References of "Maas, Stefan 50002241"
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See detailInfluence of pubic symphysis stiffness on pelvis stress distribution during single leg stance
Ricci, Pierre-Louis UL; Maas, Stefan UL; Gerich, Torsten et al

Poster (2018, July 09)

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See detailWas wissen wir über die Osteitis pubis bei Sporttreibenden?
Kelm, Jens; Ludwig, Oliver; André, Jan et al

in Sportverletzung Sportschaden : Organ der Gesellschaft für Orthopadisch-Traumatologische Sportmedizin (2018)

Hintergrund Die Osteitis pubis ist eine häufige Ursache chronischer Leistenbeschwerden. Aufgrund hoher klinischer Unsicherheit sowie dem unterschiedlichen Verlauf der Erkrankung wird die Diagnose nicht ... [more ▼]

Hintergrund Die Osteitis pubis ist eine häufige Ursache chronischer Leistenbeschwerden. Aufgrund hoher klinischer Unsicherheit sowie dem unterschiedlichen Verlauf der Erkrankung wird die Diagnose nicht selten erst spät gestellt. Das Krankheitsbild betrifft insbesondere Sportlerinnen und Sportler, wobei auch Patienten aus den Bereichen Orthopädie, Traumatologie, Neurologie, Urologie, Gynäkologie sowie der Rheumatologie betroffen sein können. Therapeutisch kommen sowohl konservative als auch operative Verfahren zum Einsatz. Material und Methoden Systematische Literaturrecherche, deskriptive Darstellung der Studienlage und Interpretation der Ergebnisse im Sinne der evidenzbasierten Medizin. Ergebnisse Das wissenschaftliche Niveau der Studien über die Osteitis pubis ist, wie die Anzahl der in Studien inkludierten Sporttreibenden, insgesamt niedrig. Aufgrund der Heterogenität der Publikationen ist ihr statistischer Vergleich methodisch schwierig. Klinisch führendes Symptom der Osteitis pubis ist die schmerzhafte Symphysis pubica, wobei ein klassisches pathognomonisches Zeichen fehlt. Die Diagnose basiert nach Ausschluss zahlreicher Differentialdiagnosen (z. B. „Sportlerleiste“, FA-Impingement, Adduktorenläsion) auf der Zusammenschau von Anamnese, klinischer Untersuchung sowie bildgebender Verfahren. Die Osteitis pubis ist eine durch Sportkarenz oftmals selbstlimitierende Erkrankung, die initial konservativ behandelt wird. Bei frustranem Verlauf sind operative Verfahren, in Abhängigkeit der Begleitpathologien, in Betracht zu ziehen. Schlussfolgerung Es existieren bis dato keine Leitlinien hinsichtlich Diagnostik und Therapie der Osteitis pubis, allerdings ein Konsens darüber, dass der operativen Behandlung eine konservative vorangehen muss. Das Evidenzniveau der Studien ist niedrig. Eine metaanalytische Auswertung ist mit den derzeitig vorhandenen Publikationen nicht möglich. Die Anzahl der untersuchten Sporttreibenden ist in Relation zu den sozioökonomischen Folgen der Erkrankung, insbesondere im Profisport, niedrig. [less ▲]

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See detailStatic and fatigue strength of a novel anatomically contoured implant compared to five current open-wedge high tibial osteotomy plates
Diffo Kaze, Arnaud UL; Maas, Stefan UL; Belsey, James et al

in Journal of Experimental Orthopaedics (2017), 4(39),

Abstract Background The purpose of the present study was to compare the mechanical static and fatigue strength of the size 2 osteotomy plate “Activmotion” with the following five other common implants for ... [more ▼]

Abstract Background The purpose of the present study was to compare the mechanical static and fatigue strength of the size 2 osteotomy plate “Activmotion” with the following five other common implants for the treatment of medial knee joint osteoarthritis: the TomoFix small stature, the TomoFix standard, the Contour Lock, the iBalance and the second generation PEEKPower. Methods Six fourth-generation tibial bone composites underwent a medial open-wedge high tibial osteotomy (HTO), according to standard techniques, using size 2 Activmotion osteotomy plates. All bone-implant constructs were subjected to static compression load to failure and load-controlled cyclic fatigue failure testing, according to a previously defined testing protocol. The mechanical stability was investigated by considering different criteria and parameters: maximum forces, the maximum number of loading cycles, stiffness, the permanent plastic deformation of the specimens during the cyclic fatigue tests, and the maximum displacement range in the hysteresis loops of the cyclic loading responses. Results In each test, all bone-implant constructs with the size 2 Activmotion plate failed with a fracture of the lateral cortex, like with the other five previously tested implants. For the static compression tests the failure occurred in each tested implant above the physiological loading of slow walking (> 2400 N). The load at failure for the Activmotion group was the highest (8200 N). In terms of maximum load and number of cycles performed prior to failure, the size 2 Activmotion plate showed higher results than all the other tested implants except the ContourLock plate. The iBalance implant offered the highest stiffness (3.1 kN/mm) for static loading on the lateral side, while the size 2 Activmotion showed the highest stiffness (4.8 kN/mm) in cyclic loading. Conclusions Overall, regarding all of the analysed strength parameters, the size 2 Activmotion plate provided equivalent or higher mechanical stability compared to the previously tested implant. Implants with a metaphyseal slope adapted to the tibia anatomy, and positioned more anteriorly on the proximal medial side of the tibia, should provide good mechanical stability. [less ▲]

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See detailA finite element model of the lower limb during stance phase of gait cycle including the muscle forces
Diffo Kaze, Arnaud UL; Maas, Stefan UL; Arnoux, Pierre-Jean et al

in BioMedical Engineering OnLine (2017), 16(138),

Abstract Background Results of finite element (FE) analyses can give insight into musculoskeletal diseases if physiological boundary conditions, which include the muscle forces during specific activities ... [more ▼]

Abstract Background Results of finite element (FE) analyses can give insight into musculoskeletal diseases if physiological boundary conditions, which include the muscle forces during specific activities of daily life, are considered in the finite element modelling. So far, many simplifications of the boundary conditions are currently made. This study presents an approach for FE modelling of the lower limb for which muscle forces were included. Method The stance phase of normal gait was simulated. Muscle forces were calculated using a musculoskeletal rigid body (RB) model of the human body, and were subsequently applied to a FE model of the lower limb. It was shown that the inertial forces are negligible during the stance phase of normal gait. The contact surfaces between the parts within the knee were modelled as bonded. Weak springs were attached to the distal tibia for numerical reasons. Results Hip joint reaction forces from the RB model and those from the FE model were similar in magnitude with relative differences less than 16%. The forces of the weak spring were negligible compared to the applied muscle forces. The maximal strain was 0.23% in the proximal region of the femoral diaphysis and 1.7% in the contact zone between the tibia and the fibula. Conclusions The presented approach based on FE modelling by including muscle forces from inverse dynamic analysis of musculoskeletal RB model can be used to perform analyses of the lower limb with very realistic boundary conditions. In the present form, this model can be used to better understand the loading, stresses and strains of bones in the knee area and hence to analyse osteotomy fixation devices. [less ▲]

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See detailMechanical strength assessment of a drilled hole in the contralateral cortex at the end of the open wedge for high tibial osteotomy.
Diffo Kaze, Arnaud UL; Maas, Stefan UL; Hoffmann, Alexander et al

in Journal of Experimental Orthopaedics (2017), 4(1),

BACKGROUND: This study aimed to investigate, by means of finite element analysis, the effect of a drill hole at the end of a horizontal osteotomy to reduce the risk of lateral cortex fracture while ... [more ▼]

BACKGROUND: This study aimed to investigate, by means of finite element analysis, the effect of a drill hole at the end of a horizontal osteotomy to reduce the risk of lateral cortex fracture while performing an opening wedge high tibial osteotomy (OWHTO). The question was whether drilling a hole relieves stress and increases the maximum correction angle without fracture of the lateral cortex depending on the ductility of the cortical bone. METHODS: Two different types of osteotomy cuts were considered; one with a drill hole (diameter 5 mm) and the other without the hole. The drill holes were located about 20 mm distally to the tibial plateau and 6 mm medially to the lateral cortex, such that the minimal thickness of the contralateral cortical bone was 5 mm. Based on finite element calculations, two approaches were used to compare the two types of osteotomy cuts considered: (1) Assessing the static strength using local stresses following the idea of the FKM-guideline, subsequently referred to as the "FKM approach" and (2) limiting the total strain during the opening of the osteotomy wedge, subsequently referred to as "strain approach". A critical opening angle leading to crack initiation in the opposite lateral cortex was determined for each approach and was defined as comparative parameter. The relation to bone aging was investigated by considering the material parameters of cortical bones from young and old subjects. RESULTS: The maximum equivalent (von-Mises) stress was smaller for the cases with a drill hole at the end of the osteotomy cut. The critical angle was approximately 1.5 times higher for the specimens with a drill hole compared to those without. This corresponds to an average increase of 50%. The calculated critical angle for all approaches is below 5°. The critical angle depends on the used approach, on patient's age and assumed ductility of the cortical bone. CONCLUSIONS: Drilling a hole at the end of the osteotomy reduces the stresses in the lateral cortex and increases the critical opening angle prior to cracking of the opposite cortex in specimen with small correction angles. But the difference from having a drill hole or not is not so significant, especially for older patients. The ductility of the cortical bone is the decisive parameter for the critical opening angle. [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 detailBiomechanik neuer Implantate für die HTO
Pape, Dietrich; Diffo Kaze, Arnaud UL; Hoffmann, Alexander et al

in Orthopade (Der) (2017), 46(7), 583-595

Biomechanical characteristics of 5 tibial osteotomy plates for the treatment of medial knee joint osteoarthritis were examined. Fourth-generation tibial bone composites underwent a medial open-wedge high ... [more ▼]

Biomechanical characteristics of 5 tibial osteotomy plates for the treatment of medial knee joint osteoarthritis were examined. Fourth-generation tibial bone composites underwent a medial open-wedge high tibial osteotomy, using TomoFix™ standard, PEEKPower®, ContourLock®, TomoFix™ small stature plates, and iBalance® implants. Static compression load to failure and load-controlled cyclic fatigue failure tests were performed. All plates had sufficient stability up to 2400 N in the static compression load to failure tests. Screw breakage in the iBalance® group and opposite cortex fractures in all constructs occurred at lower loading conditions. The highest fatigue strength in terms of maximal load and number of cycles performed prior to failure was observed for the ContourLock® group followed by the iBalance® implants, the TomoFix™ standard and small stature plates. PEEKPower® had the lowest fatigue strength. All plates showed sufficient stability under static loading. Compared to the TomoFix™ and the PEEKPower® plates, the ContourLock® plate and iBalance® implant showed a higher mechanical fatigue strength during cyclic fatigue testing, suggesting that both mechanical static and fatigue strength increase with a wider proximal T‑shaped plate design together with diverging proximal screws. Mechanical strength of the bone–implant constructs decreases with a narrow T‑shaped proximal end design and converging proximal screws (TomoFix™) or a short vertical plate design (PEEKPower®). Published results indicate high fusion rates and good clinical results with the TomoFix™ plate, which is contrary to our findings. A certain amount of interfragmentary motion rather than high mechanical strength and stiffness seem to be important for bone healing which is outside the scope of this paper. [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 detailPost-occupancy evaluation of residential buildings in Luxembourgwith centralized and decentralized ventilation systems, focusing onindoor air quality (IAQ). Assessment by questionnaires and physicalmeasurements
Ferreira Silva, Marielle; Maas, Stefan UL; Artur de Souza, Henor et al

in Energy and Buildings (2017), 148

tComplete knowledge about habits of the occupants, including their opinions regarding ventilation sys-tems is an important condition for reducing the consumption of natural resources and improving ... [more ▼]

tComplete knowledge about habits of the occupants, including their opinions regarding ventilation sys-tems is an important condition for reducing the consumption of natural resources and improving indoorcomfort. In addition, uncomforted occupants tend to take measures to improve their situation, whichmay increase energy consumption. Advanced thermal models for buildings can perhaps predict interac-tions between the IAQ determinants, e.g. energy consumption, ventilation and comfort, but do not takeinto account the behavior of residents. By questionnaires and physical measurements this study evalu-ated dwellings equipped partly with centralized and partly with decentralized ventilation systems withheat recovery. This field study involved two post-occupied residential buildings situated in the city ofEsch-sur-Alzette, Luxembourg, during spring season 2015. Thus, both the physical measurements andquestionnaires were considered. The results obtained demonstrated that more than 80% of the residentswere satisfied and the perceived IAQ was judged “normal”, “good” or even “very good”. Furthermore,the measurements performed detected in some cases malfunction of ventilation devices, wherefore theoccupants were unable. [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 detailUntersuchung des thermischen Komforts und der Luftqualität an vier neuen energieeffizienten Luxemburger Schulen mit und ohne Lüftungsanlagen
Maas, Stefan UL; Brensing, Jessica UL; Flies, Max et al

in Bauphysik (2017), 39. Jahrgang

A study was conducted in four new energy efficient schools in Luxembourg with excellent primary energy consumption values, where the indoor thermal comfort and the air quality was assessed by technical ... [more ▼]

A study was conducted in four new energy efficient schools in Luxembourg with excellent primary energy consumption values, where the indoor thermal comfort and the air quality was assessed by technical measurements and by surveys. Two schools were equipped with mechanical ventilation with heat recovery and two were without, i.e. ventilation there was manually controlled by opening the windows. Further to the C02-concentration as indicator for the air quality all other important comfort parameters were measured, why the well-known indicators according to FANGER could be calculated, i.e. the „Predicted Mean Vote (PMV)“ and the „Predicted Percentage of Dissatisfied (PPD)“. The individual perceived indoor comfort was analyzed by standardized questionnaires for a period of four weeks. One aim of the study was to compare natural ventilation by opening and closing the windows with the mechanical ventilation in all named aspects. In total there was a good agreement between the measurements and the survey. The results show that in general mechanical ventilation in schools lead to better physical measured values and to better subjective perception of the users. However those buildings suffer from a very low relative humidity, though it is rarely sensed by the occupants. Furthermore, in one of the mechanically ventilated buildings the air velocity was very high and led to draft-perception. The detected air temperature was heterogeneous and independent of the ventilation concept, leading to an individual judgement of PMV for the different buildings. Users should always have the possibility of interaction and control to adjust the indoor climate according to their individual needs and to correct smaller technical shortcomings. [less ▲]

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See detailAn advanced approach to design experiments to investigate the biomechanics of the pelvis
Ricci, Pierre-Louis UL; Maas, Stefan UL; Gerich, Torsten et al

Scientific Conference (2017)

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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 detailWie bilanzieren die europäischen Staaten in Luxemburg, Deutschland, Belgien, der Schweiz und in Frankreich? Ein Vergleich verschiedener nationaler Berechnungsvorschriften der Gesamtenergieeffizienz anhand von 9 klimatisierten Bürogebäuden und deren Realverbrauch
Render, Wolfgang; Maas, Stefan UL; Scholzen, Frank UL

in cci Zeitung - Führende Fachzeitung für die LüKK (Lüftung- Klima- Kältebranche) (2016)

Die EU-Mitgliedsstaaten sind gemäß den Richtlinien 2002/91/EG und 2010/31/EU verpflichtet, die Gesamtenergieeffizienz von Gebäuden abhängig von ihrer Art der Nutzung zu ermitteln und in einem Energiepass ... [more ▼]

Die EU-Mitgliedsstaaten sind gemäß den Richtlinien 2002/91/EG und 2010/31/EU verpflichtet, die Gesamtenergieeffizienz von Gebäuden abhängig von ihrer Art der Nutzung zu ermitteln und in einem Energiepass zu belegen. Die Ausgestaltung der Details des Berechnungsverfahrens und der Grenzwerte obliegt den Mitgliedsstaaten im Rahmen ihres nationalen Entscheidungsspielraums. Für 9 bestehende mittlere bis große Bürogebäude mit Teil- und Vollklimatisierung wurden die Berechnungen der Gesamtenergieeffizienz nach den jeweiligen Berechnungsmethoden durchgeführt und mit dem gemessenen realen Verbrauch verglichen. Die Abweichungen zwischen der berechneten Endenergie und dem tatsächlichen Verbrauch betragen zwar etliche 100% beim einzelnen Objekt, aber ca. 20 % im Mittel bei der Heizenergie. Bei der berechneten Endenergie des Stroms bestehen auch riesige Differenzen beim Einzelobjekt, aber im nationalen Vergleich im Mittel nur geringe Abweichungen zum Verbrauch, wobei der Stromverbrauch für die Büroausstattung geschätzt wurde. Die Abweichungen bei der Heizenergie und beim Strom im Mittel können als gut bezeichnet werden, wobei vor allem Belgien durch Über- und Unterschätzen beim Strom auffällt. Rund ¾ der verbrauchten Primärenergie ist auf den elektrische Energie zurück zu führen, wobei der Mittelwert von rund 400 kWh/m2 darauf hindeutet, dass die realen Gebäude noch weit vom europäischen Ziel der „Nearly Zero Energy Buildings (NZEB)“ entfernt sind. [less ▲]

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See detailEin Vergleich der nationalen Berechnungsvorschriften zur Gesamtenergieeffizienz und deren Realverbrauch anhand von 14 Bürogebäuden in Luxemburg, Deutschland, Belgien, der Schweiz und in Frankreich
Render, Wolfgang; Maas, Stefan UL; Scholzen, Frank UL

in Bauphysik (2016), 38

Die EU-Mitgliedsstaaten sind gemäß den Richtlinien 2002/91/EG und 2010/31/EU verpflichtet, die Gesamtenergieeffizienz von Gebäuden abhängig von ihrer Art der Nutzung zu ermitteln und in einem Energiepass ... [more ▼]

Die EU-Mitgliedsstaaten sind gemäß den Richtlinien 2002/91/EG und 2010/31/EU verpflichtet, die Gesamtenergieeffizienz von Gebäuden abhängig von ihrer Art der Nutzung zu ermitteln und in einem Energiepass zu belegen. Die Ausgestaltung der Details des Berechnungsverfahrens und der Grenzwerte obliegt den Mitgliedsstaaten, denen man damit einen nationalen Entscheidungsspielraum zugesteht. Für 14 bestehende einfache kleinere Bürogebäude ohne Lüftung und Klimatisierung wurden die Berechnungen der Gesamtenergieeffizienz nach den jeweiligen Berechnungsmethoden durchgeführt und mit dem gemessenen realen Verbrauch verglichen. Die Abweichungen zwischen der berechneten Endenergie und dem tatsächlichen Verbrauch betragen zwar bis über 100% beim einzelnen Objekt, aber nur ca. + 28 % im Mittel bei der Heizenergie und nur wenige Prozent beim Strom, allerdings unter Annahme eines geschätzten Stromverbrauchs für die Büroausstattung. Die Abweichungen bei der Heizenergie und beim Strom können als gut bezeichnet werden. [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 detailEnergy consumption of non-retrofitted institutional building stock inLuxembourg and the potential for a cost-efficient retrofit
Hoos, Thorsten UL; Merzkirch, Alexander UL; Maas, Stefan UL et al

in Energy and Buildings (2016), 123(2016), 162-168

The public building stock of a country, consisting of schools, offices, accommodation facilities, single-and multi-family homes, accounts for a high consumption of electrical and heat energy. Therefore ... [more ▼]

The public building stock of a country, consisting of schools, offices, accommodation facilities, single-and multi-family homes, accounts for a high consumption of electrical and heat energy. Therefore, thisstock is often subject to actions with the goal of lowering this energy usage by increasing the efficiencyof those buildings. This is usually done by applying measures to the building envelope like insulationand/or new windows and by using a more efficient HVAC technology. But often, in the initial state, thecurrent energy consumption of such a stock is unknown or only known for single buildings. In this case,the calculation of energy and cost savings is either impossible or not exact. This paper shows a way toquantify and categorize the end-energy for heat use of the public building stock in Luxembourg, whichconsists of a gross area of 1.744 million m2. This analysis was carried out in cooperation with the nationaladministration of public buildings.A certain amount of sample buildings was analyzed and then separated into three groups of low,normal and high end-energy use. The boundaries of these groups were chosen according to literaturevalues, derived from European retrofit projects, which also served as the source for possible renovationcosts. This data was extrapolated to the whole stock. This information serves as a basis for future decisionsconcerning the retrofit of those buildings and makes a calculation of costs possible.As a result, the type of buildings with the highest potential for retrofit measures was identified. Schools,offices and accommodation facilities with a “high” consumption of more than 190 kWh/(m2a) show thehighest economic potential with retrofit costs of 0.04–0.08 D /kWh if their energy consumption is loweredto values of around 90–100 kWh. Other groups of buildings show higher costs of around 0.07–0.19 D /kWh. [less ▲]

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See detailField tests of centralized and decentralized ventilation units inresidential buildings – Specific fan power, heat recovery efficiency,shortcuts and volume flow unbalances
Merzkirch, Alexander UL; Maas, Stefan UL; Scholzen, Frank UL et al

in Energy and Buildings (2016), 116(2016), 376-383

tThe energy efficient operation of mechanical ventilation systems depends on various parameters. InLuxembourg, field tests with 20 centralized and 60 decentralized mechanical ventilation systems insingle ... [more ▼]

tThe energy efficient operation of mechanical ventilation systems depends on various parameters. InLuxembourg, field tests with 20 centralized and 60 decentralized mechanical ventilation systems insingle- and multi-family homes were conducted in order to measure the actual performance of thosesystems in occupied buildings. The considered parameters were: Main air flows, internal and externalrecirculation, sensitivity to differential pressure, specific fan power and heat recovery efficiency. In manycases, the performance of the ventilation units was lower than expected. The systems showed deviationsbetween supply and exhaust flows of up to 60%. In particular, the air flow in decentralized units wasstrongly influenced by pressure differences between the inside and outside due to wind or stack effectswhich leads to a decreased heat recovery efficiency. The total mean recirculation ratio was 6.5%, with astandard deviation of 12.5% for centralized and 13 ± 6.2% for decentralized devices. As a consequence,the delivered flow of fresh air is smaller by the amount of recirculation. The specific fan power, theratio between air flow and power consumption, was measured with 0.475 ± 0.37 Wh/m3for centralizedand 0.22 ± 0.023 Wh/m3for decentralized systems. The lower value for the decentralized systems canbe explained by lower pressure losses due to the lack of ductwork. The heat recovery efficiency was0.65 ± 0.24 for centralized systems and 0.7 ± 0.17 for decentralized systems which is significantly lowerthan nominal values provided by the manufacturers. The results of this study show that the overall energyefficiency of ventilation devices installed in residential buildings under real working conditions are oftenlower than expected. These findings could possibly serve as indicators for future research & developmentat manufacturer and commissioning level. [less ▲]

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