| The use of recycled concrete can reduce carbon emissions and save natural aggregate resources,which is important to achieve the double carbon goal.However,the main inorganic hard components of construction waste,waste concrete and waste red bricks,and crushed red bricks are difficult to separate from waste concrete blocks,so this topic uses a mixture of recycled concrete prepared from recycled bricks and recycled concrete aggregates.The compressive strength,ductility and elastic modulus of the recycled concrete are lower than those of ordinary concrete,especially under the condition of high brick aggregate admixture,its water absorption is greater.Therefore,the discrete strength of recycled concrete can be controlled better by filling recycled concrete in steel tube,and the engineering application field of recycled concrete can be expanded.The concrete filled steel tube structure is a steel tube and concrete as a whole jointly stressed,the steel tube is in a two-way stress state,only when the transverse strain coefficient of the core concrete exceeds the Poisson’s ratio of steel,the steel tube can produce a restraining effect on the core concrete.When the diameter to thickness ratio of the steel tube is large,the steel tube will suffer local buckling,which leads to the reduction of the ductility of the member.In addition,the beam-column nodes of concrete filled steel tube structures are complex,which is a difficult problem for engineering applications.Steel tube-confined concrete column is a certain gap between the outer steel tube and the surface of the beam at the node of the beam column,in order to eliminate the longitudinal stress in the steel tube as far as possible.The concrete is filled with steel tubes equipped with longitudinal reinforcement or steel sections,and the longitudinal reinforcement or steel sections and concrete are subjected to axial forces and bending moments,and the steel tubes replace the role of the hoop reinforcement,which is mainly subjected to circumferential forces.Stainless steel tubes are aesthetically pleasing,durable,corrosion resistant,low maintenance,and have better post-strain strengthening ability and deformation performance and better restraint compared to carbon steel.In this paper,a stainless steel tube reinforced recycled concrete mixed structure is proposed.The use of the form of restraint(at 25mm from the upper and lower end plates of the specimen,respectively,the stainless steel tube cut two10mm ring band,so that the stainless steel tube does not directly bear the longitudinal load,only the core of the recycled concrete to play a restraint role),not only to reduce the amount of steel used,but also to reduce the workload of welding,so that the construction of the node connection is more convenient,the restraint effect on the core concrete is more obvious.Outer stainless steel tube does not directly bear the axial load,so it is not easy to yield,more fully utilize the strength of the steel and concrete,better to improve the capacity and ductility.Therefore,in this paper,a total of 36 recycled reinforced concrete stub columns confined by stainless steel tube,stainless steel tube-confined steel-reinforced recycled concrete stub columns and steel tube-reinforced recycled concrete short columns confined by stainless steel tube with circular or square cross-section are investigated in detail respectively.The specific works are as follows.(1)A total of 8 recycled reinforced concrete stub columns confined by stainless steel tube with circular and square cross-sections were studied in axial pressure tests,and 2 recycled concrete with stainless steel tube and 2 recycled concrete with steel reinforcement were set as comparison members;a total of 8 stainless steel tube-confined I-steel-reinforced recycled concrete stub columns with circular and square cross-sections were studied in axial pressure tests,and 2 stainless steel tube-confined double I-steel-reinforced recycled concrete,2 steel-reinforced recycled concrete-filled stainless steel tubular columns and 2 steel-reinforced recycled concrete columns were set as comparison members;8 steel tube-reinforced recycled concrete short columns confined by stainless steel tube were under axial compression,and 2steel tube-reinforced recycled concrete stub columns confined by stainless steel tube were set as the comparison members.The thickness of stainless steel tube(1.4 and 1.9 mm),the amount of recycled brick aggregate(RBA)admixture(0,50%and 100%)and the type of members are the main parameters investigated,and the full process of loading damage is described in detail,and the mechanical properties such as damage morphology,load-strain relationship of stainless steel tube,ultimate bearing capacity,stiffness and ductility are analyzed theoretically.(2)The finite element analysis software ABAQUS was used to analyze the axial compression force performance of short columns of circular or square recycled reinforced concrete stub columns confined by stainless steel tube,stainless steel tube-confined steel-reinforced recycled concrete stub columns,and steel tube-reinforced recycled concrete short columns confined by stainless steel tube,and the actual strength and modulus of elasticity and other coefficients of hybrid recycled concrete were substituted,and the native structure of the existing circular stainless steel tube restrained recycled concrete was corrected,and the finite element results fitted well with the test.(3)Based on the above results,the axial pressure models of the three members were calculated for a total of 702 different parameters,and the calculated results deviated from the results of design equations of the Technical Standards for Steel Tube Confined Concrete Structures,Zheng et al.The influence of diameter(width)to thickness ratio of specimen,yield strength of stainless steel tube,compressive strength of recycled concrete,recycled brick aggregate admixture,yield strength of reinforcement and reinforcement rate of longitudinal reinforcement on the axial compression performance of stainless steel tube restrained reinforced recycled concrete short column was analyzed,and the design methods of axial compression load capacity and stiffness of circular and square recycled reinforced concrete stub columns confined by stainless steel tube were proposed;the diameter(width)to thickness ratio,yield strength of stainless steel tube,compressive strength of recycled concrete were analyzed.The effects of diameter(width)to thickness ratio,yield strength of stainless steel tube,compressive strength of recycled concrete,recycled brick aggregate admixture,yield strength of steel sections and steel content of steel sections on the axial compression performance of stainless steel tube restrained steel recycled concrete short columns were analyzed,and the design methods of axial compression load capacity and stiffness of circular and square stainless steel tube-confined steel-reinforced recycled concrete stub columns were proposed;the effects of diameter(width)to thickness ratio of specimens,yield strength of stainless steel tube,sandwich or core recycled concrete The effects of the diameter(width)to thickness ratio of the specimen,the f_yvalue of the stainless steel tube,the compressive strength and brick aggregate admixture,the f_yvalue of the carbon steel tube and the diameter to thickness ratio,the inner and outer tube diameter ratio on the axial compression performance of the short column of the stainless steel tube restrained carbon steel tube recycled concrete,and the design method of the axial compression bearing capacity and stiffness of the circular and square steel tube-reinforced recycled concrete short columns confined by stainless steel tube are analyzed,which can be used for researchers and engineers. |
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