MS16.4 - Recent advances in vibration control of structures with isolation and/or energy dissipation devices

Locally resonant metamaterials (LRMs), with periodic elements that exhibit local resonance, have been recently investigated by numerous researchers as a means to pursue vibration atten-uation and wave manipulation. These structures are able to generate bandgaps in specific fre-quency ranges depending on their mass, stiffness and geometrical characteristics; however, they present certain limitations when bandgaps in the low-frequency domain are sought, since they require heavy oscillating masses. This research work harnesses the potency of a novel dy-namic directional amplifier, namely the DDA, that is introduced as a means to artificially in-crease the inertia of an oscillating mass. The DDA is realized by imposing kinematic con-straints to the degrees of freedom (DoFs) of the oscillator, hence inertia is increased by cou-pling the horizontal and vertical motion and forcing the model to move along a circumference. Herein, the DDA is applied on the resonating mass of a scaled LRM structure, assembled using LEGO® components. Experimental and analytical calculations are subsequently undertaken to investigate the dynamic properties of this DDA-enhanced metamaterial. Results showcase the low-frequency attenuation properties of the structure and serve as a proof of concept of the mechanism.

Recently, researchers have proposed an innovative negative stiffness-based vibration control concept, namely the KDamper absorber. The envisaged mechanism comprises a combination of appropriate stiffness, damping and mass elements, including a negative stiffness element. Previous studies have formulated the mathematical framework of the system, as well as design and optimization algorithms. These take into consideration the application of interest and geo-metrical and manufacturing limitations, regarding the vibration control components, including the realization of the negative stiffness mechanics. The KDamper has been numerically and analytically implemented as a vibration control concept for seismic protection of bridges, buildings as well as wind turbines and noise mitigation panels, while results indicated its beneficial effect towards vibration attenuation. For the first time , an experimental set-up of the proposed mechanism is designed by adopting an optimization procedure and tested under horizontal harmonic and seismic shaking. Results highlight the vibration control properties of the pro-posed system and validate previous numerical and analytical studies. The experimental device serves as a proof of concept of the KDamper absorber and showcases its advantages as well as application limitations that should be considered in future research.

In the context of hybrid passive control, the effectiveness of the Tuned Liquid Column Damper (TLCD) has been well-established for the seismic vibration control of base-isolated (BI) systems both numerically and experimentally. In contrast to the previous studies on TLCDs, the present study explores the possibility of equipping a BI system with a sliding model of TLCD (STLCD), until now proposed just for the suppression of wind-induced vibration of fixed base structures. Specifically, the proposed STLCD consists of a U-shaped tank partially filled with water, mounted on a roller support and connected to the BI system by a springdashpot system. Firstly, an analytical study is developed to analyze the optimal control performance of this device with focus on the reduction of displacements and accelerations of the BI system. The goodness of the theoretical results is assessed via vast shaking table testing campaign undertaken in the Laboratory of Experimental Dynamics of the University of Palermo, Italy. In implementing the experimental tests, a small-scale model of a single-degree-of-freedom (SDOF) BI structure with the STLCD is constructed and the effectiveness of the proposed combined control strategy is experimentally evaluated. Finally, comparisons with traditional TLCDs and TMDs are presented and the influence of mass ratio, damping ratio and structural frequency on control efficiency is discussed.

Seismic isolation, which at first used only for special applications, is nowadays gaining increased popularity in the field of protecting existing structures from seismic loading and it even constitutes one of the standard methods for seismic upgrade. This method can be achieved with various devices, with elastomeric bearings being the most commonly used. The main drawback of these devices is that they permit large horizontal displacements in every direction. An effective approach to mitigate these responses under earthquake events is an advanced negative stiffness damped system, termed as KDamper, which its dynamic performance has been demonstrated in recent studies. In this paper, an extension of the initial device, the EKDamper, is presented. The structural form and its negative stiffness mechanism are introduced with special emphasis placed on its dimensioning and its indicative design. More specifically, for a reference SDOF system with a mass of 1tn, the components of the EKDamper are realistically designed and a detailed assembly of the device is presented. The final model proves that the proposed device is realistic and within reasonable technological capabilities. To verify and evaluate the feasibility of this device, a numerical case study is also conducted on the SDOF system subjected to 30 artificial accelerograms. The results and the comparison with conventional and high damped elastomeric isolators demonstrate that the EKDamper can reduce both structural displacements and accelerations, proving its effectiveness and superiority over the other isolation techniques.