Research On Seismic Performance Of Large-Space Public Reinforced Concrete Frame Structure With Soft Layer

The large-space public reinforced concrete（LRC）frame structure was widely used in the city hall,museum,theater,and other large public buildings with social and historical significance in the 1950s.Due to the long service period,the old structure,and the improvement of functional requirements of such existing large public buildings,more and more attention has been paid to whether this kind of buildings still have the conditions to continue to be used,and whether they meet the current national codes.The space,depth and floor height of LRC frame structure are large.Meanwhile,there are many irregularities in the structure such as sudden change of floor height and partial discontinuity of floor,which make the structure have obvious weak parts.Therefore,the seismic performance of LRC frame structure is different from that of RC frame structure.However,at present,the research on the classification standard of seismic performance and failure state of existing LRC frame structure is insufficient,so the evaluation standard of seismic performance of LRC frame structures needs to be studied urgently.In this paper,an existing LRC frame structure with soft layer is selected as the research object,and the seismic performance of the structure is studied systematically through simulated shaking table test and numerical simulation.The evaluation standard of seismic performance and the failure grade classification are put forward,which provides a reliable basis for seismic performance evaluation and reinforcement of LRC frame structures.The following is the main research content:（1）Through the design and completion of shaking table test,the real response of LRC frame structure under various seismic intensity is obtained,the seismic performance and failure mode of the structure are mastered,and the existence of soft layer in the structure is verified.（2）The influence of soft layer on dynamic response of LRC frame structure is studied.And the influence of the soft layer on the yield mechanism of the structure.（3）The failure grade of LRC frame structure is proposed from the failure state and deformation limit index.The seismic performance of LRC frame structure is evaluated,and the seismic damage of the structure under different intensity earthquake is predicted.The research results are as follows:（1）The vertical irregularity of LRC frame structure is caused by the sudden change of story height,which leads to the soft layer appearing in the structure.The soft layer leads to the stress concentration and damage aggravation of the structure,the acceleration amplification effect of the top of the floor column is reduced,and the displacement response is significant,which greatly reduces the overall seismic performance of the structure.（2）Through the incremental dynamic analysis（IDA）,the law of variation between seismic strength parameter PGA and demand parameterθ_max is obtained.Meanwhile,the probabilistic seismic capacity analysis of LRC frame structure is carried out,and the performance state points of the structure are obtained,such as Immediate Occupancy（IO）and Collapse Prevention（CP）.（3）Based on the results of shaking table test,numerical simulation and IDA analysis,the failure grade of LRC frame structure was divided into five grades:basically intact,slight damage,moderate damage,severe damage and collapse,which included the macro description of damage state,quantifiable limit of story drift ratio and repair degree.（4）The probability of the structure exceeding the limit state under the basic fortification intensity is obtained.Meanwhile,the Collapse Margin Ratio（CMR）of the structure is calculated,which proves that the collapse resistance of LRC frame structure is weaker than that of RC frame structure.