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  • 1.
    Abbasiverki, Roghayeh
    et al.
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Concrete Structures.
    Ahmed, Lamis
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Concrete Structures.
    Nordström, Erik
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Concrete Structures. Sweco.
    Analysis of load and response on large hydropower draft tube structures2019Report (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.

  • 2. Blomdahl, Johan
    et al.
    Malm, Richard
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Concrete Structures.
    Nordström, Erik
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Concrete Structures.
    Minimiarmering i vattenkraftens betongkonstruktioner - Förstudie2016Report (Other academic)
  • 3.
    Gasch, Tobias
    et al.
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Concrete Structures.
    Malm, Richard
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Concrete Structures.
    Nordström, Erik
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Concrete Structures.
    Hassanzadeh, Manouchehr
    Lund University, Division of Building Materials.
    Non-linear analyses of cracks in aging concrete hydro power structures2016In: 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.

  • 4.
    Hassanzadeh, Manouchehr
    et al.
    Lund University, Building Materials.
    Malm, Richard
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Concrete Structures.
    Nordström, Erik
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Concrete Structures.
    Analysis of Displacements and Crack Formations in Foundations for Hydropower Generators2012Conference paper (Refereed)
    Abstract [en]

    A rather extensive program for improvement of the Swedish hydropower plants is ongoing. The aims are to secure future production and to maintain and further develop an already high dam safety. In connection with earlier work, which dealt with assessment of an existing buttress dam where a non-linear finite element model was applied to determine the cause of the observed cracks. The results showed that the non-linear finite element method is a powerful tool to determine the structural behaviour of large concrete structures. The study in this paper is a continuation of the previous project, aiming at applying the method to other parts of dam structure such as foundation supporting the generator (stator and rotor), rotor spider, turbine shaft, spiral casing, turbine and draft tube.

    The hydropower plant, which is studied, was constructed in the early forties. During the inspection, structural damages (cracks) were discovered around some of the stator and rotor spider supports. The cracks were believed to be related to the function of the stator supports and to new patterns of generator operation. In earlier times, the generators ran continuously, while nowadays there are many stops and starts, some times even several times during one day. The purpose of this study is to illuminate the complex stress conditions in the generator foundations of a hydropower plant and to reveal the causes of the stresses and to verify their role in formation of the cracks.

    The structural behaviour of a foundation has been analysed taking into account the transient thermal gradients in combination with dead loads and some of the operational loads imposed to the foundation. A three dimensional non-linear finite element model has been applied in order to analyse formation and propagation of the cracks. The analyses showed that based on the assumption made, the concrete foundation cracks mainly on the outside but also near some of the stator supports due to the combination of mechanical and thermal loads. However, the studied loads cannot explain all of the types of damages that can be found in-situ. It is likely that especially the drying shrinkage may be the one of the reasons for the cracks that has been found near the stator supports and especially the rotor spider supports.

    It is important from a dam safety perspective to determine the causes of the structural cracks that have been found in-situ and also to evaluate the effect of the reduced stiffness due to cracking, since a reduced structural stiffness can result in larger loads imposed on the structure from the magnetic eccentricity and turbine imperfections or alternatively lead to a fatigue failure of for instance the reinforcement.

  • 5.
    Hellgren, Rikard
    et al.
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Concrete Structures.
    Malm, Richard
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Concrete Structures.
    Fransson, Lennart
    Luleå University of Technology.
    Johansson, Fredrik
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Soil and Rock Mechanics.
    Nordström, Erik
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Concrete Structures.
    Westberg Wilde, Marie
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Soil and Rock Mechanics.
    Measurement of ice pressure on a concrete dam with aprototype ice load panelManuscript (preprint) (Other academic)
    Abstract [en]

    This paper presents the development and installation of a prototype ice load panel andmeasurements of ice load from February 2016 to February 2018 at the Rätan hydropower damin Sweden. The design of the 1x3 m2 panel enabling direct measurement of ice pressure on theconcrete surface is based on previous experience from similar measurements with sea ice.Important features of the design are sufficient height and width to reduce scale effects and tocover the ice thickness and variations in water level. The Rätan dam was chosen based onseveral criteria so that the ice load is considered to be reasonably idealized against the damstructure.For the three winters 2016, 2016/2017, 2017/2018, the maximum ice load recorded was 161kN/m, 164 kN/m and 61 kN/m respectively. There were significant daily fluctuations duringthe cold winter months, and the daily peak ice loads showed a visual correlation with the dailyaverage temperature and with the daily pattern of operation of the power station with itscorresponding water level variations

  • 6.
    Hellgren, Rikard
    et al.
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Concrete Structures.
    Malm, Richard
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Concrete Structures.
    Nordström, Erik
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Concrete Structures.
    Modeller för övervakning av betongdammar: Energiforskrapport 2019:5802019Report (Other academic)
    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.

  • 7.
    Malm, Richard
    et al.
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Concrete Structures.
    Fransson, Lennart
    Nordström, Erik
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Concrete Structures.
    Westberg Wilde, Marie
    Johansson, Fredrik
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Soil and Rock Mechanics.
    Hellgren, Rikard
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Concrete Structures.
    Lastförutsättningar avseende istryck2017Report (Other academic)
  • 8.
    Nordström, Erik
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Concrete Structures.
    Utvärdering efter 17 års fältexponering av sprucken stålfiberarmerad sprutbetong2016Report (Other academic)
    Abstract [sv]

    Rapporten redovisar resultaten från den senaste utvärderingen av en fältexponeringsserie som startades 1997 som en del av författarens doktorandprojekt. Föreliggande utvärdering har finansierats av BeFo och Energiforsk. Stålfibrer har vanligen både syftet att vara sprickfördelande/sprickviddsbegränsande i bruksgränstillstånd  och  att  ge  residualbärförmåga  och  duktilitet  i  brottgränstillstånd.  Studien   har   primärt   inriktats   på   om,   och   under   vilka   förutsättningar,   som   stålfiberkorrosion   riskerar   uppstå   i   sprickzonen.   Ett   vanligt   livslängdskrav   för   anläggningskonstruktioner är 100 år. Fältproverna har exponerats i tre vanligen förekommande miljöer, nämligen vägmiljö (Rv40, Borås), tunnelmiljö (Eugeniatunneln, Stockholm) och älvmiljö (Älvkarleby). De materialparametrar som varierats är sprutbetongtyp (våt-/torrsprutad), fiberlängd, acceleratortillsats och sprickvidder. Samtliga  provplatserna  uppvisar  korrosion  efter  17  års  exponering,  men  i  mycket  begränsad  omfattning  i  älvmiljön.  Korrosionsangreppet  är  kraftigast  vid  Rv40  som  utgör en miljö med kombinationen av hög fuktighet och relativt hög kloridbelastning. Tydligaste påverkan av mixtypen erhölls av prover med långa fibrer som korroderade betydligt  fortare  än  de  kortare  fibrerna  vilket  fortsatt  stärker  vikten  av  förhållandet  mellan  anod  och  katod.  Provernas  sprickvidd  hade  mest  betydelse  för  tiden  till  initiering  av  korrosion,  men  efter  initiering  utvecklas  korrosionen  i  ungefär  samma  hastighet.  Det  finns  en  tydlig  koppling  mellan  en  mer  utvecklad  fiberkorrosion  och  förlust  av  bärförmåga  vilket  blir  särskilt  tydligt  vid  utvärdering  av  bärförmågan  vid  stora  deformationer  (brottsgräns).  För  små  deformationer  (bruksstadium)  och  små  sprickvidder  (0,1  mm)  kunde  en  ökning  av  bärförmågan  ses  som  verkar  bestå  även  efter 17 års exponering.  I Dalälvsproverna noterades en urlakad zon på ca.10 mm efter 17 år. Det konstaterades också att den våtsprutade betongen utan accelerator visade ett något bättre motstånd mot urlakning och den torrsprutade bäst motstånd även om några mm urlakning kunde ses.  Kloridmängderna  i  proverna  vid  Rv40  och  Eugeniatunneln  är  höga  efter  exponeringen  och  i  tunnelmiljön  mycket  höga  vilket  accelererat  den  initierade  korrosionen   kraftigt.   Sannolikt   sker   en   ackumulering   eftersom   betongen   är   regnskyddad inne i tunneln. Det   är   tydligt   att   den   förstörande   utvärderingstekniken   inte   är   optimal   när   korrosionsprocessen gått långt p.g.a. att ”bevismaterialet” inte längre kan identifieras. De  senare  resultaten  där  korrosion  pågått  en  längre  tid  riskerar  att  underskatta  det  verkliga angreppets omfattning. Sammanfattningsvis  kan  konstateras  att  stålfiberkorrosion  i  sprucken  sprutbetong  exponerade  för  kloridutsatta  miljöer  måste  förväntas  uppträda  med  de  vanligast  förekommande  fibertyperna.  Det  är  inte  rimligt  att  anta  100  års  livslängd  med  bibehållen bärförmåga i de provade kloridutsatta miljöerna.

  • 9.
    Nordström, Erik
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Concrete Structures.
    Vägledning för val av ballast i konstruktioner för vattenbyggnad2016Report (Other academic)
    Abstract [sv]

    Det har i vattenbyggnadsbranschen uppdagats ett behov av vägledning vid val av ballast för betongkonstruktioner i Sverige med avseende på risken för alkali-silika-reaktioner (ASR). Då målsättningen för vattenbyggnadskonstruktioner vanligtvis är en livslängd på minst 100 år bör därför valet av ballast vara konservativt tills det finns forskningsresultat som bringat reda på under vilka förutsättningar som ASR uppstår.

    Föreliggande interimistiska vägledning är framtagen inom Energiforsks betongtekniska program vattenkraft i väntan på en nationell vägledning på området.

    I vägledningen rekommenderas att inte högre halt än 15 vikt-% av reaktiva eller potentiellt alkalireaktiva ballastpartiklar ska användas i betong för vattenbyggnadskonstruktioner. Rekommendationen gäller alla konstruktioner som är:

    • dämmande (eller stödjande till dämmande)

    • aggregatnära

    • exponerade för vatten från reservoar

    • del av inre/yttre vattenväg

    • utsatta för nederbörd (Omgivningsklass E2 och E3).

    Rekommendationen gäller även i kombination med användning av lågalkaliska cement, och efter redovisade resultat från funktionsprovning enl. t.ex. RILEM AAR-3.

  • 10.
    Nordström, Erik
    et al.
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Concrete Structures.
    Eriksson, Daniel
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Concrete Structures.
    Inventering av inre vattenvägsbesiktningar2019Report (Other academic)
    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.

  • 11.
    Nordström, Erik
    et al.
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Concrete Structures.
    Hassanzadeh, Manouchehr
    Sweco.
    Inblandning av flygaska i vattenbyggnadsbetong2018Report (Other academic)
  • 12.
    Nordström, Erik
    et al.
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Concrete Structures.
    Hassanzadeh, Manouchehr
    Lund University, Building Materials.
    Malm, Richard
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Concrete Structures.
    Ekström, Tomas
    Janz, Mårten
    Strukturell säkerhet hos spruckna betongdammar2019Report (Refereed)
  • 13.
    Nordström, Erik
    et al.
    Sweco Energuide AB.
    Krogh, Peter
    Sweco Energuide AB.
    Nilsson, Ola
    Sweco Energuide AB.
    Sjödin, Gunnar
    Vattenregleringsföretagen.
    Stenberg, Rickard
    Vattenregleringsföretagen.
    Hautakoski, Marcus
    Vattenregleringsföretagen.
    Upgrading of the Lossen and Ransaren dams in Sweden2015Conference paper (Refereed)
  • 14.
    Nordström, Erik
    et al.
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Concrete Structures.
    Malm, Richard
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Concrete Structures.
    Blomdahl, Johan
    Sweco.
    Tornberg, Robert
    Sweco.
    Nilsson, Carl-Oscar
    Uniper.
    Optimization of dam monitoring for long concrete buttress dams2015Conference paper (Other academic)
  • 15.
    Nordström, Erik
    et al.
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Concrete Structures.
    Malm, Richard
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Concrete Structures.
    Hassanzadeh, Manouchehr
    Sweco.
    Ekström, Tomas
    ÅF.
    Janz, Mårten
    ÅF.
    Guideline for structural safety in cracked concrete dams2019In: 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 (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.

  • 16.
    Nordström, Erik
    et al.
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Concrete Structures.
    Malm, Richard
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Concrete Structures.
    Johansson, Fredrik
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Soil and Rock Mechanics.
    Ligier, Pierre-Louis
    Lier, Öyvind
    Betongdammars brottförlopp2015Report (Other academic)
  • 17.
    Nordström, Erik
    et al.
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Concrete Structures.
    Rosenqvist, Martin
    ÅF.
    Sjödin, Gunnar
    Vattenregleringsföretagen.
    Hautakoski, Marcus
    Vattenregleringsföretagen.
    Field investigations on the risk for ASR when using potentially reactive aggregates and low alkali cements: Results after 50 years in Sweden2013Conference paper (Refereed)
    Abstract [en]

    The adverse effects from reactions of reactive aggregates in concrete dams are well known worldwide. The mechanisms ruling alkali silica reactions (ASR) are partly but not fully understood. A majority of the Swedish concrete dams are so far considered to be protected from ASR due to the common use during the 50:s, 60:s and 70:s of the Swedish low alkali cement Limhamn LH. Today there is a discussion if it still is possible to develop ASR after very long time in dams with reactive aggregates and use of low alkali cement. Via selection of seven facilities in the Swedish alpine area, where reactive aggregates are common, the current paper is aiming to compile experiences from almost 50 years of exposure. In the paper two examples on ASR in spite of use of low alkali cement are shown.

  • 18.
    Nordström, Erik
    et al.
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Concrete Structures.
    Tornberg, Robert
    Sweco.
    Kamanga, Romas
    Zesco.
    Management of ASR affected spillway structures at Kafue Gorge, Zambia2019Conference 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.

  • 19.
    Nordström, Erik
    et al.
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Concrete Structures.
    Tornberg, Robert
    Sweco.
    Kamanga, Romas
    Zesco.
    Management of ASR-affected spillway structures at Kafue Gorge, Zambia2019Conference paper (Other academic)
  • 20.
    Rosenqvist, Martin
    et al.
    Vattenfall Research & Development, Älvkarleby.
    Nordström, Erik
    Sweco Infrastructure, Gävle, Sweden.
    Hassanzadeh, Manouchehr
    Vattenfall Research & Development, Stockholm.
    Fridh, Katja
    Lund University, Lund, Sweden.
    Observations and investigations of frost damage mechanisms of concrete dams in Sweden2013Conference paper (Refereed)
    Abstract [en]

    The major part of the Swedish hydro power development took place between 1945 and1975. At that point of time, significant progress had been made regarding the use of highquality concrete for hydraulic structures. In spite of the progress made, deterioration ofconcrete due to freezing and thawing is still frequent. Superficial damage at the waterlineand spalling of concrete far below the water level on the upstream face of concrete damshave been observed. Knowledge about the deterioration processes is important in order toimprove the efficiency of maintenance of hydro power plants. Results obtained from twoexperimental studies of frost damage mechanisms are presented in this paper.

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