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See detailDamage assessment of a gradually damaged pre-stressed concrete bridge using static load tests and non-linear vibration characteristic
Waltering, Markus UL; Bungard, Volker UL; Maas, Stefan UL et al

in International Conference on Noise and Vibration Engineering (2008)

Detailed reference viewed: 83 (14 UL)
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See detailDamage Assessment of Civil Engineering Structures by the Observation of Non-linear Dynamic Behaviour
Waltering, Markus UL; Bungard, Volker UL; Waldmann, Danièle UL et al

in Proceedings of the International Conference on Experimental Vibration Analysis for Civil Engineering Structures (2007)

Detailed reference viewed: 95 (17 UL)
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See detailDamage Assessment of Civil Engineering Structures by the Observation of Non-linear Dynamic Behaviour
Waltering, Markus; Waldmann, Danièle UL; Maas, Stefan et al

in Proceedings of the International Conference on Experimental Vibration Analysis for Civil Engineering Structures (2007) (2007)

Detailed reference viewed: 29 (4 UL)
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See detailDamage assessment of concrete structures through dynamic testing methods. Part 1 - Laboartory Test
Maas, Stefan UL; Zürbes, Arno; Waldmann, Danièle UL et al

in 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: 80 (16 UL)
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See detailDamage assessment of concrete structures through dynamic testing methods. Part 2: Bridge tests
Maas, Stefan UL; Zürbes, Arno; Waldmann, Danièle UL et al

in 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: 163 (28 UL)
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See detailDamage detection for bridge structures based on dynamic and static measurements
Nguyen, Viet Ha UL; Schommer, Sebastian UL; Zurbes, Arno et al

Scientific Conference (2016, March)

Some results of damage detection for real bridge structures are reported in the present paper based on both dynamic and static measurements. Dynamic analysis relates to the identification of modal ... [more ▼]

Some results of damage detection for real bridge structures are reported in the present paper based on both dynamic and static measurements. Dynamic analysis relates to the identification of modal parameters and deduced variables… The processing of static data is based on the analyses of deflection line and its derivatives, i.e. slope and curvature. Detection methods were applied in several real concrete bridges in Luxembourg. The results are encouraging and useful for Structural Health Monitoring in civil engineering structures. [less ▲]

Detailed reference viewed: 113 (12 UL)
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See detailDamage detection in bridge structures including environmental effects
Nguyen, Viet Ha UL; Mahowald, Jean UL; Golinval, Jean-Claude et al

in the Ninth International Conference on Structural Dynamics EURODYN 2014 (2014, July)

Damage identification for two real big bridges in Luxembourg is carried out in this paper. Vibration responses were captured from different types of excitation such as measurable and adjustable harmonic ... [more ▼]

Damage identification for two real big bridges in Luxembourg is carried out in this paper. Vibration responses were captured from different types of excitation such as measurable and adjustable harmonic swept sine excitation and hammer impact. Before, different analysis methods were applied to the data measured from these structures showing interesting results. However, some difficulties are faced, especially due to environmental influences (temperature and soil-behaviour variations) overlaid to the structural changes caused by damage. These environmental effects are investigated in detail in this work. First, the modal parameters are identified from the response data by means of Wavelet Transform. In the next step, they are stochastically collected and processed through Principal Component Analysis. Damage index is based on outlier analysis. [less ▲]

Detailed reference viewed: 128 (32 UL)
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See detailDamage detection in prestressed concrete bridges based on static load testing, sagging and modal parameters, using measurements and model updating
Schommer, Sebastian UL

Doctoral thesis (2017)

Bridges are an essential part of nowadays infrastructure to cross natural and artificial obstacles like rivers, valleys or other roads and railways. Many concrete bridges were built in the last 70 years ... [more ▼]

Bridges are an essential part of nowadays infrastructure to cross natural and artificial obstacles like rivers, valleys or other roads and railways. Many concrete bridges were built in the last 70 years. The traffic density has increased immensely over the last decades and the bridges are suffering from corrosion and wear. Nevertheless, the safety of the infrastructure has to be guaranteed and therefore it is very important to find efficient methods for structural health monitoring. For this purpose, visual inspections are the most widely adopted in reality today. Considering the size of most bridge structures, it is understandable that these tests are generally very time-consuming and many personnel are needed, so they are cost-intensive. However, it is not always guaranteed that all damage can be found as only the surface is accessible. For instance, internal damage, such as corrosion of passive reinforcements or prestressed tendons, is difficult to detect. In addition, small cracks can remain undetected when covered by paints or dirt. Therefore, it is important to complement the standard methods with advanced alternatives. The aim is therefore not necessarily to replace visual inspections, but rather to find efficient methods for amendment. An idea being vigorously discussed in the scientific community is based on vibration measurements of a structure to assess its dynamic behaviour. The occurrence of damage will change the system properties, as it changes above all the stiffness distribution. So the system identification process in principle allows detection of changes of eigenfrequencies and hence stiffness. The main problem in practice on real bridges is that the robustness of a method is often insufficient, as the measured parameters are often also influenced by temperature changes. It will be shown that the impact of temperature change, e.g. between night and day, on the system properties is much higher than the influence of small damage. Furthermore, changes in soil and bearing conditions between different seasons can play a role. These environmental effects have to be taken into account while performing measurements for damage assessment. For this purpose, strategies are proposed to compensate environmental effects. Therefore, this thesis focuses on measurements under real environmental conditions, outside a laboratory. Different methods for damage assessment or stiffness tracking based on measured static and on dynamic properties of structures are deployed. Finally, the measured and analysed physical properties of the bridges in this thesis are: eigenfrequencies, mode shapes, sagging under own weight and the deflection line under a static test-loading. These quantities are tracked and artificial damage is introduced stepwise to a test-beam of a real bridge. Damage assessment and localisation is tried directly with the measured quantities but also by model-updating of a finite element model. This solid model is divided in a special way in different slices. It is possible to change the stiffness distribution along the axis of the simulated beam by varying the Young’s moduli of these slices. Furthermore, to reduce the number of free parameters for the subsequent up-dating process, an exponential damage function is introduced that describes the stiffness distribution. At first, the model was designed to fit a healthy reference state. Now measurement data from the artificially damaged test-beam are introduced and the model is updated by changing the Young’s moduli of the slices to minimise a special objective function containing the measured and simulated physical quantities. The comparison of initial and updated model allows a quantification and localisation of damage. Finally, the slice width is reduced around the identified damage region to improve the process. [less ▲]

Detailed reference viewed: 293 (42 UL)
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See detailDamage Detection on the Champangshiehl Bridge using Blind Source Separation
Nguyen, Viet Ha UL; Rutten, Christophe; Golinval, Jean-Claude et al

in Proceedings of the Third International Symposium on Life-Cycle Civil Engineering, IALCCE’12 (2012)

Detailed reference viewed: 108 (24 UL)
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See detailDamage Identification and Localisation Using Changes in Modal Parameters for Civil Engineering Structures
Mahowald, Jean UL; Maas, Stefan UL; Waldmann, Danièle UL et al

in Proceedings of the International Conference on Noise and Vibration Engineering (2012)

Detailed reference viewed: 119 (38 UL)
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See detailDamage tolerance assessment directly from CAD: (extended) isogeometric boundary element methods
Peng, Xuan; Atroshchenko, Elena; Bordas, Stéphane UL

Scientific Conference (2014, June)

Detailed reference viewed: 279 (4 UL)
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See detailDamage tolerance assessment directly from CAD: (extended) isogeometric boundary element methods (XIGABEM)
Peng, Xuan; Atroshchenko, Elena; Bordas, Stéphane UL

Scientific Conference (2014)

Detailed reference viewed: 390 (5 UL)
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See detailDamnatio memoriae
Scuto, Denis UL

Article for general public (2017)

Detailed reference viewed: 54 (5 UL)
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See detailDamnation et salut babélique dans le théâtre luxembourgeois
De Toffoli, Ian UL

in Gerflint. Synergien. Pays Germanophones. Multilinguisme: enseignement, littératures et cultures au Luxembourg (2015)

La situation sociolinguistique du Grand-Duché du Luxembourg n’est pas sans laisser de trace dans son champ littéraire. Trois langues y sont utilisées quotidiennement et simultanément. L’écrivain ... [more ▼]

La situation sociolinguistique du Grand-Duché du Luxembourg n’est pas sans laisser de trace dans son champ littéraire. Trois langues y sont utilisées quotidiennement et simultanément. L’écrivain luxembourgeois a le choix d’écrire dans l’une des trois langues, de les alterner ou de les mélanger à l’intérieur d’un même texte. Nous analyserons, dans cette brève étude, trois pièces de théâtre luxembourgeoises qui brassent les langues et déterminerons la fonction de cette polyglossie caractéristique du Luxembourg : de la mise en évidence de l’étrangéité d’un personnage, jusqu’à la mise en question d’une entente harmonieuse de différentes nations européennes dans une bousculade culturelle babélique. [less ▲]

Detailed reference viewed: 58 (5 UL)
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See detailDams and International Law
Happold, Matthew UL

in de Chazournes, L. Boisson; Salman, S.M.A. (Eds.) Les ressources en eau et le droit international/Water Resources and International Law (2005)

Detailed reference viewed: 187 (2 UL)
See detailDaniel Sternheimer
Schlichenmaier, Martin UL; Bieliavsky, Pierre

in Goemetric Methods in Physics, XXXII workshop (2014)

Detailed reference viewed: 72 (3 UL)
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See detailDank sagen, rhetorisch und idiomatisch. Zur Entstehung der Floskel ‚Danke‘
Dembeck, Till UL; Bunia, Remigius

in Binczek, Natalie; Bunia, Remigius; Dembeck, Till (Eds.) et al Dank sagen. Politik, Semantik und Poetik der Verbindlichkeit (2013)

Detailed reference viewed: 145 (1 UL)
See detailDank sagen. Politik, Semantik und Poetik der Verbindlichkeit
Dembeck, Till UL; Binczek, Natalie; Bunia, Remigius et al

Book published by Fink (2013)

Detailed reference viewed: 71 (1 UL)