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A systems approach to ice loads on concrete dams
KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Concrete Structures.ORCID iD: 0000-0003-2594-4107
2022 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

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.

Abstract [sv]

Dammar används främst för att lagra vatten för elproduktion och bevattning eller för flödesreglering. Ett kontinuerligt arbete med att säkerställa en hög dammsäkerhetsnivå är en förutsättning för att minimera risken för ett okontrollerat utsläpp av vatten från dessa dammar. En viktig del av säkerhetsutvärdering av betongdammar är förståelse för de laster som dessa utsätts för samt kunskap om dammens förväntade respons. Under normala förhållanden påverkas en betongdamms strukturella beteende främst av variationer i vattennivån och de omgivande temperaturerna. För betongdammar i kallt klimat är den stora variationen i temperatur mellan sommar och vinter särskilt betydande. Dessutom kan dessa dammar utsättas för ett tryck från expansion och rörelse hos det istäcke som kan bildas på magasinet. För betongdammar utgör storleken på denna islast en betydande osäkerhet. De nuvarande riktlinjerna är geografiskt baserade och anger att betongdammar ska dimensioneras för en linjelast med storleken 50-250 kN/m. En sådan storlek innebär att islasten, särskilt för små dammar, utgör en betydande del av den totala lasten. Trots dess relativt stora påverkan är kunskapen om islaster låg och utgör för tillfället en av de största osäkerheterna vid utvärdering av betongdammars stabilitet. Det finns dessutom en motsättning där mätningar och modeller visar att islasten är högre än de rekommenderade värdena, samtidigt som det inte finns några rapporterade dammhaverier orsakade av islast.

I denna avhandling behandlas isen och dammen som ett system för att på sätt öka förståelse kring både islaster och betongdammars beteende under normal drift. Avhandlingen innehåller sex enskilda studier som studerar dammens, isens eller systemets respons till yttre variationer. Dammen har studerats genom transienta analyser i syfte att öka förståelsen kring, och upptäcka avvikelser i betongdammars normalbeteende. Isen har studerats genom mätningar där ett stort bidrag från detta projekt är utvecklingen av en 1$\times$3m$^2$ islastpanel, installationen av denna panel på en betongdamm, och efterföljande mätningar under sex vintrar. Dessutom har en systematisk sammanställning och analys av tidigare mätningar genomförts. Dessa studier har sammanlänkats genom två studier av hela systemet. Den första av dessa är en parameterstudie där den statiska interaktionen mellan is och damm simuleras i syfte att kvantifiera hur geometriska variationer hos vattenmagasinet och isen påverkar den mekaniska islasten. Den andra studien innefattar transienta analyser av betongdammars beteende med syfte att detektera inverkan från islast i det uppmätta beteende hos betongdammar.  

Variation i vattennivå och temperatur har större påverkan på det strukturella beteendet under normaldrift hos de studerade dammarna än irreversibla förändringar orsakade av nedbrytningsprocesser och skador. Islastmätningar och simuleringar visar att islasten varierar betydande längs med dammen. Detta försvårar kvantifierandet av inverkan från yttre faktorer på islastens storlek. Trots detta visar tre oberoende analyser att istjocklek, vattennivåförändring och dammens egenskaper har en signifikant påverkan på islastens storlek. Om nuvarande riktlinjer ska uppdateras för att beakta lokala förhållanden vid dammen bör dessa parametrar inkluderas. Islaster av de storlekar som uppmätts och anges i de nuvarande riktlinjerna bör ha en tydlig påverkan på dammens beteende vid normaldrift. En sådan påverkan har dock inte observerats hos de åtta dammar som studerats i detta projekt. Det ger en indikation om att de islaster som mäts lokalt inte nödvändigtvis är representativa för den globala islasten som verkar på hela dammen.

Place, publisher, year, edition, pages
Stockholm: KTH Royal Institute of Technology, 2022. , p. 136
Series
TRITA-ABE-DLT ; 221
Keywords [en]
Ice loads, Ice pressure, Dam safety, Concrete dams, Cold regions, Monitoring, Measurements
National Category
Infrastructure Engineering
Research subject
Civil and Architectural Engineering, Concrete Structures
Identifiers
URN: urn:nbn:se:kth:diva-306937ISBN: 978-91-8040-115-9 (print)OAI: oai:DiVA.org:kth-306937DiVA, id: diva2:1626522
Public defence
2022-02-09, F3, Lindstedtsvägen 26, KTH Campus, Videolink - Password 627271 - https://kth-se.zoom.us/j/66770434327?pwd=NkZRMk9KdWU2S0U5dmtTVERsL05rZz09, Stockholm, 13:00 (English)
Opponent
Supervisors
Note

QC 20220111

Available from: 2022-01-11 Created: 2022-01-11 Last updated: 2022-06-25Bibliographically approved
List of papers
1. Performance of data-based models for early detection of damage in concrete dams
Open this publication in new window or tab >>Performance of data-based models for early detection of damage in concrete dams
2021 (English)In: Structure and Infrastructure Engineering, ISSN 1573-2479, E-ISSN 1744-8980, Vol. 17, no 2, p. 275-289Article in journal (Refereed) Published
Abstract [en]

A failure of a massive concrete dam could cause catastrophic consequences. The purpose of monitoring is to detect anomalies and damage at an early stage to prevent failure. Data-based models for anomaly detection are based on the hypothesis that the behaviour of an undamaged dam will follow an expected pattern, and deviation from this pattern is an indication of damage. In this study, simulations were used to create time series for an undamaged dam and three different damage scenarios at three different locations in the dam body. Three common data-based models were used to predict a dams crest displacements, both on the generated artificial data and the corresponding measurements from the dam. Prediction bands for future measurements were created, and the ten time-series were used to test the ability to detect damage. All models could detect instantaneous damage but struggle to detect progressive damage; the Neural network outperforms the two regression models. The choice of the mathematically optimal threshold limit leads to a large number of false alerts. Requiring three consecutive values outside the threshold before an alert is issued, increases the possibility to receive an early alert compared to the standard approach where observations are classified individually.

Place, publisher, year, edition, pages
Informa UK Limited, 2021
Keywords
anomaly detection, concrete dam, Dam safety, data analysis, false alarms, monitoring, statistical models, Concrete dams, Concretes, Data reduction, Regression analysis, Time series, Catastrophic consequences, Different damages, Massive concrete, Optimal threshold, Progressive damage, Regression model, Damage detection
National Category
Infrastructure Engineering
Identifiers
urn:nbn:se:kth:diva-274273 (URN)10.1080/15732479.2020.1737146 (DOI)000519329200001 ()2-s2.0-85081265852 (Scopus ID)
Note

QC 20250303

Available from: 2020-07-07 Created: 2020-07-07 Last updated: 2025-03-03Bibliographically approved
2. Measurement of ice pressure on a concrete dam with a prototype ice load panel
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)000506666000001 ()2-s2.0-85075037308 (Scopus ID)
Note

QC 20191125

Available from: 2019-11-23 Created: 2019-11-23 Last updated: 2022-06-26Bibliographically approved
3. Ice load measurements on Rätan concrete dam using different sensor types
Open this publication in new window or tab >>Ice load measurements on Rätan concrete dam using different sensor types
2022 (English)In: Cold Regions Science and Technology, ISSN 0165-232X, E-ISSN 1872-7441, Vol. 193, article id 103425Article in journal (Refereed) Published
Abstract [en]

Concrete dams in cold regions are designed to withstand loads from the ice sheet on top of the reservoir. However, the ice load's magnitude and return period are among the most considerable uncertainties in safety assessments of concrete dams. In a previous study, the development and installation of a 1 × 3 m2 prototype ice load panel attached at the upstream face of a concrete dam was presented. The panel is large enough for the ice sheet's cross-section to remain in contact with the panel as the water level varies, and it measures the total ice load without interpolation. This paper presents measurement results from the load panel from winters 2018–19 and 2019–20, an update to the measurement design, and additional ice pressure measurements with traditional stress cells. The panel measured seasonal maximum ice loads of 100 and 200 kN/m for the two winters, respectively. Winter 2019–20, when the panel measured the largest loads, was mild for the location, with great ice thickness near the dam face (1.2 m) and an almost snow-free ice sheet throughout the winter. Two 2.75 × 1.75 m2 dummy panels were installed adjacent to the load panel prior to the winter 2019–20 to minimize the load panel's protruding effect. These panels significantly reduced the local impact, as evident by the crack-pattern of the ice sheet near the load panel. The load panel recorded large ice loads (>75 kN/m) for all combinations with increasing/decreasing air temperature and/or water level. Identification of temperature change events and water level change events during the winters, shows that a change in air temperature, water level, or any combination of these, is not sufficient alone to explain large ice loads at Rätan dam. These findings suggest that other conditions must be satisfied before a water level or temperature change results in large ice loads. In February 2020, three panels consisting of a steel frame with four stress cells on each were placed on the dummy panels’ upstream face, and one single stress cell was placed 6 m out in the reservoir in front of the load panel. The majority of the stress cells recorded ice pressure larger than their measurement range. At the end of the ice season, only two of the panels’ twelve stress cells were still functional, and the ice vastly deformed the steel frames. From the period before the frames were damaged and unrelated to the choice of interpolation method, the recordings by the three stress cell panels at the dam are among the historically largest inferred ice loads on dams.

Place, publisher, year, edition, pages
Elsevier BV, 2022
Keywords
Ice load, Concrete dam, Load panel, Stress cells, Ice pressure. Ice thickness
National Category
Infrastructure Engineering
Research subject
Civil and Architectural Engineering, Concrete Structures
Identifiers
urn:nbn:se:kth:diva-303904 (URN)10.1016/j.coldregions.2021.103425 (DOI)000721725100002 ()2-s2.0-85117401515 (Scopus ID)
Note

QC 20250328

Available from: 2021-10-21 Created: 2021-10-21 Last updated: 2025-03-28Bibliographically approved
4. Systematic literature search and meta regression of measured static ice loads on concrete dams
Open this publication in new window or tab >>Systematic literature search and meta regression of measured static ice loads on concrete dams
(English)Manuscript (preprint) (Other academic)
Abstract [en]

This study presents a systematic literature review of ice load measurements on dams. Several hypotheses about the relationship between the maximum ice load and external variables are tested using regression analysis on the data collected from the literature. The performed tests show that ice thickness, water level change category, and dam height are factors that have a significant and relevant relationship with the magnitude of all measured ice loads. The ice thickness is the only tested variable that also shows a significant and relevant relationship with differences in ice load between winters at one dam. The variation in recorded ice load from several sensor positions at one dam during the same winter is considerable. Generally, the difference between the sensor area and the structure-ice interaction area is large, resulting in extensive extrapolation and uncertainties regarding the representativeness of the measured results.

Keywords
Ice load, Concrete dams, Load panel, Stress cells, Ice pressure. Ice thickness
National Category
Infrastructure Engineering
Research subject
Civil and Architectural Engineering, Concrete Structures
Identifiers
urn:nbn:se:kth:diva-306935 (URN)
Note

QC 20220125

Available from: 2022-01-05 Created: 2022-01-05 Last updated: 2022-06-25Bibliographically approved
5. A parametric numerical study of factors influencing the thermal icepressure along a dam
Open this publication in new window or tab >>A parametric numerical study of factors influencing the thermal icepressure along a dam
2020 (English)In: Proceedings of the 25th IAHR International Symposium on Ice (Trondheim, 2020), Trondheim, 2020, article id 8563Conference paper, Published paper (Refereed)
Abstract [en]

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.

Place, publisher, year, edition, pages
Trondheim: , 2020
Series
IAHR International Symposium on Ice, ISSN 2414-6331
Keywords
Ice load; dam; concre dam; cold regions
National Category
Infrastructure Engineering
Research subject
Civil and Architectural Engineering, Concrete Structures
Identifiers
urn:nbn:se:kth:diva-301284 (URN)
Conference
25th IAHR International Symposium on Ice
Note

Part of proceedings: ISBN 978-82-7598-120-0

QC 20210907

Available from: 2021-09-07 Created: 2021-09-07 Last updated: 2023-04-05Bibliographically approved
6. Estimating the ice loads on concrete dams based on their structural response
Open this publication in new window or tab >>Estimating the ice loads on concrete dams based on their structural response
Show others...
(English)Manuscript (preprint) (Other academic)
Abstract [en]

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.

Keywords
Ice loads, Concrete dams, Back-calculation, Dam safety, Monitoring
National Category
Infrastructure Engineering
Research subject
Civil and Architectural Engineering, Concrete Structures
Identifiers
urn:nbn:se:kth:diva-306933 (URN)
Note

QC 20220125

Available from: 2022-01-05 Created: 2022-01-05 Last updated: 2022-06-25Bibliographically approved

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