MS16.5 - Recent advances in vibration control of structures with isolation and/or energy dissipation devices

The active vibration absorber has been successfully used, both in laboratory and actual facilities, to mitigate the human-induced vibrations taking place in lively, low-damping structures such as long-span floors or pedestrian footbridges. Nonetheless, the dynamic behavior of the electrodynamic proof-mass actuators employed for this purpose may negatively affect the overall vibration attenuation features due to the interaction with the motion of the structure under optimization. In this paper, the utilization of dynamic inversion techniques to improve the force control of electrodynamic proof-mass actuators is presented. The main idea behind this approach is to find an approximate inverse model of the actuator dynamics which, upon implementation on a real-time controller, leads to an approximate cancellation of actuator dynamics, making it behave closer to an ideal one. The selected way of proceeding also accounts for the actuator-structure interaction phenomenon. This approach may be employed to improve the performance of any force based vibration control algorithm. Herein, the dynamic inversion techniques are applied to the well-known Direct Velocity Feedback algorithm which aims at emulating the behavior of a dashpot connected between the control point and the ground in its simplest version. The goodness of the proposed procedure has been assessed both by numerical simulations and experimental tests performed over a composite material pedestrian footbridge existing at the School of Civil Engineering of the Technical University of Madrid. The test results show that the dynamic inversion approach improves the force tracking of the proof-mass actuator to a great extent, therefore yielding better attenuation results that those achieved with the classical Direct Velocity Feedback scheme.

The Reduced Column Section (RCS) approach is a design approach proposed by the Authors to redesign the connection between the wind tower and its foundation. The proposed segment of hourglass shape is a passive vibration-control device that combines the advantages of several approaches used in seismic engineering, such as isolation, energy dissipation and the “rocking approach" design developed for shallow foundations. The proposed device can be designed to modify the first natural frequency of the wind turbine and to localize the maximum stresses onto the device, resulting in the dynamic protection of the wind tower and its foundation. Analytical formulas to design the proposed RCS device are established. The benefits of the proposed device are assessed on a real onshore wind turbine located in Italy. The wind turbine has been monitored to derive its modal properties and record the maximum accelerations induced by the wind. Real registrations have been used to verify a numerical 3D-finite element model, created for performing seismic and dynamic analyses. Direct integration analysis with spectrum-compatible real earthquakes and an incremental dynamic analysis are conducted to evaluate the dynamic mitigation induced by the proposed RCS device. Soil-structure interaction effects are also considered. This study shows that the proposed device can efficiently mitigate the effective stresses on the wind tower wall by up to 60% compared to the stresses computed on the existing structure.

Recently, a novel Sliding Keys on Inclined Deflecting-cantilever (SKID) device was proposed for application with Post-Tensioned (PT) frames. The SKID device has a triangular-shaped hysteretic curve; thus, it can provide hysteretic damping without an activation threshold in the PT frame. The properties of the device have been theoretically investigated and physically demonstrated. In this paper, the force-deformation relationship of the PT frame with the SKID device (the PT-SKID frame) is theoretically derived. The PT-SKID frame has a triangular flag-shaped hysteretic curve with full self-centring capability. A numerical model of a one-storey one-bay PT-SKID frame is built in OpenSees and benchmarked by the analytical equations. The model is used to investigate the dynamic characteristics of the PT-SKID frames by generating frequency response functions (FRFs) from sin-sweep excitations. More than 700 PT frame configurations with different SKID devices are numerically tested. The influence of SKID parameters on the seismic response of PT-SKID frames is highlighted. The results indicate that: (1) the PT-SKID frames show the same typical dynamic characteristics of nonlinear systems: their FRFs include two amplitude branches enveloping a coexisting solution region, but the SKID device considerably reduces the range of coexisting solutions; (2) the SKID device with larger loading stiffness and friction coefficient, and a smaller slope angle leads to a smaller seismic response amplitude.