Research On Stress Mechanism And Design Method Of Post-wrapped Steel Tube Retrofitted RC Columns Under Eccentric Compression

Post-wrapped steel tube retrofitted reinforced concrete(PSTRRC)column is a new type reinforcement method.It has the advantages of not increasing the cross-section area,greatly improving the bearing capacity of columns,improving the interface contact between old and new concrete and steel tubes,improving the viscous of structural surfaces,increasing service life and convenient construction.It has broad application prospects in building reinforcement engineering.However,at present,the research on steel tube reinforced concrete is still blank.In practical engineering,most of the columns are eccentrically loaded members.It is necessary to study the mechanical properties and design methods of eccentrically loaded PSTRRC columns.In this paper,the mechanical properties and design methods of eccentrically loaded PSTRRC short and medium-long columns are studied by experiment and finite element method.The specific work is as follows:(1)10 eccentric compression tests of PSTRRC short columns were carried out.Taking the eccentricity of short and long side and the influence coefficient of concrete area as experimental parameters.The variation of the ultimate bearing capacity,failure mode,load-axial displacement curve and surface strain of steel tube under different parameters are revealed.The ultimate bearing capacity,ductility and reinforcing effect of short columns are quantitatively analyzed by introducing bearing capacity increasing coefficient,displacement ductility coefficient and strength increasing coefficient.(2)Through ABAQUS software,the numerical model of PSTRRC short columns under eccentric compression is established.The material non-linear constitutive relation,initial stress of weld and complex contact problems of steel tube reinforced concrete are considered.The effects of steel yield strength,steel bar strength,grouting material strength,concrete strength,height-width ratio,width-thickness ratio,longitudinal reinforcement ratio and volume stirrup ratio on the mechanical properties of PSTRRC short columns under eccentric compression are revealed.The development of material stress and contact stress of steel tube,steel bar,grouting material and concrete in the whole process of short column loading is analyzed.(3)12 eccentric compression tests of PSTRRC medium-long columns were carried out.Taking the eccentricity of short and long side,the influence coefficient of concrete area and slenderness ratio as experimental parameters.The variation of the ultimatebearing capacity,failure mode,load-axial displacement curve and surface strain of steel tube under different parameters are revealed.The ultimate bearing capacity,ductility and reinforcing effect of medium-long columns are quantitatively analyzed by introducing bearing capacity increasing coefficient,displacement ductility coefficient and strength increasing coefficient.(4)Through ABAQUS software,the numerical model of eccentrically loaded PSTRRC medium-long columns is established.The material non-linear constitutive relation,initial stress of weld and complex contact problems of steel tube reinforced concrete are considered.The effects of steel yield strength,steel bar strength,grouting material strength,concrete strength,height-width ratio,width-thickness ratio,longitudinal reinforcement ratio,volume stirrup ratio and slenderness ratio on the mechanical properties of PSTRRC medium-long columns under eccentric compression are revealed.The development of material stress and contact stress of steel tube,steel bar,grouting material and concrete in the whole process of medium-long column loading is analyzed.(5)Based on the superposition principle,the calculation method of PSTRRC columns under eccentric compression is studied combined with relevant codes,relevant research results of some scholars,experimental research and finite element analysis results in this paper.The regression fitting of the test results and numerical analysis of eccentrically loaded PSTRRC short and medium-long columns is carried out respectively.The calculation formulas of the eccentric compression bearing capacity of PSTRRC short and medium-long columns are proposed.