Protocol of investigations for the preliminary assessment of the structural safety of highway overpasses

This paper presents the results of a protocol of investigations that have been carried out on 15 overpasses, located along the highway A18 in Sicily (south of Italy) and built about fifty years ago, with the aim of achieving a preliminary evaluation of the structural safety of these overpasses. The investigated overpasses are characterized by a three-span deck consisting of a reinforced concrete slab and prestressed concrete girders. The girders of the central span are simply supported by two Gerber saddles located on cantilever girders at the two ends of the same span. The safety level of the overpasses is investigated by means of different activities that include visual inspection and computation of the class of attention of the overpasses according to the Italian Bridge Guidelines for the classification and the risk management, safety evaluation and monitoring of existing bridges, laboratory and in situ tests on materials, pachometric, georadar and video-endoscopic tests on structural details, and static load tests of the overpasses. The results of the static load tests have also been used to assess the accuracy of two numerical models of the overpasses. These models are elastic but characterised by different levels of accuracy and computational burden: while the first model is the well-established and simple Courbon-Albenga method, the second is a finite element model characterised by a more refined simulation of the response of slabs, longitudinal girders and crossbeams. The results of the investigations have been critically analysed and discussed to underline the ability of the protocol to reveal possible deficiencies of the overpasses and thus identify overpasses that are liable to structural interventions or more accurate and expensive investigations.