Ambient modal identification applied to a school building in Girona (Spain)

Abstract

The main results of the operational modal analysis of a school building are shown. The building has a four-stories framed-reinforced-concrete structure and it was instrumented with 7 triaxial accelerometers, recording along eight days. Also, specific remote measurements were made with an interferometric radar. The purpose was: i) to monitor periods of activity-inactivity, ii) to identify modal frequencies; iii) to validate a numerical model of the structure and iv) to analyse the feasibility of the radar for remote operational modal analysis. This research allowed us: 1) to quantify clear variations in noise intensity, matching the school activities, 2) to identify the fundamental modes and natural frequencies, which were of 4.4 Hz and 5.4 Hz, in the longitudinal and transversal directions, respectively, 3) to observe slight variations of modal frequencies throughout the day, attributed to the loading/unloading of the building, and at night, attributed to variations in temperature; 4) to confirm the usefulness and suitability of frequency experimental measurements to improve the quality and reliability of building numerical models and, 5) to evaluate the potential of radar measurements for operational modal analysis; radar operates better in tall and flexible buildings, than in rigid ones.