Study On Seismic Behavior Of Recycled Concrete Columns With Circular Steel Tubes

With the acceleration of urbanization in China,the number of residential,commercial and other buildings has increased significantly.Therefore,a large amount of concrete is needed.The increase of concrete consumption requires a large amount of natural sand and stones.The demolition of old buildings and natural disasters and other reasons will produce a large number of construction waste,resulting in environmental pollution.Therefore,it is of great significance to make recycled concrete from waste concrete as recycled coarse aggregate for the recycling and utilization of waste concrete.However,the mechanical properties and durability of recycled concrete are poor compared with that of ordinary concrete,and the recycled concrete structure formed by pouring recycled concrete into steel pipe can make up for the deficiency of recycled concrete,so that the application of recycled concrete is popularized.In this paper,the finite element model of circular steel tubular recycled concrete column was established by ABAQUS finite element software.The simulation results were compared with the experimental results to verify the feasibility of the model.On this basis,the seismic behavior of recycled concrete columns with circular steel tubes under low cyclic loading was studied by taking the replacement ratio of recycled coarse aggregate,steel strength,steel pipe wall thickness,recycled concrete strength and axial compression ratio as the variation parameters.The results show that:(1)the replacement rate of recycled coarse aggregate has little influence on the seismic performance of recycled concrete column.The maximum horizontal bearing capacity and ductility coefficient of circular steel tube ordinary concrete column are less than 8%and 4%respectively.Under different coarse aggregate substitution rates,hysteretic curves of recycled concrete columns with circular steel tubes are similar in shape and stiffness degradation curves basically coincide.(2)steel strength has a great impact on the maximum horizontal bearing capacity of recycled concrete columns with circular steel tubes.The maximum horizontal bearing capacity of components with steel strength of Q345 is increased by 14%compared with those with steel strength of Q235,and the maximum horizontal bearing capacity of components with steel strength of Q420 is increased by 20%compared with those with steel strength of Q345.With the increase of steel strength,the area of hysteretic curve increases,energy consumption increases and ductility coefficient increases slightly.(3)with the increase of steel pipe wall thickness,hysteretic loop curve of recycled concrete column of circular steel pipe becomes more and more full,energy consumption increases and ductility coefficient slightly increases.The maximum horizontal carrying capacity of the members with the steel pipe wall thickness of 4.5mm is 10%higher than that of the members with the steel pipe wall thickness of 4mm,and the maximum horizontal carrying capacity of the members with the steel pipe wall thickness of 5mm is 22%higher than that of the members with the steel pipe wall thickness of 4.5mm.(4)the strength of recycled concrete has a small impact on the seismic performance of recycled concrete column of circular steel tube.The strength of recycled concrete increases,the maximum horizontal bearing capacity and energy consumption of recycled concrete column of circular steel tube increase slightly,ductility decreases slightly,and stiffness degradation curves basically coincide.(5)the axial compression ratio on the round steel tube had a greater influence on the seismic performance of recycled concrete column,with larger axial compression ratio,the round steel tube hysteresis curve area of recycled concrete column is reduced,the ductility coefficient reduced by 6%-16%,the maximum horizontal bearing capacity is greatly reduced,axial compression ratio 0.4 of the component is larger than that of axial compression ratio 0.2 components are 8%lower than the maximum horizontal bearing capacity,axial compression ratio 0.6 artifacts than the maximum level component bearing capacity of axial compression ratio of 0.4 20%lower.Based on the analysis of seismic performance of recycled concrete column with circular steel tube,a simplified skeleton curve model and unloading stiffness law of recycled concrete column with circular steel tube are proposed,and a restoring force model of recycled concrete column with circular steel tube is established,which provides a reference for elastic-plastic analysis of recycled concrete column with circular steel tube under the action of earthquake.