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  • 1.
    Ahmed, Lamis
    et al.
    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.
    Dynamic measurements for determination of Poisson’sratio of young concrete2017Conference paper (Refereed)
  • 2.
    Ansell, Anders
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Concrete Structures.
    Guidelines for practical use when shotcreting close to blasting and vibrations in hard rock2019Report (Other academic)
    Abstract [en]

    Uncertainty about the vibration levels that can be tolerated near newly sprayed concrete (shotcrete) often leads to excessively conservative limit values being used in the construction of tunnels and structures in rock, with additional costs and planning uncertainties as a result. Previously, it has only been possible to give general recommendations for safe vibration levels. A project with the aim of producing a set of practical vibration limit levels for shotcrete work close to blasting in hard rock has therefore been carried out. These recommendations span situations that may arise during "normal" construction in hard rock, and contain guidelines for safe distances and waiting times for newly sprayed shotcrete exposed to vibrations. In the project, the focus is on wet-mixed shotcrete on hard rock, of the type found in Sweden and Scandinavia.

    A large number of calculations have been carried out with a previously developed and relatively computationally effective numerical elastic stress wave propagation model. As input data, various combinations of the weight of explosives, distance, rock type, shotcrete type, shotcrete age and thickness are used. For each combination of input parameters, the stresses that arise at the bond interface between rock and shotcrete have been calculated. The results are saved in a database and can be illustrated graphically with a 3D surface, as a function of shotcrete age and distance to the explosive charge. This surface has then been compared with another, which represents the growth of bond strength between rock and shotcrete. The intersection curve between the two surfaces represents the limit for safe blasting, taking into account combinations of shortest distances and the youngest allowable shotcrete at time of blasting.

    The report contains a larger number of graphs showing limit values for safe blasting, which will be of value as reference in design work, enable comparisons with data from the field, and thereby feedback of experience. Based on the recommended limit values, dimensioning in the design stage will be made so that the results will be undamaged and safer shotcrete with longer life. Reduced need for re-spraying and repair leads to a high economic sustainability for large infrastructure projects and environmental sustainability when material consumption is reduced. The safety of tunnels and underground constructions will also be increased.

  • 3.
    Ansell, Anders
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Concrete Structures.
    Practical guidelines for shotcrete work close to blasting and vibration in hard rock2019In: Tunnels and Underground Cities: Engineering and Innovation meet Archaeology, Architecture and Art- Proceedings of the WTC 2019 ITA-AITES World Tunnel Congress, 2019, p. 4659-4668Conference paper (Refereed)
    Abstract [en]

    Limited knowledge on safe vibration levels near newly sprayed concrete (shotcrete) often leads to over-conservative limits in underground construction and tunnelling, with additional costs and planning uncertainties as a consequence. Work on compiling a database of practical vibration levels for shotcrete work close to blasting in hard rock have been initiated and will provide guidelines for safe distances and waiting times for newly sprayed wet-mix shotcrete. A large number of calculations are carried out with a previously developed and relatively computationally effective numerical elastic stress wave propagation model, which will result in a systematically compiled database. These guidelines, giving relationships between the amount of explosives, distance, rock type, shotcrete type, age and thickness, will be of great value as reference for design work and facilitate comparisons with in situ data. It will be possible to adopt the design to ensure undamaged and safer shotcrete constructions with longer service life.

  • 4.
    Ansell, Anders
    et al.
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Concrete Structures.
    Holmgren, Jonas
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Concrete Structures.
    Young Shotcrete subjected to Blast Induced Vibrations1999In: Nordic Concrete Research: Research projects 1999 / [ed] O.H. Wallevik, Oslo: The Nordic Concrete Federation , 1999, p. 211-213Conference paper (Refereed)
  • 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 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.

  • 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.
    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.

  • 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 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.

  • 8.
    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.

  • 9.
    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.

  • 10.
    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.
    Ansell, Anders
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Concrete Structures.
    Three-dimensional simulations of ageing concrete structures using a multiphase model formulationManuscript (preprint) (Other academic)
    Abstract [en]

    The durability of concrete structures is in no small degree determined by the quality and integrity of the concrete, where structural damages such as cracks negatively affect many of the functions of the structure. Often cracks are formed due to restrained thermal and hygral deformations, where the risk is exceptionally high during the early stages after casting. This study presents a hygro-thermo-chemo-mechanical model that accounts for phenomena such as hydration, external and internal drying, self-heating, creep, shrinkage and fracture. The model is derived as a modified version of a fully-coupled multiphase model recently proposed by Gasch et al. (2019) and implemented in the Finite Element Method. Here the governing equations are simplified, and a more efficient solution method is proposed. These modifications are made with the intention to obtain a model more suitable for structural scale simulations. To validate the model, one of the end-restrained beams tested within the French research project CEOS.fr is analyzed. Laboratory data on the concrete is used to calibrate to model and recordings of ambient conditions makes it possible to define accurate boundary conditions. Results from the simulation are compared to measured temperatures and deformations from the first 60 days after casting and are found to generally be in good agreement. Compared to the fully-coupled model by Gasch et al. (2019), the modifications proposed in this study reduce the computational cost by a factor five; without any noticeable differences to the structural results.

  • 11.
    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.
    Ansell, Anders
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Concrete Structures.
    Three-dimensional simulations of ageing concrete structures using a multiphase model formulation2019In: Materials and Structures, ISSN 1359-5997, E-ISSN 1871-6873, Vol. 52, no 4, article id 85Article in journal (Refereed)
    Abstract [en]

    The durability of concrete structures is in no small degree determined by the quality and integrity of the concrete, where structural damages such as cracks negatively affect many of the functions of the structure. Often cracks are formed due to restrained thermal and hygral deformations, where the risk is exceptionally high during the early stages after casting. This study presents a hygro-thermo-chemo-mechanical model that accounts for phenomena such as hydration, external and internal drying, self-heating, creep, shrinkage and fracture. The model is derived as a modified version of a fully-coupled multiphase model recently proposed by Gasch et al. (Cem Concrete Res 116:202–216, 2019. https://doi.org/10.1016/j.cemconres.2018.09.009) and implemented in the Finite Element Method. Here the governing equations are simplified, and a more efficient solution method is proposed. These modifications are made with the intention to obtain a model more suitable for structural scale simulations. To validate the model, one of the end-restrained beams tested within the French research project CEOS.fr is analyzed. Laboratory data on the concrete is used to calibrate to model and recordings of ambient conditions makes it possible to define accurate boundary conditions. Results from the simulation are compared to measured temperatures and deformations from the first 60 days after casting and are found to generally be in good agreement. Compared to the fully-coupled model by Gasch et al. (2019), the modifications proposed in this study reduce the computational cost by a factor five; without any noticeable differences to the structural results.

  • 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.
    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.

  • 13.
    Magnusson, Johan
    et al.
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Concrete Structures.
    Hallgren, Mikael
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Concrete Structures. Tyréns.
    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.
    Numerical analyses of shear in concrete structures subjected to distributed blast loads2019In: Engineering structures, ISSN 0141-0296, E-ISSN 1873-7323Article in journal (Refereed)
  • 14.
    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.

  • 15.
    Schönbeck, Pia
    et al.
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Concrete Structures.
    Löfsjögård, Malin
    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.
    Requirements on concrete floor structures - a comparison of medical imaging facilities2017In: Proceedings of XXIII Nordic Concrete Research Symposium in Aalborg / [ed] Marianne Tange Holst, 2017Conference paper (Refereed)
    Abstract [en]

    Requirements management in construction projects have a tendency towards production-driven processes and definition of technical solutions. The stakeholders are involved by being asked to comment on defined products which can have consequences on the performance of the end-product. This comparison describes three projects within the Stockholm County where the scope to build new medical imaging facilities with the same requirements on the concrete floor structure. The result shows that the same requirements have resulted in different solutions which could have an impact on the performance of the buildings. Further research regarding tools for systematic requirements management is needed to ensure performance and sustainability of new buildings.

  • 16.
    Sjölander, Andreas
    et al.
    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.
    Analysis of the interaction between rock and shotcrete for tunnel support2017In: XXIII Nordic Concrete Research Meeting / [ed] Marianne Tange Holst, 2017Conference paper (Refereed)
    Abstract [en]

    The first part of a project aiming at increase the knowledge and understanding of how shotcrete (sprayed concrete) in interaction with rock could better be modelled is presented. The study focus on how an irregular thickness of shotcrete will affect its structural capacity. Examples show that continuously bonded shotcrete have an ability to redistribute local stresses while partly de-bonding leads to localized, wide cracks. One goal is to obtain a better understanding for how and why cracking and bond failure is initiated. The results obtained so far are here briefly summarized and commented, also showing some examples of results.

  • 17.
    Sjölander, Andreas
    et al.
    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.
    In-Situ and Laboratory Investigation on Leaching and Effects of Early Curing of Shotcrete2019In: Nordic Concrete Research, ISSN 0800-6377, ISSN 0800-6377, Vol. 61, no 2, p. 23-37Article in journal (Refereed)
    Abstract [en]

    During the construction of a rock tunnel in Stockholm, several sections with leaching shotcrete (sprayed concrete) were found one year after the spraying was completed. An investigation was therefore conducted, and its results are presented in this paper. The amount of leaching after such a short time indicated that a one-sided water pressure existed in combination with a permeable shotcrete. The reason for the water pressure was likely a partly unsuccessful grouting that created sections with leaking water. The permeable shotcrete could be a combined result of insufficient curing and the use of accelerators, and the effect of in-situ curing was therefore investigated. A total of six slabs were sprayed and cured under different conditions in the tunnel. Test results according to standards indicated that curing has no significant effect on the development of mechanical strength or water penetration through the shotcrete. However, this is believed to be a result of the test method rather than the non-existing effect of curing. Lastly, some modifications to the test standard were proposed for future studies of in-situ curing.

  • 18.
    Sjölander, Andreas
    et al.
    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.
    Investigation of non-linear drying shrinkage for end-restrained shotcrete of varying thickness2018In: Magazine of Concrete Research, ISSN 0024-9831, E-ISSN 1751-763X, Vol. 70, no 6, p. 271-279Article in journal (Refereed)
    Abstract [en]

    Tunnels in hard, jointed rock are commonly reinforced with shotcrete (sprayed concrete) applied directly on the irregular rock surface. The thickness for such linings can be as small as 50 mm, which result in a fast drying. The resulting shrinkage of the restrained lining is a well-known phenomenon, which leads to cracking. The installation of drainage systems also results in an end-restrained shotcrete lining that is more prone to shrinkage cracking. The drying process is a complex problem that depends on multiple factors such as cement content, porosity and ambient air conditions (i.e. temperature, relative humidity and wind speed). Two numerical models capable of capturing the structural effects of drying shrinkage were compared in this study. It was found that inclusion of non-linear drying shrinkage is important for accurately describing crack initiation in an end-restrained shotcrete slab. The best fit to the experimental data was obtained when the rate of drying was described as a non-linear decreasing function.

  • 19.
    Sjölander, Andreas
    et al.
    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.
    Investigation of non-linear drying shrinkage for end-restrained shotcrete with varying thicknessIn: Magazine of Concrete Research, ISSN 0024-9831, E-ISSN 1751-763XArticle in journal (Refereed)
    Abstract [en]

    Tunnels in hard, jointed rock is commonly reinforced with shotcrete (sprayed concrete) applied directly on the irregular rock surface. The thickness for such lining can be as low as 50 mm which result in a fast drying. The resulting shrinkage of the restrained lining is a well known phenomena that causes cracking. Installation of some drainage system also results in an end-restrained shotcrete lining which is more prone to shrinkage cracking. The drying process is a complex problem that depends on multiple factors such as cement content, porosity and conditions of ambient air, i.e. temperature, relative humidity and wind speed. In this paper, two numerical models capable of capturing the structural effects of drying shrinkage was compared. Results shows that inclusion of non-linear drying shrinkage is important to accurately describe crack initiation in a end-restrained shotcrete slab. Best fit to experimental data was obtained when the rate of drying was described as a non-linear decreasing function.

  • 20.
    Sjölander, Andreas
    et al.
    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.
    Numerical simulations of restrained shrinkage cracking in glass fibre reinforced shotcrete slabs2017In: Advances in Civil Engineering / Hindawi, ISSN 1687-8086, E-ISSN 1687-8094, no 8987626Article in journal (Refereed)
    Abstract [en]

    Modern tunnels in hard rock are usually constructed by drill and blast with the rock reinforced by shotcrete (sprayed concrete) in combination with rock bolts. The irregular rock surface and the projection method of shotcrete leads to a tunnel lining of varying thickness with unevenly distributed stresses that affect the risk of cracking during shrinkage of the young and hardening material. Depending on water conditions, shotcrete is either sprayed directly onto the rock surface or over a drainage system, creating a fully restrained or an end-restrained structural system. In this paper, a method for non-linear numerical simulations has been demonstrated, for the study of differences in stress build up and cracking behaviour of restrained shotcrete slabs subjected to shrinkage. Special focus was given to the effects of the irregular shape and varying thickness of the shotcrete. The effects of glass fibre reinforcement and bond were implemented in the study by changing the fracture energy in bending and in the interaction between shotcrete and the substrate. The study verifies that an end-restrained shotcrete slab is prone to shrinkage induced cracking, and shows the importance of a continuous bond to avoid wide shrinkage cracks when shotcrete is sprayed directly onto the rock. 

  • 21.
    Sjölander, Andreas
    et al.
    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.
    Probabilistic modelling of fibre reinforced shotcrete2019In: Tunnels and Underground Cities: Engineering and Innovation meet Archaeology, Architecture and Art- Proceedings of the WTC 2019 ITA-AITES World Tunnel Congress, CRC Press, 2019, p. 3105-3112Conference paper (Refereed)
    Abstract [en]

    Shotcrete is widely used as rock support and can support the load from blocks either by bonding to the rock or by bending between rock bolts. By introducing fibres, the ductility of the shotcrete will increase and the crack widths decrease. Predictions of the structural behaviour for fibre reinforced shotcrete (FRS) are however complicated due to the large scatter normally seen in test results. The reason is mainly related to the non-uniform distribution and orientation of the fibres which could lead to uncertainties regarding the quality of in-situ shot-crete. The aim with this paper is therefore to investigate if a probabilistic material model for FRS can be used to capture the scatter in the results. An isotropic damage model that combines an exponential softening curve for unreinforced shotcrete and a bi-linear curve to account for the effect of fibres were used. Suitable distributions for each of the parameters in the model have been proposed based on fitting of experimental results. Thereafter, Monte Carlo simula-tions were used to produce results for a large number of lab tests. Results show that the model together with the proposed distributions was able to capture the scatter in test results.

  • 22.
    Sjölander, Andreas
    et al.
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Concrete Structures.
    Bjureland, William
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Soil and Rock Mechanics.
    Ansell, Anders
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Concrete Structures.
    On failure probability in thin irregular shotcrete shells2017In: Proceedings of the World Tunnel Congress 2017, 2017Conference paper (Refereed)
    Abstract [en]

    Tunnels through hard jointed rock are commonly reinforced with a combination of fibre reinforced shotcrete (sprayed concrete), FRS, and rock bolts. The design of such reinforcement is a complex task. First, the interaction between rock bolts, FRS and rock should be considered. Secondly, a natural variation in important parameters such as thickness of the shotcrete, fracture energy, and bond strength between shotcrete and rock exists. In this paper, a numerical framework for non-linear analyses of FRS suitable for Monte Carlo simulations is presented. As a case study, a 2D FE-model of a bolted shotcrete lining subjected to load from a pushing block was used to perform a sensitivity analysis for the variation in thickness. Results indicate that an irregular shotcrete thickness highly affects the failure load but has a smaller impact on ductility.

  • 23.
    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.

  • 24.
    Strömberg, Larissa
    et al.
    NCC Nordic Construction Company, Infrastructure Business Area, Solna, Sweden.
    Löfsjögård, Malin
    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.
    Hintze, Staffan
    NCC Nordic Construction Company, Infrastructure Business Area, Solna, Sweden.
    Optimization parameter sets for sustainable concrete in tunnels2019In: ISEC 2019 - 10th International Structural Engineering and Construction Conference2019, ISEC Press , 2019Conference paper (Refereed)
    Abstract [en]

    Public and private clients are beginning to set complex optimization requirements, taking into consideration environmental and cost-efficiency parameters over the built construction’s lifetime. The early design process is currently irreversible and this makes it difficult to change a concrete structure in the later detailed design stage, when more accurate information is available regarding environmental impact and life-cycle costs. There is a dilemma in complying with existing standards to achieve technical requirements while optimizing a concrete structure in order to reduce the climate impact. The long-term goal of the project is to develop a new theoretical concept for dynamic optimization strategies which can be applicable to the early design, the client-requirement preparation, the detailed design, the production and the follow-up stages. This paper presents the results of the up-start phase of the project. Our work has focused on the identification of current practice regarding clients’ requirements for technical, environmental and cost-efficiency parameters. An analysis of these requirements with sprayed concrete in a number of ongoing projects has led to the identification of optimization parameter sets. The project has also shown how the physical values of those parameters can be collected from existing statistics, experience recovery databases and previous project requirements, or calculated according to standardized methods and tools. The concept developed will be used in a demonstrative modeling in the next project step.

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