Compressive Behavior Of CFRP-steel Confined Concrete-encased Stub Column With High-strength Concrete

In recent years,fiber reinforced polymer(FRP)composites have been found increasingly wide applications in civil engineering,both in the retrofit of existing structures and in new construction.Compared with the traditional structural materials,FRP composites have some apparent advantages,including their high strength-to-weight ratio and good corrosion resistance.In steel tube confined reinforced concrete column(STCRC),the stirrup is replaced by a thin steel tube to confine ordinary SRC column.The steel tube bears no axial load therefore the main effect of the steel tube is to confine the concrete.According to the high durable requirements of new constructions of STCRC columns(especially for the rigid frame bridge piers)and in order to break the limitation of concrete strength,a new type of Fiber Reinforced Polymer(FRP)-steel tube confined steel-reinforced concrete(FSCSC)columns with high strength concrete(C80)was proposed in the paper.Further experimental study,theoretical analysis and numerical analysis of the proposed FSCSC columns were conducted under concentric compression.The main contents of this paper is as follows:(1)Taking the types of cross-section(i.e.circular and square),the number of CFRP sheet layers and the types of load application as the main variable parameters,seven circular FRP-steel tube confined reinforced concrete stub columns and seven square FRP-steel confined reinforced concrete stub columns under axial compression were tested.Based on the analysis of failure modes and load capacity,the macroscopic deformation and the axial load-axial displacement curves were obtained.The influence of different parameters on the load capacity and ductility of specimens were analyzed deeply.The confinement effect of CFRP sheets under different types of cross-section and the load application was also investigated.It is found from the experimental results that the failure modes of all specimens is shear failure with different levels.(2)Using the tested transvers strain and longitudinal strain on the specimen surface,the axial load-volumetric change curves were obtained by numerical analysis method.The peeling method was employed to analyze the stress procedure of FRP-steel tube confined reinforced concrete stub columns,including the horizontal stress and vertical stress of steel tube,the confining stress between steel tube and concrete and the one between FRP and concrete,the vertical stress of core concrete.Through the comparison analysis,the profound understanding about the interaction mechanism between reinforced steel,steel tube,core concrete and FRP can be intensified.(3)The finite element model of FRP-steel tube confined reinforced concrete stub columns was established by finite element software(ABAQUS).After the confirmation of the validity of the finite element model,the influence of steel tube ratio,yield strength of steel tube,compressive strength of concrete and the number of CFRP layer was investigated and determined.Besides,the relation between the confinement effect of FRP and other variables was studied to provide useful guidance for engineering design.On the basis of test database and FE results,the ultimate load bearing capacity for FSCSC was proposed by numerical regression and the theoretical results fit well with experimental results from this test and other literature.