Experimental and reliability analyses for fatigue-induced damage in reinforced concrete trough bridges

Reinforced concrete (RC) trough bridges form a crucial part of Europe's railway infrastructure. These structures consist of a U-shaped cross-section (two longitudinal beams and a slab) designed to accommodate the ballast. For the case of the Iron Ore Line, a critical corridor located in the north of the country, RC trough bridges represent about 40 % of the railway bridge population. Many of these bridges have surpassed 50 years of service, enduring over 10 million cycles of fatigue loading, with increases of axle loads since their construction due to demands associated with the iron ore extraction and transportation. As these structures approach critical maintenance or replacement decisions, understanding their long-term performance and remaining capacity is essential. This study experimentally investigates the degradation behavior of a full-scale RC trough bridge subjected to progressive cyclic loading, simulating fatigue effects over time. During the controlled laboratory tests, the overall performance of the bridge is assessed, focusing on the stiffness loss of slab and beams, cracking, and force redistribution. Fatigue verifications based on Eurocode EN1992–1–1 and fib Model Code 2020 are performed alongside the reliability analysis using the First-Order Reliability Method (FORM) to evaluate structural safety levels. While fatigue damage is evident in the slab's tensile zone, the overall structural response indicates that the bridge maintains its functional capacity after simulating 48 years of service. However, the code-based reliability analysis indicates lower-than-target reliability levels for reinforcement, suggesting a conservative estimation of reinforcement capacity to withstand cyclic loading.