Study On Seismic Performance Of Recycled Concrete Filled Steel Tubular Columns After Fire

With the development of the times,the amount of construction waste is increasing day by day,recycled concrete as a new type of environmental protection material is widely used in various types of buildings.The recycled concrete-filled square steel tube columns give full play to the advantages of steel tube and recycled concrete.Because of its simple nodes,convenient construction and short construction period,they are widely used in high-rise structures.As the number of high-rise buildings is increasing,the fire risk is also increasing.Especially in the earthquake area,in addition to building fires and post earthquake secondary fires,there will also be a series of aftershocks after the main earthquake.Therefore,the research on the seismic performance of recycled concrete filled square steel tube after fire is particularly important.Firstly,this paper introduces the background of the project,analyzes and summarizes the progress and current situation of related research.Secondly,the thermal and mechanical properties of steel and concrete are introduced in detail,the appropriate thermal and mechanical parameters are selected,and the stress-strain relationship of recycled concrete at high temperature is studied and improved,which lays the foundation for the follow-up research.Then,in the finite element analysis software ABAQUS,the direct coupling method is used to analyze the thermal stress coupling field,and the model of recycled concrete-filled steel tube column after fire is established for theoretical analysis.In the analysis of its seismic performance,the replacement ratio of recycled aggregate,steel content ratio,axial compression ratio and slenderness ratio are taken as parameters to analyze the impact of these parameters on the seismic performance of recycled concrete filled steel tubular columns after fire,and the following conclusions are obtained:The bearing capacity of recycled concrete-filled square steel tube columns after fire is lower than that of those without fire;the failure mode of specimens with low axial compression ratio and low slenderness ratio is similar to that of ordinary concrete-filled square steel tube columns,with bulging failure at the bottom of the square steel tube,crushed bottom of the recycled concrete,and full hysteretic curve of the specimens.For the specimens with large slenderness ratio,the hysteretic curve of the specimens is not full,and the bottom of the square steel tube buckles,which is prone to instability.The bearing capacity drops sharply,and the rigidity degenerates rapidly.Therefore,the slenderness ratio within a reasonable range is the key to maintain the plasticity and collapse resistance of the members.The bearing capacity,ductility,rigidity and energy consumption capacity of the recycled concrete-filled steel tube columns after fire disaster will follow With the increase of steel ratio in the section,the seismic capacity of recycled concrete-filled square steel tube columns after fire is not affected by the replacement rate of concrete;for the axial compression ratio,the horizontal bearing capacity will increase slightly under the large axial compression ratio,butbefore the recycled concrete-filled square steel tube columns bear the horizontal load,there is a large pre compression strain due to the existence of high axial force,and the pre compression strain makes the columns At the same time,because of the material damage after the fire,the ductility of the section becomes worse,the stiffness of the section degenerates,and the energy consumption decreases.Therefore,in order to achieve the optimal seismic performance of components,the axial compression ratio should be kept in a certain range.