Collapse of sandwich pipes with PVA fiber reinforced cementitious composites core under external pressure

Sandwich pipes (SP) with steel tubes and a lightweight flexible core are under consideration as a potential solution for ultra-deepwater submarine pipelines, combining high structural resistance with thermal insulation. Besides polymeric materials, strain hardening cementitious composites (SHCC) reinforced with polyvinyl alcohol (PVA) fibers, a micromechanically designed material with high tensile ductility, can be an option for the annular material. The purpose of this work was to investigate experimentally and numerically the collapse behavior of SP filled with SHCC under external hydrostatic pressure. The preparation procedure for SHCC and the fabrication process for SP were presented in detail. The full-scale laboratorial tests of SP were performed using a hyperbaric chamber to analyze the collapse pressure subjected to external pressure. The mechanical behavior of SHCC was simulated using a concrete damaged plasticity (CDP) model provided by the commercial finite element package ABAQUS, whose parameters were estimated by tension and compression tests. In addition, a systematic parametric study was performed to analyze the effects of ovality, thickness and outer/inner radius ratio on the collapse pressure of SP with SHCC core.