GNGTS 2016 - Atti del 35° Convegno Nazionale

GNGTS 2016 S essione 2.3 421 Seismic response of a monitored R.C. building affected by the August 24, 2016 earthquake: comparison between experimental data and SMAV model results G. Acunzo 1 , N. Fiorini 1 , D. Spina 2 1 National Research Centre - IGAG, Rome, Italy 2 Dep. of Civil Protection, Rome, Italy Introduction. Agood assessment of buildings’ behaviour after a medium-strong earthquake is a fundamental feature in the mitigation of seismic risk, because its relevance in giving useful tools for planning action needed for improving the vulnerability of existing structures. In this scenario SMAV (Seismic Model from Ambient Vibrations) methodology has been developed as a methodology able to evaluate the serviceability condition of existing buildings, using the inter-story drift ratio as reference parameter. The methodology has been initially developed for strategic buildings (Mori et al. , 2015), but has subsequently been extended to ordinary and monumental buildings (Fiorini et al. , 2015). The proposed work aims to describe an application of SMAVmethodology to a real building belonging to the Seismic Observatory of the Structures (OSS), in order to show the reliability of the methodology through a comparison of its results with the experimental seismic ones, recorded during the earthquake of August 24, 2016 (1:36:32 UTC) having a magnitude 6.0. The SMAVmethodology. SMAV methodology is a procedure based on an equivalent linear model (SMAV model) built using Operational Modal Analysis (OMA) results (Peeters et al., 2001), which is able to predict the seismic response of existing buildings up to a weak or moderate level of damage. A response spectrum as well as a recorded time history can be used as seismic input. The nonlinearity introduced by a real earthquake is modelled by reducing the natural frequencies, identified from ambient vibrations, according to probabilistic curves, reproducing the frequency vs roof drift dependency. The building floors are modelled through a certain amount of rigid polygons in which the masses are squeezed in the mass centroid. The floor masses are calculated on the basis of a simplified analysis of the structural loads, allowing to build the mass matrix required for computing the modal participating mass ratios (Acunzo et al. , 2016). In order to correctly characterise the floors, at least two points of measurements for each rigid polygon are required. SMAV can compute the accelerations and the displacements caused by the selected earthquake at any points of the building, also if not measured, giving reliable results until the threshold of severe damage in the building. Case of study: secondary school of Norcia (PG). The analysed case study is a primary school located in Norcia (PG) which belongs to the Seismic Observatory of Structure (Spina et al. , 2011), the Italian network of the permanently seismic monitored structures. The school is a three story R.C. building, with a rectangular floor plan. The sensors system configuration is reported in Fig. 1, where channel 1-2-3 are external sensor placed near the building in order to acquire the ground motion, whereas the other channels are fixed directly to the structure for measuring its seismic response. Due to the floor plan regularity SMAV model has been implemented considering only a single rigid polygon for each floor. In order to meet the regular distribution of measuring points required by the SMAV methodology, only the in-plane degrees of freedom highlighted with black dots in Fig. 1 are considered. For the considered structure, ambient vibrations recorded before the seismic event (3600 s, with sampling frequency of 200 Hz) have been elaborated for modal parameters estimation. The first three modal frequencies and mode shapes have been identified, obtaining two translational modes (4.302 and 4.917, in x and y direction respectively) and a rotational one (6.548 Hz). The SMAV model has been implemented on the basis of the available geometrical and structural information, obtaining the modal mass ratios shown in Tab. 1.