Experimental and Numerical Investigations of the Seismic Performance of Railway Gravity Piers with Low Reinforcement Ratios

Gravity pier is a widely employed pier type in railway bridges worldwide. It is characterized by a solid cross-section with a low longitudinal reinforcement ratio which can be even lower than 0.5%. These low-reinforced gravity piers have been found to be vulnerable under major earthquakes, but their seismic performance has not been fully understood. Improving the seismic safety of these piers and reducing the consumption of reinforcing steels coincide with multiple Sustainable Development Goals (SDG 6, 7, and 9). In this concern, three main objectives are achieved in the present research. Firstly, quasi-static tests were conducted on two gravity piers with low longitudinal reinforcement ratios: 0.3% and 0.4%. The tests found the reinforcement ratio significantly affected the failure mode and seismic capacity. A typical brittle failure was observed in the specimen with the 0.3% reinforcement ratio. Fracture of longitudinal reinforcing steels was heard, and only a few cracks formed within a narrow region at the pier bottom, whereas the structural behavior of the specimen with a 0.4% reinforcement ratio was ductile, and cracks were located within a wider region (800 mm) at the pier bottom. Increasing the reinforcement ratio significantly increased the energy dissipation capacity and the displacement ductility. Secondly, finite element models of two specimens built using ANSYS were validated with test results, and then a series of finite element models were built to further investigate the influences of three important parameters on the seismic capacity. The three parameters are shear span to depth ratio, axial compression ratio, and longitudinal reinforcement ratio. The validations found that the load–displacement hysteretic curves and the distributions of concrete plastic strain from finite element analyses matched well with those from tests. Further finite element analyses found that the shear span to depth ratio was inversely correlated with the peak lateral load, but positively correlated with the displacement ductility. Conversely, increasing the axial compression ratio increased the peak lateral load but decreased the displacement ductility. Thirdly, an analytical equation was proposed to predict the displacement ductility of low-reinforced gravity piers, and the predicted ductilities agreed well with those obtained from finite element analyses. The findings provide a better understanding of the seismic performance of low-reinforced gravity piers, which helps extend the application of these piers. Furthermore, the proposed analytical equation assists in the evaluation and design of these piers.