Experimental characterization of the confinement-like behaviour in radial joints of steel fibre reinforced concrete segmental linings

This paper presents an experimental investigation into the confinement-like behaviour in radial joints of steel fibre reinforced concrete (SFRC) precast segmental tunnel linings under concentrated loading. A total of 58 moulded and cored cylinders were tested under uniaxial compression to quantify the influence of fibre dosage, while qualitatively assessing the influence of fibre distribution and orientation conditions on the post-peak residual response. Additionally, 18 SFRC prismatic specimens were tested under concentric and eccentric bearing loads. Digital image correlation (DIC) was used to measure local strains, crack initiation, and propagation within the confined region. The results reveal two complementary confinement-like mechanisms: material confinement and geometric confinement. Material confinement is associated with fibre bridging in bursting and splitting cracks, which enhances the residual compressive strength and ductility with higher fibre dosage. Geometric confinement is associated with the biaxial stress field beneath the loaded area. In the prismatic specimens, geometric confinement within the upper 20% of the specimen thickness increased lateral restraint, delaying splitting and raising the effective compressive strength. Under eccentric loading, this confinement-like effect was reduced, although a more stable response was observed due to crack localisation. Comparison with an existing analytical splitting model showed that experimental contact stresses were 10–15% lower than predicted, indicating generally consistent agreement within the investigated configurations. The results provide insight into localised in-plane response of SFRC radial joints under concentrated loading and establish a basis for future investigations considering out-of-plane stress conditions.