Outstanding experimentation by the Eucentre Foundation in Arischia (AQ)

The Eucentre Foundation, in collaboration with the University of Washington (Seattle, USA), the University of Berkeley (California, USA), and the Middle East Technical University (Ankara, Turkey), conducted an unprecedented experiment in October 2024 in Arischia, a hamlet in the municipality of L’Aquila. An entire existing building, weighing approximately 2000 tons, was subjected to a series of dynamic tests as part of the ERIES funded by the European Commission and coordinated by Scuola Universitaria Superiore IUSS di Pavia. These types of seismic tests, until now carried out mainly for small to medium-sized specimens on vibrating tables in experimental laboratories, were, for the first time, performed on an actual building, thus representing a significant step forward in research on seismic risk management and mitigation.

Seismic Isolation System: Structure and Functioning

The structural scheme of the C.A.S.E. Project consists, from bottom to top, of a reinforced concrete (AC) plate on the ground, a series of steel or AC columns, a seismic isolator on each column and, above, a second foundation plate, on which the building is built. The isolation system allows, in the event of a seismic event, the relative displacement between the columns and the upper foundation plate while maintaining the load-bearing capacity against vertical loads. This system significantly reduces the accelerations transmitted to the superstructure, thus protecting the building from structural damage.

Testing the seismic response of an actual building

A first test aimed to assess the seismic behaviour of an entire building, chosen from the 185 seismically isolated buildings constructed as part of the C.A.S.E. project in response to the L’Aquila earthquake of April 6^th, 2009. The building was subjected to seismic stresses recorded in past events, applied directly to the upper foundation plate of the building, thus allowing the behaviour of the structure to be studied as if it were built in a non-seismically isolated configuration. The test result made it possible to collect essential data on the seismic response of this building, which did not suffer any particular structural damage despite the seismic actions exceeding those considered in its original design.

Dynamic test of the base isolation system

This second test involved a high-speed cyclic test involving all 32 sliding pendulum isolators installed under the building’s upper foundation plate to protect it from seismic stresses. The isolation system was then subjected to several load cycles in displacement of amplitude ±20 cm imposed on the upper foundation plate at a speed of around 30 cm/s. The test provided valuable and unique data on the ability of these devices to maintain adequate performance even 15 years after their installation.

An innovative approach: the Mobile Laboratory (MobiLAB)

In both tests, a distinctive feature was using the Eucentre Foundation’s mobile laboratory, MobiLAB. This system was designed to replicate the potential of an earthquake engineering laboratory directly on site, overcoming space limitations and perfectly representing the real built environment imposed by laboratory testing. Thanks to almost twenty years of experience in structural testing and analysis, Eucentre has developed a system that transfers the potential of advanced testing from the laboratory to the field.

The preliminary results: resilience and maintenance

The preliminary results of the dynamic test, i.e. of a seismic action applied directly to the upper foundation plate of the building, as if it were not on the isolators, indicate that the building complies with the design requirements set and is common to the various structural types constructed at the time.
Regarding the high-speed cyclic test, it was possible to confirm that the seismic isolators maintained performance comparable to that of new installations despite the natural ageing of the devices installed in situ. Both observations highlight the importance of careful design to provide the built environment with adequate ‘seismic resistance reserves’ and the importance of following current regulations regarding design structures with isolation technology at their base.
The project in Arischia, part of the ERIES programme, demonstrates the importance of in-situ testing to understand the long-term behaviour of seismically isolated structures. The dynamic and cyclic tests provided crucial data that will contribute to designing new structures and maintaining existing ones to improve overall seismic resilience.