Study On The Effect Of Stiffness Ratio On The Seismic Performance Of Structure Supported By Foundations With Different Elevations

Frame structure supported by foundations with different elevations is the most widely used form of mountain building structure in practical engineering.Due to the influence of unequal height constraints,its horizontal and vertical stiffness distributions are uneven.In this paper,the stiffness ratio is used as the research variable,and the two stiffness ratio indexes of the layered frame structure that are currently studied-left and right stiffness ratio and layer stiffness ratio are selected to measure the change of the stiffness ratio of the structure.The combination of test and finite element analysis is used methods to explore the relationship between the stiffness ratio and the seismic performance of the frame structure supported by foundations with different elevations.The main work and conclusions completed in this article are as follows:(1)A shaking table test model of a frame structure supported by foundations with different elevations is designed.Based on the prototype of the typical frame structure supported by foundations with different elevations in the shaking table test of the mountain structure in 2018,a stiffness ratio was used as a variable to design a test model of the frame structure supported by foundations with different elevations with a scale ratio of 1/8.The materials of ruler model,similarity relationship,measuring point arrangement,seismic wave selection,test loading system,model making and weight design are introduced in detail.(2)The shaking table test results were analyzed from four aspects: test phenomena,dynamic characteristics,acceleration response and displacement response.The test results show that the structure is most severely damaged at the grounding end of the upper ground layer;under the action of 7-degree and 8-degree earthquakes,the structure is basically in elastic working state,and then with the strengthening of the earthquake,the structure frequency gradually decreases.The damage continues to accumulate and the stiffness gradually degrades;the upper grounding end limits the deformation of the upper grounding layer to a certain extent,so that the deformation increase of the lower ground layer is smaller,and the deformation increase of the upper grounding layers 2 and 3 is more significant;structure The maximum inter-layer displacement angle occurs mostly in the upper ground layer to the upper 3 layers.(3)Compared with the shaking table test results of the typical falling frame structure in 2018,the differences between the two are analyzed in terms of test phenomena,dynamic characteristics,and seismic response.The results show that the damage degree of model N on the ground side of the upper ground layer is relatively light,the damage levels on the ground side and the non-ground side of the upper ground layer are closer,and the distribution of floor displacements on each floor is more uniform,and there is no greater degree of damage.The phenomenon of large sudden displacement angle between layers.To a certain extent,increasing the left-right stiffness ratio and layer stiffness ratio of the frame structure with drop-out structure is beneficial to the improvement of the seismic performance of the structure.(4)Based on the test prototype structure,a set of examples was designed by changing the structural layout.The Perform-3D software was used to analyze the elastoplastic time history of the spatial drop frame structure example,and the left and right stiffness ratio and layer stiffness ratio were compared to the drop frame.The range and degree of influence of the seismic performance of the structure.The results show that compared with the left-right stiffness ratio,the layer stiffness ratio has a more significant effect on the seismic performance of the frame structure,which is mainly reflected in the displacement angle between the upper ground layers,the hysteretic energy dissipation percentage of the structure,and the damage of the upper ground member.However,the left-right stiffness ratio can only roughly reflect the shearing force distribution of the grounding side and non-grounding side column of the upper ground layer.When designing the frame structure of the falling layer,attention should be paid to the layer stiffness ratio.