Experimental evaluation of effects of geometry and reinforcement on bearing capacity of concrete bearing pads representing substructures under spherical sliding bearings

This study examines the bearing strength of concrete pads used beneath spherical sliding bearings (SSBs) through a total of 62 tests conducted on 1/5- and 1/2-scale specimens, focusing on the effects of specimen geometry, boundary conditions, and reinforcement. The dimensional ratio H p / d , defined as the ratio of the concrete pad height ( H p ) to the characteristic length of the concrete surrounding the loading area ( d ), was found to be a key parameter, and results indicate that a minimum value of 0.6 is required for concrete pads to achieve sufficient confinement and reach their intended bearing capacity. To evaluate pads with various geometries, a new evaluation method, the Pseudo Area Method, was proposed, limiting the effective bearing area based on H p / d = 0.6. Foundation-type specimens exhibited significantly higher capacities than column-type specimens, demonstrating the structural advantage of installing pads on foundations, particularly under sudden seismic-induced axial force increases. Reinforcement was effective only when a threshold of H p / d ≥ 0.5 was satisfied. A regression-based increment factor, α r = (2.65 ρ (max ( H p / d − 0.5, 0)) + 1), was integrated into the AIJ (2022) bearing-stress formula, showing good agreement with experimental results. The findings confirm the necessity of a threshold for H p / d in pad design and support the proposed evaluation method for practical SSB applications.