| A review of previous experimental, analytical, and numerical research conducted on pipe segments subjected to combined loading indicate that very few tests were reported on (a) pipes subject to load combinations involving axial tension, internal pressure, and bending, and (b) tests involving combinations of torsion, internal pressure, and bending. Within this context, an experimental program consisting of two full-scale test series on a total of eight pipe specimens is conducted. The specimens were made of X65 material (Specified Minimum Yield Strength=448MPa) with 508mm outer diameter (OD), and a nominal diameter-to-thickness ratio (D/t) of 80. In the first test series, specimens were subjected to combinations of internal pressure, axial tension, and bending and were aimed at (a) quantify the beneficial effect of axial tension on the magnitude of critical buckling strains of pipes and (b) determine whether or not the pipes are able to attain their modified plastic moment resistance as predicted by analytically derived plastic interaction relations. In the second test series, pipe specimens were subjected to load combinations involving internal pressure, axial tension, torsion, shear, and bending and were aimed to measure the pipe modified moment capacity. The moment vs. curvature relations, peak moment values, and local buckling behavior of the specimens as obtained from the experiments are documented. The peak moments obtained are compared to the analytically predicted moments. A nonlinear shell finite element model is also developed using the Finite Element Analysis (FEA) simulator ABAQUS in order to predict the moment capacity, critical strains, and the local buckling behavior of pipe specimens. Test results were observed to compare very well with FEA predictions for the moment capacities and buckling modes. Under certain combinations of axial tension and internal pressure, experiments and FEA show that pipes with Dt=80 are able to attain their modified plastic moment resistances. The FEA predicted longitudinal compressive strains were fairly good, but less reliable than the FEA predicted moment resistances. After demonstrating the ability of the FEA to reliably predict pipe modified moment capacity in previous and current research programs, a systematic FEA parametric study is conducted to investigate the effect of geometric properties (D/t) and loading conditions (torsion, axial force, and internal pressure) on the ability of the pipes to develop their modified plastic moment capacity. As a result of this parametric study, it was observed that the ability of the pipes to develop their plastic moment capacity is strongly dependant on axial force and D/t ratio. On the other hand, internal pressure and torsion are relatively less effective on this ability. |
