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Copyright © The Author(s) 2022. Scour is the prevailing cause of bridge failure worldwide, leading not only to traffic disruption, but also to social and economic losses and even to casualties. Many vibration-based monitoring techniques have been proposed for identifying the scour location and extent, based on the evaluation of the changes of the bridge modal properties due to scour. This study describes the experimental and numerical research carried out to investigate the effects of scour on the dynamic properties of structures with shallow foundations. Although these are the most vulnerable ones, they have received less attention compared to structures founded on pile foundations. To fill some existing knowledge gaps, field experiments were carried out on EuroProteas, a structural prototype with shallow foundation that was subjected to increasing levels of scour. The changes of the dynamic properties of the system are evaluated by postprocessing the ambient vibration recordings and by developing various models of the soil–foundation–structural system with different descriptions of the soil–structure interaction problem. The study results shed light on the effects of scour on systems with shallow foundations and on the accuracy of alternative modelling approaches. They are presented here to inform the development and validation of vibration-based techniques and modelling strategies for bridge scour identification. European project “Seismology and Earthquake Engineering Research Infrastructure Alliance for Europe—SERA-TA-H2020 (Grant Agreement 730900)”.

En esta investigación se realizó un análisis espectral de la respuesta estructural de dos edificios de concreto reforzado, de 18 m y 56 m de altura y con distintos niveles de irregularidad en planta, al ser sometidos a vibraciones ambientales. Específicamente, se han usado el método básico (BFD) y de descomposición en el dominio de la frecuencia (FDD) sobre registros de vibración ambiental adquiridos mediante tres acelerómetros triaxiales para la identificación de las frecuencias y los modos naturales de vibración. Para cada edificio se identificaron al menos tres modos de vibración en un rango de frecuencias comprendido entre 1,0 Hz y 6,0 Hz. Los modos con mayor densidad espectral fueron exhibidos entre las frecuencias de 1,0 Hz y 3,0 Hz. De las formas modales, se evidenció que, entre más irregularidad en planta, mayor será la presencia de modos de torsión y el acoplamiento de estos con modos de flexión. In this investigation, a spectral analysis of the structural response of two reinforced concrete buildings, of 18 m and 56 m of height and with different plan regularity, subjected to ambient vibrations was done. Specifically, natural frequencies and modes of vibrations were determined through applying basic frequency domain (BFD) and frequency domain decomposition (FDD) methods to ambient vibration data acquired by three triaxial accelerometers. At least three vibration modes were identified for each building in a range of frequencies comprehended between 1,0 Hz and 6,0 Hz. Modes with more spectral density were exhibited between frequencies of 1,0 Hz and 3,0 Hz. From mode shapes, it was determined that structures with more plan irregularity presents more torsional modes and coupling of these with flexural modes. UCR::Vicerrectoría de Investigación::Unidades de Investigación::Ingeniería::Instituto Investigaciones en Ingeniería (INII) UCR::Vicerrectoría de Docencia::Ingeniería::Facultad de Ingeniería::Escuela de Ingeniería Civil

Local site evaluation is an essential step in understanding the amplification of seismic motion induced by the complex geological structure and their estimation for future strong earthquakes in urban regions. One of the critical parameters on evaluating amplification effects is the depth of the geophysical bedrock, whose interface to soft sediments is responsible for the development of destructive resonance phenomena. The present study is focused on the estimation of the geophysical bedrock depth along the extra-Carpathian area of Romania (Moesian Platform and surroundings) by correlating and interpolating the results obtained from single station measurements with the available geological/geophysical data. Each site was investigated through the computation of horizontal-to-vertical (H/V) spectral ratios from three-component single station measurements of ambient vibrations. The geophysical bedrock depth was computed using a two-step inversion scheme, based on the retrieval of the Rayleigh-wave ellipticity peak at each seismic station using a regional generic velocity profile. The fundamental frequency of resonance reaches the lowest value in the deepest side (0.07 Hz) and is rising to 13 Hz in the South of the Moesian Platform, where a shallow bedrock is present. The computed bedrock depths (from 30 to ~ 3100 m) show a dipping tendency towards the Southern Carpathians and complex features such as local outcrops and lateral depth variations superpose this gradually dipping trend. In the Carpathian foreland, the bedrock is interpreted as the transition between different sediment layers of Neogene, while outside this area as the Neogene—Cretaceous transition. © 2020, Springer Nature Switzerland AG. ISSN:0033-4553 ISSN:1420-9136 ISSN:1557-7368

Open access funding provided by Universita degli Studi di Perugia within the CRUI-CARE Agreement., Operational Modal Analysis (OMA) is becoming a mature and widespread technique for Structural Health Monitoring (SHM) of engineering structures. Nonetheless, while proved effective for global damage assessment, OMA-based techniques can hardly detect local damage with little effect upon the modal signatures of the system. In this context, recent research studies advocate for the use of wave propagation methods as complementary to OMA to achieve local damage identification capabilities. Specifically, promising results have been reported when applied to building-like structures, although the application of Seismic Interferometry to other structural typologies remains unexplored. In this light, this work proposes for the first time in the literature the use of ambient noise deconvolution interferometry (ANDI) to the structural assessment of long bridge structures. The proposed approach is exemplified with an application case study of a multi-span reinforcedconcrete (RC) viaduct: the Chiaravalle viaduct in Marche Region, Italy. To this aim, ambient vibration tests were performed on February 4 th and 7 th 2020 to evaluate the lateral and longitudinal dynamic behaviour of the viaduct. The recorded ambient accelerations are exploited to identify the modal features and wave propagation properties of the viaduct by OMA and ANDI, respectively. Additionally, a numerical model of the bridge is constructed to interpret the experimentally identified waveforms, and used to illustrate the potentials of ANDI for the identification of local damage in the piers of the bridge. The presented results evidence that ANDI may offer features that are quite sensitive to damage in the bridge substructure, which are often hardly identifiable by OMA., Universita degli Studi di Perugia within the CRUI-CARE Agreement

The Middle-Chelif basin, in northwestern Algeria, is located in a seismically active region. In its western part lies the El-Asnam fault, a thrust fault responsible for several strong earthquakes. The most important being the El-Asnam earthquake (Ms = 7.3) of 1980. In the present study, ambient vibration data with single-station and array techniques were used to investigate the dynamic properties of the ground and to estimate the Vs30 structure in the main cities of the basin. Soil resonance frequencies vary from 1.2 to 8.3 Hz with a maximum amplitude of 8.7 in. Collapsing behavior has also been demonstrated west of the city of El-Attaf, reflecting a strong potential for liquefaction. A Vs30 variation map and a soil classification for each city were obtained mainly by inversion of the HVSR and Rayleigh wave dispersion curves. Finally, an empirical prediction law of Vs30 for the Middle-Chelif basin was proposed.

International audience; Damage diagnosis based on global structural vibrations critically depends on the sensor layout, in particular when a small number of sensors is used for large structures under unknown excitation. This paper proposes a sensor placement strategy that yields an optimized sensor layout with maximum damage detectability in selected structural components. The optimization criterion is based on the Fisher information, which quantifies the information that the damage-sensitive feature carries on the design parameters of structural components, such as material constants or cross-sectional values. It is evaluated using a finite element model, and considers the statistical uncertainties of the damage-sensitive feature. The methodology is shown for the stochastic subspace-based damage detection method, but can be applied to any damage-sensitive feature whose distribution can be approximated as Gaussian. It is suitable to find the optimal layout for a fixed number of sensors and to choose an appropriate number of sensors. Since the Fisher information is defined component-wise, the sensor layout can be tuned to become more sensitive to damage in local structural components, such as damage hotspots, non-inspectable components, or components that are critical for the safety and serviceability of the structure. For proof of concept, the sensor layout on a laboratory beam is optimized based on numerical simulations, and it is showcased that the optimal sensor layout leads to the highest damage detectability for experimental data.

This article presents a new wireless seismic sensor network system, especially design for building monitoring. The designed prototype allows remote control, and remote and real-time monitoring of the recorded signals by any internet browser. The system is formed by several Nodes (based on the CC3200 microcontroller of Texas Instruments), which are in charge of digitizing the ambient vibrations registered by three-component seismic sensors and transmitting them to a central server. This server records all the received signals, but also allows their real-time visualization in several remote client browsers thanks to the JavaScript’s Node.js technology. The data transmission uses not only Wi-Fi technology, but also the existing network resources that nowadays can be found usually in any official or residential building (lowering deployment costs). A data synchronization scheme was also implemented to correct the time differences between the Nodes, but also the long-term drifts found in the internal clock of the microcontrollers (improving the quality of records). The completed system is a low-cost, open-hardware and open-software design. The prototype was tested in a real building, recording ambient vibrations in several floors and observing the differences due to the building structure. This study was funded by the European Union’s Horizon 2020 research and innovation program under grant agreement No 821046, the Ministerio de Economía, Industria y Competitividad through research project CGL2016-77688-R, by the Consellería de Participación, Transparencia, Cooperación y Calidad Democrática de la Generalitat Valenciana, and by Research Group VIGROB-116 (University of Alicante).

The vibration effects on the Torre della Moletta and the ruins of the Circus Maximus in Rome are analyzed in the framework of a preservation effort of this archaeological area. Thanks to its exceptional size, the Circus hosts many social events with large audience (pop-music, opera concerts, sport celebrations, etc.) every year, thus taking the structures under high anthropic and environmental stress. Recordings were completed before, during, and after the concert of a famous band, on 7 September 2019. Data were analyzed, both in time and frequency domains. The experimental dynamic recordings were coupled with a surface waves test and single-station ambient vibration recordings, which were useful for the geotechnical characterization of the soil. The results pointed out the differences in amplitudes but also in terms of frequency content of the recorded velocities during the concert with respect to before and after it. The maximum velocities recorded at various locations were almost similar to the limit values suggested by codes. The dynamic behavior of the ground and the structures is influenced by the presence of buried structures.

Dynamic measurements of two steel truss bridges for Structural Health Monitoring (SHM) were performed. The investigated bridges were: a single supported one span truss bridge and a multi-span truss bridge. Two possibilities of measuring setup were considered. A simple arrangement made up of one polygon has been used for data acquisition of the single span truss bridge. A more complex measuring setup made up of two polygons with up to 32 channels has been used for the large bridge with an entire length reaching up to 500 m. A connection of both measuring polygons was achieved by Wi-Fi antennas. The reason why the multi-span truss bridge was chosen for SHM is that the construction is nowadays overloaded. The dynamic measurements were done, ambient and semi-ambient data were analysed. After that, some mode-shapes were identified from the acquired data and then the data were compared with numerical calculations. Finally, experiences and conclusions from the ambient data measurement are summarized.

Seismic stations are usually used to record seismic event and, therefore, they are recommended to be installed far from railways and traffic roads in order to avoid the superposition of ambient noise signals to those provoked by an earthquake. In this paper, instead, seismic stations, placed intentionally in areas near railway and traffic roads, are used to characterize the subsoil spectral properties and to assess the effect of vibrations due to trains and vehicles. A cemetery in the green countryside near Florence is chosen as a reference case study to deal with this topic. Most of the buildings in the cemetery area are affected by an extensive crack pattern. In January 2020 five seismic stations were installed in order to evaluate if the trains running in the tunnels of the regional and high-speed railway lines located below and in the vicinity of the cemetery and the vehicles traveling on the nearby A1 highway and regional road can produce vibrations in the ground that justify the observed damage pattern. Collected data are analyzed using the Nakamura technique in order to estimate the dynamic properties of the ground and compared to the limits provided by the current regulations. Furthermore, the trend of the Root Mean Square average over the entire recording period is computed as well. From the obtained results, it is possible to highlight that the average daily oscillation level increases from early morning until 7 p.m. and then it decreases, and also that the highest amplitudes of transients are concentrated in the late evening and during the night, when the background noise is lower. Furthermore, the computed values of the maximum and average amplitudes are lower than those that can cause damage to buildings as defined by the guidelines, the eigenfrequency of the ground falls in a range far from that ascribable to the cemetery buildings, so that the resonance effects can be excluded. In order to confirm these results, the amplitude of ground shaking due to recorded transients is compared to that produced by two earthquakes (a 3.4 Mw local earthquake at more than 100 km and a Mw 6.6 teleseism from Turkey) which occurred during the monitoring period. One can conclude that it seems unlikely that the shaking produced by nearby vehicles and trains could be responsible for the observed damage.

Concrete gravity dams are critical infrastructures for communities to meet the basic human needs as well as rising standards of living. Most of the existing concrete gravity dams in Italy were built before the introduction of seismic regulations. Although no concrete gravity dams have as yet suffered a catastrophic collapse during or after a seismic event, their preservation remains a key aspect for communities, also in view of that older dams may have deteriorated to a critical level. For these reasons, researchers and practitioners in dam engineering are working to improve seismic fragility, and ultimately seismic risk, assessment procedures. Since no case histories are available, numerical modelling plays an important role, even though many uncertainties can affect the models and then the estimation of the seismic fragility. This paper presents a robust hierarchical Bayesian framework for the calibration of dynamic parameters of dam numerical models based on ambient vibrations, which allows an analyst to reduce uncertainties in the seismic fragility derivation. A probabilistic predictive model of the dam modal behaviour based on the general Polynomial Chaos Expansion is adopted in order to reduce the computational burden and a numerical algorithm for the solution of the inverse problem based on Markov Chain Monte Carlo is also presented. The proposed approach is applied to an existing large concrete gravity dam in Italy, and the effect of epistemic uncertainty reduction is finally evaluated in terms of fragility curves.

The use of self-organizing maps and artificial neural networks for structural health monitoring is presented in this paper. The authors recently developed a nonparametric structural damage detection algorithm for extracting damage indices from the ambient vibration response of a structure. The algorithm is based on self-organizing maps with a multilayer feedforward pattern recognition neural network. After the training of the self-organizing maps, the algorithm was tested analytically under various damage scenarios based on stiffness reduction of beam members and boundary condition changes of a grid structure. The results indicated that proposed algorithm can successfully locate and quantify damage on the structure. Scopus

The estimation of seismic shaking is essential for a realistic assessment of the local seismic hazard and the implementation of effective strategies for prevention and mitigation of the seismic risk. One of the most important aspects in the analysis of the site seismic assessment is the recognition of the seismic bedrock and its depth. Unfortunately, these data are not always easy to evaluate, especially in areas where the thickness of loose or poorly consolidated sediments is high. This article illustrates data and case studies from the Emilia-Romagna sector of the Po Plain, in order to provide examples and suggestions for the recognition of the seismic bedrock in alluvial and coastal areas characterised by significant thicknesses of unconsolidated sediments, using available data and not expensive geophysical surveys. The application of the proposed method indicates that the study area can be divided into four domains characterized by different depths of the seismic bedrock: the marginal or pede-Apennine belt, the high structural zones, the syncline/minor anticline zones, and the Po delta-coast zone.

Se presentan los resultados de cinco mediciones de vibraciones ambientales realizadas en tres distintos edificios de San José, Costa Rica. El objetivo principal fue el medir la mayor cantidad de periodos naturales en cada dirección de los edificios utilizando la técnica “peak-picking” con espectros de Fourier (EF) y funciones de transferencia (FT). También se calcularon los amortiguamientos modales para uno de los edificios por medio de la técnica de decaimiento aleatorio. Para los edificios estudiados, se concluye que las diferencias entre los periodos naturales calculados a partir de EF y FT son despreciables, así mismo para cada edificio, basta contar con dos puntos de medición, uno en el nivel inferior y otro en el superior para lograr identificar al menos cuatro periodos naturales. Para el caso del edificio de 28 pisos, se concluye que su nivel de operación no afectó la identificación de los periodos naturales. En el caso del edificio de 11 pisos, el avance constructivo provocó un cambio significativo en el periodo fundamental y amortiguamiento, únicamente para la dirección Norte-Sur. Para el edificio de 6 pisos se calibró un modelo matemático tomando en cuenta cargas gravitacionales reales, secciones no agrietadas de elementos estructurales, una rigidez infinita y restricción a la rotación en las conexiones viga-columna de todos los marcos. The results from five ambient vibration tests performed on three different buildings in San José, Costa Rica, are presented. The main goal was to estimate as much natural periods as possible in both directions of the buildings using the peak picking technique with Fourier spectrums (EF) and transfer functions (FT). The damping was also estimated for one of the buildings using the random decrement technique. For the studied buildings, it is concluded that the differences of the natural periods estimated from EF and FT are negligible, also for each building, with just two measuring points, one in the bottom and the other on the top level, it is possible to identify at least four natural periods. For the 28 story building, it is concluded that its operational level didn't affect the natural period’s identification. In the 11 story building, the construction progress caused a significant change in the fundamental period and its damping for the North-South direction. Finally, for the 6 story building a calibration of the mathematical model was perform taking into account the real gravitational loads, uncracked element sections, an infinite rigidity and a restriction to rotate on all frame beam-column connections. UCR::Vicerrectoría de Investigación::Unidades de Investigación::Ingeniería::Instituto Investigaciones en Ingeniería (INII)

In this paper, a non-destructive technique based on the monitoring of the environmental vibrations of two strategic buildings by positioning accelerometers in well-defined points was used for fixing their dynamic behavior. The accelerometers measurements were elaborated through Operational Modal Analysis (OMA) techniques, in order to identify natural frequencies, damping coefficients, and modal shapes of the structure. Once these parameters have been determined, a numerical model calibrated on the identified frequencies and verified on the corresponding mode shapes was created for each building. The structural operational efficiency index of the buildings was determined by using the Seismic Model Ambient Vibration (SMAV) methodology, which allows us to evaluate their seismic vulnerability. The results obtained from the experimental analysis (on three different tests for each analyzed building) concern the frequencies and the modal shapes of the structure. They have been compared to the results of the finite element model, with a very small error, indicating a good quality of the analysis and also the possibility of using directly well-tuned models for verifying the structural operating indices.

In the last few decades large research efforts have been devoted to the development of methods for automated detection of damage and degradation phenomena at an early stage. Modal-based damage detection techniques are well-established methods, whose effectiveness for Level 1 (existence) and Level 2 (location) damage detection is demonstrated by several studies. The indirect estimation of tensile loads in cables and tie-rods is another attractive application of vibration measurements. It provides interesting opportunities for cheap and fast quality checks in the construction phase, as well as for safety evaluations and structural maintenance over the structure lifespan. However, the lack of automated modal identification and tracking procedures has been for long a relevant drawback to the extensive application of the above-mentioned techniques in the engineering practice. An increasing number of field applications of modal-based structural health and performance assessment are appearing after the development of several automated output-only modal identification procedures in the last few years. Nevertheless, additional efforts are still needed to enhance the robustness of automated modal identification algorithms, control the computational efforts and improve the reliability of modal parameter estimates (in particular, damping). This paper deals with an original algorithm for automated output-only modal parameter estimation. Particular emphasis is given to the extensive validation of the algorithm based on simulated and real datasets in view of continuous monitoring applications. The results point out that the algorithm is fairly robust and demonstrate its ability to provide accurate and precise estimates of the modal parameters, including damping ratios. As a result, it has been used to develop systems for vibration-based estimation of tensile loads in cables and tie-rods. Promising results have been achieved for non-destructive testing as well as continuous monitoring purposes. They are documented in the last sections of the paper.

Rock slope failures can lead to huge human and economic loss depending on their size and exact location. Reasonable hazard mitigation requires thorough understanding of the underlying slope driving mechanisms and its rock mass properties. Measurements of seismic ambient vibrations could improve the characterization and detection of rock instabilities since there is a link between seismic response and internal structure of the unstable rock mass. An unstable slope near the village Gondo has been investigated. The unstable part shows strongly amplified ground motion with respect to the stable part of the rock slope. The amplification values reach maximum factors of 70. The seismic response on the instable part is highly directional and polarized. Re-measurements have been taken 1 year later showing exactly the same results as the original measurements. Neither the amplified frequencies nor the amplification values have changed. Therefore, ambient vibration measurements are repeatable and stay the same, if the rock mass has not undergone any significant change in structure or volume, respectively. Additionally, four new points have been measured during the re-measuring campaign in order to better map the border of the instability., Earth, Planets and Space, 69, ISSN:1343-8832, ISSN:1880-5981

The Church of Gesù and the tower of the Cathedral were stricken and damaged by Emilia-Romagna earthquake sequence of May 2012. This paper presents the procedure for the structural identification of the most widespread types of religious monuments. The dynamic behavior was analyzed using the ambient vibrations test to measure the dynamical properties (mode of vibration, frequencies, displacements and damping ratios) of the constructions using a modal identification of output-only systems. The operational modal analysis OMA has been carried out to identify the modal characteristics through poly-reference Least Square Complex Frequency-domain (pLSFC) estimator. The global structural health monitoring was carried out to define the real dynamic behavior of the damaged constructions that are subjected to different mechanism. These researches are useful for the structural rehabilitation and to define the possible changes in the structural behavior.

Historical churches have shown a dramatic vulnerability in several recent earthquakes, especially when they are adjacent to bell towers. Due to their great number and their societal relevance, low cost and nondestructive survey and investigation procedures are necessary for the seismic assessment. Accurate and fast geometric models can be obtained through digital photo-modeling, and they are the base for finite element models. These models can be updated through ambient vibration testing, which delivers a robust estimate of the fundamental period of the building especially in the case of cantilever-like bell towers. Elastic modulus and boundary conditions can be evaluated through numerical and physical comparison, provided that in situ sampling suggests a masonry density value. Then, compressive strength can be estimated, yielding a more robust seismic assessment. The proposed procedure is applied to the Cathedral of Matera, Southern Italy.

International audience; This article describes an improved data acquisition system from a previous system dedicated to one-sensor site studies, aimed at recording ambient vibrations (microtremors). A multi-channel and/or remote triggering system is proposed. The system was conceived by IRD-Leas, France, and used at ISTerre, France, for research activities. The size, weight of this high quality system and its autonomy (no need to be connected to a laptop) make it a real portable device. The sys- tem acquires data with 24-bit delta-sigma ADCs in the 10 - 1000 sps range at 10 - 20 bit resolution on up to 18 channels in the multi-channel version. The input stage dynamics is available at ±2.5 V or ±5 V. The dynamic range varies, for example, from 108 dB at 100 sps to 90 dB at 250 sps. Gain is selectable from 1 (0 dB) to 8192 (78 dB) by powers of two (6 dB). Its very low level of internal noise allows recording of very low tension signals without missing code. Con- tinuous recording and GPS may also be implemented in the system. While primarily dedicated to ambient vibration recordings, this system can be connected to any type of device delivering an output tension in the ±5 V range.

Energy harvesting is getting significant interest due to the emergence of Internet of Things (IoT). As IoT devices are required to generate power on their own, several researchers are studying ferroelectric materials for voltage generation. However, ferroelectric materials suffer from high resistance at low frequencies, which reduces the output power. Domain wall propagation in ferromagnetic materials, as induced by stress and a pickup voltage using coils, is investigated as an alternate form of energy harvesting. Such studies, which are reported in multiferroic structures, feature a voltage applied to induce the stress, which defeats the purpose of self-power generation. Here, power generation from mechanical vibrations in purely ferromagnetic structures is shown. These results are achieved by showing that the domain walls can be moved entirely by stress in a trilayer stack of ferromagnetic microwires. The use of flexible substrates with low Young's modulus and a trilayer magnetic stack enables the achievement of significant magnetization rotation or domain wall motion even from ambient vibrations. Here, the rotation of magnetization or domain wall motion is exploited to induce voltages in the pickup coils. The results shown here provide an alternative way to power IoT devices. Accepted version

The paper provides results of dynamic numerical analysis of piezoelectric cantilever-type microgenerator intended for wireless MEMS applications. This analysis constitutes an initial phase of ongoing research work aimed at microgenerator optimal design. It is based on beneficial utilization of higher vibration modes, which may offer significant benefits in terms of dynamic performance. Here we report preliminary results of simulations that were performed with a developed 3-D finite element model of the microgenerator that constitutes a bilayer cantilever structure with proof mass at the free end. The structure was subjected to harmonic base excitation by applying vertical acceleration through body load. The resulting characteristics reveal strong dependence of magnitude of generated voltage on design and excitation parameters (frequency, acceleration). Initial findings indicate the necessity to develop microgenerator design with self-tuning of the resonance frequency, i.e. the device should adapt to varying excitation frequency so as to be driven in resonance thereby achieving maximal electrical power output.

International audience; Over recent years there has been a growing interest in the building frequency analysis for earthquake and structural engineering fields using ambient vibrations. Simultaneously, velocity measurements with LASER remote sensing techniques have gained more interest for several applications. This paper details the comparison of the frequency analysis obtained using sensitive velocimeter sensor and coherent LIDAR (Light Detection and Ranging) sensor, and applied to one RC existing building. Ambient vibrations recordings were processed using the Frequency Domain Decomposition method for defining the frequencies and mode shapes of the building target, while LASER remote sensing approach used coherent LIDAR method for velocity and frequency measurement. The results of the two systems are discussed. A good agreement is observed, which let us conclude on the ability of the coherent LIDAR to assess the frequency of existing buildings for structural and earthquake engineering fields at long range and without any retroreflector on the structure.

Continuous broad-band measurements of vibrations on the 3rd floor of the building of the Department of Geophysics, Faculty of Sciences and Mathematics (DGFSM) in Zagreb provided high quality data that enabled monitoring of fluctuations of the building’ s basic dynamic parameters (fundamental frequencies and the corresponding damping). It was found that nonlinear behaviour is present even for the small strains induced by ambient vibrations, which was manifested in measurable reduction of fundamental frequency and increase of damping for larger excitation levels. These effects were also observed in response of the structure to two small local earthquakes which occurred during the observation period. Correlation of the observed long-term wander of dynamic parameters with the change of meteorological elements revealed notable correspondence of the variations of the fundamental frequency and the relative air humidity (which was related to soil saturation, thus causing variability of soil-structure interaction). The damping was found to vary synchronously with the air temperature. The results point to the importance of considering all aspects of nonlinearity of building response even for small strains.

cited By 0; Conference of 2014 Joint IEEE International Symposium on the Applications of Ferroelectric, International Workshop on Acoustic Transduction Materials and Devices and Workshop on Piezoresponse Force Microscopy, ISAF/IWATMD/PFM 2014 ; Conference Date: 12 May 2014 Through 16 May 2014; Conference Code:108512; International audience; Energy harvesting has been studied with great interest in recent years. Ambient vibration is a potential energy resource for low-power devices or electronic devices in extreme/remote area. Methods on enhance the energy conversion amount has been long been a main subject in energy harvesting field. The present study developed a precise model working under hybrid of electrical and mechanical excitations in an Ericsson loop cycles which highly increases the converted energy. Consideration of the dynamic behavior of the nonlinearity of the piezoceramic under high amplitude excitation, the model gives precise prediction of energy conversion amount. This technique can be applied in both energy harvesting and monitoring area. Experiments have been done for different kinds of samples. Comparisons between energy conversion with or without the new coupling technique have been reported and it allows validating this new configuration. © 2014 IEEE.

Economic and environmental imperatives lead to an ever growing need to extend the service life of the existing building stock without putting the users at risk. In zones prone to moderate seismic hazard, many buildings were built without considering seismic actions. The design and assessment of efficient seismic retrofitting rely on physical models of the buildings. However, model errors resulting from simplifications and other assumptions might lead to a biased and thus unreliable diagnosis. Therefore, structural measurements are interpreted to reduce the uncertainty related to the ambiguous task of inferring the real structural response of existing buildings, even in the linear elastic range.This contribution includes the assessment of the retrofitting of an existing masonry building through ambient vibration field measurements. Measured frequencies and mode shapes are interpreted using an error-domain model-falsification framework that allows explicit representation of uncertainties related to modelling and measurement errors. A simple continuous Timoshenko cantilever beam, characterizing the linear elastic dynamic response of the building, is used to model the building. It is concluded that such interpretation of ambient vibration data is useful to assess the efficiency of seismic retrofitting.

The knowledge of fundamental frequency and damping ratio of structures is of uppermost importance in earthquake engineering, especially to estimate the seismic demand. However, elastic and plastic frequency drops and damping variations make their estimation complex. This study quantifies and models the relative frequency drop affecting low-rise modern masonry buildings and discusses the damping variations based on two experimental data sets: Pseudo-dynamic tests at ELSA laboratory in the frame of the ESECMaSE project and in situ forced vibration tests by EMPA and EPFL. The relative structural frequency drop is shown to depend mainly on shaking amplitude, whereas the damping ratio variations could not be explained by the shaking amplitude only. Therefore, the absolute frequency value depends mostly on the frequency at low amplitude level, the amplitude of shaking and the construction material. The decrease in shape does not vary significantly with increasing damage. Hence, this study makes a link between structural dynamic properties, either under ambient vibrations or under strong motions, for low-rise modern masonry buildings. A value of 2/3 of the ambient vibration frequency is found to be relevant for the earthquake engineering assessment for this building type. However, the effect of soil–structure interaction that is shown to also affect these parameters has to be taken into account. Therefore, an analytical methodology is proposed to derive first the fixed-base frequency before using these results.

In this paper, dynamic properties and results of the identification process on the Manhattan Bridge are described. Accelerations during ambient vibrations have been recorded using an advanced MEMSbased system,whose main features are the transmission of the data in digital formand the possibility of performing some system analyses directly on-board of the sensors, transmitting synthetic data only to the main computer. 28 MEMS accelerometers have been used and 4 different experimental setups adopted. Several modes of the main span are identified, with natural frequencies in the range 0.2-1.0 Hz. A FE model updating procedure is also performed by means of an improved Evolutionary Algorithm. After the updating procedure, numerical modal frequencies and mode shapes match well the experimental data. This work is part of a research that aims at investigating how real-time monitoring systems can be used to detect the occurrence of fatigue phenomena induced by vibrations and distortion modes in existing steel bridges. © 2013 Taylor & Francis Group, London.

A large number of buildings in regions with low to medium seismic hazard have been designed without considering earthquake actions. Retrofitting of all buildings that fail to meet modern code requirements is economically, technically and environmentally unsustainable. Decision-making regarding retrofitting necessity and prioritization is complex. Ambient vibrations are non-destructive and easy to measure, and thus an attractive data source. However, ambient vibrations have very low amplitudes, which potentially lead to sensitivity to testing conditions and stiffness contributions from non-structural elements. Seismic assessment necessitates non-linear behavior extrapolation from linear measurements, which results in biased model predictions. Error-domain model falsification is a data-interpretation methodology that is robust to multi-source uncertainties with unknown and changing correlation values. In this contribution, static non-linear behavior predictions of an existing building in Lausanne, Switzerland, are presented. Ambient-vibration data has been gathered under changing conditions: from undamaged in-service to gradual removal of non-structural elements. Low sensitivity to non-structural elements are found. A numerical model based on the applied-element method is generated and shows potential utility of linear measurements for decision-making using non-linear models involving EDMF under uncertain conditions.

The monitoring of flexible structures such towers, antennas and pylons comprising critical infrastructure for power transmission and telecommunications is necessary in order to ensure their continuous operation. This particular field of engineering comes under the umbrella of structural health monitoring, which in recent years has been given high priority in developed countries. There, the built infrastructure is both extensive, encompassing diverse groups of systems such as energy, telecommunication, utility and transportation networks, while at the same time is ageing rapidly. The goal is to set up monitoring schemes with a stand-alone configuration and a wireless transmission of data to central locations for further processing. Thus, it becomes necessary for the sensors employed to have some structural analysis capabilities that can be used in tandem with their data processing functions, all within an artificial intelligence environment. To this end, we develop analytical models for vibrations in elastic waveguides that model flexible structures of variable cross-section and demonstrate their efficiency and accuracy through comparisons with finite element models.