Ultimate strength behaviour of sandwich pipes filled with steel fiber reinforced concrete

Sandwich pipes (SP) can be an effective solution for the ultra-deepwater submarine pipeline, combining high structural resistance with thermal insulation capability. Besides polymer, steel fiber reinforced concrete (SFRC) can be an another choice for the annular material, based on the characteristics of high fracture toughness and good adhesion with metal. The purpose of this work was to investigate numerically the ultimate strength of SP filled with SFRC under external pressure and longitudinal bending. The mechanical behaviour of SFRC was simulated using a Concrete Damaged Plasticity (CDP) model whose parameters were estimated by uniaxial tension, compression and four-point bending tests. The applicability of the parameters obtained was verified by simulating the compression and four-point bending tests, where the results showed good correlation between measured and predicted numerical values. Pressure–curvature ultimate strength for SP with perfect adhesion and no adhesion interface condition was obtained. Besides, a parametric study was performed to investigate the effect of the thickness of each layer on the pressure–curvature collapse envelope of SP. It was found that the adhesion between layers and the lateral confinement effect on SFRC play a dominant role in the ultimate strength behaviour of SP, which lead to the non-monotonicity of the collapse envelope.

► Ultimate strength of SP under external pressure and bending loads was investigated numerically.
► Mechanical behaviour of SFRC was simulated using a Concrete Damaged Plasticity model.
► Pressure–curvature ultimate strength for SP with different bonding condition was presented.
► Effect of thickness of each layer on the pressure–curvature collapse envelope of SP was studied.
► Non-monotonicity of the pressure–curvature collapse envelope of SP was found.