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Non-linear analyses of cracks in aging concrete hydro power structures
KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Concrete Structures.ORCID iD: 0000-0002-8000-6781
KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Concrete Structures.
KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Concrete Structures.ORCID iD: 0000-0001-6840-9986
Lund University, Division of Building Materials.
2016 (English)In: Dam Engineering, ISSN 0958-9341Manuscript (preprint) (Other (popular science, discussion, etc.))
Abstract [en]

The concrete structures at Swedish hydro power facilities were built during the early to mid-20th century and many of them are starting to exhibit age related wear and deterioration. It isimportant to ensure the integrity of these concrete structures from a dam safety perspectiveand also to secure a safe operation of the power facility in the future. With the latter in mind,this paper aims to study the concrete structures that house the power generating machinery ofthe facility, especially the parts close to the generator where the loads from the power unit aresupported. Cracks observed in these structures will reduce its stiffness, which affects theoperation of the rotating machinery. This paper presents and discusses some generalconsiderations and loads that are of importance for this type of structures and highlights sometypical cracks that have been observed in Swedish hydro power facilities. To complement thisdiscussion, a case study is presented of a hydro power facility where cracks have been foundin the concrete support structure of the power unit, especially at the interconnections betweenthe unit and the concrete. The most likely cause of these cracks are investigated through nonlinearfinite element analysis considering mechanical loads as well as physical loads such asdrying shrinkage and temperature variations. It is concluded that the long-term physicalloading is the most probable cause of the observed cracks. However, the operation of thepower unit and changes in its operational pattern can cause further propagation of thesecracks. Finally, suggestions on possible enhancement of the analysis methods used in the casestudy are proposed and discussed for further studies of this type of concrete structures.

Place, publisher, year, edition, pages
International Water Power & Dam Construction , 2016.
Keyword [en]
concrete, hydro power, cracks, finite element analysis, non-linear, drying shrinkage, thermal strains
National Category
Infrastructure Engineering
Research subject
Civil and Architectural Engineering
Identifiers
URN: urn:nbn:se:kth:diva-186144OAI: oai:DiVA.org:kth-186144DiVA: diva2:925708
Note

QC 20160503

Available from: 2016-05-03 Created: 2016-05-03 Last updated: 2016-05-03Bibliographically approved
In thesis
1. Concrete as a multi-physical material with applications to hydro power facilities
Open this publication in new window or tab >>Concrete as a multi-physical material with applications to hydro power facilities
2016 (English)Licentiate thesis, comprehensive summary (Other academic)
Abstract [en]

During its lifetime, a concrete structure is subjected to many different actions, ranging from mechanical loads to environmental actions. To accurately predict its integrity from casting and throughout its service life, a modelling strategy is required that considers mechanical loading but also implicitly accounts for physical effects such as temperature and moisture variations. This is especially true for large concrete structures found in many infrastructure applications such as bridges, nuclear power plants and dams. Modelling concrete as a multi-physical material is becoming an increasingly used approach for which large research efforts are being made, including the development of more refined mathematical and numerical methods as well as considering more physical and chemical variables in the coupled model.

The research project, of which this licentiate thesis is the first phase, aims at investigating aging concrete structures at hydro power facilities, with focus on the internal structures of the power plants. This thesis presents a review of advanced mathematical methods and concepts for modelling aging concrete found in the literature which can later be applied to study such structures. The focus is on models that describe the deformational behaviour of concrete where aspects such as aging, cracking, creep and shrinkage are investigated. However, in order to accurately describe such phenomena, a multi-physical approach is adopted where moisture and temperature variations in the concrete are studied. Also, models that describe the chemical behaviour related to hydration and thus in extension aging, are also reviewed and introduced in the multi-physical framework. The use of such models are discussed in the context of the finite element method (FEM), in which coupled models are implemented, verified and applied in the appended papers using two different FE codes.

Several verification examples are presented covering different aspects of the implemented models, both in isolation and coupled in a multi-physical setting. By comparing the numerical results with experimental data from the literature it can be shown that it is possible to predict most aspects of aging concrete that have been of interest here. While these examples are all on a laboratory scale, numerical examples and case studies are also provided that exemplify how the models can be applied on a structural scale. By using the developed analysis tools, valuable information and insights can be gained on aging concrete structures and these tools will in the next phase of the research project be applied to large concrete structures at hydro power facilities.

Abstract [sv]

En betongkonstruktion utsätts under sin livstid för många olika laster, alltifrån mekaniska till olika miljöbetingade. För att kunna göra en noggrann uppskattning av dess integritet, från gjutning och under hela dess livslängd, krävs ett modelleringssynsätt där inte bara mekaniska laster beaktas utan där även fysikaliska effekter så som temperatur- och fuktvariationer beaktas. Detta blir extra viktigt för de stora betongkonstruktioner som påträffas i infrastrukturtillämpningar som till exempel broar, kärnkraftverk och dammar. Modellering av betong som ett multi-fysiskt material har blivit en allt vanligare metod där betydande forskningsinsatser idag görs, både vad gäller utveckling av avancerade matematiska och numeriska metoder men även genom att studera fler fysikaliska och kemiska processer i en och samma modell.

Det forskningsprojekt som den här licentiatuppsatsen är en del av syftar till att undersöka åldrande betongkonstruktioner vid vattenkraftanläggningar med focus på aggregatnära konstruktioner. Uppsatsen presenterar en genomgång av avancerade matematiska metoder och koncept från litteraturen för att simulera åldrande betong, vilka sedan kan användas för att studera aggregatnära konstruktioner. Fokus ligger på modeller för att beskriva deformationer i betong och relaterade fenomen där bland annat åldring, sprickbildning, krypning och krympning studeras. För att mer exakt kunna beskriva sådana fenomen är det viktigt att det används kopplade modeller där även temperatur- och fuktvariationer i betongen inkluderas. Även modeller för att beskriva de kemiska reaktionerna kopplade till hydratation och i förlängingen även åldring studeras och introduceras i de kopplade modellerna. Vidare diskuteras hur denna typ av modeller kan tillämpas med den finita elementmetoden (FEM) med vilken kopplade modeller har implementerats, verifierats och använts i de bilagda artiklarna med hjälp av två olika FE koder.

Ett flertal verifikationsexempel presenteras, vilka behandlar olika aspekter av de implementerade modellerna för både isolerade mekanismer och även för kopplade problem. Genom att jämföra de numeriska resultaten med försöksdata från litteraturen visas det att modellerna kan återge de fenomen som relateras till åldrande betong så som har avsetts. Medan dessa exempel är utförda för betong i en laboratoriemiljö ges även numeriska exempel och fallstudier som exemplifierar hur modellerna kan tillämpas även på en strukturell nivå. Genom att använda de utvecklade analysverktygen kan värdefull information och kunskap fås om åldrande betongkonstruktioner och dessa verktyg kommer i nästa fas av forskningsprojektet att tillämpas på stora betongkonstruktioner vid vattenkraftanläggningar.

Place, publisher, year, edition, pages
Stockholm: KTH Royal Institute of Technology, 2016. xii, 131 p.
Series
TRITA-BKN. Bulletin, ISSN 1103-4270 ; 139
National Category
Civil Engineering
Research subject
Civil and Architectural Engineering
Identifiers
urn:nbn:se:kth:diva-186154 (URN)
Presentation
2016-05-23, B25, Brinellvägen 23, KTH Campus, Stockholm, 10:00 (Swedish)
Opponent
Supervisors
Note

QC 20160503

Available from: 2016-05-03 Created: 2016-05-03 Last updated: 2016-05-03Bibliographically approved

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