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Introduction

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September 1990 - present

## Publications

Publications (231)

In this work, we examine the influence of a crack in the span of a beam as it is being
traversed by a point force with constant velocity. This problem presents two types of
discontinuities: one spatial, where the crack is modelled as a discontinuity in the slope of the
deflection curve of the beam, and a temporal one, with the former derived as...

In this work, we investigate analytical solutions for beams with sizeable mass attachments under externally induced base motions. Specifically, a point arises because the boundary conditions involving the presence of a large mass attached to the beam complicates the underlying eigenvalue problem and a straightforward separation of variables in the...

This work reports on the influence that mass attachments and soft soil support conditions have on the vibratory motion of flexible pylons with non-uniform cross-section, both for axial and flexural vibrations induced by ground motion. The use of such structures is pervasive, both in civil and in mechanical engineering. In particular, the tapered py...

In this work, we investigate the transient response of a model bridge traversed by a heavy mass moving with constant velocity. Two response regimes are identified, namely forced vibrations followed by free vibrations as the moving mass goes past the far support of the simply supported span of the bridge. Despite this being a classical problem in st...

The influence of passive mass dampers and base isolators on the vibratory motion of flexible beams with uniform cross-section, viewed as a special case of the non-uniform one, is examined herein for both axial and flexural vibrations. Use of such beams is widespread, both in a mechanical engineering setup (e.g., wind turbines, aircraft blades) as w...

In this work, we report on field measurements of a flexible pylon under the influence of external loads for the purpose of developing a structural health monitoring system capable of operating continuously and in remote mode. The basic idea behind such a system is to use the minimum number of sensors, enhanced with structural analysis capabilities,...

Operational modal analysis (OMA) methods are frequently applied for obtaining information on structural dynamic parameters, such as natural frequencies and mode shapes. While synchronization between acceleration response data sets used in OMA is not a prerequisite for estimating natural frequencies, synchronization discrepancies may lead to non-neg...

Αντικείμενο της παρούσας εργασίας αποτέλεσε η διερεύνηση της απόκρισης του ενοργανωμένου κτιρίου Ο/Σ του Δημαρχείου της Λευκάδας κατά τη διάρκεια δύο σεισμών της Κεφαλονιάς (23-5-2013, μέγεθος 4.8 και 24-11-2015, μέγεθος 4.3), λαμβάνοντας υπόψη το φαινόμενο της αλληλεπίδρασης εδάφους-κατασκευής, με σκοπό την αποτίμηση της ορθότητας διαφόρων παραδοχ...

In 2004, two R/C residential buildings were retrofitted by using a hybrid base isolation system in Solarino, Sicily, and subsequently five free vibration tests were carried out in one of these buildings. The hybrid base isolation system combined high damping rubber bearings with low friction sliders. In terms of numerical modeling, a single-degree-...

Operational modal analysis (OMA) is frequently employed in structural health monitoring (SHM) for obtaining information on the dynamic properties, e.g. natural frequencies and mode shapes, of monitored structures. To extract accurate estimates of mode shapes, absolute synchronization between sets of acceleration response data collected from the mon...

The present work focuses on the response of pipelines traversing slopes under asynchronous acceleration time histories induced by earthquakes. To this end, nonlinear generalized mechanical models are developed and used in order to describe the soil-pipe interaction phenomena. More specifically, two basic types of models are used: the first one comp...

In this work, we extend a previously developed numerical model for the seismic response of a base isolation system comprising rubber dampers and friction sliders, to include stochastic energy measures. The said model is a trilinear, five-parameter hysteretic model in conjunction with a single-parameter Coulomb slider that has been calibrated using...

Historically, a number of major catastrophic earthquakes have resulted in a real loss of life and property worldwide. During the last decades, in particular, the overall exposure to seismic risk has increased not only due to the higher population density but also due to the more challenging construction methods and the multilayered connection betwe...

The aim of this study is to develop an efficient numerical technique using the non-hypersingular, traction boundary integral equation method (BIEM) for solving wave propagation problems in an anisotropic, viscoelastic plane with cracks. The methodology can be extended from the macro-scale with certain modifications to the nano-scale. Furthermore, t...

Numerical methods for the solution of dynamical problems in engineering go back to 1950. The most famous and widely-used time stepping algorithm was developed by Newmark in 1959. In the present study, for the first time, the Newmark algorithm is developed for the case of the trilinear hysteretic model, a model that was used to describe the shear be...

Two R/C residential buildings were retrofitted by using a hybrid base isolation system in Solarino, Sicily, in 2004 and subsequently five free vibration tests were carried out in one of these buildings. The hybrid base isolation system combined high damping rubber bearings with low friction teflon sliders. For numerical modeling purposes, a single-...

In this chapter, general remarks about the BIEM, fundamental solutions, and modern computational techniques for inhomogeneous 2D elastic domains
are discussed, together with applications to seismic wave propagation problems. More specifically, a closer look with scales of hundreds of km reveals the Earth is both strongly inhomogeneous with a sharp...

In this chapter, we continue our BIEM implementation to cover seismically induced anti-plane strain
wave motion in an inhomogeneous geological region
containing tunnels. This category of problems is best approached by developing the hybrid numerical techniques, in order to handle both the inhomogeneous medium and its discontinuities. More specifica...

In this chapter, we focus on the derivation of time-harmonic fundamental solutions for the general case of anisotropic, inhomogeneous continua under in-plane
and anti-plane conditions
in closed form using the Radon transform
. Of course, there are alternative methods such as algebraic transforms, Fourier transforms, and Hankel transforms, but the R...

In this chapter, we
continue our quest for the recovery of Green’s functions. More specifically, we focus on in-plane and anti-plane representations of the inhomogeneous in-depth half-plane. The reader will notice that it is possible to reuse fundamental solutions instead, but the traction-free boundary condition at the horizontal free surface will...

In this chapter, we examine a class of inhomogeneous half-plane dynamic problems and proceed to derive analytical ?plane-wave? solutions. More specifically, quadratic and exponential variations of the inhomogeneity in terms of the depth coordinate are considered for both the isotropic and the orthotropic half-plane, and wave motion in these media i...

This chapter presents the basic formulation for the elastodynamic field equations
and the ensuing BVPs for inhomogeneous 2D domains. Furthermore, this formulation is extended in domains with discrete heterogeneities, which includes cavities, inclusions, and cracks.

In this chapter, elastic wave
propagation
in a complex discrete inhomogeneous and heterogeneous geological media
is investigated. The new element here is that the medium under consideration is a two-phase material, namely a poroelastic continuum
. To simplify the representation, we replace the two-phase material by a single-phase one that exhibits...

The time-harmonic response of a multilayered soil deposit resting on the elastic half-plane
under the influence of incoming pressure and shear waves is numerically investigated by a hybrid boundary integral equation-plane wave decomposition method in this chapter. The multilayered deposit is finite-sized, with non-parallel layers
and contains free-...

This book presents what can be construed as high-performance computational tools based on the 2D BIEM for modelling seismic wave fields and local zones of dynamic stress concentration in both inhomogeneous and heterogeneous geological media

This work addresses the evaluation of the displacement field in an elastic matrix due to the presence of an embedded homogeneous inclusion under time-harmonic SH-wave loads. We consider the bond between the circular cylindrical inclusion and the surrounding matrix of infinite extent to be partly damaged in the circumferential direction. The materia...

A hybrid base isolation system was used to retrofit two residential buildings in Solarino, Sicily. Subsequently, five free vibration tests were carried out in one of these buildings to assess its functionality. The hybrid base isolation system combined high damping rubber bearings with low friction sliders. In terms of numerical modeling, a single-...

The purpose of this work is to study the effects of site conditions on the inelastic dynamic analysis of a reinforced concrete (R/C) bridge by simultaneously considering an analysis of the surrounding soil profile via the Boundary Element Method (BEM). The first step is to model seismic waves propagating through complex geological profiles and acco...

An energy approach is employed here for assessing model quality for dynamic soil-structure interaction (SSI) analysis. Concurrently, energy measures are introduced and calibrated as general indicators of structural response accuracy. More specifically, SSI models built at various abstraction levels are investigated according to various coupling sce...

We develop a boundary integral equation (BIE) method for the numerical simulation of seismic motions in geological media containing multiple cavities under anti-plane strain conditions. We consider a half-plane of heterogeneous structure subjected to either time-harmonic incident shear waves or to body waves radiating from a seismic point source. T...

This work focuses on the dynamic response of nuclear power plant mechanical subsystems (i.e., main cooling system, steam generators, emergency cooling injection tanks and piping) that are housed within the containment structure and are associated with power generation. More specifically, the numerical modeling procedure focuses on the internal R/C...

This work focuses on the dynamic response of nuclear power plant mechanical sub-systems (i.e., main cooling system, steam generators, emergency cooling injection tanks and piping) that are housed within the containment structure and are associated with power generation. More specifically, the numerical modeling procedure focuses on the internal R/C...

Current nuclear regulatory codes specify design considerations for extreme seismic scenarios, focusing primarily on the response of the containment structure of a nuclear power plant. However, in current state-of-practice and in most seismic regulations worldwide, the consideration of soil-structure interaction and potential development of geometri...

In
this chapter, elastic wave scattering
by cracks in inhomogeneous geological continua with quadratically or exponentially varying material parameters and under conditions of plane strain is studied. A restricted case of inhomogeneity is considered, where Poisson’s ratio is fixed at one-quarter, while both shear modulus and density profile vary al...

In this chapter, three basic models for SH wave propagation in inhomogeneous domains with exponential or quadratic variation in-depth are considered based on the theoretical developments given in Part I. Thus, numerical results are presented based on BIEM implementation of problems of engineering interest. Furthermore, numerical results are given f...

This book provides state of the art coverage of important current issues in the analysis, measurement, and monitoring of the dynamic response of infrastructure to environmental loads, including those induced by earthquake motion and differential soil settlement. The coverage is in five parts that address numerical methods in structural dynamics, so...

Current nuclear regulatory codes specify design considerations for extreme seismic scenarios, focusing primarily on the response of the containment structure of a nuclear power plant. However, in current state-of-practice and in most seismic regulations worldwide, the consideration of soil-structure interaction and potential development of geometri...

The best known model for numerically simulating the hysteretic behavior of
various structural components is the bilinear hysteretic system. There are two possible
mechanical formulations that correspond to the same bilinear model from a mathematical
viewpoint. The first one consists of a linear elastic spring connected in series with a parallel
sys...

High damping rubber bearings have been in use for seismic isolation of buildings worldwide for almost
30 years now. In the present work, a brief introduction to the process leading to their manufacturing is
first given. Next, a series of novel 1D mechanical models for high damping rubber bearings is proposed,
based on the combination of simple and...

High damping rubber bearings (HDRB) are the most commonly used base isolators in buildings and are often combined with other systems, such as sliding bearings. Their mechanical behaviour is highly nonlinear and dependent on a number of factors. At first, a physical process is suggested here to explain the empirical formula introduced by J.M. Kelly...

The assumption of strain-rate dependence in the rubber layers of high damping rubber bearing
(HDRB) isolators is necessary in order to best interpret experimental results on the transmission of motion
between upper and lower surfaces of these isolators. More specifically, the particular stress-relaxation
phenomenon over time observed in HRDB can be...

In this work, we suggest a physical process to explain the empirical formula introduced by J.M. Kelly
in 1991, where the dissipated energy of a high damping rubber bearing (HDRB) under cyclic testing at constant frequency is proportional to the amplitude of the shear strain raised to a power of approximately n=1.50. The physical process is best des...

In the present study, we develop an efficient boundary integral equation method for estimation of seismic motion in a graded medium with multiple cavities under anti-plane strain conditions. This inhomogeneous and heterogeneous medium is subjected to either time-harmonic incident shear seismic waves or to body waves radiating from a point seismic s...

In this work, we present a web-based educational package for teaching structural dynamics, as well as for providing an easily accessible on-line tool for interactive experimentation that is useful for both undergraduate and graduate training. Current version of the package comprises five software modules, namely (1) response history analysis of a s...

In this work, elastic wave motion in a continuously inhomogeneous geological medium under antiplane
strain conditions is numerically investigated using the boundary integral equation method (BIEM).
More specifically, the geological medium possesses a variable velocity profile, in addition to the presence
of either parallel or non-parallel graded la...

This work addresses the elastodynamic problem for a finite-sized, elastic solid matrix containing multiple nano-heterogeneities of arbitrary shape, number and geometric configuration. The problem is formulated under plane strain conditions, and time-harmonic motions are assumed to hold. The aim is to evaluate the non-uniform stress and strain field...

A fractional derivative Zener (FDZ) model connected in parallel with a linear viscous damper and a Coulomb friction slider is used to numerically simulate the mechanical behavior of a base isolated (BI) building tested under free vibration conditions in Solarino, Sicily. This hybrid BI system comprises high damping rubber bearings in combination wi...

In this work, we study elastic wave scattering and diffraction at the nanoscale by multiple heterogeneities such as cavities and inclusions embedded in an otherwise homogeneous elastic matrix. The dynamic loads are the result of pressure and shear waves propagating through the heterogeneous continuum under two-dimensional conditions. The mathematic...

In this work, we present a 2D elastodynamic model for the seismic response of subway tunnels embedded in a laterally inhomogeneous, multilayered geological region overlying the half-plane. To this end, a finite difference-boundary element methodology (FDM-BEM) is developed, with the latter method embedded in the former so as to capture near-site fi...

This study presents a numerical investigation of the influence of spatial variability of earthquake ground motion, site effects and Soil-Structure Interaction (SSI) phenomena on the inelastic dynamic analysis of bridge structures, considering a 2D analysis of the soil profile via Boundary Element Method (BEM). First, seismic waves propagating throu...

Die dynamische Interaktion von eingebetteten Baustrukturen in großen, geologischen Boden-strukturen stellt ein anspruchsvolles numerisches Problem durch die vorhandene Modellie-rungsgröße und die existierende mehrphasige, heterogene Bodenstruktur dar. Oft ist es nicht möglich die komplexe Untergrundstruktur als ein mehrphasiges, poröses Medium, ein...

The issue of modal shape identification for a flexible steel stairway located
within the building complex comprising the Civil Engineering department of
Aristotle University in Thessaloniki, Greece is presented here. The
aforementioned stairway is a system with continuous distribution of mass and
stiffness, a fact that makes structural identificati...

It is well established that local site conditions can exert a crucial influence on the severity of structural damage (especially in extended structures) and its spatial distribution during earthquakes. Such influence is traditionally evaluated using simple models based on 1D description of local soil profile and seismic wave propagation. Thus, the...

This work addresses wave diffraction and scattering in a homogeneous, elastic matrix containing multiple heterogeneities at nano-scale. The source of wave motion is an incident, time harmonic elastic pressure (P) wave propagating through the heterogeneous matrix. The approach followed here is based on a combination of (a) classical elastodynamic th...

Local site effects and the study of seismic waves through soil constitute the link between seismology and earthquake engineering. To that purpose the present study investigates the influence of local site effects on the nonlinear response of conventional multi-storey R/C buildings. The first step is to model seismic waves propagating through comple...

A 2D elastodynamic model for the seismic response of Metro tunnels embedded in a laterally inhomogeneous, multilayered geological region overlying a rock stratum is developed herein. We employ a hybrid, finite difference-boundary element method (FDM-BEM), with the latter method embedded in the former so as to capture the near-site field details. Mo...

In this work, a 2D problem in elastodynamics that involves the finite elastic solid containing multiple cylindrical and elliptical inclusions and/or cavities of arbitrary size, number, material properties and geometrical configuration is solved. More specifically, anti-plane strain conditions are assumed to hold and all external loads have a time h...

In this work, we study the elastic wave fields that develop in an isotropic half-plane which contains different types of heterogeneities such as free-surface relief, unlined and lined tunnels, as well as multiple buried inclusions. The half-plane is swept by traveling harmonic waves, namely pressure waves, vertically polarized shear waves and Rayle...

In this work, we develop a technique for performing system identification in typical pedestrian bridges, using routine equipment at a minimal configuration, and for cases where actual structural data are either sparse or absent. To this end, two pedestrian bridges were examined, modelled and finally instrumented so as to record their dynamic respon...

In this work, we examine the seismic response of multiple tunnels reinforced with liners and buried within the elastic homogeneous half-plane in the presence of surface relief. The seismic waves are upward propagating, time-harmonic, horizontally polarized shear (SH) waves. More specifically, we examine: (a) the scattered wave fields along the free...

A basic problem of elastodynamics, namely the anisotropic half-plane weakened by cavities of arbitrary shape and swept by upward moving, time harmonic SH-waves is considered here. The method of analysis used is the boundary integral equation method, in both displacement and non- hypersingular traction forms, which is based on Green's function for a...

We study seismically induced, anti-plane strain wave motion in a non-homogeneous geological region containing tunnels. Two different scenarios are considered: (a) The first models two tunnels in a finite geological region embedded within a laterally inhomogeneous, layered geological profile containing a seismic source. For this case, labelled as th...