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

In the event of an earthquake, building structures will inevitably experience the reciprocating course of deformation circulation, which will lead irrecoverable plastic deformation in plastic hinge regions of structural members, and cause different degrees of damage and destruction. When the earthquake intensity is well beyond the seismic design level, Structure collapse is under control of the first criterion. In fact, building structures will undergo a cyclical process from small local damage on its members to the overall collapse. Building structures usually undergo reciprocating cycle for several times even a dozen times before collapse, which is called cumulative damage. In recent years, concrete filled steel tubular frame column has been widely used in high-rise buildings, and many scholars also make deep researches on its seismic performance and find its better seismic performance and good ductility. However, researches on the low cycle fatigue damage performance of concrete filled steel tubular columns, especially low cycle fatigue damage process and damage rule are lack of profound understanding under seismic actions, and how to prevent the occurrence of low-cycle fatigue damage in seismic design is barely researched. Therefore, assessing the cumulative damage degree of building structure and its critical components and determining whether it can be used continually after the earthquake have important practical significance.The experiment and theoretical research about low cycle fatigue behavior of 7 high-strength concrete filled square steel tubular(HCFSST) columns have been carried out through the pseudo-static test under different loading regimes in this paper. The low cycle fatigue damage process and the cumulative damage degree of HCFSST columns are analyzed based on the test results, and the low cycle fatigue life prediction formula is established, which can provide a reference for the seismic design of the HCFSST structure.The main researches in the paper include:1.The experimental research about the low cycle fatigue performance of the HCFSST columnsAccording to different loading regimes, low cycle fatigue tests of seven HCFSST columns are carried out,and the bearing capacity, hysteretic performance and energy dissipation capacity of HCFSST columns are analyzed based on the experimental data. The test results show that hysteresis curves of HCFSST columns have good fullness under different loading regimes,which indicates that HCFSST columns have good deformation ability and energy dissipation, and show good seismic performance.2.The theoretical research about the low cycle fatigue performance of the HCFSST columnsIgnoring the contribution of internal concrete, only considering the effect of square steel tube, the theoretical prediction formula of HCFSST columns under constant amplitude loading is established through the regression of experimental data. Then, language of MATLAB is used to write the corresponding rain flow counting method program, and the closed hysteresis loop under the random displacement loads is counted, and the corresponding amplitude is got. Finally the low cycle fatigue cumulative damage of the HCFSST columns is evaluated through the Miner rule and double parameters of seismic damage model.