Proceedings of IMAC XXXII Dynamics of Coupled Structures

in Firkret, Necati Catbas (Ed.) Damage Detection in Civil Engineering Structure Considering Temperature Effect (2014, February)

This paper concerns damage identification of a bridge located in Luxembourg. Vibration responses were captured from measurable and adjustable harmonic swept sine excitation and hammer impact. Different ... [more ▼]

This paper concerns damage identification of a bridge located in Luxembourg. Vibration responses were captured from measurable and adjustable harmonic swept sine excitation and hammer impact. Different analysis methods were applied to the data measured from the structure showing interesting results. However, some difficulties arise, especially due to environmental influences (temperature and soil-behaviour variations) which overlay 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. In the next step, they are statistically collected and processed through Principal Component Analysis (PCA) and Kernel PCA. Damage indexes are based on outlier analysis. [less ▲]

Simulated and experimental results on heat recovery from hot steel beams in a cooling bed applying modified solar absorbers

in Journal of Cleaner Production (2014), (68), 261-271

In recent years, the steel industry has undertaken efforts to increase energy efficiency by reducing energy consumption and recover otherwise lost heat. About 60% of the energy consumed in a steel plant ... [more ▼]

In recent years, the steel industry has undertaken efforts to increase energy efficiency by reducing energy consumption and recover otherwise lost heat. About 60% of the energy consumed in a steel plant is lost in cooling beds where the hot steel beams are cooled down by natural convection and radiation. In this paper, the potential of heat recovery by radiation in a cooling bed was determined. Firstly, numerical simulations of the heat flux were done and validated with experimental measures. Secondly, a pilot test to recover the heat with modified solar absorbers was installed at the side of the cooling bed. The standard solar panels were painted with high absorption paint in the wavelength range of the hot beams. The results showed that up to 1 kW/m2 could be recovered with a temperature of 70°C at the side of the cooling bed, with a thermal efficiency of approximately 40%. As the experimental results were promising, further research is suggested to find an adequate selective coating and glazing. This would maximize the absorption at the wavelength range of the hot beams and minimize the emissivity at operational temperature of the absorber (100°C). Additionally, it would be of interest to find the optimum position for the absorbers in the cooling bed, which maximizes the heat recovery and does not interfere in the production process. [less ▲]

Measured and perceived indoor comfort versus energy efficiency and users‟ control in Luxembourg‟s new school buildings

Scientific Conference (2013, September)

Room climate can be evident for job productivity and individual ́s health. Its realisation is often of high relevance for the building ́s energy consumption e.g. air conditioning vs. natural ventilation ... [more ▼]

Room climate can be evident for job productivity and individual ́s health. Its realisation is often of high relevance for the building ́s energy consumption e.g. air conditioning vs. natural ventilation. New school buildings in Luxembourg differ significantly regarding to energy consumption, heating, air-conditioning technology and technical control as well as interaction means given to the user. Several studies have shown that personal control plays an important role for the satisfaction with the room climate. Central research question was, how the technological control has to be designed that energy is used efficiently and users are still satisfied with the room climate. In this study technical features to control the room climate e.g. features for ventilation, opening windows and heating systems were summarized to an overall control factor to be compared with perceived control by the users. Physical room climate and its users ́ satisfaction level were measuredas well as the buildings ́ individual energy consumption levels were taken into account. 342 Teachers were asked by a standardised questionnaire during winter 2010/2011 in 31 new school buildings in Luxembourg, in 17 schools technical devices for air temperature, quality and humidity were installed. The results show a strong correlation between perceived control and room climate satisfaction as well as a significant correlation between the technical control factor and perceived control. Further results will be examined. [less ▲]

DETECTION AND LOCALISATION OF DAMAGE ON INDUSTRIALLY PRODUCED CONCRETE SLABS THROUGH TIME- AND FREQUENCY-DOMAIN APPROACHES

in Carrera, E.; Miglioretti, F; Petrolo, M. (Eds.) 6th ECCOMAS Thematic Conference on Smart Structures and Materials (SMART2013), Torino 24-26 June 2013 (2013, June)

The objective of this work is to address the problem of damage detection in civil engineering structures using non-destructive techniques and dynamic measurements. To this purpose, time- or frequency ... [more ▼]

The objective of this work is to address the problem of damage detection in civil engineering structures using non-destructive techniques and dynamic measurements. To this purpose, time- or frequency-domain methods are used for the diagnostics. It consists in practical output-only techniques as Stochastic Subspace Identification (SSI) for modal identification or Enhanced Principal Component Analysis (EPCA) for detecting the presence of damage. The use of the Hankel matrix instead of the observation matrix improves effectively the robustness of these methods. Damage localization is based on Frequency Response Functions (FRFs) and sensitivity analysis of PCA results. The efficiency of the above-mentioned methods has been demonstrated in earlier studies mainly on numerical examples and small-scale laboratory experiments. It was also tested successfully on industrial examples to perform machine condition monitoring using a reduced set of sensors. In this work, the investigation is performed on precast prestressed and non-prestressed concrete slabs. Successive damages were artificially introduced in the slabs by loading heavy weights and by cutting steel wires, which induced cracks in the structure. The examples show the consequences of the considered techniques for damage identification. The results that are very different between prestressed and non-prestressed slabs may be used as input for the condition control of this kind of structures. [less ▲]

Energy performance assessment of an existing double-skin façade: measurements and simulation

in Energy Forum - Solar Building Skins, 06 - 07 December 2012, Italy (2012, December)

An existing office building with an active double skin façade in Luxembourg has been analyzed. In the first step in-situ measurements have been performed. For this purpose outside, inside and cavity ... [more ▼]

An existing office building with an active double skin façade in Luxembourg has been analyzed. In the first step in-situ measurements have been performed. For this purpose outside, inside and cavity conditions have been measured for representative summer and winter conditions. In a second step, a thermal simulation using TRNSYS was performed. The simulation model has been compared to the time limited series of measurements and thus has been validated for some of the annual meteorological conditions. Then the model has been extrapolated to a whole year in order to assess the energy performance of the given façade. Further a parametric study of alternative façades has been carried out based on the validated simulation model to assess their own performances. For the given case study building, the double skin concept energetically performs well compared to other concepts with non outside (non weather exposed) solar protection, but worse than an external solar protection. The thermal comfort level in the rooms has also been determined by simulation - the calculated room averaged comfort level is quite optimal, but further investigations regarding the local comfort close to the glazed façades still have to be achieved. [less ▲]

Modern damage detection by using static assessment methods for efficient rehabilitation

in Proceedings (2012, September)

WIE VIEL ENERGIE VERBRAUCHEN NEUE UNTERRICHTS- UND BÜROGEBÄUDE IN LUXEMBURG?

in Cahier Scientifique - Revue Technique Luxembourgeoise (2012)

In Luxemburg hat sich in den vergangenen Jahren der nationale Energieverbrauch ebenfalls verstärkt zum Gebäudesektor hin verändert. Während 1990 noch 71 % des gesamten Energieverbrauches auf den ... [more ▼]

In Luxemburg hat sich in den vergangenen Jahren der nationale Energieverbrauch ebenfalls verstärkt zum Gebäudesektor hin verändert. Während 1990 noch 71 % des gesamten Energieverbrauches auf den Industriesektor zurückzuführen waren und nur 20 % auf die Gebäude, hat sich dies bis zum Jahr 2009 deutlich verändert. Demzufolge entfallen nur noch 30 % auf den Industriesektor, 25 % auf Verkehr (nach Abzug der Treibstoffexporte) und 45 % auf den Verbrauch des Tertiären Sektors3, welcher sowohl die privaten und die öffentlichen Haushalte, als auch Dienstleistungsgebäude beinhaltet. Die Direktive 2010/31/EG2 fordert von den Mitgliedstaaten die nationalen Normen weiterhin zu verschärfen und Pläne zu erstellen, um die Anzahl an Niedrigstenergiegebäuden weiter zu erhöhen. Um die Energieströme in Gebäuden besser zu verstehen, Sparmaßnahmen zu erarbeiten und mögliche Bewertungen über das Energieeinsparpotential für Gebäude durchführen zu können, sind jedoch aussagekräftige Verbrauchsdatenanalysen notwendig, die leider oftmals noch nicht in verlässlicher Qualität vorliegen. In der Direktive wird zudem empfohlen für die Berechnung eine Unterteilung aller Gebäude in angemessene Kategorien vorzunehmen, welche von Einfamilienhäusern (EFH), über Bürogebäude und Unterrichtsgebäude bis hin zu Krankenhäuser, Hotels und Sportanlagen reicht. In einer ersten Studie der Universität Luxemburg4 wurden bereits neuere EFH in Luxemburg hinsichtlich ihres realen Energieverbrauches untersucht und ausgewertet. [less ▲]

Dynamic damage identification using linear and nonlinear testing methods on a two-span prestressed concrete bridge

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

Dynamische Methoden zur Schadensidentifikation an einer kontinuierlich geschädigten vorgespannten Zweifeldbrücke

in VDI-Berichte 2160 (2012)

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

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 ▲]