Mechanical Properties Of Locally Corroded Square Concrete-filled Steel Tubular Stub Columns Under Axial Compression

Concrete-filled steel tube(CFST)structure combined with the advantages of concrete and steel,steel tube can effectively confine concrete,so that the axial compression capacity is higher than the simple composition of steel tube and concrete.At present,CFST has been widely used in practical projects.However,when steel tubes are exposed to the natural environment for a long time,due to the metallic chemical properties of steel,corrosion is inevitable.Especially when the anti-corrosion layer of the structural components falls off or damages,the steel is exposed to the air,and corrosion is easy to occur,which caused durability problems of CFST.The presence of local corrosion on the surface of CFST will reduce the cross-sectional area of the outer steel tube,weaken the confinement of the outer steel tube,meanwhile change the centroid position of the section,lead to the performance degradation of CFST,and even appear safety problems.In order to simulate the influence of local corrosion on the mechanical properties of CFST members,this paper adopts artificial notch or holes to simulate local corrosion,and conducts experimental research and numerical analysis on the performance of square CFST axial compression stub columns with large-area corrosion or pitting corrosion.The main contents are as follows:(1)Sixteen square CFST axial compression stub columns with large-area corrosion will be tested,including 15 specimens of square CFST axial compression stub columns with large-area corrosion and 1 contrast specimen of ordinary CFST axial compression stub column.The influences of the longitudinal length,transverse length,depth,shape,and relative position of the corrosion zone on the performance of the square CFST axial compression stub columns with large-area corrosion will be studied.Combined with the deformation development process and failure model,the stress mechanism of the component will be analyzed.The experimental results show that the initial stiffness,compressive strengths,and ductility of the specimen are reduced with the increase of the transverse length of the corrosion zone,and with the increase of the longitudinal length or depth of the corrosion zone,the compressive strengths and ductility of the specimen are decreased.(2)Ten square CFST axial compression stub columns with pitting corrosion will be tested,including 9 specimens of square CFST axial compression stub columns with pitting corrosion and 1 contrast specimen of ordinary CFST axial compression stub column.The effects of volume loss rate of steel tube,the ratio of corrosion pit diameter to depth,and arrangement mode of pit on mechanical properties of the square CFST axial compression stub columns with pitting corrosion will be studied.The strain and deformation of the key parts will be monitored during the test,and the failure mode and stress mechanism of the components will be analyzed.The test results show that the compressive strengths decrease obviously with the increase of steel tube volume loss rate.Under the same volume loss rate,the pattern of corrosion pit arrangement affects the compressive strengths of the specimen.(3)The numerical analysis model of CFST with local corrosion will be established by finite element software of ABAQUS,and the calculation results will be compared with the failure mode and axial load-displacement relationship curve of the test to verify the rationality of the finite element model.Based on the finite element models,the influence of the geometrical size,shape,relative position of the corrosion zone on the compressive strengths of the square CFST axial compression stub columns with large-area corrosion will be discussed,and the influences of the volume loss rate of steel tube and the diameterdepth ratio on the compressive strengths of the square CFST axial compression stub columns with pitting corrosion were be analyzed,and the influence of concrete strength,steel ratio,steel strength on the compressive strengths of locally corroded square CFST axial compression stub column will be analyzed.Finally,based on the existing design methods of concrete-filled steel tube,a formula for calculating the compressive strengths of square CFST axial compression stub columns with local corrosion is proposed.