Study On The Axial Compression Performance Of FRP-confined Hollow Sandwich Circular Steel Tube Concrete Member

Concrete and steel provide a solid material guarantee for China’s urbanization process and large-scale infrastructure construction.However,the traditional concrete and steel,its production process of energy consumption,heavy environmental pollution,seriously restricted the sustainable development of China’s national economy.As one of the main raw materials of concrete,natural river sand is a non-renewable resource.Due to the increasing demand for building sand,it is urgent to seek a new sand source to replace it.Mechanized sand（hereinafter referred to as M sand）refers to the processing of large concrete materials from natural ore and construction waste with different rules and sizes,which can partially or completely replace natural river sand to prepare concrete,so as to achieve the purpose of environmental protection and sustainable development.Generally speaking,the mechanical sand concrete prepared by using M sand instead of natural river sand has higher strength but lower ductility,which is more prone to brittle failure.In order to make full use of the advantages of M sand,accelerate its application in practical engineering,therefore,this paper adopts steel tube to effectively restrict the deformation of internal core M sand concrete development,provide effective constraints,make the concrete in a three-way constraint state,to improve the ductility of M sand concrete,so as to improve the strength,stiffness and ductility of components.Considering the hollow sandwich concrete filled steel tube composite structure with high bearing capacity,lateral stiffness,good ductility,small component weight advantage,and GFRP has lightweight,high strength,corrosion resistance,and to prevent steel tube and concrete empty,so this paper adopts GFRP constraint hollow sandwich round steel tube M sand concrete,this structure form in the steel tube and concrete advantages and make up for each other’s defects,and can greatly improve the structure system corrosion resistance,showing high bearing,high ductility and high durability of excellent working performance.In order to explore the axial compression performance of hollow sandwich round steel tube with GFRP constraint,45 hollow sandwich circular steel tube were designed for the shaft compression test of the wet accumulation density,load strain curve,the test failure mode and the ultimate bearing capacity of the test data results.The test results show that（1）the high wet accumulation density value can improve the strength and bearing capacity of the specimen;（2）the increase of GFRP layers can significantly improve the bearing capacity and deformation resistance of the specimen;（3）the smaller the hollow section ratio,the greater the bearing capacity of the specimen,the better the ductility.Compared with the current domestic and foreign standard calculation limit carrying capacity formula and the actual test results found that the prediction of the specification is too conservative,so on the basis of the parameters of equivalent stress,hollow section ratioand wet accumulation density,the accuracy and feasibility of the derivation formula are proved by comparing the actual test results.