Axial tensile behaviour of steel–concrete double-skin composite submarine pipeline

Steel-concrete double-skin (SCDS) composite pipelines demonstrate a competitive application prospect in the deep-sea energy exploitation. The active confinement effect generated by deep-water hydraulic pressure will change the steel-concrete interface behavior, thereby affecting the exertion of bearing capacity. This paper conducts an analytical research on the axial tensile behavior of SCDS composite pipe influenced by the hydraulic pressure. A finite-element model was developed and validated to examine the full-range tensile mechanism of SCDS composite pipe subjected to hydraulic pressure, revealing that a greater active confinement stress can be induced by the external pressure for the steel–concrete interfaces and the tensile strength is decreased compared with the benchmark specimen without pressure. Influences of diameter-to-thickness ratios of outer (D_o/t_o) and inner (D_i/t_i) tubes, yielding strengths of outer (f_yo) and inner (f_yi) tubes, concrete strength (f_c), hollow ratios (χ), water depth (H) and internal medium pressure (p_i) are subsequently analysed. Increasing the internal medium pressure can increase the tensile capacity; and increasing hollow ratios under the higher hydraulic pressure gradually decreases the tensile capacity, which is exactly the opposite of the pattern without pressure. Finally, a design method considering the influence of hydraulic pressure is proposed to estimate the tensile capacity.