Hybrid Passive Control Strategies for Reducing the Displacements at the Base of Seismic Isolated Structures

In this paper, the use of hybrid passive control strategies to mitigate the seismic response of a base-isolated structure is examined. The control performance of three different types of devices used for reducing base displacements of isolated buildings is investigated. Specifically, the Tuned Mass Damper (TMD), the New Tuned Mass Damper (New TMD) and the Tuned Liquid Column Damper (TLCD), each one associated to a Base Isolated structure (BI), have been considered. The seismic induced vibration control of base-isolated structures equipped with the TMD, New TMD or the TLCD is examined and compared with that of the base-isolated system without devices, using real recorded seismic signals as external input. Data show that the New TMD is the most effective in controlling the response of base-isolated structures so that it can be considered as a practical and appealing means to mitigate the dynamic response of base-isolated structures

Editorial to special issue “Recent mechanics-based developments in structural dynamics and earthquake engineering”

In structural dynamics, the inertia of accelerated masses and the cornucopia of phenomena that contribute to damping have a significant influence on the internal forces and deformation of building structures. Typical problems of structural dynamics are the prediction of the vibration response of dynamically excited structures, for instance, induced by earthquakes, the identification of structural parameters based on the dynamic response, and the design of vibration-mitigating measures from the fundamental study to the implementation. Many traditionalmethods of structural dynamics and earthquake engineering are based on empirical approaches rather than rigorous application of fundamental mechanical principles. However, dramatic advances in mechanics now make it increasingly possible not only to model but also to solve and predict complex phenomena in dynamics. We are very pleased that, in response to these advances, this special issue of Acta Mechanica provides an insight into the latest mechanics-based developments in various branches of structural dynamics and earthquake engineering. It contains 20 contributions that we selected based on the reactions and feedback we received to our invitation. The first four papers deal with complex dynamic vehicle–bridge interaction (VBI). In the first paper, Homaei et al. [1] investigate the effect of VBI and highlight its similarities and differences to the effect of vibration dampers under earthquake excitation. Based on knowledge of recent experimental studies, König and Adam [2] present a new modeling approach for railway bridges under high-speed traffic, which takes into account both the horizontal and vertical interaction between track and structure. Hirzinger and Nackenhorst [3] apply a model-correction-based strategy for efficient reliability analysis of the uncertain VBI system, where a low-fidelity model is calibrated to the corresponding high-fidelity model close to the most probable point. The paper of Lei et al. [4] proposes a two-step bridge damage detection method based on wavelet transform analysis of the residual contact response of the moving front and rear vehicle wheels to reduce the impact of road surface roughness. Suitably, the next paper by Yang et al. [5] uses a numerical model based on the wave finite element method of wave propagation and attenuation in periodic supported rail, capturing the complex cross-section deformation of the waves. Changing topics away from railways, Amendola et al. [6] also seek a waveform solution but of nonlocal nanobeams dissipating thermal energy by radiation, employing an extension of Type II Green–Naghdi theory. The paper by Abdelnour and Zabel [7] is devoted to the identification of the modal information of complex three-dimensional space truss structures characterized by closely spaced modes as well as global and local vibration mechanisms. Pirrotta and Russotto [8], on the other hand, develop a new operationalmodal analysismethod based on signal filtering and the Hilbert transform of the correlation function matrix for dynamic system identification. The next two papers deal with machine learning in structural dynamics. Milicevic and Altay [9] present a theoretical data generation framework for test-integrated modeling of nonlinear systems in structural dynamics. In particular, a feedforward neural network is used for inverse modeling of nonlinear restoring forces. On the other hand, Maqdah et al. [10] build an unsupervised machine learning model capable of detecting patterns in arch forms under seismic loading and distinguishing between their stress and displacement contours. In one of the three contributions on structures under seismic loads, Zakian and Kaveh [11] provide a comprehensive review on seismic design optimization of engineering structures. Refined probabilistic seismic response evaluation of high-rise reinforced concrete structures is subject of Lyu et al. [12]. In the third contribution, Karaferis et al. [13] present a roadmap for determining comprehensive fragility curves for individual or groups of spherical pressure vessels, tackling the thorny issues of correlation and operational realities. Six other papers can be classified under the topic of vibration control. Rajana and Giaralis [14] introduce a nonlinear rooftop tuned mass damper-inerter system and numerically investigate its efficiency for seismic response mitigation of buildings. The hysteretic tuned mass damper system presented in Xiang et al. [15] is optimized for acceleration control of seismically excited structures. In Masnata et al. [16], both theoretical and experimental studies are conducted on the control performance of a sliding model of a tuned liquid column damper for short-period systems. The study of Li et al. [17] shows that the use of high-static–low-dynamic stiffness floating raft vibration isolation system is beneficial for the shock performance. De Castro Motta et al. [18] present a mechanical model for thermoplastic polyurethane membranes used as components in seismic isolators based on an experimental study. Sezer et al. [19], on the other hand, report the results of experimental investigations on the coefficient of friction at the interface of a PVC-sand-PVC layer, used as part of a low-cost geotechnical seismic isolation system. This special issue is completed with a paper by Minafò et al. [20] on the effect of interface model parameters on the numerical behavior of a finite element model for predicting the bond between fabric-reinforced cementitious matrix and masonry. We would like to thank all the authors who accepted our invitation to contribute to this special issue and the reviewers for their thorough and valuable comments on these studies. Our particular thanks go to Professor Hans Irschik, Editor-in-Chief, for the opportunity to publish this special issue in “Acta Mechanica” and for his guidance during its development. We thank Dr. Michael Stangl, editorial assistant, for his continued support, always responding to our requests in an efficient and timely manner

Efficient estimation of tuned liquid column damper inerter (TLCDI) parameters for seismic control of base-isolated structures

This paper presents an enhanced base-isolation (BI) system equipped with a novel passive control device composed of a tuned liquid damper and an inerter (TLCDI). With the aim of reducing the seismic response of BI systems, this contribution focuses on the design of the TLCDI providing analytical solutions for the optimal TLCDI parameters, easily implementable in the design phase. The effectiveness of the proposed approach in terms of seismic response reduction and computational gain is validated by comparison with classical numerical optimization techniques. The control performance of two different base-isolated TLCDI-controlled structures is assessed by employing real-ground motion records, and relevant comparisons with both uncontrolled base-isolated structures and equipped with a conventional TLCD are presented

Sliding TLCD for vibration control of base-isolation systems: Experimental comparison with traditional TLCD and TMD

In the context of hybrid passive vibration control, the effectiveness of the Tuned Liquid Column Damper (TLCD) for seismic protection of base-isolated (BI) systems has been demonstrated 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 introduced only for the suppression of wind-induced vibrations 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 via a spring dashpot system. The validity of the introduced mathematical model is assessed by means of an extensive shaking table testing campaign at the Laboratory of Experimental Dynamics at the University of Palermo, Italy. For 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 made and the control efficiency is discussed with emphasis on the reduction of the accelerations of the BI system

Assessment of the tuned mass damper inerter for seismic response control of base-isolated structures

In this paper, the hybrid control of structures subjected to seismic excitation by means of tuned mass damper inerter (TMDI) and base-isolation subsystems is studied with the aim of improving the dynamic performance of base-isolated structures by reducing the displacement demand of the isolation subsystem. The seismic performance of TMDI hybrid controlled structures is investigated in a comparative study, considering simple isolated systems and systems equipped with other absorber devices such as the tuned mass damper (TMD) and the tuned liquid column damper (TLCD). The TMDI has been optimized by performing a simplified approach based on minimizing the base-isolation subsystem displacement variance, which provides simple analytical formulae for a quick definition of the TMDI parameters. The reliability of this approach is demonstrated by a comparison with a more accurate and computationally complex numerical optimization procedure. The control performance of three types of hybrid controlled structures exposed to a set of 44 recorded ground motions is investigated. Numerical results show that the TMDI can more efficiently control the structural response of low-damped isolated structures, even compared to the TMD and the TLCD

A novel identification procedure from ambient vibration data

Ambient vibration modal identification, also known as Operational Modal Analysis, aims to identify the modal properties of a structure based on vibration data collected when the structure is under its operating conditions, i.e., no initial excitation or known artificial excitation. This procedure for testing and/or monitoring historic buildings, is particularly attractive for civil engineers concerned with the safety of complex historic structures.However, since the external force is not recorded, the identification methods have to be more sophisticated and based on stochastic mechanics. In this context, this contribution will introduce an innovative ambient identification method based on applying the Hilbert Transform, to obtain the analytical representation of the system response in terms of the correlation function. In particular, it is worth stressing that the analytical signal is a complex representation of a time domain signal: the real part is the time domain signal itself, while the imaginary part is its Hilbert transform. A 3DOF numerical example will be presented to show the accuracy of the proposed procedure, and comparisons with data from other methods assess the reliability of the approach. Finally, the identification method will be extended to the real case study of the Chiaramonte Palace, a historic building located in Palermo and known as “Steri”

A new dataset and empirical relationships between magnitude/intensity and epicentral distance for liquefaction in central-eastern Sicily

Strong earthquakes can trigger several phenomena inducing soil deformation, such as liquefaction, ground fracturing and landslides, which can often cause more damage than the seismic shaking itself. A research performed on numerous historical accounts reporting descriptions of seismogeological effects in central-eastern Sicily, allowed the authors to update the previous liquefaction datasets. 75 liquefaction-induced phenomena observed in 26 sites, triggered by 14 earthquakes, have been used to define relationships between intensity/magnitude values and epicentral distance from the liquefied sites. The proposed upper bound-curves, at regional scale for central- eastern Sicily, are realized by using the updating liquefaction dataset and also the new CPTI04 Italian earthquake parametric catalogue. These relationships can be useful in hazard assessment to evaluate the minimum energy of an earthquake inducing liquefactions

COVID-19 vaccinations: An overview of the Italian national health system's online communication from a citizen perspective

COVID-19 vaccine hesitancy is still widespread. During the pandemic, the internet has been the preferred channel for health-related information, especially for less-educated citizens who tend to be the most hesitant about vaccination. A well-structured web communication strategy could help both to overcome vaccine hesitancy and to ensure equity in healthcare service access. This study investigated how the various regional and local health authorities in Italy used their institutional websites to inform users about COVID-19 vaccinations between March and April 2021. We browsed 129 institutional websites, checking the availability, quality and quantity, actionability and readability of information using a literature-based common grid. Descriptive statistics and statistical tests were performed. The online public dissemination of COVID-19 vaccination information in Italy was fragmented, both across and within regions. The side effects of vaccinations, were often not reported on the websites, thus missing an opportunity to enhance vaccination uptake. More focus should also be placed on readability, since readability indexes showed that they were difficult to understand. Our research revealed that several actions could be implemented to enhance online communication on COVID-19 vaccination. For instance, simplifying texts can make them more understandable and the information reported actionable

Role of Advanced Glycation End-Products and Oxidative Stress in Type-2-Diabetes-Induced Bone Fragility and Implications on Fracture Risk Stratification

Type 2 diabetes (T2D) and osteoporosis (OP) are major causes of morbidity and mortality that have arelevant health and economic burden. Recent epidemiological evidence suggests that both of these disorders are often associated with each other and that T2D patients have an increased risk of fracture, making bone an additional target of diabetes. As occurs for other diabetic complications, the increased accumulation of advanced glycation end-products (AGEs) and oxidative stress represent the major mechanisms explaining bone fragility in T2D. Both of these conditions directly and indirectly (through the promotion of microvascular complications) impair the structural ductility of bone and negatively affect bone turnover, leading to impaired bone quality, rather than decreased bone density. This makes diabetes-induced bone fragility remarkably different from other forms of OP and represents a major challenge for fracture risk stratification, since either the measurement of BMD or the use of common diagnostic algorithms for OP have a poor predictive value. We review and discuss the role of AGEs and oxidative stress on the pathophysiology of bone fragility in T2D, providing some indications on how to improve fracture risk prediction in T2D patients

Recent activity and kinematics of the bounding faults of the Catanzaro trough (Central Calabria, italy): new morphotectonic, geodetic and seismological data

A multidisciplinary work integrating structural, geodetic and seismological data was performed in the Catanzaro Trough (central Calabria, Italy) to define the seismotectonic setting of this area. The Catanzaro Trough is a structural depression transversal to the Calabrian Arc, lying in-between two longitudinal grabens: the Crati Basin to the north and the Mesima Basin to the south. The investigated area experienced some of the strongest historical earthquakes of Italy, whose seismogenic sources are still not well defined. We investigated and mapped the major WSW–ENE to WNW–ESE trending normal-oblique Lamezia-Catanzaro Fault System, bounding to the north the Catanzaro Trough. Morphotectonic data reveal that some fault segments have recently been reactivated since they have displaced upper Pleistocene deposits showing typical geomorphic features associated with active normal fault scarps such as triangular and trapezoidal facets, and displaced alluvial fans. The analysis of instrumental seismicity indicates that some clusters of earthquakes have nucleated on the Lamezia-Catanzaro Fault System. In addition, focal mechanisms indicate the prevalence of left-lateral kinematics on E–W roughly oriented fault plains. GPS data confirm that slow left-lateral motion occurs along this fault system. Minor north-dipping normal faults were also mapped in the southern side of the Catanzaro Trough. They show eroded fault scarps along which weak seismic activity and negligible geodetic motion occur. Our study highlights that the Catanzaro Trough is a poliphased Plio-Quaternary extensional basin developed early as a half-graben in the frame of the tear-faulting occurring at the northern edge of the subducting Ionian slab. In this context, the strike-slip motion contributes to the longitudinal segmentation of the Calabrian Arc. In addition, the high number of seismic events evidenced by the instrumental seismicity, the macroseismic intensity distribution of the historical earthquakes and the scaling laws relating to earthquakes and seismogenic faults support the hypothesis that the Lamezia-Catanzaro Fault System may have been responsible for the historical earthquakes since it is capable of triggering earthquakes with magnitude up to 6.9