Valutazione del comportamento sismico e recupero strutturale di edifici in struttura mista: il caso del complesso Piave

The technical-scientific turmoil provoked by the Industrial Revolution induced deep innovations in the constructive routine of last century with the introduction of new materials that overturned the usual constructive procedures. The early 1900 building resulted composed of hybrid buildings, the so-called mixed structure buildings, which mixed the presence of traditional materials, masonry and wood with innovative materials, steel or reinforced concrete. The introduction of reinforced concrete has particularly altered the construction field, in particular the constructive systems that mixed masonry with reinforced concrete frames has been used for long, either for new constructions, and in the interventions of transformation of existing buildings. This thesis study is addressed to mixed buildings dating back to the early 20th century, with a masonry structure coupled with reinforced-concrete frames. The introduction of reinforced elements was inspired by temporary and functional needs, rather than structural ones, so the lack of a seismic response are evident, as in most cases, they were used without following any engineering principles or were planned only for vertical loads. First, the process of intervention on the existing structures is described; it is based on the Italian code, and aims at acquiring an adequate level of knowledge of the structure analysed, in terms of geometry, constructive details, materials characterization and state of conservation. The diagnostic techniques are described, useful for the definition of the geometrical and material parameters of the constructive components and the mechanical characterization of the materials used. The provisions and indications, according the Italian and the European codes, about the issue are assessed, though they provide concise and insufficient in terms of operational provisions. For this reason, there is a list of research studies and experimentations carried out in order to define the scientific framework about the issue. There is a framework of the seismic behaviour of ordinary masonry, a list of the different mechanisms of collapse and the related criteria of resistance. The aim of this phase is to illustrate the philosophy that inspired the modelling methods of the last thirty years, and assess the current advanced methods. The convenience of the modelling methods analysed is defined according to the basic concepts used in the pushover analysis, strongly suggested for the existing structures. The practical part is about the seismic behaviour of a residential building located in Bari, with a load-bearing system in masonry associated to reinforced-concrete frames with strong characteristics of structural irregularity either in plan and in elevation. Indeed, the irregular planimetric layout are complementary to some innate complexities, due to the presence of a distribution walkway, whose structure is of reinforced-concrete column and beam, in contact with the masonry; and the presence of a basement shelter, dating back to the pre-war period, equipped with a box-structure made of reinforced-concrete walls. The modelling phase is carried out, according to the Equivalent Frame approach, using the code TREMURI, implemented in the namesake software. The assessment of the seismic response is done through pushover analysis, that allow to study quantitatively the interactions that arise, under horizontal load, between the load-bearing systems made of masonry and reinforced concrete. In conclusion, the final part is about the planning of interventions or combinations of these: the characteristic aspects of the innovative intervention techniques for the seismic improvement of the existing structures are described. A hypotesis of intervention of improvement of the seismic response of the building is provided and it is assessed according to the quantitative and qualitative parameters associated to the specified case.