1,720,982 research outputs found
Finite element model updating of the Stange railway overpass using operational modal analysis
Get PDFThe growing demand for public transportation and the need for trains at higher speeds highlights the importance of assessment and rehabilitation of train bridges. A challenge of rehabilitation is to restore or improve the structure without knowing the exact condition of the already existing bridge. This study determines and investigates the dynamic and modal parameters, responses, and properties of the easter Stange railway bridge, carrying track two with most of its traffic being northbound. The thesis also studies the maximum accelerations of both the eastern bridge carrying track two, and the western bridge carrying track one.
Vibration measurements were conducted to both bridges, one bridge at the time, using a total of ten sensors which was installed on each of the two bridges with an equal but mirrored layout. The measurements were carried out over six days in February and March 2022.
The data were uploaded in Matlab where flies containing from half an hour to an hour of data was sorted and cropped into individual train passings. The anomalies where also removed. Using operational modal analysis and Covariance-driven Stochastic Subspace Identification the natural frequencies, damping ratios and mode shapes for the train passings where found.
An initial model of the eastern bridge was created, with the dynamic analysis program CSiBridge, which produced initial modal responses to give an estimation of the model’s credibility and accuracy. The model provided plausible results in the expected range of frequencies and with probable mode shapes. The model was updated with the results from the operational modal analysis to produce more accurate dynamic responses.
In addition, the maximum accelerations of each train passing were compared to the requirement of standard NS-EN 1990. The study succeeded to update the model and additionally concludes that all the maximum accelerations on track two are within the standards of NS-EN 1990, while 36% of the maximum accelerations on track one are not.publishedVersio
Use of Smartphones for Indirect Vibration-based Frequency Identification of Pedestrian Bridges
Get PDFAgeing bridge infrastructure and limited maintenance resources highlight the need for scalable structural health monitoring (SHM) solutions. The goal is to detect changes in the dynamic response to assess the presence of structural damage or signs of deterioration. Traditional bridge monitoring employs sensors mounted on the structure to record various dynamic parameters, a method referred to as direct testing. The indirect method involves mounting sensors on vehicles, enabling one sensor unit to collect data from multiple bridges. A preliminary study applied both methods to 13 pedestrian bridges in Oslo using an electric scooter for data collection. The recorded data were analysed using Fast Fourier Transform to extract the bridge frequency. The direct testing provided a clear indication of the bridge’s natural frequency, whereas the indirect testing was characterized by a high level of noise. This may originate from several factors, such as the vehicle system and road roughness. To isolate the vehicle’s dynamic signature, additional tests were conducted in a parking garage with a nearly smooth surface. To further develop the indirect method, three test days were conducted on the Akrobaten bridge. Vehicle-induced frequencies were first characterized through isolated testing, and various signal processing techniques, including the Welch method and Hanning window, were applied. During the test days, a bicycle was implemented as a new type of test vehicle, and a semi-direct method was introduced.
The results indicated that the dynamic response signal was relatively weak, whereas the noise introduced by the motion and operation of the test vehicles was significantly higher. Although the bridge frequency was identified through direct testing, serving as ground truth, it remained obscured by dominant noise components in all indirect tests. Despite efforts to refine the indirect method, including the use of two vehicle types and signal processing, the measurements remained dominated by noise. The study concludes that although the bridge’s natural frequency is present in the data, it cannot be reliably identified through indirect testing alone without prior knowledge. Future research should aim to isolate and filter vehicle-induced components to enable more accurate bridge frequency detection through indirect methods
Finite element model updating of the Stange railway overpass using operational modal analysis
No full textThe growing demand for public transportation and the need for trains at higher speeds highlights the importance of assessment and rehabilitation of train bridges. A challenge of rehabilitation is to restore or improve the structure without knowing the exact condition of the already existing bridge. This study determines and investigates the dynamic and modal parameters, responses, and properties of the easter Stange railway bridge, carrying track two with most of its traffic being northbound. The thesis also studies the maximum accelerations of both the eastern bridge carrying track two, and the western bridge carrying track one.
Vibration measurements were conducted to both bridges, one bridge at the time, using a total of ten sensors which was installed on each of the two bridges with an equal but mirrored layout. The measurements were carried out over six days in February and March 2022.
The data were uploaded in Matlab where flies containing from half an hour to an hour of data was sorted and cropped into individual train passings. The anomalies where also removed. Using operational modal analysis and Covariance-driven Stochastic Subspace Identification the natural frequencies, damping ratios and mode shapes for the train passings where found.
An initial model of the eastern bridge was created, with the dynamic analysis program CSiBridge, which produced initial modal responses to give an estimation of the model’s credibility and accuracy. The model provided plausible results in the expected range of frequencies and with probable mode shapes. The model was updated with the results from the operational modal analysis to produce more accurate dynamic responses.
In addition, the maximum accelerations of each train passing were compared to the requirement of standard NS-EN 1990. The study succeeded to update the model and additionally concludes that all the maximum accelerations on track two are within the standards of NS-EN 1990, while 36% of the maximum accelerations on track one are not
Going Beyond Counting First Authors in Author Co-citation Analysis
Get PDFThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Variations on the Author
Get PDF“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
Appropriate Similarity Measures for Author Cocitation Analysis
Get PDFWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
Dispelling the Myths Behind First-author Citation Counts
Get PDFWe 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
- …
