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See detailA Study of Temperature and Aging Effects on Eigenfrequencies of Concrete Bridges for Health Monitoring
Nguyen, Viet Ha UL; Mahowald, Jean UL; Schommer, Sebastian UL et al

in Engineering (2017), 9

This paper discusses the influence of environmental factors and of normal material aging on the eigenfrequencies of concrete bridges based on monitoring data registered during 4 years of a specific bridge ... [more ▼]

This paper discusses the influence of environmental factors and of normal material aging on the eigenfrequencies of concrete bridges based on monitoring data registered during 4 years of a specific bridge. It is a new composite steel-concrete bridge built in 2006 in Luxembourg. The measurements are analyzed and compared to literature data. The final objective is the use of real monitored eigenfrequencies for structural health monitoring and damage detection based on identification of stiffness losses in practical applications. Therefore, it is very important to identify and compensate for outdoor influences namely temperature, excitation force level and normal aging effects, like creep and shrinkage of concrete and their impact on material properties. The present paper aims at describing these effects in order to separate them from damage effects. It is shown that temperature change rates and temperature gradients within the bridge have an influence on the eigenfrequencies. Hence the key idea for assessment from the full database is to select only measurements with small temperature differences and slow temperature change rates. [less ▲]

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See detailSome remarks on the influence of temperature-variations, non-linearities, repeatability and ageing on modal-analysis for structural health monitoring of real bridges
Maas, Stefan UL; Schommer, Sebastian UL; Nguyen, Viet Ha UL et al

in MATEC Web of Conferences (2015, October 19), 24(Article No. 05006),

Structural Health Monitoring (SHM) intends to identify damage by changes of characteristics as for instance the modal parameters. The eigenfrequencies, mode-shapes and damping-values are either directly ... [more ▼]

Structural Health Monitoring (SHM) intends to identify damage by changes of characteristics as for instance the modal parameters. The eigenfrequencies, mode-shapes and damping-values are either directly used as damage indicators or the changes of derived parameters are analysed, such as e.g. flexibilities or updated finite element models. One common way is a ontinuous monitoring under environmental excitation forces, such as wind or traffic, i.e. the so-called output-only modal analysis. Alternatively, a forced measured external excitation in distinct time-intervals may be used for input-output modal analysis. Both methods are limited by the precision or the repeatability under real-life conditions at site. The paper will summarize everal field tests of artificially step by step damaged bridges prior to their final demolishment and it will show the changes of eigenfrequencies due to induced artificial damage. Additionally, some results of a monitoring campaign of a healthy bridge in Luxembourg are presented. Reinforced concrete shows non-linear behaviour in the sense that modal parameters depend on the excitation force amplitude, i.e. higher forces lead often to lower eigenfrequencies than smaller forces. Furthermore, the temperature of real bridges is neither constant in space nor in time, while for instance the stiffness of asphalt is strongly dependant on it. Finally, ageing as uch can also change a bridge’s stiffness and its modal parameters, e.g. because creep and hrinkage of concrete or ageing of elastomeric bearing pads influence their modulus of elasticity. These effects cannot be considered as damage, though they influence the measurement of modal parameters and hinder damage detection. [less ▲]

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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 ▲]

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See detailA signal processing method to remove environmental effects for damage detection in bridge structures
Nguyen, Viet Ha UL; Mahowald, Jean UL; Maas, Stefan UL et al

Poster (2014, July)

This paper consists in damage diagnosis for several real bridges in Luxembourg. Before, different analysis methods were applied to the data measured from these structures showing interesting results ... [more ▼]

This paper consists in damage diagnosis for several real bridges in Luxembourg. 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) which overlaid the structural changes caused by damage or confuse damage levels. These environmental effects are investigated in detail and removed in this work through Principal Component Analysis. Damage index is based on outlier analysis [less ▲]

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See detailSome conclusions from the measurements of temperatures and their gradients on eigenfrequencies of bridges
Mahowald, Jean UL; Maas, Stefan UL; Nguyen, Viet Ha UL et al

Scientific Conference (2014, June 30)

The ambient air temperature and solar radiation are affecting the soil and asphalts’ stiffness and hence the eigenfrequencies of a bridge. Very often eigenfrequencies are automatically determined by ... [more ▼]

The ambient air temperature and solar radiation are affecting the soil and asphalts’ stiffness and hence the eigenfrequencies of a bridge. Very often eigenfrequencies are automatically determined by special algorithms from structural response data generated by ambient excitation and measured by permanently installed sensors that is sometimes called “output only analysis” or “operating modal analysis”. Additionally the ambient air temperature is registered and finally the eigenfrequencies are analyzed versus the air temperature. The graph is normally a scatter diagram and each point is one measurement. In general the eigenfrequencies decrease with increasing temperature, whereas often linear regression is used to determine the line of best fit. But the slope of this straight line and the width of the scatter around the regression line differ from bridge to bridge. Especially this scatter field around the mean value at a determined temperature complicates the detection of damage, which is also often based on eigenfrequencies’ reduction. Hence the difficulty among others consists in separating damage from environmental effects. [less ▲]

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See detailUse Of Time- And Frequency-Domain Approaches For Damage Detection In Civil Engineering Structures
Nguyen, Viet Ha UL; Mahowald, Jean UL; Maas, Stefan UL 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. 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 detailProceedings of IMAC XXXII Dynamics of Coupled Structures
Nguyen, Viet Ha UL; Mahowald, Jean UL; Golinval, Jean-Claude et al

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 ▲]

Detailed reference viewed: 79 (7 UL)
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See detailUSE OF TIME- AND FREQUENCY-DOMAIN APPROACHES FOR DAMAGE DETECTION IN CIVIL ENGINEERING STRUCTURES
Nguyen, Viet Ha UL; Mahowald, Jean UL; Golinval, Jean-Claude et al

in Maia, NNM; Matos Neves, M.; Chedas Sampaio, R.P. (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 detailDETECTION AND LOCALISATION OF DAMAGE ON INDUSTRIALLY PRODUCED CONCRETE SLABS THROUGH TIME- AND FREQUENCY-DOMAIN APPROACHES
Nguyen, Viet Ha UL; Mahowald, Jean UL; Golinval, Jean-Claude et al

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 ▲]

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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)

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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)

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See detailStatic and dynamic testing on prestressed concrete slab elements with artificial bond deficiencies
Mahowald, Jean UL; Maas, Stefan UL; Waldmann, Danièle UL et al

in Proceedings of the 4th Bond in Concrete Conference, Vol. 1: General Aspects of Bond (2012)

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See detailDynamic damage identification using linear and nonlinear testing methods on a two-span prestressed concrete bridge
Mahowald, Jean UL; Maas, Stefan UL; Scherbaum, Frank UL et al

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

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See detailInfluence of environmental changes on modal characteristics
Waldmann, Danièle UL; Bungard, Volker UL; Mahowald, Jean UL et al

in Federation for Structural Concrete (fib) (2011)

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See detailAmbient Vibration and Forced Excitation Tests of a Composite Bridge: Environmental influences and nonlinear effects on the dynamic properties
Bungard, Volker UL; Mahowald, Jean UL; Waldmann, Danièle UL et al

in Proceedings of the International Conference on Noise and Vibration Engineering, ISMA (2010)

Detailed reference viewed: 59 (15 UL)