Seismic Retrofit of a Reinforced Concrete Arch Bridge Using Low-Mass Tuned Mass Dampers

Reinforced concrete (RC) arch bridges constructed prior to modern seismic codes often exhibit severe vulnerabilities under earthquake loading due to brittle detailing, geometric irregularities, and long-term material degradation. This design-feasibility oriented paper concerns the proposal of a retrofit solution for a case-study RC arch bridge built in the late 1950s in Northern Italy and designed by Riccardo Morandi. The bridge features a 90-m span arch and short, shear-deficient spandrel columns above the arch keystone, which were identified as the most critical elements. Indeed, nonlinear time-history (NLTH) analyses of the as-built configuration predicted their premature brittle failures under life safety limit state seismic demand. The novelty of the proposed retrofit solution lies in the combination of (1) the use of low-mass (total mass ratio μ = 1.9%) tuned mass dampers (TMDs), typically employed for serviceability or wind-induced vibration control rather than for seismic strengthening of bridges, and (2) the implementation of a mechanically decoupled layout, in which the TMDs’ sliding masses are supported by the massive arch extrados, while the spring–damper units are connected to the above slender deck, allowing transverse seismic control without increasing gravity demands on the superstructure. Optimal TMDs’ tuning frequency is identified through NLTH parametric analyses, as classical linear tuning rules are inadequate for structures exhibiting nonlinear seismic response. In the examined case study, the proposed TMDs’ configuration is effective in reducing the transverse drift demand of the most critical piers, achieving reductions of up to 49% under oscillatory seismic ground motions. Conversely, a markedly lower effectiveness is observed under pulselike events. Given the specific characteristics of the investigated bridge and the limited number of seismic records (five oscillatory and five impulsive) employed in NLTHs, further investigations are required to assess the robustness and broader applicability of the proposed solution.