References of "Nguyen, Viet Ha 50009108"
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See detailBRIDGE MONITORING WITH HARMONIC EXCITATION AND PRINCIPAL COMPONENT ANALYSIS
Nguyen, Viet Ha UL; Golinval, Jean-Claude; Maas, Stefan UL

in The Baltic Journal of Road and Bridge Engineering (2019)

Principal Component Analysis is used for damage detection in structures excited by harmonic forces. Time responses are directly analysed by Singular Value Decomposition to deduct two dominant Proper ... [more ▼]

Principal Component Analysis is used for damage detection in structures excited by harmonic forces. Time responses are directly analysed by Singular Value Decomposition to deduct two dominant Proper Orthogonal Values corresponding to two Proper Orthogonal Modes. Damage index is defined by the concept of subspace angle that a subspace is built from the two Proper Orthogonal Modes. A subspace angle reflects the coherence between two different structural health states. An example is given through the application on a part of a real prestressed concrete bridge in Luxembourg where different damage states were created by cutting a number of prestressed tendons in four scenarios with increasing levels. Results are better by using excitation frequency close to an eigenfrequency of the structure. The technique is convenient for practical application in operational bridge structures. [less ▲]

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See detailModeling of a prestressed concrete bridge with 3D finite elements for structural health monitoring using model updating techniques
Schommer, Sebastian UL; Kebig, Tanja UL; Nguyen, Viet Ha UL et al

in ISMA2018 International Conference on Noise and Vibration Engineering (2018)

This paper presents a linear finite element model for a prestressed concrete beam, which was part of a real bridge. Static and dynamic tests were carried out and compared to the numerical simulation ... [more ▼]

This paper presents a linear finite element model for a prestressed concrete beam, which was part of a real bridge. Static and dynamic tests were carried out and compared to the numerical simulation responses. A solid finite element model was created including the prestressed concrete beam, permanent dead load, two additional live loads and a shaker. A well planned finite element model is very important for later detection and localization of damage. Therefore, a mapped mesh was used to define so-called ‘slices’, which enables describing stiffness changes, e.g. damage. The model validation was performed by comparing simulated results to measured responses in the healthy state of the beam. After validation of the reference model, it is possible to modify the bending stiffness along the longitudinal axis of the beam by modifying Young’s moduli of different slices to adapt for the effect of damage. [less ▲]

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See detailModel updating for structural health monitoring using static and dynamic measurements
Schommer, Sebastian UL; Nguyen, Viet Ha UL; Maas, Stefan UL et al

in Procedia Engineering (2017), 199

Structural health monitoring is tracking static or dynamic characteristics of a structure to identify and localize stiffness reductions for damage detection. Different damage indicators are used and any ... [more ▼]

Structural health monitoring is tracking static or dynamic characteristics of a structure to identify and localize stiffness reductions for damage detection. Different damage indicators are used and any indicator presents advantages and drawbacks. Hence the idea comes up to combine them in a model-updating procedure using a finite element model. In a first step, a model is fit to match the healthy reference state of the examined structure. Therefore it relies on minimizing a special objective function adding and weighting the differences between measured and calculated static and dynamic structural characteristics. For doing structural health monitoring the measurements are repeated in distinct time intervals and the finite element model is updated again, using the same objective function and minimization procedure. Damage can be identified and localized by highlighting reductions in the stiffness matrix of the model compared to the initial model. The efficiency of the method is illustrated by in-situ tests, where a single beam is examined that was part of a real prestressed concrete bridge. For static tests, 8 displacement transducers were disposed along the length of 40m, while the beam was mass-loaded and the deflection line is analyzed. Modal analysis was performed with swept sine excitation with constant force amplitude to identify eigenfrequencies and mode shapes. Stepwise artificial damage was provoked by cutting multiple prestressed tendons inside the concrete beam. A finite element model with a mapped mesh was created, allowing a variation of Young’s modulus in grouped sections. On real bridges temperature is neither homogenous nor constant over time, which often has a considerable influence on measured static and dynamic characteristics as the stiffness of asphalt and/or bearings can be affected. The proposed methods show their efficiency when temperature effects were excluded or compensated after measurement, which is a topic on its own and not discussed here. [less ▲]

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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 detailHealth Monitoring based on Dynamic Flexibility matrix: Theoretical Models versus in-situ Tests
Schommer, Sebastian UL; Mahowald, Jean; Nguyen, Viet Ha UL et al

in Engineering (2017), 09(02), 37-67

The paper focuses on damage detection of civil engineering structures and especially on concrete bridges. A method for structural health monitoring based on vibrational measurements is presented and ... [more ▼]

The paper focuses on damage detection of civil engineering structures and especially on concrete bridges. A method for structural health monitoring based on vibrational measurements is presented and discussed. Experimentally identified modal parameters (eigenfrequencies, mode shapes and modal masses) of bridge structures are used to calculate the inverse stiffness matrix, the so-called flexibility matrix. By monitoring of the stiffness matrix, damage can easily be detected, quantified and localized by tracking changes of its individual elements. However, based on dynamic field measurements, the acquisition of the flexibility matrix instead of the stiffness matrix is often the only choice and hence more relevant for practice. But the flexibility-based quantification and localisation of damage are often possible but more difficult, as it depends on the type of support and the location of the damage. These issues are discussed and synthetized, that is an originality of this paper and is believed useful for engineers in the damage detection of different bridge structures. First the theoretical background is briefly repeated prior to the illustration of the differences between stiffness and flexibility matrix on analytical and numerical examples. Then the flexibility-based detection is demonstrated on two true bridges with real-time measurement data and the results are promising. [less ▲]

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See detailProgramming the material point method in Julia
Sinaie, Sina; Nguyen, Viet Ha UL; Nguyen, Chi Thanh et al

in Advances in Engineering Software (2017), 105

This article presents the implementation of the material point method (MPM) using Julia. Julia is an open source, multi-platform, high-level, high-performance dynamic programming language for technical ... [more ▼]

This article presents the implementation of the material point method (MPM) using Julia. Julia is an open source, multi-platform, high-level, high-performance dynamic programming language for technical computing, with syntax that is familiar to Matlab and Python programmers. MPM is a hybrid particle-grid approach that combines the advantages of Eulerian and Lagrangian methods and is suitable for complex solid mechanics problems involving contact, impact and large deformations. We will show that a Julia based MPM code, which is short, compact and readable and uses only Julia built in features, performs much better (with speed up of up to 8) than a similar Matlab based MPM code for large strain solid mechanics simulations. We share our experiences of implementing MPM in Julia and demonstrate that Julia is a very interesting platform for rapid development in the field of scientific computing. [less ▲]

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See detailStatic load testing with temperature compensation for structural health monitoring of bridges
Nguyen, Viet Ha UL; Schommer, Sebastian UL; Maas, Stefan UL et al

in Engineering Structures (2016), 127(2016), 700-718

The paper presents a series of repeated static loading tests on a prestressed concrete beam, which was originally part of a real bridge and then subjected to stepwise artificial damage. The tests were ... [more ▼]

The paper presents a series of repeated static loading tests on a prestressed concrete beam, which was originally part of a real bridge and then subjected to stepwise artificial damage. The tests were done during a one-month period that four levels of damage were introduced by cutting tendons until visible cracking occurred. The deflection line was measured by means of several displacement sensors and the retrieved information is used in different ways for damage detection. At first, the sensor spacing requirement is analyzed with respect to measurement accuracy as well as necessary resolution for the numerical derivations of the deflection line to obtain the rotational angle and the curvature of the beam. These derived quantities may be used as damage indicators in addition to the deflection. Damage of concrete goes very often along with non-linear phenomena like cracking of concrete and plastic strain of reinforcement steel. These effects are discussed and their influence on the repeated loading tests as well the test procedure for condition monitoring is deployed. Progressive damage goes along with progressive sagging of the bridge due to gravity, which can also be used as damage indicator. Finally, the effect of varying outdoor temperatures are discussed and assessed. Though these effects can be reduced by choosing cloudy days without high temperature changes and without high solar irradiation, the outdoor temperature is never constant. Hence, a compensation algorithm is proposed which reflects the measured data according to a reference temperature. This compensation visibly improved the regularity of data. [less ▲]

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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 ▲]

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See detailStructural health monitoring based on static measurements with temperature compensation
Nguyen, Viet Ha UL; Schommer, Sebastian UL; Zürbes, Arno et al

in QUALITY SPECIFICATIONS FOR ROADWAY BRIDGES, STANDARDIZATION AT A EUROPEAN LEVEL (2016)

The paper presents the main results from static tests in a prestressed concrete beam taken out from a real bridge. The tests were achieved during about one month with several scenarios of damage that ... [more ▼]

The paper presents the main results from static tests in a prestressed concrete beam taken out from a real bridge. The tests were achieved during about one month with several scenarios of damage that loaded and unloaded states were monitored for each scenario. Damages in 4 levels were simulated by cutting prestressed tendons. There were 8 transducers distributed along the length’s beam to measure displacements. Deflection lines resulted from the static measurements from every state allow discovering the location of damages. Moreover, the calculation of slope and curvature lines leads also to very interesting issues for damage localization. [less ▲]

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See detailModelling interfacial cracking with non-matching cohesive interface elements
Nguyen, Viet Ha UL; Nguyen, Chi Thanh; Bordas, Stéphane UL et al

in Computational Mechanics (2016), 58(5), 731-746

Interfacial cracking occurs in many engineering problems such as delamination in composite laminates, matrix/interface debonding in fibre reinforced composites etc. Computational modelling of these ... [more ▼]

Interfacial cracking occurs in many engineering problems such as delamination in composite laminates, matrix/interface debonding in fibre reinforced composites etc. Computational modelling of these interfacial cracks usually employs compatible or matching cohesive interface elements. In this paper, incompatible or non-matching cohesive interface elements are proposed for interfacial fracture mechanics problems. They allow non-matching finite element discretisations of the opposite crack faces thus lifting the constraint on the compatible discretisation of the domains sharing the interface. The formulation is based on a discontinuous Galerkin method and works with both initially elastic and rigid cohesive laws. The proposed formulation has the following advantages compared to classical interface elements: (i) non-matching discretisations of the domains and (ii) no high dummy stiffness. Two and three dimensional quasi-static fracture simulations are conducted to demonstrate the method. Our method not only simplifies the meshing process but also it requires less computational demands, compared with standard interface elements, for problems that involve materials/solids having a large mismatch in stiffnesses. [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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