Research on I steel reinforced concrete-filled GFRP tubular short columns

This paper presents an experimental investigation on I steel reinforced concrete-filled glass fiber reinforced plastic (GFRP) tubular short columns under axial load. The study aimed to explore the effect of three parameters of steel ratio, thickness of GFRP tube and concrete strength on the mechanical behavior of I steel reinforced concrete-filled GFRP tubular short columns under axial load. A total of twenty-seven I steel reinforced concrete-filled GFRP tubular short column specimens were tested with steel ratio of 4.6%, 6.8% and 8.3%, thicknesses of GFRP tube of 5, 8 and 10 mm and concrete strengths from 20 to 40 MPa. What's more, three reference tests including the pure I-section, pure GFRP tube and fully filled GFRP tube without I-sections were conducted in this paper to compare with the proposed composite sections. The failure modes, axial load-strain relationships, axial load-axial displacement relationships and ultimate loads are presented in this paper. The strength index is proposed to better evaluate the section behavior of the composite columns. Experimental results show that the failure modes of all the specimens are basically the same. The transverse strain of GFRP tube is smaller than the axial strain under the same axial load in the linear stage. Specimens with higher concrete strength obtain higher load-bearing capacity but lower deformation capacity and strength index. Increasing steel ratio fails to improve the load-bearing capacity and stiffness, but can lighten the weight of the columns. The results also indicate that thicker GFRP tube can both improve the load-bearing capacity and obtain better deformation capacity but generate a problem of low cost-efficient. Design formulas for the load-bearing capacity of I steel reinforced concrete-filled GFRP tubular short columns under axial load are proposed.