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Showing results 21 to 31 of 31
   Damage assessment of concrete structures through dynamic testing methods. Part 2: Bridge testsMaas, Stefan  ; ; Waldmann, Danièle et alin Engineerig Structures (2012), 34 The present paper is split into two parts: in the first part the different dynamic damage indicators are defined and applied to beam and slab structures under laboratory conditions, whereas the present ... [more ▼] The present paper is split into two parts: in the first part the different dynamic damage indicators are defined and applied to beam and slab structures under laboratory conditions, whereas the present second part deals with experiments carried out on two real post-tensioned bridges. The damage indicators defined in part one are based on swept sine excitation and esveal the drop of the eigenfrequencies, the changes in damping, the varying dependency range of the first eigenfrequency on excitation force amplitude and the occurrence of higher harmonics, which changed the Total Harmonic Distorsion (THD) and a special transfer-function called TF or FRFsmall. In the first part it was proved that the amount of nonlinearities varies with damage and that harmonic excitation is favorable for good test conditions. In the laboratory this can easily be done using an electric or hydraulic shaker, but on real bridges this kind of excitation becomes more complicated due to the higher forces and the necessity to provide counter bearing for any shaker system. That is why two machines were designed and used to excite big structures harmonically, e.g. real bridges in this part. The different indicators are applied to assess the state of two post-tensioned bridges, which had been in good order and condition before artificial damage in multiple steps was caused. It turns out that the decrease in the eigenfrequencies is the most important damage indicator, provided temperature and mass dependant effects can be eliminated. All other indicators may be used as supplements to give correct tendencies, but no strict limits. [less ▲] Detailed reference viewed: 198 (33 UL)Damage assessment of concrete structures through dynamic testing methods. Part 1 - Laboartory TestMaas, Stefan ; ; Waldmann, Danièle et alin Journal of Engineering Structures (2012), 34 The present paper is split into two parts: Part 1 is about laboratory tests whereas the second part deals with experiments on real bridges. This article aims at summarizing several experimental dynamic ... [more ▼] The present paper is split into two parts: Part 1 is about laboratory tests whereas the second part deals with experiments on real bridges. This article aims at summarizing several experimental dynamic testing methods with different damage indicators to evaluate the state of prestressed as well as of passively reinforced concrete structures. First the differences between prestressed and passively reinforced concrete are repeated for static behavior, before the transition to dynamics is made. As it will be proved in the following that the amount of nonlinearities increases with damage, harmonic excitation is favorable to realize good testing conditions. It is applied to visualize variations in linear as well as in non-linear structural characteristics, which are subsequently used as damage indicators, e.g. the drop of the eigenfrequencies, the changes in damping and modeshapes, the occurrence of higher harmonics and a varying dependency of the eigenfrequency on excitation force amplitude. These different indicators will be used on passively reinforced beam elements and industrially produced prestressed slabs in the first part and on two real post-tensioned bridges in the second part. All these structures were in good order and condition before artificial damage was applied in multiple steps and the sensitivity of each damage indicator was analyzed. [less ▲] Detailed reference viewed: 113 (18 UL)Steel fibres as only reinforcement for flat slab construction; Waldmann, Danièle ; et alin Construction and Building Materials (2011) Detailed reference viewed: 50 (5 UL)Study of the vibrating stationary state of a sheet pile during a vibratory pile driving; ; et al in Proceedings of ISMA 2010 - International Conference on Noise and Vibration Engineering (2010, September 20) Detailed reference viewed: 39 (1 UL)Tragverhalten von Flachdecken aus Stahlfaserbeton im negativen Momentenbereich und Bemessungsmodell für das Gesamtsystem; Waldmann, Danièle ; et alin Beton- und Stahlbetonbau (2010) Detailed reference viewed: 91 (1 UL)Acoustics During the Vibratory Pile Driving of Sheet Piles: Measurement Conditions and Key Parameters of the Noise GenerationHanus, Vincent ; ; Maas, Stefan et alin Acta Acustica United with Acustica (2010), 96(1-1), This paper studies the sound generation during the vibratory pile driving of double sheet piles for different crosssections with the aims to give guidelines how to make high-quality acoustic measurements ... [more ▼] This paper studies the sound generation during the vibratory pile driving of double sheet piles for different crosssections with the aims to give guidelines how to make high-quality acoustic measurements and to find the keyparameters in this noise generation. These objectives are reached by studying the assumed hypotheses when performing the acoustic measurements and by using a beamforming system; details about the vibratory pile driving are also given to obtain reproducible and representative measurements. The experiment results confirm some previouslypresented hypotheses and show two key parameters involved in the sound generation: the space between the welds of the common interlock of a double sheet pile and the wall height above the soil of a neighbouring wall. [less ▲] Detailed reference viewed: 117 (6 UL)Rotameter: A Non-Invasive and Simple Device for an In Vivo Analysis of Rotational Knee Laxity; ; et al in 44th Gesellschaft für Biomedizinische Technik (DGBMT) (2010) Detailed reference viewed: 49 (3 UL)Betrachtung von Leichtbauplatten mit Wabenstruktur unter dem Gesichtspunkt der Schwingfestigkeit.Bauer, J. ; ; Greger, Manfred et alin DVM-Tag 2008- PROCEEDINGS (2008) Detailed reference viewed: 86 (0 UL) Der Energieverbrauch von Einfamilienhäusern in LuxemburgMaas, Stefan ; Waldmann, Danièle ; et alin Gesundheits-Ingenieur (2008) Die luxemburgische Wärmeschutzverordnung von 1995, die im Grunde nur den k- oder U-Wert begrenzt, muss infolge der EU-Direktive 2002/91/EG über die Gesamtenergieeffizienz von Gebäuden novelliert werden ... [more ▼] Die luxemburgische Wärmeschutzverordnung von 1995, die im Grunde nur den k- oder U-Wert begrenzt, muss infolge der EU-Direktive 2002/91/EG über die Gesamtenergieeffizienz von Gebäuden novelliert werden. Das Wirtschaftsministerium hat im August 2006 einen Entwurf für die Neufassung publiziert [9], welcher wohl ab 01.01.2008 verbindlich wird. Daher stellt sich aktuell die Frage, wo Luxemburg im Vergleich mit seinen Nachbarn steht und wohin die neue Verordnung führen wird. Genau dies hat die Ingenieurgruppe der Universität Luxemburg in den letzten Jahren untersucht [1], was im Folgenden zusammengefasst wird. [less ▲] Detailed reference viewed: 359 (24 UL)Damage Assessment of Civil Engineering Structures by the Observation of Non-linear Dynamic Behaviour; Waldmann, Danièle ; et alin Proceedings of the International Conference on Experimental Vibration Analysis for Civil Engineering Structures (2007) (2007) Detailed reference viewed: 48 (4 UL)Entwicklung von hybriden Mauersteinen mit verbesserten wärmedämmenden Eigenschaften; Waldmann, Danièle ; Maas, Stefan et alPresentation (2006, December) Detailed reference viewed: 130 (15 UL)
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