Numerical and experimental investigation into field joint strain concentration in concrete-weight coated pipelines under bending

Strain localisation at the field joint (FJ) for concrete-weight coated (CWC) pipelines subjected to bending during installation and operation remains a critical design concern. This study develops a high-fidelity finite element model (FEM), validated against newly available full-scale bending tests, to characterise the nonlinear mechanical behaviour of CWC pipelines. The model accurately reproduces the measured bending response, local strain behaviour, and displacement profile, and captures the progression of cracking, interfacial slip, and strain concentration factor (SNCF) observed during testing. The results show that tensile SNCF at the field joints governs the response and defines the onset of critical behaviour, with concrete crushing marking the serviceability limit. A direct comparison of the obtained results with DNV-RP-F105 reveals significant limitations in the existing stiffness-ratio formulation for predicting SNCF. To address this issue, a set of normalised master curves is established, providing an efficient and generalisable framework for assessing field-joint performance across a range of practical geometries. The influence of internal pressure on strain localisation is also quantified, demonstrating its beneficial role in reducing tensile SNCF. The overall outcomes provide valuable insights into the interaction between coating geometry, internal pressure, and localised strain behaviour, leading to safer and cost-effective offshore pipeline design practices.