analysis.By analyzing the performance points of each structure,the axial force distribution of the first layer column and the development law of plastic hinge,the influence law of different mixed brace layout schemes on the failure process of the structure is revealed.(4)On the basis of determining the failure grade of each structure,the elastic-plastic time-history analysis under the rarely occurred earthquake was carried out to compare the displacement response,maximum floor shear,time history curve of vertex acceleration,maximum axial force and hysteresis curve of each structure,so as to analyze the working state of some supports in the structure,and determine a more reasonable hybrid brace layout scheme.