Study On Axial Compressive Performance Of Reinforced Concrete With PVC/GFRP Pipe Confined Seawater And Sea Sand Concrete Cores

At present,due to the shortage of river sand resources,seawater and sea sand are gradually applied to the project,but the chloride and sulfate in the sea water and sea sand will cause the corrosion of steel bars.Therefore,it is proposed to use PVC pipes and GFRP pipes to isolate the corrosion effect of seawater and sea sand.There are many studies on the axial compression performance of concrete-filled steel tube columns at home and abroad,but there is a lack of research on the mechanical properties of reinforced concrete with PVC/GFRP pipe confined seawater and sea sand concrete cores.This article uses axial compression test of reinforced concrete with PVC/GFRP pipe confined seawater and sea sand concrete cores,analyze the failure phenomenon and force mechanism of the specimen during the loading process,and study the influence of different test parameters on the axial compression performance of the composite structure.The specific work carried out is as follows:(1)The influence of factors such as outer concrete strength,core column concrete strength,inner pipe restraint form,inner pipe restraint area,CFRP cloth wrap layer number,CFRP strip spacing,GFRP pipe diameter-thickness ratio and the presence or absence of sand sticking on the axial compressive properties of the specimen are discussed.Among them,the test pieces are divided into three groups according to the inner pipe restraint form: PVC ordinary pipe,PVC corrugated pipe,GFRP pipe.The test process and the final failure mode of 26 axial compression test pieces are described,At the same time,the axial compression properties such as strength index-longitudinal strain curve,load and strain curve at different positions,peak load,axial bearing capacity,axial compression stiffness and ductility coefficient are compared and analyzed.(2)The research results show that with the increase of the strength of the outer concrete,the bearing capacity of the specimens is significantly improved but the brittleness is increased.With the increase in the strength of the core column concrete,the bearing capacity and axial stiffness of the specimens do not increase significantly.The PVC pipe reduces the bonding performance between the inner pipe and the concrete,and there will be slight slippage during the test loading process,which also affects the ultimate bearing capacity of the laminated column.The GFRP pipe has better bonding and restraint effects than the PVC pipe.Pasting CFRP cloth outside the PVC pipe is a good way to improve the bearing capacity and rigidity.The test piece basically does not show a decrease in bearing capacity before failure.The ductility of the test piece is better.Increasing the number of wrapping layers will also improve the performance of the laminated column.Bearing capacity.Reducing the diameter-tothickness ratio of the GFRP tube not only enhances the axial stiffness of the specimen,but also improves the bearing capacity and ductility.(3)Based on the Mander model,analyzing the mechanism of confined concrete,the composite column concrete is divided into strong confined concrete,weak confined concrete,and unconfined concrete.By calculating the effective lateral stress and strength coefficients in different areas,a semi-theoretical and semi-empirical stressstrain model of the built-in PVC/GFRP pipe seawater sea sand concrete core column laminated column is deduced.At the same time,a more widely applicable bearing capacity calculation formula is proposed based on the force mechanism.(4)The stress-strain model of confined concrete proposed above is applied to ABAQUS finite element,and the results calculated by the software are compared with the test results.The axial compression bearing capacity and stiffness of the specimens are in good agreement with each other.It can well verify the rationality of the stressstrain model of the laminated column derived in this paper.The paper has 59 pictures,15 tables,and 124 references.