An Integrated Framework for Seismic Retrofit Strategy Selection in Existing RC Road Bridges

<jats:p>The accelerated deterioration of reinforced concrete (RC) road bridges built in the second post-war period, combined with increasingly stringent seismic-performance requirements, calls for structured and scientifically grounded procedures for selecting retrofit strategies. This paper proposes an integrated four-phase methodology combining: (i) calculation of the Verified Safety Index (ISV) according to the VAL4 procedure; (ii) estimation of the discounted Life-Cycle Cost (LCC) over a 100-year horizon; (iii) GIS analysis of alternative traffic routes; and (iv) a two-level Simple Additive Weighting (SAW) multi-criteria analysis, supported by five deterministic weighting scenarios. The framework is applied to a three-span Gerber-type RC road bridge (L = 78 m), classified in the highest urgency category (Attention Class CdA 1) according to the Italian bridge-management guidelines, with an initial seismic safety index ISV = 0.06. Three intervention alternatives are compared: (A) in-situ structural upgrading with carbon-fibre-reinforced polymers (CFRP) and concrete jacketing; (B) partial demolition of the central span with FRP upgrading of the retained spans; and (C) full demolition and reconstruction. Alternative C obtains the highest base-case SAW score and remains first in all five weighting scenarios examined. At the base real discount rate of 2%, the 100-year LCC values are €3.98 M for C, €4.45 M for A and €5.84 M for B, preserving the same ranking as the undiscounted estimates. The case study therefore shows that full replacement may be both structurally and economically preferable. The proposed framework offers a transparent and replicable decision-support procedure for public authorities managing seismically vulnerable bridge assets.</jats:p>