Dynamic Performance Improvement and Fatigue Mitigation of Strengthened Box Girder Bridges With External Posttensioned Tendons: Modeling and Strategies

Abstract

ABSTRACT This study evaluates the dynamic and fatigue performance of high‐speed railway (HSR) box girder bridges strengthened with external posttensioned tendons, using validated three‐dimensional finite element models and a fracture energy‐based fatigue model that integrates extended finite element and direct cyclic analyses. Tendon eccentricity and deviator placement are shown to be critical to minimizing midspan acceleration and displacement, with multiple‐deviator configurations outperforming single‐ and no‐deviator schemes. Increasing prestressing force and tendon eccentricity reduces the first three bending modal frequencies by up to only 1% and 0.5%, respectively, confirming the inherent dynamic robustness of these high‐stiffness girders across practical design ranges. Fatigue analysis further shows that positioning external tendons below, rather than within, the box girder increases eccentricity and substantially improves resistance to cyclic loading, reducing displacement accumulation and extending fatigue life under high‐cycle conditions.