Design method and seismic vulnerability of bridges using UHPC-NSC composite pier

The focus of this investigation is the application of ultra-high-performance concrete (UHPC) and normal strength concrete (NSC) in constructing composite piers. The UHPC-NSC composite pier, comprising the external UHPC jacket and internal NSC, demonstrates a marked enhancement in both load-bearing capacity and control of seismic damage. However, the lack of suitable seismic design methodologies presents a significant barrier to the practical application of the composite pier. Drawing on extensive experimental and theoretical research, this paper proposes an optimization formula that determines the diameter of the composite pier and the thickness of the UHPC jacket. This formula aims to maximize the use of UHPC material, manage the damage, and equalize sectional moment resistance with the original reinforced concrete section. Utilizing the proposed design approach, UHPC-NSC composite piers were implemented in a typical continuous beam bridge. Seismic vulnerability analyses were conducted to quantitatively substantiate the performance of the composite pier following the aforementioned design approach. The analysis affirmed that the composite pier effectively reduced the exceeding probability of all damage levels under small and moderate earthquakes, and extensive damage level under strong earthquakes.