The shear-tensile strength of closed-type winding GFRP stirrups

Closed-type winding GFRP (CW-GFRP) stirrups are obtained by winding continuous fibers fully impregnated with resin on the mould layer by layer. Compared to pultruded stirrups, the CW-GFRP stirrups have a higher bend strength and no overlap sections. For concrete beams with CW-GFRP stirrups subjected to shear, due to the angle between the stirrup and the diagonal crack, the main tensile stresses acting on the stirrup can be resolved into a tensile force along the stirrup and a shear force perpendicular to the stirrup. The strength of the stirrup straight section in this composite state was called the shear-tensile strength. So far, there are few studies about the shear-tensile strength of CW-GFRP stirrups. In this paper, a new shear-tensile test method was proposed and tested for 23 specimens, including twenty CW-GFRP stirrups and three pultruded GFRP stirrups. The main parameters included the cross-sectional dimensions and diagonal crack angle. The test results showed that the bend strength of CW-GFRP stirrups was improved by 81% ∼ 115% and the shear-tensile strength was enhanced by 4% ∼ 19% compared with those of pultruded stirrups. Besides, as the angle of diagonal cracks increased from 35° to 55°, the shear-tensile strength decreased by 10% ∼ 28%, and the decrease was related to the cross-sectional dimensions of CW-GFRP stirrups. The greater the width-to-thickness ratio, the more significant the decrease. Furthermore, the shear-tensile strength overall increased with increasing thickness and decreased with increasing width. When the cross-sectional area was certain, the shear-tensile strength decreased with increasing width-to-thickness ratio and the bend strength exhibited opposite trends. Finally, a shear-tensile strength prediction model for CW-GFRP stirrups was proposed. For the application of CW-GFRP stirrups in beams, width-to-thickness ratios ranging from 1.5 to 2.67 and taking 60% of the tensile strength as the shear-tensile strength are recommended.