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511 results on '"Waldmann, Danièle"'

155. Damage assessment of concrete structures through dynamic testing methods. Part 1 - Laboartory Test

Author

FSTC, RUES [research center], University of Luxembourg - UL [sponsor], Administration des Ponts & Chaussées, Luxembourg [sponsor], Maas, Stefan, Zürbes, Arno, Waldmann, Danièle, Waltering, Markus, Bungard, Volker, De Roeck, Guido, FSTC, RUES [research center], University of Luxembourg - UL [sponsor], Administration des Ponts & Chaussées, Luxembourg [sponsor], Maas, Stefan, Zürbes, Arno, Waldmann, Danièle, Waltering, Markus, Bungard, Volker, and De Roeck, Guido

Abstract

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.

Published
2012

156. Damage assessment of concrete structures through dynamic testing methods. Part 2: Bridge tests

Author

FSTC, RUES [research center], University of Luxembourg - UL [sponsor], Administrations des Ponts et Chaussées, Luxembourg [sponsor], Maas, Stefan, Zürbes, Arno, Waldmann, Danièle, Waltering, Markus, Bungard, Volker, De Roeck, Guido, FSTC, RUES [research center], University of Luxembourg - UL [sponsor], Administrations des Ponts et Chaussées, Luxembourg [sponsor], Maas, Stefan, Zürbes, Arno, Waldmann, Danièle, Waltering, Markus, Bungard, Volker, and De Roeck, Guido

Abstract

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.

Published
2012
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162. Shear stresses in honeycomb sandwich plates: Analytical solution, finite element method and experimental verification

Author

University of Luxembourg - UL and Eurocomposites [sponsor], Wahl, Laurent, Maas, Stefan, Waldmann, Danièle, Zürbes, Arno, Frères, Patrick, University of Luxembourg - UL and Eurocomposites [sponsor], Wahl, Laurent, Maas, Stefan, Waldmann, Danièle, Zürbes, Arno, and Frères, Patrick

Abstract

Honeycomb composite structures are used in airplanes, railway cars and vehicles. The sandwich panels consist of two stiff face sheets of aluminium, which are bonded to a very lightweight honeycomb core of aluminium. Compared to normal plates, sandwich panels have a very high stiffness and simultaneously a low weight. The core of these structures is mainly subjected to shear stresses. The shear stresses depend strongly on the angle of the load application. The distribution and the level of the shear stresses are investigated using analytical calculations. The load direction which induces highest stresses in the honeycomb core is derived. This direction is not the W-direction, which is the most compliant one. When doing finite element simulations of honeycomb cores, often the core is homogenized in order to reduce the calculation time. In this article, some equations are derived in order to calculate the real shear stresses from the shear stresses of the homogeneous core. The equations are validated by finite element simulations and partially by tests. Three-point bending tests and additionally some Food Cart Roller Tests were conducted in order to test the panels in different angles.

Published
2012
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163. Shear Stresses in Honeycomb Sandwich Plates: Analytical Solution, Finite Elemente Method and Experimental Verification

Author

FSTC, Engineering Sciences [research center], University of Luxembourg - UL & Eurocomposites [sponsor], Wahl, Laurent, Maas, Stefan, Waldmann, Danièle, Zürbes, Arno, Frères, Patrick, FSTC, Engineering Sciences [research center], University of Luxembourg - UL & Eurocomposites [sponsor], Wahl, Laurent, Maas, Stefan, Waldmann, Danièle, Zürbes, Arno, and Frères, Patrick

Abstract

Honeycomb composite structures are used in airplanes, railway cars and vehicles. The sandwich panels consist of two stiff face sheets of aluminium, which are bonded to a very lightweight honeycomb core of aluminium. Compared to normal plates, sandwich panels have a very high stiffness and simultaneously a low weight. The core of these structures is mainly subjected to shear stresses. The shear stresses depend strongly on the angle of the load application. The distribution and the level of the shear stresses are investigated using analytical calculations. The load direction which induces highest stresses in the honeycomb core is derived. This direction is not the W-direction, which is the most compliant one. When doing finite element simulations of honeycomb cores, often the core is homogenized in order to reduce the calculation time. In this article, some equations are derived in order to calculate the real shear stresses from the shear stresses of the homogeneous core. The equations are validated by finite element simulations and partially by tests. Three-point bending tests and additionally some Food Cart Roller Tests were conducted in order to test the panels in different angles.

Published
2012
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169. Fatigue in Aluminium Honeycomb-core Plates

Author

University of Luxembourg - UL and Eurocomposites [sponsor], Wahl, Laurent, Zürbes, Arno, Maas, Stefan, Waldmann, Danièle, Frères, Patrick, Wintgens, Willy, University of Luxembourg - UL and Eurocomposites [sponsor], Wahl, Laurent, Zürbes, Arno, Maas, Stefan, Waldmann, Danièle, Frères, Patrick, and Wintgens, Willy

Abstract

Honeycomb composite lightweight structures made of aluminium or aramid fibres are used in airplanes, railway carriages and automobiles. These structures are subjected to dynamic loading but hardly any fatigue properties of the honeycomb core exist in current literature. Hence here a theoretical and experimental approach is presented.

Published
2011

170. Dynamic simulations to develop a natural ventilation concept for an office building

Author

FSTC, RUES [research center], University of Luxembourg - UL [sponsor], Thewes, Andreas, Maas, Stefan, Scholzen, Frank, Waldmann, Danièle, Zuerbes, Arno, FSTC, RUES [research center], University of Luxembourg - UL [sponsor], Thewes, Andreas, Maas, Stefan, Scholzen, Frank, Waldmann, Danièle, and Zuerbes, Arno

Abstract

The Sustainability Group of the University of Luxembourg defined for their new buildings a maximum thermal end-energy of 14 kWh/(m3a) and an electricity consumption for HVAC and lighting below 6 kWh/(m3a). Therefore it was necessary to avoid active cooling loads and mechanical ventilation in the offices and small lecture rooms. The well insulated and air-tight façade, including special outside shading elements which were designed as a grid over the complete building envelope, was an essential given architectural element of the building. Therefore further external shading devices were not applicable. The only possibility to have an influence on solar gains was to optimize the window size, the glazing type and potentially an internal shading device. Furthermore, to prevent the risk of overheating during the summer period, it was necessary to reduce the internal gains from lighting and IT-equipment. Hence detailed dynamic simulations using TRNSYS and TRNFLOW were done to evaluate the thermal comfort without air-conditioning and mechanical ventilation. The effects of optimizations like a state-of-the-art lighting control system or a window-based night ventilation, as well as the influence of the effective thermal inertia of the building were analyzed. The assumed natural ventilation rates were calculated by combining TRNFLOW and TRNSYS simulations and by the software LESOCOOL.

Published
2010

172. Acoustics During the Vibratory Pile Driving of Sheet Piles: Measurement Conditions and Key Parameters of the Noise Generation

Author

University of Luxembourg - UL [sponsor], ArcelorMittal [sponsor], Ministry of Economy Luxembourg [sponsor], Hanus, Vincent, Zürbes, Arno, Maas, Stefan, Waldmann, Danièle, University of Luxembourg - UL [sponsor], ArcelorMittal [sponsor], Ministry of Economy Luxembourg [sponsor], Hanus, Vincent, Zürbes, Arno, Maas, Stefan, and Waldmann, Danièle

Abstract

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.

Published
2010
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196. Der Energieverbrauch von Einfamilienhäusern in Luxemburg

Author

University of Luxembourg - UL [sponsor], Fonds National de la Recherche - FnR [sponsor], Maas, Stefan, Waldmann, Danièle, Zürbes, Arno, Scheuren, Jean-Jacques, Heinrich, Hermann, University of Luxembourg - UL [sponsor], Fonds National de la Recherche - FnR [sponsor], Maas, Stefan, Waldmann, Danièle, Zürbes, Arno, Scheuren, Jean-Jacques, and Heinrich, Hermann

Abstract

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.

Published
2008

197. Non-destructive Damage Assessment Using Non-linear Vibration

Author

Waltering, Markus, Bungard, Volker, Maas, Stefan, Zürbes, Arno, Waldmann, Danièle, De Roeck, Guido, Waltering, Markus, Bungard, Volker, Maas, Stefan, Zürbes, Arno, Waldmann, Danièle, and De Roeck, Guido

Published
2008

198. Structural Health Monitoring of a Composite Bridge

Author

Bungard, Volker, Waltering, Markus, Waldmann, Danièle, Maas, Stefan, Zürbes, Arno, De Roeck, G., Bungard, Volker, Waltering, Markus, Waldmann, Danièle, Maas, Stefan, Zürbes, Arno, and De Roeck, G.

Published
2008

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