Experimental and analytical investigations of the flexural behavior of hollow ±55° filament wound GFRP tubes

The behavior of +/- 55 degrees filament wound glass fiber-reinforced polymer (GFRP) tubes under flexural loading was examined experimentally and analytically. A total of 15 tubes were tested under four-point bending. The main test parameter was the ratio of inner diameter (D) to wall thickness (t), (D/t) ratio. The inner diameters of the tubes were 76 and 203 mm, while their wall thicknesses varied from 1.7 to 6.7 mm, giving D/t ratios of 20-75. All tests exhibited a nonlinear load-deflection response and a similar failure mechanism, namely a progressive tensile weakening until a sudden compression failure occurs. The tests showed that the moment capacity of the tubes increased with both tube diameter and nominal pressure rating. The tubes also exhibited a prolonged postpeak behavior. An iterative cross-sectional analytical technique was developed to model both the moment-curvature and load-deflection behavior of the tubes. The model accounts for the potential failure due to local buckling as well as compression failure and was shown to accurately predict the behavior of the tubes. A parametric study was performed to find the moment capacity of tubes with ratios beyond the range tested and was used to establish a simple design equation for moment capacity.