| The "strong column weak beam" failure mechanism,which means that the frame beam produces plastic hinges before the frame column under earthquake action,is one of the important concepts in seismic design of RC frame structures.The mechanism of "strong columns and weak beams" makes RC frame structures exhibit good ductility and energy dissipation capacity on the whole.In China’s seismic design code,it is recommended to take corresponding measures to ensure the failure mechanism of "strong columns and weak beams" in RC frame structures.However,previous earthquake damage investigations have shown that many RC frame structures designed in accordance with current codes have unsatisfactory failure mechanisms,namely,column hinge mechanisms,which means that frame columns produce plastic hinges earlier than frame beams,resulting in structural collapse.Infilled walls are essential non structural components in RC frame structures,and their stiffness and constraint effects significantly affect the seismic response of the main structure.However,in the process of structural design,the i MPact of infilled walls on the structural bearing capacity is negligible,and the interaction between infilled walls and frame structures has an i MPact on the realization of the "strong column weak beam" failure mechanism.This paper studies the role of infilled walls in the failure mechanism of "strong columns and weak beams" in RC frame structures.Considering three different infilled wall arrangements,four floors,and five different column end moment amplification factors,60 RC frame structures are designed.Through static elastoplastic analysis and dynamic time history analysis,seismic performance such as interlayer displacement angle,floor absolute acceleration,failure mode,vulnerability,and economic loss are studied.The main research contents are as follows:(1)On the Open Sees platform,a finite element model of infilled wall RC frame structure is established and verified through experiments.According to Chinese codes,design a three story,six story,nine story,and twelve story RC frame structure,maintain a constant reinforcement of the beam section,and change the reinforcement of the column section to make the column end moment amplification coefficients of the structure equal to 1.2,1.4,1.6,1.8,and 2.0,respectively,to obtain 20 RC frame structures.Considering three types of infilled wall layout schemes: empty frame,full infilled wall frame,and bottom weak infilled wall frame,60 finite element models of RC frame structures were established,and the natural vibration periods of different structures were studied.Through static elastoplastic analysis,the effects of factors such as column end moment amplification factor,and infilled wall on the seismic performance of RC frame structures were studied.(2)44 far field non pulse ground motions and 44 near field pulse ground motions were selected and amplitude modulated in the order of frequent,fortified,rare,extremely rare,and peak acceleration of 0.6g.Secondly,nonlinear dynamic time history analysis was performed on 60 RC frame structures.The effects of column end moment amplification factor and infilled wall arrangement on the structural response of RC frame structures under two different types of ground motions are studied.The results show that co MPared to empty frames,the maximum inter story displacement angle of fully filled wall frames decreases significantly,while the maximum inter story displacement angle of weakly filled wall frames at the bottom increases significantly.Under large seismic intensity,the number of beam hinge failure nodes in three structures,namely,empty frame,fully filled frame,and bottom weak frame,decreases in turn.However,the number of beam hinge failure nodes in empty frame is evenly distributed along the floor,and the number of beam hinge failure nodes in fully filled frame gradually decreases along the floor.The beam hinge failure nodes in bottom weak frame are mainly concentrated in the bottom layer,which is the most dangerous situation.With the increase of the moment amplification factor at the column end,the number of beam hinge failure nodes in empty frame structures decreases the most,followed by fully filled wall structures,and the change in bottom weak frames is minimal.Therefore,filled walls are not conducive to achieving the "strong column weak beam" failure mechanism of the structure.(3)Using the spectral acceleration Sa(T1)as the ground motion intensity index and the maximum interlayer displacement angle as the structural damage index,incremental dynamic analysis was conducted on 60 structures,respectively.The seismic vulnerability curves of each structure under five failure states,namely,slight,moderate,severe,and collapse,were obtained.The effects of infilled wall layout and column end moment amplification factor on the seismic vulnerability curves of RC frame structures were studied.The results show that when the local seismic intensity Sa(g)is relatively large,co MPared to empty frame structures,under the same seismic intensity Sa(g),the collapse probability of fully filled wall structures significantly decreases,while the collapse probability of bottom weak filled wall structures significantly increases.With the increase of the moment amplification factor at the column end,the exceedance probability of each structure under the same ground motion intensity Sa(g)gradually decreases,and the seismic performance of each structure gradually increases.(4)Considering the effect that when the structural damage is greater than a certain degree,it cannot be repaired,a discrete evaluation method is used to study the direct economic losses of RC frame structures under earthquake action,combined with the vulnerability curves of 60 structures.According to the ratio of indirect economic losses to direct economic losses,the indirect economic losses of each structure are calculated,and the overall economic loss curve of the structure is finally obtained.The results show that when the ground motion intensity Sa(g)is 0.6g,co MPared to empty frame structures,the economic losses and casualties of fully filled wall structures are significantly reduced,while the economic losses and casualties of bottom weak filled wall frames are significantly increased.With the increase of the moment amplification coefficient at the column end,the economic losses and casualties of each structure under the same ground motion intensity Sa(g)gradually decrease. |
