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| 2. |
- Bennerstedt, Patrik, et al.
(author)
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Konstruktion av avbördningsanordningar : En jämförelse av nuvarande, nya, äldre och internationellt använda normer - Energiforskrapport 2019:572
- 2019
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Reports (other academic/artistic)abstract
- 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.
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| 3. |
- Eriksson, Daniel, 1987-, et al.
(author)
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Assessment of frost damage in hydraulic structures using a hygro-thermo-mechanical multiphase model
- 2019
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In: Sustainable and Safe Dams Around the World. ; , s. 332-346
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Conference paper (peer-reviewed)abstract
- 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.
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| 4. |
- Hellgren, Rikard, 1988-, et al.
(author)
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A parametric numerical study of factors influencing the thermal icepressure along a dam
- 2020
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In: Proceedings of the 25th IAHR International Symposium on Ice (Trondheim, 2020). - Trondheim.
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Conference paper (peer-reviewed)abstract
- The uncertainty regarding size and variation of the ice pressure constitute one of the mainsignificant sources of concern for condition assessment of concrete dams in cold regions. Inmost current dam safety guidelines, the design ice load is determined solely from thegeographic location of the dam. However, factors such as variation in temperature and waterlevel, the slope of the banks, wind etc. may also influence the size of the load. Previousmeasurements indicate that the pressure on a dam varies along the dam line during the sametime and that the average ice pressure decreases as the area of the ice-structure interface isincreased. This paper presents numerical studies on how the ice pressure varies along the damwall. A finite element model that includes several dam monoliths, the ice and the beaches ofthe reservoirs are used to simulate thermal ice loads. The pure elastic load caused by therestrained expansion of an ice sheet subjected to a change in thermal gradient are greater thanthe design ice load in current dam safety guidelines and the loads measured. The simulationsshow that the ice load vary significantly along the dam, and the variation in cross-sectionstiffness along the dam greatly influence the magnitude of the total ice pressure. Theparameter study shows that the elastic thermal ice load increases with an increased slope ofthe banks, reservoir length, and ice thickness and decreases as the angle of the connectionbetween the dam and bank increases. However, the difference in ice load between theindividual monoliths with the same geometry and temperature change are in several cases ofthe same magnitude as the variation in the external factors.
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| 5. |
- Hellgren, Rikard, 1988-
(author)
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A systems approach to ice loads on concrete dams
- 2022
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Doctoral thesis (other academic/artistic)abstract
- Dams are mainly used for the storage of water to electricity production and irrigation, or for river regulation. Continuous work to assure a high dam safety level is a prerequisite to minimize the risk for the uncontrolled release of water. An essential part of the safety evaluation of concrete dams is to understand the loads they are exposed to and the expected response of the dam. Under normal conditions, the behaviour of concrete dams is, to a great extent, governed by the ambient variation in temperature and water level. For concrete dams in cold climates, the large variation in ambient temperatures between summer and winter is particularly significant. In addition, these dams may be subjected to a pressure load from the expansion or movement of an ice sheet on the reservoir. The current guidelines for these ice loads are based on the dam's location and state that concrete dams must be designed for a line load of 50-250 kN/m. Thus, the ice load constitutes a significant part of the total load, especially for small dams. Despite its relatively significant impact, the knowledge about ice loads is insufficient, and the magnitude and return period of ice loads constitute one of the greatest uncertainties during stability evaluations of concrete dams. Furthermore, an apparent contradiction is that measurements and models indicate that ice loads are higher than the recommended values. Simultaneously, there are no reported dam failures where the ice-load has been addressed as the reason for the breach.To increase the knowledge about ice loads and the structural behaviour of concrete dams, this thesis applies an approach where the ice and the dam are parts of a structural system. The thesis contains six studies investigating the dam's, the ice's or the system's response to external loads. Studies of the dam are aimed at increasing the understanding of the normal behaviour of concrete dams. Studies of ice loads include measurements, and a major contribution from this project is the development of a 1$\times$3 m$^2$ ice load panel, the installation of the panel on a concrete dam, and subsequent measurements during six winters. In addition, a systematic review and meta-analysis of previous measurements have been performed. The studies of the different parts have been connected through two studies of the entire system. The first is a parameter study where the static interaction between ice and dam is simulated to quantify how geometric variations of the reservoir and ice affect the mechanical ice loads. The second study searches for detectable influence from the ice load in the measured behaviour of concrete dams.The results show that the structural behaviour of concrete dams under normal conditions is primarily governed by the variation in water level and temperature. For the studied dams, these effects are significantly larger than the influence from damage and degradation. Ice load measurements and simulations show that ice loads varies significantly along the dam. This variation makes it difficult to quantify the impact of external factors on the magnitude of ice loads. Despite this difficulty, three independent analyses show that ice thickness, water level change, and the dam's properties have an evident effect on the magnitude of ice loads. If current guidelines are to be updated to consider local conditions at the dam, these three parameters should be included. Ice loads of the magnitudes measured and specified in the current guidelines should have a notable impact on the behaviour of a dam during normal operation. However, such an impact has not been found in the eight dams studied within this project. This result indicates that the ice loads measured locally do not necessarily represent the global ice load that acts on the entire structure.
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| 6. |
- Hellgren, Rikard, 1988-
(author)
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Condition assessment of concrete dams in cold climate
- 2019
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Licentiate thesis (other academic/artistic)abstract
- 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.
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| 7. |
- Hellgren, Rikard, 1988-, et al.
(author)
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Estimating the effect of ice load on a concrete dams displacement with regression models
- 2017
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In: <em>Proceedings ICOLD 2017 International Symposium</em>. - Prag.
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Conference paper (peer-reviewed)abstract
- 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.
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| 8. |
- Hellgren, Rikard, 1988-, et al.
(author)
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Estimating the ice loads on concrete dams based on their structural response
-
Other publication (other academic/artistic)abstract
- In the assessment of concrete dams in cold climate, it is common that the theoretical stability becomes insufficient for load cases that includes ice loads. However, the magnitude and return period of these ice loads have a high degree of uncertainty. This study estimates the magnitude of ice loads on eight concrete dam monoliths using measurements of their displacement from 29 winters. In the displacement signals, events are identified and assumed to be caused solely by ice loads. The observed displacement during an event is interpreted as an ice load using a load-displacement relationship derived from FE simulations of each dam. These simulations show that ice loads of the magnitudes given in design guidelines and recorded in previous measurements would significantly affect the structural response of the studied dams. However, only small traces of ice loads can be found in the observed responses of the studied dams. The estimated ice loads are significantly lower than the ice loads recorded in traditional ice load measurements. These results indicate that the average magnitude of ice load on an entire monolith is significantly lower than the measured local pressures. This would imply that ice loads may be a smaller concern regarding the dam safety than previously believed.
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| 9. |
- Hellgren, Rikard, 1988-, et al.
(author)
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Estimating the Ice Loads on Concrete Dams Based on Their Structural Response
- 2022
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In: Water. - : MDPI AG. - 2073-4441. ; 14:4
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Journal article (peer-reviewed)abstract
- In the assessment of concrete dams in cold climate, it is common that the theoretical stability becomes insufficient for load cases that include ice loads. However, the magnitude and return period of these ice loads have a high degree of uncertainty. This study estimates the magnitude of ice loads on eight concrete dam monoliths using measurements of their displacement from 29 winters. In the displacement signals, events are identified and assumed to be caused solely by ice loads. The observed displacement during an event is interpreted as an ice load using a load-displacement relationship derived from FE simulations of each dam. These simulations show that ice loads of the magnitudes given in design guidelines and recorded in previous measurements would significantly affect the structural response of the studied dams. However, only small traces of ice loads can be found in the observed responses of the studied dams. The estimated ice loads are significantly lower than the ice loads recorded in traditional ice load measurements. These results indicate that the average magnitude of ice load on an entire monolith is significantly lower than the measured local pressures. This would imply that ice loads may be a smaller concern regarding dam safety than previously believed.
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| 10. |
- Hellgren, Rikard, 1988-, et al.
(author)
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Fluid structure interaction
- 2015
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In: International Water Power and Dam Construction. - 0306-400X. ; :8, s. 40-45
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Journal article (peer-reviewed)abstract
- The aim of this study is to investigate how Fluid-Structure interaction may beincluded in numerical earthquake analyses of dams. The basis for this project is theme Afrom ICOLDs 12th international benchmark workshop on numerical analysis of dams,which was held in October 2013. The focus of theme A was on how to account for fluidstructure interaction in numerical earthquake analyses of dams. In this study, parametricnumerical analyses have been performed where the purpose was to isolate someimportant parameters and investigate how these influence the results in seismic analysesof dams. These analyses were performed through the use of the finite element methodare the choice of Rayleigh damping parameters, reservoir boundaries and waveabsorption in the foundation-reservoir interface. The use of acoustic elements has proven to be a powerful approach for FSI analyses of adam-reservoir-computation time, while allowing for more advanced features such as bottom absorptionand non-be a challenging task, where it has a significant impact on the results. The methodproposed by Spears and Jensen has a physical meaning in the sense that this methodexcites the same e ective mass for the Rayleigh damped case as for the modal dampedcase. If a constant modal damping is desired or prescribed in a standard, this methodprovides a reasonable and sound method to choose the Rayleigh damping parameters fora complex structure. A more straightforward method is to choose the two frequencies insuch a way that the span between the frequencies covers about 80% of the e ective mass.The choice of reservoir boundary conditionsparameter showed to be the one that least a ected the results in the time-history analysis.results and this coe cient should be used carefully.
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