Behavior of FRP-HSC-Steel Double-Skin Tubular Columns under Cyclic Axial Compression

This paper presents an experimental study on the behavior of fiber-reinforced polymer (FRP)-concrete-steel double-skin tubular columns (DSTCs) under cyclic axial compression. The experimental program included 30 DSTCs, 22 of which were manufactured using a high-strength concrete (HSC). The key parameters considered were the FRP type, FRP tube thickness, concrete strength, inner steel tube diameter, and presence (absence) of concrete filling inside the steel tube. The results show that both normal-and high-strength concrete DSTCs exhibit a highly ductile behavior under cyclic axial compression. However, for a given nominal confinement ratio, hollow HSC DSTCs tend to develop lower strength and strain enhancement ratios than their normal-strength concrete (NSC) counterparts. It is found that the residual plastic strain of concrete in DSTCs is linearly related to the envelope unloading strain, and this relationship is not influenced significantly by any of the test parameters investigated in this study. The results also show that DSTCs manufactured with aramid FRP tubes exhibit a slightly higher stress enhancement and a slightly lower strain enhancement ratio than the companion DSTCs manufactured with S-glass FRP tubes. It is observed that concrete-filling inner steel tubes results in an increase in the compressive strength of confined concrete in DSTCs. On the other hand, hollow DSTCs develop slightly higher ultimate axial strains than the companion concrete-filled DSTCs. The experimental results are subsequently compared with predictions from a model developed for confined concrete in monotonically loaded hollow DSTCs. The comparison suggests that the model provides reasonably accurate predictions of the ultimate conditions of concrete in hollow DSTCs. (C) 2014 American Society of Civil Engineers.