At the end of May 2012, a seismic sequence struck the Emilia region in northern Italy, with two main events of local magnitude ML 5.9 and 5.8. Emilia has been classified as a seismic area only recently. Consequently almost all of the precast buildings that have been erected in the past decade haven't been designed with provisions for seismic resilience. Surveys after the earthquake allowed the identification of the damage types and their location: column base, column top, on shed beam, on roof element, on cladding/ infill panels. The scenario confirmed structural damages surveyed after the earthquake in L'Aquila (Menegotto, 2009), (Colombo, 2012). Particularly, it has been pointed out that the weakest elements in precast buidings are connections.
Indeed, in precast structures, unlike traditional RC buildings, the design and construction of efficient connections is still a open issue. The connections of cast-in-situ structures present a higher degree of continuity between adjacent elements, also due to passing reinforcing bars. In case of seismic events, joints represent a source of energy dissipation and allow for a redistribution of internal forces (if properly designed). These characteristics lack in many precast buildings, especially in those with industrial applications, which are usually characterized by beams/roof elements simply supported by columns. In such structures, seismic improvement can’t be performed through the introduction of rigid connections, which would increase the stiffness of the structure (which is initially flexible) and lead to unpredictable and sometime negative results such as an increase of the base shear. Moreover, it is not simple to design connections strong enough to resist to stresses induced by earthquakes.
Passive control techniques use devices that don’t need energy to work, thus they are very reliable because they won’t malfunction if a black-out occurs. They seem a promising solution for seismic improvement of precast existing buildings. A possible intervention is the introduction of dissipative connections, which would lead to an increase of the behavior factor through energy dissipation. Dissipative connections can be located between different structural/non-structural elements: between roof elements and edge beams, between pillars and edge beams, or between infill panels.
This work is focused on the introduction of dissipative connections between roof elements and the substructure. In particular, the objective is finding an algorithm to define the yielding force of connections in function of the maximum relative displacement allowed between roof elements and substructure. The complex phenomenon, which involves plasticity and the dynamic response of the system, is described through simple equations in order to have a powerful but simple instrument for design. The proposed algorithm allows to define the yielding force of roof connections in function of the elastic and inertial features of the examined system, with no need of non-linear dynamic analysis which are difficult to perform and usually lead to ambiguous results
