Oss - Seismic Observatory of Structures
The Seismic Observatory of Structures (Oss) was conceived, designed, and managed by the technical staff of the Department's Seismic Risk Unit, which implemented it with own funds and European tenders. The Ministry of Infrastructure and Transport, the Regions, Local and other Public Bodies co-operate to choose structures for the permanent Oss network and for the temporary emergency network, sometimes contributing financially and operationally. Through a special maintenance service, a very high efficiency rate is granted to the network (around 97%).
Through the Oss national network, the Civil Protection Department monitors the oscillations caused by earthquake in 173 publicly owned buildings: 160 buildings (including 70 schools, equal to 44%, 46 municipal buildings and prefectures, equal to 29%, 29 hospitals, equal to 18%, and 15 other types, equal to 9%), as well as 7 bridges and 6 dams. These buildings are located in municipalities classified mainly in seismic zones 1 (35%) and 2 (54%).
The Oss allows the damage caused by an earthquake to monitored structures to be assessed, extending to similar structures in the affected area, thus providing useful information for Civil Protection activities immediately after an earthquake.
On the one hand, Oss allows strategic structures for managing seismic emergencies to be monitored and their damage assessed. On the other hand, it provides the technical-scientific community with original data that helps to understand how structures respond to earthquakes.
These data also provide useful background information for updating technical standards for construction in seismic areas.
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. Immediately after the event, the server automatically processes the data and produces a summary sheet of the main dynamic response parameters of all structures affected by the earthquake.
In particular, the maximum value of the building's inter-floor displacement can provide a useful indication for assessing structural damage following a seismic event. Immediately after data processing and report generation, the results are automatically sent to Civil Protection Department staff and relevant experts. Information about the seismic event and its impact on affected structures is published on an online platform: https://oss.protezionecivile.it/osspublic/#/.
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 coordination centres for the emergency management.
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.