Experimental and analytical study of hollow section concrete-filled GFRP tubes in bending

The flexural response of hollow section concrete-filled GFRP tubular (HS-CFGT) members has been examined experimentally and reported in this paper. A total of 14 specimens was tested, including four-point bending tests on reduced-scale specimens in the laboratory and cantilever bending tests on full-scale specimens on the construction site. The details of the test rigs and procedures, as well as the key test observations, including the ultimate moment capacities, load-displacement curves and failure modes, are fully reported. The test results were analysed to evaluate the influence of key variables on the structural performance of the HS-CFGT tubes, including concrete infill, GFRP tubes, slips between concrete and GFRP tubes and confinement of concrete infill. Fibre analysis approach was adopted to determine the moment capacity of the examined HS-CFGT sections. A total of four representative stress-strain curves of concrete were evaluated for their applicability to the HSCFGT sections in bending. It was found that the concrete models proposed for general FRP-confined concrete columns are not applicable to the examined HS-CFGT sections in bending, and the uniaxial concrete model leads to rather conservative moment predictions, whereas, the FRP-confined concrete model used for beams provides great accuracy in predicting the moment capacities for both reduced-scale and full-scale HS-CFGT members.