Oss - Seismic Observatory of Structures
The OSS was conceived and is being designed and managed by the technical staff of the DPC Service for Seismic Risk. DPC builds it up through European tenders, using its own funds. MIT, Regions, Local and other Public Bodies co-operate to choose structures for the permanent OSS network and for the temporary emergency network, contributing sometimes funding and operational support. Through a special maintenance service, a very high efficiency rate is granted to the network (around 97%).
Through the Italian national network of the Seismic Observatory of Structures (Osservatorio sismico delle strutture - OSS), the Department of Civil Protection (DPC) monitors the oscillations caused by earthquake in 172 constructions of public property: 159 buildings (among which 69 schools equal to 44%, 46 city halls and prefectures equal to 29%, 29 hospitals equal to 18%, 15 other typologies equal to 8%), plus 7 bridges and 6 dams. In 2018, 2 dams more will be monitored. These constructions are located in municipalities classified mainly in seismic zone 1 (33%) and 2 (60%).
The OSS allows the damage to be estimated, occorred to the monitored structures because of an earthquake. Similar damage level can be considered for similar structures located in the striken area, thus providing information that is useful for civil protection activities just after the earthquake.
Through the OSS, structures that are of strategic importance for the seismic emergency management can be kept under control. Moreover, original data can be supplied to the technical-scientific community, that allow to improve the understanding of the response of structures to earthquake.
Finally, such data contribute a useful background for updating the technical regulations for constructions in seismic zones.
When an OSS construction is striken by a significant earthquake, its monitoring system records both the ground and the structure movement, and sends immediately data to the OSS central server in Rome.
The server processes automatically the recordings, incoming from all affected structures, thus producing a synthetic report which provides the maximum measured values and some descriptive parameters, that allow both the incoming earthquake and the structure vibrations and the damage distribution to be assessed.
Within about 20’ after a seismic event of magnitude greater than or equal to 4, the report is distributed via e-mail to DPC and Regional Administrations, and is also published automatically, together with the recordings, on the public OSS website: http://www.mot1.it/ossdownload.
Moreover, in the first hours after a severe earthquake, in epicentral area a temporary network of at least 4 semplified monitoring systems is deployed, integrated at once in the OSS. In this case the structures chosen to be monitored are mainly buildings used as co-ordination centres for the emergency management, such as.
A “detailed” OSS monitoring system consists of sensors distributed over every building floor and on the ground: in average 20 measures of acceleration, that allow to reconstruct adequately the structure vibration and estimate the damage.
Sensors are cable-connected to a seismic central unit, ADSL-linked to the OSS server in Rome. There are 131 OSS monitoring systems of this kind. On the other hand, there are 29 permanent OSS systems with “simplified” layout, similar to the temporary emergency network layout. In this case there are sensors just at ground and top floor level, independent and connected to each other through wifi network, for usually 7 measures of acceleration.
This system is less expensive as far as the supply and the installation (for lack of cabling) are concerned, but it provides poorer information.
In order to better understand the seismic behaviour, experimentally observed through OSS systems, in addition to collecting the available technical documentation, in situ surveys are carried out of the monitored structure, on whose ground a mathematical model of it is developed, which allows to simulate its behaviour under seisms of increasing intensity and to evaluate the corresponding damage.
The collected documentation, the monitoring system description, the survey, the models and all of the data produced by OSS systems since 1999 are available, upon registration, in the website ISS (structure study and monitoring within OSS): http://www.mot1.it/iss.