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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.
    Direct shear strength of high-strength fibre concrete2010In: Magazine of Concrete Research, ISSN 0024-9831, E-ISSN 1751-763X, Vol. 62, no 5, p. 379-390Article in journal (Refereed)
    Abstract [en]

    An experimental and theoretical study of the shear behaviour of steel-fibre-reinforced concrete is presented. Twenty-seven direct shear push-off tests were carried out on high-strength concrete, with and without steel fibre reinforcement. The test series contained uncracked and precracked specimens for the study of the slipping response and the shear stress that can be transferred across an open crack. The test variables were the fibre content and the reinforcement ratio. The test results were compared with information provided by the available codes and other, previous results. The test results indicated that incorporation of steel fibres and bars in concrete members subjected to shear leads to an improved mechanical behaviour before failure. Based on the presented experimental results, an equation governing the direct shear strength is proposed and verified against test results from other test series.

  • 2.
    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.
    Laboratory investigation of stress waves in young shotcrete on rock2012In: Magazine of Concrete Research, ISSN 0024-9831, E-ISSN 1751-763X, Vol. 64, no 10, p. 899-908Article in journal (Refereed)
    Abstract [en]

    To study the behaviour of shotcrete under dynamic load, a non-destructive laboratory experiment was set up with P-wave propagation along a concrete bar, with properties similar to rock. Cement-based mortar with properties that resemble shotcrete was applied to one end of the bar with a hammer impacting the other. The shape of the stress waves travelling towards the shotcrete was registered using accelerometers positioned along the bar. Finite-element modelling was used to verify the test results, which showed that the laboratory model with an impacting hammer could be used to initiate the same type of stress waves that result from blasting in good-quality rock. Previously recommended maximum allowed peak particle vibration velocities were verified.

  • 3.
    Ansell, Anders
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Concrete Structures.
    Recommendations for shotcrete on rock subjected to blasting vibrations, based on finite element dynamic analysis2005In: Magazine of Concrete Research, ISSN 0024-9831, E-ISSN 1751-763X, Vol. 57, no 3, p. 123-133Article in journal (Refereed)
    Abstract [en]

    Shotcrete is sprayed concrete applied pneumatically on, for example, a rock surface to prevent fallout of rock blocks and thereby securing the arch-shape of a tunnel profile. A finite element model, especially adapted to the dynamic analysis of shotcrete on rock that is subjected to vibrations from blasting, has been developed and tested. The model consists of spring and beam elements that are used to simulate the behaviour of an elastic concrete area, bound to a rock surface through adhesion. This facilitates the calculation of a two-dimensional displacement field, using mode superposition and Duhamel integral. The loads applied on the model are accelerations that give rise to inertia forces on the system. The accelerations are calculated from given weights of explosives, geometrical conditions and rock properties. The presented numerical examples demonstrate the response of shotcrete to vibrations, based on material data from an extensive literature survey. A series of calculations are compiled to give recommendations for how close to shotcrete blasting in rock can be allowed.

  • 4.
    Ansell, Anders
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Concrete Structures.
    Shotcrete on rock exposed to large-scale blasting2007In: Magazine of Concrete Research, ISSN 0024-9831, E-ISSN 1751-763X, Vol. 59, no 9, p. 663-671Article in journal (Refereed)
    Abstract [en]

    Shotcrete sprayed on rock is vulnerable to stress waves from large-scale blasting in tunnels and mines. Shotcrete support in a Swedish underground mine is studied through numerical analysis and comparisons with previous results, measurements and observations in situ. A previously developed finite-element model that consists of beam and spring elements is used to calculate the response of shotcrete to vibrations from production blasts in the mine. The modelling approach is similar to that of a building during an earthquake, with accelerations measured in situ used as loads. The analysis shows that the calculated bond stresses exceed the strength in the interface between shotcrete and rock close to the blasts. The results show that it is possible to optimise the scheme of the blasting so that shotcrete is protected from damaging vibrations. Also recommended, for practical use, are minimum distances to large amounts of explosives given. This set of recommendations is a supplement to previously given guidelines valid for small amounts of explosives at short distances from shotcrete on rock.

  • 5.
    Broms, Carl Erik
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Structural Design and Bridges.
    Ductility reinforcement for flat slabs in seismic areas2006In: Magazine of Concrete Research, ISSN 0024-9831, E-ISSN 1751-763X, Vol. 58, no 4, p. 243-254Article in journal (Refereed)
    Abstract [en]

    The reinforcement concept `ductility reinforcement' has previously been shown to give fat slabs such extremely ductile behaviour that the punching failure mode for gravity loading can be considered safely eliminated. That concept is now tested for imposed cyclic storey drift during earthquakes and found to be capable of resisting even severe earthquakes without any additional precautions than those already taken for normal gravity loading. The specimens were loaded with gravity load up to about 75% of their flexural yield capacity in order to simulate the ultimate limit load case involving seismic loads. Design recommendations are given based on these findings, where assessment of transferred moment between slab and column as currently dictated by North American practice is not required.

  • 6.
    Broms, Carl Erik
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Structural Design and Bridges (name changed 20110630).
    Ductility Reinforcement for Flat Slabs in Seismic as well as Non-seismic Areas2005In: Magazine of Concrete Research, ISSN 0024-9831, E-ISSN 1751-763XArticle in journal (Other academic)
  • 7.
    Bryne, Lars Elof
    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.
    Holmgren, Jonas
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Concrete Structures.
    Shrinkage testing of end-restrained shotcrete on granite slabs2014In: Magazine of Concrete Research, ISSN 0024-9831, E-ISSN 1751-763X, p. 1300348-Article in journal (Refereed)
    Abstract [en]

    This study investigated the shrinkage of shotcrete (sprayed concrete), especially the case of shotcrete sprayed on drains – a part of tunnel lining not continuously bonded to the rock. A newly developed method for testing the shrinkage of end-restrained shotcrete slabs is presented and evaluated. The test setup, which is designed to capture in situ behaviour, consists of shotcrete sprayed on an instrumented granite slab partly covered with a plastic sheet. The primary goal was to practically use and evaluate the test method with shotcreted test samples. Results from restrained shrinkage tests are presented along with results for free shrinkage. It is shown that the method realistically captures the behaviour of shotcrete drains on hard rock in situ. In addition, the corresponding compressive strength and flexural crack strength as functions of shotcrete age are also reported. The test method can be used for an evaluation of different solutions for avoiding shrinkage cracks in shotcreted soft drains, or in shotcrete that is fully bonded to a rock surface, with respect to preventing cracking or distributing the shrinkage strain into several fine cracks instead of one wide crack.

  • 8.
    Liu, Fangzhou
    et al.
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Structural Engineering and Bridges.
    Battini, Jean-Marc
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Structural Engineering and Bridges.
    Pacoste, Costin
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Structural Engineering and Bridges.
    Finite-shell-element models for the dynamic analysis of hollow-core concrete floor2019In: Magazine of Concrete Research, ISSN 0024-9831, E-ISSN 1751-763X, Vol. 71, no 10, p. 519-532Article in journal (Refereed)
    Abstract [en]

    Precast and prestressed hollow-core concrete slabs are widely used in construction. The combination of low self-weight and high strength of such slabs makes it possible to design floors with long spans. However, this also implies that the slabs are sensitive to human-induced vibrations. The purpose of this work was to develop a methodology to implement finite-shell-element models that can be used to analyse the dynamic behaviour of hollow-core concrete slabs. Three different shell models with different material properties (orthotropic material, isotropic material with strips and isotropic material) were designed and tested. The models were calibrated and assessed using experimental results obtained on a test structure of dimensions 10 m × 7·2 m consisting of six hollow-core elements.

  • 9.
    Magnusson, Johan
    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.
    Hansson, Håkan
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Concrete Structures.
    Air-blast-loaded, high-strength concrete beams. Part II: Numerical non-linear analysis2010In: Magazine of Concrete Research, ISSN 0024-9831, E-ISSN 1751-763X, Vol. 62, no 4, p. 235-242Article in journal (Refereed)
    Abstract [en]

    The results from this investigation demonstrate the ability to perform numerical simulations of dynamic structural response of concrete elements subjected to air blast loading. Beams of both high-strength concrete (HSC) and normal-strength concrete (NSC) were studied. Also beams with two concrete layers of different strength were simulated. It is of particular interest to investigate the use of material models for implementation with software for the explicit analysis of non-linear dynamic events. The influences of concrete strength, amounts of reinforcement, the bond between concrete and reinforcement, bi-linear strain softening of concrete, the strain rate dependence of reinforcement and boundary conditions at the supports were studied. The simulations were performed with the text data as reference through comparison between numerical examples and experimental test results. It was possible numerically to analyse the dynamic behaviour of beams tested in situ and to describe the observed failure modes of these beams. The analysis tool will be used for evaluating the dynamic strength of future protective structures of HSC, possibly with parts consisting of NSC elements.

  • 10.
    Magnusson, Johan
    et al.
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Concrete Structures.
    Hallgren, Mikael
    Tyréns AB.
    Ansell, Anders
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Concrete Structures.
    Air-blast-loaded, high-strength concrete beams. Part I: Experimental investigation2010In: Magazine of Concrete Research, ISSN 0024-9831, E-ISSN 1751-763X, Vol. 62, no 2, p. 127-136Article in journal (Refereed)
    Abstract [en]

    The structural behaviour of concrete beams subjected to air blast loading was investigated. Beams of both high-strength concrete (HSC) and normal-strength concrete (NSC) were subjected to air blasts from explosives in a shock tube and for reference were also loaded statically. Concrete with nominal compressive strengths of 40, 100, 140, 150 and 200 MPa were used and a few beams also contained steel fibres. Furthermore, beams with two concrete layers of different strength were tested. All beams subjected to static loading failed in flexure. For some beam types, the failure mode in the dynamic tests differed from the failure mode in the corresponding static tests. In these cases, the failure mode changed from a ductile flexural failure in the static tests to a brittle shear failure in the dynamic tests. Beams without fibres and with high ratio of reinforcement exhibited shear failures in the dynamic tests. It was observed that the inclusion of steel fibres increased the shear strength and the ductility of the beams. The investigation indicates that beams subjected to air blast loading obtain an increased load capacity when compared with the corresponding beams subjected to static loading.

  • 11.
    Malm, Richard
    et al.
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Structural Design and Bridges (name changed 20110630).
    Holmgren, Jonas
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Concrete Structures.
    Cracking in deep beams owing to shear loading. Part 1: Experimental study and assessment.2008In: Magazine of Concrete Research, ISSN 0024-9831, E-ISSN 1751-763X, Vol. 60, no 5, p. 371-379Article in journal (Refereed)
    Abstract [en]

    In this paper, laboratory tests to failure of ten large deep beams with I-shaped cross-sections are presented. All beams had the same geometry with a shear span-to-depth ratio of 1.25 but differed in the amount of the vertical and horizontal web reinforcement. The presented results from the measurements consist of load-deformation curves, crack widths and crack patterns and strain distribution near the supports. The ultimate loads for these beams have been calculated with two strut-and-tie models and one truss model. The first strut-and-tie model calculates the tensile contribution of both reinforcement and concrete and takes into account their influence on the principal tensile stress. The second strut-and-tie model is a modification of the first one where the stress distribution along the strut is redefined. The third method is the truss model that is incorporated in a Design Code. The truss model gave the best result for the beams with a higher reinforcement ratio that exhibited in a shear compressive failure. The diagonal tensile failure that occurred in the beams with a small amount of web reinforcement was best captured with the modified strut-and-tie model.

  • 12.
    Malm, Richard
    et al.
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Structural Engineering and Bridges.
    Holmgren, Jonas
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Concrete Structures.
    Cracking in deep beams owing to shear loading. Part 2: Non-linear analysis2008In: Magazine of Concrete Research, ISSN 0024-9831, E-ISSN 1751-763X, Vol. 6, no 5, p. 381-388Article in journal (Refereed)
    Abstract [en]

    In this paper, analyses based on laboratory tests of ten large deep beams with I-shaped cross-sections loaded to failure are presented. All beams had the same geometry with a shear span-to-depth ratio of 1.25, but differed in the amount of the vertical and horizontal web reinforcement. All beam tests resulted in shear failure, either diagonal tensile failure or shear compressive failure, depending on the amount of reinforcement. The diagonal tensile failure is generally considered to be the most difficult failure to treat numerically. In this study different material models incorporated in commercial numerical analysis tools are studied. Material models based on fracture mechanics with either rotated or fixed crack directions as well as a plasticity-based model are used in the analyses. The analyses show that the plasticity-based model in Abaqus gives good agreement with the experiments regarding crack pattern, load-displacement response and estimated crack widths. The models based on fracture mechanics in Atena and Response tend to give too stiff behaviour in the load-displacement response, but generally give a good estimation of the load capacity. The analyses performed with Atena gave good estimations of the crack pattern, and the models with a fixed crack direction also gave good estimates of the crack width.

  • 13.
    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.

  • 14.
    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.

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