# A Methodological Framework for Bridge Surveillance
## 1 Introduction  
Economic and social development is strictly related to the services that a country can offer to its users, and one of these is undoubtedly the road networks. Today more than ever, an absence or an inadequate connection between the urban agglomerations presents a very important issue, firstly in terms of safety for the people that benefit from the infrastructures and secondly in terms of continuity of service in order to guarantee a functional socio-economic network. From this point of view, the weak points of the network are undoubtedly presented by infrastructures such as bridges, viaducts, and tunnels. As such, a stretch of tens of kilometers can be threatened by problems associated with a single overpass. The Italian roads are a highly articulated and complex network due to the country's morphology and extend over 180,000 km, of which approximately 6700 km are highways, 19,800 km state roads, and up to 100,000 km are managed by the provinces. It is possible to estimate [1,2] the following assets:* 3 international tunnels (25.4 km), 566 tunnels (516 km), 1718 bridges and viaducts (681 km) along the tool highway;
* Approximately 1200 tunnels and 11,000 bridges and viaducts along the network managed by ANAS (motorways and state roads);
* Approximately 30,000 bridges, viaducts, and tunnels along the road managed by the provinces. The most flourishing time in the construction of Italian roads was that of the period following the Second World War, with 52% of the bridges built before the 1980s (Figure 1). Each road has been designed and built according to the particular environmental conditions of the crossed areas and the rules of construction at that time. Bridge typologies, even if on the same route, can present relevant differences concerning the materials, the geometric dimensions, the static schemes, and the construction details. Moreover, the oldest structures are characterized by a general absence of design documents. This situation presents a possible difficulty in developing an efficient standard Bridge Management System (BMS). The main Italian rules relating to road infrastructures can be summarized as follows:  
* Circular of the Ministry of Public Works of 19 July 1967 No. 6736/61/AI [3], in which the importance of an assiduous, agile, and systematic surveillance of the road asset is highlighted for the essential purposes of public safety, without excluding the economic aspects of the good conservation;
* Circular of the Ministry of Public Works No. 34233 of 25 February 1991-law No. 64 of 2 February 1974-art. 1 Ministerial Decree 4 May 1990 [4], instructions relating to the technical regulation of road bridges defining new technical standards for the design, execution, and testing of bridges were issued. In particular, for the existing bridges, it was proposed to manage the roads at various existing levels and to acquire full knowledge of the bridges' current state ensuring the following fundamental topics: supervision, inspection, maintenance (ordinary and extraordinary), and static interventions (restoration, adaptation, and restructuring);
* Ministerial Decree of 17 January 2018, Update of the New Technical Standards for Construction (NTC2018) [5] and Ministerial Circular of 21 January 2019, Instructions for the application of the Update of the \"Technical Standards for Construction\" referred to in the Ministerial Decree of 17 January 2018 [6], where, related to all type of Existing  
Figure 1: Age of Italian bridges. Construction, the aspects concerning safety assessment, classification of interventions, and definition of the reference model for analysis are defined;
* Law Decree No. 109 of 28 September 2018, which contains urgent measures for the city of Genoa, the safety of the national infrastructure and transport network, the seismic events of 2016 and 2017, work and other emergencies [7]. Among the requirements law there was the creation of the National Information Archive of Public Structures (AINOP--Archivio Informativo delle Opere Pubbliche), listed in Art.