Axial compressive behavior of concrete-filled FRP-steel wire reinforced thermoplastics pipe hybrid columns

This paper presents investigations on a new column form, namely, concrete-filled fiber-reinforced polymer-steel wire reinforced thermoplastics pipe (FRP-SRTP) columns (CFFSCs) which consist of a SRTP tube with an outer FRP confinement system and concrete filled in the core area. A series of axial compression tests were performed on CFFSCs, and parameters including the number of FRP layers, the FRP fiber type and the clear spacing of the FRP rings were investigated. The test results demonstrate that the concrete-filled SRTP tube columns have an excellent ductility and the outer FRP confinement system provides efficient confinement to CFFSCs. The dilation behavior of the concrete in CFFSCs with polyethylene terephthalate FRP is different to that of the concrete in CFFSCs with carbon FRP. Four existing design-oriented models are adopted to generate the ultimate axial stresses and their corresponding strains of concrete in CFFSCs. By comparing the test results and the theoretical predictions, it is found that the existing models provides inaccurate predictions for CFFSCs. The new column form is particularly suitable as a form of standing support for underground mines, where a novel supporting system requires both a large deformation capacity and a good structural integrity.