Calibration and Evaluation of an IMK Hysteretic Model for Seismic Fragility Assessment of Urban Rail RC Solid Piers

Rapid post-earthquake assessment of urban rail viaducts requires nonlinear pier models that capture cyclic deterioration at manageable computational costs. This study calibrates and evaluates the established Ibarra–Medina–Krawinkler (IMK) formulation for reinforced-concrete solid piers rather than proposing a new hysteretic law or experimental database. Seven previously reported quarter-scale tests are reused for direction-specific parameter identification and calibration-set assessment. The new contribution is a multilevel accuracy–efficiency evaluation covering cyclic metrics, a scaled 12 m Fiber benchmark, nonlinear dynamics, incremental dynamic analysis (IDA), computational cost, and fragility. For the specimens, final secant stiffness achieved R2 = 0.891 and a 9.93% mean absolute percentage error; cumulative energy achieved R2 = 0.893 but a 27.79% error. For the prototype, the intermediate-backbone force difference was 3.83%. Under eight representative records, mean differences were 2.64% for peak base shear and 4.15% for peak displacement. Across 60 records scaled from PGA = 0.1 to 1.5 g, peak–displacement and peak–base–shear comparisons yielded R2 values of 0.854 and 0.931. The corresponding mean absolute percentage errors were 15.95% and 11.32%. The IMK model reduced wall-clock time by 96.37%, a 27.55-fold speed-up. Paired fragility curves differed by 3.14 percentage points on average, and median PGA capacities differed by 11.23%; Sa(T1) and capacity-dispersion checks preserved the main comparison. Because the record groups were not matched in spectral amplitude or velocity, their ranking is interpreted as an association rather than a causal pulse-period effect. The calibrated IMK model is therefore suitable for rapid global demand and fragility assessment within its calibration domain, whereas Fiber models remain preferable for local damage, residual deformation, and detailed energy dissipation.