Ductile Behavior of Reinforced Concrete Arch Ribs
Reinforced concrete arch bridges offer unique functionality and aesthetic appeal---particularly when the use of typical column bents are impractical due to local topography or other conflicting infrastructure. When subjected to strong earthquake loading, plastic hinging is likely to occur in arch ribs. These structural elements must be designed with adequate ductility to withstand imposed seismic displacements. This study investigates the behavior of arch ribs through laboratory testing and analysis.
Four specimens were constructed to represent the critical region of an arch rib near the springing. Specimen details were based on two prototypical arch bridges. The primary test variables were the type and amount of confining reinforcement, spacing of transverse hoops, and amount of axial load. Confinement details included both circular hoops and rectilinear hoops with crossties. Specimens were tested under constant axial load and cyclic lateral displacements of increasing amplitude. Tests indicated that the use of circular hoops were capable of improved ductility compared with rectilinear hoops and crossties for similar reinforcing ratios, but that the effectiveness of circular hoops was reduced for large hoop spacing.
Results for analytical plastic hinge lengths are also presented. Test results show that existing empirical expressions are reasonable for predicting plastic hinge lengths of arch ribs near the ultimate curvature of the cross sections. A new model is presented which correlates curvature to plastic hinge length at multiple limit states, thereby providing a tool for use in performance-based design.
An analytical model of an archetypal arch bridge is used to investigate the global behavior of reinforced concrete arch ribs. Nonlinear pushover analyses indicated the potential for plastic hinging away from the arch springings---a behavior which should be considered in the design and detailing of new arch bridges.