Vibration control of structures under environmental loading

The present paper illustrates preliminary results of the project TELLUS STABILITA, an ongoing three-year project funded by the Italian Ministry of Research focusing on modern technologies to mitigate the structural damage caused by environmental dynamic loading. Innovative schemes for vibration control of civil structures have been assessed both analytically and experimentally. Two scaled steel multi-storey (2- and 4-storeys) frames were designed according to modern codes of practice for seismic and wind loads, respectively. Dynamic properties, i.e. modes of vibrations, natural frequencies, modal damping and generalized masses, of the sample structures were obtained by means of identification tests carried out with shaking tables. Such properties were used to calibrate refined finite element models used to simulate the response of the sample structures. Two different innovative devices were utilized to control the dynamic response of the sample steel frames. A friction-damper employing piezoelectric actuation was designed for the two-storey frame. A reduced model of the friction-damper was assembled and tested under both static and dynamic loads. The results of the experimental tests were used to validate the numerical models utilized for the design of the damper and for setting-up the layout of the full scale device. Magneto-rheological fluid dampers were employed for the 5-storey sample frame. Commercial type dampers were selected to control the vibrations of the frame; nevertheless, it was necessary to optimize such devices to achieve the structural performance target. A number of static and dynamic tests were conducted on magneto-rheological fluid dampers to validate the control performance estimated via numerical algorithms. The most suitable location of the dampers along the height of the sample frame was identified by using advanced genetic algorithms and modal parameters. Extensive numerical analyses were carried out on the frames equipped with the friction damper and magneto-rheological devices. Those devices were found very effective in reducing the lateral drifts and accelerations of the sample frames. Procedures to test the dynamic properties of structural systems with innovative vibration control devices are also outlined and the results of the performed tests on the 2- and 4-storey frames discussed. Three full-scale tests are going to be performed on RC multi-storey frames for buildings. These frames are typical structures designed for gravity loads only; they have been retrofitted with buckling restrained braces. The systems will be subjected to reversal loads at increasing displacement amplitudes to identify the progressive collapse of the sample structural systems. These tests are carried out on site, thus also accounting for soil-structure-interaction.