GNGTS 2017 - 36° Convegno Nazionale

GNGTS 2017 S essione 2.2 325 FEM ANALYSIS FOR THE SEISMIC RISK MITIGATION OF A SCHOOL BUILDING IN CATANIA (ITALY) THROUGH A COUPLED SOIL-STRUCTURE SYSTEM APPROACH G. Abate, S. Corsico, S. Grasso, M.R. Massimino Department of Civil Engineering and Architecture, University of Catania, Italy Introduction. Seismic design of new structures, as well as retrofitting and/or improving of existing ones basically depend on local site effects and the dynamic interaction between the foundation soil and the structure. The accurate investigation on the structure and the surrounding soil is the first fundamental step for a realistic evaluation of the seismic performance of the coupled soil-structure system. The present paper deals with the dynamic behavior of a coupled soil-structure system, i.e. a school building in Catania, characterized by a high seismic hazard (Caruso et al. , 2016; Castelli et al. , 2016), highlighting the important role of the soil non-linearity. The case history. This paper deals with the evaluation of the seismic input, which could hit the Nazario Sauro school in Catania. The building was designed and built in the period between 1971 and 1975. It is made by reinforced concrete frames with isolated footings located at different levels. The building and its subsoil was subjected to recent investigations in the framework of the Project POR-FESR Sicilia 2007-2013 finalized to the reduction of the seismic risk in the eastern Sicily. Geological and geotechnical characterization of the foundation soil. Recently, a deep geotechnical investigation survey was performed in the framework of the Project POR-FESR Sicilia 2007-2013 finalized to the reduction of the seismic risk in the eastern Sicily. The soil modeling has been based on this geotechnical characterization. Two boreholes S1 and S2 were carried out to a depth of 40 meters and 30 meters, respectively, from ground level. By the two boreholes a litho-stratigraphic section that involves the entire school building was achieved and reported in figure 1. Moreover, two seismic dilatometer tests were performed in the borehole S1, called SDMT 2a and SDMT 2b, from ground level to a depth of 17.5 m and 29.5 m, respectively. From the Vs profile, it is possible to affirm that the foundation soil is of type E according to the Italian technical code (NTC, 2008). Inside the analyzed area, a microtremor survey (HVSR test) was also conducted to check the seismic properties of the soil. By these tests, the fundamental frequency of the soil foundation is evaluated approximately equal to 4 Hz. More detailed information was obtained thanks to the following laboratory tests: grain size determination, simple shear tests, uniaxial compression tests. No resonant column test were performed for the Nazario Sauro school site; so, the G-γ and D-γ curves have been hypothesized, with reference to well-known sites characterized by similar nature, grain size and mechanical characteristics of the Nazario Sauro school site. Tab. 1 shown the geotechnical properties of the soil foundation. Input and seismicity of the area. Six synthetic accelerograms are adopted at the base of the model, conventionally located at 30 m from the ground level, assuming the source to be along the Hyblean-Maltese fault (Grasso et al. , 2005). Moreover, one accelerogram recorded during the 1990 earthquake at the Sortino station is used. The synthetic seismograms has been obtained by generating the seismic ground motion scenario (1693 earthquake), characterized by Tab. 1 - Geotechnical properties of the soil foundation. Soil Depth Vs E ν γ c’ φ [°] Type [m] [m/s] [MPa] [kN/m 3 ] [kN/m 2 ] (NTC08) Sand and volcanic debris 0-14 400 794.17 0.30 20.29 18 37 E basaltic rock 14-24 1200 8300 0.25 23.56 20 37 Sand and volcanic debris 24-30 800 3421 0.30 21.85 30 37