Experimental Research On Seismic Behavior Of Reinforced Concrete Frame Substructure Considering Soil Structure Interaction

All previous major earthquakes have caused a large number of reinforced concrete frame structures to be destroyed even collapsed,which causes a great threat to people's lives and property safety.By investigating the damaged reinforced concrete frame structures in earthquake disaster area,it is found that the columns at the bottom of frame are seriously damaged and both ends of columns appear a large number of plastic hinges,which is inconsistent with the expected yield mechanism of "strong columns and weak beams".There are many factors affecting the yield mechanism of frame structures.One of the important factors is the restraint capability of the isolated footing to the upper frame structure under the soil-structure interaction.In order to research the effect of soil-structure interaction on the seismic performance of concrete frame structures,firstly,a set of simulated foundation device is designed based on Winkler foundation model,then,a two-story and two-span isolated footing-frame substructure specimen on the simulated foundation is experimented by the quasi-static test way,and the seismic performance of the specimen after considering the effect of foundation soil is analyzed.The finite element model for the isolated footing-frame substructure on the simulated foundation was established based on ABAQUS.Linear spring element in the ABAQUS is used to simulate the effect of foundation soil to the isolated footing.The calculated load-displacement curve,structural yield mechanism,structural damage,reinforcement stress are compared with the experimental results to prove accuracy and applicability of the finite element model.And then,the finite element model of frame substructure with the condition of fixed support of bottom column is established by restraining the degree of freedom of base surface of isolated footing.The calculated results are compared with the results of finite element calculation under the condition of simulated foundation.The analysis resu lts show that the bearing capacity of structure decreases,the lateral displacement increases,the restraint of isolated footing to column base decreases and the column base damages after considering the soil-structure interaction mitigate,the damage at the both ends of the three-layer columns is more severe.Based on the former isolated footing-frame substructure finite element model,the finite element parameter analysis is carried out to study the bearing capacity and deformation performance,yield mechanism and failure mode of the structure under the influence of different parameters.The parameters of the analysis are: reinforcement ratio of foundation,foundation coefficient and axial compression ratio.The analysis results show that when the reinforc ement ratio of foundation,the foundation coefficient and the axial compression ratio decrease,the restraint of the isolated footing to the column base decreases,and the damage of the three-story column ends of the structure are more severe.When the reinforcement ratio of foundation is small or the axial compression ratio of the column is large,Bending reinforcement bar in foundation will yield when the structure damage.The yielding mechanism of the structure is changed.