Retrofitting Alternatives for an Existing Maillart-Arch-Type Bridge: A Case Study

This article examines different retrofit approaches for a still-in-use deck-stiffened arch bridge, the Viadotto Olivieri in Salerno (A3 Highway—South Italy). In its current state, the viaduct is characterized by a central Maillart-arch system, separated by 6 cm-deep joints from two lateral girder portions: the whole system works as an isostatic scheme on a global scale. Dating back to the 1960s, it derives from an early design approach, not including the effects of seismic actions. Considering the demands of current codes, also in light of recent bridge collapses and the resulting plan for assessing the structural safety and vulnerability of existing bridges, studies on seismic capacity become necessary to highlight the potentials and deficits of such complex structures. Analysing a still-in-use example of a Maillart-arch-type bridge, the article examines two different retrofit approaches. The first retrofit alternative includes the strengthening and partial modification of the original deck bridge: it exploits the beneficial effects of making the slender vault collaborate with a more rigid single deck, resulting from joint closure. Moving in the opposite direction, the second alternative considers the application of seismic isolation to the original scheme. An intermediate Isolation System (IS) has been postulated, inserting rubber devices—High Damping Rubber Bearings (HDRBs)—below the deck, at the top of the cross-walls. The advantages of an IS are clear, observing a great reduction of base reactions; moreover, the introduction of the IS completely modifies the original static scheme and exacerbates bridge deformability, at the expense of slender cross-walls, suffering for buckling. A comparison between these retrofit alternatives is argued in the article, evaluating the impact of different types of solution on the valuable original structural scheme.