INVESTIGATION OF THE SOIL-STRUCTURE INTERACTION BASED ON THE ACQUIRED DYNAMIC RESPONSE DATA

This thesis will analyze the pavilion of the former Neuro-Psychiatric Hospital of Racconigi named "Chiarugi". The criticality of the structural framework, which has progressively worsened over the years, is essentially due to the poor mechanical characteristics of the substrates present below the laying surface of the foundations which show a liquefaction problem which combined with the relatively shallow hydrometric level of the aquifer has generated a series of differential settlements responsible of the current cracking framework and the most serious and recent collapses. The complex soil-structure interaction will be assessed through a reverse process: normally the first data to start from are the results of the geotechnical investigations to calculate the structure's subsidence, displacements and vibrations; the starting point in this case will instead be the experimental data obtained from a series of accelerometers placed inside the building; the acceleration values, originating from natural vibrations induced for example by the surrounding vehicular traffic or by the wind, have made it possible to trace the structure's ways of vibrating through specific algorithms; the parameters obtained were taken as a reference for calibrating a finite element model. The model updating process was basically divided into two steps in which the physical parameters of the model were initially calibrated: elastic modulus and specific weight, in order to fictitiously recreate the state of cracking and damage present in the building; in fact, wanting to create a finite element model of a damaged structure, the first difficulty is precisely the definition of the mechanical characteristics of the materials that compose it as a cracked and damaged material has a very different behavior compared to a material intact or in good condition: not being able to physically sample and insert every single crack and damage present in the structure for both practical and objective difficulties within a Fem model, it was decided to use the physical parameters of the materials that constitute it appropriately reducing them in order to recreate a global behavior that is as realistic as possible. In a second phase, the soil-structure interaction was calibrated; starting from the physical parameters previously obtained for the structural materials, additional two-dimensional elements were modeled connected on one side to the foundations of the structure and on the other rigidly bound; each element was then assigned an initial "K" stiffness; through an algorithm called Dommu, the stiffness value of these fictitious elements was iteratively varied in order to obtain results on the finite element model comparable to those obtained by accelerometers. Several analyzes were carried out in order to compare the solutions obtained from different models of stiffness variation related to depth. The results obtained are useful in order to assess the seismic vulnerability of the building in a more realistic way with a view to safeguarding the historical heritage and in order to evaluate the effectiveness of future improvement and recovery interventions.