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  • 1.
    Axhag, F.
    et al.
    Luleå tekniska universitet.
    Johansson, Bernt
    Tension flange instability of I-beams1999In: Journal of constructional steel research, ISSN 0143-974X, E-ISSN 1873-5983, Vol. 49, no 1, p. 69-81Article in journal (Refereed)
    Abstract [en]

    The possible lateral-torsional instability of an I-beam with braced compression flange is studied. It is shown that taking the sagging prior to lateral-torsional buckling into account gives a finite critical moment. A solution for a uniform I-beam under uniform bending is presented. It is further shown that this solution can be approximated by a simple geometrical relation for the critical strain. This approximation is a lower bound also where the bending is causing inelastic deformations. For normal structures tension flange instability will not be a problem but it may be necessary to consider it for very high strength shallow beams or if plastic rotations occur in the sagging region.

  • 2.
    Collin, Peter
    et al.
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Structural and Construction Engineering.
    Möller, Mikael
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Structural and Construction Engineering.
    Johansson, Bernt
    Lateral-torsional buckling of continuous bridge girders1998In: Journal of constructional steel research, ISSN 0143-974X, E-ISSN 1873-5983, Vol. 45, no 2, p. 217-235Article in journal (Refereed)
    Abstract [en]

    The resistance of bridge girders with respect to lateral-torsional buckling at support is strongly influenced by the moment gradient. In most design methods this influence is taken into account by the use of a correct critical bending moment in the slenderness parameter λ. This critical moment is influenced by the shape of the moment diagram as well as the distortion of the cross-section and the restraint from the web and stiffeners, if any. In this paper, a method for the calculation of the critical moment is presented. A further effect of the moment gradient is that the stresses due to lateral bending of the flange in connection with lateral-torsional buckling does not coincide with the maximum of stresses caused by bending in the vertical plane. This is taken into account by performing the check for lateral-torsional buckling in a design section at some distance from the support. A design procedure based on this concept has been introduced in Eurocode 3 Part 2: Steel Bridges

  • 3.
    Graciano, Carlos
    et al.
    Luleå tekniska universitet.
    Edlund, Bo
    Chalmers University of Technology.
    Failure mechanism of slender girder webs with a longitudinal stiffener under patch loading2003In: Journal of constructional steel research, ISSN 0143-974X, E-ISSN 1873-5983, Vol. 59, no 1, p. 27-45Article in journal (Refereed)
    Abstract [en]

    The failure mechanism of slender girder webs stiffened by a single longitudinal stiffener under patch loading is addressed. Experimental results have shown that failure is due to crippling in the web panel formed between the loaded flange and the stiffener. This mechanism is similar to the one for unstiffened webs, which is characterized by the presence of elastoplastic deformations in the compression flange (plastic hinges) and in the web (yield lines). A longitudinal stiffener with normal position, b1 less than or equal 0.3hw, and rigidity restricts the size of the buckle in the upper web panel, and in some cases the distance between the outermost plastic hinges in the loaded flange is reduced. Based on the upper bound theorem of plastic collapse an expression for the patch loading resistance of webs stiffened by a single horizontal stiffener is presented. Theoretical predictions are in good agreement with experimental results. © 2002 Elsevier Science Ltd. All rights reserved.

  • 4.
    Graciano, Carlos
    et al.
    Luleå tekniska universitet.
    Johansson, Bernt
    Resistance of longitudinally stiffened I-girders subjected to concentrated loads2003In: Journal of constructional steel research, ISSN 0143-974X, E-ISSN 1873-5983, Vol. 59, no 5, p. 561-586Article in journal (Refereed)
    Abstract [en]

    This paper presents a design procedure for the determination of the ultimate resistance of longitudinally stiffened girder webs to concentrated loads. The influence from the longitudinal stiffener is considered in the slenderness parameter λ, through the buckling coefficient kf. This procedure is harmonized with other design procedures currently used for describing buckling problems in steel structures. An expression is developed for the buckling coefficient based on finite element analysis. The interaction between the web plate with flanges and a longitudinal stiffener was considered in the analysis. The ultimate strength according to the design procedure presented herein and the results are compared with available experimental results. The interaction with bending is also investigated

  • 5.
    Graciano, Carlos
    et al.
    Universidad Simon Bolivar, Departamento de Mecanica.
    Lagerqvist, Ove
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Structural and Construction Engineering.
    Critical buckling of longitudinally stiffened webs subjected to compressive edge loads2003In: Journal of constructional steel research, ISSN 0143-974X, E-ISSN 1873-5983, Vol. 59, no 9, p. 1119-1146Article in journal (Refereed)
    Abstract [en]

    The resistance of steel plate girders subjected to concentrated load can be described using a strength curve, which includes a gradual transition from yielding to buckling depending on the slenderness ratio of the web. The slenderness is a function of the ratio of the yield resistance to the critical buckling load. This paper describes a methodology for the determination of buckling coefficients for longitudinally stiffened plate girders subjected to partial edge loading or concentrated loads. After an extensive parametric analysis, the optimum parameters that govern the change from a global buckling mode to a more local buckling mode were found. As in similar buckling problems, the results show that the location and the relative flexural/torsional rigidity of the stiffener are relevant parameters that govern the final buckling shape. Finally an expression for the buckling coefficient used to determine the critical buckling load for longitudinally stiffened girder webs is presented.

  • 6.
    Granath, Per
    et al.
    Chalmers University of Technology.
    Lagerqvist, Ove
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Structural and Construction Engineering.
    Behaviour of girder webs subjected to patch loading1999In: Journal of constructional steel research, ISSN 0143-974X, E-ISSN 1873-5983, Vol. 50, no 1, p. 49-69Article in journal (Refereed)
    Abstract [en]

    This paper concerns the behaviour of bridge girder webs subjected to concentrated forces that are introduced in the web during launching, a load case usually referred to as patch loading. So far, this type of loading has, in engineering practice, been dealt with using formulas originating from investigations concerning the ultimate load carrying capacity. Numerous bridge launchings have, however, led to unwanted damages of the girder web, i.e. plastic deformations of such magnitudes that the webs had to be repaired. To avoid these damages it is necessary to have a design method, for launching situations, which focuses more on avoiding some irreversible behaviour than on the ultimate load carrying capacity. Such a design method has to be based on a deeper understanding of the behaviour of the girder. In Ref. [1] the first author discusses the fact that yielding of the flange occurs only after the web plate has been severely damaged. This paper describes the deformation behaviour of the web plate due to patch loading. For small loads the deformations will be similar to the first linear buckling mode. As the load increases a smaller buckle, in the opposite direction, will start to develop in the web plate close to the load. This behaviour, which may be named post-critical buckling, occurs also for girders of a perfectly elastic material. The investigations are based on laboratory tests and non-linear finite element analyses of three typical girders representing different slenderness categories.

  • 7.
    Granlund, Jan
    et al.
    Luleå tekniska universitet.
    Olsson, Anders
    Modelling of the plastic behaviour of structural steel based on biaxial testing1998In: Journal of constructional steel research, ISSN 0143-974X, E-ISSN 1873-5983, Vol. 46, no 1-3, p. 404-405Article in journal (Refereed)
    Abstract [en]

    The biaxial testing of structural steel in the principal plane σ1-σ2 is presented. The initial yield criterion of the steel falls between the von Mises and Tresca criteria. The subsequent yield criteria are characterized by a pronounced Bauschinger effect and more gradual transition into plastic state in subsequent loading opposite to preloading.

  • 8.
    Heistermann, Christine
    et al.
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Structural and Construction Engineering.
    Veljkovic, Milan
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Structural and Construction Engineering.
    Simões, R.
    ISISE, Department of Civil Engineering, University of Coimbra.
    Rebelo, C.
    ISISE, Department of Civil Engineering, University of Coimbra.
    Silva, L. Simões da
    ISISE, Department of Civil Engineering, University of Coimbra.
    Design of slip resistant lap joints with long open slotted holes2013In: Journal of constructional steel research, ISSN 0143-974X, E-ISSN 1873-5983, Vol. 82, p. 223-233Article in journal (Refereed)
    Abstract [en]

    Current design procedures for slip resistant connections according to Eurocodes and American specifications are reviewed. Although failure of a slip resistant connection is defined at different levels of slip, 0.15 mm and 0.5 mm respectively, the calculation of the resistance is similar. Most of the research is performed on bolts in normal clearance holes. A testing program was conceived to evaluate the influence of long open slotted holes on the behavior of slip resistant lap joints with tension control bolts because of possible use of such connections in towers for wind turbines. In comparison to specimens with normal clearance holes it is found that the friction coefficient is about 4% lower. This reduction is lower than suggested by the current correction factors. Since none of the design procedures takes the reduction in bolt forces by time into account, the loss of pretension force is experimentally studied and an approximation is proposed. A second testing program was carried out with friction standard specimens in order to determine the slip factor for different surface treatments and steel grades in range between S275 and S690. The achieved slip factors for different surface preparations are in accordance with the classification of friction surfaces in EN 1090-2:2008 and differences obtained are addressed to variations in exposure to weather conditions. The steel grade does not have a significant influence.

  • 9.
    Heistermann, Tim
    et al.
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Structural and Construction Engineering.
    Koltsakis, Efthymios
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Structural and Construction Engineering.
    Veljkovic, Milan
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Structural and Construction Engineering.
    Lopes, Fernanda
    University of Coimbra, Department of Civil Engineering.
    Santiago, Aldina
    ISISE, Department of Civil Engineering, University of Coimbra.
    Silva, Luís Simões da
    Virginia Polytechnic Institute and State University, Universidade de Coimbra , ISISE, Department of Civil Engineering, University of Coimbra.
    Initial stiffness evaluation of reverse channel connections in tension and compression2015In: Journal of constructional steel research, ISSN 0143-974X, E-ISSN 1873-5983, Vol. 114, p. 119-128, article id 4268Article in journal (Refereed)
    Abstract [en]

    The so-called Reverse Channel connection has been conceived for the purpose of accommodating the thermal expansion of beams so that premature failure due to thermal buckling is avoided. The connection is made of a channel-shaped element, welded along the tips of its flanges onto the face of a hollow section column; an endplate welded on the beam is bolted onto the web of the channel. In a fire situation, the thermal expansion of a reverse-channel supported beam causes extensive bending deformation of the connection, therefore preventing the development of significant axial stress in the beam. Furthermore, this connection offers a high rotational capacity, if designed properly, which is beneficial in a fire situation where excessive deflections of beams can be expected. This paper aims to provide analytical stiffness assessment tools for reverse channel connections in compression and tension under uniform temperatures. The proposed analytical models are compared to results of Finite Element simulations, which in turn have been benchmarked with experiments. In addition, a comprehensive parametric study is conducted in order to identify all influencing factors on the initial stiffness response: reverse channel geometry and thickness, plate thickness, bolt position, and bolt diameter. Correction factors that account for 3D effects and bolt size are presented and discussed. The obtained expressions for the reverse channel stiffness are found to provide an accuracy that is acceptable for structural applications and can, therefore, be used as a design tool

  • 10.
    Hällmark, Robert
    et al.
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Structural and Fire Engineering. Swedish Transport Administration, Luleå, Sweden.
    Collin, Peter
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Structural and Fire Engineering. Ramboll, Luleå, Sweden.
    Hicks, Stephen J.
    Heavy Engineering Research Association, Auckland, New Zealand.
    Post-installed shear connectors: Fatigue push-out tests of coiled spring pins2019In: Journal of constructional steel research, ISSN 0143-974X, E-ISSN 1873-5983, Vol. 153, p. 298-309Article in journal (Refereed)
    Abstract [en]

    The number of heavy vehicles and their weight have been increasing over time, implying that many bridges are experiencing traffic loads with higher magnitude and frequency than they were originally designed for. In some cases, it will be necessary to either replace or strengthen the structures to keep the bridges in service. For existing non-composite steel girder bridges, post-installation of shear connectors can often be used to increase the traffic load capacity significantly. One type of shear connector that is suitable for post-installation, even though not commonly used, is the Coiled Spring Pin. These interference fit connectors can be installed from below the bridge deck during traffic, in order to minimize the impact on road users. This paper describes an experimental study on the fatigue strength of Coiled Spring Pins and a compilation of previously performed fatigue tests on this type of connector. The new test series, with nine specimens, are evaluated statistically and a fatigue strength design equation is proposed. The results show that there are large variations between different test series, while tests within the same series show good agreement. The reasons for this are discussed in the paper along with recommendations for future testing.

  • 11.
    Hällmark, Robert
    et al.
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Structural and Fire Engineering. Swedish Transport Administration, Luleå, Sweden.
    Collin, Peter
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Structural and Fire Engineering. Ramboll, Luleå, Sweden.
    Hicks, Stephen J.
    Heavy Engineering Research Association, Auckland, New Zealand.
    Post-installed Shear Connectors: Push-out Tests of Coiled Spring Pins vs. Headed Studs2019In: Journal of constructional steel research, ISSN 0143-974X, E-ISSN 1873-5983, Vol. 161, p. 1-16Article in journal (Refereed)
    Abstract [en]

    Steadily increasing traffic volumes and traffic loads lead to a continuously growing demand for bridge rehabilitation, strengthening and replacement projects. For existing steel girder bridges with non-composite concrete decks, the traffic load capacity can often be increased significantly if composite action can be created afterwards. Different kinds of shear connectors are more or less suitable for post-installation. Coiled spring pins are one type of interference fit connector that can be installed from below the bridge deck during traffic, in order to minimize the impact on road users. This paper describes an experimental study on the static capacity and stiffness of coiled spring pins used as shear connectors at steel-concrete interfaces. Six push-out test series are presented, with a total of 28 tests, together with an alternative type of test set-up. The results show that the failure of the coiled spring pins is very ductile and that the load capacity is predictable and sufficient for a cost-effective application. The tests also indicate a significantly lower stiffness of the connectors in comparison to welded headed studs of similar dimensions, which might be of great importance if an existing shear connection is strengthened.

  • 12.
    Jesus, Abílio M.P. de
    et al.
    IDMEC/Engineering Department, School of Sciences and Technology, University of Trás-os-Montes and Alto Douro.
    Matos, Rui
    ISISE, Department of Civil Engineering, University of Coimbra.
    Fontoura, Bruno F.C.
    IDMEC/Engineering Department, School of Sciences and Technology, University of Trás-os-Montes and Alto Douro.
    Rabelo, Carlos
    ISISE, Department of Civil Engineering, University of Coimbra.
    Silva, Lois Simões da
    ISISE, Department of Civil Engineering, University of Coimbra.
    Veljkovic, Milan
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Structural and Construction Engineering.
    A comparison of the fatigue behavior between S355 and S690 steel grades2012In: Journal of constructional steel research, ISSN 0143-974X, E-ISSN 1873-5983, Vol. 79, p. 140-150Article in journal (Refereed)
    Abstract [en]

    The use of higher strength steels allows the design of lighter, slenderer and simpler structures. Nevertheless, the increase of the yield strength of the steels does not correspond to a proportional increase of fatigue resistance, which makes the application of high strength steels on structures prone to fatigue, a major concern of the design. This paper presents a comparison of the fatigue behavior between the S355 mild steel and the S690 high strength steel grades, supported by an experimental program of fatigue tests of smooth specimens, performed under strain control, and fatigue crack propagation tests. Besides the cyclic elastoplastic characterization, the fatigue tests of smooth small size specimens allow the assessment of the fatigue crack initiation behavior of the materials. Results show that the S690 steel grade presents a higher resistance to fatigue crack initiation than the S355 steel. However, the resistance to fatigue crack propagation is lower for the S690 steel grade, which justifies an inverse dependence between static strength and fatigue life, for applications where fatigue crack propagation is the governing phenomenon. Consequently, the design of structural details with the S690 steel should avoid sharp notches that significantly reduce the fatigue crack initiation process.

  • 13. Johansson, Bernt
    et al.
    Lagerqvist, Ove
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Structural and Construction Engineering.
    Resistance of plate edges to concentrated forces1995In: Journal of constructional steel research, ISSN 0143-974X, E-ISSN 1873-5983, Vol. 32, no 1, p. 69-105Article in journal (Refereed)
    Abstract [en]

    The prediction of the resistance of plate edges to concentrated loads has been dealt with in numerous studies of a more or less empirical nature. The normal approach is to use two criteria for the resistance, one based on yielding and one based on instability. This study aims at a procedure that is harmonized with those normally used for describing other buckling problems. It has been carried out as part of the work with drafting Eurocode 3 Part 2 and the paper is intended as a background document for the suggested design rules.

  • 14. Johansson, Bernt
    et al.
    Maquoi, René
    Sedlacek, Gerhard
    New design rules for plated structures in Eurocode 32001In: Journal of constructional steel research, ISSN 0143-974X, E-ISSN 1873-5983, Vol. 57, no 3, p. 279-311Article in journal (Refereed)
    Abstract [en]

    This paper gives an overview of Eurocode 3 Part 1.5 Design of Steel Structures. Supplementary rules for planar plated structures without transverse loading have been developed together with the Eurocode 3-2 Steel bridges. It covers stiffened and unstiffened plates in common steel bridges and similar structures. This paper presents the background and justification of some of the design rules with focus on the ultimate limit states. The design rules for buckling of stiffened plates loaded by direct stress are presented and explained. For shear resistance and patch loading the new rules are briefly derived and compared with the rules in Eurocode 3-1-1. Finally, the statistical calibration of the rules to tests is described.

  • 15. Johansson, Bernt
    et al.
    Olsson, Anders
    Luleå tekniska universitet.
    Current design practice and research on stainless steel structures in Sweden2000In: Journal of constructional steel research, ISSN 0143-974X, E-ISSN 1873-5983, Vol. 54, no 1, p. 3-29Article in journal (Refereed)
    Abstract [en]

    The current design practice in Sweden is using codes for structural steel also when working with stainless steel. For load cases governed by instability this may produce non-conservative errors amounting to 10% while it may greatly underestimate the ultimate resistance in cases when instability is not governing. Three ongoing research projects are briefly described, one on weldbonding, one on plastic forming and one on the behaviour of structural components. A part of the latter concerns fundamental work regarding the material behaviour which in general is described using too simple models. This is presented in some detail and its results will be used to provide improved finite element simulations.

  • 16.
    Lagerqvist, Ove
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Structural and Construction Engineering.
    Resistance of bridge girder webs subjected to concentrated forces1998In: Journal of constructional steel research, ISSN 0143-974X, E-ISSN 1873-5983, Vol. 46, no 1-3, p. 62-64Article in journal (Refereed)
    Abstract [en]

    A model for the ultimate resistance of bridge girder webs to concentrated forces that are introduced in the web during launching is presented. The model is formulated on the basis of observations from tests with welded girders made from a high strength, quenched and tempered steel, as well as available 379 test results for different steel grades. The design model is compared with results from finite element calculations on large bridge girder cross sections and a discussion concerning the serviceability limit state. A simplified form of the design procedure is used in Eurocode 3 Part 1.5 and has also been proposed for use in Eurocode 9.

  • 17.
    Lagerqvist, Ove
    et al.
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Structural and Construction Engineering.
    Johansson, Bernt
    Resistance of I-girders to concentrated loads1996In: Journal of constructional steel research, ISSN 0143-974X, E-ISSN 1873-5983, Vol. 39, no 2, p. 87-119Article in journal (Refereed)
    Abstract [en]

    This paper presents the results from an experimental investigation including tests with welded girders and rolled beams subjected to three different cases of concentrated loads applied to the girder flanges. The welded girders were made from a high strength, quenched and tempered steel, while the rolled beams were of an ordinary steel grade. The results from the experimental investigation presented herein have been added to test results taken from the literature and used for a formulation of a design procedure for the resistance to concentrated loads. The suggested design procedure is unified for the three different load applications and also harmonized with the design procedures normally used for describing buckling problems in the steel codes. The design procedure is a further development of the design procedure for patch loading suggested in B. Johansson & O. Lagerqvist [J. Construct. Steel Res., 32 (1995) 69-105] and has in a simplfied form been suggested for use in Eurocode 3 Part 2 (Bridges), as well as in Eurocode 9.

  • 18.
    Möller, Mikael
    et al.
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Structural and Construction Engineering.
    Johansson, Bernt
    Collin, Peter
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Structural and Construction Engineering.
    New analytical model of inelastic local flange buckling1997In: Journal of constructional steel research, ISSN 0143-974X, E-ISSN 1873-5983, Vol. 43, no 1-3, p. 43-63Article in journal (Refereed)
    Abstract [en]

    This paper deals with analytical modelling of inelastic local flange buckling of compressed I-beam flanges. A short discussion of the relevance of different constitutive models for the inelastic material behaviour is carried out. It is claimed that what is known as the `plastic buckling paradox' is not at all a paradox but a result of improper use of plasticity theory. An analytical model for the inelastic local buckling of an I-beam flange is proposed. The model considers the buckling process as being composed of two pans. The first is associated with inelastic torsional buckling of a compressed flange and the second part corresponds to a yield line plate buckling configuration which includes the effect of stress redistribution due to large deformations. The transition between these phases is left out in the model. The model is capable of predicting approximately the force-deformation relation of a locally buckling stocky flange for different stress-strain relations. The model is evaluated against experiments and the agreement is found quite reasonable.

  • 19.
    Olsson, Anders
    Luleå tekniska universitet.
    Constitutive modelling of stainless steel1998In: Journal of constructional steel research, ISSN 0143-974X, E-ISSN 1873-5983, Vol. 46, no 1-3, p. 457-Article in journal (Refereed)
    Abstract [en]

    An extensive program of biaxial testing of three different grades of stainless steel, two austenitic and one austenitic-ferritic grade, was conducted. The tests comprise one preloading and then one reloading and were performed in the full principal stress plane σ1-σ2, also in compression. Flat cruciform specimens were used. A significant reduction of the yield strength in a direction opposite to preloading, that is the Bauschinger effect is very evident. In directions transverse to the preloading an increased yield strength is observed. To predict the mechanical response at reloading of stainless steel subjected to one preloading, a constitutive model has to include these experimentally observed phenomena

  • 20.
    Pavlovic, Marko
    et al.
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Structural and Construction Engineering.
    Heistermann, Christine
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Structural and Construction Engineering.
    Veljkovic, Milan
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Structural and Construction Engineering.
    Pak, Daniel
    Institut für Stahlbau, Institute for Steel Construction, RWTH Aachen, University.
    Feldmann, Markus
    Institut für Stahlbau, Institute for Steel Construction, RWTH Aachen, University.
    Rebelo, Carlos
    ISISE, Department of Civil Engineering, University of Coimbra.
    Silva, Luís Simões da
    ISISE, Department of Civil Engineering, University of Coimbra.
    Connections in towers for wind converters: part I: Evaluation of down-scaled experiments2015In: Journal of constructional steel research, ISSN 0143-974X, E-ISSN 1873-5983, Vol. 115, p. 445-457Article in journal (Refereed)
    Abstract [en]

    The cost of a tubular steel tower supporting a wind converter becomes increasingly important in a competitive energy market. In-situ connection between tower segments is an important factor of the design. The tower segments are usually connected by welded ring flanges. An alternative solution based on a novel single lap friction connection is analysed. The purpose of the research presented in this paper is to thoroughly analyse the behaviour of both connections by an experimental testing programme and advanced finite element analysis (FEA). Down-scaled experiments of ring flange and friction connection in circular towers were performed using a 4-point bending test set-up. Altogether eight connections joining cylindrical shell, 1 m diameter, plate thickness 8 mm and total span of about 7 m were tested. A friction connection with long open slotted holes and two different cases of the ring flange connection are considered: with perfectly flat flanges and flanges with geometric imperfection. Results of advanced quasi-static FEA, using explicit dynamic solver and ductile damage material model for bolts, are compared to experiments. Failure modes, bolt forces and distribution of meridional membrane stresses in the shell in the vicinity of connections are analysed. Existing hand-calculation models, for the bolt force and normal stress distribution in the shell are validated by experiments and FEA.

  • 21.
    Pavlovic, Marko
    et al.
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Structural and Construction Engineering.
    Heistermann, Christine
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Structural and Construction Engineering.
    Veljkovic, Milan
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Structural and Construction Engineering.
    Pak, Daniel
    Institut für Stahlbau, Institute for Steel Construction, RWTH Aachen, University.
    Feldmann, Markus
    Institut für Stahlbau, Institute for Steel Construction, RWTH Aachen, University.
    Rebelo, Carlos
    ISISE, Department of Civil Engineering, University of Coimbra.
    Silva, Luís Simões da
    ISISE, Department of Civil Engineering, University of Coimbra.
    Connections in towers for wind converters: Part II: The friction connection behaviour2015In: Journal of constructional steel research, ISSN 0143-974X, E-ISSN 1873-5983, Vol. 115, p. 458-466Article in journal (Refereed)
    Abstract [en]

    A novel friction connection consisting of a single lap joint with long open slotted holes is proposed for use in tubular towers for wind converters for in-situ connections. This is a competitive alternative to the common ring flange connection as it has been shown in the European Project “HISTWIN”. Two sets of experiments are analysed: the down-scaled tubular steel tower 4-point bending experiments using high-strength bolts M20 and a single lap joint using plate thickness 25 mm and tension control bolts M30.The main motivation for this paper is a much higher bending resistance obtained in the 4-point bending experiments compared to predictions based on hand-calculation models.Results of experiments are used to validate finite element analysis (FEA). Explicit solver and the most realistic geometry of the bolts are the main characteristics of the FEA performed. Very good agreement between the experiments and FEA results is obtained, which provides credibility of the computational approach used to thoroughly examine experimental results. New evidences of the friction connection behaviour are provided: a short-term loss of preloading force due to external loading, transfer of shear force in the single lap joint and influence of the slotted hole on the joint resistance.Results obtained from hand-calculation models are used to predict the loss of preloading, the bending resistance of the connection and meridional stresses in the tower shell in the vicinity of the connection, which are compared to the experiments and the FEA. Recommendations related to use of the hand-calculation models in the design are provided.

  • 22.
    Pavlović, Marko
    et al.
    Faculty of Civil Engineering, University of Belgrade.
    Marković, Zlatko
    Faculty of Civil Engineering, University of Belgrade.
    Veljkovic, Milan
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Structural and Construction Engineering.
    Buđevac, Dragan
    Faculty of Civil Engineering, University of Belgrade.
    Bolted shear connectors vs. headed studs behaviour in push-out tests2013In: Journal of constructional steel research, ISSN 0143-974X, E-ISSN 1873-5983, Vol. 88, p. 134-149Article in journal (Refereed)
    Abstract [en]

    Prefabrication of concrete slabs reduces construction time for composite steel–concrete buildings and bridges. Different alternatives for shear connectors (bolts and headed studs) are analysed here to gain better insight in failure modes of shear connector in order to improve competiveness of prefabricated composite structures. Casting of high strength bolted shear connectors in prefabricated concrete slabs offers the higher level of prefabrication comparing to a standard method of grouting welded headed studs in envisaged pockets of concrete slabs. In addition, bolted shear connectors can easily be dismantled together with the concrete slab thus allowing the improved sustainability of the construction, simpler maintenance, and development of modular structural systems. Bolted shear connectors have been rarely used in construction, actually just for rehabilitation works, because there is a lack of design recommendation. The first step towards the design recommendation is to understand the difference between the headed shear studs and the bolted shear connectors in a push-out test. Push-out tests, according to EN1994-1-1, using 4 M16 — grade 8.8 bolts with embedded nut in the same layout and test set-up as for previously investigated headed studs were performed. Finite element models for both shear connectors were created, and good match with experimental data was obtained. Basic shear connector properties such as: shear resistance, stiffness, ductility and failure modes have been compared and discussed in detail by using experimental and FE results. Parametric FE analyses of shear connector's height are carried out and shear resistance reduction factor has been proposed for bolted shear connectors.

  • 23.
    Ranby, Anders
    Luleå tekniska universitet.
    Structural fire design of thin walled steel sections1998In: Journal of constructional steel research, ISSN 0143-974X, E-ISSN 1873-5983, Vol. 46, no 1-3, p. 303-304Article in journal (Refereed)
    Abstract [en]

    The Swedish Institute of Steel Construction runs a project for developing structural fire design of thin walled cold formed steel sections. The object is to find out actual steel temperatures, how it varies across the steel section and the effect on the load bearing resistance. With this information a method to design thin walled cold formed steel sections and frames will be developed. It is also important to show that the Eurocode 3 Part 1.2, limiting the maximum temperature to 350 deg C for class 4 cross sections, is too restrictive. When calculating the load bearing resistance of thin walled cold formed steel section in case of fire the influence of local buckling must be taken into account. The influence of initial deflections also has to be considered. The load bearing resistance will of course then also depend on the actual reduced yield strength and elastic modulus. In this paper the plate buckling resistance is estimated with different methods and the results are fairly consistent. The resistance is estimated by FEM analysis as well. This method using a nonlinear solution and a stress-strain relationship from Eurocode 3 Part 1.2 shows results rather in accordance with the analytical solutions. The current work shows that initial deflections have the same relative influence on the load bearing resistance at room temperature as in case of fire. Furthermore, the results show that a calculation of the plate buckling resistance according to Eurocode 3 Part 1.3 with reduced yield strength and elastic modulus is accurate enough also at elevated temperatures provided that the yield strength is taken as the 0.2 percent proof stress.

  • 24.
    Tran, Anh Tuan
    et al.
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Structural and Construction Engineering.
    Veljkovic, Milan
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Structural and Construction Engineering.
    Rebelo, Carlos
    University of Coimbra, ISISE, Department of Civil Engineering, University of Coimbra.
    Silva, Luís Simões da
    Virginia Polytechnic Institute and State University, Universidade de Coimbra , ISISE, Department of Civil Engineering, University of Coimbra.
    Resistance of cold-formed high strength steel circular and polygonal sections: Part 1: Experimental investigations2016In: Journal of constructional steel research, ISSN 0143-974X, E-ISSN 1873-5983, Vol. 120, p. 245-257Article in journal (Refereed)
    Abstract [en]

    This paper presents results from experiments performed on cold-formed high strength steel circular and polygonal sections. The test specimens were conceived to provide necessary information for development of tubular towers for wind turbines. A total of 32 high strength steel specimens were tested under uniaxial compression. Various thicknesses, openings and geometric imperfections were studied. Sixteen specimens without opening and sixteen specimens with opening were tested under axial compression in order to investigate influences of opening on the resistances. Tensile tests of coupon specimens taken from flat part, circular part and corner part were used to investigate basic properties of high strength steel material S650 and to evaluate influence of corner on the material strength and ductility. Initial geometric imperfections of the specimens were determined by using a 3D laser scanning method. The coupon test results were used to calibrate the ductile damage material models for modelling of fracture. Results from the experiments are fully described in this paper

  • 25.
    Tran, Anh Tuan
    et al.
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Structural and Fire Engineering.
    Veljkovic, Milan
    Delft University of Technology.
    Rebelo, Carlos
    University of Coimbra, ISISE, Department of Civil Engineering, University of Coimbra.
    Silva, Luís Simões da
    Virginia Polytechnic Institute and State University, Universidade de Coimbra , ISISE, Department of Civil Engineering, University of Coimbra.
    Resistance of cold-formed high strength steel circular and polygonal sections: Part 2: Numerical investigations2016In: Journal of constructional steel research, ISSN 0143-974X, E-ISSN 1873-5983, Vol. 125, p. 227-238Article in journal (Refereed)
    Abstract [en]

    This paper is the second part of the study on the cold-formed high strength steel circular and polygonal sections intended to be used in tubular wind towers. Results from 32 numerical finite element analysis (FEA) models were compared with and calibrated against results of the tests on 32 corresponding specimens. The FEA results agreed well with the experimental results in terms of resistances and load-displacement curves. Further investigations on the numerical models were performed. Yield stress used in the FEA significantly affected the resistances of the numerical models. Using 0.2% proof stress leaded to higher resistance than the experimental results. Corners significantly influenced buckling behaviour in the polygonal section models. Analyses of an oval opening in the tubular specimens showed that peak stresses around the opening were considerably higher in the polygonal section models than in the circular section models. Finally, investigation of sensitivity to geometrical imperfections indicated that failure modes of numerical models with geometrical imperfections according to EC3 significantly differed from those of tested specimens and numerical models with geometrical imperfections obtained from the 3D scans.

  • 26.
    Uppfeldt, Björn
    et al.
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Structural and Construction Engineering.
    Outinen, T. Ala
    VTT.
    Veljkovic, Milan
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Structural and Construction Engineering.
    A design model for stainless steel box columns in fire2008In: Journal of constructional steel research, ISSN 0143-974X, E-ISSN 1873-5983, Vol. 64, no 11, p. 1294-1301Article in journal (Refereed)
    Abstract [en]

    A study of stainless steel cold-rolled box columns at elevated temperatures is presented, which is a part of an on-going RFCS project "Stainless Steel in Fire", 2004-2007. Experimental results of six, class 4, stub columns at elevated temperature, tested by Ala-Outinen [Members with Class 4 cross-sections in fire: Work package 3, ECSC project stainless steel in fire. Contract no. RFS-CR-04048, Espoo, Finland; 2005], were used to evaluate the finite element (FE) model. The FE analysis obtained using the commercially available software, ABAQUS, shows that the critical temperature was closely predicted. Further, a parametric study was performed using the same numerical model. This was a basis to check the quality of prediction of a newly proposed improvement for design rules of class 4 cross-sections in fire according to EN 1993-1-4 [Eurocode 3 - Design of steel structures - Part 1-4: General rules - Supplementary rules for stainless steels, CEN; 2006] and EN 1993-1-2 [Eurocode 3: Design of steel structures - Part 1.2: General rules - Structural fire design, CEN; 2005].

  • 27.
    Veljkovic, Milan
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Structural and Construction Engineering.
    Influence of load arrangement on composite slab behaviour and recommendations for design1998In: Journal of constructional steel research, ISSN 0143-974X, E-ISSN 1873-5983, Vol. 45, no 2, p. 149-178Article in journal (Refereed)
    Abstract [en]

    A parametric study of the behaviour of composite slabs consisting of profiled steel sheeting and concrete is presented. The FEM program DIANA was used to model the slab as a two-dimensional structure. Non-linear material and interface properties are considered as well as discrete cracking of the concrete. The main parameter is the horizontal shear transfer between the sheeting and the concrete; this is varied with respect to strength, ductility and influence of strain level in the sheeting. The FEM simulations have been validated by comparison with full-scale tests. It is clear from these comparisons that the full-scale behaviour can be described accurately using interface properties determined with small-scale push tests. The results of the simulations show clearly the importance of cracking of the concrete, which has a strong influence on the distribution of horizontal shear between the sheeting and the concrete. The largest slip will be at the so-called governing crack; at such a location the strains in the sheeting are high. For sheeting where the shear transfer relies on indentations, the strains in the sheeting reduce the shear transfer. The partial interaction method for design described in Eurocode 4 part 1 requires a very ductile connection between sheeting and concrete. The purpose of this study was to investigate the distribution of horizontal shear when the connection is less ductile, and to compare results for different load arrangements in order to develop a more general design method. The new method is based on detailed test results and FE analysis. Background information of the proposed method is given.

  • 28.
    Veljkovic, Milan
    et al.
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Structural and Construction Engineering.
    Johansson, Bernt
    Design of hybrid steel girders2004In: Journal of constructional steel research, ISSN 0143-974X, E-ISSN 1873-5983, Vol. 60, no 3-5, p. 535-547Article in journal (Refereed)
    Abstract [en]

    A hybrid steel girder is a welded girder with different steel grades in flanges and web. Usually, the flanges are made of high strength steel (HSS) like S690 and the web of a lower grade say S355 but combinations like S460 and S355 are also used. Such girders are more economical than homogenous girders. Hybrid girders have been used in the US since long but they are not commonly used in Europe. Some examples of the use of hybrid girders in Sweden are presented together with economic comparisons. Design rules for hybrid girders are presented together with justifications. Typically, hybrid girders are of cross-section class 4 according to Eurocode 3. The resistance in bending in ultimate limit state is influenced by the local yielding of the web, which limits the stresses in the web and affects the effective width of the web as well. Simplified formulae for the bending resistance are presented. For serviceability limit states, the local yielding of the web has to be accepted but the requirement of reversible behaviour will still be fulfilled. For the limit state of fatigue, Eurocode 3 states a restriction that the stress range should not exceed 1.5 times the yield strength. For hybrid girders, it is shown that this restriction applies to the yield strength of the flanges and that yielding of the web does not influence the fatigue strength.

  • 29.
    Veljkovic, Milan
    et al.
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Structural and Construction Engineering.
    Johansson, Bernt
    Thin-walled steel columns with partially closed cross-section: tests and computer simulations2008In: Journal of constructional steel research, ISSN 0143-974X, E-ISSN 1873-5983, Vol. 64, no 7-8, p. 816-821Article in journal (Refereed)
    Abstract [en]

    Cold formed sections can be optimized for different purposes and they are fairly inexpensive to produce in small series. They have an inherent weakness in their small torsional stiffness, which is unfavourable for columns. One solution presented here is to make a closed section by adding a thin cover plate connected discretely with self-tapping screws. It is here called a partially closed cross-section because it is not continuously and rigidly connected. The aim of this paper is to evaluate the efficiency of this solution by comparing the behaviour of partially closed and open cross-section. Four columns were tested within the project, two of them with centric axial load and two with eccentricities. Numerical analysis was performed using ABAQUS for establishing the influence of the cover plate on the critical load and the resistance. A good agreement between non-linear FEM and experiments were found. After this verification of the FE model a parametric study was carried out. Results of experiments and numerical analysis were compared with the predicted resistance by Eurocode 3, Part 1-3, and the Direct Strength Method. Both design methods give good predictions of the resistance.

  • 30.
    Widman, J.
    Luleå tekniska universitet.
    Environmental impact assessment of steel bridges1998In: Journal of constructional steel research, ISSN 0143-974X, E-ISSN 1873-5983, Vol. 46, no 1-3, p. 291-293Article in journal (Refereed)
    Abstract [en]

    The Swedish Institute of Steel Construction has made LCAs on steel and concrete composite road bridges in order to detect important environmental impact parameters and to find areas where improvements are necessary. Two of the most common bridge types were studied. Combustion engines in vehicles contribute to a big share of the airborne emissions, such as CO2 and NOx. In spite of the small amounts, alloys as Molybdenum contribute to most of the environmental burden from the materials according to one assessment method. This put steel in a less favourable position when comparing LCA results with other materials. The concrete in steel bridges contributes to almost 50% of the environmental impact and the fact that steel bridges need less material than concrete bridges, shows that steel bridges are good environmental choices. Three assessment methods have been used to get multi-comparable and objective assessment results. The use of the bridge (traffic) is the most polluting part during the life cycle. The study has resulted in a report, SBI Report 183:1. (LCA: life cycle assessment.)

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