Study On Seismic Behavior Of Concrete Filled Steel Tubular Columns With PVC/GFRP Pipe Confined And Sea Water And Sea Sand Concrete Corse

River sand,as a bulk material in the field of civil engineering,has been over exploited in recent years.Sea sand and river sand have similar mechanical properties,but it is difficult to replace river sand due to the existence of chloride.In this paper,the corrosion-resistant PVC /GFRP pipe is used to confine the seawater and sea sand concrete and is placed in the concretefilled steel tubular structure as the core column to prevent the corrosion of chloride on the steel.In recent years,steel pipe,FRP pipe and concrete composite structures emerge in endlessly.This column have good ductility and energy dissipation capacity.This kind of composite structure has various forms,but most of them use FRP pipe with higher circumferential tensile strength,and less use PVC pipe with low price.The current research is mainly on the axial compression performance of composite columns,and there is less research on the seismic performance of composite columns and the influence of different materials on the seismic performance.In view of the above problems,this paper carries out the quasi-static analysis of nine new composite structures under low cycle reciprocating load The main research contents are as follows:（1）In this paper,nine concrete-filled steel tubular（CFST）columns with PVC / GFRP pipes embedded in seawater and sea sand concrete were tested under cyclic loading.The main parameters included the shape and size of the outer steel tube,the material and size of the inner steel tube,and the presence or absence of CFRP wrapping.Through the final test results,the failure process and morphology,hysteretic curve,skeleton curve,bearing capacity and stiffness degradation curve,curvature moment relationship curve,ductility and energy dissipation capacity of each specimen are compared and analyzed.（2）Through comparative analysis,the hysteretic curves of the composite structures in this paper are full,and the failure modes are compression bending failure,which has good seismic performance.The material and form of the inner tube have little influence on the peak bearing capacity of the specimen.Increasing the thickness of the sandwich concrete within a certain range can slightly improve the peak bearing capacity of the member.The ductility of the circular steel tube is better than that of the square steel tube.The built-in GFRP tube can significantly improve the ductility of the component compared with the PVC tube.The effect of wrapping the plastic hinge area of the PVC tube with CFRP cloth on the ductility and peak bearing capacity of the structure is not obvious.The results show that the energy consumption performance of different inner pipes is similar,and PVC double arm corrugated pipe is the most prominent.（3）In this paper,the axial compression capacity,pure flexural capacity,flexural capacity and flexural shear capacity of square and circular composite structures are calculated according to relevant codes and literatures of concrete-filled steel tube and FRP confined concrete,and the differences of calculation formulas and results among three codes are compared.By comparing the experimental results,it is found that the theoretical calculated value is close to the experimental value,which is generally more conservative and more safe.（4）In this paper,finite element software ABAQUS was used to model different specimens and apply uniform horizontal displacements to draw the skeleton curve and stress cloud map.Compared with the peak bearing capacity,the stiffness of the simulation results is larger than the test value,but they are generally close.The stress nephogram can also reflect the ultimate failure form of the specimen,which has a certain reference significance.The paper consists of 70 figures,19 tables and 106 references.