PSI - Issue 62

Marco Menegotto et al. / Procedia Structural Integrity 62 (2024) 1014–1019 Menegotto, M.,. Fieno, L., Rocchi, M.C.

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A24 counts about 66 km of viaducts and A25 about 42 km, comprising 174 works, each one consisting of two separate viaducts (one per carriageway), i.e., altogether 348 items. They also comprise 54 tunnels totalling 70 km, including the Gran Sasso twin road tunnel, Europe’s longest, and numerous minor works. As for viaducts, 19% were built in the late 1960s, 60% in the 1970s and the rest after 1980. Viaducts’ decks are made 82% in prestressed concrete, 10% in reinforced concrete and 5% in steelwork or mixed, according to the following types: 50% parallel beams, 37% boxed cross-section, 13% hollow-core slabs. Prestressed works are mainly post-tensioned (85%), 14% are pre-tensioned and 1% are assembled by segmental construction. Structural schemes are 82% simply supported and 18% continuous. Sections of the motorways were opened to traffic in different times, throughout a span of 40 years. Minor works, additional junctions and side-roads keep being built (see fig. 2). Therefore, many differences appear in the features of the existing works, due to: (i) advancement of construction technology and materials; (ii) changes in technical standards and codes; (iii) evolution of design methods and tools, particularly referring to seismic design. Common design practice those times was not much familiar with durability and seismic problems. 2. Maintenance, repair and upgrade SdP took in charge the State-owned infrastructure, through a European tender, in form of State Concession, with the annexed Agreement stating the technical, financial and chronological matters, to be checked stepwise, with proposals from the company and approvals by the State, represented by the Ministry of Infrastructures and Transport (MIT), who provides funding, within a financial program jointly worked out, too. The company inherited the maintenance problems at a moment when structures already needed deep repair and strengthening. Concrete works were yet suffering widespread degradation, in lack of a substantial maintenance, after having been built in times when professionals were not aware of durability problems, codes of practice were not accounting for them, seismic engineering was primordial, and structural standards, referring to actions, zoning, design and execution, were rather poor. The task of organizing maintenance was then faced with a holistic approach, adopting a systematic long-term planning of interventions, updating it rationally with a timing accounting for priorities linked to safety (also concerning seismic risk), serviceability (both structural and related to traffic flow effectiveness), conservation and financial sustainability (including insurance aspects); all coordinated with the unpostponable maintenance of the road platform and subject to odd spot events, like severe earthquakes. Referring to finance, the income of users’ toll, kept socially allowable for commuters and suppliers, is far from covering the expenses. Therefore, no-return investments are provided by the State for compensation, to be permanently assessed; a factor which strongly affects the timing. The evolution of road safety standards and of structural codes, which updates the requirements related to static and seismic resistance as well as to durability, adds the number of variables, too. SdP performs constant monitoring of all works (bridges, viaducts, over- and under-passes, tunnels, sewers), with quarterly inspections up to year 2020 and, later on, according to the Attention Classes , as defined in the Guidelines for Bridges of MIT (April 2020); they are repeated in any case after seismic shocks, even low, and odd events. Procedures are codified, according to the standards of the Public Administration and implementing the Numerical Assessment Method (MVN) produced by the Centro Internazionale di Aggiornamento Sperimentale – Scientifico of Bolzano, Italy, which allows for scoring the state of the works related to degradation, as well as for yielding timely detection of alerts and, consequently, investigations, verifications and actions to take, as follows. Apart from pointing out urgent pre-emptive actions, necessary to face immediate risks, lists of works needing maintenance are set, based on numerical assessment of the relative defectiveness (Dr); namely: - works listed for short-term interventions (one year) - works listed for interventions within two years - works listed for medium-term interventions (five years) - works listed for long-term interventions (ten years)