Seismic retrofit of precast structures

In the last decades, RC precast structures were extensively used in all Europe as industrial buildings. However, both the poor knowledge of their seismic behavior and the lack of specific code provisions led to a high seismic vulnerability of the existing precast estate. During recent seismic events, indeed, significant and extensive damages were exhibited by precast structures. These scenarios demonstrated that the structural safety of precast structures is an important issue for both the human safety and the social/economic management of whole regions/countries. Three significant losses items are imputable to seismic damage mostly for precast structures. The first one is related to the casualties, injuries and its amount is proportional to the exposure of the structure. The second losses item is strictly related to the structural damage, and it consists in repair/replacement costs. The last ones, instead, depends on the down time in which the productive activities are interrupted in order to allow the interventions of structural rehabilitation. This work focuses on typical one-story precast buildings, designed without any seismic criteria, characterized by isolated columns fixed in socket foundations and connected to the beams by friction connections. Roof elements are arranged so that no rigid diaphragm is provided and the seismic force at the roof level is transferred to the lateral resisting system by masses proportional criteria which lead to plan irregularities. For the above considerations, it is recognized that seismic retrofitting interventions are required for the existing precast structures. However, two main issues should be faced: first, the code recommendations for seismic retrofit of the precast structures are still poor; second, the retrofit strategies typically adopted for the reinforced cast-in situ buildings are not suitable to fix the specific vulnerabilities related to the structural scheme of the precast buildings. The present work aims at presenting different retrofit strategies for the beam-to-column friction connections of existing precast structures. In particular, it aims at comparing two different strategies based on displacement or velocity activation. The seismic performance of the retrofitting solutions is demonstrated by means of experimental and numerical results.