Repeatable dynamic release tests on a base-isolated building

The main activities and the relevant results of an experimental program aim ed at evaluating the dynamic characteristics of a large seismically isolate d building axe described. The building is situated in Potenza (Italy) and i s the largest of five seismically isolated blocks of the University of Basi licata. Cyclic shear tests on scaled isolators and some small amplitude fre e vibration tests were preliminarily carried out. The latter ones were aime d at getting a preliminary linear characterisation of the structure. Finall y, many in situ release tests on the isolated structure were carried out, u sing a mechanical device purposely designed to statically move the building and then suddenly release it, thus making it vibrate freely. The variation s of the dynamic characteristics of the system while the oscillation amplit ude decreases have been evaluated by using the "Short Time Fourier Transfor m (STFT)". The results were elaborated in terms of stiffness and equivalent damping and compared to the results of the laboratory tests on scaled isol ators, finding an excellent agreement.