Agathoklis Giaralis | City, University of London (original) (raw)

Papers by Agathoklis Giaralis

The tuned-mass-damper-inerter (TMDI) is a linear passive dynamic vibration absorber for the seism... more The tuned-mass-damper-inerter (TMDI) is a linear passive dynamic vibration absorber for the seismic protection of buildings. It couples the tuned-mass-damper (TMD), comprising an oscillatory secondary mass installed at top building floor via a spring and a damper, with an inerter device developing acceleration-dependent resisting force. In the TMDI configuration, the inerter connects the secondary mass to a lower than the top floor and recent work established that the more floors the inerter spans the more effective the TMDI becomes over the TMD. Recognizing that spanning more than one floors may not be practically appealing in low-to-midrise buildings due to increased space utilization requirements, this paper examines the seismic performance of TMDI-equipped buildings with inerter spanning only one (the top) floor upon softening the top floor. Numerical results pertaining to a linear 10-storey shear frame structure demonstrate that TMDIs spanning one floor ("-1" TMDI) are more effective than TMDIs spanning two floors ("-2" TMDI) upon top-floor softening by 80%. This is shown by considering "-1" and "-2" TMDIs with wide range of inertial properties optimally tuned to minimize penultimate floor deflection variance for coloured stationary excitation compatible with the Eurocode 8 response spectrum. Moreover, improved performance of "-1" TMDI with top floor softening compared to "-2" TMDI by 85% or more is found in terms of root-mean-square and peak values for penultimate floor deflection, storey drift, and acceleration by considering response history analyses to optimal TMDI-equipped structures for a suite of 7 ground motions spectrally matched to Eurocode 8 response spectrum. It is concluded that the herein proposed structural modification (top-floor softening) may improve significantly the seismic performance of TMDI-equipped building structures.

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XI International Conference on Structural Dynamics, 2020

In this paper the tuned mass-damper-inerter (TMDI) is considered for passive vibration control an... more In this paper the tuned mass-damper-inerter (TMDI) is considered for passive vibration control and energy harvesting in harmonically excited structures. The TMDI couples the classical tuned mass-damper (TMD) with a grounded inerter: a two-terminal linear device resisting the relative acceleration of its terminals by a constant of proportionality termed inertance. In this manner, the TMD is endowed with additional inertia, beyond the one offered by the attached mass, without any substantial increase to the overall weight. Closed-form analytical expressions for optimal TMDI parameters, stiffness and damping, given attached mass and inertance are derived by application of Den Hartog’s tuning approach to suppress the response amplitude of force and base-acceleration excited single-degree-of-freedom structures. It is analytically shown that the TMDI is more effective from a same mass/weight TMD to suppress vibrations close to the natural frequency of the uncontrolled structure, while it ...

The recently proposed by the first two authors Vibrating Barrier (ViBa) can be interpreted as a l... more The recently proposed by the first two authors Vibrating Barrier (ViBa) can be interpreted as a large-scale linear mass-damper unit buried in the ground and tuned/designed to protect surrounding structures without being directly in contact to them through a structure-soil-structure interaction mechanism. Previous research demonstrated that ViBa achieves significant structural response reduction at a cost of excessive required vibrating mass of the order of the mass of the structure sought to protect. To this end, this paper considers coupling ViBa with a grounded inerter device acting as a mass amplifier to reduce the required mass/weight of ViBa in suppressing seismically induced vibrations in structures amenable to modelling as single-degree-of freedom (SDOF) damped oscillators. The equations of motion and transfer function of a grounded inerter ViBa (IViBa) fused with a SDOF structure are derived. Two different optimal design approaches are discussed to tune the IViBa to minimize...

Passive tuned mass-dampers (TMDs) are widely considered for suppressing large-amplitude lowfreque... more Passive tuned mass-dampers (TMDs) are widely considered for suppressing large-amplitude lowfrequency oscillations in relatively large-scale dynamically excited primary structures as well as for generating energy by such oscillations [1]. They consist of a secondary vibrating mass attached to the oscillating primary structure through stiffeners and dampers designed to minimise primary structure motion. Energy generation is achieved by using electromagnetic motors (EMs) with energy harvesting capabilities as damping devices. Marian and Giaralis [2] demonstrated analytically that by supporting the secondary TMD mass through an ideal inerter (i.e., a device resisting relative acceleration) to a different location from the one that the TMD mass is attached to the host structure enhances significantly the TMD motion control efficiency. Further, it was shown in [3,4] that improved vibration control and energy harvesting is achieved by employing EMs in TMDs with secondary mass supported to ...

Structural Control and Health Monitoring, 2021

The tuned mass damper inerter (TMDI) is a linear passive dynamic vibration absorber widely consid... more The tuned mass damper inerter (TMDI) is a linear passive dynamic vibration absorber widely considered in the literature to mitigate the motion of dynamically excited primary structures. Previous studies focused on optimal TMDI tuning approaches and connectivity arrangements to improve motion control efficiency for some given primary structure. This paper investigates the influence of the elastic and mass properties of the primary structure to the TMDI motion control performance. This is pursued through an innovative parametric study involving a wide range of tapered beam-like cantilevered primary structures with different continuously varying flexural rigidity and mass distributions equipped with TMDIs optimally tuned for resonant harmonic and for white noise excitations. Optimal TMDI tuning and performance assessment are expedited through a novel simplified two-degree-of-freedom dynamic model, which accounts for the properties of the primary structure. It is found that reduced free-end displacement and TMDI stroke are achieved for primary structures in which the ratio of flexural rigidity over mass decreases faster with height resulting in vibration modal shapes with higher convexity. The latter is quantified though the average modal curvature shown to be well correlated with TMDI motion control improvement. It is concluded that judicial shaping

ASCE-ASME J Risk and Uncert in Engrg Sys Part B Mech Engrg, 2021

This paper examines the performance of a regenerative dynamic vibration absorber, dubbed energy h... more This paper examines the performance of a regenerative dynamic vibration absorber, dubbed energy harvesting-enabled tuned mass-damper-inerter (EH-TMDI), for simultaneous vibration suppression and energy harvesting in white-noise-excited damped linear primary structures. Both single-degree-of-freedom (SDOF) structures under force and base excitations and multi-degrees-of-freedom (MDOF) structures under correlated random forces are studied. The EH-TMDI includes an electromagnetic motor (EM), assumed to behave as a shunt damper, sandwiched between a secondary mass and an inerter element connected in series. The latter element resists relative acceleration at its ends through a constant termed inertance known to be readily scalable in actual inerter device implementations. In this regard, attention is herein focused on gauging the available energy for harvesting at the EM and the displacement variance of the primary structure as the inertance increases through comprehensive parametric in...

Engineering Structures, 2018

Risk-informed optimization of the tuned mass-damper-inerter (TMDI) for the seismic protection of ... more Risk-informed optimization of the tuned mass-damper-inerter (TMDI) for the seismic protection of multi-storey building structures. Engineering Structures, 177, pp. 836-850.

Earthquakes and Structures, 2012

In this paper a novel non-iterative approach is proposed to address the problem of deriving non-s... more In this paper a novel non-iterative approach is proposed to address the problem of deriving non-stationary stochastic processes which are compatible in the mean sense with a given (target) response (uniform hazard) spectrum (UHS) as commonly desired in the aseismic structural design regulated by contemporary codes of practice. This is accomplished by solving a standard over-determined minimization problem in conjunction with appropriate median peak factors. These factors are determined by a plethora of reported new Monte Carlo studies which on their own possess considerable stochastic dynamics merit. In the proposed approach, generation and treatment of samples of the processes individually on a deterministic basis is not required as is the case with the various approaches found in the literature addressing the herein considered task. The applicability and usefulness of the approach is demonstrated by furnishing extensive numerical data associated with the elastic design UHS of the current European (EC8) and the Chinese (GB 50011) aseismic code provisions. Purposely, simple and thus attractive from a practical viewpoint, uniformly modulated processes assuming either the Kanai-Tajimi (K-T) or the Clough-Penzien (C-P) spectral form are employed. The Monte Carlo studies yield damping and duration dependent median peak factor spectra, given in a polynomial form, associated with the first passage problem for UHS compatible K-T and C-P uniformly modulated stochastic processes. Hopefully, the herein derived stochastic processes and median peak factor spectra can be used to facilitate the aseismic design of structures regulated by contemporary code provisions in a Monte Carlo simulationbased or stochastic dynamics-based context of analysis.

SPIE Proceedings, 2016

Use of inerter devices for weight reduction of tuned mass-dampers for seismic protection of multi... more Use of inerter devices for weight reduction of tuned mass-dampers for seismic protection of multi-storey buildings: the tuned mass-damper-interter (TMDI).

International Journal of Sustainable Materials and Structural Systems, 2015

The relative wavelet entropy (RWE) is a commonly considered in the literature damage-sensitive in... more The relative wavelet entropy (RWE) is a commonly considered in the literature damage-sensitive index derived by wavelet transforming linear response acceleration signals from healthy/reference and damaged states of a given structure subject to broadband excitation. Herein, four different energypreserving wavelet analysis filter banks are employed to compute the RWE for two benchmark structures via algorithms that may efficiently run on-board wireless sensors for decentralised structural health monitoring. It is shown that filter banks of wavelet bases compactly supported in the frequency domain are advantageous since they achieve enhanced frequency selectivity among scales and, therefore, the scale/frequency dependent contributors to the RWE become easier to interpret. Moreover, it is demonstrated that filter banks with large constant Q values (i.e., ratio of effective frequency over effective bandwidth) are better qualified to capture damage information associated with high frequencies, while non-constant Q analysis filter banks are most effective for RWE-based stationary damage detection.

Safety, Reliability, Risk and Life-Cycle Performance of Structures and Infrastructures, 2014

Proceedings of the 6th International Conference on Computational Stochastic Mechanics(CSM-6), 2011

In this paper the problem of deriving non-stationary stochastic processes defined by a parametric... more In this paper the problem of deriving non-stationary stochastic processes defined by a parametric evolutionary power spectrum (EPS) compatible with a given (target) design spectrum is addressed. An inverse stochastic dynamics problem is formulated and solved in a least-square sense to determine the requisite EPS. This involves the incorporation of a "peak factor" which is used to relate statistically the target spectrum to the EPS. Special attention is focused on deriving design spectrum compatible processes of specific "effective duration" as commonly defined in the field of earthquake engineering. Specifically, the design spectrum of the Chinese GB 50011 aseismic code is considered as a paradigm of a target spectrum. Comprehensive Monte Carlo analyses are undertaken to numerically estimate GB 50011-compatible median peak factor spectra, given in a polynomial form. These spectra are associated with the first passage problem for linear oscillators excited by uniformly modulated colored non-stationary processes of various durations. The derived peak factor spectra used in conjunction with the herein adopted stochastic formulation yield an excellent level of agreement between the GB 50011 spectrum and the ensemble average response spectra of simulated EPS-compatible accelerograms of different effective durations. Additional numerical results pertaining to the design spectra of the European EC8 code and the GB 50011 code are included to show how the behavior of the target spectrum in the range of long periods affects the choice of the assumed spectral form of the EPS. It is envisioned that the herein derived stochastic processes can be used to facilitate the aseismic design of structures regulated by contemporary code provisions in a Monte Carlo-based or random vibration-based context of analysis.

Geotechnical, Geological and Earthquake Engineering, 2015

This chapter delineates all the required computational and logical steps involved in the analysis... more This chapter delineates all the required computational and logical steps involved in the analysis stage of seismic design of ordinary reinforced concrete (r/c) buildings according to Eurocode 8 (EC8) by means of detailed self-contained flowcharts and pertinent comments. Special focus is given to verification checks for structural regularity in plan and elevation, on the classification of building structures based on torsional sensitivity, on the determination of the maximum allowed behavior factor by EC8, and on the selection and implementation of the two equivalent linear methods of analysis considered by EC8, namely the lateral force method and the modal response spectrum method. Furthermore, additional flowcharts and comments are included for the implementation of EC8-prescribed post-analysis verification checks based on deformations, that is, verification check of second-order effects via the interstorey drift sensitivity coefficient and verification check for maximum interstorey drift to ensure that damage limitation requirements of EC8 are met. Practical recommendations expediting the implementation of EC8-compliant analysis of ordinary r/c buildings are provided. Finally, the required detailing and verification checks for the design of r/c structural members according to Eurocode 2 and Eurocode 8 are presented in the form of self-explanatory flowcharts, along with the special requirements for the determination of seismic design bending moment and shear force diagrams.

Vulnerability, Uncertainty, and Risk, 2014

A novel scaling algorithm for ground motion accelerograms (GMs) is proposed in support of increme... more A novel scaling algorithm for ground motion accelerograms (GMs) is proposed in support of incremental dynamic analysis used to establish dependable statistical relationships between scalable intensity measures (IMs) and engineering demand parameters (EDPs) within a performance based earthquake engineering framework. Specifically, an iterative harmonic wavelet based scheme is employed to accomplish "surgical" changes to the spectral shape of suites of GMs to span various pre-defined levels of the spectral acceleration at the structural fundamental natural period, the most widely adopted IM. Since the target IM values may not be accomplished precisely by the local spectral modifications, a second step involving global uniform GM scaling is further considered. The proposed algorithm requires significantly smaller global (amplitude) scaling factors compared to the currently used scaling approach in which no initial local GM modification is undertaken. A numerical application of the proposed algorithm to elastoplastic structural systems shows the extent to which spectral shape may influence the displacement response of yielding structures and explains the conservative bias introduced by uniform global scaling.

In this paper a compressive sensing (CS), sub-Nyquist, non-uniform deterministic sampling techniq... more In this paper a compressive sensing (CS), sub-Nyquist, non-uniform deterministic sampling technique is considered in conjunction with a computationally efficient power spectrum estimation approach for frequency domain output-only system identification of linear white noise excited structural systems. The adopted CS sensing spectral estimation approach assumes multi-band input random signals/stochastic processes without posing any signal sparsity requirements and therefore it is applicable to linear structures with arbitrary number of degrees of freedom and level of damping. Further, it applies directly to the sub-Nyquist (CS) measurements and, thus, it bypasses the computationally demanding signal reconstruction step from CS measurements. Numerical results pertaining to the acceleration response of a damped structure with closely-spaced natural frequencies are provided to demonstrate the effectiveness of the considered approach to provide reliable estimates of natural frequencies by means of the standard frequency domain peak-picking algorithm of operational modal analysis using up to 90% fewer measurements compared to the Nyquist rate sampled data. It is envisioned that this study will further familiarize the structural dynamics community with the potential of CS-based techniques for vibration-based structural health monitoring and condition assessment of engineering structures.