Arches, vaults and roof trusses are typical elements of historical buildings. In many cases suitable structural details (concrete curbs, steel tie rods) for absorbing the out-of-plane horizontal thrust exerted by such structural elements are missing or inadequate. Furthermore, many historical buildings were built for a lower seismic intensity compared to similar modern structures. Seismic retrofit measures, integrated into the building without altering its character and appearance, are then needed.
Steel tie rods are normally used to reinforce this type of structures, but the temperature changes significantly modify the pre-load used to take up the horizontal thrust.
Shape memory alloys (SMA) are metals which exhibit two peculiar properties, pseudo-elasticity and the shape memory effect.
A post-tensioning system based on the pseudo-elasticity properties of SMA is proposed, as a protection device to be used in combination with the currently used metallic tie rods.
The main advantages of the proposed SMA system, compared to the mere use of traditional metallic ties, are:
- limiting force changes in the steel tie due to temperature variations and seismic deformation;
- controlling structural deformations, if a given target displacement is exceeded under unexpected earthquakes;
- avoiding buckling under negative seismic displacements;
- calibrating the stress during the post-tensioning process;
- application of force without tearing on the anchorage;
- dissipating energy during the earthquake.