The local site response for upgrading the existing buildings against seismic hazard

The analysis of seismic ground response at the site was conducted using a numerical method, which is developed in three main phases: the definition of the geometric, geological and geotechnical model of the subsurface, the definition of the seismic input, the choice of one or more computer codes to use and the processing of the results. The reconstruction of the geological and geotechnical model of the subsurface has highlighted a morphology quite irregular especially with regard to the covers. In order to assess the effects due to the local stratigraphy, it has been decided to carry out seismic 1-D response analyses, using the computer codes EERA and STRATA. The 1-D analysis was also used for the calibration of computer codes by the modelling of simplified systems and comparing the results obtained by the different codes in order to verify its adequacy. The site response analyses have been developed for some sites in the city of Catania (Italy). On the sites some strategic buildings are localised to upgrade against seismic risk. In situ investigations were carried out in order to determine the soil profile and the geotechnical characteristics for the sites under consideration, with special attention given to the variation of shear modulus and damping with depth. Seismic Dilatometer Marchetti Tests (SDMT) have been carried out, with the aim of evaluating the soil profile of shear wave velocity (Vs). Moreover the following investigations in the laboratory were carried out on undisturbed samples: Resonant Column tests; Direct shear tests; Triaxial tests. The available data obtained from the Seismic Dilatometer Marchetti Tests results enabled us to evaluate the shear modulus profile.