Time and Frequency Domain output-only system identification from earthquake-induced structural response signals

Output-only Time and Frequency Domain system identification techniques are developed in this doctoral dissertation towards the challenging assessment of current structural dynamic properties of buildings from earthquake-induced structural response signals, at simultaneous heavy damping. Three different Operational Modal Analysis (OMA) techniques, namely a refined Frequency Domain Decomposition (rFDD) algorithm, an improved Data-Driven Stochastic Subspace Identification (SSI-DATA) procedure and a novel Full Dynamic Compound Inverse Method (FDCIM) are formulated and implemented within MATLAB, and exploited for the strong ground motion modal dynamic identification of selected buildings. First, the three OMA methods are validated by the adoption of synthetic earthquake-induced structural response signals, generated from numerical integration on benchmark linear shear-type frames. Then, real seismic response signals are effectively processed, by getting even closer to real Earthquake Engineering identification scenarios. In the end, the three OMA methods are systematically applied and compared. The present thesis demonstrates the reliability and effectiveness of such advanced OMA methods, as convenient output-only modal identification tools for Earthquake Engineering and Structural Health Monitoring purposes

Photonic heat amplifier based on a disordered semiconductor

A photonic heat amplifier designed for cryogenic operations is introduced and analyzed. This device comprises two variable-range-hopping reservoirs connected by lossless lines, which allow them to exchange heat through photonic modes. This configuration enables negative differential thermal conductance, which can be harnessed to amplify thermal signals. To achieve this, one reservoir is maintained at a high temperature, serving as the source terminal of a thermal transistor. Concurrently, in the other reservoir, we establish tunnel contacts to metallic reservoirs, which function as the gate and drain terminals. With this arrangement, it is possible to control the heat flux exchange between the source and the drain by adjustment of the gate temperature. We present two different parameter choices that yield different performances: the first emphasizes modulation of the source-drain heat current, while the second focuses on the modulation of the lower-temperature variable-range-hopping reservoir. Lastly, we present a potential design variation in which all electronic reservoirs are thermally connected through only photonic modes, allowing interactions between distant elements. The proposed photonic heat amplifier addresses the lack of thermal transistors and amplifiers in the millikelvin range, while being compatible with the rich toolbox of circuit quantum electrodynamics. It can be adapted to various applications, including sensing and the development of thermal circuits and control devices at subkelvin temperatures, which are relevant to quantum technologies

Photonic negative differential thermal conductance enabled by NIS junctions

Due to their sensitivity to temperature variations, normal metal–insulator-superconductor (NIS) junctions are utilized in various thermal devices. This study illustrates that two NISIN reservoirs can achieve a measurable negative differential thermal conductance (NDTC). This phenomenon is enabled by photon-mediated heat exchange, which is profoundly affected by the temperature-dependent impedance matching between the reservoirs. Under suitable configurations, the heat current is suppressed for increasingly large temperature gradients, resulting in NDTC. We also propose experimental configurations that allow for the unambiguous discrimination of this effect. We employ superconducting aluminum in conjunction with either silver or epitaxial InAs to facilitate the experimental observation of NDTC at low temperatures over significant sub-Kelvin ranges. This advances the development of devices that exploit NDTC to enhance the regulation of heat and temperature in cryogenic environments, such as thermal switches, transistors, and amplifiers

INNOVATIONS in earthquake risk reduction for resilience: RECENT advances and challenges

The Sendai Framework for Disaster Risk Reduction 2015-2030 (SFDRR) highlights the importance of scientific research, supporting the ‘availability and application of science and technology to decision making’ in disaster risk reduction (DRR). Science and technology can play a crucial role in the world’s ability to reduce casualties, physical damage, and interruption to critical infrastructure due to natural hazards and their complex interactions. The SFDRR encourages better access to technological innovations combined with increased DRR investments in developing cost-effective approaches and tackling global challenges. To this aim, it is essential to link multi- and interdisciplinary research and technological innovations with policy and engineering/DRR practice. To share knowledge and promote discussion on recent advances, challenges, and future directions on ‘Innovations in Earthquake Risk Reduction for Resilience’, a group of experts from academia and industry met in London, UK, in July 2019. The workshop focused on both cutting-edge ‘soft’ (e.g., novel modelling methods/frameworks, early warning systems, disaster financing and parametric insurance) and ‘hard’ (e.g., novel structural systems/devices for new structures and retrofitting of existing structures, sensors) risk-reduction strategies for the enhancement of structural and infrastructural earthquake safety and resilience. The workshop highlighted emerging trends and lessons from recent earthquake events and pinpointed critical issues for future research and policy interventions. This paper summarises some of the key aspects identified and discussed during the workshop to inform other researchers worldwide and extend the conversation to a broader audience, with the ultimate aim of driving change in how seismic risk is quantified and mitigated

On the processing of earthquake-induced structural response signals by suitable Operational Modal Analysis identification techniques

In the present study, two different Operational Modal Analysis (OMA) techniques, namely a refined Frequency Domain Decomposition (rFDD) and an improved Data-Driven Stochastic Subspace Identification (SSI-DATA), are specifically conceived towards assessing current modal dynamic properties of buildings under seismic excitation and simultaneous heavy damping (in terms of identification challenge). Synthetic earthquake-induced response signals, generated from a set of different frame structures and earthquake baseexcitations, have been investigated, in order to make a serious step forward in assessing the OMA effectiveness of the two techniques at seismic response input. According to the present investigation, best up-to-date, re-interpreted, output-only algorithms may be effectively used to characterize the current dynamic behaviour of structures and to identify potential structural modifications along the experienced seismic histories, thus allowing for possible Structural Health Monitoring approaches in the Earthquake Engineering range

Experimental and numerical investigations for the structural characterization of a historic RC arch bridge

A comprehensive rational methodology for the structural assessment of existing bridges is presented and specifically applied to a historic reinforced concrete arch bridge. The methodology is based on the use of non-destructive testing tools and structural model updating procedures and involves: (a) preliminary documented research and on-site geometric surveys (aimed at collecting information on the "as built" geometry); (b) ambient vibration testing performed by using a grid of conventional high-sensitivity accelerometers, aimed specifically at investigating the vertical dynamic characteristics of the bridge and c) development of an updated Finite Element (FE) model of the structure. The investigated bridge, completed in May 1917, crosses the Adda river between Brivio (province of Lecco) and Cisano Bergamasco (province of Bergamo), about 50 km North-East from Milano, Northern Italy. Given the still strategic position of the bridge in the current road transportation network and within a systematic surveillance program of main infrastructures by the Province of Lecco, dynamic tests were performed under operational conditions. Main results in terms of Operational Modal Analysis and FE modelling and updating are presented and discussed. A hierarchy of FE models with different levels of refinement is developed, with the purpose of a future selection of the model that better reproduces the current structural properties of the bridge. In this paper an automated system identification procedure has been developed and applied to the simplest of the assembled (consistent) FE models, whose results will constitute a benchmark for further studies upon the other most refined models. The aim is to perform a final baseline reference model to be used for reliability assessment within Structural Health Monitoring (SHM) purposes

A refined FDD algorithm for Operational Modal Analysis of buildings under earthquake loading

An autonomously-developed, refined Frequency Domain Decomposition (FDD) algorithm implemented within MATLAB is applied to the modal dynamic identification of civil frame buildings subjected to a set of strong ground motions. The performed research deals, as a necessary validation condition, with pseudo-experimental signals generated prior to the dynamic identification, from the numerical response of several shear-type frames. Strong motion modal parameters are then extracted and estimated successfully at given seismic input, taken as base excitation. Results turn-out very much consistent with targeted values, with quite limited errors in the modal parameter estimates, including for the modal damping ratios, ranging from low to high values. Notice that seismic excitation responses shall not fulfill traditional input assumptions of FDD techniques. This highlights the consistency of the present refined FDD algorithm in such a challenging framework. This paper shows that, in principle, a comprehensive modal dynamic identification of frame buildings through a refined FDD algorithm looks possible at seismic input

Graphite-gated graphene junctions: toward fractional quantum Hall Josephson devices

In this thesis, I demonstrate the fabrication and the experimental study of graphite-gated niobium-graphene weak links. This kind of device is fundamental for the development of an experimental platform combining superconductivity and fractional quantum Hall effect, exploitable for the achievement of topological quantum computation. I elaborated and executed fabrication protocols for such devices, producing both standard weak links and other devices implementing a double-gate geometry not experimented before. The effectiveness of the procedures is proven by low-temperature transport measurements. We observed gating action from graphite, ballistic transport of carriers and induced superconductivity. The new double-gate design enabled local control of parallel channels, both in the normal and superconducting regimes. This is a proof of concept for devices with electrostatically defined geometry, a design choice that can bring substantial improvements in terms of quantum coherence, as already demonstrated in the field of edge-state interferometry

Time and Frequency Domain output-only system identification from earthquake-induced structural response signals

Output-only Time and Frequency Domain system identification techniques are developed in this doctoral dissertation towards the challenging assessment of current structural dynamic properties of buildings from earthquake-induced structural response signals, at simultaneous heavy damping. Three different Operational Modal Analysis (OMA) techniques, namely a refined Frequency Domain Decomposition (rFDD) algorithm, an improved Data-Driven Stochastic Subspace Identification (SSI-DATA) procedure and a novel Full Dynamic Compound Inverse Method (FDCIM) are formulated and implemented within MATLAB, and exploited for the strong ground motion modal dynamic identification of selected buildings. First, the three OMA methods are validated by the adoption of synthetic earthquake-induced structural response signals, generated from numerical integration on benchmark linear shear-type frames. Then, real seismic response signals are effectively processed, by getting even closer to real Earthquake Engineering identification scenarios. In the end, the three OMA methods are systematically applied and compared. The present thesis demonstrates the reliability and effectiveness of such advanced OMA methods, as convenient output-only modal identification tools for Earthquake Engineering and Structural Health Monitoring purposes