Evaluating Seismic Source Effects on the Collapse Modes of Existing Curved Viaduct

Curved bridges subjected to strong ground motions have shown high seismic vulnerability in many countries. Several published studies analyze curved-bridge failures, focusing on collapses observed after severe earthquakes, which are frequently linked to loss of seating length. Other studies assess seismic fragility based on expected pier damage, and most published work uses numerical models derived from existing bridge portfolios that do not include specific real bridges. Many studies also aim to correlate the dynamic properties of existing bridges, estimated from ambient vibration measurements, with those of numerical models. The approaches mentioned above estimate the expected seismic response for specific bridge types that may not accurately represent real structures, and examine the most common failure mechanisms. Unlike these studies, the current research provides valuable and novel insights into the expected behavior of curved viaducts designed in accordance with modern standards and regulations. It shows that, in these cases, the most frequently reported failure in the literature, loss of seating length, is less likely than other failure mechanisms. The results apply to a real curved bridge whose numerical model was previously calibrated using ambient vibration measurements. Another distinctive feature is the assessment of reliability indices for a real structure, evaluating the values that current regulations would expect to observe during infrequent seismic events. Uncertainties in site amplification are reduced because a nearby seismic station is available. Nonlinear analyses were performed using two sets of seismic records from interplate and intraplate earthquake sources, scaled to match the expected seismic intensity at the bridge site, to assess damage progression in the bridge under both design and infrequent earthquake intensities. The study also emphasizes the significant effects of the selected ground-motion population and the frequency content of interplate and intraplate earthquakes on bridge seismic performance. Unlike the failure mechanism most commonly observed in curved bridges during high-intensity seismic events, which involves loss of superstructure seating length, this case study of a curved bridge designed under modern seismic regulations shows failure when shear demands exceed the bridge piers’ shear capacity.