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- Bernstone, Christian
(author)
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Automated performance monitoring of concrete dams
- 2006
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Doctoral thesis (other academic/artistic)abstract
- The Swedish hydropower industry operates a large number of power plants and dams geographically spread over the country. The level of safety of a specific dam is to a large extent determined during the design and construction phases that in the case of Swedish hydropower plants took place several decades ago. Condition monitoring of concrete dams, or hydropower concrete structures, has until recently been an area of relatively low priority. Nevertheless, these structures represent a significant economical value. From a dam safety perspective, the reasons for condition monitoring are not significant. But as high availability has high priority, condition monitoring should be considered as one of the tools to use for assuring this. The objectives of the research carried out within the scope of this Ph.D. thesis have been to adapt and develop cost-effective methods and methodology for the automated performance monitoring of concrete dams and their foundations, with specific attention paid to prioritised damage types. The objective has also been to build new knowledge regarding sensor technology. By doing this, the thesis contributes to improving current praxis for the condition monitoring of concrete structures. The thesis covers a series of tasks that are central to condition monitoring: - The introductory chapter of this thesis is devoted to the set automated performance monitoring of hydropower concrete structures in context: The operation and maintenance of hydropower infrastructure are outlined. Statistics about the dam population are given, together with an outline of the main types of ageing processes and an international outlook on concrete dam condition monitoring. Included is also a condensed state-of-the-art review of instrumentation. An outline is given of how the information gained can be used as part of the technical management of hydropower concrete structures. - The methods-chapter includes the choice of deterioration mechanisms and the methods for monitoring the progress of damage. Each method is described, together with identified requirements for development. - The results-chapter builds upon five technical papers. The results achieved in developing the chosen technologies to the state that they can be applied to real structures in the field are summarised. Results from tests in both the laboratory and in the field are presented. - The discussion and conclusions chapter discuss the results versus the goals, and concludes the improved knowledge established. The barriers to employment are discussed, and the drawings of conclusions about how the results can be used to assist improved decision support regarding maintenance measures are made. Finally, there is a discussion about future improvements. Based on three country reviews of the status of concrete dams, three prioritised damage mechanisms have been identified to be followed up by condition monitoring: crack growth, uplift pressure, and dam-crest deformation. Research has been directed to technology options that have proven records in other applications. Based on the state-of-the-art review, three methods were chosen for further development: Time-domain reflectometry (TDR), Digital imaging together with Image processing, and GPS. An assessment of costs shows that the most cost-effective method is digital imaging and image processing, while the most expensive method is GPS. In total, four condition-monitoring investigations have been demonstrated. These include (i) uplift pressure and (ii) dam crest investigations of the Storfallsdammen in River Dalälven, and crack growth/deformation investigations of (iii) draft tube wall of a hydropower plant (Porjus) and (iv) a commuter bridge (Alvik). In cooperation with other research projects, it has been shown that reliability-based stability safety analysis is a good tool for assessing existing concrete dams. Overall, the work contained in this research contributes to improving the knowledge base on how owners of hydropower concrete structures can incorporate condition monitoring into their regular maintenance work. As a result of the research project, it is judged that the introduction of new tools for the maintenance work practised within the Swedish hydropower industry may be possible with, once installed, only a minor increase in the workload of the maintenance organisations.
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- Bernstone, Christian, et al.
(author)
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DC resistivity mapping of internal landfill structures: two pre-excavation surveys.
- 2000
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In: Environmental Geology. - : Springer Science and Business Media LLC. - 0943-0105 .- 1432-0495. ; 39:3-4, s. 360-371
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Journal article (peer-reviewed)abstract
- Geophysical investigations using 2-D DC resistivity were carried out on old parts of two similar landfills, with waste of different ages. The data sets, which included high data density in both vertical and horizontal directions, were interpreted with 2-D smoothness constrained inversion. The landfills were excavated after the surveying. The objective was to test the capability of the resistivity method as a pre-characterization technique. The objectives were only partially fulfilled. First, the moisture content was the parameter that appeared to exert the dominant control over the resistivity distribution of the landfill. The most important potential information that can be recovered is, therefore, an indication of the waste piles hydraulics. Second, it was neither possible to estimate the amount of recoverable soils, nor to correlate the type of waste with the resistivity models. However, discrete anomalies were identified, and if specific materials are searched for, the resistivity models indicate possible places to search.
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- Bernstone, Christian, et al.
(author)
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Image analysis for monitoring of crack growth in hydropower concrete structures
- 2009
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In: Measurement. - : Elsevier BV. - 0263-2241 .- 1873-412X. ; 42:6, s. 878-893
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Journal article (peer-reviewed)abstract
- A digital image analysis technique for crack monitoring using a standard web-camera has been further developed to acquire continuous data sets on crack development in concrete dams. The method is based on an existing robust and straightforward non-contact method for experimental deformation analysis. It allows for the measurement of suspected serious cracks, identified from inspections, through a sequence of images captured at intervals. The crack opening displacements at the surface of investigated objects are obtained by an algorithm that makes it possible to automatically track the motions of discrete markers painted on the object surface markers and compute their centre of mass in a sequence of images. The data acquisition process is straightforward and is well suited for this type of environment. Results from laboratory experiments and a field-test on a commuter bridge in Sweden are presented. The study implies that the technique can be useful for hydropower concrete structure applications. (C) 2009 Elsevier Ltd. All rights reserved.
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- Bernstone, Christian, et al.
(author)
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Structural Assessment of a Concrete Dam Based on Uplift Pressure Monitoring
- 2009
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In: Journal of Geotechnical and Geoenvironmental Engineering. - 1090-0241. ; 135:1, s. 133-142
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Journal article (peer-reviewed)abstract
- The context of structural monitoring of concrete dams as part of hydropower assets management is described. A tool that fits well into this context is the control of the uplift pressure of concrete dams. A monitoring technique suitable for this purpose was developed based on an automated water-level measurement technique using time-domain reflectometry and standard air-dielectric coaxial cable sensors. The signal is interpreted automatically by applying a threshold method to determine the apparent water level, which is then used to calculate the uplift pressure. A field test at a concrete dam column displayed consistent results, which were used as input to a reliability-based stability safety analysis. The results show that this technique can be very useful for uplift pressure monitoring. The information determined can serve as input to the maintenance work as well as assist engineering decisions.
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- Bernstone, Christian, et al.
(author)
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Verifiering av struktur och fuktmekaniska beräkningsverktyg : Tillämpning på reaktorinneslutningars betongkonstruktioner, Vercors Fas 1
- 2017
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Reports (other academic/artistic)abstract
- Électricité de France har utanför Paris byggt en 1/3 skalmodell av en reaktorinneslutning motsvarande en fransk fullskalereaktor modell P4. Anläggningen möjliggör studier av hur åldringsprocesser påverkar förspända reaktorinneslutningar. Syftet är att efter de 7 år som ett övergripande forskningsprojektet vid på anläggningen pågår, uppnå påverkan motsvarande den åldring som en fullskalereaktor har utsatts för efter 6o års drift.Konstruktionen har försetts med ett omfattande instrumenteringsprogram som gör det möjligt att följa konstruktionens beteende i tidigt skede och över tid. Ett av anläggningens forskningsprojekt omfattar en benchmark av olika beräkningsverktygs möjlighet att kunna förutse konstruktionens beteende i tidigt skede och under själva åldrandet, dess täthet till följd av åldrandet och beteende under svåra haveriförhållanden. Denna benchmark har genomförts via en öppen inbjudning till intresserade experter att delta. I projektet, benämnt VeRCoRs , bidrar deltagande organisationer med egna modelleringsarbeten utifrån de tre olika teman. Arbetet med det första temat startade 2015 (tidigt skede), därefter följer den åldrade konstruktionen (2017) och svåra haverisituationer (2021). Denna rapport redovisar det arbete som har gjorts för det första temat (Tema 1) inom ramen för ett Energiforskuppdrag.Modelleringsarbetet har till största delen genomförts av LTH i nära samarbete med KTH och Vattenfall. Simuleringar har gjorts för den unga betongens beteende under den ett år långa byggfasen, med hänsyn tagen till betongens hydratation (temperaturberäkningar/värmeutveckling), uttorkning (självuttorkning och fukttransport) och deformationer (temperatur-, fukt-, kryp-, och spänningsrelaterade deformationer). Resultatet har jämförts mot data från anläggningens instrumentering. Dessutom så har en genomgång gjorts av resultaten från övriga deltagares arbeten i Tema 1.Sammanfattningsvis så visar resultaten på de fördelar som finns med att genom avancerade beräkningar verifiera designparametrar och prognostisering av reaktorinneslutningars funktion, men också på utmaningar. Med hjälp av FEmodellering så kan det tidiga skedet efter färdigställd konstruktion beskrivas både vad gäller temperatur- och deformationer med rimlig tillförlitlighet. Det finns dock potential till förbättringar. Även om betongens temperatur kan predikteras noggrant så kan det skilja kraftigt i uppskattningen av inducerade påkänningar. En viktig orsak till dessa skillnader beror på osäkerheter i bestämning av krypning och krympning i betongen tidiga skede.
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