Seismic Performance Of FRP-steel Composite Tube Confined RC Columns

FRP-steel composite tube (FSCT) is manufactured using steel tube as mould toexternally wrap fiber-reinforced polymer. It not only saves consumption of steelmaterial and formwork, but also uses FRP wraps to protect the steel tube from localbuckling and corrosion. Existing limited literature adopted the constructionprocedure of concrete-filled steel tube (CFT) columns that FSCT got through thebeam-column joints and there was no internal reinforcement in the tube. In order toavoid the complexity of the beam-column connection, this dissertation proposes anew hybrid member called FSCT confined RC column that FSCT don’t get throughthe beam-column joints and is just used to transversely confine RC column. Themain research on seismic performance of FSCT confined RC column is included asfollows:(1) In order to verify the confinement of FSCT, a total of ten circularspecimens of250mm in diameter and500mm in height which included one steeltube confined RC column and nine FSCT confined RC columns were tested undermonotonic axial compression load. The test parameters were the type of fiber, thenumber of FRP layers, the volumetric ratio of internal hoop steel reinforcement andthe loading mode. Test results indicate:(i) the load carrying capacity and ductilityof steel tube confined RC column can be significantly enhanced by the external FRPwraps, and the combination of GFRP and steel tube can be more effective;(ii) thebehavior of FSCT confined RC column is a little influenced by the internalreinforcement of hoops and the loading mode which differs from total cross-sectionto the concrete core.(2) Based on the test results of this dissertation and other literature, astress-strain model was developed for FSCT confined RC column under monotonicaxial compression. The model is shown to provide reasonably prediction of the testresults.(3) Five full-size specimens of400mm in diameter were tested under constantaxial load and horizontal cyclic loading aimed at investigating seismic behavior ofRC column, FRP confined RC column, steel tube confined RC column and FSCTconfined RC column. Test results were:(i) the confinement of FSCT provides moreductility and energy dissipation capacity than that of FRP or steel tube;(ii) thehorizontal bearing capacity is improved with the increase of axial compession ratiofor FSCT confined RC column, but the ductility and energy dissipation capacityslightly decrease.(4) Based on OpenSees finite element analysis software and the stress-strain model proposed earlier, the seismic behavior of FSCT confined RC column waswell predicted. The further parametric analysis shows:(i) the limited value of axialcompression ratio ranges from0.7to0.8;(ii) the horizontal bearing capacity andductility of columns can be improved with the additional of layers of FRP, but theimprovement may be weaken with the excessive confinement of FRP;(iii) theheight of FRP wraps has little influence on the seismic behavior of FSCT confinedRC column;(iv) the horizontal bearing capacity of FSCT confined RC column canbe enhanced with the increase of internal steel reinforced ratio.