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  • 1.
    Bergström, Markus
    et al.
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering.
    Täljsten, Björn
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Structural and Construction Engineering.
    Carolin, Anders
    Failure load test of a CFRP strengthened railway bridge in Örnsköldsvik, Sweden2009In: Journal of Bridge Engineering, ISSN 1084-0702, E-ISSN 1943-5592, Vol. 14, no 5, p. 300-308Article in journal (Refereed)
    Abstract [en]

    The results obtained when performing a load test to failure of an existing structure are valuable when assessing calculation models, updating finite element models, and investigating the true structural behavior. In this paper a destructive testing and monitoring of a railway bridge in Örnsköldsvik, Sweden is presented. In this particular test the shear capacity of the concrete girders was of primary interest. However, for any reasonable placement of the load (a line load placed transverse to the track direction) a bending failure would occur. This problem was solved by strengthening for flexure using carbon fiber reinforced polymer (CFRP) rectangular rods epoxy bonded in sawed up slots, e.g., near surface mounted reinforcement. The strengthening was very successful and resulted in a desired shear failure when the bridge was loaded to failure. The load-carrying capacity in bending for the unstrengthened and strengthened bridge as well as the shear capacity was predicted with Monte Carlo simulations. The particular calculation presented showed that there was a 25% probability of a bending failure instead of a shear failure. Monitoring showed that the strengthening reduced the strain in the tensile steel reinforcement by approximately 10%, and increased the height of the compressed zone by 100 mm. When the shear failure occurred, the utilization of the compression concrete and CFRP rods were 100 and 87.5%, respectively. This indicates that a bending failure indeed was about to occur, even though the final failure was in shear.

  • 2.
    Cremona, Christian
    et al.
    Technical Department for Transport, Roads, Bridges and road Safety Bagneux Cedex.
    Eichler, Bjorn
    Johansson, Bernt
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Structural and Construction Engineering.
    Larsson, Tobias
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Structural and Construction Engineering.
    Improved assessment methods for static and fatigue resistance of old metallic railway bridges2013In: Journal of Bridge Engineering, ISSN 1084-0702, E-ISSN 1943-5592, Vol. 18, no 11, p. 1164-1173Article in journal (Refereed)
    Abstract [en]

    A large number of the bridges in the European railway networks are metallic bridges. The increasing volume of traffic and axle weight of trains mean that for many structures the loads today are much higher than those envisaged when they were designed. This paper presents a summary of the different recommendations and advices proposed in "Guidelines for Load and Resistance Assessment of Existing European Railway Bridges" of the European Union founded project "Sustainable bridges" for assessing old metal railway bridges. The knowledge of the material properties of existing metal bridges is essential for the resistance assessment and the determination of the remaining lifetime of old metallic bridges. Furthermore, old bridges require more exact and efficient assessment methods that call for a precise description of the material. Among the problems met in metal bridges and material properties estimation, fatigue is the most common cause of failure. To be able to make accurate assessments of existing bridges, it is important to know the behaviour of bridges exposed to fatigue, and how the old materials behave due to cyclic exposure. The main question answered herein is how to make a safe estimation concerning the remaining life in service. The possible traffic load on steel rail bridges is usually limited by the fatigue resistance, but for certain situations the static resistance has also to be checked. Most design rules for steel structures, for instance those in Eurocode 3, are applicable also to riveted structures. However, some information is missing on how to deal with the special case that elements are intermittently connected in contrast welded structures that are connected continuously. As the traditional methods for assessing the resistance of steel bridges are based on elastic analysis, a method for utilizing a limited redistribution of bending moments based on beam theory is proposed.

  • 3.
    Ekevad, Mats
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Wood Science and Engineering.
    Jacobsson, Peter
    Martinssons Träbroar AB.
    Forsberg, Göran
    SP Trätek.
    Slip between glulam beams in stress-laminated timber bridges: finite element model and full-scale destructive test2011In: Journal of Bridge Engineering, ISSN 1084-0702, E-ISSN 1943-5592, Vol. 16, no 2, p. 188-196Article in journal (Refereed)
    Abstract [en]

    Stress laminated timber bridge decks consist of several sawn timber beams or glulam beams held together with prestressed steel bars. Frictional shear stresses between the beams transfer loads between individual beams. The vertical (transverse) shear stress component has been discussed extensively before; this paper further considers the horizontal shear stress. A full-scale test and corresponding finite element simulations for a specific load case confirmed the occurrence of horizontal slip between beams. The finite element model handled both vertical and horizontal frictional slip using an elastic-plastic material model. The results showed that the finite element model gives reliable results and that slip in general leads to permanent deformations that may increase with load cycling. Horizontal slip between beams over a large area of the bridge deck begin at a low load, resulting in a redistribution of load between beams, but do not lead to immediate failure. Vertical slip between beams start at a high load close to the load application point and lead to failure.

  • 4.
    Ekholm, Kristoffer
    et al.
    Chalmers University of Technology.
    Ekevad, Mats
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Wood Science and Engineering.
    Kliger, Robert
    Chalmers University of Technology.
    Modeling slip in stress-laminated timber bridges: comparison of two finite-element-method approaches and test values2014In: Journal of Bridge Engineering, ISSN 1084-0702, E-ISSN 1943-5592, Vol. 19, no 9, article id 4014029Article in journal (Refereed)
    Abstract [en]

    Finite-element (FE) simulations of the deformation behavior of a 5.4-m-long, 8-m-wide, and 0.27-m-thick stress-laminated timber bridge deck were conducted. The simulation results were compared with full-scale test results when using a load resembling an axle load placed near the edge and when cycling the load between a high and low value. Two separate approaches to nonlinear FE modeling were used. The first FE model simulates a frictional slip between the glulam beams with an elastic-plastic material model. The second FE model simulates a frictional slip by modeling each discrete contact surface between each beam in the deck. The results show good agreement between simulation and test results and reveal that the simulation model that models contact surfaces produces slightly better results at the expense of a greater modeling effort and increased computational time. Hysteresis in the load versus deformation curves is clearly visible and was due to significant slip between the glulam beams, which was successfully simulated.Read More: http://ascelibrary.org/doi/abs/10.1061/%28ASCE%29BE.1943-5592.0000595

  • 5.
    Elfgren, Lennart
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Structural and Fire Engineering.
    Discussion of “Failure Load Test of a CFRP Strengthened Railway Bridge in Örnsköldsvik, Sweden” by Marcus Bergström, Björn Täljsten, and Anders Carolin2011In: Journal of Bridge Engineering, ISSN 1084-0702, E-ISSN 1943-5592, Vol. 16, no 3, p. 490-Article in journal (Refereed)
    Abstract [en]

    The authors have written an interesting paper on the test to failure of a strengthened railway bridge. However, the failure mode analysis of the bridge as built is not correct. The failure mode is the same for the bridge as built as for the strengthened bridge, i.e., crushing of the compression concrete with yielding of the steel in tension. For the strengthened bridge, bond failure of the carbon-fiber-reinforced polymer (CFRP)reinforcement also played an important part in the initiation of the final collapse. Eq. (1) in the original paper underestimates the bending moment capacity M1 of the bridge as built almost by a factor of 2 as loading up to crushing of the concrete was not considered. Instead, Eq. (8) should have been used with a zero contribution from strengthening. In Eq. (8) there is also a printing error as the coefficient β2 is left out in the last parentheses (it should read “h - β2x2” instead of “h - 2”). The underestimation of the capacity of the bridge as built gives erroneous results in Table 2 and in Fig. 5. In Table 2 the height x1 of the compression zone for the bridge as built should be about half the given value of 291 mm. The value M1 corresponding to the bridge as built should be about twice the given value of 4.5 MN. The given flexural capacities M1 and M2, of the as built and strengthened bridges, respectively, refer to the corresponding applied vertical load P causing the flexural moments and not to the moments themselves. This explains why the unit MN is used instead of MN·m. Furthermore, the shear capacity V also refers to the corresponding applied vertical load P causing the shear and not to the shear capacity itself (which is about half the value of the applied load P). Furthermore, in Table 2 the comment to the shear capacity V should be referring to Eq. (11) instead of to Eq. (6). In Fig. 5, all the load values refer to the values of the applied load P causing the shear and flexure;  not to the moments M1 and M2 or to the shear force T. After the corrections mentioned previously, the values corresponding to the two moments M1 and M2 will be located much closer to each other. 

    The corrections do not change the main conclusions of the paper, and the discusser agrees with the authors that the tested bridge gives a good example of the complex interaction of bending and shear in concrete bridges. Additional information about the test and the different analysis of it and the European Research Project, which it was a part of, can be found in Elfgren et al. (2008), Puurula et al. (2008), Feltrin et al. (2008), Helmerich et al. (2008), Jensen et al. (2008), Täljsten et al. (2008), and Sustainable Bridges (2008).

  • 6.
    Nilimaa, Jonny
    et al.
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Structural and Construction Engineering.
    Blanksvärd, Thomas
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Structural and Construction Engineering.
    Täljsten, Björn
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Structural and Construction Engineering.
    Elfgren, Lennart
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Structural and Construction Engineering.
    Unbonded Transverse Posttensioning of a Railway Bridge in Haparanda, Sweden2014In: Journal of Bridge Engineering, ISSN 1084-0702, E-ISSN 1943-5592, Vol. 19, no 3, article id 4013001Article in journal (Refereed)
    Abstract [en]

    The majority of railway lines in Sweden are designed to support axle loads of up to 250 kN. Because of increased transport needs on some lines, an axle load limit of at least 300 kN would be beneficial. To upgrade the Haparanda line in northern Sweden to 300 kN, the slabs in existing concrete trough bridges require a higher transverse shear resistance. Methods for in situ strengthening of bridge slabs in this way have not been fully developed, and this paper discusses the possibility of increasing the load capacity by horizontal prestressing. Internal, unbonded posttensioning was performed on one bridge on the Haparanda line, and the strengthening effects were investigated. The strengthening was designed according to the European Eurocode design regulations, and testing was conducted before and after the implementation. Strains in the main transverse reinforcement, caused by a train with an axle load of 215 kN, were completely counteracted by eight prestressing bars, stressed with 430 kN/bar. The results indicate that the actual strengthening effect is larger than what is predicted by the design equations. The Haparanda project showed that unbonded posttensioning can be implemented relatively fast and does not obstruct the ongoing railway traffic during installation

  • 7.
    Pétursson, Hans
    et al.
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Structural and Construction Engineering.
    Kerokoski, O.
    Tampere University of Technology, Department of Civil Engineering.
    Monitoring and analysis of abutment‐soil interaction of two integral bridges2013In: Journal of Bridge Engineering, ISSN 1084-0702, E-ISSN 1943-5592, Vol. 18, no 1, p. 54-64Article in journal (Refereed)
    Abstract [en]

    Field tests of two jointless bridges are presented, focusing on the magnitude and significance of earth pressure behind the abutments. The Haavistonjoki Bridge is a 56 m long, continuous three span bridge. Instrumentation was used to measure the horizontal displacement of an abutment, abutment rotation, abutment pile strains, earth pressures behind the abutments, superstructure displacements, frost depth and air temperature. The measured earth pressures were compared with pressures that had been calculated on the basis of Nordic codes of practice and the Eurocodes pertaining to bridges. The bridge over the Leduån is a single span composite bridge with a cast‐in‐place concrete deck on top of two steel beams. This bridge, spanning 40 m, is slender, with a 1.7 m high superstructure. The bridge was fitted with strain and displacement gauges and short term measurements were made using a loaded truck. The field test results for this bridge were verified with calculations based on an abutment rotation stiffness calculation model developed during the research presented in this paper

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