Experimental And Theoretical Research On Low Cycle Fatigue Performance Of High - Strength Concrete Filled Circular Steel Tubular Columns

In the event of an earthquake, frame columns, especially the bottom frame columns of high-rise structures in seismic region will inevitably experience the course of deformation circulation, and repeat access to the inelastic range, that may undergo low cycle fatigue damage . In recent years, some research on the hysteretic performance of the concrete filled steel tubular frame columns have been carried out and some important research results have been published.However, research on the low cycle fatigue damage performance of concrete filled steel tubular(CFST) columns, especially low cycle fatigue damage rule and damage process under non-equal displacement amplitude mode lacked profound understanding, mechanism of fatigue damage caused by the earthquake and how to prevent the occurrence of low-cycle fatigue damage in seismic design is poorly understood. Therefore, it is particularly important to carry out research on the low cycle fatigue damage performance and seismic design method of CFST columns.The experiments about low cycle fatigue behavior of the high-strength concrete filled circular steel tubular (HCFCST) columns have been carried out through the pseudo-static test in this paper. On the basis nonlinear finite element analysis is carried out on the HCFCST columns. And low cycle fatigue life prediction method for HCFCST columns is studied. It has laid the foundation for establishing the calculation theory of the structure seismic design of the HCFCST columns.The main research in the paper include:1. The experimental research about the low cycle fatigue performance of the HCFCST columnsAccording to different loading regime, three HCFCST columns were designed and tested under low cyclic loading,to study the bearing capacity, the deformation ability, the hysteretic performance and the energy dissipation capacity. The test results show that hysteresis curve of load-displacement has good stability and fullness. Therefore, the HCFCST columns have good deformation ability, ductility and energy dissipation, and showed good seismic performance.Based on the experiment resuls, the nonlinear finite element analysis of the HCFCST columns is simulated by commercial software ABAQUS. The simulated skeleton curves was achieved and compared with the test curve. The results show that the approving results of nonlinear finite element analysis is obtained.2. The low cycle fatigue properties of the HCFCST columnsFirstly, the concept of ultra-low cycle fatigue is issued, that is the cycles numbers of low cycle fatigue damage of the structure or component less or equal to 300 times under seismic action. Then, language of MATLAB is used to write the corresponding rain flow counting method program, and counted the closed hysteresis loop under the random displacement loads. Finally the prediction theoretical formula of the HCFCST columns under low cycle fatigue damage life is studied.The result of this paper can be used as the reference for the concrete filled circular steel tubular in the seismic design.