Effect of UHPC jacket-to-footing connection method on mechanical behavior of railway bridge piers with low longitudinal reinforcement ratio under cyclic loading

The ultra-high performance concrete (UHPC) jacket-to-footing connection method has a significant impact on the enhancement of seismic performance of bridge piers. However, the effect of various interfacial connection methods on seismic behavior of the UHPC jacket strengthened the railway pier with low longitudinal reinforcement ratio remains unclear. This study investigated the crack distribution, failure mode, loading capacity, deformation capacity, energy-consuming capacity, stress-strain distribution of three pier specimens using the UHPC jacket-to-footing connection with or without dowels. The experimental results and numerical analyses showed that UHPC jackets with different interfacial connections affected the distribution of major cracks in pier specimens with low longitudinal reinforcement ratio, but not the failure mode (i.e., the fracture of reinforcements). The loading capacity and cumulative energy-dissipating capacity were increased, while the deformation capacity was attenuated. The UHPC jackets changed the stress distribution of the longitudinal reinforcement in the pier specimens. In the absence of any connecting measure between the UHPC jacket and footing, the enlargement of the cross-section of the pier specimen caused simultaneous development of concentrated cracks at the bottom of cross-section and an unstrengthened cross-section at the top position of the UHPC jacket. The reinforcement stresses in all major cracks went to the yield stage, increasing the energy dissipation capacity of the pier specimens. In the pier specimen using the UHPC jacket with dowels, the location of damage was shifted to the unstrengthened cross-section due to the synergistic effect of longitudinal reinforcements and dowels, which accelerated the growth of reinforcements strain in concentrated cracks. In summary, the UHPC jacket without dowels facilitates a balance between the loading capacity and deformation capacity of railway piers with low longitudinal reinforcement ratio.