Novel parameters in load capacity and failure of coaxial steel tubes jointed by wrapped GFRP sleeve

In this paper, the uniaxial load capacity of two coaxial steel tubes joined by glass fiber reinforced plastic (GFRP) was investigated. The axial connection was made by hoop winding of textile woven fabrics on circular hollow steel tubes. A simple efficient theory was selected to estimate the load capacity of sleeve joint. To define novel parameters in load capacity and failure, tensile tests were conducted on several specimens. Based on fracture mechanics experimental observations showed that three kinds of failure modes occurred including GFRP rupture, adhesive failure and mixed mode. The wetted cross-ply textile of woven glass was used in order to study the effect of the number of plies. One novel parameter named lamination cohesion rate was introduced to explore the GFRP rupture. The results revealed that increasing the number of plies leads to maximize the allowable axial tensile load. A second novel parameter was introduced for Adhesive failure. By employing more plies, fracture mode changes from GFRP rupture to adhesive failure resulting in a considerable increase in the load capacity. However, in this fracture mode, by increasing the number of plies the joint average shear stress increases but the maximum shear stress approximated from theories decreases. In the case of load capacity, a good agreement was found between theoretical and experimental results. By using this joining method, steel tubes can be toughly connected and withstand stresses up to steel ultimate tensile stress.