Bending, Crushing, and Connector Behavior of Pultruded Glass FRP Tubes

Understanding the complex mechanics involved in the behavior of thin-walled fiber reinforced polymer (FRP) composite tubes is essential for optimal structural applications. Flexural, crushing, and connection tests were performed on large-diameter thin-walled (D/t \u3e 20) cylindrical tubes comprised of glass FRP composites manufactured using pultrusion process. The tubes were made of either a vinyl ester or a polyurethane matrix, using high pressure resin infusion during pultrusion.;Full scale bending tests were performed with 16 and 12 inch diameters spanning 320 and 240 inches, respectively. The test data revealed that the tubes possessed superior mechanical properties, with ultimate bending strengths of 50-70 ksi and elastic moduli ranging from 5.5-6.6 Msi. The failure mode from the full scale four point bending tests was determined to be crushing on the compression face coupled with local buckling. In addition, two types of connection tests were executed: a transverse bolt test and a washer test. The transverse bolt test exhibited maximum loads of 18-25 kips. The washer data ranged from 14-27 kips with failure occurring as local cracking. Coupon tests under tension, flexure, and compression were conducted after cutting them from full size tubes, resulting in maximum tensile stresses from 95-107 ksi. Also conducted on full scale specimens were four-point bending fatigue tests up to 200 cycles at 40% of the ultimate static bending stress and further tested to failure under static load conditions. The results revealed that polyurethane outperformed vinyl ester. The vinyl ester was shown to outperform in the transverse bolt test because of vinyl ester\u27s higher strength and stiffness under localized load conditions.;Investigation of the four-point bending results revealed a bilinear load versus strain response during loading. The bilinear response is shown to be caused by cross section deformation, aka, ovalization. This deformation was captured through video footage of the experiment and confirmed by finite element analysis. Application of classical lamination theory and finite element modeling was performed and found to under-predict the full scale bending stiffness in relation to experimental results. A failure prediction technique for the full scale four point bending is proposed that includes local buckling effect. A more direct approach proposed herein modifies the typical bending stress calculations by accounting for a local compression stress. Good agreement is found between the proposed technique and experimental data with errors ranging from 4-8%. This proposed technique is compared with the standard bending stress formulation and is shown to be more accurate, thus confirming the proposed approach\u27s ability to account for the local effects