101,856 research outputs found
A new automated procedure of modal identification in operational conditions
No full textStructural Health Monitoring (SHM) strategies are aimed at the assessment of structural performance, using data acquired by sensing systems. Among the different available approaches, vibration-based methods - involving the automation of the modal parameter estimation (MPE) and modal tracking (MT) procedures - are receiving increasing attention. In the context of vibration-based monitoring, this paper presents an automated procedure of modal identification in operational conditions. The presented algorithms can be used to effectively manage the results obtained by any parametric identification method that involves the construction and the interpretation of stabilization diagrams. The implemented approach introduces improvements related to both the MPE and the MT tasks. The MPE procedure consists of three key steps aimed at: (1) filtering a high number of spurious poles in the stabilization diagram; (2) clustering the remaining poles that share same characteristics in term of modal parameters; (3) improving the accuracy of the modal parameter estimates. In the MT procedure the use of a simple statistical approach to define adaptive thresholds together with continuously updated dynamic reference list guarantee an efficient tracking of the most representative structural modes. The advantages obtained through the proposed procedures are exemplified using data continuously collected on the historic masonry tower of San Gottardo in Corte, located in the centre of Milan, Italy. In addition, the ability of the automated algorithms to identify contributions inherent to different vibration modes, even if they are characterized by closely-spaced frequencies and a low discriminant between mode shapes, will be described in details
Development and application of automated OMA algorithms
No full textWithin the contest of vibration-based monitoring, the paper summarizes the conceptual development of automated procedures of modal parameter estimation (MPE) and modal tracking (MT). The performance of the proposed algorithms is demonstrated using data collected both in single data-sets and over a period of continuous monitoring. The MPE process, based on the automated interpretation of the stabilization diagram associated to any parametric identification methods, is exemplified by using the SSI-Cov technique and consists of three key steps: (1) filtering a high number of spurious poles in the stabilization diagram (2) clustering process and (3) improving the accuracy of the estimates. Eventually, the mean modal parameters are computed for each clustered mode. The MT task is based on the definition of: (a) a pre-selected list of baseline modes with adaptive thresholds and (b) a dynamic reference list of modes associated to fixed thresholds
Automated modal identification of a historic bell-tower
No full textContinuous monitoring of the structural response under ambient excitation is especially suitable to Cultural Heritage structures because of the fully non-destructive and sustainable way of testing, that is performed by just measuring the dynamic response under ambient excitation and does not involve additional loads rather than those associated to normal operational conditions. Within the context of vibration-based monitoring of historic masonry structures, the paper presents the development of an automated procedure of modal parameters estimation and tracking, as well as its application in the continuous dynamic monitoring of a masonry bell-tower. The proposed algorithm of modal parameters estimation is based on the interpretation of the stabilization diagram associated to parametric identification methods and consists of three key steps aimed at: (1) filtering a high number of spurious poles in the stabilization diagram; (2) clustering the stabilization diagram; (3) improving the accuracy of the estimates. The developed procedure is exemplified using the data collected on the bell-tower of the church of San Gottardo in Corte in Milan. Following the practice adopted by the authors for masonry towers, a simple dynamic monitoring system is installed in the tower: the monitoring system includes two bi-axial seismometers (electro-dynamic velocity transducers), one 24-bit digitizer (6 channels, A/D converter, 8 Gb Ram on board for data storage) and one UMTS modem for data transfer. After a concise presentation of the developed automated algorithm, the paper focuses on the results obtained in several months of continuous monitoring of the tower
Automated modal identification in operational conditions using 3D stabilization diagrams
No full textThe development of efficient vibration-based Structural Health Monitoring (SHM) methodologies capable to timely detecting the onset of anomalies and possible damage in structures is still a challenging task, especially for large infrastructures, complex constructions and historic buildings. SHM strategies are often based on the automated extraction of the modal parameters from the signals collected during normal (operational) conditions and different approaches have been proposed in the literature for the automation of Operational Modal Analysis (OMA). Within this context, the paper focuses on the development of a new automated OMA procedure, which involves the construction and the automated interpretation of tridimensional stabilization diagrams, avoiding the initial tuning of the input parameters characterizing the SSI techniques and resulting in modal estimates with improved accuracy. The algorithm is exemplified through its application to data collected by continuous dynamic monitoring of two different bridges
Anomaly Detection Based on Automated OMA and Mode Shape Changes: Application on a Historic Arch Bridge
No full textThe development of efficient vibration-based Structural Health Monitoring (SHM) methodologies, capable to timely detecting the onset of anomalies and damages in the structures, is still a challenging task for Civil Engineering community. Most of SHM strategies are based on automated operational modal analysis (OMA, i.e. the extraction of the modal parameters from the signals collected in operational conditions) and often on the monitoring of resonant frequencies. Alternatively, when a well distributed measurement grid is available on the structure, a further strategy for damage assessment should rely on evaluating the mode shape changes. Within this context, the paper is focused on a damage detection strategy based on the variation in time of mode shape (using MAC) and mode complexity (using MPC and/or MPC). The reliability of this approach is exemplified using a short period of monitoring of the San Michele bridge in which the structure was subjected to extreme environmental conditions. The analysis was carried out through a fully automated procedure based on the interpretation of the stabilization diagrams (provided by SSI-Cov technique) and adaptable thresholds in the modal tracking process
Vibration-Based Novelty Detection of Masonry Towers Using Pattern Recognition
No full textDuring the last decades, the increased availability of continuously monitored structures has attracted the attention of the Structural Health Monitoring (SHM) community towards the development of automated techniques capable of continuously providing useful information to timely assess the health state of a structure. Over the years, especially the SHM procedures based on Operational Modal Analysis (OMA) have proved to be effective tools for the continuous assessment of large infrastructures and ancient constructions. Within this context, the paper presents the development and validation of a vibration-based novelty detection strategy based on the application of pattern recognition models to the identified natural frequencies, with the latter being used as damage-sensitive features. The methodology presented herein is based on the forming of a decision boundary through the use of a Support Vector Machine (SVM) model: hence, SVM is exploited to separate data into two classes, associated to two different structural conditions (i.e., undamaged and damaged), without any prior assumptions on the propriety of the data. The robustness of the developed approach is exemplified using the natural frequencies automatically identified during the continuous monitoring of a historic masonry tower. Due to the occurrence of a far-field earthquake, the tower underwent structural damage demonstrated by a slight permanent variation in the natural frequencies. The obtained results highlight the capability of the proposed approach to automatically reveal slight damages in structures without any user interaction and without performing any removal of environmental and operational effects
Bibliographie Hilarion G. Petzold 1958 – 2009 mit Anhang als Einführung
No full textDieses Archiv enthält die Gesamtbibliographie der Werke des Autors nebst einiger Texte „Über H. G. Petzold“ im Schlussteil der Bibliographie sowie einen Anhang mit einer Einführung in die Architektur des Werkes in seinem wissenslogischen Aufbau als Ausarbeitung seines „Tree of Science Modells“ (2007).This archive contains the complete bibliography of the author and some texts about H. G. Petzold, moreover an epilogue with an introduction to the architecture of the works in its epistemological structure and composition and as an elaborations of Petzold’s „Tree of Science Modell (2007).https://www.fpi-publikation.de/polyloge/01-2009-petzold-h-g-gesamtbibliographie-h-g-petzold-1958-2009-updating-november2009/peerReviewedpublishedVersio
Dispelling the Myths Behind First-author Citation Counts
No full textWe conducted a full-scale evaluative citation analysis study of scholars in the XML research field to explore just how different from each other author rankings resulting from different citation counting methods actually are, and to demonstrate the capability of emerging data and tools on the Web in supporting more realistic citation counting methods. Our results contest some common arguments for the continued
use of first-author citation counts in the evaluation of scholars, such as high correlations between author rankings by first-author citation counts and other citation
counting methods, and high costs of using more realistic citation counting methods that are not well-supported by the ISI databases. It is argued that increasingly available digital full text research papers make it possible for citation analysis studies to go beyond what the ISI databases have directly supported and to employ more
sophisticated methods
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3346: Samuel G. Freedman, author, 2013
No full textPhotograph of author Samuel G. Freedman, at NT Daily Slash meeting in the Mayborn School of Journalism at UNT
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