Study On Static And Seismic Performance Of Concrete Filled Steel Tubular Pier In Corrosive And Freeze Thaw Environment

Concrete filled steel tubular(CFST)pier serving in corrosive and freeze thaw environment will inevitably deteriorate their mechanical properties due to the adverse factors of corrosion and freeze-thaw,which will affect the safety of components and even the whole structure.In view of this,the static and seismic performance of the CFST pier in sulfate corrosive and freeze thaw environment are systematically studied in this paper,the main work is as follows:(1)Experimental study on damage mechanical properties of low carbon steel in sulfate corrosion environmentTaking corrosion rate and steel wall thickness as test parameters,the fracture mode,micro and macro morphology of corrosion surface and tensile fracture of low carbon steel after corrosion were obtained firstly.Then the curve relationships of stress-strain of low carbon steel after corrosion were analyzed.Finally,based on the measured data,the change rules between steel mechanical properties and corrosion rate were explored.And the simplified calculation formulas were obtained by regression.(2)Experimental study on axial compression static performance of the CFST pier in corrosion and freeze thaw environmentTaking the steel content,freeze-thaw cycles,corrosion rate and alternation times as test parameters,the mechanical characteristics and failure modes of the specimens were obtained firstly.Then the axial load-axial displacement curves of the specimens were measured.Finally,the influence of the different test parameters on the mechanical properties of the specimens,such as axial compressive strength,axial compressive stiffness,ductility,transverse deformation coefficient of the steel tube and restraint effect were obtained.The results show that the influence of corrosion on the mechanical properties of the specimens is greater than that of freeze-thaw cycles,and both corrosion and freeze-thaw will weaken the interaction between steel tube and concrete.(3)Calculation of axial bearing capacity of the CFST pier in corrosive and freeze thaw environmentBased on ABAQUS 6.13 software,firstly,the static performance analysis model of the CFST considering the influence of corrosion and freeze-thaw cycle was established.Secondly,the working mechanism of the CFST under axial compression load was revealed,including the whole process curve relationship of axial load-axial displacement,and the longitudinal stress distribution of the concrete and steel tube.Finally,the influence of section size,material strength,alternation times,steel ratio and other parameters on the reduction coefficient of axial compressive strength was given.On this basis,the calculation of the axial compressive strength bearing capacity of the CFST pier in corrosive and freeze thaw environment was proposed.(4)Research on the ductility of the CFST pier in corrosive and freeze thaw environmentBased on ABAQUS 6.13 software,a nonlinear model of the hysteretic behavior of the CFST pier under low cyclic cyclic loading was established,which could take into account the effects of the corrosion and freeze-thaw cycles.Then,on the basis of ensuring the rationality of the model,the influences of axial compression ratio,material strength,alternation times,steel ratio and other parameters on the hysteretic curve and skeleton curve of horizontal load lateral displacement and the reduction coefficient of horizontal bearing capacity were given.Finally,the calculation of the horizontal bearing capacity of the CFST pier under axial compression in corrosion and freeze thaw environment was proposed.(5)Research on seismic performance of the CFST bridge under corrosion and freeze-thaw environmentBased on ABAQUS 6.13 software,the dynamic calculation model of the whole structure of an urban expressway bridge was established,and the dynamic response of the whole bridge was analyzed.Then,the natural period,top horizontal displacement and top acceleration of CFST piers of the whole bridge structure under earthquakes and the influence of different environmental factors were given.