Change search
Refine search result
1 - 21 of 21
CiteExportLink to result list
Permanent link
Cite
Citation style
  • apa
  • 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.
    Eriksson, Daniel
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Concrete Structures.
    Numerical models for degradation of concrete in hydraulic structures due to long-term contact with water2018Licentiate thesis, comprehensive summary (Other academic)
    Abstract [en]

    The durability of concrete is of major concern in all types of concrete structures where the combined effect of exposure conditions and the type and quality of the concrete material usually determines the rate of degradation. Furthermore, there are synergy effects between different deterioration mechanisms, which means that the combined rate of degradation is higher than the sum of the individual rates of each mechanism. Therefore, to accurately predict the residual service life of existing structures or when designing new structures, it is essential to consider all these aspects. This means that various chemical and physical processes, as well as how these interact, must be taken into account in models aiming to be used for service life predictions.

    This thesis presents the first part of a research project with the aim to investigate common deterioration mechanisms of concrete in hydraulic structures, and to improve the knowledge how these and other related phenomena can be described using mathematical models. The objective is also to study how different mechanisms interact and to find suitable approaches to account for these interactions in the models. To this end, a literature survey on commonly detected damage in hydraulic structures is presented. In addition, it also addresses in what types of and where in hydraulic structures the various damage types are usually observed. The mathematical models presented in this part of the project are focused on long-term water absorption in air-entrained concrete as well as on freezing of partially saturated air-entrained concrete. Both models are based on a multiphase description of concrete and poromechanics to describe the coupled hygro-thermo-mechanical behaviour. The thesis also presents some of the basic concepts of multiphase modelling of porous media, including discretization of the models using the finite element method (FEM). Furthermore, it covers the simplifications that are usually introduced in the general macroscopic balance equations for mass, energy and linear momentum when modelling cement-based materials.

    To verify the developed models and to show their capabilities, simulation results are compared with experimental data, in situ measurements and other simulations from the literature. The results indicate that both models perform well and can be used to predict long-term moisture conditions in hydraulic structures as well as freezing-induced strains in partially saturated air-entrained concrete, respectively. Even though no interactions with other deterioration mechanisms are included in the models, the development and use of these have given insights to which parameters that are important to consider in such extensions. Furthermore, based on the insights gained, the complexity of describing the full interactions between several mechanisms in mathematical models is also discussed. It is concluded that models aiming to be used for service life predictions of hydraulic structures in day-to-day engineering work need to be simplified. However, the type of advanced models presented in this thesis can serve as a basis to study which aspects and parameters that are essential to consider in simplified prediction models.

  • 2.
    Eriksson, Daniel
    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.
    Comparison of mechanistic and phenomenological approaches to model drying shrinkage of concrete2017In: Nordic Concrete Research: Proceedings of the XXIII Nordic Concrete Research Symposium / [ed] Marianne Tange Hasholt, 2017, p. 287-290Conference paper (Refereed)
    Abstract [en]

    Drying shrinkage of concrete is often estimated using a phenomenological approach where it is assumed that shrinkage is proportional to the change in internal humidity. In this study, a mechanistic approach was used which instead aims to mathematically describe the physical processes of drying shrinkage. Simulations of two laboratory tests were made and compared to results from two models based on the phenomenological approach. The results show that the developed model can describe drying shrinkage of concrete equally well as the phenomenological models but without the need to specify the final drying shrinkage strain.

  • 3.
    Eriksson, Daniel
    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 air voids in multiphase modelling for service life prediction of partially saturated concrete2018In: Computational Modelling of Concrete Structures / [ed] Günther Meschke, Bernhard Pichler, Jan G. Rots, London, UK: CRC Press, 2018, p. 317-326Conference paper (Refereed)
    Abstract [en]

    The purpose of this study is to show the influence and significance of including water filling of air pores when studying moisture conditions in concrete structures cast with air-entrained concrete and in contact with free water. Especially if the aim is to assess the risk for frost damages in different regions of the structure, based on a critical degree of saturation, in order to ultimately perform a service life prediction. A hygro-thermo-mechanical multiphase model that includes the effect of water filling in air pores, recently presented by the authors, is briefly described and applied in two numerical examples. The results show moisture distributions that would not be possible to capture without the air pore filling included in the model. More importantly, the general shape of these distributions complies well with measured distributions in real concrete structures as well as with distributions obtained in laboratory measurements.

  • 4.
    Eriksson, Daniel
    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.
    Ansell, Anders
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Concrete Structures.
    A hygro-thermo-mechanical multiphase model for long-term water absorption into air-entrained concreteManuscript (preprint) (Other academic)
    Abstract [en]

    Many concrete structures located in cold climates and in contact with free water are cast with air-entrained concrete. The presence of air pores significantly affects the absorption of water in the concrete, and it might take decades before these are fully saturated. This generally improves the long-term performance of such structures and in particular their frost resistance. To study the long-term moisture conditions in air-entrained concrete, a hygro-thermo-mechanical multiphase model is presented, where the rate of water filling of air pores is described as a separate diffusion process. The driving potential is the concentration of dissolved air, obtained using an averaging procedure with the air pore size distribution as the weighting function. The model is derived using the Thermodynamically Constrained Averaging Theory (TCAT) as a starting point. Two examples are presented to demonstrate the capabilities and performance of the proposed model. These show that the model is capable of describing the complete absorption process of water in air-entrained concrete, and yield results that comply with laboratory and in situ measurements.

  • 5.
    Eriksson, Daniel
    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.
    Ansell, Anders
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Concrete Structures.
    A Hygro-Thermo-Mechanical Multiphase Model for Long-Term Water Absorption into Air-Entrained Concrete2019In: Transport in Porous Media, ISSN 0169-3913, E-ISSN 1573-1634, Vol. 127, no 1, p. 113-141Article in journal (Refereed)
    Abstract [en]

    Many concrete structures located in cold climates and in contact with free water are cast with air-entrained concrete. The presence of air pores significantly affects the absorption of water into the concrete, and it may take decades before these are fully saturated. This generally improves the long-term performance of such structures and in particular their frost resistance. To study the long-term moisture conditions in air-entrained concrete, a hygro-thermo-mechanical multiphase model is presented, where the rate of filling of air pores with water is described as a separate diffusion process. The driving potential is the concentration of dissolved air, obtained using an averaging procedure with the air pore size distribution as the weighting function. The model is derived using the thermodynamically constrained averaging theory as a starting point. Two examples are presented to demonstrate the capabilities and performance of the proposed model. These show that the model is capable of describing the complete absorption process of water in air-entrained concrete and yields results that comply with laboratory and in situ measurements.

  • 6.
    Eriksson, Daniel
    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.
    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.
    Freezing of partially saturated air-entrained concrete: A multiphase description of the hygro-thermo-mechanical behaviourManuscript (preprint) (Other academic)
    Abstract [en]

    Even though air-entrained concrete is usually used for concrete structures located in cold climates that are exposed to wet environments, frost damages are frequently detected during inspections. However, it is often hard to assess the extent and severity of these damages and, thus, there is a need for better tools and aids that can complement already established assessment methods. Several studies have successfully shown that models based on poromechanics and a multiphase approach can be used to describe the freezing behaviour of air-entrained concrete. However, these models are often limited to the scale of the air pore system and, hence, hard to use in applications involving real structures. This study proposes a hygro-thermo-mechanical multiphase model which describes the freezing behaviour of partially saturated air-entrained concrete on the structural scale. The model is implemented in a general FE-code and two numerical examples are presented to validate and show the capabilities of the model. The first concerns a series of experimental tests of air-entrained cement pastes, whereas the second aims to show the capability of the model to account for an initial non-uniform distribution of moisture. The results show that the model can reproduce the freezing behaviour observed in the experimental tests on a structural scale as well as being capable of describing freezing induced deformations caused by non-uniform moisture distributions.

  • 7.
    Eriksson, Daniel
    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.
    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.
    Freezing of partially saturated air-entrained concrete: A multiphase description of the hygro-thermo-mechanical behaviour2018In: International Journal of Solids and Structures, ISSN 0020-7683, E-ISSN 1879-2146, Vol. 152-153, p. 294-304Article in journal (Refereed)
    Abstract [en]

    Even though air-entrained concrete is usually used for concrete structures located in cold climates that are exposed to wet environments, frost damage is frequently detected during inspections. However, it is often hard to assess the extent and severity of the damage and, thus, there is a need for better tools and aids that can complement already established assessment methods. Several studies have successfully shown that models based on poromechanics and a multiphase approach can be used to describe the freezing behaviour of air-entrained concrete. However, these models are often limited to the scale of the air pore system and, hence, hard to use in applications involving real structures. This study proposes a hygro-thermo-mechanical multiphase model which describes the freezing behaviour of partially saturated air-entrained concrete on the structural scale. The model is implemented in a general FE-code and two numerical examples are presented to validate and show the capabilities of the model. The first concerns a series of experimental tests of air-entrained cement pastes, whereas the second aims to show the capability of the model to account for an initial non-uniform distribution of moisture. While the model predictions underestimate the magnitude of the measured strains, the results still show that the model can capture the general freezing behaviour observed in the experimental tests on the structural scale. Furthermore, the results demonstrate that the model is capable of describing freezing induced deformations caused by non-uniform moisture distributions.

  • 8.
    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.
    Simulering av frostsprängning i betong2018In: Bygg och Teknik, ISSN 0281-658X, no 7, p. 19-22Article in journal (Other (popular science, discussion, etc.))
    Abstract [sv]

    Betongkonstruktioner belägna i kalla och fuktiga miljöer riskerar att skadas av frostsprängning under de kyliga vintermånaderna på grundav vattnets nioprocentiga volymsexpansion då det fryser inuti betongen. För att begränsa denna problematik är det vanligt att till exempel dammar, broar och betongvägar byggs med lufttillsatt betong i både Sverige och andra delar av världen. Trots detta observerasfrostskador frekvent i sådana konstruktioner. Det är därför viktigtatt kunna uppskatta när i tiden frostskador förväntas uppkomma i en konstruktion samt kunna bedöma omfattningen av en redan uppkommen skada. För att göra detta, utvecklades numeriska modeller i ett pågående doktorandprojekt vid KTH, finansierat av Svenskt Vattenkraftscentrum (SVC). Doktorandprojektet har som mål att bidra till en förbättring av dessa typer av bedömningar genom att beskriva de komplexa processer som är förknippade med frysning i lufttillsatt betong.

  • 9.
    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.

  • 10.
    Gasch, Tobias
    et al.
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Concrete Structures.
    Eriksson, Daniel
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Concrete Structures.
    Ansell, Anders
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Concrete Structures.
    On the behaviour of con-crete at early-ages: A multiphase description of hygro-thermo-chemo-mechanical properties2019In: Cement and Concrete Research, ISSN 0008-8846, E-ISSN 1873-3948, Vol. 116, p. 202-216Article in journal (Refereed)
    Abstract [en]

    Understanding the early-age behaviour of concrete is of importance for designing durable concrete structures. To contribute to the improvement of this, a hygro-thermo-chemo-mechanical model is presented that accounts for phenomena such as hydration, external and internal drying, self-heating, creep, shrinkage and fracture. The model is based on a multiphase porous media framework, using the Thermodynamically Constrained Averaging Theory (TCAT) as starting point to derive the governing equations of the system. This allows for a systematic treatment of the multiscale properties of concrete and how these develop during hydration, e.g. chemical and physical fixation of water. The proposed mathematical model is implemented within the context of the Finite Element Method (FEM), where all physical fields are solved in a fully-coupled manner. Chosen properties of the model are demonstrated and validated using three experimental results from the literature. Generally, the simulated results are in good agreement with the measurements.

  • 11.
    Gasch, Tobias
    et al.
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Concrete Structures. Vattenfall R&D.
    Facciolo, Luca
    Vattenfall R&D.
    Eriksson, Daniel
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Concrete Structures.
    Rydell, Cecilia
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Concrete Structures. Vattenfall R&D.
    Malm, Richard
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Concrete Structures. Vattenfall R&D.
    Seismic analyses of nuclear facilities with interaction between structure and water: Comparison between methods to account for Fluid-Structure-Interaction (FSI)2013Report (Other academic)
    Abstract [en]

    Methods to describe the interaction between fluids and solids has been one of the biggest focus points for the research within the field of computationalengineering for the recent years. This area is of interest to a variety ofengineering problems, ranging from flow in blood vessels, aerodynamics andof course the interaction between water and civil engineering structures. Thetypical civil engineering application of fluid-structure interaction (FSI)encountered in a nuclear facilities is obtained at seismic loading, where the nuclear facilities consists of water filled pools of various sizes, for example the spent fuel and condensation pools. These water filled pools contribute with added mass to the structure, which lowers the natural frequency of thestructure as well as hydrostatic and hydrodynamic pressure that acts on thewalls of the pool due to wave propagation in the fluid. In addition, as the pools also have a free water surface towards the environment of thestructure, free surface wave propagation also has to be accounted for; i.e.sloshing. This introduces extra non-linearity to the problem, since a freesurface constitutes a boundary condition with an unknown location.

    The main part of this report constitutes as a state-of-the-art summary whereconcepts important for FSI analyses are presented and important differencesare discussed. Due to the different interests of the numerous disciplinesengaged in this research area, a large number of methods have been developed, where each has different strengths and weaknesses suited for the problem in mind when developing the method. The focus of this report havebeen to describe the most important numerical techniques and the categories of methods that or of most interest for civil engineering problems, such as simplified analytical or mass-spring models, Acoustic Elements, ArbitraryLagrangian-Eulerian (ALE) and coupled Eulerian-Lagrangian (CEL).

    Thereafter two benchmark examples are presented, intended to highlightdifferences between the different methods. In the first study, sloshing of aliquid tank is studied where the numerical methods are compared toexperimental results, regarding the movement of the free water surface. In addition, the hydrodynamic (fluid) pressures on the walls of the tanks arecompared between the different numerical methods. It was shown that mostanalysis methods give accurate results for the sloshing wave height whencompared with the experimental data. It should however be mentioned that the tank was only excited by a simple harmonic motion with a frequency thatdo not give rise to any resonance waves in the water body.

    Also when it comes to fluid pressure good agreement between the differentanalysis methods was found, although no experimental data was available forthis parameter. It was also noticed that for the sloshing tank, most of the change in pressure occurred close to the free surface of the water, which indicates that it mainly consists of a convective pressure, i.e. from the sloshing. Thereby, finite element programs that account the impulsive mass incivil engineering FSI problems should not be used for this type of analysis. In the second study, the numerical methods are compared based on differenttypes of seismic input, such as a large earthquake with mainly low frequencycontent typically like an earthquake on the US west coast and one smallerearthquake with relatively higher degree of high frequency content typicallylike a Swedish type of earthquake. One important observation was that the relative increase in induced stresses in the structure, with and withoutconsideration of the water was significantly larger for the Swedish earthquakethan for the US earthquake. One possible reason for this may be that the Swedish earthquake is not large enough to excite the relatively stiff structurewithout any water, but it will induce significant dynamic effects in the waterwhich give rise to higher stresses in the concrete as well. However, this shows that it is very important to include water in seismic analyses.

  • 12.
    Gasch, Tobias
    et al.
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Concrete Structures.
    Malm, Richard
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Concrete Structures.
    Eriksson, Daniel
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Concrete Structures.
    Hassanzadeh, Manouchehr
    Vattenfall Engineering .
    Probabilistic analyses of crack propagation in concrete dams: Part II2013Report (Other academic)
    Abstract [en]

    Several concrete buttress dams in northern Sweden have been found to be subjected to, more or less severe, cracks according to recent assessments and investigations. Theoretical analyses and field measurements have shown that most of these cracks have developed or propagated as a result of the seasonal temperature variations. Most dams in Sweden were built for more than 50 years ago and it is therefore important to also consider the influence of long-term effects and degradation to assess the dam. The ordinary sliding and overturning stability analyses may not be sufficient when the supporting structure is cracked, since the cracks may comprise the integrity and the homogeneity of the structure.

    The work presented in this report is a continuation of the work on advanced numerical methods for studying crack propagation in concrete dams presented in Björnström et al. (2006), Ansell et al. (2008), Ansell et al. (2010) and Malm et al. (2013). In the latter parts of the project the main focus has been on the development of probabilistic analysis methods for studying crack propagation, mainly with respect to the stochastic variation of material properties of concrete but also with regard to loading conditions. The concepts of the used probabilistic analysis methods were introduced in a previous part of the project, (Malm et al. 2013).  In the previous part, stochastic spatial distribution of material properties was only studied within local areas where a crack was expected to be developed. In the work presented in this report, this concept has been expanded to cover stochastic spatial distribution of material properties within an entire buttress wall of one monolith. A sensitivity study is also presented regarding variations in the assumed temperatures of the seasonal temperature loading.

    To increase the accuracy of the numerical model a new FE-model was developed with a refined mesh compared to previously used meshes. The new mesh size was chosen with respect to the smallest characteristic crack length of a concrete sample in the stochastic population. All other aspects of the model were defined equally as in previous models.

    The results of the probabilistic analyses with respect to variation in material properties showed a significant increase in developed cracks, compared to a deterministic analysis. The main crack patterns were, however, similar, but additional cracks were developed adjacent to previous cracks and the inclination of some cracks was changed. These findings should be included when assessing different dam stability failure modes of buttress dams. The sensitivity study of the assumed temperatures showed that it was mainly the low temperatures in combination with temperature differences that initiate cracking in the monolith.

  • 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.
    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.

  • 14.
    Malm, Richard
    et al.
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Concrete Structures.
    Eriksson, Daniel
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Concrete Structures.
    Gasch, Tobias
    Vattenfall Power Consultant.
    Hassanzadeh, Manouchehr
    Lund University, Building Materials.
    Probabilistic Analyses of Thermal Induced Cracking in a Concrete Buttress Dam2011In: Risk Analysis, Dam Safety, Dam Security and Critical Infrastructure Management / [ed] Ignacio Escuder-bueno, Enrique Matheu, Luis Altarejos-garcfa, 2011Conference paper (Refereed)
    Abstract [en]

    Recent assessments and investigations of buttress dams in northern Sweden reveal several types of cracks. The theoretical analysis and field measurements have showed that the most of the cracks are either developed or propagated as a result of the seasonal temperature variations. Cracks influence the behaviour of the dams in different ways, such as reducing the tightness of the dam and increasing the hydraulic pressure within the material/structure. Furthermore, cracks may have an impact on the stiffness and stability of the dam. The ordinary sliding and overturning stability analyses are not sufficient when the supporting structure is cracked. The cracks may comprise the integrity and the homogeneity of the structure. A cracked, and for that matter even repaired structure, can’t be regarded as a homogenous structure and should be treated accordingly. Consequently, other types of models instead of the conventional design models should be utilized for the stability analyses of the cracked and repaired dams.

    The mode of the failure is one of the decisive elements considering determination of the probability of the failure. The conditions for crack initiation and the trajectory of the crack propagation are the decisive factors which govern the failure mode. Ordinary design methods and advanced numerical models which are based on the elastic behaviour of the structure can’t be utilized, since these models are not able to describe the non-linear behaviour and to predict the failure mode of the structure.

    A finite-element model based on non-linear fracture mechanics is being utilized to study crack development in a buttress dam. The aim of the study was to reveal crack trajectories and different probable failure modes, and moreover to determine the influences of the cracks on the overall behaviour of the structure. In a real structure the loading (mechanical and environmental) and boundary conditions are decisive factors regarding initiation, propagation and trajectory of the cracks. Furthermore, the material properties and their statistical distribution may influence the formation of cracks and the mode of failure.

  • 15.
    Malm, Richard
    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.
    Eriksson, Daniel
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Concrete Structures.
    Hassanzadeh, Manouchehr
    Vattenfall Engineering.
    Evaluating Stability Failure Modes due to Cracks in a Concrete Buttress Dam2013In: Changing Times: Infrastructure Development to Infrastructure Management, United States of America: U.S. Society on Dams , 2013, p. 415-424Conference paper (Refereed)
    Abstract [en]

    Several concrete buttress dams in northern Sweden have been found to be subjected to, more or less severe, cracks according to recent assessments and investigations. Theoretical analyses and field measurements have shown that most of these cracks have developed or propagated as a result of the seasonal temperature variations. Most dams in Sweden were built for more than 50 years ago and it is therefore important to also consider the influence of long-term effects and degradation to assess the condition of the dam. In this paper, simulations have been performed with detailed 3D nonlinear numerical analyses in order to study crack initiation and crack propagation due to stochastic variation in material properties, which represent concrete degradation. The structural response due to loads from gravity, hydrostatic water pressure and thermal seasonal effects have been considered in the studies. It was shown that weak material properties near the crack-tip will govern the trajectory of the crack. According to the analyses, significant amount of cracking can occur in the front-plate and buttress if the strength of the concrete is reduced, which lead to new potential failure modes. In addition, the extent of cracking in the buttress dam is largely governed by the induced cracking in the front-plate since these cracks have a tendency to propagate into the concrete buttress. Based on the calculated extent of cracking in the dam body, different failure modes can be assessed in order to determine the dam stability failure.

  • 16.
    Malm, Richard
    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.
    Eriksson, Daniel
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Concrete Structures.
    Hassanzadeh, Manouchehr
    Vattenfall R&D.
    Probabilistic analyses of crack propagation in concrete dams: Part 12013Report (Other academic)
    Abstract [en]

    Several concrete buttress dams in northern Sweden have been found to be subjected to, more or less severe, cracks according to recent assessments and investigations. Theoretical analyses and field measurements have shown that most of these cracks have developed or propagated as a result of the seasonal temperature variations. Most dams in Sweden were built for more than 50 years ago and it is therefore important to also consider the influence of long-term effects and degradation to assess the dam. The ordinary sliding and overturning stability analyses may not be sufficient when the supporting structure is cracked, since the cracks may comprise the integrity and the homogeneity of the structure.

    This project is a continuation from previous projects presented by Björnström et al. (2006), Ansell et al. (2008) and Ansell et al. (2010). In these previous projects, Storfinnforsen hydropower dam located in northern part of Sweden was studied and the purpose of the projects was to explain the cause for cracking found in situ. In the present project, the previously developed numerical model was verified against measured variations in crest displacement and crack width due to temperature variations during one year. The results showed that the numerical model, which was used, could predict both variations in displacements and crack width with good accuracy compared to the measurements on the actual dam.

    The studies of this project which are presented in this report are focused on the crack propagation due to stochastic variations in material properties. This was performed with probabilistic analyses based on a local model of an inclined crack in the supporting buttress. Monte-Carlo simulations were performed where each element was randomly assigned a concrete strength according to an assumed material distribution. It was shown that weak material properties near the crack-tip will govern the propagation and the trajectory of the crack. The results also showed that the average crack propagation from the probabilistic analyses differed both regarding inclination and length compared to the deterministic analysis which was based on mean values. In addition to the local analyses, global analyses were also performed, where stochastic variations in material properties were assigned to the whole monolith. The analyses showed that using design values or characteristic values of the material strength may give a different failure mode compared to the case where mean values of the material properties are used. When considering nonlinear properties for verification analyses, it is important to base the material properties on as accurate material properties as possible. In addition, the extent of cracking in the buttress dam is largely governed by the induced cracking in the front-plate since these cracks have a tendency to propagate into the concrete buttress. The results also showed that if the dam have been subjected to degradation and thereby has reduced concrete strength, the thermal stresses could induce significant cracking in the monolith which could lead to new failure modes. Based on the calculated extent of cracking in the dam body, different failure modes should be assessed in order to determine the dam stability failure.

  • 17.
    Malm, Richard
    et al.
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Concrete Structures.
    Hassanzadeh, Manouchehr
    Lund Universiity, Building Materials.
    Gasch, Tobias
    Vattenfall Power Consultant.
    Eriksson, Daniel
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Concrete Structures.
    The Influence of Cracks on the Structural Behaviour of a Buttress Dam2011In: Studies on Modern Technologies and Long-term Behavior of Dams / [ed] Jia Jinsheng, Zhang Shugang, Xu Zeping, Xu Yao, China WaterPower Press , 2011, p. 677-685Conference paper (Refereed)
    Abstract [en]

    Buttress dams located in cold areas are often subjected to severe environmental conditions. Recent assessments and investigations of buttress dams in northern Sweden reveal several types of cracks. Theoretical analysis and field measurements have showed that the most of the cracks are either developed or propagated as a result of the seasonal temperature variations.

    Cracks influence the behaviour of the dams in different ways, such as reducing the tightness of the dam and increasing the hydraulic pressure within the cracks. Furthermore, cracks may have impact on the stiffness and stability of the dam. The ordinary sliding and overturning stability analyses are not sufficient when the supporting structure is cracked. The cracks may comprise the integrity and the homogeneity of the structure. A cracked, and for that matter even repaired structure, can’t be regarded as a homogenous structure and should be treated accordingly. Consequently other types of models instead of the conventional design models should be utilized for the stability analyses of the cracked and repaired dams.

    There are at least two major aspects which must be considered when a cracked or repaired structure is being analysed. The first aspect is the principle of superposition and the second aspect is probability of the failure. It is well known that a cracked structure does not behave linearly, consequently the principle of superposition can’t be applied to determine the overall effects of the several simultaneously acting events.

    The mode of failure is one of the decisive elements considering determination of the probability of the failure. The condition for crack initiation and the trajectory of the crack propagation are the decisive factors which govern the failure mode. Ordinary design methods and advanced numerical models which are based on the elastic behaviour of the structure can’t be utilized, since these models are not able to describe the non-linear behaviour and to predict the failure mode of the structure.

    A finite-element model based on the non-linear fracture mechanics has been utilized to study crack development in a buttress dam. The aim of the project was to study crack trajectories and to determine the influences of cracks on the overall behaviour of the structure, for instance in the global stiffness of the structure and possible failure modes. The paper will present the structure, the numerical model and the results.

  • 18.
    Malm, Richard
    et al.
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Concrete Structures.
    Hassanzadeh, Manouchehr
    Lund University, Building Materials.
    Gasch, Tobias
    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.
    Nordström, Erik
    Vattenfall Hydro.
    Cracking in the concrete foundation for hydropower generators: Analyses of non-linear drying diffusion, thermal effects and mechanical loads2013Report (Other academic)
    Abstract [en]

    An extensive program for improvement of the hydropower plants in Sweden is currently on-going. The aims are to secure future production and to maintain and further develop an already high dam safety.

    During inspection, cracks were discovered in the concrete foundation, near the stator and rotor spider supports, at some hydropower stations in Sweden. The cracks were believed to be related to the function of the stator supports and to new patterns of generator operation. In earlier times, the generators ran continuously, while nowadays there are many stops and starts, sometimes even several times during one day. The objective of this study is to understand the complex interaction between the power generating system (stator, rotor, turbine, etc.) and the supporting concrete structure. It is important from a dam safety perspective to determine the causes of the structural cracks that have been found in-situ.

    A three dimensional non-linear finite element model has been developed in order to analyse formation and propagation of the cracks. Several different load effects have been studied in this project in addition to the mechanical loads during operation. The new pattern of generator operation with several starts and stops lead for instance to variations in temperature which have been studied. Besides this, the uneven drying shrinkage of concrete has also been studied in this project. Thereby, the structural behaviour of a concrete foundation for the power generating system has been analysed taking into account the transient thermal and moisture gradients in combination with dead loads and some of the operational loads imposed to the foundation.

    The analyses shows that reinforced concrete structure that constitute a support to the generator is subjected to cracking due to the loads considered in this study, where the cracks near the supports are caused by a combination of mechanical loads, long-term drying shrinkage and temperature variations. The analyses showed that even after 20 years, the moisture content in the centre of the thicker part in the concrete foundation still had a high relative humidity. At the same time the concrete close to the free surfaces and the slender parts of the concrete foundation had reached the same relative humidity as the environment. Thereby, a large difference in drying shrinkage is obtained between different parts of the concrete foundation and thereby large forces due to restrain. The analyses showed that the drying shrinkage induced cracking inside the concrete foundation and especially close to the supports of the stator and the rotor spider which coincides with location of the cracks found in-situ.

    The results show that the cracks found in-situ can be simulated and explained with advanced numerical methods. The results also indicate that the dynamic effect from the loads caused by the power generating system have to be studied further, since a reduced structural stiffness due to cracking may result in larger loads imposed on the structure from the magnetic eccentricity and turbine imperfections or alternatively lead to a fatigue failure of for instance the reinforcement.

  • 19.
    Nordström, Erik
    et al.
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Concrete Structures.
    Eriksson, Daniel
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Concrete Structures.
    Inventering av inre vattenvägsbesiktningar2019Report (Other academic)
    Abstract [en]

    The water is transported by the waterways from the reservoir, past the dam and further downstream in a hydropower station. Generally, the waterways can be categorized to be either of channel-type or tunnel-type. The waterways of tunneltype include a number of different structures such as intakes, headrace tunnels, penstocks, intake sumps, spirals, draft tubes, surge shafts, surge galleries and tailrace tunnels. These structures are usually either fully or partially filled with water, which means that they in many cases are hard to inspect. Moreover, it is seldom financially justifiable to drain the tunnels solely to perform an inspection due to the loss of energy production that this measure entails. However, in connection to stoppage of the energy production to repair, inspect or replace some of the energy-producing parts, an opportunity to inspect the waterways of tunneltype is usually given.

    In this study, a review of documentation from inspections of waterways of tunneltypes has been performed on behalf of Energiforsk to improve the state of knowledge regarding common damage types and deterioration mechanisms in this type of waterways. The collection of data has been performed by inquiring data from representatives of the utility companies in the steering committee of the research program for concrete in hydropower at Energiforsk. The obtained material includes both reports from inspections as well as compilations of observed damage in the waterways for a total of 53 different hydropower stations in Sweden.

    From the analysis of the obtained material in this study, it could be concluded that erosion was the most common type of damage observed in waterways of tunneltype if all types of such structures are considered. However, the results become a bit different if the different types of structures are studied individually, even though erosion often is observed to be one of the most commonly observed damage types. Previous research has, however, shown that an observed damage often is a consequence of a series of deterioration mechanisms that together cause a degradation of the material. Therefore, it is hard to isolate one single deterioration mechanism that is the only reason why erosion is the most commonly observed damage type in waterways of tunnel-type. Furthermore, it could be concluded that the documentation of performed inspections generally is inadequate at the utility companies and consequently also the documentation of observed damage and defects in the waterways. It should, however, be noticed that all companies stated that they have performed inspections but that the documentation from these is either missing or hard to find.

    With results from the study in mind a need for improvement in the management of the inner waterways is obvious. Especially regarding the knowledge on the status of long headrace and tailrace tunnels in rock with different degree of support. For facilities with common head-/tailrace tunnels for several units, the consequences of a larger failure could be substantial in terms of financial losses from no production. It is recommended to develop a strategy for management of inner waterways.

  • 20.
    Rydell, Cecilia
    et al.
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Concrete Structures. Vattenfall R&D.
    Gasch, Tobias
    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.
    Ansell, Anders
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Concrete Structures.
    Stresses in water filled concrete pools within nuclear facilities subjected to seismic loads2014In: Nordic Concrete Research, ISSN 0800-6377, no 51, p. 43-62Article in journal (Refereed)
    Abstract [en]

    This paper presents a study on water filled pools within nuclear facilities subjected to seismic loads. The type of structure studied is an elevated rectangular concrete tank, supported by the reactor containment, which is a high cylindrical concrete structure. Seismic analysis is performed using finite element models, accounting for fluid-structure interaction (FSI) between the water and the concrete structure. The stresses in a concrete pool are calculated, also investigating the changes in stresses as additional cross-walls are added. The effects from earthquakes dominated by low and high frequencies are evaluated, representative for conditions at the West coast of North America and Northern Europe, respectively. It is shown that the coupled fluid-structure systems have more significant modes in the high frequency range compared to the models without water, that is, for frequencies at which the Northern European type earthquake has significant energy compared to the Western North American earthquake. The seismic analyses show that the relative increase of hydrodynamic pressure is higher when the outer walls of the pool are stiffened due to the inclusion of additional cross-walls. With the inclusion of additional cross-walls, modes with lower natural frequencies, although still relatively high, become more important for the hydrodynamic pressure response. Leading to a higher stress response in the outer walls of the pool for models including the additional cross-walls compared to models without cross-walls. The study indicates that the effect from fluid-structure interaction is of great importance also for seismic loads with relatively high-frequency content.

  • 21.
    Rydell, Cecilia
    et al.
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Concrete Structures. Vattenfall R&D.
    Gasch, Tobias
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Concrete Structures.
    Facciolo, Luca
    Vattenfall Engineering.
    Eriksson, Daniel
    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.
    Interaction between structure and water in seismic analyses of nuclear facilities2013Conference paper (Refereed)
    Abstract [en]

    The objective of this paper is to evaluate different approaches to account for fluid-structure interaction (FSI) in seismic analyses of nuclear facilities. Different methods to account for FSI, from simplified to highly advanced numerical methods, are briefly reviewed and some important concepts are discussed. A benchmark example of a simple tank sloshing problem is included to evaluate the use of different FSI methods.

    The main conclusion from the study is that it is of great significance to first of all include the effect of FSI. When considering the response of a tank subjected to a load of periodic nature, as in the benchmark example, the hydrodynamic effects are very important, since they increase the load effect on the structure. It is also observed that the simplified methods, in which the hydrodynamic effects are included as a mass-spring system, results in much higher stresses in the structure than if the fluid is included as continuum elements. However, the more advanced methods lead to extra computational time and also require more from the analyst. With the focus of this project being the global response of the structure, most methods describe the fluid unnecessarily complicated and phenomena such as splashing and turbulence are of little interest. The main aspects that influence the structure are the mass and inertia of the fluid along with the surface waves, the sloshing. Considering this, simplified methods such as elements with acoustic equations, and even mass-spring systems, to represent the fluid, often give results that are accurate enough.

1 - 21 of 21
CiteExportLink to result list
Permanent link
Cite
Citation style
  • apa
  • 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