Hybrid double tube sections utilising seawater and sea sand concrete, FRP and stainless steel

This article presents an experimental and theoretical study on axially compressed hybrid double tube SWSSC (seawater and sea sand concrete) columns (DTCCs), which consists of FRP/SS (stainless steel) tubes and SWSSC. The structural behaviours of DTCCs (e.g., load-axial strain curves, dilation properties, loads carried by individual components) are discussed and compared with the corresponding concrete fully filled and double-skin tubes. It is found that the load carrying capacity of a DTCC with SS as inner tube can be estimated as the sum of the loads carried by the outer tube with encased concrete and that by the inner SS tube. On the other hand, the load in a DTCC with FRP as inner tube could be divided as the loads carried by the outer tube with encased annular concrete and by the confined inner FRP tube with encased core concrete. Finally, based on existing analysis-oriented models for concrete fully filled tubes, theoretical models are proposed to predict the load-axial strain curves of DTCCs, which shows reasonable accuracy as verified by the experimental results.