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Publications (10 of 16) Show all publications
Hellgren, R., Malm, R., Fransson, L., Johansson, F. & Westberg Wilde, M. (2020). Measurement of ice pressure on a concrete dam with a prototype ice load panel. Cold Regions Science and Technology, 170, Article ID 102923.
Open this publication in new window or tab >>Measurement of ice pressure on a concrete dam with a prototype ice load panel
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2020 (English)In: Cold Regions Science and Technology, ISSN 0165-232X, E-ISSN 1872-7441, Vol. 170, article id 102923Article in journal (Refereed) Published
Abstract [en]

This paper presents the development and installation of a prototype ice load panel and measurements of ice load from February 2016 to February 2018 at the Rätan hydropower dam in Sweden. The design of the 1 × 3 m2 panel enables direct measurement of ice pressure on the concrete 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 to cover the ice thickness and variations in water level. The Rätan dam was chosen based on several criteria so that the ice load is considered to be reasonably idealized against the dam structure.

For the three winters 2016, 2016/2017, 2017/2018, the maximum ice load recorded was 161 kN/m, 164 kN/m and 61 kN/m respectively. There were significant daily fluctuations during the cold winter months, and the daily peak ice loads showed a visual correlation with the daily average temperature and with the daily pattern of operation of the power station with its corresponding water level variations.

Place, publisher, year, edition, pages
Elsevier, 2020
National Category
Engineering and Technology Building Technologies
Research subject
Civil and Architectural Engineering, Structural Engineering and Bridges
Identifiers
urn:nbn:se:kth:diva-264210 (URN)10.1016/j.coldregions.2019.102923 (DOI)2-s2.0-85075037308 (Scopus ID)
Note

QC 20191125

Available from: 2019-11-23 Created: 2019-11-23 Last updated: 2019-11-25Bibliographically approved
Eriksson, D., Malm, R. & Hellgren, R. (2019). Assessment of frost damage in hydraulic structures using a hygro-thermo-mechanical multiphase model. In: Jean-Pierre Tournier, Tony Bennett & Johanne Bibeau (Ed.), Sustainable and Safe Dams Around the World: . Paper presented at ICOLD 2019 Symposium (pp. 332-346). , 2
Open this publication in new window or tab >>Assessment of frost damage in hydraulic structures using a hygro-thermo-mechanical multiphase model
2019 (English)In: Sustainable and Safe Dams Around the World / [ed] Jean-Pierre Tournier, Tony Bennett & Johanne Bibeau, 2019, Vol. 2, p. 332-346Conference paper, Published paper (Refereed)
Abstract [en]

This paper presents an extension of a novel hygro-thermo-mechanical multiphase model for simulation of freezing of partially saturated air-entrained concrete on the structural scale to account for the effect of damage in the material. The model is applied in an example which investigates the extent and severity of frost damage caused by extremely cold climate conditions in a typical concrete wall in a waterway constructed with air-entrained concrete. The results were concluded to comply with observations made in experimental work and testing of freezing air-entrained concrete under exposure conditions similar to those in hydraulic structures. Furthermore, the results indicate that the effect of short periods of time with high rates of freezing was rather small on the obtained damage. Additionally, increasing the depth of the boundary region with an initially high degree of water saturation on the upstream side had also a rather small effect on the damaged zone.

National Category
Civil Engineering
Research subject
Civil and Architectural Engineering
Identifiers
urn:nbn:se:kth:diva-253820 (URN)
Conference
ICOLD 2019 Symposium
Note

QC 20190624

Available from: 2019-06-18 Created: 2019-06-18 Last updated: 2019-06-24Bibliographically approved
Hellgren, R. (2019). Condition assessment of concrete dams in cold climate. (Licentiate dissertation). Stockholm: KTH Royal Institute of Technology
Open this publication in new window or tab >>Condition assessment of concrete dams in cold climate
2019 (English)Licentiate thesis, comprehensive summary (Other academic)
Alternative title[sv]
Tillståndsbedömning av betongdammar i kallt klimat
Abstract [en]

Dams in many countries are approaching their expected service life. Proper assessment of the aging dams structural health increase the knowledge of the current safety, and allow for better planning of renovation and rebuilding investments. The behavior of concrete dams is, to a great extent, governed by the ambient variation in temperature and water level. In cold regions, the ice sheet formed in the reservoir may subject a pressure load on the dams. Theoretically, this load has a significant impact on the structural behavior of dams. Despite this, the maximum magnitude, as well as the seasonal variation of the ice load, constitute the most considerable uncertainty in the safety assessment of dams.

This thesis presents research that examines how to model the expected behavior of dams in cold climate. The underlying problem is to predict the response of dams due to variation in the external conditions. Since the ice load is such a vital part of the external conditions in cold climate, the understanding and modeling of ice loads have been given extra attention. Models suitable to predict the long-term behavior of dams can be divided between theoretical, data-based, and hybrid. Prediction accuracy is essential to set alert thresholds, and in that regard, the data-based models are generally superior.

The major contribution of this thesis is the design and installation of a prototype ice load panel with direct measurement of the ice pressure acting on a dam. The panel is attached on the upstream face of the dam and is large enough so that the whole thickness of the ice sheet is in contact with the panel. The predicted ice load from the best available model that includes loads from both thermal events and water level changes did not correspond to the measured ice loads. As there are no validated models or measurement methods for ice load on the dam, continued research is necessary, both through further measurements to increase knowledge and development of models.

Abstract [sv]

I många länder närmar sig vattenkraftsdammarna deras förväntade tekniska livslängd. Korrekt utvärdering av dammens strukturella status ökar kunskapen om det nuvarande säkerhetsläget och möjliggör för bättre planering av renoveringar och ombyggnadsinvesteringar. Betongdammarnas beteende styrs till stor del av variationen i omgivande temperaturer och vattennivå. I kalla regioner kan is som bildas i magasinet utsätta dammen för en tryckande last. Teoretiskt har denna belastning en betydande inverkan på dammarsstrukturella beteende. Trots detta är den maximala storleken såväl som säsongsvariationen för islasten en av de mest betydande osäkerheterna vidsäkerhetsbedömningen av dammar.

Denna uppsats presenterar forskning som undersöker hur förväntat beteendehos dammar i kallt klimat kan modelleras. Den underliggande frågeställningen är att förutsäga en damms respons orsakad av variation i de yttre förhållandena. Extra fokus har lagts på förståelsen och modelleringen av islasten då den är en viktig del av de yttre förhållandena för dammar i kalla klimat. Modeller som är lämpliga för att förutsäga dammars beteende kan delas upp i teoretiska, databaserad, och hybridmodeller. Förutsägbarhetsnoggrannhet är avgörande för att ställa in varningsnivåer, och i det avseendet är de databaserade modellerna i allmänhet överlägsna.

Det huvudsakliga bidraget från detta projekt är utvecklandet och installationen av en prototyp av en islast panel, fäst på en damms uppströmssida. Panelen mäter istrycket direkt mot dammen och är tillräckligt stor så att helaisens tjocklek förblir i kontakt med panelen. Panelen bidrar till ökad kunskap om säsongsvariationen i istryck och mekanismen för islaster orsakad av variation i vattennivån. Den predikterade islaten från den bästa tillgängliga islastmodellen som inkluderar termiska islaster och islaster från vattennivåförändringar överensstämmer inte med de uppmätta islastpanelen som uppmätts med panelen. Då det saknas validerade modeller eller mätmetoder för islast är det viktigt med fortsatt forskning, dels genom ytterligare mätningar för att öka kunskapen men även fortsatt modellutveckling.

Place, publisher, year, edition, pages
Stockholm: KTH Royal Institute of Technology, 2019. p. 104
Series
TRITA-ABE-DLT ; 1934
Keywords
dam safety, dams, data analysis, monitoring, statistical models, hydraulic structures, static ice loads, concrete dams, cold regions
National Category
Civil Engineering Civil Engineering
Research subject
Civil and Architectural Engineering, Concrete Structures
Identifiers
urn:nbn:se:kth:diva-259719 (URN)978-91-7873-301-9 (ISBN)
Presentation
2019-10-23, B25, Brinellvägen 23, Stockholm, 10:00 (English)
Opponent
Supervisors
Note

QC 20190926

Available from: 2019-09-26 Created: 2019-09-25 Last updated: 2019-09-26Bibliographically approved
Bennerstedt, P., Hellgren, R., Bond, H., Halvarsson, A. & Bond, H. (2019). Konstruktion av avbördningsanordningar: En jämförelse av nuvarande, nya, äldre och internationellt använda normer - Energiforskrapport 2019:572. Stockholm, Sweden
Open this publication in new window or tab >>Konstruktion av avbördningsanordningar: En jämförelse av nuvarande, nya, äldre och internationellt använda normer - Energiforskrapport 2019:572
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2019 (Swedish)Report (Other academic)
Abstract [sv]

Under 2017 uppdaterades RIDAS Tillämpningsvägledning för betongdammar så att lastkombinering för tvärsnittsdimensionering av betongdammar sker enligt Eurokoderna. I denna rapport presenteras en utredning av de konsekvenser som kan förväntas om RIDAS Tillämpningsvägledning för betongdammar (TV 7.3) tillämpas även för dimensionering av avbördningsanordningar. Detta görs genom en genomgång av hur vanligt förekommande laster inom vattenbyggnad hanteras och genom jämförande beräkningar. Även en internationell jämförelse presenteras där de standarder som används internationellt för dimensionering av avbördningsanordningar dokumenterats. Tyngdpunkten i den internationella jämförelsen ligger på länder som använder Eurokoderna. Dessutom har en historisk tillbakablick genomförts där de normer, som har använts i Sverige under tidsperioden då stora delar av dagens avbördningsanordningar byggdes, har dokumenterats. Den internationella jämförelsen visar att de i Sverige använda partialkoefficienterna ger lägre totalsäkerhetsfaktor än övriga studerade länder. Eurokoderna används för dimensionering av avbördningsanordningar i Finland, Tyskland och Norge där respektive land applicerar de dammsäkerhetsrelaterade lasterna olika. Även jämförelsen av koefficienter med äldre svenska normer visar att nuvarande riktlinje RIDAS TV 7.4, som hänvisar till BSK, samt en tillämpning av RIDAS TV 7.3 exklusive korrektionskoefficienten γk ger lägre totalsäkerhetsfaktor än äldre stålbyggnadsnormer (StBK 70 och Järnbestämmelser 1931). Jämförande beräkningar har utförts för utvalda bärande delar tillhörande en segmentlucka enligt nuvarande riktlinjer RIDAS TV 7.4 (BSK), enligt RIDAS TV 7.3 (Eurokoder) samt enligt DIN 19704 (Eurokoder). I jämförelsen av de tre beräkningsnormerna visas att en tillämpning av RIDAS TV 7.3 (exklusive korrektionskoefficienten γk) ger ungefär samma totalsäkerhet som nuvarande riktlinjer men lägre totalsäkerhet än DIN 19704. Slutsatsen är att Eurokoderna bör användas vid dimensionering av nya avbördningsanordningar och lastkombinering bör göras likt RIDAS TV 7.3. Vidare bör implementerandet av en korrektionskoefficient utredas för att konstruktionerna inte ska designas med lägre totalsäkerhet än internationellt.

Abstract [en]

The current RIDAS application guidelines for concrete dams, updated in 2017, refers to Eurocode for cross-sectional design. This report presents an investigation of the consequences from using RIDAS application guidelines for concrete dams (TV 7.3) for the design of spillway gates. A comparison between how different design guidelines for hydraulic structures treats loads are performed together with calculations that compare the different guidelines. Besides this, a review of international guidelines for spillway gates has been performed with the focus on countries which apply Eurocode. In addition, a historical presentation of the design guidelines used in Sweden during the time period when a majority of today's gates were built is presented. The international comparison shows that partial coefficients applied in Sweden result in steel members with lower overall safety factor than all other studied guidelines. Eurocode applies for the design of spillway gates in Finland, Germany, and Norway. The countries have separate and different approaches on how to apply loads and load combinations. Older Swedish guidelines for steel design (StBK 70 and Järnbestämmelser, 1931) indicate a higher coefficient of safety than RIDAS TV 7.4 (BSK) and RIDAS TV 7.3 (Eurocode) without the corrective coefficient. Design calculations for major members of a segment gate were conducted according to BSK/BKR, to RIDAS TV 7.3 (Eurocode) and to DIN 19704 (Eurocode). The conclusion from comparing the results was that applying RIDAS TV 7.3 results in similar overall safety as BSK/BKR but lower than DIN 19704. This study concludes that Eurocode should be applied for the design of spillway gates and load combination should be performed similarly as for cross-sectional design of concrete dams. Whether a corrective coefficient should be included in the guidelines to achieve an overall safety which is not substantially lower than internationally should be further investigated.

Place, publisher, year, edition, pages
Stockholm, Sweden: , 2019. p. 46
National Category
Civil Engineering
Identifiers
urn:nbn:se:kth:diva-255285 (URN)9789176735725 (ISBN)
Note

QC 20190902

Available from: 2019-07-28 Created: 2019-07-28 Last updated: 2019-09-02Bibliographically 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
Hellgren, R., Malm, R. & Eriksson, D. (2019). Modelling of the ice load on a Swedish concrete dam using semi-empirical models based on Canadian ice load measurements. In: Jean-Pierre Tournier, Tony Bennett & Johanne Bibeau (Ed.), Sustainable and Safe Dams Around the World: . Paper presented at ICOLD 2019 Symposium (pp. 3068-3080). , 2
Open this publication in new window or tab >>Modelling of the ice load on a Swedish concrete dam using semi-empirical models based on Canadian ice load measurements
2019 (English)In: Sustainable and Safe Dams Around the World / [ed] Jean-Pierre Tournier, Tony Bennett & Johanne Bibeau, 2019, Vol. 2, p. 3068-3080Conference paper, Published paper (Refereed)
Abstract [en]

In cold regions where the water surface of a river or lake freezes during the winter, concrete dams may be subjected to a pressure load from the ice sheet. This pressure load may constitute a large portion of the total horizontal load acting on a small dam. From a dam safety perspective, it is important to determine the design value of the ice load. In February 2016, a prototype of an ice load panel was installed on a Swedish concrete dam. The 1x3m2 panel measures the ice pressure with three load cells. In this paper, the ice load measured on the Swedish dam is predicted using a Canadian empirical model, previously developed from a 9-year field program to estimate the ice loads caused by thermal effects and variation in water level. The predictions from the model could not accurately predict the measured ice loads. Since the current understanding of ice load is limited, it is not possible to determine whether the measurement, the model or both are inaccurate.

National Category
Civil Engineering
Research subject
Civil and Architectural Engineering
Identifiers
urn:nbn:se:kth:diva-253821 (URN)
Conference
ICOLD 2019 Symposium
Note

QC 20190624

Available from: 2019-06-18 Created: 2019-06-18 Last updated: 2019-09-25Bibliographically approved
Hellgren, R., Malm, R., Persson, A. & Klasson Svensson, E. (2017). Estimating the effect of ice load on a concrete dams displacement with regression models. In: Proceedings ICOLD 2017 International Symposium: Knowledgebased dam engineering. Paper presented at ICOLD 2017 International Symposium: Knowledge based Dam Engineering. Prag
Open this publication in new window or tab >>Estimating the effect of ice load on a concrete dams displacement with regression models
2017 (English)In: Proceedings ICOLD 2017 International Symposium: Knowledgebased dam engineering, Prag, 2017Conference paper, Published paper (Refereed)
Abstract [en]

In colder climates, the ice load is an important factor to consider when assessing the dam safety. The size of the ice load is associated with uncertainties, regarding both its maximum size and seasonal variation. There is today no reliable method to determine the ice load acting on a dam, since available measurements and theories results in a large scatter regarding the maximum ice loads.

In this project, the possibility to determine the ice load based on traditional measurements of a dam behavior is investigated. It’s evaluated if the ice thickness is a significant predictor for the displacement of a Swedish arch dam. A case study on inverted pendulums was performed where dynamic regression models were used to calculate the displacement of the dam.

The model showed significant results which could explain the displacements. The ice thickness shows an effect on a 5 % significance level. The results indicate that the seasonal ice load is large enough to be traceable, and could be determined from conventional pendulum measurements. Since pendulums are installed on a large number of dams, a method that estimates the ice load from those measurements could vastly reduce uncertainties regarding ice loads on dams.

Place, publisher, year, edition, pages
Prag: , 2017
Keywords
Ice pressure
National Category
Infrastructure Engineering
Research subject
Land and Water Resources Engineering
Identifiers
urn:nbn:se:kth:diva-220979 (URN)
Conference
ICOLD 2017 International Symposium: Knowledge based Dam Engineering
Note

QCR 20180115

Available from: 2018-01-10 Created: 2018-01-10 Last updated: 2018-01-15Bibliographically 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
Malm, R., Johansson, F., Hellgren, R. & Ríos Bayona, F. (2017). Load Capacity of Grouted Rock Bolts Due to Degradation: 2017:374. Energiforsk AB
Open this publication in new window or tab >>Load Capacity of Grouted Rock Bolts Due to Degradation: 2017:374
2017 (English)Report (Other academic)
Abstract [en]

In this report, the influence of degradation on the strength of rock bolts has been studied. A literature study has been performed in order to determine the degradation rate and to present observations and conclusions from available assessments of rock bolts. All cases found in the literature have shown that the rock bolts on concrete dams are in good condition with only minor superficial corrosion even after 50 years of service. In the project, a methodology to account for the degradation mechanism in evaluations of dam safety is presented, where all possible failure modes of rock bolts are considered. The contribution of the rock bolts to the dam stability is based on the failure mode with the lowest strength. The degradation has been taken into account based on a German DIN standard based on the chemical content of the water. Most available field tests have only measured the load capacity of bolts, where the deformation is typically not recorded. The relationship between forces and deformations is however important input to verify numerical and analytical analyses. Therefore, field tests have been performed on rock bolts that been in service for 50 years. A previously developed test rig had been modified in this project to register both load and deflection of the pull-out test. The test rig consists of a hydraulic jack that presses a cylinder towards the rock surrounding the bolt. Due to this configuration of the test equipment, a rock cone failure cannot be captured. The results showed that the test rig may influence the obtained load capacity if the failure occurs in the grout. A case study is presented where analytical, probabilistic and finite element analyses were performed to assess the dam safety. Based on the numerical analyses, it was possible to study the development of forces in the rock bolts due to successively increasing loads. The numerical analyses showed (as expected) that the rock bolts are subjected to both shear and tensile forces at the same time. In addition, the shear force was constantly higher than the tensile forces and that the shear forces were about 10% of the total shear resistance for normal loads. This implies that it is important to use a failure criterion for the rock bolts that considers combinations of tensile and shear forces. Besides this, the probabilistic analyses showed that pure overturning failure is extremely unlikely and cannot be considered as a relevant failure mode. The numerical analyses showed that the deformation start as for overturning failure resulting in that parts of the contact surface (on the upstream side) lose its contact. Thereby, the shear forces have to be transmitted over a reduced area which initiates the sliding failure. This implies that it is more suitable to define a criterion that limits the tensile forces in the upstream toe from serviceability loads, rather than having an overturning failure criterion.

Abstract [sv]

I föreliggande rapport har bärförmågan hos slaka bergsförankringar (bergbultar) studerats med hänsyn till inverkan av nedbrytning. Detta projekt har som första steg genomförts som en litteraturstudie för att bestämma lämplig spridning på korrosionshastigheten, men även för att hitta information från genomförda inspektioner och statusbedömningar. Samtliga fall som har hittats i litteraturen visar att bergbultar för förankring av betongdammar varit i mycket god kondition med endast begränsad ytlig korrosion, trots att bultarna kan ha varit i drift i mer än 50 år. I projektet har en metodik utvecklats där nedbrytningen av bergbultar kan inkluderas vid stabilitetsberäkningar av betongdammar. I denna metod inkluderas samtliga potentiella brottmoder, där den med lägst bärförmåga blir styrande. Eventuell reduktion av bärförmågan sker genom att nedbrytningen skattas baserat på vattnets kemiska innehåll i enlighet med en tysk DIN norm. De flesta fältprovningar av bergbultar redovisar endast lastkapaciteten d.v.s. själva deformationsförloppet vid provdragning saknas. Detta är dock mycket viktig input till att kunna verifiera numeriska och analytiska beräkningar. Inom projektet har därför även egna fältprovningar genomförts av bergbultar som varit i drift i ca 50 år. En vidareutveckling av den testrigg som använts vid tidigare försök genomfördes för att kunna registrera både belastning och deformation. Testriggen består av en hydrauliskkolv som trycker en cylinder mot berget som omsluter bergbulten. På grund av testriggens utformning går det ej att fånga ett eventuellt konbrott i berget. Resultaten visade dock att denna metod kan överskatta bärförmågan i de fall då brottet sker i bruket, p.g.a. inspänningseffekter från testutrustningen. En fallstudie presenteras i rapporten avseende stabilitetsberäkningar med den analytiska metodiken, finita elementanalyser samt probabilistiska analyser. De numeriska analyserna visade, som väntat, att bultarna belastas av kombinationer av drag- och skjuvkrafter. Resultaten visade även att skjuvkrafterna konstant var högre än normalkrafterna i bulten, och att dessa motsvarande ca 10 % av totala skjuvmotståndet mot glidning vid normala lastnivåer. Detta illustrerar vikten av att inkludera ett brottvillkor där kombinationer av drag och skjuvkrafter kan beaktas. De probabilistiska analyserna visade att sannolikheten för stjälpning är extremt låg, därmed bör denna knappast anses vara en rimlig brottmod. Från de numeriska analyserna framgick att deformationen ofta startar enligt en stjälpningsbrottmod där uppströmstån förlorar kontakten, detta leder dock till att skjuvkraften måste bäras av en mindre yta vilket initierar ett glidbrott. Detta indikerar att det vore mer lämpligt att definiera en brottmod som avser begränsning av dragspänningar i uppströmstån för bruks¬gräns¬tillstånd, istället för en stjälpningsbrottmod.

Place, publisher, year, edition, pages
Energiforsk AB, 2017. p. 71
National Category
Infrastructure Engineering
Identifiers
urn:nbn:se:kth:diva-221063 (URN)978-91-7673-374-5 (ISBN)
Note

QC 20180115

Available from: 2018-01-11 Created: 2018-01-11 Last updated: 2018-01-15Bibliographically approved
Malm, R., Hassanzadeh, M. & Hellgren, R. (Eds.). (2017). Proceedings of the 14th ICOLD International Benchmark Workshop on Numerical Analysis of Dams. Paper presented at 14th ICOLD International Benchmark Workshop on Numerical Analysis of Dams. KTH Royal Institute of Technology
Open this publication in new window or tab >>Proceedings of the 14th ICOLD International Benchmark Workshop on Numerical Analysis of Dams
2017 (English)Conference proceedings (editor) (Refereed)
Abstract [en]

Every second year, the Technical Committee A (Computational Aspects of Dam Analysis and Design) of ICOLD organizes an international benchmark workshop on numerical analysis of dams. The purpose is to share knowledge and experience regarding numerical modelling within the fields of dam safety, planning, design, construction as well as operation and maintenance of dams. The Terms of Reference for Committee A state; ”BenchmarkWorkshops are organised to compare numerical models between one another and/or with reference solutions, including the dissemination and publication of results”.

 The 14th ICOLD International Benchmark Workshop on Numerical Analysis of Dams was held from the 6th to the 8th September 2017 in Stockholm, the capital of Sweden. It was organized by the Local Organizing Committee, on behalf of the Swedish National Committee of ICOLD (SwedCold) and the ICOLD Technical Committee A. It was hosted by KTH Royal Institute of Technology, Sweden’s largest technical research and learning institution and one of Europe’s leading technical universities. With respect to hydropower and dam engineering, KTH has for many years been active within of the Swedish hydropower Center (SVC), a key centre for research and educational activities in Sweden. SwedCOLD established in 1931, and is one of the oldest members of the International Commission On Large Dams, ICOLD. The development of hydro power for electricity production was initiated in the late 19th century and made the large scale industrialisation in Sweden possible. About 2000 hydropower plants are in operation in Sweden today, producing almost half of the total electricity supply. Considering the many and relatively old dams in Sweden, organizing the benchmark workshop was important to increase the knowledge regarding managing aging hydropower structures.

The 14th ICOLD International Benchmark Workshop has addressed current challenges regarding design and maintenance of existing dams and improved the understanding of these by exchange of experience on the use of numerical modelling for design, performance evaluation and safety assessment of dams. On behalf of the organizing committee, I would like to express my sincere appreciation to the formulators/moderators of each theme for their outstanding work to prepare the themes, reviewing the papers and evaluating the results. I also want to thank all participants to the benchmark workshop for their contributions and their presence to this benchmark workshop. Finally, the support from the Technical Committee A and the support from the companies and organizations that sponsored this benchmark workshop is gratefully acknowledged.

Place, publisher, year, edition, pages
KTH Royal Institute of Technology, 2017. p. 720
Series
TRITA-ABE-RPT ; 1802001
Keywords
numerical analyses, dams, hydropower, concrete dams, embankment dams
National Category
Infrastructure Engineering Water Engineering Geotechnical Engineering
Research subject
Civil and Architectural Engineering
Identifiers
urn:nbn:se:kth:diva-223593 (URN)
Conference
14th ICOLD International Benchmark Workshop on Numerical Analysis of Dams
Note

QC 20180306

Available from: 2018-02-28 Created: 2018-02-28 Last updated: 2018-03-06Bibliographically approved
Organisations
Identifiers
ORCID iD: ORCID iD iconorcid.org/0000-0003-2594-4107

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