Axial Compressive Behaviors Of Elliptical Concrete-filled FRP Tube (ECFFT) And Elliptical FRP-concrete-steel Double-skin Tubular Columns (EDSTCs)

In recent years,FRP-concrete-steel double-skin tubular columns have received extensive research attention.This new composite structure consists of an outer FRP tube,an inner steel tube,with the space between filled with concrete.At present,the research was mainly majored in circular cross-section columns and square cross-section columns.It has been proved by researches that the circular cross-section can be used as an optimized cross-section of square section specimens to effectively improve the stress concentration phenomenon,but the optimized cross-section form of rectangular cross-section has not been studied yet.Therefore,the text proposes an optimized cross-section of an elliptical FRP-concrete-steel double-skin tubular column as a rectangular cross-section composite column,and this article has designed the axial compression experiment in order to gain a deep understanding of this new type of hybrid column Structural behavior and propose a simple design-oriented stressstrain model to meet the engineering requirements.The specific work is as follows:(1)A total of 56 axial compression test specimens were produced,including 32 ECFFT colunms,16 EDSTCs columns,and 8 elliptical hollow columns.(2)This article has analyzed the failure mode of each sample,and has analyzed the effect of the ratio of the long and short axis of the elliptical cross section,the type of FRP,the thickness of the FRP,and the hollow ratio on the ductility,and the ultimate stress and ultimate strain of the confined concrete.The results has shown that,the curvature of the elliptic section has a great influence on the performance of the FRP material.For the ECFFT with an ordinary fiber cloth(such as GFRP/CFRP),with the cross section ratio,the smaller the limit state of the test piece is.For large constrained concrete columns constrained by large strain fiber cloths,the ultimate stress of specimens is similar to that of larger strain ratios,but the ultimate strain is larger.The effect of hollow rate on ultimate stress of confined concrete for elliptical FRP-concrete-steel double-walled hollow tubular columns Smaller,but in the scope of this study hollow rate,the greater the hollow rate,the greater the ultimate strain of the specimen.(3)Based on the database and theoretical analysis,this article has proposed a new design-oriented model of ECFFT,and proposed a new design-oriented of concrete-filled LRS FRP tube.