Seismic Retrofit Strategy Selection and Prioritisation for Existing RC Road Bridges

The accelerated deterioration of reinforced concrete (RC) road bridges built in the postWorld War II 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 threespan Gerber-type RC road bridge (L = 78 m), classified in the highest urgency category (attention class CdA 1) according to 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 ranks first in four of the five weighting scenarios examined and in about 99% of 20,000 randomly sampled weight vectors; Alternative A prevails only when traffic impact receives a weight close to its upper bound and seismic safety a weight close to its lower bound. At the base real discount rate of 2%, the 100-year LCC values are EUR 3.98 M for C, EUR 4.45 M for A, and EUR5.84 Mfor 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.