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Highlights: We used array-based ambient vibration modal analysis and eigenfrequency modeling to characterize the dynamic behavior and structural conditions of a partly collapsed lava tube roof. Multiple resonance modes were identified from spectral and cross-correlation analyses, and used to calibrate a heterogeneous numerical model of the lava tube. Our study shows that the combination of experimental and numerical modal analysis is a valuable tool for mapping and structural characterization of underground cavity roofs. [ABSTRACT FROM AUTHOR]

In this study, we determine the properties of the maar volcanic structure using ambient vibration analysis. We performed several ambient vibrations surveys at Mýtina maar (West-Bohemia, Czechia) to map amplification by site-to-reference spectral ratios and to estimate average shear wave velocities by array methods. As the maar diatreme is formed by a deep concave body of broken rock, strong 3D resonances develop. The site-to-reference amplification factors reach a value of 20 in the central part of the maar. Using the noise data, we demonstrate possibility of mapping the lateral dimensions of the maar infills by ambient noise measurements. To understand these observations, we developed a simplified 3D viscoelastic velocity model and simulated synthetic ambient vibrations by the finite difference method. The simulated response fitted both, measured fundamental frequencies and the amplification levels. The maximum depth of the crater was estimated to be at least 800 m. [ABSTRACT FROM AUTHOR]

One of the main strategies of disaster risk reduction policies in seismic-prone areas is to assess a building's susceptibility to critical structural behaviour, which could induce and aggravate seismic damage. Subsequently, it is important to implement structural upgrading interventions to remove or reduce such critical issues. For existing buildings, this strategy is a core aspect of vulnerability assessment methods, and it is usually inferred by analysing specific features of site and building conditions. Both vulnerability assessments and structural upgrading interventions would benefit from a rapid check aimed at verifying, through on-site measurements, if the presumed structural behaviour (before and/or after the interventions) corresponds to the actual situation. This paper presents an integrated methodology, conceived to account for the above-mentioned issues, based on the acquisition and interpretation of ambient vibrations. The paper illustrates the use of the proposed methodology in different applications, first, for a preliminary characterisation of the situations, then, as a support in the assessment and definition of actions to reduce the structural vulnerability, and finally, for a-posteriori effectiveness control of the upgrading interventions being implemented. To conclude, the paper provides some considerations on the strengths and limitations concerning the use of the methodology for seismic risk reduction purposes. [ABSTRACT FROM AUTHOR]

We introduce non-invasive seismic methods for identifying and characterizing maar sedimentary infills. We conducted a dense ambient vibration survey and employed state-of-the-art 3D resonance analysis techniques to map the lateral extent and depths of the sedimentary layers, a challenge with traditional geophysical methods due to unfavorable aspect ratios (depth > lateral dimension). The ambient vibrations of maars are predominantly driven by normal mode motions due to 3D resonance of crater infills. Dense station coverage enabled detailed images of the normal mode shapes revealing infill symmetries. The resonance results in extreme ground motion amplification, with factors reaching up to 30 on the vertical component, challenging conventional beliefs about site effects and methodologies based on widely used horizontal-to-vertical spectral ratios. These results are supported by numerical simulations of the maar's seismic response. The observed response is so specific that it can be used to identify partly eroded maar structures in the field. • 3D resonance in the maar infill with amplification of ground motion of factor 30. • Ambient vibration used to constrain depth, width, and internal structure of the maar. • The widely used HVSR does not work in the case of deep maar sediments. [ABSTRACT FROM AUTHOR]

The reliability of non-invasive shear wave velocity (Vs) profiling techniques is assessed for four Ontario highway sites in comparison to invasive methods (N60, su, laboratory bender element Vs, borehole geology). Our non-invasive Vs profiles are obtained from joint inversion of surface wave dispersion and microtremor horizontal to vertical spectral ratio peak(s). The overall inter-method average relative difference in soil Vs is 15%. Non-invasive and invasive methods provide consistent Vs30 and earthquake site classification. Multi-method site classification demonstrates greater success of non-invasive and invasive methods to determine the Vs profile and soil properties respectively. [ABSTRACT FROM AUTHOR]

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 reinforced-concrete (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. [ABSTRACT FROM AUTHOR]

Seismic behavior of masonry walls has been heavily investigated, especially by means of laboratory experiments employing cyclic tests to determine the mechanical parameters and seismic capacity. Nevertheless, the dynamic properties of the tested walls often remain unknown, even though the nature of the seismic response is dynamic and profoundly affected by the structure's dynamic properties. This paper presents an investigation on the dynamic properties of three different masonry wall panels in healthy and damaged states, and examines if damage quantification via tracking the changes in dynamic properties is feasible. Ambient vibration and impact measurements are used for the dynamic identification of wall panels, before and after they are tested in reversed-cyclic in-plane shear-compression tests. The natural frequencies, damping ratios, and mode shapes of the walls are determined and compared to each other. Moreover, the damage progression and its effect on the dynamic features of the URM wall panel is investigated using a discrete element model of the benchmark wall that is validated in terms of the force-displacement response and damage pattern of the wall. The results of the study indicate that changes in natural frequencies and mode shapes are traceable, although it is difficult to infer damage quantification relationships from these changes. The outcomes of this study also highlight that numerical models verified with the nonlinear quasi-static behavior do not necessarily match the wall's dynamic behavior, and that more research is required to update nonlinear numerical models. Overall, the results contribute to the knowledge regarding the dynamic characteristics of masonry walls in healthy and damaged conditions, and to quantify the damage in masonry walls as well as the changes in their dynamic properties. • Cyclic shear-compression tests on three stone masonry wall panels. • Dynamic identification in healthy state and after damage. • Effects of damages on the dynamic properties of the walls. • Effects of strengthening on the dynamic properties of the walls. • Numerical investigation of modal properties in healthy and damaged states. [ABSTRACT FROM AUTHOR]

This paper presents results from the dynamic monitoring of a reinforced concrete school building located in Camerino (central Italy) during the seismic swarm following the first main shock of the Central Italy earthquake that occurred in August 2016. After the main shock of August 24th, ambient vibration tests were executed on the building to identify its modal dynamic behavior, which was assumed as benchmark to study changes in the structural response because of the subsequent events. A three-day dynamic monitoring was then performed with the aim of investigating changes in the dynamic behavior of the building subjected to ambient and seismic excitations. A procedure to identify the nonlinear response of the structure subjected to seismic events is presented, starting from an optimization methodology that permits the identification of the structure dynamics within time windows in which the building dynamic behavior can be considered linear time-invariant. Data show the variability of the modal properties, resonance frequencies, and damping ratios of the building, with the earthquake intensity. [ABSTRACT FROM AUTHOR]

The ambient vibration horizontal-to-vertical spectrum method (HVSR) is widely used in microzonation and structural studies, assuming stability and reproducibility of HVSR frequency peaks. A 35-day continuous HVSR monitoring performed in the suburbs of Algiers (Algeria) reveals that HVSR peaks are not always stable and reproducible both in frequency and amplitude. HVSR curves show a first peak, which varies from 0.9 to 1.8 Hz with amplitudes from 0.9 to 3.3, and a second peak from 5 to 7.7 Hz with amplitudes from 1.4 to 4. These results show that HVSR peak frequencies and amplitudes are highly sensitive to nearby anthropogenic sources. [ABSTRACT FROM AUTHOR]

Twenty-nine single-station noise measurements, processed through the Horizontal to Vertical Spectral Ratio (HVSR) technique, a Multichannel Analysis of Surface Waves (MASW) survey, and two 2D array measurements were performed in Durrës to provide useful elements for a geophysical subsoil characterisation. Results from noise measurements defined a zone eastwards of the historical centre, where the characteristics of shallow soil layers are responsible for modification to the seismic response. In particular, HVSR curves in this area showed amplitude higher than 3.4 at a period higher than 1 s. From the analysis of the collected data, four different groups of HVSR curves were recognised, whereas noise measurements were also used to retrieve a preliminary bedrock depth map. These results are potentially useful for correlating construction typologies and vibration period of the buildings with the site amplification and with the damages observed during the seismic sequence for which the highest magnitude event was the MW 6.2, 26 November 2019 earthquake. Moreover, two shear waves velocity VS profiles were obtained from a joint inversion of Rayleigh curves with ellipticity. In one case, it revealed the presence of a soil of very poor mechanical properties, which was classified as D soil according to the international codes (EC8, NEHRP); in the other case, the VS profile allowed us to retrieve important information about the seismic bedrock to be used in numerical modelling for the third level of seismic microzonation. [ABSTRACT FROM AUTHOR]

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-negligible errors in the estimation of mode shapes. Synchronization discrepancies are predominantly associated with wireless structural health monitoring systems, where each wireless sensor node functions as a separate data acquisition unit (DAQ), and clock synchronization is therefore not intrinsic. However, synchronization discrepancies may also occur in cable-based systems, particularly when more than one DAQ is used. In this paper, a synchronization method for detecting and correcting synchronization-induced errors in OMA is proposed. Unlike existing approaches on removing synchronization-induced errors at the output stage, the method proposed herein yields synchronized structural response data at an intermediate stage of OMA. Specifically, time lags between acceleration response data sets are detected based on estimates of the mode shapes obtained either from preliminary structural analysis or from engineering judgment assuming classical damping. The applicability of the proposed method is verified through simulations of a multi-degree-of-freedom oscillator and validated through ambient vibration field tests on a pedestrian overpass bridge. [ABSTRACT FROM AUTHOR]

This paper presents the experimental application of a new method for seismic vulnerability assessment of buildings recently introduced in literature, the SMAV (Seismic Model Ambient Vibration) methodology with reference to their operational limit state. The importance of this kind of evaluation arises from the civil protection necessity that some buildings, considered strategic for seismic emergency management, should retain their functionality also after a destructive earthquake. They do not suffer such damage as to compromise the operation within a framework of assessment of the overall capacity of the urban system. To this end, for the characterization of their operational vulnerability, a Structural Operational Index (IOPS) has been considered. In particular, the dynamic environmental vibrations of the two considered strategic buildings, the fire station and the town hall building of a small town in the South of Italy, have been monitored by positioning accelerometers in well-defined points. These measurements were processed through modern Operational Modal Analysis techniques (OMA) in order to identify natural frequencies and modal shapes. Once these parameters have been determined, the structural operational efficiency index of the buildings has been determined evaluating the seismic vulnerability of the strategic structures analyzed. his study aimed to develop a model to accurately predict the acceleration of structural systems during an earthquake [ABSTRACT FROM AUTHOR]

Summary: The aim of this paper is to identify, both through microtremor analysis and visual inspection, the collapse mechanisms of the Nepalese wood‐masonry monuments damaged by the 2015 seismic event that struck Kathmandu and its valley. The research analyses two case studies as the "Radha Krishna" temple located in Teku, a district in Kathmandu, and the "Pancha Deval complex" in Pashupati area. More specifically, after a careful anamnesis based on visual inspection and hypotheses on the temple's structural behaviour, global nondestructive testing (microtremor) was carried out for qualitative characterization of the structural system. The visual damage survey allowed to identify the recurring collapse mechanisms in the two case studies with the identification of typical Nepali expected damage. The case of Radha Krishna temple denotes a Nepali collapse mechanism typical in the corner of temples made of timber masonry, in which the mechanical contribution of the timber is manifested through columns and windows. The ambient vibration analysis carried out by tromograph device and microtremor evaluation allowed to dynamically characterize the two bases by identifying the peak frequencies both for Radha Krishna and for Pancha Deval complex. With the same device, the two historic constructions have been also studied in evaluating local modes and frequency. In the Pancha Deval complex, a relationship between damage, frequencies, and the amplification of the base was observed. In detail, the five buildings have similar damage and similar first frequencies (2.72–2.9 Hz). The most damaged sides are those with the frequencies close to the base (2.05–2.38 Hz). [ABSTRACT FROM AUTHOR]

Study on applicability of two modal identification techniques in irrelevant cases is made in this paper. The following techniques are considered: peak picking based on correlation analysis (PP-CA), dedicated for ambient vibrations and eigensystem realization algorithm (ERA), formulated for free-decay vibrations investigation. Irrelevant cases are found when analyzed signals are different than recommended to a given technique. The study is conducted on examples of two real structures: masonry tower and steel railway bridge. Both cases are diverse in age, material, excitation and vibrations energy. The signals measured on the tower are suitable for the PP-CA technique (ambient vibrations), while the signals measured on the bridge are suitable for the ERA (free-decay vibrations). However, both methods have been applied to both systems. Natural frequencies, mode shapes and damping ratios are identified and the effectiveness of the irrelevant technique is assessed in relation to the results obtained by the relevant method in each case. [ABSTRACT FROM AUTHOR]

This paper reports the results of an experimental campaign carried out on prestressed concrete beams (PCB), equipped both with bonded and unbonded strands, with the aim to employ Operation Modal Analysis (OMA) techniques to detect early warning signs (i.e., variation of natural frequencies and/or relevant mode shapes) associated to the onset of structural damages. With respect to similar past experimental studies, the main novelties presented hereafter concern the application of OMA to the following situations: (1) a PCB equipped with bonded strands and affected by a "almost pure" shear-cracks pattern; (2) a PCB equipped with unbonded strands and affected by an almost negligible (i.e., reversible) flexural damage. Among the outcomes of this study, it was found that, especially in the second case, the assessment of variations in the PCB natural fundamental frequencies, is not always an effective index of damage. On the contrary, a qualitative comparison between the undamaged and damaged identified mode shapes can be helpful even for the spatial location of the damage. Eventually, despite the diverging opinions in the reference literature, it is found that OMA technique is not a suitable tool to assess the potential influence of variations of the precompression load on the PCB fundamental frequencies, unless this variation is so high to cause cracking. • Operation Modal Analysis (OMA) applied to prestressed concrete beams (PCBs). • Beam-1 equipped with bonded strands and affected by almost pure shear-cracks. • Beam-2 equipped with unbonded strands and affected by negligible (i.e., reversible) flexural cracks. • Surprisingly, variations in the PCB natural fundamental frequencies are not always an effective index of damage. • On the contrary, a qualitative comparison between the undamaged and damaged identified mode shapes can be helpful even for the spatial location of the damage. • OMA technique is not a suitable tool to verify the potential influence of variations of the actual strands' tensile load on PCB fundamental frequencies. [ABSTRACT FROM AUTHOR]

Summary: This paper describes a miniaturized energy harvester based on the interaction of two permanent magnets placed on both ends of a folded cantilever made with piezoelectric thin films. A unique design of the folded cantilever structures is developed to efficiently collect ambient vibrational energy over a wide frequency bandwidth for the operation of battery‐free electronic devices. The output performance of the two energy harvesters is observed to improve significantly through the use of the mutual coupling technique. The folded cantilever structure also demonstrates improved space efficiency compared with the conventional rectangular cantilever design. A wide frequency band and sufficient energy‐harvesting ability were successfully achieved by the optimally manufactured device. The maximum output power of the miniaturized energy harvester was 41.6 μW with an impedance of 0.3 MΩ. Furthermore, a pedometer was powered completely by the energy harvester without the need for any battery and external power source, demonstrating the potential of the proposed design for self‐powered electronics applications in a vibrational environment. [ABSTRACT FROM AUTHOR]

Summary: This paper describes a miniaturized energy harvester based on the interaction of two permanent magnets placed on both ends of a folded cantilever made with piezoelectric thin films. A unique design of the folded cantilever structures is developed to efficiently collect ambient vibrational energy over a wide frequency bandwidth for the operation of battery‐free electronic devices. The output performance of the two energy harvesters is observed to improve significantly through the use of the mutual coupling technique. The folded cantilever structure also demonstrates improved space efficiency compared with the conventional rectangular cantilever design. A wide frequency band and sufficient energy‐harvesting ability were successfully achieved by the optimally manufactured device. The maximum output power of the miniaturized energy harvester was 41.6 μW with an impedance of 0.3 MΩ. Furthermore, a pedometer was powered completely by the energy harvester without the need for any battery and external power source, demonstrating the potential of the proposed design for self‐powered electronics applications in a vibrational environment. [ABSTRACT FROM AUTHOR]

• Efficient and compact low frequency electromagnetic energy harvester. • Stacked orthoplanar springs increase compactness by enclosing components within them. • Magnets disposition enhances energy conversion at low excitation amplitudes. • Improved energy conversion far from eigenfrequency of the system broadens the voltage signal bandwidth. • 3D printing additive manufacturing process proves the affordability and accessibility to build the harvester. Electromagnetic energy harvesters are commonly known for their high performances in terms of power output conversion, and they are suitable for low frequency environmental vibrations. This work reports the study, design, development and experimental validation of a new extremely compact, low frequency, electromagnetic energy harvester based on two stacked ortho -planar springs, which exploits a promising magnets disposition. The device is composed by two stacked ortho -planar springs connected externally by a rigid frame. The two internal moving parts are connected to each other by a central pivot where an array of magnets is fixed on in a peculiar disposition: a half has a magnetic field directed upward, while the other half directed downward. A copper coil is wound into a housing fixed on the external frame. It comes a central massive cursor that axially moves, exploiting the springs compliance, relatively to the external frame. The prototype was almost completely realized by using Filament Fused Fabrication (FFF) additive manufacturing process in Onyx material, carbon fibre reinforced nylon. In the experimental assessment an oscillating excitation was applied on the external frame in multiple linear sweep frequency tests with different amplitude signals. The experimental validation shows a large bandwidth, from 10 to 30 Hz, and consistent output voltage and power signals. [ABSTRACT FROM AUTHOR]

Damage localization based on ambient vibration data in combination with finite element models can be challenging, in particular due to the large number of parameters in the model and noisy measurement data. Changes in different structural parameters can cause similar changes in data-driven features, and vice versa, it can be challenging to identify which parameter caused the deviation in the data. The problem is ill-conditioned and slight variations in the features, due to inherent statistical uncertainty, can lead to significant errors in the result interpretation. A possible solution is sensitivity-based statistical tests in combination with a parameter clustering approach that considers the uncertainties of data-driven features. In this context, this paper introduces the concept of damage localizability , and provides a framework to evaluate it based on the minimum detectable parameter changes, possible false alarms in unchanged parameters, as well as the achievable damage localization resolution. Since clustering approaches depend on user-defined hyperparameters, such as the number of clusters, the second objective of this paper is to optimize the performance of the damage localization, by adjusting the hyperparameters for clustering. A particular strength of the approach is that the analysis can be conducted based on data and a numerical model from the undamaged structure alone, making it a suitable approach to assess and to optimize the diagnosis performance before damage occurs. For proof of concept, a laboratory case study on a simply-supported steel beam is presented, where the localizability of mass changes is analyzed and optimized. • An approach is developed to assess and optimize the performance of damage localization tests. • Clustering of sensitivity vectors avoids ill-conditioning. • Localizability is defined by the three criteria: resolution, detectability, and false alarms. • All criteria can be quantified based on data from undamaged structures, and a numerical model. • Experimental data confirm the predictive capabilities of the performance assessment. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

In this study, two different historical structures built in Trabzon have been processed by ambient vibrations and seismic refraction measurements. One of the investigated historical structures is the Atatürk Pavilion built in the nineteenth century, and the other one is Hagia Sophia which was built in the thirteenth century. These two buildings are among the most important historical buildings in Trabzon and are very important for the tourism of the city. In order to determine peak/s frequency and amplitude from the horizontal-to-vertical spectral ratios (HVSRs), we have performed several measurements of ambient vibrations both inside (at different floors) and outside (on the ground) of structures. We have also conducted seismic prospecting to evaluate the vertical 1D and 2D profile of longitudinal and shear seismic waves, Vp and Vs, respectively. To this purpose, we have performed seismic refraction tomography and MASW. Ambient vibrations and seismic measurements were compared with each other. The results show that average predominant frequencies and HVSR amplitudes of inside and outside of Atatürk Pavilion are 4.0 Hz, 7.8 Hz and 2.6, 2.3, respectively. The Vp values vary from 300 to 2070 m/s, and the Vs for maximum effective depth is up to 790 m/s in Atatürk Pavilion. On the other hand, average predominant frequencies and HVSR amplitudes of inside and outside of Hagia Sophia and its tower are 4.7, 4.4 and 2.4 Hz and 1.6, 1.8 and 6.9, respectively. Vp values range from 450 to 2200 m/s, and Vs for maximum effective depth is also up to 1000 m/s in Hagia Sophia. The frequency values (F0 = Vs/4 h) calculated from the velocities up to the maximum effective depth for Atatürk Pavilion are in good agreement with the predominant frequency values determined from ambient vibrations. Atatürk Pavilion and Hagia Sophia soils have been classed according to Eurocode 8 by using VS30 values. The class was defined as "B." Moreover, the bedrock in studied area is basalt. The high Vp and Vs values are also compatible with the lithology. The HVSR curves measured at the Hagia Sophia show the presence of clear peaks when compared to the Atatürk Pavilion. At the same time, there are marked velocity changes in the Vs sections calculated in both areas. As a result, in both areas there are significant impedance contrasts in the subsoil. However, this impedance contrast is more evident in Hagia Sophia. This could be also compatible with a lithological transition. The possible soil-structure interaction was investigated by using all the results and evaluated in terms of resonance risk. It is thought that the probability of resonance risk at Atatürk Pavilion is low according to the ambient vibrations measurements. However, resonance risk should be taken into consideration at Hagia Sophia site since the predominant frequency values are very close to each other. Finally, this site should be investigated in detail and necessary precautions should be taken against the risk of resonance. [ABSTRACT FROM AUTHOR]

On December 13th 1990 a magnitude 5.6 seismic event, felt throughout Sicily, and having maximum seismic intensity VII-VIII, occurred. Although, it is classified as moderate magnitude, it caused causalities and the collapse of a few buildings. Two of the most struck cities were Carlentini and Lentini, located in south-eastern Sicily at about 20 km from the instrumental epicenter. In order to evaluate the influence of ground features on the damage distribution, both vulnerability and damage maps were drawn using information collected in about 6000 forms coming from official ascertainments. Significant damage observed in some portions of the investigated areas, appears related to the modest quality of the buildings that were classified as medium to high vulnerability. To evaluate the role played by the geologic setting, two sites were instrumented to measure shear-wave velocity of the main lithotypes. Sixty-three ambient vibrations measurements were also performed both in free field and inside some buildings. Moreover, using information coming from geological and geophysical surveys, 1D numerical modelling were done to achieve information about the main ground motion parameters. The results highlight the occurrence of significant site effects and the potential presence of resonance phenomena between site and structure during the occurrence of a seismic event. Seismic site amplifications together with the buildings' vulnerability, observed through damage surveys, contributed to enhance the inherent seismic risk of the investigated area. [ABSTRACT FROM AUTHOR]

In this work we study in terms of Tsallis statistical mechanics the properties of microtremors’ fluctuations in two church bell towers, which are monuments of cultural heritage, in the city of Chania (Crete, Greece). We have shown that fluctuations of ambient vibrations recordings in the Church tower bells follow a q -Gaussian distribution. The behavior of Tsallis q parameter with the level (high) of the measuring point within the tower and the amplification factors at that points as extracted from horizontal-to-vertical (HVSR) spectral ratios are presented and discussed. Since q decreases as the amplification factor increases, we could suggest q as a vulnerability index, where, as q decreases approaching unity, then the structural system is getting more vulnerable. The latter approach suggests that introducing ideas of Tsallis statistics could be useful in characterizing extremely complex processes as that governed the estimation of seismic vulnerability in which a multidisciplinary approach is required. [ABSTRACT FROM AUTHOR]

• Complex modal parameter identification under ambient excitation is studied. • A Bayesian strategy is adopted to find the uncertainty in identified parameters. • Objective function gradient is employed to make the optimization efficient. • Phased optimization technique is prescribed for better convergence. • An experimental study is included to investigate the applicability of the method. In this work, we present a Bayesian time–domain method for identifying the complex modal parameters of a linear dynamic system from ambient vibration data. Complex modal parameter identification is valid for both classically and non-classically damped systems, in contrast to real modal parameter identification, which is exclusively applicable to classically damped systems. A Bayesian method is adopted here which makes it possible to determine the joint posterior Probability Density Function (PDF) of the modal parameters for given measured data and modeling assumptions. For sufficient data, it is seen that the modal parameters are globally identifiable, and the posterior PDF is approximated by a Gaussian distribution with mean at the optimal parameters that maximize the posterior PDF. The uncertainty in the identified modal parameters is given by the covariance matrix of the posterior PDF. Analytical expressions are derived for computing the gradient for efficient optimization and the Hessian for determining the covariance matrix. Further, it is shown that the assumption of classical damping during analysis results in poor prediction of damping ratios in the case of non-classically damped systems. The application of the proposed approach is illustrated by means of simulated examples and an experimental study. [ABSTRACT FROM AUTHOR]

Introduction- The construction of long-span bridges, especially box girder type, has been increasing in recent years in Colombia. Due to the importance that these structures represent for the infrastructure of the country, there is a need to monitor their structural integrity to analyze their behavior throughout their life cycle, detect changes caused by possible damages and establish maintenance plans. This monitoring can be carried out through the characterization of the dynamic properties of the structure. Objective- This study shows the results of the structural health monitoring baseline carried out in the Gómez Ortiz bridge. The dynamic characterization of the structure is performed and discussed, as well as the process of adjusting a numerical model based on the experimental results. Methodology- The dynamic characterization of the structure was carried out using the experimental technique based on ambient vibration tests. Four different techniques were used to post-processing the data obtained in these tests such as Peak Picking (PP), Frequency Domain Decomposition (FDD), Enhanced Frequency Domain Decomposition (EFDD), and the Stochastic Subspace Identification (SSI). Results- Experimental information of the dynamic properties of the bridge was obtained in the study, such as fundamental frequencies, modal shapes, and damping ratios. Conclusions- The results of the study demonstrated that the four techniques show similar results, except for damping ratios, which confirms the uncertainty of the experimental techniques to define this parameter. [ABSTRACT FROM AUTHOR]

The challenges of accurately identifying the dynamic characteristics of bridge structures from ambient vibration responses persist because, unlike in the ideal laboratory environment, elevated levels of noise in data are unavoidable at any in-situ testing site and may have detrimental effects on the modal parameter identification process and results. This is especially true for vibration tests conducted under weak ambient excitation sources resulting in poorer signal-to-noise ratios (SNRs). This paper presents an investigation into the feasibility and reliability of modal identification using operational modal analysis (OMA) techniques under such weak excitation circumstances and with responses measured by inexpensive stand-alone accelerometers/data recorders. An eleven-span concrete motorway off-ramp bridge, closed to traffic, was excited only by ground vibrations generated by traffic on the motorway passing underneath the bridge as well as on nearby motorway on- and off-ramps, weak winds, and possible micro tremors. A high spatial resolution of measuring points on the bridge deck was used to collect vibration responses. Three output-only modal parameter identification algorithms were utilised to extract the modal properties, namely the peak picking (PP), the frequency domain decomposition (FDD) and the data driven stochastic subspace identification (SSI) method. Nine lateral and three vertical modal frequencies below 10 Hz could be identified despite the weakness of the environmental excitations and noise in sensors. The identified experimental natural frequencies were stable, damping ratios, however, had a marked scatter. A comparison with the results of a numerical modal analysis using a finite element model revealed, however, that several higher order vertical modes were missing from the experimental results altogether, and some of the OMA methods missed the fundamental lateral mode. Overall the PP method was the most successful in finding the largest number of frequencies but the SSI method yielded the highest quality mode shapes. The SSI method is, however, computationally more expensive that the remaining two methods. For quick, preliminary results, the PP and FDD methods can still be useful and detailed analyses could use SSI and FDD. Overall, the study argues that output-only system identification can provide useful quantitative insights into the modal properties of stiff bridges even under weak environmental excitations, or poorer SNRs, but its limitations need to be acknowledged. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

This study uses ambient vibrations to monitor rock bolting works, the efficacy of which is usually difficult to estimate. The test site is a 760 m 3 unstable limestone column located in the Bourne valley (Vercors, France). The rock column's resonance frequencies ( f X ) were identified, corrected for reversible thermal effects and monitored over time. We observed clear increases in f X up to ~ 17% resulting from the additional stiffness provided by the steel rock bolts. Numerical modeling helped to confirm that the rebar elements were grouted on both sides of the fracture. The major column's resonance features, such as the resonance frequencies and mode shapes, were successfully simulated, including their evolution with bolting. The amount of f X increase depends on the mode considered, likely controlled by bolt location in comparison with the modal shape. This study confirms the potential of ambient vibrations to provide global in-depth information on the stability evolution of rock compartments, with versatile applications for monitoring potential rockfalls or reinforcement works. [ABSTRACT FROM AUTHOR]

A 3-storey residential building with OSB-sheathed light-frame timber walls and timber-concrete composite slabs was subjected to dynamic excitation in two different stages of construction. The experiments consisted of measurements of the accelerations resulting from forced horizontal vibrations which were excited by means of a hydraulic actuator shaking a mass of 940 kg. The exciter was positioned on the second floor of the building and rigidly anchored in the slab. It excited the building in its two main directions to vibrations with frequencies within a range of 0.2-14 Hz. Natural frequencies, modal damping ratios and mode shapes of the building were estimated using accelerations of the building measured in the four external corners of each upper floor. For increasing displacement amplitude (1/8000 mm → 0.7 mm) the natural frequencies decreased moderately (−15 %) whereas the modal damping ratios increased markedly (+100 %). Modal damping ratios computed using ambient vibration data were generally smaller than modal damping ratios obtained from forced vibration tests, which suggests that modal damping for the levels of vibration in interest in design might be significantly underestimated if based on results from ambient vibration tests. However, the mode shapes computed using ambient vibration data turned out to be reliable. The differences in dynamic properties assessed in the different stages of construction were much smaller than expected. Compared to the natural frequencies estimated by the designer by applying a simple single degree of freedom model, the measured natural frequencies were considerably higher. This may be attributed to the impact of non-structural internal walls and walls with openings not accounted for in the designer's model. [ABSTRACT FROM AUTHOR]

The 2001 Mw 7.6 earthquake sourced in the Kachchh rift of northwest India led to extensive damage in the city of Bhuj, located ~70 km southwest of its epicenter. The building stock of this densely populated city was a mix of modern, single, and multistoried structures as well as traditional and non-engineered abodes, most of which were not designed to withstand severe shaking effects. Although there was extensive liquefaction and ground failure in the meizoseismal area, they were not observed in Bhuj, but the damage was severe here. In this study, we apply horizontal to vertical spectral ratio method to ambient vibrations (HVSR-AV) to obtain fundamental resonance frequency (f0) and H/V peak amplitude (A0) to examine if site response had any significant role in the observed damage. The patterns of H/V curves as well as spatial distributions of f0 (0.6-1.4 Hz) and A0 (1.5-4.4) suggest absence of any strong impedance contrast within the subsurface. Similar results obtained for ambient vibrations and earthquake signals suggest the efficacy of the HVSR-AV method as most useful for regions of low-level seismicity. The weathered sandstone that is generally exposed in the city represents the resonating layer whose thickness is approximately estimated as ~66-155 m, based on 1D assumption. The current set of available data precludes any quantitative modeling, but our preliminary inference is that site effects were not significant during the 2001 earthquake damage observed in Bhuj. [ABSTRACT FROM AUTHOR]

Cascais County, located in the central part of the Portuguese mainland, is a very attractive place due to its interesting and recognized natural and cultural heritage. Leisure and cultural activities attract many people every day, which leads us to the importance of safeguarding from possible risks. Taking into account the historical seismicity, in particular the damage caused by the 1755 earthquake and tsunami in Cascais, it becomes clear that the seismic risk is relevant in Cascais County. In this paper, we present a methodology to obtain a seismic susceptibility map based on a soil characterization study using the refraction microtremor technique and ambient vibration measures ( H/ V Nakamura technique). This kind of map gives a detailed picture of the zones that can suffer larger seismic ground motion that can be easily consulted and understood by technicians, making it a suitable work tool. Considering the extent and geological diversity of the area, we selected some representative sites to perform the experiments, taking into consideration the different surface geological formations, paying particular attention to situations with the greatest potential risk. [ABSTRACT FROM AUTHOR]

This research demonstrates an integrated non-invasive assessment method of monumental structures based on dynamic monitoring through ambient vibrations as well as non destructive and microdestructive testing. The investigation involves the analysis of a very complex and extraordinary case study, i.e., the Rialto Bridge in Venice. Dynamic monitoring based on natural vibration sources as inputs from pedestrian traffic, wind and the waves of the Canal Grande – was exploited by dynamic identification process to determine damping coefficient, frequency and modal shapes. The non-destructive and microdestructive tests included sonic and georadar methods and the extraction of very small samples of masonry for destructive tests in laboratory. The experimental investigation on the whole was conceived to avoid any type of invasive action on the prestigious monument. The aim of this research is to propose a new integrated protocol potentially suitable and generalizable for the assessment of monumental structures. The new features in the combined method include two types of results – qualitative and quantitative types – through a flow chart to explain the methodology and generalize the different phases of the approach for historical constructions. [ABSTRACT FROM AUTHOR]

This paper proposes an automatic modal analysis approach for signals of high-rise buildings recorded under real-world ambient excitations. The fact of working over such type of signals is faced with several challenges: the time-domain convolution between the system impulse response and the seismic noise, the existence of several components, the presence of closely-spaced frequency modes, with high additive noises, and low, exponential and damped amplitudes. The proposed approach handles these challenges simultaneously without the need for a user intervention. It is based on a filter-free Random Decrement Technique to estimate the free-decay response, followed by a spectral-based method for a rough modal estimate and finalized by a Maximum-Likelihood Estimation process to refine the modal estimates. Each of these processes is responsible to tackle one or more of the aforementioned challenges in the aim to provide an automatic and moreover a reliable modal analysis of the studied signals. [ABSTRACT FROM AUTHOR]

The city of Oran experienced several earthquakes. Therefore, the characterization of its subsurface is crucial for a better evaluation of the seismic hazard. Using ambient vibration single-station and array measurements at 193 sites, the HVSR curves showed a variation of the fundamental frequency peak between 0.3 and 7.4 Hz, growing towards the west, with maximum amplitude of ∼6. The shallow structure has been explored by means of F–K analysis. Joint inversion of the HVSR and Rayleigh wave dispersion curves showed 3 layers of soft and stiff sediments of varying thicknesses overlying the bedrock. The shear-wave velocity (Vs) of the sediments varies between 280 and 1300 m/s and that of the bedrock can reach 2500 m/s. Cross sections show a decrease in sediments thickness from east to west where bedrock outcrops. The maximum depth of bedrock is 1050 m northeast of the city. The obtained Vs models support a soil classification ranging from stiff soil to hard rock. • Ambient vibrations methods are applied for the first time in Oran city. • Joint-inversion of HVSR and dispersion curves led to a model of the 3D Vs structure. • Boreholes data constrained the Vs profiles resulting from the joint-inversion. • This study contributes to the estimation of the seismic hazard in Oran. [ABSTRACT FROM AUTHOR]

A blind comparison of independent invasive (downhole, standard penetration, bender element) and non-invasive microtremor shear-wave velocity ( V S ) profiling is presented for 11 strong-motion stations in central and southern Chile that recorded the 2010 M W 8.8 Maule earthquake. For the majority of stations, site classification based on average V S in the upper 30 m ( V S30 ) is consistent irrespective of methodology. For a variety of geological conditions, excellent to good agreement is obtained between invasive and non-invasive V S structure at five stations over the entire borehole length and in the uppermost layer at three stations. Site classification based on site period is evaluated using earthquake and microtremor recordings. Short site periods are observed at stiff coarse-grained stations whereas longer site periods are observed at soft fine-grained stations. The use of both V S30 and site period criteria are recommended in future revisions of the Chilean building code for robust earthquake site response characterization. [ABSTRACT FROM AUTHOR]

The paper presents the modal characteristics of a tall building in Bucharest (BRD-SG Tower) identified from earthquake and ambient vibration records. The building was built in the early 2000's and has a reinforced concrete structure (inner shear wall tube and perimeter frames) with 3 underground stories, ground floor and 18 stories. The seismic instrumentation of the building consists of a seismic station with two triaxial acceleration sensors located at the top of the building (+69.6 m) and at the third basement (-9.3 m). The dynamic characteristics of the building are estimated from the seismic records from 23 earthquakes (with moment magnitudes MW between 3.7 and 6.0) that occurred during the period 2004/2010. The results obtained from the earthquake records are compared with those obtained from 35 ambient vibration records from the period 2003/2010. [ABSTRACT FROM AUTHOR]

Energy harvesters based on Micro-electromechanical systems (MEMS) are well known nowadays due to their small features, ability for monolithic integration with the integrated circuit in a single platform, robust, and easily fabricated in bulk. The piezoelectric (PZT) and the electromagnetic (EM) generators are examples of such energy harvesters. To further increase their effectiveness in harvesting ambient energy, researchers started to venture into hybrid energy harvesters. Few literature reviews may be found on MEMS harvesting devices, but not on hybrid harvesters in specific. This paper intended to further elaborate on the hybrid energy harvesters, reported Literature on such harvesters for recent years with different architectures, models, and results are presented. Table of power comparison between the reported harvesters is presented and discussed. [ABSTRACT FROM AUTHOR]

Results of an extensive ambient vibration surveys carried out by different research teams in the area damaged by May-June 2012 seismic sequence in Emilia Romagna (Northern Italy) are summarized and analysed. In particular, ambient vibrations were acquired by both single station and seismic array configurations. Average horizontal to vertical spectral ratios (HVSR) at single station measurements were considered to evaluate local resonance phenomena. Despite the fact that general trends that can be detected are the effect of the subsoil configuration, H/V spectral ratios show a significant dependence on meteo-climatic conditions: in particular, HVSR amplitudes in the low frequency range (<0.5 Hz) correlate significantly with the sea wave activity in the Central Mediterranean. Anyway, resonance frequencies estimated from HVSR peaks appear persistent and have been used to estimate the local depth of impedance contrasts responsible for seismic resonance phenomena. To this purpose, average V values up to any depth $$ h(\bar{V}_{S} (h)) $$ were assessed in the form of a standard power law constrained by Rayleigh dispersion curves deduced from the seismic arrays, and borehole data. In the whole area (except in the Mirandola area) two significant interfaces have been identified corresponding to two main resonance frequencies around 0.8-0.9 and 0.25-0.3 Hz respectively. The first one is attributed to a seismic impedance contrast located in the depth range 60-110 m. The second one corresponds to a deeper interface, possibly located at several hundreds of meters of depth. As concerns the Mirandola area, a single interface has been identified with depths varying in the range 50-115 m corresponding to resonant frequencies in the range 0.8-1.4 Hz. Finally a tentative geological interpretation of the above resonant interfaces is presented. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

This paper proposes a relative displacement sensor developed to measure directly the relative slip between slab and girder in composite bridges for assessing the health condition of shear connections. The structure, design principle, features, and calibration of the developed relative displacement sensor are presented. The design of the sensor ensures that there are no voltage outputs for the tension, compression, bending, and torsion effects, but only for the relative displacement between the two connecting pads of the sensor. The accuracy of the developed sensor in measuring the relative displacement response and using it for monitoring the conditions of shear connectors was tested on a composite bridge model in the laboratory. Shear connection condition was monitored under ambient vibrations, then static load tests were conducted to introduce cracks into the composite bridge. Both the vertical deflections and relative displacements were used for the crack detection. Experimental studies demonstrate that the developed sensor is very sensitive to the relative displacement and has a decent performance for the structural health monitoring of composite bridges. Copyright © 2014 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

Abstract: This study aims at investigating the fundamental period of vibration of infilled RC frame buildings using measurements of ambient vibrations and numerical analyses. Ambient vibrations were measured at the roof level of 29 selected buildings with heights of one to six stories. Using Nakamura technique, the horizontal-to-vertical spectral ratio curves were obtained in the two orthogonal building directions. The estimated period values ranged between 44% and 91% of elastic periods suggested by the local code. Preliminary period–height relations were proposed using regression analysis of the measured periods. Limited by the availability of structural details, the periods of vibration of 15 buildings only were evaluated using linear modal analysis of three dimensional computer models including the effect of stone–concrete infills. Considering cracking of the structural concrete elements increased the period of vibration by 40–50% compared to the elastic value. Analytical period values showed large differences with both the measured and code values. [Copyright &y& Elsevier]

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. • Gaussian vibration-based features are employed for statistical damage detection. • The sensor layout is optimized to maximize the feature's sensitivity and minimize its uncertainty. • The optimization criterion allows one to tune the sensor layout for high detectability in critical components. • A custom-made genetic algorithm efficiently finds a close-to-optimal solution for large structures. • The optimization is based on a numerical model and validated in a lab experiment. [ABSTRACT FROM AUTHOR]

Abstract: Despite much research in recent years, large amplitude vibrations of inclined cables continue to be of concern for cable-stayed bridges. Various excitation mechanisms have been suggested, including rain–wind excitation, dry inclined cable galloping, high reduced velocity vortex shedding and excitation from the deck and/or towers. Although there have been many observations of large cable vibrations on bridges, there are relatively few cases of direct full-scale cable vibration and wind measurements, and most research has been based on wind tunnel tests and theoretical modelling. This paper presents results from full-scale measurements on the special arrangement of twin cables adopted for the Øresund Bridge. The monitoring system records wind and weather conditions, as well as accelerations of certain cables and a few locations on the deck and tower. Using the Eigenvalue Realization Algorithm (ERA), the damping and stiffness matrices are identified for different vibration modes of the cables, with sufficient accuracy to identify changes in the total effective damping and stiffness matrices due to the aeroelastic forces acting on the cables. The damping matrices identified from the full-scale measurements are compared with the theoretical damping matrices based on the quasi-steady theory, using three different sets of wind tunnel measurements of static force coefficients on similar shaped twin or single cables, with good agreement. The damping terms are found to be dependent on Reynolds number rather than reduced velocity, indicating that Reynolds number governs the aeroelastic effects in these conditions. There is a significant drop in the aerodynamic damping in the critical Reynolds number range, which is believed to be related to the large amplitude cable vibrations observed on some bridges in dry conditions. Finally, static drag coefficients are back-calculated from the full-scale vibration measurements, for first time, with reasonable agreement with direct wind tunnel measurements. The remaining discrepancies are believed to be due to the higher turbulence intensity on site than in the wind tunnel. [Copyright &y& Elsevier]

This paper presents a technique for enhancing the power output from vibration-based charge-constrained electrostatic energy harvesters (EEHs). Starting from a diode-based charge pump and a buck converter stage with an inductive energy flyback scheme, a novel controller integrated circuit is proposed to monitor and control the charging/discharging events of the electrostatic converter. The fundamental challenges of designing self-powered event-synchronization circuits for charge-constrained EEHs are addressed. Synchronous energy conversion is accomplished with minimal power dissipation without the complexity of precise timing circuitry. Experimental results are presented for the design, implemented in AMI 0.7-\mu \m high-voltage CMOS process, using a macroscale electrostatic converter prototype. The energy-harvesting circuit produces a measured 1.688 \mu \W of power for a power investment of 417 nW. The measured power consumption associated with the on-chip controller unit is 24nW, approximately 1.42% of the total power harvested. [ABSTRACT FROM PUBLISHER]

The seismic performance assessment of existing masonry buildings involves many uncertainties, whose impact can be reduced to some extent by using non-destructive in-situ tests of such buildings, at least when destructive in-situ tests, which can provide more reliable results, cannot be performed. In this paper the extent of the potential beneficial effects achievable by calibration of a structural model of a building to its experimentally estimated vibration periods has been investigated. This was done by performing measurements of ambient and forced vibrations on an old two-storey masonry building, and by then assessing its seismic performance using a simplified nonlinear method. The results of numerical investigations revealed that the natural vibration periods of such buildings can be reproduced with sufficient accuracy, although it is possible that they will be overestimated or underestimated by analysts by up to around 40 %. This means that the accuracy of the prediction of the intermediate results of the seismic performance assessment of any particular building can be significantly increased by calibration of the structural model. Additionally, the beneficial effects of such calibration were observed even in the case of the final outcome of the nonlinear analysis, which is expressed through the near-collapse limit state capacity in terms of the peak ground acceleration. [ABSTRACT FROM AUTHOR]

Abstract: Following the Mw 7.3 Martinique earthquake, November 29th, 2007, a post-seismic survey was conducted by the Bureau Central Sismologique Français (BCSF) for macroseismic intensities assessment. In addition to the inventories, ambient vibration recordings were performed close to the particularly damaged zones in the free-field and the buildings. The objective of the paper is to show the relevancy of performing ambient vibration recordings for post-earthquake surveys. The analyses of the recordings aim at explaining the variability of the damages through site effects, structure vulnerability or resonance phenomena and to help the characterization of the post-seismic building integrity. In three sites prone to site effects, we suspect damage to be related to a concordance between soil fundamental frequency and building resonance frequency. Besides, the recordings of ambient vibrations at La Trinité hospital before and after the earthquake allow us to quantify the damage due to earthquake in terms of stiffness loss. [Copyright &y& Elsevier]

The paper presents the investigation taken on Old Bridge in Mostar. In order to get cognitions about the seismic stability of the bridge, experimental testing was done by the ambient vibration method to define dynamic characteristics - own frequencies, mode shapes and damping coefficients. Numerical analysis of the bridge was done in Tower 3D program package at which different cases of overloads were taken in consideration. Comparing results and dynamical characteristics of the bridge obtained by experimental investigation with performed analysis of the mathematical model of the bridge we can see the compatibility. The obtained results present a qualitative base for performing further investigation of this respective monument. [ABSTRACT FROM AUTHOR]

Vibration energy harvesting has been receiving a considerable amount of interest as a means of powering wireless sensors and low power devices. In this paper, a novel hybrid energy harvester integrated with piezoelectric and electromagnetic energy harvesting technique is investigated. It consists of a cantilever beam bonding with two piezoelectric plates for piezoelectric energy conversion, and a permanent magnet attached on the end of the beam as a tip mass for inspiring the vibration and adjusting the resonance frequency, at the same time relative motion of the magnet with a conductor coil induces an electromotive force in the coil. An analytical model is developed to analyze the nonlinear vibration and electrical output performances of the harvester. A prototype is fabricated and tested. The experimental results show close agreement with the analytical results in trend. The maximum of load power of the hybrid harvester achieves 10.7 mW on the optimal load resistance of 50 \Omega at the resonant frequency of 50 Hz with the acceleration of 0.4 g, which is increased by 81.4% compared with 5.9 mW of the single electromagnetic technique. [ABSTRACT FROM AUTHOR]