Experimentally Derived Scour Fragility Curves for Pile-Supported Bridge Piers under Lateral Loading: A Risk-Oriented Framework for Flood Hazards

Abstract The climate-change–driven intensification of extreme hydrologic events poses escalating risks to bridge infrastructure. This study presents a self-contained experimental framework that derives scour fragility curves for pile-supported bridge piers from controlled large-scale flume tests under subcritical clear-water-scour conditions. Pier-top inclination is adopted as a measurable serviceability indicator, with paired time histories of scour-depth ratio (SDR) and inclination from six independent scour histories on a four-pile pier. Lognormal fragility functions are estimated by maximum likelihood and verified via Kolmogorov–Smirnov (K–S) tests, with the 5% critical band serving as a nonparametric envelope on residual uncertainty. Scour-induced capacity loss is expressed as an equivalent lateral demand, enabling a reliability formulation p f = P ( S ≥ k R ) and a calibrated linear map k = 19.10 · θ + 0.049 ( R 2 = 0.972 ) between the reliability factor k and the allowable pier-top inclination θ within the calibrated range 0.002–0.0089 rad. The major-state exceedance probability approaches unity at SDR ≈ 0.8 (loss of 80% of pile embedment), a conservative lower bound owing to the relatively low bearing capacity of the laboratory sand. The resulting fragility family is portable across serviceability thresholds and codes, supports risk-consistent warnings, maintenance triggers, and rapid postevent screening, and remains grounded in laboratory observables. Because the formulation is load-based, it extends naturally to multihazard contexts where scour acts jointly with seismic or other lateral effects, advancing climate-resilient bridge asset management.