SEISMIC BASE ISOLATION: RETROFITTING APPLICATION IN STRUCTURES DAMAGED BY EARTHQUAKE Antonello SALVATORI 1 ABSTRACT The ever-increasing use of the most advanced seismic protection technologies in structural design can often lead to unexpected results in terms of system efficiency, expexially when the application of technologies is not carried out by satisfying some simple concepts derived from other branches of engineering. Both anti-seismic isolation devices and their correct application in existing structure can lead to a decrease in the safety level in structures with base isolation respect to less innovative anti-seismic technologies in conventional structures. The work presents some critical features in the existing structures with seismic isolation, and the proper controls that the test should highlight to avoid problems in the correct application of the technology, to obtain a real seismic security higher than that of traditional structures. After L’Aquila 6,3 Mw earthquake of 2009, April 6th, about fifty percent of the buildings in the city were severely damaged. Its historical centre and all the surrounding suburbs were severely damaged, causing 309 casualties, and more than 1500 people injured. L'Aquila has been the first Italian important city directly destroyed by a near fault earthquake since Messina earthquake (1908). Many buildings collapsed completely, both in masonry structure and in reinforced concrete ones. Innovative anti-seismic techniques are illustrated, mainly the base isolation anti-seismic systems. Some examples of application in existing building damaged by L’Aquila earthquake (2009) in Italy are shown, demonstrating how the isolation techniques can be applied in concrete structure and even in masonry structure, diminishing the vulnerability level in both cases. Several additional control phases must be applied, regarding the seismic gaps permitting the building movement during earthquakes. Keywords: Seismic isolation; existing building; damage; earthquake 1. INTRODUCTION L'Aquila city was struck down by a 6.3 Mw earthquake in 2009 April 6th. Its historical centre and all the surrounding suburbs were severely damaged, causing 309 casualties, and more than 1500 people injured. L'Aquila has been the first Italian important city directly destroyed by a near fault earthquake since Messina earthquake (1908). Many buildings collapsed completely, both in masonry structure and in reinforced concrete ones. This work analyse the most relevant collapses of many buildings, the relevant causes of the collapse, the lack in design, construction and maintenance of the buildings (both of public interest or private ones), and the impact the collapses have caused to the urban centre. Many important buildings and structures have not been totally collapsed, and the application of the most innovative repair and seismic retrofitting techniques are applied to restore them, especially those with historical and artistic relevance. The first Italian application of seismic isolation to masonry and monumental buildings have been studied, and a combination of both seismic isolation and tunnelling techniques are analysed and developed to repair and seismically retrofit some important monumental building in the historical centre of the city. Several applications of retrofitting seismic isolation to existing and severely damaged buildings are shown, concerning building uplifting, pillar cut and underpinning structures. 1 Associate Professor, Member GLIS, Department of Civil Engineering DICEAA, University of L’Aquila, L’Aquila, antonello.salvatori@univaq.it