Research On Mechanical Properties Of Recycled Concrete Filled Steel Tubular Short Columns Under Axial Compression At Normal And High Temperatures

With the rapid economic development of our country,the number of buildings being demolished and rebuilt has also increased,resulting in a large amount of construction waste.In order to make rational use of construction waste,the construction waste is formulated into recycled concrete and applied to the project,which not only solves the troubles caused by construction waste to people’s lives,but also saves the consumption of construction materials.Recycled concrete still has shortcomings such as high brittleness and low durability.In order to improve the shortcomings,recycled concrete is poured into steel pipes to form steel pipe recycled concrete structures.In this paper,ABAQUS finite element analysis software is used to establish the model of steel tube recycled concrete axial compression short column at room temperature and high temperature.The simulation results are compared with the test results to verify the feasibility of the model.A total of 43 specimen models at room temperature and 30 specimens under high temperature are established.Specimen model to analyze the mechanical properties of steel tube recycled concrete short columns under normal temperature and high temperature under axial compression.In order to further analyze the mechanical properties of the short column of recycled concrete with square steel tube under axial compression,the equivalent section theory is used to establish the mechanical model of the short column of recycled concrete with circular steel tube under axial compression to verify the rationality of the mechanical model of the short column of recycled concrete with circular steel tube.The influence law of section form on ultimate bearing capacity of steel tube recycled concrete column.The results of the study show that the stress process of the axially compressed steel tube recycled concrete short column at room temperature and high temperature consists of an elastic phase,an elastoplastic phase,a descending phase and a gentle phase.There is no obvious deformation in the horizontal and vertical directions of the components in the elastic stage;there is no obvious deformation in the horizontal direction of the components in the elastic-plastic stage,and the vertical direction is slightly flattened;the middle part of the descending stage is obviously protruding,and the whole is compressed in the vertical direction.Flat;in the smooth stage,the ability of the component to resist the horizontal and vertical deformation is weakened,and the component is destroyed.Under the action of axial compression at room temperature,the peak load decreases with the increase of the replacement rate,and increases with the increase of the steel pipe thickness,steel strength and the strength of recycled concrete;the initial stiffness of the axial compression decreases with the increase of the replacement rate and steel strength.It increases with the increase of steel pipe thickness and recycled concrete strength;displacement ductility coefficient decreases with the increase of recycled aggregate replacement rate and recycled concrete strength,and increases with the increase of steel pipe thickness and steel strength.Different section forms have little effect on the ultimate bearing capacity of the member.The calculation formula of the concrete-filled steel tube column was corrected by using the calculation formula of the specimen bearing capacity proposed in the "Code for Design of Concrete Filled Steel Tube Structures",and the calculation formula of the bearing capacity of the recycled concrete filled steel tubular column was obtained to verify the correctness of the revised calculation formula.Under the action of high temperature axial compression,the bearing capacity coefficient decreases with the increase of recycled aggregate replacement rate,steel pipe thickness and steel strength,and increases with the increase of recycled concrete strength;the initial stiffness of axial compression increases with the replacement rate and the strength of steel decreases with the increase,and increases with the increase of the thickness of steel pipe and the strength of recycled concrete.On the basis of the calculation formula of steel tube recycled concrete axial compression short column under normal temperature,the calculation formula of steel tube recycled concrete axial compression short column under high temperature is corrected by using the fire time as a parameter,which provides a reference for future engineering applications.