Study On Axial Compression Behavior Of FRP-high Performance Concrete-steel Double Skin Tubular Stub Column

Ultra High Performance Concrete(UHPC)is a high-performance concrete with a number of advantages,such as high strength and high toughness and good durability,and has large potential application in long-span bridge engineering,ocean engineering and super high-rise structures.Engineered cementitious composite(ECC)is another high-performance cementious composite material,with similar strength to normal strength concrete(NSC)but salient tensile features such as high toughness and ultimate strain(above 4%),making it well-suited for application with tensile zone of structure to substantially enchance its deformation and energy dissipation capacity.FRP-concrete-steel composite structure(DSTC)is a new hybrid composite structure with low weight,high load-carrying capacity,good ductility and corrosion resistance.In this study,UHPC or ECC was used in DSTC column in the purpose to further enhance its load-capacity(with UHPC),ductility and deformability(with ECC),and crack-resistance(with ECC).Nevertheless,a review of existing documents reveals that most of the existing studies were conducted on DSTCs using NSC,whereas very few studies have been carried out on the DSTCs using UHPC or ECC.To explore the behavior of DSTC using UHPC/ECC,a total of 24 large-scale specimens,were designed and tested;based on the test results,the effects of concrete types(i.e.using UHPC or ECC),the thicknesses of GFRP tube and steel tube were investigated and compared with the axial compressive behavior of concrete-filled FRP tubular(CFFT)columns and steel tube confined with concrete layer.Furthermore,based on the existing theory of confined concrete,analyical analyses have also been conducted on the axial behavior(load capacity and intital stiffness)of the DSTCs using the said high-performance concretes.The results in the research can lead to the following conclusions.(1)Among the DSTCs using different concrete(NSC,UHPC and ECC),those using UHPC(GFRP-UHPC-steel double skin tubular column)attain the highest load-capacities compared to their counterparts using NSC or ECC,whereas the ductility of the former is the lowest among the three DSTCs;those using ECC attain the best performance in terms of deformaction capacity,ductility and energy dissipation capacity.(2)Increasing GFRP tube thickness is beneficial to the increase of the peak load and peak strain at peak load,as well as the deformation capacity;while increasing steel tube thickness has an obvious positive effect on the load-capacity and energy dissipation capacity.(3)With a consideration of the effect of void ratio,modifications have been proposed to to existing stress-strain models for FRP-confined NSC/ECC/UHPC,and the modified models have been applied to predict the test results of DSTCs under axial compression;it was shown that the modified models can provide a satisfactory predictions on the peak load for DSTCs using NSC/ECC/UHPC,and provide satisfactory predictions on axial strain at the peak load for DSTCs using NSC/ECC.