Behavior and modeling of FRP-concrete-steel double-skin tubular columns made of full lightweight aggregate concrete

Fiber-reinforced polymer (FRP)-concrete-steel double-skin tubular column (DSTC) is a new type of composite columns which consist of an outer FRP tube and an inner steel tube, with concrete filled in the space between the two tubes. The composite column can be optimally designed to obtain several advantages over existing forms of columns which include high ductility, excellent corrosion resistance, and what's more, lightweight due to the hollow cross-section. To give full play to the lightweight potentials of DSTC, the most obvious approach is to reduce the weight of concrete sandwiched between the two tubes. This paper thus develops a new type of DSTCs that is filled with full lightweight aggregate concrete (FLAC) and reports a systematic study on the compression performance of the FLAC-filled DSTCs at the first time. The results indicate that FLAC in between the FRP and steel tubes is effectively confined, resulting in an excellently ductile behavior in compression and that the ultimate strength and strain of FLAC-filled DSTCs are increased by a factor of 1.7 and 3, respectively. The void ratio has limited effect on the ultimate strength of FLAC-filled DSTC while the impact on the ultimate strain is significant. On the basis of the stress-strain model developed for FRP-confined FLAC, a stress-strain model for FLAC-filled DSTC is proposed, which provides a satisfactory agreement with the experimental results.