Mid-20th-century slender orthotropic steel highway bridges exhibit a significant vulnerability to high-cycle fatigue accumulation induced by modern heavy goods vehicles. As complete bridge replacements impose severe economic and environmental burdens, alongside significant traffic disruptions, the civil engineering sector urgently requires sustainable, low-intervention solutions. As an alternative to traditional stiffening, which adds mass statically, this research evaluates the efficacy of implementing passive vibration-control devices, specifically tuned mass dampers, as a dynamic retrofitting strategy to extend the fatigue life of critical welded details within these structures.

A multi-scale numerical investigation was conducted utilising a finite element model based on the steel arch Bridge Roosteren as a reference structure. The transient structural dynamic response was simulated for a single passage of a moving load, corresponding to the Eurocode 1 lorry silhouette A, along the most critical path. From this passage, the fatigue damage was systematically quantified at three primary connections (Rib-to-Deck, Rib-to-Crossbeam, and Deck-to-Crossbeam) using the hot spot stress method, rainflow-counting algorithms, Miner's linear cumulative damage rule, and Eurocode 3 S-N curves.

The integration of parametrically tested passive tuned mass dampers did not result in an overall extension of the structure's global fatigue life. Whilst secondary connections, such as the Deck-to-Crossbeam detail, demonstrated a localised fatigue life extension, the governing Rib-to-Deck connection experienced a fatigue damage increase across all evaluated configurations. A unique geometric alignment was induced by the relationship between the reference structure and the considered vehicle. Specifically, the relation of the 4.5 m longitudinal vehicle axle spacing to the 2.424 m transverse crossbeam spacing induced substantial secondary bending moments. This alignment, coupled with the inherent stiffness of the finite element model, limited the dynamic mitigation potential of the tuned mass dampers. Furthermore, the spatial arrangement of the tuned mass dampers, which primarily targeted global dynamic behaviour, was deemed ineffective because the governing fatigue-critical details are mostly driven by high-frequency excitations rather than low-frequency global bending. Consequently, the tuned mass dampers did not induce a significant reduction in the stress ranges at all details, thereby failing to yield a notable improvement in the overall fatigue life.
Although the study did not yield an overall extension of the fatigue life, the findings indicate the potential viability of dynamic retrofitting strategies. To further define this potential, future research should explore the application of semi-active vibration-control devices to capture a broader bandwidth of traffic-induced vibrations. Alternatively, investigations should target localised high-frequency responses by attaching smaller tuned mass dampers directly to the stiffening ribs rather than the crossbeams. These studies should include influential dynamic factors such as stochastic traffic modelling and vehicle-bridge interaction, explicitly accounting for vehicle inertia, suspension mechanics, and road surface roughness. Until effective dynamic retrofitting strategies are fully validated, static stiffening should continue to be prioritised.
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