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Publications (10 of 17) Show all publications
Abbasiverki, R., Ahmed, L. & Nordström, E. (2019). Analysis of load and response on large hydropower draft tube structures. Energiforsk AB
Open this publication in new window or tab >>Analysis of load and response on large hydropower draft tube structures
2019 (English)Report (Refereed)
Abstract [en]

In a reaction turbine, the runner outlet is connected to a diffuser which is called the draft tube. Large hydropower units with large effect and large discharge normally require large dimensions on the waterways. In some large-scale facilities, the total width of the draft tube is so large there is a need for a supporting centre wall in the draft tube. In the Swedish hydropower business, there are several cases where damages or cracks have been reported in the contact between the roof and the supporting centre wall. The most likely reason for cracking between wall and roof is when refilling the draft tube after it has been drained for inspection. A too quick refilling will give an upwards lifting force on the roof that can be larger than the capacity in the joint. There are still uncertainties regarding the risk for a long-term scenario where any operational pattern could give continued crack propagation.

Vattenfall Hydropower has made an installation with pressure and strain sensors in one of their facilities with a centre wall supported draft tube and a cavity between the roof and the rock cavern. The aim of the project is to get a better understanding on the behaviour of the roof and centre wall during different operational events by evaluating measurements from the draft tube and investigating possible load cases that can create continued crack propagation during operation. In this regard, in this project, the measurements are analysed to discover the different operational patterns and the corresponding effect on applied pressure on draft tube central wall and roof and structure response. A simplified finite element model of the draft tube is demonstrated and the response from the structure due to extracted load patterns is compared with the measurements.

One-year measurements of the unit operation indicated that unit operates over the whole range with many start/stops. Three major types of operation were: normal operation (working in daytime and downtime at night), continuous operation with no stop and start-stop events with sharp start/stop in the morning and afternoon. The analysis of pressure measurements indicated that the fluid motion in the straight diffuser is turbulent and possibly influenced by vortex formation under the runner. Therefore, the pressure on the right side of the central wall was higher than on the left side.

The quality of the strain measurements showed to be of insufficient quality and lack of information regarding the set-up. This has given questions on the possibility to get reliable results in the evaluation. Nevertheless, an evaluation has been performed. The evaluation of strain measurements demonstrated higher strain values at the upstream side of the central wall and roof. Moreover, the strain on underside of the roof was higher than on the central wall. Sudden fluctuation during continuous operation and sequence of start/stop were the cases that in long-term may cause damage to the structure due to fatigue problems. The results from finite element model indicated high tensile strength at the upstream side of the straight diffuser, in contact between the roof and the central wall where a crack has been detected in the real structure.

Place, publisher, year, edition, pages
Energiforsk AB, 2019. p. 78
National Category
Civil Engineering
Identifiers
urn:nbn:se:kth:diva-261088 (URN)978-91-7673-567-1 (ISBN)
Note

QC 20191002

Available from: 2019-10-01 Created: 2019-10-01 Last updated: 2019-10-02Bibliographically approved
Nordström, E., Malm, R., Hassanzadeh, M., Ekström, T. & Janz, M. (2019). Guideline for structural safety in cracked concrete dams. In: Sustainable and safe dams around the world : proceedings of the ICOLD 2019 symposium, (ICOLD 2019), June 9-14, 2019, Ottawa, Canada = Un monde de barrages durables et sécuritaires : publications du symposium CIGB 2019, Juin 9-14, 2019, Ottawa, Canada: . Paper presented at ICOLD 2019 Annual Meeting/Symposium. June 9-14, Ottawa, Canada (pp. 1681-1696). CRC Press
Open this publication in new window or tab >>Guideline for structural safety in cracked concrete dams
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2019 (English)In: Sustainable and safe dams around the world : proceedings of the ICOLD 2019 symposium, (ICOLD 2019), June 9-14, 2019, Ottawa, Canada = Un monde de barrages durables et sécuritaires : publications du symposium CIGB 2019, Juin 9-14, 2019, Ottawa, Canada, CRC Press, 2019, p. 1681-1696Conference paper, Published paper (Refereed)
Abstract [en]

Several concrete dams show cracking, and their condition and remaining service

life must be determined. Assessment and service life prediction of cracked dams should include an investigation to determine the cause and consequences of cracks. Cracks can be caused by different mechanisms, which also may act together. Some mechanisms act during a short period of time, e.g. in the beginning after construction, while other mechanisms may influence the dam during the whole service-life. Therefore, it is important to combine observations, measurements, laboratory tests and theoretical analyses investigating the causes of the cracks, their future development and the influence they may have on the performance of the dam. Lessons learned and knowledge concerning crack propagation in concrete and rock, general material engineering, durability concerns caused by cracks, structural analysis issues connected to cracks, field measurements and design of remedial measures has been compiled in a Swedish guideline. The guideline highlights issues that should be looked for in inspections and contains a methodology to determine the residual strength and serviceability of cracked concrete dams and how to review dam safety criteria’s. This in turn will provide the dam owner with a better means to manage and prioritize rehabilitation and maintenance work.

Place, publisher, year, edition, pages
CRC Press, 2019
National Category
Civil Engineering
Identifiers
urn:nbn:se:kth:diva-261090 (URN)978-0-367-33422-2 (ISBN)
Conference
ICOLD 2019 Annual Meeting/Symposium. June 9-14, Ottawa, Canada
Note

QC 20191011

Available from: 2019-10-01 Created: 2019-10-01 Last updated: 2019-10-11Bibliographically approved
Nordström, E. & Eriksson, D. (2019). Inventering av inre vattenvägsbesiktningar. Stockholm
Open this publication in new window or tab >>Inventering av inre vattenvägsbesiktningar
2019 (Swedish)Report (Other academic)
Abstract [sv]

Det är via vattenvägarna som vatten transporteras från reservoaren, förbi dammen och sedan vidare nedströms i en vattenkraftsanläggning. Vattenvägarna vid en vattenkraftsanläggning kan generellt sett delas upp i yttre och inre konstruktioner. De inre vattenvägarna omfattar ett flertal konstruktioner som intag, tilloppstunnel, tilloppstub, intagssump, spiral, sugrör, svallschakt, svallgalleri och utloppstunnel. Dessa konstruktioner är vanligtvis helt eller delvis vattenfyllda vilket medför att de i många fall är svåråtkomliga för inspektion. Det är sällan ekonomiskt försvarbart att torrlägga de inre vattenvägarna enbart för inspektion till följd av det avbrott i elproduktionen som då uppstår. Dock uppkommer emellanåt möjligheten att få inspektera de inre vattenvägarna i samband med driftstopp för reparation, inspektion eller utbyte av de elgenererande delarna.

På uppdrag av Energiforsk har en genomgång av den rapportering som finns från genomförda inspektioner gjorts i ett försök att förbättra kunskapsläget gällande eventuella typskador och nedbrytningsförlopp i de inre vattenvägarna. Insamlingen av underlag har gjorts genom förfrågningar hos ägarrepresentanterna i styrgruppen för vattenkraftens betongprogram inom Energiforsk. Det erhållna underlaget omfattade både besiktningsrapporter och sammanställningar över observerade skador i de inre vattenvägarna för sammanlagt 53 olika vattenkraftverk.

Utifrån analysen av det erhållna materialet i denna studie kunde det konstateras att erosion var den vanligast förekommande skadetypen då samtliga typer av inre vattenvägar beaktas. Dock blev självklart bilden en liten annan i det fall de olika typerna av vattenvägar studeras enskilt även om erosionsskador oftast återfinns högt upp i listan över observerade skador och brister. Tidigare forskning har dock visat att det ofta är en samverkan mellan olika nedbrytningsmekanismer som resulterar i en observerad skada. Av denna anledning är det därför svårt att isolera en enskild nedbrytningsmekanism som ensam är orsaken till att just erosionsskador är den vanligast förekommande skadetypen. Det kunde också konstateras att dokumentationen av genomförda inspektioner och därmed observerade skador och brister i de inre vattenvägarna generellt sett är bristfällig hos flertalet anläggningsägare. Det bör dock poängteras att samtliga tillfrågade anläggningsägare angivit att de genomfört inspektioner men att just dokumentationen från dessa antingen saknas eller är svår att hitta.

Med ledning av resultaten från inventeringen går det att konstatera ett förbättringsbehov i förvaltningen av de inre vattenvägskonstruktionerna. Särskilt stora brister verkar råda på kännedomen om statusen hos långa tillopps- och utloppstunnlar av berg med olika grad av förstärkning. För anläggningar med gemensamma tunnlar för till- eller utlopp kan konsekvenserna av ett större tunnelras kunna vara betydande ur ekonomisk synvinkel i form av långvariga produktionsbortfall. Det rekommenderas att en strategi för hantering av detta utvecklas.

Abstract [en]

The water is transported by the waterways from the reservoir, past the dam and further downstream in a hydropower station. Generally, the waterways can be categorized to be either of channel-type or tunnel-type. The waterways of tunneltype include a number of different structures such as intakes, headrace tunnels, penstocks, intake sumps, spirals, draft tubes, surge shafts, surge galleries and tailrace tunnels. These structures are usually either fully or partially filled with water, which means that they in many cases are hard to inspect. Moreover, it is seldom financially justifiable to drain the tunnels solely to perform an inspection due to the loss of energy production that this measure entails. However, in connection to stoppage of the energy production to repair, inspect or replace some of the energy-producing parts, an opportunity to inspect the waterways of tunneltype is usually given.

In this study, a review of documentation from inspections of waterways of tunneltypes has been performed on behalf of Energiforsk to improve the state of knowledge regarding common damage types and deterioration mechanisms in this type of waterways. The collection of data has been performed by inquiring data from representatives of the utility companies in the steering committee of the research program for concrete in hydropower at Energiforsk. The obtained material includes both reports from inspections as well as compilations of observed damage in the waterways for a total of 53 different hydropower stations in Sweden.

From the analysis of the obtained material in this study, it could be concluded that erosion was the most common type of damage observed in waterways of tunneltype if all types of such structures are considered. However, the results become a bit different if the different types of structures are studied individually, even though erosion often is observed to be one of the most commonly observed damage types. Previous research has, however, shown that an observed damage often is a consequence of a series of deterioration mechanisms that together cause a degradation of the material. Therefore, it is hard to isolate one single deterioration mechanism that is the only reason why erosion is the most commonly observed damage type in waterways of tunnel-type. Furthermore, it could be concluded that the documentation of performed inspections generally is inadequate at the utility companies and consequently also the documentation of observed damage and defects in the waterways. It should, however, be noticed that all companies stated that they have performed inspections but that the documentation from these is either missing or hard to find.

With results from the study in mind a need for improvement in the management of the inner waterways is obvious. Especially regarding the knowledge on the status of long headrace and tailrace tunnels in rock with different degree of support. For facilities with common head-/tailrace tunnels for several units, the consequences of a larger failure could be substantial in terms of financial losses from no production. It is recommended to develop a strategy for management of inner waterways.

Place, publisher, year, edition, pages
Stockholm: , 2019. p. 34
Series
Energiforsk rapport ; 2019:566
National Category
Civil Engineering
Research subject
Civil and Architectural Engineering
Identifiers
urn:nbn:se:kth:diva-244975 (URN)978-91-7673-566-4 (ISBN)
Note

QC 20190305

Available from: 2019-03-04 Created: 2019-03-04 Last updated: 2019-03-05Bibliographically approved
Nordström, E., Tornberg, R. & Kamanga, R. (2019). Management of ASR affected spillway structures at Kafue Gorge, Zambia. In: : . Paper presented at ICOLD Symposium, June 9-14, Ottawa, Canada, 2019.
Open this publication in new window or tab >>Management of ASR affected spillway structures at Kafue Gorge, Zambia
2019 (English)Conference paper, Published paper (Refereed)
Abstract [en]

The Kafue Gorge dam along Kafue River in Zambia was commissioned in 1971. In 1988 one of the spillway gates was jammed due to concrete expansion. Measures were taken, but signs of expansion and cracking continued. After rehabilitation works on one of the spillway gates in 2011 five stop-logs were stuck in position due to concrete expansion. In 2012, ZESCO and SWECO performed an in-depth assessment of the spillway structure with crack mapping and core sampling. Extensive cracking on the upstream side of the spillway piers with crack widths of up to 30 mm was found under water. Concrete analysis verified ongoing ASR. Numerical simulations on the behavior of the dam (with major cracks and ASR-expansion) showed that there was a need for stabilizing measures. SWECO designed remedial measures to restore full integrity of the dam and resolve the problem with the jammed stop-logs that caused reduced discharge capacity. During 2019 post-tensioned tendons are installed to ensure a monolithic behavior of the structure and improve the stability. All major cracks will be sealed to reduce the contact area of concrete and water. Finally, the jammed stop-logs will be removed to restore the discharge capacity of the spillway.

National Category
Civil Engineering
Identifiers
urn:nbn:se:kth:diva-260980 (URN)978-0-367-33422-2 (ISBN)
Conference
ICOLD Symposium, June 9-14, Ottawa, Canada, 2019
Note

QC 20191022

Available from: 2019-10-01 Created: 2019-10-01 Last updated: 2019-10-22Bibliographically approved
Nordström, E., Tornberg, R. & Kamanga, R. (2019). Management of ASR-affected spillway structures at Kafue Gorge, Zambia. In: : . Paper presented at AFRICA 2019 Conference, 2-4 April, Windhoek, Namibia.
Open this publication in new window or tab >>Management of ASR-affected spillway structures at Kafue Gorge, Zambia
2019 (English)Conference paper, Published paper (Other academic)
National Category
Civil Engineering
Identifiers
urn:nbn:se:kth:diva-261132 (URN)
Conference
AFRICA 2019 Conference, 2-4 April, Windhoek, Namibia
Note

QC 20191022

Available from: 2019-10-01 Created: 2019-10-01 Last updated: 2019-10-22Bibliographically approved
Hellgren, R., Malm, R. & Nordström, E. (2019). Modeller för övervakning av betongdammar: Energiforskrapport 2019:580. Stockholm, Sweden, 580
Open this publication in new window or tab >>Modeller för övervakning av betongdammar: Energiforskrapport 2019:580
2019 (Swedish)Report (Other academic)
Alternative title[en]
Models for monitoting of concrete dams
Abstract [sv]

Inom dammövervakning används begreppen larm och varning för meddelanden om upptäckten av en potentiell dammsäkerhetsrisk. Larm är kopplade till ett akut farligt beteende och en varning till ett oförväntat beteende. Dammövervakning är således ett klassificeringsproblem där varje nytt uppmätt beteende ska klassificeras som säkert eller osäkert, alternativt som förväntat eller oförväntat. Ett farligt beteende innebär att dammsäkerheten är hotad akut medan ett oförväntat värde uppstår när dammen inte beter sig enligt förväntan utifrån rådande yttre förhållanden. En sådan avvikelse betyder inte per automatik att något är fel eller att säkerheten är hotad men en oskadad damm bör bete sig enligt ett förväntat mönster och en avvikelse från det förväntade beteende kan indikera en initiering av en skada hos dammen.För att bestämma det förväntade mätvärdet behövs någon typ av prediktionsmodell som förutsäger dammens beteende utifrån de yttre förhållandena. I denna rapport delas prediktionsmodellerna upp i teoribaserade och databaserade modeller. De teoribaserade modellerna bygger på en fysikalisk koppling mellan yttre förhållanden så som vattennivå och temperaturer och dammens beteende. I de databaserade modellerna är denna koppling istället empirisk och utan fysikalisk koppling.Det finns flertalet olika typer av instrument och givare för dammövervakning. I denna rapport sammanfattas vanliga typer avsedda för dammätningar, inklusive dess mätnoggrannhet. Dessutom diskuteras användningen av olika givare baserat på om de lämpar sig som detektorer vid ett potentiellt dammbrott eller om givarna främst är att anse som stödinstrumentering vars syfte är att bidra mer information om dammens beteende eller yttre förhållanden.Varje modelltyp har unika egenskaper med för- och nackdelar. Det är därför viktigt att välja modelltyp utifrån behov och syfte. En teoribaserad modell, t.ex. FE-modell, ger möjligheten att tolka resultaten och hitta fysikaliska samband, men är sämre på att förutsäga exakt beteende. De mest avancerade databaserade modellerna är utan fysikalisk mening, men kan förutsäga framtida beteenden väldigt bra. Att välja den ena modelltypen framför den andra innebär, något tillspetsat, ett val mellan förståelse och prestation. Lyckligtvis utesluter inte användandet av en modelltyp en annan. De fysikbaserade modellerna som hjälper oss att förstå och tolka en damms beteende kommer alltid ha en plats i dammsäkerhetsarbetet. Det är dessutom den modelltyp som bäst kan användas för att studera dammbrottsscenarion och därmed användas för definition av eventuella larmnivåer. Som ett komplement till dessa kan de databaserade modellerna användas för att ge tidiga indikationer när dammens beteende skiljer sig från det förväntade och lämpar sig därmed väl för val av varningsnivåer. De databaserade metoderna ger tidigare indikationer på eventuella avvikelser eftersom de generellt presterar bättre med mindre spridningsmått än motsvarande teoribaserade modeller.

Abstract [en]

In the field of dam surveillance, alert and alarm values are used for error detection to notify about the discovery of a potential dam safety risk. Alarm values are used to notify that a dangerous behavior have been reached. Alert values (warnings) are used to notify that the measured data is out of the expected range. Dam surveillance can thereby be considered as a classification problem where every measured response should be classified as safe or unsafe, or alternatively as expected or unexpected. Dangerous behavior implies that the safety of the dam may be compromised (e.g. the coefficient of safety may be surpassed), while an unexpected value occurs when the dam no longer acts according to the predicted behavior based on current conditions. Such a discrepancy does not necessarily mean that the dam safety is compromised, but could indicate that the dam is damaged.In order to determine the expected behavior, some type of prediction model is required that can predict the dam behavior based on ambient conditions. In this report, the prediction models are defined as either theory-based or empirical. The theory-based models are based on physics with correlation between ambient conditions such as water level and temperatures and the response of the dam. In the empirical models, this coupling is purely empirical without any physical meaning.There are several types of sensors that can be used for dam surveillance. In this report, the instruments commonly used within the field of dam engineering and their expected accuracy are discussed. In addition, the use of different sensors based on their purpose in the surveillance program is discussed where sensors are denoted as detectors or support instruments. The detectors are considered as sensors suitable to be used to monitor a potential failure mode while the purpose of the support instruments is to provide additional information about the dam response or the ambient conditions.Every type of model has unique properties with different pros and cons. It is therefore important to choose the type of model based on the need and purpose of the monitoring or evaluation of the dam response. A finite element model gives good possibilities to interpret the results and find the physical meaning of a specific behavior, but is not as good to give exact predictions. The most advanced empirical models are defined without any physical meaning, but are capable to give precise predictions of the expected response. To choose one type of model over another can thereby be described as choosing between understanding and performance. Luckily, the use of one model does not exclude the use of others. The models based on physics helps us understand and interpret the dam behavior and will therefore always have a use in the dam safety work. It is also the type of model that best can be used to study scenarios during dam failure and thereby to define alarm values. As a compliment to these, the empirical models can be used to give early warnings when the dam behavior is out of the ordinary and is therefore most suited for definition of alert values. These models generally perform better and has smaller deviation than the corresponding theoretical models.The case studies presented in this report shows that the simple empirical models with some physical meaning gives very good predictions of the expected behavior.

Place, publisher, year, edition, pages
Stockholm, Sweden: , 2019. p. 83
National Category
Civil Engineering
Identifiers
urn:nbn:se:kth:diva-255284 (URN)9789176735800 (ISBN)
Note

QC 20190828

Available from: 2019-07-28 Created: 2019-07-28 Last updated: 2019-08-28Bibliographically approved
Nordström, E. & Hassanzadeh, M. (2018). Inblandning av flygaska i vattenbyggnadsbetong. Energiforsk
Open this publication in new window or tab >>Inblandning av flygaska i vattenbyggnadsbetong
2018 (Swedish)Report (Other academic)
Place, publisher, year, edition, pages
Energiforsk, 2018. p. 52
Series
Energiforsk Rapport ; 2018:479
National Category
Civil Engineering
Identifiers
urn:nbn:se:kth:diva-261125 (URN)978-91-7673-479-7 (ISBN)
Note

QC 20191008

Available from: 2019-10-01 Created: 2019-10-01 Last updated: 2019-10-08Bibliographically approved
Malm, R., Fransson, L., Nordström, E., Westberg Wilde, M., Johansson, F. & Hellgren, R. (2017). Lastförutsättningar avseende istryck.
Open this publication in new window or tab >>Lastförutsättningar avseende istryck
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2017 (Swedish)Report (Other academic)
Publisher
p. 76
Series
Energiforsk report ; 2017:439
National Category
Infrastructure Engineering
Identifiers
urn:nbn:se:kth:diva-235735 (URN)
Note

QC 20181009

Available from: 2018-10-03 Created: 2018-10-03 Last updated: 2018-10-09Bibliographically approved
Blomdahl, J., Malm, R. & Nordström, E. (2016). Minimiarmering i vattenkraftens betongkonstruktioner - Förstudie.
Open this publication in new window or tab >>Minimiarmering i vattenkraftens betongkonstruktioner - Förstudie
2016 (Swedish)Report (Other academic)
Publisher
p. 60
Series
Energiforsk report ; 2016:234
National Category
Infrastructure Engineering
Identifiers
urn:nbn:se:kth:diva-235728 (URN)9789176732342 (ISBN)
Note

QC 20181009

Available from: 2018-10-03 Created: 2018-10-03 Last updated: 2018-10-09Bibliographically approved
Gasch, T., Malm, R., Nordström, E. & Hassanzadeh, M. (2016). Non-linear analyses of cracks in aging concrete hydro power structures. International Water Power & Dam ConstructionDam Engineering
Open this publication in new window or tab >>Non-linear analyses of cracks in aging concrete hydro power structures
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
Keywords
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:nbn:se:kth:diva-186144 (URN)
Note

QC 20160503

Available from: 2016-05-03 Created: 2016-05-03 Last updated: 2019-03-15Bibliographically approved
Organisations
Identifiers
ORCID iD: ORCID iD iconorcid.org/0000-0001-6840-9986

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