Finite element study for assessing the influence of reinforcement cage and infill material on strain concentration at field joints of concrete-weight coated pipelines

The structural integrity of concrete weight-coated (CWC) pipelines at field joints is critical to safe installation and long-term performance. The field joint region is susceptible to strain concentration under bending due to the abrupt stiffness mismatch between the coated and uncoated sections. Previous studies have focused on pipeline geometry and global stiffness characteristics, but the influence of reinforcement cages and infill materials on field-joint strain concentration remains insufficiently quantified. In this study, a previously validated three-dimensional finite-element framework is used to investigate the individual effects of reinforcement configuration and infill stiffness across different pipe diameters and CWC thicknesses. The study examines their combined influence for a representative pipeline configuration as an illustrative assessment. The results demonstrate that reinforcement cages generally increase the strain concentration factor (SNCF) by increasing the local stiffness discontinuity adjacent to the field joint, with the magnitude of this effect depending on reinforcement configuration and pipeline geometry. In contrast, introducing infill material improves deformation compatibility across the field-joint transition and reduces SNCF, although the magnitude of the reduction depends strongly on pipe diameter, CWC thickness, and infill stiffness. Among the investigated configurations, the maximum SNCF reduction of approximately 8% is observed for the smaller-diameter pipeline with a 120 mm CWC thickness. For the representative combined configuration, infill partially mitigates the reinforcement-induced increase in SNCF, although the combined response remains slightly above that of the base configuration. Overall, the findings highlight the importance of considering reinforcement configuration, infill stiffness, and pipeline geometry collectively in assessing strain concentration at CWC field joints.