Evolution of mechanical performance of pier bearing padstones during bearing replacement and experimental study on UHPC strengthening

Railway bridge bearings are prone to aging and deterioration under long-term exposure to complex environmental conditions and high-stress cyclic loading. If not addressed in a timely manner, such deterioration can adversely affect the force transfer mechanism of the superstructure and pose a serious threat to railway operational safety. To investigate the influence of bearing replacement on the load-bearing performance of pier bearing padstones and to explore effective strengthening measures, this study takes the bearing padstone of a middle pier in a railway continuous girder bridge as the research object. Three 1:3 scaled model specimens were designed and fabricated, and axial compression tests were conducted to examine the mechanical behavior of the padstones under different working conditions. In addition, a finite element model was established to perform parametric analyses. The results indicate that local chiseling of the padstone during bearing replacement leads to reductions in both load-bearing capacity and deformation capacity. In contrast, external strengthening of the padstone using ultra-high-performance concrete (UHPC) significantly enhances the bearing capacity and effectively delays damage evolution. After strengthening, the damage process of the padstone initiates with concrete crushing in the bearing region. Subsequently, stress redistribution toward the surrounding areas induces tensile cracking at the bottom of the UHPC strengthening layer, eventually resulting in structural failure. Furthermore, the thickness of the strengthening layer, concrete strength, and reinforcement ratio of the padstone all exert notable influences on the bearing performance. The recommended ranges for these parameters are 40–60 mm for strengthening layer thickness, C100–C140 for concrete strength grade, and 1.4%–2.1% for reinforcement ratio.