Research On Seismic Behavior Of Full-scale Reinforced Concrete Column With Variable Axial Force

Earthquakes are one of the biggest natural disasters at this stage,and the damage to the frame structure is very serious.Previous studies on frame structures under earthquake action mainly focused on only horizontal earthquake.Some actual earthquake damage analysis shows that the change of axial force caused by vertical earthquake has a great influence on the performance of frame structural members.In this paper,the seismic performance of reinforced concrete columns when the axial force changes especially when the axial force changes are caused by vertical earthquake action is researched.The main work completed in this article is as follows:First,a 7-story 3-span RC frame is designed as a prototype according to the current specifications,and the bottom center column with the largest axial force change during bidirectional seismic action is taken as the research object.Three full-length RC columns are made,and related materials are tested for their properties.The basic composition and working principle of Multiple Usage Structural Tester of Hunan University(HNU-MUST)are introduced and its feasibility is cited.Secondly,a regular pseudo-static test and a irregular pseudo-static test with variable axial forces are performed on two full-scale RC columns.The fixed-axis force pseudo-static test considers the case of ignoring the change of the axial force during the horizontal earthquake.The value of the axial force is the response value of the axial force of the bottom column under the gravity load of the frame mentioned above,and the lateral cyclic displacement is graded at horizontal.The pseudo-static test for irregular variable-axis force considers the case of bidirectional seismic action.Axial force and lateral displacement are relative to the results of the two-direction seismic time-history analysis of the frame mentioned above under the action of EL centro waves.The test results show that when the axial force is fixed,the peak lateral force of the test column,the loading and unloading stiffness,the hysteresis curve and the damage of the specimen are relatively symmetric,and the curve shows a certain pinch effect.When the variable axial force is irregularly loaded,the hysteresis curve of the specimen is obviously biased to one side,and the failure state of the specimen is also biased to one side.And the overall energy consumption is stronger than that of the fixed axial force.The ultimate failure form of the two specimens is bending failure.After that,a brief explanation to the pseudo-dynamic test software PSDMSB edited by ourselves is introducted.Based on this program,the aforementioned planar frame is simplified and a two-direction seismic frame substructure pseudo-dynamic test is carried out with 2 waves and 5 working conditions,and the results are compared with the pseudo-static test completed previously.The results show that the peak value of the lateral force of the test substructure(column)under the bidirectional earthquake is close to the previous two columns,but the hysteresis curve of the column is fuller,the energy consumption is stronger,and the ductility is relatively better.The final failure mode of the column is also bending failure.Finally,the numerical simulation of the quasi-static test column based on the ABAQUS solid element and the Open Sees fiber element are carried out.Also,the numerical simulation of the pseudo-dynamic test column based on Open Sees fiber element is carried out.Then,the applicability of the two elements is discussed.The comparison results show that the two situations have different advantages and disadvantages in simulating the pseudo-static test column,but overall the numerical simulation based on the Open Sees fiber flexibility element is better.When simulating the pseudo-dynamic test column,the Open Sees fiber flexibility element can generally fit the test results well.