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Larsson, J. & Flansbjer, M. (2020). An Approach to Compensate for the Influence of the System Normal Stiffness in CNS Direct Shear Tests. Rock Mechanics and Rock Engineering
Open this publication in new window or tab >>An Approach to Compensate for the Influence of the System Normal Stiffness in CNS Direct Shear Tests
2020 (English)In: Rock Mechanics and Rock Engineering, ISSN 0723-2632, E-ISSN 1434-453XArticle in journal (Refereed) Epub ahead of print
Abstract [en]

Applying accurate normal load to a specimen in direct shear tests under constant normal stiffness (CNS) is of importance for the quality of the resulting data, which in turn influences the conclusions. However, deficiencies in the test system give rise to a normal stiffness, here designated as system normal stiffness, which results in deviations between the intended and actual applied normal loads. Aiming to reduce these deviations, this paper presents the effective normal stiffness approach applicable to closed-loop control systems. Validation through direct shear tests indicates a clear influence of the system normal stiffness on the applied normal load (13% for the test system used in this work). The ability of the approach to compensate for this influence is confirmed herein. Moreover, it is demonstrated that the differences between the measured and the nominal normal displacements are established by the normal load increment divided by the system normal stiffness. This further demonstrates the existence of the system normal stiffness. To employ the effective normal stiffness approach, the intended normal stiffness (user defined) and the system normal stiffness must be known. The latter is determined from a calibration curve based on normal loading tests using a stiff test dummy. Finally, a procedure is presented to estimate errors originating from the application of an approximate representation of the system normal stiffness. The approach is shown to effectively reduce the deviations between intended normal loads and the actual applied normal loads. © 2020, The Author(s).

Place, publisher, year, edition, pages
Springer, 2020
Keywords
Calibration, CNS, Dilatancy, Direct shear test, Normal load, Stiffness test system, Closed loop control systems, Testing, Calibration curves, Constant normal stiffness, Normal displacement, Normal loads, Normal stiffness, Stiffness tests, Stiffness
National Category
Natural Sciences
Identifiers
urn:nbn:se:ri:diva-44085 (URN)10.1007/s00603-020-02051-0 (DOI)2-s2.0-85079467556 (Scopus ID)
Note

Funding details: BeFo 391; Funding details: Svensk Kärnbränslehantering, SKB; Funding details: Nuclear Waste Management Organization, NWMO; Funding text 1: Open access funding provided by RISE Research Institutes of Sweden. The authors would like to acknowledge the research funding granted by BeFo Rock Engineering Research Foundation (grant proposal BeFo 391) and SKB, Swedish Nuclear Fuel and Waste Management Co, Solna, Sweden. The authors would also like to thank Adjunct Professor Diego Mas Ivars at SKB, Swedish Nuclear Fuel and Waste Management Co; Associate Professor Fredrik Johansson at KTH Royal Institute of Technology; and Adjunct Professor Erland Johnson at RISE Research Institutes of Sweden AB for their valuable contribution to this work.

Available from: 2020-02-26 Created: 2020-02-26 Last updated: 2020-04-07Bibliographically approved
Williams Portal, N., Flansbjer, M., Carró-Lopez, D. & Fernandez, I. (Eds.). (2020). Analysis of tensile behavior of recycled aggregate concrete using acoustic emission technique. Paper presented at 3RD RILEM Spring Convention 2020, Ambitioning a Sustainable Future for Built Environment: comprehensive strategies for unprecedented challenge, March 10-14, 2020, Guimaraes, Portugal. Bagneux, France: Rilem publications
Open this publication in new window or tab >>Analysis of tensile behavior of recycled aggregate concrete using acoustic emission technique
2020 (English)Conference proceedings (editor) (Refereed)
Abstract [en]

Recycled concrete aggregate (RCA) was processed from reinforced concrete edge beams sourced from a demolished bridge. This material replaced different ratios of coarse aggregate in a benchmark concrete. The tensile behavior of the developed concrete mixes was characterized via monotonic and cyclic uni-axial tensile tests performed on notched cylinders. Such tensile tests allow for the quantification of the fracture energy and softening behavior of the concrete. Moreover, acoustic emission (AE) measurements were conducted in conjunction with the cyclic tests to characterize e.g. micro-crack initiation and development, as well as crack localization. The tensile behavior of the various materials was found to be similar with minimal variation in the results. However, the softening behavior suggests that the RCA materials are slightly more brittle compared to both the mother and benchmark materials. The corresponding AE measurements also indicated similarities between the micro-crack initiation and development for these mixes. It can be constituted that if the concrete used to produce RCA is of high quality and from one source, the resulting RAC will have adequate tensile properties with minimal variation, despite the aggregate replacement ratio.

Place, publisher, year, edition, pages
Bagneux, France: Rilem publications, 2020. p. 12
Keywords
Recycled aggregates, Recycled aggregate concrete, Acoustic emission, Tensile behaviour
National Category
Infrastructure Engineering Composite Science and Engineering Construction Management
Identifiers
urn:nbn:se:ri:diva-44727 (URN)
Conference
3RD RILEM Spring Convention 2020, Ambitioning a Sustainable Future for Built Environment: comprehensive strategies for unprecedented challenge, March 10-14, 2020, Guimaraes, Portugal
Available from: 2020-04-15 Created: 2020-04-15 Last updated: 2020-05-28Bibliographically approved
Robuschi, S., Lundgren, K., Fernandez, I. & Flansbjer, M. (2020). Anchorage of naturally corroded, plain reinforcement bars in flexural members. Materials and Structures, 53(2), Article ID 38.
Open this publication in new window or tab >>Anchorage of naturally corroded, plain reinforcement bars in flexural members
2020 (English)In: Materials and Structures, ISSN 1359-5997, E-ISSN 1871-6873, Vol. 53, no 2, article id 38Article in journal (Refereed) Published
Abstract [en]

Reinforced concrete structures are often damaged by corrosion, which affects the interaction between reinforcement bars and concrete. Earlier studies mostly applied artificial corrosion to test the bond between deformed bars and concrete. However, there is a lack of knowledge on the effects of natural corrosion on plain bars. In this paper, 20 beams with naturally corroded plain bars and varying amount of damage were taken from an 80-year-old bridge and tested in three-point bending. All but three of the specimens anchored the yield force of the bars after the opening of one or two major bending cracks. At large deflections, the load-carrying mechanism changed from beam to arch action. Eventually, end-slip of the reinforcement bars was observed. The bars were extracted, cleaned, three-dimensionally scanned, and tested in tension. The average bond strength in the unyielded zone was found to be equal to 7.39 MPa, with a standard deviation of 3.33 MPa. The casting position was identified as an important factor: when uncorroded, bottom-cast bars had a higher bond strength than that of top-cast bars. However, they were more prone to splitting cracks and, consequently, loss of bond strength for small corrosion levels. Top-cast bars had increasing bond strength with increasing corrosion levels, owing to the absence of external cracks. These differences were likely related to a denser concrete surrounding the bottom-cast bars. The remaining bond capacity in the yielded zones was evaluated to be approximately 1.0 MPa. © 2020 The Author(s).

Place, publisher, year, edition, pages
Springer, 2020
Keywords
Bond strength, Concrete, Natural corrosion, Plain bars, Post-yielding, Three-point bending test, Arch bridges, Bond strength (materials), Concretes, Rebar, Reinforced concrete, Corrosion levels, Large deflection, Plain reinforcement, Reinforcement bar, Standard deviation, Three point bending, Corrosion
National Category
Natural Sciences
Identifiers
urn:nbn:se:ri:diva-44713 (URN)10.1617/s11527-020-01471-2 (DOI)2-s2.0-85082592124 (Scopus ID)
Note

Funding details: Svenska Forskningsrådet Formas; Funding details: Trafikverket; Funding text 1: The work was funded by the Swedish research council Formas and the Swedish Transport Administration.

Available from: 2020-04-27 Created: 2020-04-27 Last updated: 2020-04-27Bibliographically approved
Flansbjer, M., Williams Portal, N., Hall, S. & Engqvist, J. (2019). Analysis of Fiber-matrix Interaction in FRC using X-ray Tomography and Digital Volume Correlation. In: proc. of 10th International Conference on Fracture Mechanics of Concrete and Concrete Structures (FraMCoS-X): . Paper presented at 10th International Conference on Fracture Mechanics of Concrete and Concrete Structures (FraMCoS-X), Bayonne, France, 23-26 June 2019. Bayonne, France: International Association of Fracture Mechanics for Concrete and Concrete Structures
Open this publication in new window or tab >>Analysis of Fiber-matrix Interaction in FRC using X-ray Tomography and Digital Volume Correlation
2019 (English)In: proc. of 10th International Conference on Fracture Mechanics of Concrete and Concrete Structures (FraMCoS-X), Bayonne, France: International Association of Fracture Mechanics for Concrete and Concrete Structures , 2019, , p. 8Conference paper, Published paper (Refereed)
Abstract [en]

Fiber pull-out is generally considered to be the dominating failure mechanism in fiber reinforced concrete (FRC). Accordingly, pull-out tests are typically performed to characterize the fiber-matrix interaction. However, little direct insight can be gained on the actual mechanisms ofthe pull-out from such a test. Deeper understanding could however be gained through the addition of non-destructive techniques to pull-out tests to enable the visualization and quantification of the mechanical interaction. Pull-out mechanisms for different common steel fibers were investigated using adapted pull-out tests performed in-situ in an X-ray micro tomography (µXRT). High resolution volume images from the µXRT scans enable clear visualization of aggregates, pores, fiber and fiber-matrix interface. Furthermore, the natural density speckle pattern from aggregate distribution and pores was found to be suitable for Digital Volume Correlation (DVC) analysis. From the DVC results it was possible to visualize and quantify the strain distribution in the matrix around the fiber at different load levels up to final failure, being marked by either pull-out or fiber rupture. The load transfer mechanism was initially dominated by shear along the fiber. As the load increased, slip occurred in the end-hook region and mechanical locking became the governing mechanism. This study demonstrates that strain measurements within the concrete matrix and passive end-slip can be obtained successfully using µXRT imaging and DVC analysis, which leads to an increased understanding of the interaction mechanisms in fiber reinforced concrete under mechanical loading.

Place, publisher, year, edition, pages
Bayonne, France: International Association of Fracture Mechanics for Concrete and Concrete Structures, 2019. p. 8
Keywords
Fiber reinforced concrete; pull-out behavior; X-ray Computed Tomography, Digital Volume Correlation
National Category
Infrastructure Engineering
Identifiers
urn:nbn:se:ri:diva-39953 (URN)10.21012/FC10.233198 (DOI)
Conference
10th International Conference on Fracture Mechanics of Concrete and Concrete Structures (FraMCoS-X), Bayonne, France, 23-26 June 2019
Available from: 2019-09-23 Created: 2019-09-23 Last updated: 2019-09-27Bibliographically approved
Williams Portal, N. & Flansbjer, M. (2019). Assessment of Fire Exposed Concrete with Full-field Strain Determination and Predictive Modelling. In: : . Paper presented at 10th International Conference on Fracture Mechanics of Concrete and Concrete Structures (FraMCoS-X). Bayonne, France: International Association of Fracture Mechanics for Concrete and Concrete Structures
Open this publication in new window or tab >>Assessment of Fire Exposed Concrete with Full-field Strain Determination and Predictive Modelling
2019 (English)Conference paper, Published paper (Refereed)
Abstract [en]

A condition assessment of civil engineering structures is typically performed after the occurrence of a fire incident to determine the remedial actions required out of a structural point of view. A condition assessment is based on the mapping of damage on the given structure, which is traditionally executed via methods that yield indirect results related to surface and/or geometric properties. To be able to predict the accurate fire resistance performance of a given structure, it is most suitable to apply a mapping method which can be directly coupled to the change in material properties of concrete at high temperatures. The aim of this study is to explore the potential of applying an innovative damage mapping methodology directly coupled to the change in material properties of concrete at high temperatures. This methodology consists of optical full-field strain measurements based on Digital Image Correlation (DIC) coupled with a predictive model based on finite-element analysis (FEA). An experimental study was firstly conducted to expose concrete slabs to a standard fire curve. Subsequently, compression tests were performed on drilled cores taken from the damaged induced specimens, all while optically measuring the full-field strain on a specimen surface. As a preliminary step, an FE model of a fire exposed core was developed based on input data from standard temperature-dependent properties. The analysis consisted of a sequentially coupled thermal stress analysis to solve the multiphysics problem. The model was able to capture the temperature distribution in the concrete with enough certainty given the choice of input data. The resulting strain along the height of the core was also comparable to the experimental optical strain measurements, particularly as the distance increased from the fire exposed surface. These results can be practical when assessing the required strengthening actions to restore the load carrying capacity and durability of the concrete structure.

Place, publisher, year, edition, pages
Bayonne, France: International Association of Fracture Mechanics for Concrete and Concrete Structures, 2019. p. 10
Keywords
concrete, fire, damage assessment, digital image correlation, finite element analysis
National Category
Other Civil Engineering
Identifiers
urn:nbn:se:ri:diva-39952 (URN)10.21012/FC10.232063 (DOI)
Conference
10th International Conference on Fracture Mechanics of Concrete and Concrete Structures (FraMCoS-X)
Available from: 2019-09-23 Created: 2019-09-23 Last updated: 2019-11-25Bibliographically approved
Lindström, C., Flansbjer, M., Appelquist, K., Brander, L. & Sjöqvist, L. (2019). Kvantifiering av mikrostrukturer och dess inverkan på sprickbildning i berg.
Open this publication in new window or tab >>Kvantifiering av mikrostrukturer och dess inverkan på sprickbildning i berg
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2019 (Swedish)Report (Other academic)
Abstract [en]

A new methodology based on monitoring of crack propagation during small-scale mechanical tests on sawn rock prisms under tension has been developed. The methodology includes a combination of different experimental methods and measuring techniques at different scale levels. Material testing is performed through a tensile stage. Crack monitoring is performed by means of Digital Image Correlation and Acoustic Emission. After the test, microcrack and fracture patterns are studied and quantified in thin-sections using fluorescent light under a petrographic microscope.

By using Digital Image Correlation it is possible to follow crack propagation in relation to the microstructure on the surface of the specimen in a detailed way, whereas Acoustic Emission offers real-time measurement of the crack activity within the specimen. By combining these techniques, it is possible to relate the Acoustic Emission signal characteristics to different phases of the cracking process, such as crack initiation, propagation and bridging of microcracks into macrocracks as well as the creation and localization of the final fracture. After the tensile stage test, crack patterns and the final fractures are studied in detail using polarizing and fluorescence microscopy, establishing the relationship of these. The methodology is practiced to increase the knowledge of critical parameters affecting cracking processes in rock materials and to show how this is related to the material's microstructure as well as mesostructure.

Publisher
p. 84
Series
RISE Rapport ; 2019:37
Keywords
Acoustic Emission, digital image correlation, direct tensile test, polarization microscopy, fluorescent light petrography, rock mechanics, microcracks, fracture
National Category
Natural Sciences
Identifiers
urn:nbn:se:ri:diva-38314 (URN)978-91-88907-64-6 (ISBN)
Available from: 2019-04-04 Created: 2019-04-04 Last updated: 2019-04-04
Williams Portal, N., Flansbjer, M. & Honfi, D. (2019). Testing of self-supporting laminated glass balustrades.
Open this publication in new window or tab >>Testing of self-supporting laminated glass balustrades
2019 (Swedish)Report (Other academic)
Abstract [en]

The work carried out within Task 2 Experimental work of the ÅForsk funded project "Structural safety of glass components" is presented in this report. The main goal of this project was to improve the understanding about the structural safety of self-supporting glass components. In particular, the results of the project intended to extend the current knowledge about the effect of impact and related testing methods regarding the safety of glass structures.

Static and impact tests were conducted on a self-supporting glass balustrade with point-fixings. The laminated glass consisted of two 10 mm thick layers of laminated glass and a 0.76 mm thick interlayer made of EVA (ethylene vinyl acetate). A static line load was cyclically applied to the top of the specimen to gain an understanding of the static behaviour of the glass structure and to minimize the settlement in the structure prior to applying impact loading. The specimen was subsequently subjected to dynamic loading by impact tests based on EN 12600 (pendulum impact) with different drop heights until attaining failure. The dynamic structural response of the glass balustrade was analysed by three-dimensional Digital Image Correlation (3D-DIC). This measurement technique made it possible to directly relate the measurement of any point to the specimen and to study the deformed 3D shape in detail during the impact test. The FE-analysis (FEA) conducted using SJ Mepla was found to correlate rather well with the dynamic test results particularly up to the initial peak displacement.

Keywords
safety, impact testing, glass balustrade, laminated glass, digital image correlation, finite-element analysis
National Category
Natural Sciences
Identifiers
urn:nbn:se:ri:diva-40857 (URN)978-91-89049-65-9 (ISBN)
Available from: 2019-11-25 Created: 2019-11-25 Last updated: 2019-11-25Bibliographically approved
Flansbjer, M., Williams Portal, N. & Vennetti, D. (2019). Verification of the structural performance of textile reinforced reactive powder concrete sandwich facade elements. Applied Sciences, 9(12), Article ID 456.
Open this publication in new window or tab >>Verification of the structural performance of textile reinforced reactive powder concrete sandwich facade elements
2019 (English)In: Applied Sciences, E-ISSN 2076-3417, Vol. 9, no 12, article id 456Article in journal (Refereed) Published
Abstract [en]

As a part of the SESBE (Smart Elements for Sustainable Building Envelopes) project, non-load bearing sandwich elements were developed with Textile Reinforced Reactive Powder Concrete (TRRPC) for outer and inner facings, Foam Concrete (FC) for the insulating core and Glass Fiber Reinforced Polymer (GFRP) continuous connectors. The structural performance of the developed elements was verified at various levels by means of a thorough experimental program coupled with numerical analysis. Experiments were conducted on individual materials (i.e., tensile and compressive tests), composites (i.e., uniaxial tensile, flexural and pull-out tests), as well as components (i.e., local anchorage failure, shear, flexural and wind loading tests). The experimentally yielded material properties were used as input for the developed models to verify the findings of various component tests and to allow for further material development. In this paper, the component tests related to local anchorage failure and wind loading are presented and coupled to a structural model of the sandwich element. The validated structural model provided a greater understanding of the physical mechanisms governing the element's structural behavior and its structural performance under various dead and wind load cases. Lastly, the performance of the sandwich elements, in terms of composite action, was shown to be greatly correlated to the properties of the GFRP connectors, such as stiffness and strength

Place, publisher, year, edition, pages
MDPI AG, 2019
Keywords
Finite element analysis (FEA), Foam concrete (FC), Reactive powder concrete (RPC), Sandwich elements, Textile reinforced concrete (TRC), Wind loading
National Category
Natural Sciences
Identifiers
urn:nbn:se:ri:diva-39376 (URN)10.3390/app9122456 (DOI)2-s2.0-85068191709 (Scopus ID)
Available from: 2019-07-08 Created: 2019-07-08 Last updated: 2019-07-08Bibliographically approved
Flansbjer, M., Williams Portal, N., Hall, S. & Engqvist, J. (2018). Analysis of Failure Modes in Fiber Reinforced Concrete Using X-rayTomography and Digital Volume Correlation. In: : . Paper presented at 18th International Conference on Experimental Mechanics, Brussels, Belgium, 1–5 July 2018..
Open this publication in new window or tab >>Analysis of Failure Modes in Fiber Reinforced Concrete Using X-rayTomography and Digital Volume Correlation
2018 (English)Conference paper, Published paper (Refereed)
Abstract [en]

Pull-out mechanisms for different common steel fibers were investigatedusing adapted pull-out tests performed in-situ in an x-ray micro tomograph(µXRT). High-resolution volume images from the µXRT scans enable clearvisualization of aggregates, pores, the fiber and the fiber-matrix interface.Furthermore, the natural density speckle pattern from aggregate distributionand pores was found suitable for Digital Volume Correlation (DVC) analysis.From the DVC results it was possible to visualize and quantify the straindistribution in the matrix around the fiber at the different load levels up tofinal failure, being marked by either pull-out or fiber rupture. This studydemonstrates that strain measurements within the concrete matrix can beobtained successfully using µXRT imaging and DVC analysis, which leads to anincreased understanding of the interaction mechanisms in fibre reinforcedconcrete under mechanical loading.

Keywords
Fiber reinforced concrete; pull-out behavior; X-ray Computed Tomography, Digital Volume Correlation
National Category
Infrastructure Engineering
Identifiers
urn:nbn:se:ri:diva-35557 (URN)
Conference
18th International Conference on Experimental Mechanics, Brussels, Belgium, 1–5 July 2018.
Available from: 2018-11-05 Created: 2018-11-05 Last updated: 2018-11-05Bibliographically approved
Williams Portal, N., Flansbjer, M. & Mueller, U. (Eds.). (2018). Analysis of the Flexural Behavior of Textile Reinforced Reactive Powder Concrete Sandwich Elements Using Optical Measurements. Paper presented at 18th International Conference on Experimental Mechanics, Brussels, Belgium, 1–5 July 2018.. MDPI
Open this publication in new window or tab >>Analysis of the Flexural Behavior of Textile Reinforced Reactive Powder Concrete Sandwich Elements Using Optical Measurements
2018 (English)Conference proceedings (editor) (Refereed)
Abstract [en]

Prefabricated and non-load bearing sandwich façade elements were developed using Textile Reinforced Reactive Powder Concrete (TRRPC) along with low density Foamed Concrete (FC) and Glass Fiber Reinforced Polymer (GFRP) continuous connecting devices. Four-point bending tests were performed on large-scale TRRPC sandwich element beams to characterize the structural performance, which included the flexural capacity, level of composite action, resulting deformation, crack propagation and failure mechanisms. Optical measurements based on Digital Image Correlation (DIC) were taken simultaneously to enable a detailed analysis of the underlying composite action. The structural behavior of the developed elements was found to be highly dependent on the stiffness and strength of the connectors to ensure composite action between the two TRRPC panels.

Place, publisher, year, edition, pages
MDPI, 2018
Keywords
Reactive Powder Concrete; Textile Reinforced Concrete; Foam Concrete; Glass Fiber
National Category
Building Technologies
Identifiers
urn:nbn:se:ri:diva-33930 (URN)10.3390/ICEM18-05221 (DOI)
Conference
18th International Conference on Experimental Mechanics, Brussels, Belgium, 1–5 July 2018.
Funder
EU, FP7, Seventh Framework Programme, 608950
Available from: 2018-06-11 Created: 2018-06-11 Last updated: 2018-08-16Bibliographically approved
Identifiers
ORCID iD: ORCID iD iconorcid.org/0000-0002-3481-1368

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