Change search
Refine search result
1 - 17 of 17
CiteExportLink to result list
Permanent link
Cite
Citation style
  • apa
  • harvard1
  • ieee
  • modern-language-association-8th-edition
  • vancouver
  • Other style
More styles
Language
  • de-DE
  • en-GB
  • en-US
  • fi-FI
  • nn-NO
  • nn-NB
  • sv-SE
  • Other locale
More languages
Output format
  • html
  • text
  • asciidoc
  • rtf
Rows per page
  • 5
  • 10
  • 20
  • 50
  • 100
  • 250
Sort
  • Standard (Relevance)
  • Author A-Ö
  • Author Ö-A
  • Title A-Ö
  • Title Ö-A
  • Publication type A-Ö
  • Publication type Ö-A
  • Issued (Oldest first)
  • Issued (Newest first)
  • Created (Oldest first)
  • Created (Newest first)
  • Last updated (Oldest first)
  • Last updated (Newest first)
  • Disputation date (earliest first)
  • Disputation date (latest first)
  • Standard (Relevance)
  • Author A-Ö
  • Author Ö-A
  • Title A-Ö
  • Title Ö-A
  • Publication type A-Ö
  • Publication type Ö-A
  • Issued (Oldest first)
  • Issued (Newest first)
  • Created (Oldest first)
  • Created (Newest first)
  • Last updated (Oldest first)
  • Last updated (Newest first)
  • Disputation date (earliest first)
  • Disputation date (latest first)
Select
The maximal number of hits you can export is 250. When you want to export more records please use the Create feeds function.
  • 1.
    Bennerstedt, Patrik
    et al.
    WSP.
    Hellgren, Rikard
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Concrete Structures. WSP.
    Bond, Håkan
    WSP.
    Halvarsson, Andreas
    WSP.
    Bond, Håkan
    WSP.
    Konstruktion av avbördningsanordningar: En jämförelse av nuvarande, nya, äldre och internationellt använda normer - Energiforskrapport 2019:5722019Report (Other academic)
    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.

  • 2.
    Eriksson, Daniel
    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.
    Hellgren, Rikard
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Concrete Structures.
    Assessment of frost damage in hydraulic structures using a hygro-thermo-mechanical multiphase model2019In: Sustainable and Safe Dams Around the World / [ed] Jean-Pierre Tournier, Tony Bennett & Johanne Bibeau, 2019, Vol. 2, p. 332-346Conference 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.

  • 3.
    Hellgren, Rikard
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Concrete Structures.
    Condition assessment of concrete dams in cold climate2019Licentiate thesis, comprehensive summary (Other academic)
    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.

  • 4.
    Hellgren, Rikard
    et al.
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Concrete Structures.
    Gasch, Tobias
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Concrete Structures.
    Fluid structure interaction2015In: International Water Power and Dam Construction, ISSN 0306-400X, E-ISSN 1538-6414, no 8, p. 40-45Article in journal (Refereed)
    Abstract [en]

    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.

  • 5.
    Hellgren, Rikard
    et al.
    WSP Bridge and Hydraulic Design.
    Gasch, Tobias
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Concrete Structures. Vattenfall Engineering, Stockholm, Sweden.
    Influence of fluid structure interaction on a concrete dam during seismic excitation2015Conference paper (Refereed)
    Abstract [en]

    The aim of this study is to investigate how Fluid-Structure interaction may be included in numerical earthquake analyses of dams. The basis for this project is theme A from 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 fluid structure interaction in numerical earthquake analyses of dams. In this study, parametric numerical analyses have been performed where the purpose was to isolate some important parameters and investigate how these influence the results in seismic analyses of dams. These analyses were performed through the use of the finite element methodare the choice of Rayleigh damping parameters, reservoir boundaries and wave absorption 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 absorption and non- be a challenging task, where it has a significant impact on the results. The method proposed by Spears and Jensen has a physical meaning in the sense that this method excites the same e ective mass for the Rayleigh damped case as for the modal damped case. If a constant modal damping is desired or prescribed in a standard, this method provides a reasonable and sound method to choose the Rayleigh damping parameters for a complex structure. A more straightforward method is to choose the two frequencies in such 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.

  • 6.
    Hellgren, Rikard
    et al.
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Concrete Structures.
    Gasch, Tobias
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Concrete Structures.
    Influence of fluid structure interaction on a concrete dam during seismic excitation2015In: Dam Engineering, ISSN 0958-9341, Vol. XXVI, no 2, p. 1-15Article in journal (Refereed)
    Abstract [en]

    The aim of this study is to investigate how fluid-structure interaction (FSI) may be included in numerical earthquake analyses of dams. The basis for this project is Theme A from ICOLD’s 12th International Benchmark Workshop on Numerical Analysis of Dams[5], which was held in October 2013 in Austria. The focus of Theme A was on how to account for fluid-structure interaction in numerical earthquake analyses of dams. In this study, parametric numerical analyses have been performed, where the purpose was to isolate some important parameters and investigate how these influence the results in seismic analyses of dams. These analyses were performed through the use of the finite element method, where the reservoir was modelled with acoustic finite elements. The studied parameters are the choice of Rayleigh damping parameters, reservoir boundaries, and wave absorption in the foundation-reservoir interface.

     

    The use of acoustic elements has proven to be a powerful approach for FSI analyses of a dam-reservoir-foundation system. The acoustic finite elements provide reasonable computation time, while allowing for more advanced features such as bottom absorption and non-reflecting boundaries. The choice of Rayleigh damping coefficients has proven to be a challenging task,

    where it has a significant impact on the results. The method proposed by Spears & Jensen[1] has a physical meaning in the sense that this method excites the same effective mass for the Rayleigh damped case as for the modal damped case. If a constant modal damping is desired, or prescribed in a standard, this method provides a reasonable and sound method to choose the Rayleigh damping parameters for a complex structure. A more straightforward method is to choose the two frequencies in such a way that the span between the frequencies covers about 80% of the effective mass. The choice of reservoir boundary conditions was based on the assumption of an infinite reservoir. A conservative approach is to use a fixed boundary condition, where the pressure waves are reflected at the upstream boundary of the reservoir. However, this parameter proved to be the one that least affected the results in the time-history analysis. The reflection coefficient describing bottom absorption showed to greatly influence the results, and this coefficient should be used  carefully.

  • 7.
    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.
    Stability assessment of concrete dams with non-linear FEA2017In: Nordic Concrete Research Publications / [ed] Marianne Tange Holst, 2017, p. 299-302Conference paper (Refereed)
    Abstract [en]

    In dam safety assessments, it must be shown that concrete dams are safe against sliding and overturning failure modes. This is typically performed with analytical calculations based on force equilibrium of a rigid body. In more complex cases, these analyses are time-consuming and have to be based on assumptions regarding the dam’s behaviour or simplifications. By using non-linear finite element analyses (FEA), more detailed and realistic analyses can be performed where it is possible to include cracks, degradation, material strength, dam-rock interaction etc. A method to perform these analyses is presented, based on the same safety concept as for the classical methods.

  • 8.
    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.
    Ansell, Anders
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Concrete Structures.
    Performance of data-based models for early detection of damage inconcrete damsManuscript (preprint) (Other academic)
    Abstract [en]

    A failure of a massive concrete dam could cause catastrophic consequences. Thepurpose of monitoring is to detect anomalies and damage at an early stage to preventfailure. Data-based models for anomaly detection are based on the hypothesis thatthe behaviour of an undamaged dam will follow an expected pattern, and deviationfrom this pattern is an indication of damage. In this study, simulations were usedto create time series for an undamaged dam and three different damage scenariosat three different locations in the dam body. Three common data-based modelswere used to predict a dams crest displacements, both on the generated artificialdata and corresponding measurements from the dam. Prediction bands for futuremeasurements were created, and the ten time-series were used to test the ability todetect damage. All models could detect instantaneous damage but struggle to detectprogressive damage; the Neural network outperforms the two regression models. Thechoice of the mathematically optimal threshold limit leads to a large number of falsealerts. Requiring three consecutive values outside the threshold before an alert isissued, increases the possibility to receive an early alert compared to the standardapproach where observations are classified individually.

  • 9.
    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.
    Eriksson, Daniel
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Concrete Structures.
    Modelling of the ice load on a Swedish concrete dam using semi-empirical models based on Canadian ice load measurements2019In: Sustainable and Safe Dams Around the World / [ed] Jean-Pierre Tournier, Tony Bennett & Johanne Bibeau, 2019, Vol. 2, p. 3068-3080Conference 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.

  • 10.
    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

  • 11.
    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.
    Johansson, Fredrik
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Soil and Rock Mechanics.
    Ríos Bayona, Francisco
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Soil and Rock Mechanics.
    Pull-out tests of 50-year old rock bolts2016In: Proceedings of the International Symposium on Appropriate technology to ensure proper Development, Operation and Maintenance of Dams in Developing Countries, Johannesburg, 2016, p. 263-272, article id 258Conference paper (Refereed)
    Abstract [en]

    In this paper, detailed numerical and analytical calculations are presented with the aim to study the effect of rock bolts and the influence of degradation on the dam safety. In addition, results from inspections and pull-out tests are presented from a case study with rock bolts that has been installed for 50 years. All tested bolts have with margin withstood higher stresses than the maximum allowed stresses according to Swedish standards. At visual inspection, no bolts have shown any major signs of degradation and all investigate bolts are in very good condition.

  • 12.
    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.

  • 13.
    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.
    Persson, Anton
    Klasson Svensson, Emil
    Estimating the effect of ice load on a concrete dams displacement with regression models2017In: Proceedings ICOLD 2017 International Symposium: Knowledgebased dam engineering, Prag, 2017Conference 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.

  • 14.
    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)
  • 15.
    Malm, Richard
    et al.
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Concrete Structures.
    Hassanzadeh, ManouchehrSWECO.Hellgren, RikardKTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Concrete Structures.
    Proceedings of the 14th ICOLD International Benchmark Workshop on Numerical Analysis of Dams2017Conference 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.

  • 16.
    Malm, Richard
    et al.
    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.
    Hellgren, Rikard
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Concrete Structures.
    Ríos Bayona, Francisco
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Soil and Rock Mechanics.
    Load Capacity of Grouted Rock Bolts Due to Degradation: 2017:3742017Report (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.

  • 17.
    Sjölander, Andreas
    et al.
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Concrete Structures.
    Hellgren, Rikard
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Concrete Structures.
    Ansell, Anders
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Concrete Structures.
    Modelling aspects to predict failure of a bolt-anchored fibre reinforced shotcrete lining2018In: 8th International Symposium on Sprayed Concrete: Modern Use of Wet Mix Sprayed Concrete for Undergro­und Support / [ed] Thomas Beck, Synnove A. Myren, Siri Engen, Trondheim, 2018, p. 278-292Conference paper (Refereed)
    Abstract [en]

     Tunnels in hard and jointed rock are normally excavated with an arch shape to enable the rock to carry itself. The arch effect depends on the stability of individual blocks and too high or too low horizontal stresses could cause blocks to be pushed out or to fall down. To prevent this, systematic rock bolting in combination with fibre reinforced sprayed concrete (FRSC) is commonly used to support the rock. To understand the failure mechanism of the lining when subjected to the load from one block is therefore important for the design. In this paper, the three main failure mechanisms for a rock support shotcrete lining has been identified as failure in the fibre reinforced concrete, bond failure between shotcrete and rock or failure of rock bolts. For each of the failure modes, a short review of numerical methods is presented followed by a selection of a preferred modelling approach. The selected methods are then verified against experimental results from the literature. The selected methods all shows good agreements with tests and demonstrates the ability to simulate each failure mode one by one.

1 - 17 of 17
CiteExportLink to result list
Permanent link
Cite
Citation style
  • apa
  • harvard1
  • ieee
  • modern-language-association-8th-edition
  • vancouver
  • Other style
More styles
Language
  • de-DE
  • en-GB
  • en-US
  • fi-FI
  • nn-NO
  • nn-NB
  • sv-SE
  • Other locale
More languages
Output format
  • html
  • text
  • asciidoc
  • rtf