PSI - Issue 44

R. Siano et al. / Procedia Structural Integrity 44 (2023) 1038–1044 R. Siano, A. Fatnassi, F. V. De Maio, P. Basso, M. Cademartori / Structural Integrity Procedia 00 (2022) 000–000

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1. Introduction A large portion of the building heritage in Italy has not been built to resist the seismic shaking caused by earthquakes. According to main international codes, seismic assessment of building structures starts from a knowledge process which significantly influences the following analysis. Such process includes geometry of structural elements, reinforcement details and mechanical characteristics of materials. The latter aspect can limit the knowledge level, thus influencing the applicability of more advanced analysis methodologies, due to the disadvantages of destructive tests. With regards to a large public buildings stock, characterized by strategic uses and located in Italy, the paper describes the procedure applied to perform seismic vulnerability analyses starting from the description of the geometry, material characteristics and main structural details of the buildings. Then the definition of the buildings seismic vulnerability and structural criticalities was performed and assumed as starting configuration for the design of the retrofit scenarios. The study was conducted by means of numerical models whose level of details was calibrated as a function of the available documentations and data. Linear dynamic and non-linear analyses were performed to study the seismic performance of each building and identify the structural criticalities. Different retrofit scenarios were at last defined to improve the seismic performance of the buildings up to the 100% of the structural safety with reference to the performance levels of Life Safety (LS) and Immediate Occupancy (IO). Finally, simplified cost-benefit analyses provided indications for an optimization of the economic investment as a function of the effective improvement in the seismic performances determined by the retrofit measures. 2. Description of the buildings sample The buildings sample is located in Italy, in regions highly susceptible to natural disasters and characterized by a frequent incidence of earthquakes from low to high intensity. The analyzed structures can be divided in 4 groups according to their in plan architectural configurations. Based on the definition of “regularity in plan” and “regularity in elevation” provided by NTC 2018, the architectural configurations examined can be defined regular and irregular. A brief description of the building stock is provided in the following: - Group 1: “L” type configuration consists of a single structural body with three stories, irregular in plan and regular in elevation; - Group 2: rectangular type configuration with1-3 stories, regular in plan and in elevation; - Group 3: trapezoidal configuration with 1-2 stories, irregular in plan and in elevation; - Group 4: “T” type configuration with six stories, regular in plan and irregular in elevation. The current Italian building code (NTC 2018) requires engineers to design earthquake-resistant structures in compliance with predefined performance thresholds, or limit states (CS.LL.PP., 2008, 2018), for ground-motion intensities that have a specified exceedance probability in a given time interval at the building site. The mentioned standards were assumed as main reference for performing all the structural analysis and design the retrofit scenarios. 3. Data collection The knowledge of the materials’ mechanical properties of constituent materials (concrete and steel) is a preliminary and important step in the seismic vulnerability assessment of existing buildings. In order to achieve this goal, destructive and non-destructive test methods have been adopted, either alone or combined. Such estimation has been complemented by default values in accordance with standards reference available at the time of construction. The characterization of the structural materials of an existing structure is closely linked to the definition of the level of knowledge that can be achieved. Type and number of in situ test depend on the level of knowledge: Limited (LC1), Adequate (LC2) and Careful (LC3). In compliance with the Italian code NTC 2018 the level of knowledge has been defined as a function of the following parameters: