Seismic performance of a 1000 m-scale steel-UHPFRC composite truss arch bridge under non-uniform excitations

Abstract

Given the superior mechanical properties of ultra-high-performance fiber-reinforced concrete (UHPFRC), a novel 1000 m-scale steel-UHPFRC composite truss arch bridge scheme has recently been proposed to address key challenges associated with traditional long-span arch bridges including excessive self-weight and construction complexity and to further extend the feasible span limit of this bridge type beyond 600 m. While previous studies on this new bridge scheme have primarily focused on the conceptual design of the arch ribs under static loads, its seismic resistance system and overall seismic performance—particularly under spatially varying ground motions—remain insufficiently explored, especially given its unprecedented span. In this study, a preliminary design of the seismic resistance system including the spandrel columns and the seismic isolation system is first performed to improve the distribution of seismic forces throughout the structure. A detailed nonlinear finite element model is then established and subject to multiple sets of spatially varying ground motions simulated with power spectral density and coherence loss function models to numerically evaluate its seismic behavior under strong earthquake shaking. The seismic performance of arch rib sections and spandrel columns is quantified using column and moment–curvature interaction diagrams to identify critical sections that are seismically vulnerable. The results show that the designed seismic isolators can effectively reduce internal force demands on the columns and improve the uniformity of the force distribution. Compared to uniform excitations, non-uniform excitations can significantly amplify internal force demands in the arch ribs, with average amplification ratios of 11 %, 12 %, and 6 % for axial force, in-plane, and out-of-plane bending moments, respectively. For the spandrel columns, the average amplification in in-plane and out-of-plane bending moments is 6 % and 13 %, respectively. Additionally, non-uniform excitations also increase displacement demands and result in large residual displacements in the arch ribs. Furthermore, under non-uniform excitations, the rotational capacity of the spring sections is insufficient to meet seismic demands, leading to compressive crushing of the UHPFRC. Only a small number of sections near the spring exhibit tensile failure, indicating that these locations are the most vulnerable along the arch. These findings suggest that future optimization efforts should focus on enhancing the rib cross-section at the spring or increasing the stirrup ratio to improve the compressive strength of the core concrete. In contrast, damage observed in the columns is limited to tensile cracking of the UHPFRC at the column ends, with no yielding detected in the longitudinal reinforcement. This study demonstrates the seismic viability of the proposed 1000m-scale steel–UHPFRC composite truss arch bridge and its potential failure mechanism under strong non-uniform excitations, which provides valuable insights for the design of super-long-span arch bridges.