References of "Maas, Stefan"
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See detailDamage Detection in Civil Engineering Structure Considering Temperature Effect
Nguyen, Viet Ha; Mahowald, Jean; Maas, Stefan et al

in Proceedings of IMAC XXXII Dynamics of Coupled Structures (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 ▲]

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See detailUse of Time- and Frequency-Domain Approaches for Damage Detection in Civil Engineering Structures
Nguyen, Viet Ha; Mahowald, Jean; Maas, Stefan et al

in Shock and Vibration (2014), 2014

The aim of this paper is to apply both time- and frequency-domain-based approaches on real-life civil engineering structures and to assess their capability for damage detection. The methodology is based ... [more ▼]

The aim of this paper is to apply both time- and frequency-domain-based approaches on real-life civil engineering structures and to assess their capability for damage detection. The methodology is based on Principal Component Analysis of the Hankel matrix built from output-only measurements and of Frequency Response Functions. Damage detection is performed using the concept of subspace angles between a current (possibly damaged state) and a reference (undamaged) state. The first structure is the Champangshiehl Bridge located in Luxembourg. Several damage levels were intentionally created by cutting a growing number of prestressed tendons and vibration data were acquired by the University of Luxembourg for each damaged state. The second example consists in reinforced and prestressed concrete panels. Successive damages were introduced in the panels by loading heavy weights and by cutting steel wires. The illustrations show different consequences in damage identification by the considered techniques. [less ▲]

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See detailDetection and Localisation of Damage on Industrially Produced Concrete Slabs Through Time- and Frequency-Domain Approaches
Nguyen, Viet Ha; Mahowald, Jean; Golinval, Jean-Claude ULg et al

in Carrera, E; Miglioretti, F; Petrolo, M (Eds.) 6th ECCOMAS Thematic Conference on Smart Structures and Materials (SMART2013) (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 models and small-scale laboratory experiments [3, 4]. It was also tested successfully on industrial examples to perform machine condition monitoring using a reduced set of sensors [2]. 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 ▲]

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See detailUse of Time- and Frequency-Domain Approaches for Damage Detection in Civil Engineering Structures
Nguyen, Viet Ha; Mahowald, Jean; Maas, Stefan et al

in Maia, NMM; Neves, NM; Sampaio, RPC (Eds.) International Conference on Structural Engineering Dynamics : ICEDyn 2013, Sesimbra 17-19 June 2013 (2013, June)

The aim of this paper is to apply both time- and frequency-domain-based approaches on real-life civil engineering structures and to assess their capability for damage detection. The first structure is the ... [more ▼]

The aim of this paper is to apply both time- and frequency-domain-based approaches on real-life civil engineering structures and to assess their capability for damage detection. The first structure is the Champangshiehl Bridge located in Luxembourg. Several damage levels were intentionally created by cutting a growing number of prestressed tendons and vibration data were acquired by the University of Luxembourg for each damaged state. The second example consists in reinforced and prestressed concrete panels. Successive damages were introduced in the panels by loading heavy weights and by cutting steel wires. The illustrations show different consequences in damage identification by the considered techniques. [less ▲]

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See detailExperimentation and Simulation of a Small-Scale Adsorption Cooling System in Temperate Climate
Thomas, Sébastien ULg; Hennaut, Samuel ULg; Maas, Stefan et al

in Energy Procedia (2012), 30

This paper focuses on the analysis of the operation of a solar cooling system based upon an adsorption chiller. The air-conditioned building studied is a laboratory located in a temperate climate region ... [more ▼]

This paper focuses on the analysis of the operation of a solar cooling system based upon an adsorption chiller. The air-conditioned building studied is a laboratory located in a temperate climate region (Belgium). The monitoring reveals thermal and electrical coefficient of performance (COP) of the cooling system for different time scale (10s to 1 month). The whole system including solar collectors, adsorption machine, recooling unit and hot storage is simulated. The models are then confronted to the measurements. Measurement period is shared between 2011 and 2012. Enhancements have been achieved during winter 2011 to have a more efficient system operation. The aim of this experimental work is to describe, for both measurement periods, the influence of operating conditions on the energy efficiency (thermal behavior and electrical consumption). On the simulation point of view, the main objective is to find accurate models for all the components. The adsorption chiller model is not yet precise enough to evaluate the performance of solar cooling in other conditions. [less ▲]

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See detailDamage Detection on the Champangshiehl Bridge using Blind Source Separation
Nguyen, Viet Ha; Rutten, Christophe; Golinval, Jean-Claude ULg et al

in Strauss, Alfred; Frangopol, Dan M.; Bergmeister, Konrad (Eds.) Life-Cycle and Sustainability of Civil Infrastructure Systems (2012)

This paper addresses the problem of damage detection in civil engineering structures using characteristic subspaces obtained from principal component analysis (PCA) of output-only measurements. Damage ... [more ▼]

This paper addresses the problem of damage detection in civil engineering structures using characteristic subspaces obtained from principal component analysis (PCA) of output-only measurements. Damage detection is performed by comparing subspace features between a reference (healthy) state and a current (possibly damaged) state. The damage indicator used in this study is the angular coherence between sub-spaces. The considered damage detection procedure is illustrated on the Champangshiehl Bridge which is a two span concrete box girder bridge located in Luxembourg. Before its destruction, multiple damage levels were inten-tionally created by cutting a growing number of prestressed tendons. Vibration data were acquired by the University of Luxembourg for each damaged state at many locations on the bridge. As previous studies dem-onstrated the large importance of environmental factors on modal identification, special care was taken to evaluate this influence during the test campaign. [less ▲]

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See detailPerformance assessment of a small-scale adsorption chiller integrated to an already existing solar heating system
Thomas, Sébastien ULg; Andre, Philippe ULg; Maas, Stefan

in Proceedings of 4th International Conference Solar Air-Conditioning (2011, October 12)

In the context of the solar air-conditioning systems analysis, it is crucial to assess system performance by experimentations in real-time conditions. In this way, it is possible to calculate the energy ... [more ▼]

In the context of the solar air-conditioning systems analysis, it is crucial to assess system performance by experimentations in real-time conditions. In this way, it is possible to calculate the energy savings to minimize environmental impact and CO2 production induced by the operation of such a system in buildings operation. It is proposed to measure the thermal behaviour and the energy performance of a smallscale solar air-conditioning system used to cool a laboratory building in the South of Belgium. The experimental system is recently installed and fully instrumented for both thermal and electrical COP computation. Results of two months operation and data analysis are presented in this work. [less ▲]

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