Actual Applications of Base Isolation yo Heritage Buildings After the 2009 L'Aquila Earthquake

Most historical buildings were built using stiff, heavy and low strength masonry structures. These characteristics make them particularly vulnerable to seismic attacks, leading to large damage and even failures; the earthquake resistance of these structures can result further reduced by the deterioration due to aging. Seismic isolation is a relatively recent technique which has already been applied for the seismic protection of existing constructions. The work presented in this paper shows the use of seismic isolation as a practical method to retrofit "historical" buildings. The investigations focus on structural typologies of existent historical buildings built in Italy in the last centuries. The applications demonstrate that base isolation can represent the optimum system to solve the fundamental problem of the historical buildings that are highly vulnerable to earthquakes, indeed it allows for the reduction of both the structural deformations and floor accelerations, improving the protection of structure and contents. The high stiffness of masonry structures easily allows for the separation of the oscillating modes with a good efficiency of the isolation option, leading to the full protection against the maximum expected earthquake without works on walls in the elevation portion. Two actual applications of the base-isolation technique for the retrofitting of historical buildings damaged by the 2009 L'Aquila earthquake are presented and discussed. The actual constructive methods for the underpinning and for the insertion of the isolation system at the base of the buildings are drawn up.