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Detecting early damage in civil structures is highly desirable. In the area of vibration-based damage detection, modal flexibility (MF)-based methods have proven to be promising tools for promptly identifying changes in the global structural behavior. Many of these methods have been developed for specific types of structures, giving rise to different approaches and damage-sensitive features (DSFs). Although structural type classification is an important part of the damage detection process, this part of the process has received little attention in most literature and often relies on the use of a-priori engineering knowledge. Moreover, in general, experimental validations are only performed on small-scale laboratory structures with controlled artificial damage (e.g., imposed stiffness reductions). This paper proposes data-driven criteria for structure-type classification usable in the framework of MF-based damage identification methods to select the most appropriate algorithms and DSFs for detecting and localizing structural anomalies. This paper also tests the applicability of the proposed classification criteria and the damage identification methods on full-scale reinforced concrete (RC) structures that have experienced earthquake-induced damage. The considered structures are a seven-story RC wall building and a five-story RC frame building, which were both tested on the large-scale University of California, San Diego-Network for Earthquake Engineering Simulation (UCSD-NEES) shaking table.

Smart devices for structural health monitoring provide edge computing capabilities to reduce wireless transmission and, thus, power consumption. Although effective algorithms have been proposed in the last few decades, traditional microcontrollers require heavy data flow between the memory and the central processing unit that involves a considerable fraction of the total energy consumption. Phase change memory has recently emerged as an attractive solution in the field of resistive non-volatile memory for analog in-memory computing, which is a valid approach to avoid data being conveyed among distinct elaboration units. However, it has never been envisaged in structural health monitoring applications. As this technology is still in an embryonic state, several challenges related to nonlinearities and nonidealities of the memory elements and the energy expenditure related to the memory reprogramming process may undermine its usage. In this paper, the application of a novel identification approach for civil infrastructures is investigated using phase change memories. The main computational core of the presented algorithm, consisting of 1-dimensional convolutions, is particularly suitable for implementations involving analog in-memory computing, thus showing the great potential of this technology for structural health monitoring applications. The test unit is an embedded phase change memory provided by STMicroelectronics and designed in 90-nm smart power bipolar complementary metal-oxide-semiconductor (CMOS)-double-diffused metal-oxide-semiconductor (DMOS) technology with a Ge-rich Ge-Sb-Te alloy for automotive applications. Experimental results obtained for a viaduct of an Italian motorway support the efficacy of the method. Moreover, the influence of nonidealities on the outcomes of damage identification based on both dynamic and quasi-static structural parameters is examined.

In this paper, a new strategy for vibration-based structural health monitoring is proposed, specifically designed for smart sensors with edge computing capabilities organized in a line topology. This solution is aimed at maximizing resource optimization and enables the identification of modal parameters even for large or densely instrumented structures, where star-topology monitoring systems are typically unsuitable. In particular, an efficient data management procedure is proposed to reduce data transmission, thus improving efficiency and minimizing maintenance interventions for battery replacement in wireless applications. The maximum volume of transmitted data can be selected by the user, based on the specific requirements of the network. Although the considerable reduction of data size, the proposed approach enables accurate estimation of the structural parameters in challenging scenarios where other techniques generally fail. Modal parameters are identified in an online fashion, enabling near real-time detection and localization of early damage. Applications to a real case study instrumented with a dense sensor network show the effectiveness of the proposed approach and the possibility of localizing structural defects in slightly damaged civil structures.

This paper proposes a novel method suitable for vibration-based damage identification of civil structures and infrastructures under ambient excitation. The damage-sensitive feature employed in the presented algorithm consists of a vector of multivariate autoregressive parameters estimated from the vibration responses collected at different locations of the analyzed structure. Outlier analysis and statistical pattern recognition are exploited for damage detection and localization. In particular, the Mahalanobis distance between a set of reference (i.e., “healthy”) and inspection parameters is evaluated. A threshold is then selected to determine whether the inspection vectors refer to damaged or undamaged conditions. The effectiveness of the proposed approach is proved using numerical simulations and experimental data from a benchmark test. The analysis results show that the largest values of Mahalanobis distance can be found in the proximity of those sensors closest to the damaged elements. Thus, the Mahalanobis distance applied to vectors of multivariate autoregressive parameters has proven to be a robust indicator for damage detection and localization.

Recent developments in the field of smart sensing systems enable performing simple onboard operations which are increasingly used for the decentralization of complex procedures in the context of vibration-based structural health monitoring (SHM). Vibration data collected by multiple sensors are traditionally used to identify damage-sensitive features (DSFs) in a centralized topology. However, dealing with large infrastructures and wireless systems may be challenging due to their limited transmission range and to the energy consumption that increases with the complexity of the sensing network. Local DSFs based on data collected in the vicinity of inspection locations are the key to overcome geometric limits and easily design scalable wireless sensing systems. Furthermore, the onboard pre-processing of the raw data is necessary to reduce the transmission rate and improve the overall efficiency of the network. In this study, an effective method for real-time modal identification is used together with a local approximation of a damage feature, the interpolation error, to detect and localize damage due to a loss of stiffness. The DSF is evaluated using the responses recorded at small groups of sensors organized in a decentralized topology. This enables the onboard damage identification in real time thereby reducing computational effort and memory allocation requirements. Experimental tests conducted using real data confirm the robustness of the proposed method and the potential of its implementation onboard decentralized sensor networks.

Real-time structural health monitoring (SHM) acquires countless importance when applied to large-scale civil infrastructures, where the damage should be managed immediately to avoid both economic and human loss. Recent studies in the field of real-time identification of bridges generally assume linear time-varying (LTV) structural models, justified on the grounds that continuously varying traffic load may slightly change the structural behavior over time. Time-varying load also involves non-stationary input excitation, which cannot be modeled as Gaussian white noise, as in the traditional output-only identification methods, and may be characterized by time-varying frequency spectrum which could affect the effectiveness of commonly used identification algorithms. In this paper, the Modal Assurance Distribution (MAD) is employed for the dynamic identification of LTV structures. Based upon the instantaneous operating deflection shapes (ODSs) evaluated through the wavelet packet decomposition, the MAD represents the instantaneous ODS similarity between narrow-band signal components, highlighting the presence of time-varying modal responses. Compared to the most used traditional time-frequency representations (TFRs), representing the distribution of energy through the time-frequency plane, the MAD enables a clearer reading of the modal responses, facilitating their extraction for real-time damage identification. The practical application to a benchmark structure shows the potential of the MAD as a novel TFR which could give rise to a new family of system and damage identification methods.

For time-varying systems in structural engineering, such as bridges with vehicular traffic and structures during construction or seismic events, the application of traditional vibration-based identification methods may not be admissible, since the hypotheses of stationarity of the signal may be far from the real situation. Moreover, in some cases, real-time approaches to visualize the identified parameters are desirable to allow for a rapid decision-making process, which assumes the utmost importance for the early warning in structures near to excavation or demolition sites and strategic infrastructures after seismic events. Time-frequency representations have been largely used for the instantaneous identification of linear time-varying systems. However, traditional algorithms generally suffer from issues related to the identification of closely-spaced modes, which make the modal decomposition a non-trivial task. Moreover, by tracking only natural frequencies, some variations of the dynamic behavior could not be perceived, or the variations induced by other environmental and operational conditions could prevail over those due to a modification in the structural properties (e.g., due to ongoing damage). In this paper, a Decomposition Algorithm based on Modal Assurance (DAMA) is applied to separate modal responses, in order to allow a near real-time identification of modal parameters of structures with time-varying features. In particular, a Modal Assurance Distribution (MAD) obtained from the analysis of multi-variate signals is used to track the variations of modal parameters, considering both natural frequencies and modal shapes. The DAMA is applied to a full-scale structure subjected to a series of dynamic tests performed in different structural conditions. The analysis of multi-variate signals consisting of acceleration recordings collected at different locations of the structure allows the online identification of varying dynamic parameters, which can be used to assess the structural state of health.

Effective methods for vibration-based damage diagnosis in building structures are based on the estimation of structural deflections from identified modal flexibility (MF) matrices. However, most of the existing methods and previous studies that use MF-based deflections were developed by considering the case of buildings that can be modeled as planar structures (e.g. plan-symmetric buildings) both in the baseline and possibly damaged states. In an attempt to fill this research gap, a deflection-based method for output-only damage diagnosis in building structures tested under ambient vibrations is proposed in this paper. The method is applicable for simple rectangular plan-symmetric “box type” 3D building structures which may experience asymmetric damage, and it can be used for detecting, localizing and quantifying the damage. One of the main differences between the proposed and the existing methods is related to the inspection loads adopted to estimate the MF-based deflections. The inspection loads of the proposed method are more complex than the uniform translational loads adopted in the existing methods. Such proposed loads in fact can be assembled only after having estimated the position of the center of stiffness for each story of the structure. According to the proposed approach, the locations of the centers of stiffness are extracted from the experimentally-derived modal flexibility matrices, before performing the damage diagnosis process. The effectiveness and validity of the proposed method was demonstrated both through numerical analyses and by executing experimental ambient vibration tests on a frame building. The results of the proposed method were also compared with the existing approach which was developed for planar structures. This comparison (made both through numerical and experimental analyses) demonstrated that only the proposed approach can be used to perform a correct damage diagnosis process in plan-symmetric buildings which may experience asymmetric damage, especially when considering the damage quantification problem.

In civil engineering structures it is highly desirable to detect the presence of damage and changes in the global structural behavior at the earliest possible stage, and, among the many existing strategies for vibration-based damage detection, modal flexibility (MF)-based approaches are promising tools. However, in most of the existing studies, the experimental validation of such approaches has been performed on small-scale laboratory structures, where damage has been artificially imposed as stiffness reductions, for example by substituting some structural elements. It is thus important to continue to test the effectiveness of such MF-based approaches on full-scale structures characterized by more realistic damaged conditions. This paper focuses on the methods for output-only damage detection and localization that are based on the estimation of structural deflections from modal flexibility, and the objective of this paper is to test the applicability of such methods for locating damage in a full-scale reinforced concrete (RC) structure that has experienced earthquake-induced damage. The considered structure is a shear wall building that can be modeled as a bending moment-deflecting cantilever structure, and was tested on the large-scale University of California, San Diego—Network for Earthquake Engineering Simulation (UCSD-NEES) shaking table. Two approaches, which are based, respectively, on the estimation of the curvature and the damage-induced rotation from the deflections, have been applied and compared on the data of the considered case study. These approaches have been applied in different scenarios characterized by different data sets and by a different number of degrees-of-freedom measured on the considered structure.

Thanks to emerging techniques in the field of signal processing and due to improvements in smart sensing systems which enable the event‐triggered acquisition of high‐fidelity data at the occurrence of strong ground motion events, seismic structural health monitoring has grown considerably in the last few decades. In this paper, the modal assurance distribution, an alternative time‐frequency representation of the modal features of multivariate and multicomponent signals, is extended for application to short‐term nonstationary vibrational structural responses in which the system may manifest its nonlinear behavior. A general procedure for the extraction of the decoupled normal modes is presented, which allows the identification of instantaneous modal parameters in order to investigate in detail the structural behavior during earthquakes. Valuable information that cannot be recovered by means of traditional criteria can thus be exploited for accurate damage assessment. The results obtained for two case studies consisting of a numerical model with softening nonlinear behavior and a full‐scale experimental reinforced concrete benchmark show the potential and applicability of the method proposed for the integrity assessment of civil structures.

none 5 si Modal flexibility-based methods are recognized in the literature as effective methods for detecting damage in structures using vibration measurements. However, the application of such methods with output-only data (as is the case of civil structures tested under ambient excitations) is challenging, because the mass normalization factors required for assembling the modal flexibility matrix cannot be estimated directly from the data. To address this issue, a method for output-only damage detection and localization in building structures that can be applied with minimal or no a-priori information about the structural masses has been proposed in a previous work by the authors. In the method, to estimate the mass distribution and to assemble the proportional flexibility matrices, the modal orthogonality relationships that involve the mode shapes and the structural masses are used to form a system of equations, and through that system of equations, an inverse problem is solved for the estimation of the mass distribution. Reducing the number of available modes, however, reduces the number of available equations, while the number of unknowns (i.e., the number of degrees of freedom) stay the same; hence, the approach cannot be applied when the modal space is severely truncated. This paper proposes a technique for estimating the mass distribution and assembling proportional flexibility matrices from output-only vibration data that overcomes the mentioned limitations and that can be applied for any number of identified modes, including the case in which the modal space is severely truncated. The proposed technique is then integrated into the above-mentioned method for output-only damage detection in building structures, to verify the applicability of the whole procedure when considering the case of severely truncated modal spaces. Numerical simulations and experimental vibration tests were used to demonstrate the validity and effectiveness of the approaches proposed in this paper. mixed Bernagozzi G.; Mukhopadhyay S.; Betti R.; Landi L.; Diotallevi P.P. Bernagozzi G.; Mukhopadhyay S.; Betti R.; Landi L.; Diotallevi P.P.

Most damage identification methods used in the field of structural health monitoring are based on comparing the modal parameters estimated at different time intervals. Since natural frequencies can be evaluated even by using limited instrumentation and does not require any signal synchronization procedure, frequency-based identification methods are of great interest for applications in real-time monitoring by means of low-cost sensing systems. In the last decades, several damage-sensitive features have been proposed in order to conduct damage identification minimizing the occurrence of errors under varying environmental conditions. However, the amplitude of input excitation can also lead to short-term frequency variations, due to a non-linear behaviour of civil structures. This paper proposes a procedure aimed at damage detection in non-linear structures based on frequencies and amplitudes of modal responses, estimated assuming a locally-linear structural behaviour. It is shown that, by analysing a set of instantaneous parameters, it is possible limit the problems related to an incorrect identification of the structural state of health when the effects of non-linearities on modal parameters prevail over those of an actual state of damage. The method proposed is applied to a set of data recorded on a reinforced concrete structure with strongly non-linear behaviour.

Recent approaches for vibration-based damage detection in building structures are based on the calculation of modal flexibility (MF) based deflections. These deflections are estimated by applying uniform loads (UL) to experimentally derived modal flexibility matrices of the structures, and the interstory drifts are considered as damage-sensitive features (DSFs). However, in practical applications only a limited number of modes is usually identified from vibration data, and thus modal truncation effects are introduced on the deflections. To address this problem a mass proportional load (MPL) has been proposed, in a previous study by the authors, as an alternative to the uniform load with the aim of reducing the truncation effects on the displacement components of MF-based deflections of structures with mass irregularities. The objective of this work is to investigate further the mentioned problem by evaluating the truncation errors that affect the MF-based interstory drifts of frame buildings (i.e. the DSFs that can be conveniently used for damage detection). For structures with mass irregularities the truncation errors related to the application of the proposed MPL are thus compared with those related to the UL. Parametric studies were carried out on numerical models of shear-type frame buildings by considering structures with a different number of stories and various distributions of the story mass ratios, and by considering different subsets of modes included in the calculations.

This paper presents an application of an output-only structural identification algorithm specifically designed for low-cost monitoring systems on a structure with strongly non-linear behavior. The identification procedure is conducted simulating the presence of a single smart sensor node on the specimen, in order to identify the natural frequencies and amplitudes of collected accelerations in real time. The estimated parameters are used to develop a non-linear frequency-amplitude model representing the structural response, subsequently employed for damage detection.

none 3 no Themain purpose of this work is to investigate the usability of easily obtainable parameters instead of the modal traditional ones, in the context of a flexibility-based damage detection procedure, under the assumption of unknown structural masses. To this aim, a comparison is made between two different approaches: the first involves the calculation of the flexibilitymatrix by using traditional modal parameters, such as natural frequencies and modal vectors, normalized to unitary values, while the second involves the use of singular vectors, obtained through a simple matrix actorization.Themodal parameters and the singular vectors necessary for the implementation of the damage detection procedure are evaluated through two different techniques: the Eigensystem Realization Algorithm and a wavelet-based procedure, for which a variant is proposed by introducing the energy reassignment concept into the original algorithm. Through the latter approach, in particular, it is possible to obtain a high number of singular vectors even in the case of reduced availability of sensors. The study is performed under the assumption of nonstationary excitation, in order to achieve general results, and the effectiveness of the procedures is evaluated through simulated tests regarding different structural schemes. open Said Quqa, Luca Landi, Pier Paolo Diotallevi Said Quqa, Luca Landi, Pier Paolo Diotallevi

The purpose of this research is to investigate the effectiveness of different vertical and in-plan distributions of the damping coefficients of nonlinear viscous dampers for the seismic retrofit of existing buildings with plan-asymmetry. The different distributions were examined within a procedure proposed in literature for the design of viscous dampers applied to 3D plan-asymmetric buildings. In particular, simple distribution criteria, based on specific structural properties, were considered with the purpose to improve the design of the damping system in terms of cost without significant change of response. All the distributions were applied considering, for comparison, both a simplified and an extended design method, by neglecting or considering, respectively, the plan-asymmetry in the design. The effectiveness of the different distributions was examined by performing time-history analyses of a case study with different configurations of dampers adopting a nonlinear behaviour both for the viscous dampers and the frame members. The dampers were dimensioned considering that the structure can exceed the elastic limit, with the only condition to satisfy the prefixed performance limit. The considered case study is a two bay RC frame with six storeys and an irregular plan configuration. The examined response parameters were maximum interstorey drifts, residual interstorey drifts, peak floor accelerations and maximum damper forces.

One of the main purposes of modal identification is to estimate the structural mechanical properties, in order to detect a possible damage over time. Several researches have been conducted recently to implement identification techniques based on the assumption of modest number of sensors. Such methods are needed both in the case of decentralized systems of wireless smart sensors, where operating units interact with each other in small groups, and in the case of repeated tests, carried out to identify large structures with a low availability of sensors. In this paper we propose a hybrid adaptive technique for natural vibration-based dynamic identification in the time-frequency domain. The proposed method involves the introduction of a novel procedure for decoupling the modal responses contained in the recorded signals, led by a clustering-based decomposition and reconstruction process; subsequently, decoupled signals, considered as single degree of freedom responses, are subjected to identification procedures in time domain, with the aim of studying the trend of instantaneous modal parameters. Since the procedure involves the real time estimation of dynamic parameters through a wavelet-based technique, it is particularly suitable for non-stationary signals. From the estimated parameters, a structural damage detection procedure is applied by using a flexibility-based technique. In order to test the effectiveness of the proposed method, the identification and damage detection procedures are simulated on a finite element model that represents a reinforced concrete plane frame.

Widespread monitoring of bridges is yet rarely employed at a territorial level due to the high costs of monitoring systems. However, the aging of civil infrastructures, combined with the growing traffic demand, poses the need for a simple and automatic tool that helps emergency management. In this paper, an integrated algorithm for the identification of dynamic and dense quasi-static structural features exploiting moving vehicles is proposed. Filtering raw acceleration structural responses, triggered by passing vehicles, enables the identification of modal parameters and curvature influence lines. The procedure can be implemented efficiently as its main computational core consists of convolutions. The definition of a curvature-based damage index leads to accurate localization and quantification of structural anomalies using few sensors. The proposed procedure is tested on three viaducts of the Italian A24 motorway. Moreover, a numerical model is studied to evaluate the potentialities of the strategy for damage localization.

The object of this paper is the study of simplified probabilistic procedures for the seismic assessment of nonlinear structures equipped with nonlinear fluid viscous dampers. The considered reference probabilistic approach is the SAC-FEMA method, which allows to obtain the probability of exceeding a given performance level. The specific purpose is to study the correlation between the results obtained through the probabilistic seismic assessment method for structures with and without dampers, with emphasis on these results in terms of dispersion. A wide set of recorded ground motions was therefore selected and applied to the considered RC frames. The study was performed without applying scaling factors to the earthquake records, but by selecting different sets of records for increasing values of seismic intensity. All the obtained results were examined considering different criteria, in order to determine the set of time-history analyses to be used for the probabilistic evaluation. Different methods were then applied to obtain the dispersion of the seismic demand. With reference to the application of the SAC-FEMA method, a sensitivity analysis was also performed, considering different procedures to interpolate the hazard curve. From the analyses, it was possible to derive the expressions that allow the results for structures with and without dampers to be correlated, as well as to offer suggestions for applying the SAC-FEMA method. A second purpose of the paper is to propose and apply, in the probabilistic assessment, a direct procedure. This procedure was recently presented by some of the authors as a method to be used for obtaining the response of nonlinear structures with nonlinear viscous dampers as an alternative to expensive nonlinear dynamic analyses.

This document aims to support the dental professional in choosing the adequate diagnostic technique, minimising the radiation dose in observance of the As Low As Reasonably Achievable (ALARA) principle (7). This principle states that the biological cost can only be justifed when the beneft, that is, the diagnosis, outweighs the risk related to radiation exposure. In this guideline paper, we report recommendations for radiologists, medical physicists, paediatrician, dentists and maxillofacial surgeons, with reference to the specifc felds.

Il saggio analizza le cause del degrado del cunicolo di collegamento della fontana col palazzo Apostolico, mediante l'analisi e il rilievo dettagliato dell'umidità presente nel cunicolo e mediante la rappresentazione delle sottoservizi presenti nella piazza. Inoltre prende in esame la costruttività dell'opera; attraverso l'esercizio di indagini non distruttive eseguite con gli ultrasuoni, con il georadar e termografiche vengono determinati gli spessori dei materiali che compongono il basamento e il catino del complesso statuario i cui elementi tecnici sono rappresentati in tridimensionale, al fine di comprenderne le giunzioni e quali possano essere le cause che hanno indotto e inducono percolamenti costanti all'interno del cunicolo. Infine il saggio prende in esame le modalità tecniche di intervento per eliminare le cause delle ingressioni delle acque meteoriche all'interno del cunicolo mediante interventi graduali nel tempo.

Background AtrioVentricular (AV) and InterVentricular (VV) delay optimization can improve ventricular function in Cardiac Resynchronization Therapy (CRT) and is usually performed by means of echocardiography. St Jude Medical has developed an automated algorhythm which calculates the optimal AV and VV delays (QuickOpt™) based on Intracardiac ElectroGrams, (IEGM), within 2 min. So far, the efficacy of the algorhythm has been tested acutely with standard lead position at right ventricular (RV) apex. Aim of this project is to evaluate the algorhythm performance in the mid- and long-term with RV lead located in mid-septum. Methods AV and VV delays optimization data were collected in 13 centers using both echocardiographic and QuickOpt™ guidance in CRTD implanted patients provided with this algorhythm. Measurements of the aortic Velocity Time Integral (aVTI) were performed with both methods in a random order at pre-discharge, 6-month and 12-month follow-up. Results Fifty-three patients were studied (46 males; age 68 ± 10y; EF 28 ± 7%). Maximum aVTI obtained by echocardiography at different AV delays, were compared with aVTI acquired at AV delays suggested by QuickOpt. The AV Pearson correlations were 0.96 at pre-discharge, 0.95 and 0,98 at 6- and 12- month follow-up respectively. After programming optimal AV, the same approach was used to compare echocardiographic aVTI with aVTI corresponding to the VV values provided by QuickOpt. The VV Pearson Correlation were 0,92 at pre-discharge, 0,88 and 0.90 at 6-month and 12- month follow-up respectively. Conclusions IEGM-based optimization provides comparable results with echocardiographic method (maximum aVTI) used as reference with mid-septum RV lead location.

This research focuses on the different modelling approaches for the simulation of the seismic response of structures with friction pendulum isolation systems. The behaviour of such systems is strongly affected by several parameters, as for example the friction coefficient and the axial load. The latter has a particular importance in presence of seismic actions characterized by the simultaneous presence of high horizontal and vertical accelerations. To study these aspects, several nonlinear dynamic analyses have been performed considering a two degree of freedom model isolated at the base and subjected to recorded horizontal and vertical ground motions. The response of the selected isolation systems has been studied through different models, starting by the more simple ones based on a constant friction coefficient to the more complex ones based on a friction coefficient varying with the sliding velocity and axial force. A set of ground motions with near field records characterized by different values of the ratio between peak vertical and horizontal accelerations has been considered. The results have allowed to compare the different models and to study the effect of the vertical seismic component on the response of the isolators.

One of the latest trends in structural health monitoring involves the use of wireless decentralized sensing systems, developed to reduce costs and speed up the whole monitoring process. The main purpose of this paper is to present a novel decentralized procedure for the instantaneous modal identification of time-varying structures, also suitable in the presence of environmental variations and non-stationary ambient excitation. In particular, a modal assurance criterion (MAC)-based clustered filter bank (CFB) is obtained, capable of decomposing structural responses into modal components for the evaluation of time-varying natural frequencies and modal shapes through a nonlinear energy operator. The proposed algorithm is relatively simple and usable with low-cost smart sensing systems, as it requires low computational effort and works with few data at a time. To prove the effectiveness of the presented method, a simulated near-real-time modal identification procedure has been performed on a full-scale bridge under progressive damage scenarios. The estimated modal parameters have then been used for damage diagnosis. The results reveal a good correspondence between identified modal parameters and reference values, showing also promising outcomes for both damage detection and localization.

BACKGROUND: The rate of device replacement in pacemaker recipients has not been investigated in detail. HYPOTHESIS: Current pacemakers with automatic management of atrial and ventricular pacing output provide sufficient longevity to minimize replacement rate. METHODS: We considered a cohort of 542 pacemaker patients (age 78 ± 9 years, 60% male, 71% de‐novo implants) and combined 1‐month projected device longevity with survival data and late complication rate in a 3‐state Markov model tested in several Monte Carlo computer simulations. Predetermined subgroups were: age < or ≥ 70; gender; primary indication to cardiac pacing. RESULTS: At the 1‐month follow‐up the reported projected device longevity was 153 ± 45 months. With these values the proportion of patients expected to undergo a device replacement due to battery depletion was higher in patients aged

Methods based on the evaluation of structural deflections from experimental modal flexibility matrices are important tools in vibration-based damage detection, especially for building structures. Modal flexibility matrices, however, can not be directly estimated when dealing with output-only vibration data (e.g. in the important case of structures tested under ambient vibrations). One can use an a-priori estimate of the mass matrix of the structure or the added mass method to obtain the modal normalization constants needed to assemble the flexibility matrix, but these operations can be challenging for real-life civil structures. To address this problem, a modal flexibility-based approach for output-only damage detection and localization in building structures that can be applied with minimal or no a-priori information on the structural masses is proposed in this paper. This approach is also able to deal with the general case in which mass modifications, e.g. due to operational variability in structures, are present before and after damage. The approach is based on the estimation (directly from output-only data) of modal flexibility-based deflections of building structures that are proportional with respect to the corresponding true deflections. From analytical investigations it was found that the missing scaling factor between the two deflections can be made theoretically equal to the total mass of the structure, as proposed in the paper. Then, interstory drifts evaluated from the proportional deflections are used for damage detection and localization according to two proposed strategies. The first strategy can be applied with minimal a-priori information on the masses (i.e. using a parameter that quantifies an eventual relative modification of the total mass of the structure before and after damage). The second one is a more advantageous strategy that can be applied from output-only data without any a-priori information on the masses, even in the case in which the masses are varied before and after damage. The effectiveness of the proposed approach was demonstrated using both numerical simulations and experimental vibration tests on frame building structures.

In this article, one of the procedures proposed in literature for the design of viscous dampers to be inserted in existing buildings is examined and extended to 3D eccentric buildings. The proposed procedure has been verified through a case study characterized by a six-story RC building. Both plan-symmetric and plan-asymmetric configurations have been considered for comparisons. The effect of considering the plan-asymmetry in the design has been studied. Moreover, also the importance of considering the higher modes has been investigated. The effectiveness of the design procedure has been then evaluated through the comparison with nonlinear dynamic analyses.

The main purpose of this research has been to investigate the effectiveness of different vertical distributions of the damping coefficients of nonlinear viscous dampers for the seismic retrofit of existing multi-storey reinforced concrete frames. In particular, different simple distributions were compared with other procedures proposed in literature, including two energy methods and a repetitive simplified sequential search algorithm. The effectiveness of the different distributions was then examined by performing time-history analyses and considering a nonlinear behaviour for both the viscous dampers and the structural members. The structures being considered are five RC frames with a different number of storeys and both regular and irregular configurations in elevation. The results of the nonlinear dynamic analyses were examined in terms of maximum and residual interstorey drifts, peak floor accelerations and maximum damper forces. The energy methods, in particular, provided good results in terms of reduction in cost, efficiency of the distribution and simplicity of application, compared to other effective, but more complex methods.

Composite materials have been used for both the structural strengthening of single RC elements and the complete retrofit of buildings for over 20 years. The composites mainly used are based on carbon, aramid or glass fibres, laminated with epoxy resins matrices. As known, one of the limitations of epoxy resins is the poor fire resistance of the matrix, and this can often influence how composite materials are used in building construction. In this research, an experimental investigation was carried out on reinforced concrete beams strengthened with unidirectional carbon fibre reinforcements and two-component resins of the Interpenetrated Polymer Network (IPN) water-based type that have greater thermal resistance than epoxy resins. In the experimental campaign, several beam specimens were reinforced using different strengthening configurations for bending and shear. In particular, the results obtained for the beams strengthened using water-based resins were compared with those for equivalent specimens strengthened with epoxy resins. The results showed good mechanical properties for the reinforcements with the IPN matrix, where the values of the collapse load were similar to those of the reinforcements with epoxy resins.

In this paper a modal flexibility-based approach for damage diagnosis is presented and discussed. Modal flexibility matrices of structural systems can be derived from vibration tests and changes in these matrices can be associated to structural damage. One of the main challenges is to apply modal flexibility-based methods on real-life civil structures, to detect damage on structures using ambient vibration data. A recent method has been formulated for damage detection, localization, and quantification of building structures; it is based on the modal flexibility-based deflections of such structures under uniform loads. The method was originally formulated for frame buildings that can be modeled as plane shear-type structures. The objective of the paper is to test this methodology on generic buildings that, in principle, cannot be easily modeled as plane shear-type structures. The method was applied to the ambient vibration data of a steel frame structure that has a monitoring system with acceleration sensors. Various damage configurations were induced to the structure by removing diagonal braces on the external surface of the frame. The results showed that the method is able to identify the stories and the directions of the frame that have been affected by the damage.

It is of interest in the fields of vibration-based structural identification and damage detection to analyze the truncation effects introduced on modal flexibility (MF) based deflections that are estimated using only a subset of structural modes. To address this problem, an approach for truncation error analysis on MF-based deflections of structural systems subjected to a generic load is proposed in this paper. The approach is based on the determination of the relative contribution of each mode to the deflection by means of a proposed load participation factor (LPF). This factor, as derived analytically, depends both on the applied load and on the distribution of the structural masses. The validation of the proposed approach was carried out both on numerical models of shear-type frame buildings and on experimental data of a steel frame structure tested under ambient vibrations (i.e. the benchmark study sponsored by the IASC-ASCE Task Group on SHM). In both cases, results show that the LPF factors can give an a priori indication of the truncation effects expected on the MF-based deflections. The relationship between the proposed approach and the approach based on the mass participation factors, introduced by Zhang and Aktan (1998) for the case of uniform load (UL) deflections, is discussed since the two approaches are equal only if a special load, which is a mass proportional load (MPL), is considered. Thus, the application of this MPL load for mass irregular structures is also investigated. Numerical analyses performed both on a shear-type frame building and on a simply-supported beam, showed that for the great majority of the analyzed configurations, the truncation errors on the MF-based deflections due to the MPL are lower compared to those related to the UL.

This paper describes a simplified procedure to calculate the supplemental damping ratio that must be provided in order to rehabilitate existing buildings with viscous dampers. The proposed method has been developed according to both analytical and graphical approaches. The graphical formulation is based on the construction of constant design acceleration or constant design displacement curves. These curves allow to estimate the required effective damping as a function of the effective period, associated to the secant stiffness at maximum displacement. Combining these curves with constant ductility curves, which provide a correlation between the effective damping and the supplemental damping for given available ductility and damper typology, it is possible to determine the required supplemental damping and to design the damping system. The proposed method has then been verified through nonlinear dynamic analyses considering a set of RC plane frames. Finally it has been applied to a case study regarding an existing building located in Italy and designed without considering the earthquake action.

SUMMARY The insertion of fluid viscous dampers in building structures is an innovative technology that can improve significantly the seismic response. These devices could be very useful also in the retrofit of existing buildings. The effect of this typology of damping system is usually identified with an equivalent supplemental damping ratio, which depends on the maximum displacement of the structure, so that iterative procedures are required. In this paper, a simplified direct assessment method for nonlinear structures equipped with nonlinear fluid viscous dampers is proposed. The method proposed in this study is composed by two steps. The first one yields the direct estimate of the supplemental damping ratio provided by nonlinear viscous dampers in presence of a linear elastic structural response. The second step extends the procedure to structures with nonlinear behavior. Both graphical and analytical approaches have been developed. The proposed method has then been verified through several applications and comparisons with nonlinear dynamic analyses. Moreover, an investigation has been performed with regard to the influence of the relations that define the damping reduction factor and the hysteretic damping. Copyright © 2014 John Wiley & Sons, Ltd.

Aims We investigated the applicability of the Ventricular Capture Control (VCC) and Atrial Capture Control (ACC) algorithms for automatic management of cardiac stimulation featured by Biotronik pacemakers in a broad, unselected population of pacemaker recipients. Methods and results Ventricular Capture Control and Atrial Capture Control were programmed to work at a maximum adapted output voltage as 4.8 V in consecutive recipients of Biotronik pacemakers. Ambulatory threshold measurements were made 1 and 12 months after pacemaker implant/replacement in all possible pacing/sensing configurations, and were compared with manual measurements. Among 542 patients aged 80 (73–85) years, 382 had a pacemaker implant and 160 a pacemaker replacement. Ventricular Capture Control could work at long term in 97% of patients irrespectively of pacing indication, lead type, and lead service life, performance being superior with discordant pacing/sensing configurations. Atrial Capture Control could work in 93% of patients at 4.8 V maximum adapted voltage and at any pulse width, regardless of pacing indication, lead type, and service life. At 12-month follow-up, a ventricular threshold increase ≥1.5 V had occurred in 4.4% of patients uneventfully owing to VCC functioning. Projected pacemaker longevity at 1 month was strongly correlated with the 12-month estimate, and exceeded 13 years in >60% of patients. Conclusion These algorithms for automatic management of pacing output ensure patient safety in the event of a huge increase of pacing threshold, while enabling maximization of battery longevity. Their applicability is quite broad in an unselected pacemaker population irrespectively of lead choice and service of life.

The work aims at performing the dynamic modal identification of the long-span laminated timber footbridge built on the Marecchia River near Rimini, Italy. A first sine vibration test has been performed adopting a mechanical shaker just after the footbridge construction in 2000 in order to check the structural behavior that has been assumed in the project. A second test has been replicated in 2005 using the same excitation and almost the same test set-up adopted in the first one. The dynamic modal extraction is performed on the FRFs through both the peak picking method, applied together with the half power bandwidth technique, and the circle-fit method. The orthogonal properties of the identified mode shapes are verified through the Modal Assurance Criterion (autoMAC). Finally, the results obtained for the two tests and through the two techniques are mutually compared. It is worth noting that the FRFs, evaluated for different intensity levels of the exciting force, reveal an inherent non-linear behavior of the footbridge. The analyses also show that the first natural frequencies of the structure are included in the frequency range of the human step and this could lead to unpleasant feelings for the pedestrians.

The present work aims at applying and comparing some methods for vibration-based damage detection of civil structures starting from ambient vibration data. The analyzed procedures are based on a dynamic identification of the modal parameters that is performed in output-only conditions; this is a typical situation that occurs when structural health monitoring strategies are applied to civil structures. The here investigated damage-sensitive features are the modal parameters, the modal flexibility matrix and the damage-induced deflection, due to unitary inspection loads, of the identified structure; possible variations in these parameters can be adopted in order to detect, localize and quantify the damage. A damaged condition is analytically simulated through a stiffness reduction in the elements of a RC shear-type plane frame. The output-only modal identification is performed through the Eigensystem Realization Algorithm, combined with the Random Decrement technique, on the simulated responses due to a white noise ground motion of both the undamaged and the damaged structures. At the end, the effectiveness of the different identified damage features is evaluated and the accuracy related to the identified modifications, due to damage, is determined through a comparison with the initially assumed variations in the structural model.

The aim of this study was to propose an extension of the displacement-based assessment procedure for infilled reinforced concrete (RC) frames. Two fundamental steps of the displacement-based approach were studied: the determination of the equivalent viscous damping and the definition of the limit-state displacement profile. The proposed criteria were derived by examining the results of two different numerical investigations regarding the nonlinear seismic response of single- and multi-story infilled RC frames. Lastly, the effectiveness of the method was verified through comparisons, in terms of displacement demand, with the results of nonlinear dynamic analyses.

The expressions proposed in literature for the supplemental damping ratio provided by nonlinear viscous dampers usually include a term related to the structural response, so that iterative procedures are required. This article proposes a simplified method for the direct assessment of the supplemental damping ratio on the basis of a new dimensionless parameter, called damper index. The methodology has been verified through numerical investigations, considering single- and multi-degree of freedom systems subjected to harmonic excitations and ground motions. A procedure is also proposed for obtaining design spectra of the damping ratio in terms of the damper index.

In this paper a simplified direct assessment method for nonlinear structures equipped with nonlinear fluid viscous dampers is proposed. The effect of this typology of damping system is usually identified with an equivalent supplemental damping ratio which depends on the maximum displacement of the structure, so that iterative procedures are required. The method proposed in this study is composed by two steps. The first one requires the direct estimate of the supplemental damping ratio under elastic conditions. The second step extends the procedure to structures with nonlinear behaviour. The method has then been verified through several applications and comparisons with nonlinear dynamic analyses. Finally it has been extended and ap-plied for probabilistic evaluations.

The main purpose of this research is to investigate the effects of different vertical distributions of the properties of nonlinear fluid-viscous dampers for the retrofit of existing multi-story reinforced concrete frames. In particular, the different distributions are defined on the basis of the same value of the supplemental damping ratio. Since the viscous dampers are used for the retrofit of existing buildings, they are dimensioned assuming that the structure can exceed the elastic limit, with the only condition to satisfy the prefixed performance limit. In the design phase the different vertical distributions of damper properties are compared in terms of the total sum of the damping coefficients. The effectiveness of the different distributions is then examined by performing time-history analysis of several case studies considering a nonlinear behavior both for the viscous dampers and for the structural members. The results of the nonlinear dynamic analyses are examined in terms of inter-story drifts and dampers forces. The considered case studies are five RC frames characterized by different number of stories (3, 6 and 9 stories) and also by different properties in terms of regularity in elevation. In this way it is also possible to investigate the effect of the vertical distribution of the damper properties for regular and irregular frames.

Background: Obstructive sleep apnea (OSA) has been linked to increased prevalence and recurrence of atrial fibrillation (AF). We hypothesized that OSA may aggravate AF in patients with pacemakers implanted for sinus bradycardia who had documented paroxysmal AF. Methods: Seventy-two patients (36 M, aged 77 ± 6 years) completed the study. All patients received a dual-chamber pacemaker equipped with diagnostic and preventive functions for AF. OSA was diagnosed with the Berlin Questionnaire, which is validated to identify patients with OSA. Four-month continuous pacemaker recordings were collected for all patients. Results: OSA was diagnosed in 28% of patients. Patients at high risk for OSA (HR group) and patients at low risk for OSA (LR group) were equivalent for gender, age, and body mass index. The rate of hypertension was higher in HR than in LR group (90% vs 44%, P < 0.01). The prevalence of paroxysmal AF during the study period was similar in HR and LR group (53% vs 44%, P = NS). Overall number of AF episodes per month was not significantly different between HR and LR group (7 ± 13 vs 36 ± 122, P = NS). Similarly, AF burden (AF%) was not significantly different between HR and LR group (0.3 ± 0.6 vs 2.0 ± 4.8, P = NS). Circadian distribution of AF episodes was similar in both groups. Conclusion: Long-term pacemaker recording of AF recurrence, AF burden, and its circadian distribution is similar in patients with paroxysmal AF at high risk for OSA and those at low risk for OSA.

Transvenous left ventricular (LV) leads are primarily inserted "over-the-wire" (OTW). However, a stylet-driven (SD) approach may be a helpful alternative. A new polyurethane-coated, unipolar LV lead can be placed either by a stylet or a guide wire, which can be inserted into the lead body from both ends. The multicenter OVID study evaluates the clinical performance of this new steroid- and nonsteroid eluting lead. The primary endpoint is the LV lead implant success rate after identification of the coronary sinus (CS). Secondary endpoints include complication rate, short- and long-term lead characteristics, overall procedure and LV lead placement duration, total fluoroscopy time, and lead handling characteristics ratings. To date, 96 patients with heart failure (68 +/- 9 years old, 76% men) are enrolled. The CS was identified in 95 patients and, in 85 (88.5%), the LV lead was successfully implanted. The final lead positioning was lateral in 41%, posterolateral in 35%, anterolateral in 18%, and great cardiac vein in 6% of patients. In 70%, the 85 successful implantations, both stylet-driven and guide-wire techniques were used, a stylet only was used in 22%, and a guide wire only in 8%. Mean overall duration of 85 successful procedures was 112 +/- 40 minutes, total fluoroscopy time 28 +/- 15 minutes, and the duration of LV lead placement was 35 +/- 29 minutes. During a 3-month follow-up, the loss of LV capture occurred in three and phrenic nerve stimulation in six patients. The mean long-term pacing threshold is 0.8 V/0.5 ms and pacing impedance is 550 Omega. The OVID data suggest that these new leads are safe and effective. The choice of both OTW and SD techniques during lead implantation offers greater procedural flexibility.

The purpose of the research presented in this paper was to investigate the effectiveness of several conventional, multi-modal and adaptive pushover procedures. In particular, an extensive numerical study was performed considering eight RC frames characterized by a variable number of storeys and different properties in terms of regularity in elevation. The results of pushover analyses were compared with those of nonlinear dynamic analyses, which were carried out considering different earthquake records and increasing values of earthquake intensity. The study was performed with reference to base shear-top displacement curves and to different storey response parameters. The obtained results allowed a direct comparison between the pushover procedures, which in general were able to give a fairly good estimate of seismic demand with a tendency to better results for lower frames. The advanced procedures, in particular the multi-modal pushover, provided an improvement of the results, more evident for the irregular frames.

In patients with myocardial infarction, thrombolytic therapy induces a paradoxical activation of the hemostatic mechanism. In patients with unstable angina, the effect of thrombolysis on the coagulation cascade is unknown. We prospectively measured the plasma concentrations of prothrombin fragment 1 + 2 and fibrinopeptide A in consecutive patients with unstable angina randomized to receive placebo alone (n = 23), streptokinase 1,500,000 IU over 1 hour followed by a 48-hour placebo infusion (n = 21), or streptokinase 250,000 over 1 hour followed by a continuous infusion of 100,000 IU per hour over 48 hours (n = 20). All the patients received intravenous heparin for 72 hours. The plasma levels of the different markers were measured at baseline, 90 minutes, 24 hours, and 48 hours after the start of therapy. The median baseline plasma concentrations of prothrombin fragment 1 + 2 and fibrinopeptide A were similar in the three treatment groups. In comparison with placebo, an increase in plasma prothrombin fragment 1 + 2 and fibrinopeptide A, was observed after 90 minutes in the two groups receiving thrombolysis. After 24 and 48 hours, the prothrombin fragment 1 + 2 levels remained significantly higher only in the patients receiving the 48-hour streptokinase infusion. In patients with unstable angina, thrombolytic therapy induces an activation of the hemostatic mechanism, despite concomitant heparin administration; in those receiving a prolonged streptokinase infusion, the activation of coagulation persists for as long as the drug is administered.