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Studie zur Entwicklung von Meßeinrichtungen zur fortlaufenden Messung und Registrierung von windinduzierten Bewegungen turmartiger Bauwerke / W. Mohlenbrink (1976)

Public Titre : Studie zur Entwicklung von Meßeinrichtungen zur fortlaufenden Messung und Registrierung von windinduzierten Bewegungen turmartiger Bauwerke Titre original : [Étude pour développer les équipements de mesurage pour la mesure et l'enregistrement en continu des mouvements provoqués par le vent d'édifices en forme de tour] Type de document : Monographie Auteurs : W. Mohlenbrink, Auteur Editeur : Munich : Bayerische Akademie der Wissenschaften Année de publication : 1976 Collection : DGK - B Sous-collection : Angewandte Geodäsie num. 215 Importance : 73 p. Format : 21 x 30 cm ISBN/ISSN/EAN : 978-3-7696-8520-6 Note générale : Bibliographie Langues : Allemand (ger) Descripteur : [Vedettes matières IGN] Topographie [Termes IGN] accéléromètre [Termes IGN] auscultation d'ouvrage [Termes IGN] déformation d'édifice [Termes IGN] inclinomètre (topographie) [Termes IGN] tour (bâtiment) Index. décimale : 32.00 Topographie - généralités Résumé : (Auteur) The study investigates three methods to measure wind induced vibrations or tall buildings: a) measurement of the horizontal motion with a vertically directed laser beam for reference and an array of photodiodes laser as detector; b) measurement of the acceleration of a building with accelerometers of high resolving power; c) measurement of the inclination of a building with the aid of inclinometers with electronic scanning and computation of the horizontal displacement on the basis of the derived bending line. The first chapter presents the dynamic bending line of a homogeneous, rigidly fixed girder with constant thickness as a model for tall buildings (1st order theory). Acceleration and inclination are derived as functions of height and amplitude. Based on this mathematical model and proceeding from the assumption that a 160 m high tower performs basic oscillations of 1 cm amplitude at 0.2 c.p.s. characteristic frequency and second harmonics of 1 mm amplitude at 1" c.p.s. characteristic frequency, accelerations and inclinations to be expected are calculated and illustrated graphically. The investigations show that the magnitudes of acceleration and inclination are large enough to be registered with commercial motion transducers. In addition to the model calculations non-wind-induced motions of buildings are discussed. They may pose a problem if motions caused by wind only are under investigation. Chapter 2.1 treats the measurement with a vertical laser beam and investigates the reliability of this method. Due to air turbulence and laser-inherent instabilities of direction, accidental errors up to 2 and 3 cm may be expected. Hence large arrays are required, which are not yet mass-produced; the method is therefore considered uneconomic for the present. Furthermore the relatively high costs involved would probably limit measurements to one point of a tower, which is certainly not sufficient. The measurement of acceleration and distances with seismic systems are dealt with in chapter 2.2. The equation of motion of the free and the induced vibration of a one dimensional damped spring-mass is set up as mathematical model for discussing motion transducers. The discussion does not only cover the precision required from inclinometers for measuring acceleration but also an estimate of the influence of the earth's gravitational field and the inclination of the accelerometers on the measurement results. Various instruments for the measurement of inclination with electronic scanning devices are described in chapter 2.3. The required measuring accuracy as well as possible measuring errors are evaluated. An instrument very suitable for the purpose seems to be the electronic level "Talyvel". Its resolving power is as" high as 0.01", the precision of the inclination-measurement 0.1". With additio-nal monitoring amplifiers these accuracies may be even exceeded. In the third chapter an installation for digital registration of the measured quantities is explained and the technical and financial efforts for automatic measurement and registration of wind and motion are pointed out. Finally, a simultaneous and synchronous measurement of acceleration and inclination in different sections of the building is proposed. The accuracy of such measurements, at a 200 m high tower for instance, may be in the order of +_2 mm to + 4 mm for the basic oscillation and in the order of + 0.1 mm to + 0.3 mm for the first harmonic. To arrive at such results it is indispensable to under-take a comprehensive calibration of the complete installation - measuring as well as registering devices - prior and after the measurements. The calibration should also include all cables used in the set up. The, calibration is, in essence, the crucial point of the proposed measuring system. The aim of the measurements is to separate the motions caused by wind only from the "noise", which originates from other sources. Moreover, all systematic errors located in the measuring equipment itself are to be kept small by frequent calibrations. Considering costs and accuracies obtainable a synchronous acceleration - and inclination measurement may be the appropriate method in spite of the high effort for calibrating such a system. Numéro de notice : 33060 Affiliation des auteurs : non IGN Thématique : POSITIONNEMENT Nature : Monographie Permalink : https://documentation.ensg.eu/index.php?lvl=notice_display&id=63706

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Code-barres	Cote	Support	Localisation	Section	Disponibilité
33060-01	32.00	Livre	Centre de documentation	Topographie	Disponible