investigation into cyclic behavior of steel pipes under different boundary conditions

today, sea-going pipelines are mostly non-buried on the sea bed. by changing the flow field around the tube, the sediments under the tube begin to move, and the scouring phenomenon of the bed happens. the presence of roughness in the seabed, leads to the phenomenon of free spans in the pipelines. the simultaneous combination of this phenomenon under cyclic loading is considered as one of the causes of failure of sea pipelines and there is a potential for all kinds of collapses such as yielding and buckling. in this research, numerical and experimental evaluation of two steel tube specimens, one with two-ends fixed boundary condition and 177 cm length, with a constant thickness of 0.2 cm, and a cantilever one with 100 cm length with a constant thickness of 0.2 cm, was carried out under cyclic loading according to sac loading protocol. the results obtained from the test showed that the compressive and tensile strength decreased with increasing loading cycles after local buckling in the specimens and boundary conditions were effective on the cyclic behavior of the specimens, with the exception of the two-end boundary conditions in the sample, with increasing loading cycles, the gradual decrease in the thickness of the samples at the load location, a gap was created and low cycle fatigue problem was observed on the sample. but in the specimen with cantilever boundary condition, loading continued until the last cycle, without creating any gap in the sample.