Issue 46

F. Bazzucchi et alii, Frattura ed Integrità Strutturale, 46 (2018) 400-421; DOI: 10.3221/IGF-ESIS.46.37 401 This requires, especially in relation to recent events, a particular attention to the evaluation of existing infrastructures and to the planning of improvement and/or modification works. In particular, attention must be focused on the need to assess the degradation and estimation of the residual capacity of the structures in operational conditions. The road infrastructures are very vulnerable, as they are afflicted by design (structural and technological) deficiencies essentially linked to the construction period, the applied technologies and the used materials together with, especially in the last years, to a lack of appropriate maintenance. Most of bridges and viaducts in Italy were built between the '50s and '60s, when the economic boom generated unlimited confidence in the use of concrete as a durable material for eternity. Moreover, the majority of these structures of the Italian road network have been realized through the technology - not yet mature at the time - of the prestressed reinforced concrete, hardly compatible, with the actual concepts of reliability and control. These structures are difficult to analyze because they do not have what is today defined as a plastic reserve: in the moments before the collapse, in general, there are no evidence of structural failure. This lack of ductility can not be considered as a design error. It would be more appropriate to highlight that in the sixties there were two fundamental factors that led to this situation:  1. there was no awareness that reinforced concrete could have such a short life and could suffer attacks and deterioration due to atmospheric and/or environmental agents.  2. there were no automatic calculation tools, therefore, where possible, statically determined schemes were preferred, much simpler to calculate. It was even said that they had to be preferred to the undetermined ones because they were adaptable to temperature variations and constraint settlements. In reality, as it will be showed in the next, also most recent realizations (Fossano viaduct) suffered not for this immature technology, rather than an excessive confidence with the technology. It can be affirmed without any doubt that prestressed concrete structures need a redundancy in control during the realization phases. Therefore, the main purpose of this work is to analyze the possible critical issues related to the structural safety of Italian road infrastructures in order to stimulate new efforts to be put in novel investigation methods, especially for a large-scale diagnosis, and strategic management. In particular, Petrulla viaduct (2014), Annone (2016) and Ancona (2017) overpasses, Fossano viaduct (2017) and Polcevera (2018) bridge will be briefly discussed to highlight the differences in terms of collapse causes which are a clear example of how much the Italian infrastructural system needs attention. Another purpose is to stimulate the sensitivity of civil engineers who are called to face the great challenge of "knowing how to read" the existing buildings, establishing a connection between the past (full understanding of the project, detailed analysis, etc.) and the future, through the use of innovative diagnostic techniques. To do so, investments must bring nourishment to a sector, that did not have important technological evolutions in the recent years. Moreover this topic does not attract particularly the interest of the scientific world for a long period and just for that has large margin of growth, and, at the same time, desperate need of innovative technologies. It is also time to learn from our past errors and use them as background to define the requirements of a new cultural paradigm. C RITICAL ISSUES EMERGED IN THE LATEST COLLAPSES OF ROAD BRIDGE INFRASTRUCTURES Petrulla viaduct: construction and durability he Petrulla viaduct is situated along the S.S. 626 “Valle del Salso”, at km 4+500, in Sicily. The viaduct consists in a series of 12 simply supported beams, each of them with a 40 m span (Fig. 1(a)). On July 7, 2014, one span collapsed, injuring 4 persons. The breakage occurred in mid-span circa, and then, shear failure occurred where the deck impacted ground (Fig. 1(b)). The deck, 11.30 m wide, was made of 4 precast and prestressed concrete I-beams equally spaced by 2.850 m. Five transverse beams realized the girder that supported the pavement slab (Fig. 1(c)). The investigation, conducted after the collapse, evidenced an exceeding state of material decay for the steel components: diffused oxidation in the prestressing cables, severe corrosions of the metallic sheathing and large absence of the protective grout inside the cables (Fig. 2(a), Fig. 2(b)). Since the bridge was built in the mid-80s, this degradation pattern was not compatible with 30 years of service life, especially because the concrete exhibited good signs preservation (Fig. 2(c)). The investigations have evidenced several construction flaws, in particular related to finishing operations of the prestressing. The grout injection was superficially carried out and the vent pipes were not accurately sealed (Fig. 2(d)). Under these circumstances, humidity found a preferential way into the cables, and its continuous content variation generated an aggressive environment for steel oxidation. Other additional deficiencies for this particular degradation scenario were addressed to:  not sufficient cover due to malposition of the prestressing cables;  not adequate workability and fluidity of the concrete; T