Experimental Research On Cyclic Behavior Of Concrete-filled Square Steel Tubular Columns With Sustained Axial Load After Exposure To Fire

With the wide application of concrete-filled steel tube in civil engineering field, its performance is also been studied constantly in depth. Whether it is at room temperature, under fire, or after fire, studies put emphasis upon concrete-filled circular steel tubes; while researches on concrete-filled square steel tubes are not a lot. In fact, due to its advantages of simple nodes, simple fabrication, short construction period, etc, concrete-filled square steel tubes will be more widely used in high-rise buildings, however its fire risk becomes bigger and bigger. Therefore, it is imperative to make systematic researches on post-fire behaviors of concrete-filled square steel tubes. Under the premise of the whole process of fire test of concrete-filled square steel tubular columns using high-temperature test furnace, experimental researches on post-fire hysteretic behavior of concrete-filled square steel tubular columns had been carried out in this thesis; at the same time, corresponding theoretical researches had also been carried out using the finite element software ABAQUS. Experimental researches and corresponding theoretical researches will provide references for repairing and strengthening on concrete-filled square steel tubular columns. The main works carried out in this thesis are summarized as follows:(1) Experimental researches on the whole process of fire test of two concrete-filled square steel tubular columns had been carried out under sustained axial load using high-temperature test furnace. Axial deformations were measured to discover the axial deformation versus time history of concrete-filled square steel tubular columns. At the same time, the mechanical properties of column’s compressive stiffness after fire, residual deformation, etc, affected by heating time, had also been studied.(2) The experiment measured the time-temperature curve of each measuring point on section of concrete-filled square steel tubular columns by embedding thermocouples. A temperature field analysis model was developed using finite element software ABAQUS to simulate the temperature distributions of concrete-filled square steel tubular columns and the analysis result agreed with the experimental result well, which provided the basis for theoretical analysis of the hysteretic behavior.(3) The hysteretic behavior of three concrete-filled square steel tubular columns including one under room temperature and two after the whole process of fire test, were experimentally studied under sustained axial load. Effects of the heating time on bearing capacity, flexural stiffness, ductility and dissipated energy of the columns were analyzed, which will provide references for the evaluation of seismic performance, the repairing and strengthening method on concrete-filled square steel tubular columns.(4) The numerical analysis model using the finite element software ABAQUS was developed to analyze post-fire hysteretic behavior of concrete-filled square steel tubular columns and the analysis result agreed with the experimental result.