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High frequent total station measurements for the monitoring of bridge vibrations / Werner Lienhart in Journal of applied geodesy, vol 11 n° 1 (March 2017)  

Public [article]  inJournal of applied geodesy > vol 11 n° 1 (March 2017) . - pp 1 - 8 Titre : High frequent total station measurements for the monitoring of bridge vibrations Type de document : Article/Communication Auteurs : Werner Lienhart, Auteur ; Matthias Ehrhart, Auteur ; Magdalena Grick, Auteur Année de publication : 2017 Article en page(s) : pp 1 - 8 Note générale : Bibliographie Langues : Anglais (eng) Descripteur : [Vedettes matières IGN] Applications de géodésie spatiale [Termes IGN] pont [Termes IGN] surveillance d'ouvrage [Termes IGN] tachéomètre électronique [Termes IGN] topométrie de précision [Termes IGN] vidéotachéomètre Résumé : (Auteur) Robotic total stations (RTS) are frequently used for the measurement of temperature induced bridge deformations or during load testing of bridges. In experimental setups, total stations have also been used for the measurement of dynamic bridge deformations. However, with standard configurations the measurement rate is not constant and on average an update rate of 7–10Hz can be achieved. This is not sufficient for the vibration monitoring of bridges considering their natural frequencies which are also in the same range. In this paper, we present different approaches to overcome these problems. In the first two approaches we demonstrate how the measurement rate to prisms can be increased to 20Hz to determine vertical deformations of bridges. Critical aspects like the measurement resolution of the automated target tracking and the correct sequence of steering commands are discussed. In another approach we demonstrate how vertical bridge vibrations can be measured using an image assisted total station (IATS) and corresponding processing techniques. The advantage of image-based methods is that structural features of a bridge like bolts can be used as targets. Therefore, no expensive prisms have to be mounted and access to the bridge is not required. All approaches are verified by laboratory investigations and their suitability is proven in a field experiment on a 74m long footbridge. In this field experiment the natural frequencies derived from the total station measurements are compared to the results of accelerometer measurements. Numéro de notice : A2017-280 Affiliation des auteurs : non IGN Thématique : POSITIONNEMENT Nature : Article DOI : 10.1515/jag-2016-0028 En ligne : https://doi.org/10.1515/jag-2016-0028 Format de la ressource électronique : URL article Permalink : https://documentation.ensg.eu/index.php?lvl=notice_display&id=85313 [article]

Geodetic monitoring of subrosion-induced subsidence processes in urban areas / Tobias Kersten in Journal of applied geodesy, vol 11 n° 1 (March 2017)  

Public [article]  inJournal of applied geodesy > vol 11 n° 1 (March 2017) . - pp 21 - 30 Titre : Geodetic monitoring of subrosion-induced subsidence processes in urban areas Type de document : Article/Communication Auteurs : Tobias Kersten, Auteur ; Martin Kobe, Auteur ; Gerald Gabriel, Auteur ; Ludger Timmen, Auteur ; Steffen Schön, Auteur ; Detlef Vogel, Auteur Année de publication : 2017 Article en page(s) : pp 21 - 30 Note générale : Bibliographie Langues : Anglais (eng) Descripteur : [Vedettes matières IGN] Applications de géodésie spatiale [Termes IGN] église [Termes IGN] gravimétrie [Termes IGN] Hambourg [Termes IGN] nivellement [Termes IGN] positionnement par GNSS [Termes IGN] réseau de surveillance géophysique [Termes IGN] subsidence [Termes IGN] surveillance géologique [Termes IGN] Thuringe [Termes IGN] tour (bâtiment) [Termes IGN] zone urbaine Résumé : (Résumé) The research project SIMULTAN applies an advanced combination of geophysical, geodetic, and modelling techniques to gain a better understanding of the evolution and characteristics of sinkholes. Sinkholes are inherently related to surface deformation and, thus, of increasing societal relevance, especially in dense populated urban areas. One work package of SIMULTAN investigates an integrated approach to monitor sinkhole-related mass translations and surface deformations induced by salt dissolution. Datasets from identical and adjacent points are used for a consistent combination of geodetic and geophysical techniques. Monitoring networks are established in Hamburg and Bad Frankenhausen (Thuringia). Levelling surveys indicate subsidence rates of about 4–5 mm per year in the main subsidence areas of Bad Frankenhausen with a local maximum of 10 mm per year around the leaning church tower. Here, the concept of combining geodetic and gravimetric techniques to monitor and characterise geological processes on and below the Earth's surface is exemplary discussed for the focus area Bad Frankenhausen. For the different methods (levelling, GNSS, relative/absolute gravimetry) stable network results at identical points are obtained by the first campaigns, i.e., the results are generally in agreement. Numéro de notice : A2017-281 Affiliation des auteurs : non IGN Thématique : POSITIONNEMENT Nature : Article DOI : 10.1515/jag-2016-0029 En ligne : https://doi.org/10.1515/jag-2016-0029 Format de la ressource électronique : URL article Permalink : https://documentation.ensg.eu/index.php?lvl=notice_display&id=85314 [article]

Monitoring of vertical deformations by means high-precision geodetic levelling. Test case : The Arenoso dam (South of Spain) / M. Clara de Lacy in Journal of applied geodesy, vol 11 n° 1 (March 2017)  

Public [article]  inJournal of applied geodesy > vol 11 n° 1 (March 2017) . - pp 31 - 42 Titre : Monitoring of vertical deformations by means high-precision geodetic levelling. Test case : The Arenoso dam (South of Spain) Type de document : Article/Communication Auteurs : M. Clara de Lacy, Auteur ; M. Isabel Ramos, Auteur Année de publication : 2017 Article en page(s) : pp 31 - 42 Note générale : Bibliographie Langues : Anglais (eng) Descripteur : [Vedettes matières IGN] Applications de géodésie spatiale [Termes IGN] barrage [Termes IGN] déformation verticale de la croute terrestre [Termes IGN] Espagne [Termes IGN] génie civil [Termes IGN] nivellement direct [Termes IGN] réseau géodésique spécifique [Termes IGN] surveillance d'ouvrage [Termes IGN] topométrie de précision Résumé : (Auteur) The Arenoso reservoir is created by an embankment dam, with central clay core, slates and greywacke shoulders. This kind of engineering structure is subject of deformation due to factors such as changes of water level of the reservoir, seat structure, climate changes, etc. In general, dam monitoring involves measurements both outside (external shell) and inside the structure. A number of control points is established around the area of the dam and the measurements of the displacements of the control points take place at several epochs. In this study high-precision levelling techniques have been used to monitor the vertical deformations. In particular five high-precision levelling profiles were measured in five surveys: February and July 2008, March and July 2013 and August 2014. In this study the design, observations and results are presented. On the one hand the results put in evidence the precision of the observations that are always under 1-mm level. On the other hand these results indicate downstream (southeastward) motion of the thrust block center of the dam probably during the fall and winter. The subsidence reachs here the maximum with a value of −14 cm in 2014 (in respect of February 2008). The displacements observed at the berms of the dam exhibit a similar trend to the displacements observed at the crest but they are significantly smaller, as expected. The accumulative vertical displacements and the settlement index indicate the magnitude of the movements decrease in time, confirming the dam tends to stabilize. Numéro de notice : A2017-282 Affiliation des auteurs : non IGN Thématique : POSITIONNEMENT Nature : Article DOI : 10.1515/jag-2016-0034 En ligne : https://doi.org/10.1515/jag-2016-0034 Format de la ressource électronique : URL article Permalink : https://documentation.ensg.eu/index.php?lvl=notice_display&id=85315 [article]