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  • 1.
    Atashipour, Seyed Rasoul
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Wood Science and Engineering. Department of Architecture and Civil Engineering, Division of Structural Engineering, Chalmers University of Technology.
    Girhammar, Ulf Arne
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Wood Science and Engineering.
    Challamel, Noël
    Université de Bretagne Sud, UBS – Institut Dupuy de Lôme, Centre de Recherche.
    A weak shear web model for deflection analysis of deep composite box-type beams2018In: Engineering structures, ISSN 0141-0296, E-ISSN 1873-7323, Vol. 155, p. 36-49Article in journal (Refereed)
    Abstract [en]

    Deep box-type beams, consisting of framing members and sheathings, are sensitive to shear deformations and hence appropriate refined theories or complicated magnification factors are needed to be used to obtain accurate results. For sheathings or webs between the framing members that are weak in shear, additional shear deformations occur corresponding to the relative axial displacement between the framing members. These sandwich-type or partial interaction-type of in-plane shear behaviour between the framing members, needs to be taken into account, especially when the web shear stiffness is very low. The composite box-type beam treated here is composed of three framing members with sheathings on both sides. To incorporate effects of the sheathings shear deformations between the framing members on the deflection, the sheathings, here called web interlayers, are modelled as shear media with equivalent slip moduli corresponding to a partially interacting composite beam model. Governing equilibrium equations of the model are obtained using the minimum total potential energy principle and solved explicitly. The obtained results are compared with those based on different conventional beam theories and 3-D finite element (FE) simulations. It is shown that the model is capable of predicting accurately the deflection for a wide range of geometry and property parameters. It is demonstrated that the deflection of such deep box-type beams can be expressed as the summation of three different effects, namely bending deformations, conventional shear deformations in the framing members and sheathings, and additional in-plane shear deformations or shear slips of the weak web causing relative axial displacements between the framing members.

  • 2.
    Bagge, Niklas
    et al.
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Structural and Fire Engineering.
    Nilimaa, jonny
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Structural and Fire Engineering.
    Elfgren, Lennart
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Structural and Fire Engineering.
    In-situ methods to determine residual prestress forces in concrete bridges2017In: Engineering structures, ISSN 0141-0296, E-ISSN 1873-7323, Vol. 135, p. 41-52Article in journal (Refereed)
    Abstract [en]

    Levels of residual prestress forces are key parameters when assessing the structural behaviour of existing prestressed concrete bridges. However, these parameters are often unknown and not easy to determine. To explore them, two existing non-destructive and destructive approaches have been further developed for practical application and demonstrated on a multi-span continuous girder bridge. The evaluation of the prestress forces was part of an extensive experimental programme aimed to calibrate and develop assessment methods. Due to the pursuit of practical applications for existing bridges, the main focus was on non-destructive methodology, combining experimental data and finite element modelling to obtain the residual prestress forces. Assuming that the initial prestress force corresponded to 85% of the characteristic 0.2% proof strength of the reinforcing steel, estimated losses in investigated sections ranged between 5 and 70%. However, determined residual prestress forces were generally higher than theoretically based estimates accounting for friction and time-dependent losses in the prestressing system. In addition to describing in detail the methods for prestress evaluation, this paper presents suggestions for improvements and further studies, based on experiences from the field tests.

  • 3.
    Bagge, Niklas
    et al.
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Structural and Construction Engineering.
    O'Connor, Alan
    Department of Civil, Structural and Environmental Engineering, Trinity College Dublin.
    Elfgren, Lennart
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Structural and Construction Engineering.
    Pedersen, Claus
    Department of Bridges, Rambøll Danmark A/S.
    Moment redistribution in RC beams: A study of the influence of longitudinal and transverse reinforcement ratios and concrete strength2014In: Engineering structures, ISSN 0141-0296, E-ISSN 1873-7323, Vol. 80, p. 11-23Article in journal (Refereed)
    Abstract [en]

    In this paper, the results from an experimental programme, aimed at investigating moment redistribution in statically indeterminate reinforced concrete structures, are presented and compared with theoretical analysis of the structural behaviour. Due to the nonlinear structural behaviour of reinforced concrete structures, linear elastic analysis can lead to an inaccurate assessment of the behaviour and, therefore, it can become necessary to use more advanced methodologies to achieve sufficiently accurate analysis. Furthermore, more advanced methods can enable a higher degree of performance optimisation of structures than those resulting from the simplified approaches adopted by existing design codes based on linear elastic analysis with redistribution of internal forces. In order to assess the load-carrying capacity at the ultimate limit state (ULS), a model combining plastic and nonlinear analysis is presented. The evolution of moment redistribution to structural collapse was studied experimentally for continuous two-span beams. The focus of the experiments was on the influence of the longitudinal tensile reinforcement ratio at the intermediate support, the transverse reinforcement ratio and the concrete strength. The experimental response at the ULS was further compared with the predicted distribution of internal forces according to the theoretical model. Evaluation of the experimental study indicated a highly nonlinear structural behaviour of the tested beams with the distribution of moment differing from linear elastic analysis, even for low load levels. The evolution of moment redistribution and the moment redistribution at the ULS were appreciably dependent on the arrangement of longitudinal reinforcement, whilst the transverse reinforcement ratio had a marginal impact up to yielding of the longitudinal reinforcing steel, with the concrete strength slightly reducing the degree of moment redistribution. For those beams which failed in flexure, predictions from the theoretical model presented were in good agreement with the experimental results. However, several beams collapsed in shear-related failure modes.

  • 4.
    Challamel, Noël
    et al.
    Université Européenne de Bretagne.
    Girhammar, Ulf Arne
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Structural and Construction Engineering.
    Lateral-torsional buckling of vertically layered composite beams with interlayer slip under uniform moment2012In: Engineering structures, ISSN 0141-0296, E-ISSN 1873-7323, Vol. 34, p. 505-513Article in journal (Refereed)
    Abstract [en]

    The lateral-torsional stability of vertically layered composite beams with interlayer slip is investigated in this paper, based on a variational approach. Vertically layered elements are typically used in timber engineering but also in case of laminated glass elements. Both across-longitudinal or vertical slip due to rotation and longitudinal or horizontal slip due to lateral deflection are discussed. The theoretical framework of the lateral-torsional buckling problem is given, and some engineering closed-form solutions are presented for partially composite beams under uniform bending moment. Simplified kinematical relationships neglecting the axial and vertical displacements of the sub-elements give unrealistic values for the lateral-torsional buckling moment. Refined kinematical assumptions remove this peculiarity and render sound buckling moment results. Inclusion of the horizontal and vertical slips significantly affect the lateral-torsional buckling moment of these vertically laminated elements. A single lateral-torsional buckling formulae is derived, depending on both the horizontal and the vertical connection parameters.

  • 5.
    Challamel, Noël
    et al.
    University of Europeenne Bretagne, Laboratory Genie Civil & Genie Mecan.
    Girhammar, Ulf Arne
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Structural and Construction Engineering.
    Variationally-based theories for buckling of partial composite beam-columns including shear and axial effects2011In: Engineering structures, ISSN 0141-0296, E-ISSN 1873-7323, Vol. 33, no 8, p. 2297-2319Article in journal (Refereed)
    Abstract [en]

    This paper is focused on elastic stability problems of partial composite columns: the conditions for the axial load not to introduce any pre-bending effects in composite columns; the equivalence, similarities and differences between different sandwich and partial composite beam theories with and without the effect of shear, with and without the effect of axial extensibility, and also the effect of eccentric axial load application. The basic modelling of the composite beam-column uses the Euler-Bernoulli beam theory and a linear constitutive law for the slip. In the analysis of this reference model, a variational formulation is used in order to derive relevant boundary conditions. The specific loading associated with no pre-bending effects before buckling is geometrically characterized, leading to analytical buckling loads of the partial composite column. The equivalence between the Hoff theory for sandwich beam-columns, the composite action theory for beam-columns with interlayer slip and the corresponding Bickford-Reddy theory, is shown from the stability point of view. Special loading configurations including eccentric axial load applications and axial loading only on one of the sub-elements of the composite beam-column are investigated and the similarity of the behaviour to that of imperfect ordinary beam-columns is demonstrated. The effect of axial extensibility on kinematical relationships (according to the Reissner theory), is analytically quantified and compared to the classical solution of the problem. Finally, the effect of incorporating shear in the analysis of composite members using the Timoshenko theory is evaluated. By using a variational formulation, the buckling behaviour of partial composite columns is analysed with respect to both the Engesser and the Haringx theory. A simplified uniform shear theory (assuming equal shear deformations in each sub-element) for the partial composite beam-column is first presented, and then a refined differential shear theory (assuming individual shear deformations in each sub-element) is evaluated. The paper concludes with a discussion on this shear effect, the differences between the shear theories presented and when the shear effect can be neglected. (C) 2011 Elsevier Ltd. All rights reserved.

  • 6.
    Edskär, Ida
    et al.
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Industrilized and sustainable construction.
    Lidelöw, Helena
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Industrilized and sustainable construction.
    Dynamic Properties of Cross-Laminated Timber and Timber Truss Building Systems2019In: Engineering structures, ISSN 0141-0296, E-ISSN 1873-7323, Vol. 186, p. 525-535Article in journal (Refereed)
    Abstract [en]

    Incorrect prediction of dynamic properties of tall buildings can lead to discomfort for humans. It is therefore important to understand the dynamic characteristics such as natural frequency, mode shape and damping and the influence they have on acceleration levels. The aim of this study is to compare two timber building system, one with cross laminated panels and one with post-and-beam elements with diagonals for stabilisation. Empirical formulae for predicting the natural frequency and mode shape are compared to measured and numerical results. Tall building assumptions such as ‘line-like’ behaviour and lumped mass at certain points were evaluated for both systems. The post-and-beam system showed a stiffer behaviour than the cross laminated system where more shear deformation occurred. Empirical formulae should be used with care until more data is collected.  For the post-and-beam systems an assumption of linearity may be appropriate, but for cross laminated systems the approximation can give results on the unsafe side. Finally, the relationship between stiffness and mass for cross laminated timber systems and its effect on dynamic properties needs to be further investigated.

  • 7.
    Gervásio, Helena
    et al.
    ISISE, Department of Civil Engineering, University of Coimbra.
    Rebelo, Carlos
    ISISE, Department of Civil Engineering, University of Coimbra.
    Moura, André
    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.
    Silva, Luis Simões da
    ISISE, Department of Civil Engineering, University of Coimbra.
    Comparative life cycle assessment of tubular wind towers and foundations: Part 2: Life cycle analysis2014In: Engineering structures, ISSN 0141-0296, E-ISSN 1873-7323, Vol. 74, p. 292-299Article in journal (Refereed)
    Abstract [en]

    In the first part of the paper the design of tubular towers and respective onshore foundations was addressed. The considered solutions were based on steel, concrete and hybrid steel-concrete tubular towers supporting multi-megawatt turbines of 2, 3.6 and 5 MW power with hub heights of 80, 100 and 150 m respectively. In this second part of the paper, the life cycle analysis of the designed case studies is performed and conclusions about their environmental impact are drawn. Two different scenarios concerning the lifetime of the towers were established. The first scenario considers 20 years lifetime and two different construction methods for the connection of the steel segments, the first based in current technology using flange connections and the second using newly developed friction connections. Assuming equal importance for all environmental categories in this scenario, it may be concluded that for heights up to 100 m hybrid towers with friction connections are the most efficient solution. For higher heights, the concrete tower becomes more efficient. The second scenario considers an increased total lifetime of 40 years, assuming the reuse of the tower after 20 years of operation. In this case, the use of friction connections in steel towers enhances the possibility of dismantling and reusing the tower potentiating much better performance in relation to the environmental category of global warming.

  • 8.
    Girhammar, Ulf Arne
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Wood Science and Engineering.
    Jacquier, Nicolas
    Byggtekniska Byrån.
    Källsner, Bo
    Department of Building Technology, Linnaeus University.
    Stiffness model for inclined screws in shear-tension mode in timber-to-timber joints2017In: Engineering structures, ISSN 0141-0296, E-ISSN 1873-7323, Vol. 136, p. 580-595Article in journal (Refereed)
    Abstract [en]

    A stiffness model for inclined screws in timber joints, or as shear connectors in composite timber-to-timber members, is presented. Elastic conditions applicable to the initial or linearized part of the load-deformation response in the serviceability limit state are assumed. The model for the stiffness or slip modulus is general in nature; it includes both the dowel (or shearing) action and withdrawal action of the screw, the friction between the members and it takes into account possible dissimilar properties and geometries of the different parts of the joint configuration. The model is simplified in the sense that the screw is assumed rigid and the withdrawal stresses along the length of the screw are assumed evenly distributed. However, the effects of flexibility and extensibility of the screw are taken into account by applying a theoretically derived correction factor for the embedment and withdrawal stiffness modulus, respectively. The proposed model is illustrated showing the total stiffness versus the inclination, as well as the relative contributing effect from the shearing and withdrawal stiffness, respectively, the influence of the friction coefficient. Also, the effect of dissimilar properties and geometries between the two parts of the joint is illustrated. Experimental verification of the proposed model is also given. Comparisons with other stiffness models are also made.

  • 9.
    Girhammar, Ulf Arne
    et al.
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Structural and Construction Engineering. Department of TFE-Civil Engineering, Faculty of Science and Technology, Umeå University.
    Källsner, Bo
    Department of Building Technology, Linnaeus University.
    Elasto-plastic model for analysis of influence of imperfections on stiffness of fully anchored light-frame timber shear walls2009In: Engineering structures, ISSN 0141-0296, E-ISSN 1873-7323, Vol. 31, no 9, p. 2182-2193Article in journal (Refereed)
    Abstract [en]

    In order to stabilize timber-framed buildings against lateral loads, the diaphragm action of roofs, floors and walls is often used. This paper deals with the influence of imperfections such as gaps and uplift on the stiffness and the horizontal displacement of fully anchored shear walls. The significance of analyzing the effects of imperfections is evident when evaluating the stiffness of shear walls; tests of walls show that the horizontal displacement is underestimated in calculations using the stiffness of sheathing-to-framing joints as obtained from experiments. Also, in real structures where hold-downs are used, the influence of gaps and uplift should be included in order to obtain realistic displacements in the serviceability limit state. The analytical model is based on ideal plastic behavior of the mechanical sheathing-to-timber joints with stresses parallel to the perimeter of the frame and on linear elastic behavior for stresses perpendicular to the bottom rail. Using this elasto-plastic model, the equations for the stiffness and the deflection versus the number of segments in the wall are derived. The fully anchored condition for the shear walls is simulated by applying a diagonal load to the shear wall. Three types of imperfections are evaluated: Walls with gaps at all studs, a gap only at the trailing stud, and gaps at all studs, except at the trailing stud. It is shown that the effect of imperfections on the stiffness of the wall in the initial stage is considerable. Depending on the distribution of the gaps and the number of segments included in the shear wall, the displacement of the shear wall is increased several times compared to that of a fully anchored wall diaphragm with no gaps; e.g. for a single segment wall more than four times. However, for walls with more than six segments the effect of imperfections can be neglected. Finally, the theoretical model is experimentally verified

  • 10.
    Huang, Zheng
    et al.
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Structural and Fire Engineering. School of Civil Engineering, Southeast University, Nanjing, China.
    Tu, Yongming
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Structural and Fire Engineering. School of Civil Engineering, Southeast University, Nanjing, China.
    Meng, Shaoping
    School of Civil Engineering, Southeast University, Nanjing, China.
    Bagge, Niklas
    Department of Bridge & Hydraulic Design, WSP Sverige AB, Gothenburg, Sweden.
    Nilimaa, Jonny
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Structural and Fire Engineering.
    Blanksvärd, Thomas
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Structural and Fire Engineering.
    Validation of a numerical method for predicting shear deformation of reinforced concrete beams2019In: Engineering structures, ISSN 0141-0296, E-ISSN 1873-7323, Vol. 197, article id 109367Article in journal (Refereed)
    Abstract [en]

    The objective of this paper is to validate a 2D nonlinear finite element (FE) model for estimating the post-cracking shear deformation of reinforced concrete (RC) beams. The proposed FE model treated the cracked concrete as an orthotropic material in the framework of the fixed-crack approach. The experimental data for both the overall response (including the total and shear-induced deflection) and the detailed response (including the mean shear strain, mean vertical strain and principal compressive strain angle) of five I-section RC beams, monitored by the main authors of this paper with the Digital Image Correlation technique, were used to verify the proposed model. In addition, 27 further test beams evaluated in independent research programs were collected to assemble a database. The proposed FE model was further verified against the database. Two additional FE models (the rotating-crack model developed in this work and Response-2000 developed by Bentz (2000)) were also evaluated by simulating the detailed responses of the beams in the database. The results obtained validate the proposed FE model for predicting the post-cracking shear deformation of RC beams and indicate that the proposed FE model is more suitable for simulating the shear behaviour of RC beams than the rotating-crack model or Response-2000.

  • 11.
    Huang, Zheng
    et al.
    School of Civil Engineering, Southeast University, Nanjing, China.
    Tu, Yongming
    School of Civil Engineering, Southeast University, Nanjing, China.
    Meng, Shaoping
    School of Civil Engineering, Southeast University, Nanjing, China.
    Sabau, Cristian
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Structural and Fire Engineering.
    Popescu, Cosmin
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Structural and Fire Engineering.
    Sas, Gabriel
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Structural and Fire Engineering. Infrastructure, Materials and Structures, Norut, Narvik, Norway.
    Experimental study on shear deformation of reinforced concrete beams using digital image correlation2019In: Engineering structures, ISSN 0141-0296, E-ISSN 1873-7323, Vol. 181, p. 670-698Article in journal (Refereed)
    Abstract [en]

    This paper presents an experimental program aimed at providing reliable and comprehensive experimental data for assessing the available models of predicting the shear deformation of diagonally-cracked reinforced concrete (RC) beams. The non-contact measuring technique, Digital Image Correlation (DIC), was used to monitor the full-field displacement and strain in the shear span of five RC beams with thin webs. Virtual measuring grids were created to measure the mean shear strain and other critical deformation results which reflects the mechanism of shear deformation after shear cracking (i.e. the principal compressive strain angle, the principal compressive strain, the mid-depth longitudinal strain and the mean vertical strain). The experimental mean shear strain and other critical deformation results were compared with the predictions with several available models. The comparison indicates the available models fail to reproduce the principal compressive strain angle, the mid-depth longitudinal strain and the mean vertical strain which constitute the key parameters in estimating the shear deformation after shear cracking. As a result, significant discrepancies in the shear deformation of the beams tested in this paper are observed between the experimental and calculated results. It is also found that the predicted shear deformation of a number of beam specimens tested by other researchers with the available models deviates considerably from the experimental results. In general, the existing models are not capable of providing accurate predictions of the shear deformation of RC beams and further investigation into this topic is needed.

  • 12.
    Källsner, Bo
    et al.
    Department of Building Technology, Linnaeus University.
    Girhammar, Ulf Arne
    Department of TFE-Civil Engineering, Faculty of Science and Technology, Umeå University.
    Plastic models for analysis of fully anchored light-frame timber shear walls2009In: Engineering structures, ISSN 0141-0296, E-ISSN 1873-7323, Vol. 31, no 9, p. 2171-2181Article in journal (Refereed)
    Abstract [en]

    In order to stabilise timber-framed buildings against lateral loads, the diaphragm action of roofs, floors and walls is often used. This paper deals with plastic analysis models for fully anchored sheathed shear walls. The models are based on the assumption of plastic load-slip relations for the sheathing-to-framing joints. Only static loads are considered. The basic structural behaviour and assumptions for the plastic models are elucidated. Both upper and lower bound methods are applied. The load-bearing capacity and the deformation of the shear walls in the ultimate and serviceability limit states, respectively, are derived. Both a discrete point description and a continuous flow per unit length modelling of the fasteners are discussed. Also, the forces and displacements of the fasteners and sheathing are derived. The influence of flexible framing members and shear deformations in the sheets, and also the effect of vertical loads on the shear wall, both with respect to tilting and second order effects, on the horizontal load-bearing capacity and displacement are evaluated. The stress distribution and the reaction forces at the ends of the different framing members are derived. The elastic model is experimentally verified and an illustrative example is given. The main objective of this work is to contribute to a better understanding of the structural behaviour of these fully anchored walls and form the basis for establishing a new plastic design method for partially anchored shear walls, i.e. a design method capable of analysing the more practical conditions of no or partial anchorage of the studs and/or bottom rail in real structures

  • 13.
    Mahal, Mohammed
    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.
    Sas, Gabriel
    Northern Research Institute.
    Using digital image correlation to evaluate fatigue behavior of strengthened reinforced concrete beams2015In: Engineering structures, ISSN 0141-0296, E-ISSN 1873-7323, Vol. 105, p. 277-288Article in journal (Refereed)
    Abstract [en]

    The fatigue behavior of reinforced concrete beams externally strengthened with carbon fiber reinforced polymer plates and near-surface mounted bars has been investigated using a digital image correlation (DIC) technique. Displacement fields obtained from digital images recorded during specific load cycles in fatigue tests are analyzed to provide information on crack width, beam deflection and curvature, and major principal strains to enable crack detection. The results obtained in this way were compared to data gathered using conventional sensors, revealing that the DIC technique provided very accurate and detailed information. The experimental results for plate-strengthened, bar-strengthened, and unstrengthened beams are discussed.

  • 14.
    Mpidi Bita, Hercend
    et al.
    Wood Science, University of British Columbia, Canada.
    Huber, Johannes Albert Josef
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Wood Science and Engineering.
    Voulpiotis, Konstantinos
    Institute of Structural Engineering, ETH Zurich, Switzerland.
    Tannert, Thomas
    Wood Engineering, University of Northern British Columbia, Canada.
    Survey of contemporary practices for disproportionate collapse prevention2019In: Engineering structures, ISSN 0141-0296, E-ISSN 1873-7323, Vol. 199, article id 109578Article in journal (Refereed)
    Abstract [en]

    This paper summarises contemporary practices and implementations of the existing codes and guidelines with respect to disproportionate collapse prevention. Here, focus is given to structural robustness, defined as the ideal method to decrease the probability of disproportionate collapse in buildings following an initial damage. The results from a global survey with 171 participants (mainly structural engineers) are presented. By comparing practices applied to different structural materials (steel, concrete and timber) and in different regions (Canada, USA, Europe, Australia/New Zealand), areas of improvements for the existing codes and guidelines as well as further research are identified. The results emphasise the importance of including specific recommendations for structural robustness in building codes, applicable to high importance and high occupancy structures. A performance-based approach is preferable, rather than prescriptive requirements, for practical and economic solutions. In addition, the obtained responses highlight the need to further develop the existing indirect and direct methods for disproportionate collapse prevention and structural robustness to include material-specific considerations.

  • 15.
    Nagy-György, Tamas
    et al.
    Politechnica University of Timisoara.
    Sas, Gabriel
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Structural and Construction Engineering.
    Dăescu, Cosmin
    Politechnica University of Timisoara.
    Barros, Joaquim
    University of Minho.
    Stoian, V.
    Politechnica University of Timisoara.
    Experimental and numerical assessment of the effectiveness of FRP-based strengthening configurations for dapped-end RC beams2012In: Engineering structures, ISSN 0141-0296, E-ISSN 1873-7323, Vol. 44, p. 291-303Article in journal (Refereed)
    Abstract [en]

    This paper presents experimental and numerical assessments of the effectiveness of strengthening dapped-end reinforced concrete beams using externally bonded carbon fiber reinforced polymers (CFRP). The research was prompted by a real application, in which the dapped-ends of several precast/prestressed concrete beams developed diagonal cracks due to errors during assembly. Hence, the dapped-ends were strengthened on-site using CFRP plates to limit further crack opening. In the empirical phase of the study, four similar specimens were tested: one unstrengthened reference specimen, two strengthened with high-strength CFRP plates, and one with high-modulus CFRP sheets. The specimens strengthened with plates had slightly higher load carrying capacity than the reference element, but failed by debonding, while the specimens strengthened with sheets showed no increase of capacity and failed by the fibers rupturing. Nonlinear finite element analysis of the specimens under the test conditions indicated that: a) debonding is more likely to occur at the inner end of dapped-ends, and b) the capacity could have been increased by up to 20% if the plates had been mechanically anchored.

  • 16.
    Nilforoush, Rasoul
    et al.
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Structural and Fire Engineering.
    Nilsson, Martin
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Structural and Fire Engineering.
    Elfgren, Lennart
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Structural and Fire Engineering.
    Experimental evaluation of tensile behaviour of single cast-in-place anchor bolts in plain and steel fibre-reinforced normal- and high-strength concrete2017In: Engineering structures, ISSN 0141-0296, E-ISSN 1873-7323, Vol. 147, p. 195-206Article in journal (Refereed)
    Abstract [en]

    Cast-in-place anchor bolts embedded in plain and steel fibre-reinforced normal- and high-strength concrete members were subjected to monotonic tensile loads. The influence of the concrete member thickness, concrete strength, and the addition of steel fibres to the concrete mixture, on the anchorage capacity and performance was evaluated. The experimental results were evaluated in terms of anchorage capacity, anchorage ductility and stiffness as well as failure mode and geometry. Furthermore, the validity of Concrete Capacity (CC) method for predicting the tensile breakout capacity of anchor bolts in plain and steel fibre-reinforced normal- and high-strength concrete members was evaluated.

    The anchorage capacity and ductility increased slightly with increasing member thickness, whereas the anchorage stiffness decreased slightly. In contrast to the anchorage ductility, the anchorage capacity and stiffness increased considerably with increasing concrete compressive strength. The anchorage capacity and ductility also increased significantly with the addition of steel fibres to the concrete mixtures. This enhanced capacity and ductility resulted from the improved flexural tensile strength and post-peak cracking behavior of steel fibre-reinforced concrete.

    The average ratio of measured strengths to those predicted by the CC method for anchors in plain concrete members was increased from 1.0 to 1.17 with increasing member thickness. In steel fibre-reinforced concrete, this ratio varied from 1.29 to 1.51, depending on the member thickness and the concrete strength.

  • 17.
    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.
    Friction connection vs. ring flange connection in steel towers for wind converters2015In: Engineering structures, ISSN 0141-0296, E-ISSN 1873-7323, Vol. 98, p. 151-162Article in journal (Refereed)
    Abstract [en]

    Tubular steel towers are the most commonly used structures to support wind converters. Towers are fabricated in welded segments, complying with the traffic requirements for transportation, and in-situ assembled. Ring flange connections are used to connect two segments. Fatigue endurance of the ring flange to the shell weld, class 71, is often the design criterion and imposes a limit on the shell thickness. Recently studied friction connections with long opened slotted holes, in HISTWIN and HISTWIN2 projects, provides a remedy for this limitation. The main purpose of this paper is to compare performance of the ring flange connection and the novel friction considering connection of a real tubular tower segment 3.37 m in diameter and 24 mm shell thickness. This cross-section is designed for the ultimate load MEd = 45.8 MNm and the steel grade S355. Finite Element Method is used to investigate possible failure modes of the connection. Advanced FEA comprise the realistic geometry of the connection, ductile damage material model and element removal using explicit dynamic solver. This allows sophisticated analysis of the behaviour and direct comparison of the results for both connection alternatives. The FEA is validated by down-scaled experiments performed previously within the HISTWIN project. The friction connection is thoroughly examined: geometry of the connection, influence of the shell imperfection in the vicinity of the connection and possible use of higher resistance steel grades. By focusing on key issues of the friction connection recommendations for the design are provided together with a numerical example

  • 18.
    Popescu, Cosmin
    et al.
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Structural and Construction Engineering.
    Sas, Gabriel
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Structural and Construction Engineering. NORUT, Department of Infrastructure Structures and Materials.
    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.
    Concrete walls weakened by openings as compression members: A review2015In: Engineering structures, ISSN 0141-0296, E-ISSN 1873-7323, Vol. 89, p. 172-190Article in journal (Refereed)
    Abstract [en]

    The purpose of this paper is to review the advances that have been made in the design of monolithic and precast reinforced concrete walls, both with and without openings, subject to eccentrically applied axial loads. Using the results of previous experimental studies, a database was assembled to enable statistical assessment of the reliability of existing design models. Several design aspects are highlighted, including the size and position of openings, and the roles of boundary conditions and geometric characteristics. In addition, the performance of fiber-reinforced polymers in strengthening wall openings is discussed. Overall it is found that design codes provide more conservative results than alternative design models that have been proposed in recent studies. Research into the strengthening of walls with openings is still in its early stages, and further studies in this area are needed. The paper therefore concludes by highlighting some areas where new investigations could provide important insights into the structural behaviour of strengthened elements.

  • 19.
    Popescu, Cosmin
    et al.
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Structural and Fire Engineering.
    Schmidt, Jacob W.
    Department of Civil Engineering, Technical University of Denmark, Technical University of Denmark, Division of Structural Engineering.
    Goltermann, Per
    Technical University of Denmark, Division of Structural Engineering.
    Sas, Gabriel
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Structural and Fire Engineering.
    Assessment of RC walls with cut-out openings strengthened by FRP composites using a rigid-plastic approach2017In: Engineering structures, ISSN 0141-0296, E-ISSN 1873-7323, Vol. 150, p. 585-598Article in journal (Refereed)
    Abstract [en]

    Building refurbishment works frequently require the cutting of new openings in concrete walls. Cutting new openings weakens the overall response of such elements, so they usually require strengthening. However, current design codes offer little guidance on strengthening walls with openings, and less still on the use of non-metallic reinforcements such as FRP (Fibre Reinforced Polymers) to ensure sufficient load bearing capacity. This paper proposes a new procedure based on limit analysis theory for evaluating the ultimate load of walls with cut-out openings that have been strengthened with carbon-FRP (CFRP). First, the approach is verified against transverse (out-of-plane) and axial (in-plane) loading for unstrengthened specimens. These loading types result in different failure mechanisms: transverse loading leads to failure due to yielding/rupture of the steel reinforcement while axial loading leads to failure by concrete crushing. Second, the proposed method is further developed for CFRP-strengthened specimens under axial loading. It accounts for the contribution of CFRP indirectly, by updating the concrete model with an enhanced compressive strength as a result of confining the piers. Predictions made using the new method agree closely with experimental results.

  • 20.
    Rebelo, Carlos
    et al.
    ISISE, Department of Civil Engineering, University of Coimbra.
    Moura, André
    ISISE, Department of Civil Engineering, University of Coimbra.
    Gervásio, Helena
    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.
    Silva, Luis X Luis Simões da
    ISISE, Department of Civil Engineering, University of Coimbra.
    Comparative life cycle assessment of tubular wind towers and foundations: Part 1: Structural design2014In: Engineering structures, ISSN 0141-0296, E-ISSN 1873-7323, Vol. 74, p. 283-291Article in journal (Refereed)
    Abstract [en]

    The use of tubular towers made of steel, concrete or hybrid steel–concrete has become standard in the wind energy industry. However, more powerful wind energy generators are leading to the need for increasing the towers height. This implies rethinking of existing solutions for the support onshore structure composed of tower and foundation, including design concept, life cycle and environmental repercussion. The need for transportation of larger prefabricated elements and more complex processes of assembling on site become important issues. This paper addresses the comparative study concerning the influence of increasing height on the structural design and outcome of different structural solutions. Steel, concrete and hybrid steel–concrete wind towers with heights of 80, 100 and 150 m supporting multi-megawatt turbines of 2, 3.6 and 5 MW power respectively are addressed. The design of the towers is made in accordance with the structural Eurocodes. Two different scenarios are addressed, the first considering common lifetime of 20 years and the second considering increased lifetime of 40 years with reuse of tower parts. In-situ erection of steel tubular parts is achieved using flange connections or newly developed friction connections. Conclusions point out that, for towers up to 80 m, the use of steel tubular sections and flange connections are the most suitable. Friction connections are suitable for higher towers, leading to less material consumption. The use of concrete towers, particularly for heights above 100 m, is penalized when seismic risk is considered in special in the dimensions of the slab foundations

  • 21.
    Richard, Benjamin
    et al.
    University Paris-Est, Laboratoire Central des Ponts et Chaussées.
    Epaillard, Sébastien
    University Paris-Est, Laboratoire Central des Ponts et Chaussées.
    Cremona, Chrisitian
    Ministry of Ecology, Energy, Sustainable Development and Sea.
    Adelaide, Lucas
    University Paris-Est, Laboratoire Central des Ponts et Chaussées.
    Elfgren, Lennart
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Structural and Construction Engineering.
    Nonlinear finite element analysis of a 50 years old reinforced concrete trough bridge2010In: Engineering structures, ISSN 0141-0296, E-ISSN 1873-7323, Vol. 32, no 12, p. 3899-3910Article in journal (Refereed)
    Abstract [en]

    In this paper, a nonlinear finite element model of a full scale bridge (Örnsköldsvik bridge, Sweden) is presented in connection with load tests. In order to quantify the carrying capacity of the bridge, a collapse load test was performed within the European Union founded project ‘‘Sustainable Bridges - Assessment for Future Traffic Demands and Longer Lives''. The finite element model introduces new constitutive material models. Four materials are in particular modelled in accordance with the bridge characteristics: concrete, steel reinforcement bars, CFRP bars and steel/concrete interface. The concrete is described by a damage mechanics based model developed within the framework of the irreversible processes thermodynamics. This ensures consistency with respect to the well known physics principles (conservation and evolution). The steel reinforcement bars and the CFRP bars are modelled using classical elasto-plastic constitutive laws with an isotropic hardening. The steel/concrete interface is developed in such a way that it may include corrosion. The numerical results are very close to the experimental measurements. Based on that finite element model, the influence of local degradation due to uniform corrosion is then studied. Two effects are considered for this purpose: steel cross section reductions and bond strength variations at the steel/concrete interface. Although these latter results remain informative due to the lack of documented data regarding the corrosion content in the bridge, they allow corroborating experimental measurements published in the literature.

  • 22.
    Sabau, Cristian
    et al.
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Structural and Fire Engineering.
    Popescu, Cosmin
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Structural and Fire Engineering.
    Bagge, Niklas
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Structural and Fire Engineering.
    Sas, Gabriel
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Structural and Fire Engineering.
    Blanksvärd, Thomas
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Structural and Fire Engineering.
    Täljsten, Björn
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Structural and Fire Engineering.
    Local and global behavior of walls with cut-out openings in multi-story reinforced concrete buildings2019In: Engineering structures, ISSN 0141-0296, E-ISSN 1873-7323, Vol. 187, p. 57-72Article in journal (Refereed)
    Abstract [en]

    This paper presents the finite element analysis (FEA) results of a multi-story reinforced concrete (RC) building having precast and cast-in-place load bearing walls. Door-type cut-out openings (height: 2.1 m, width: 0.9–4.4 m) were created at the first and second story of the building. Results from experimental tests on axially loaded RC panels were used to verify the modeling approach. The influence of cut-out openings on the response of individual RC panels, failure modes, and load redistribution to adjacent members was analyzed. Moreover, the wall bearing capacities obtained from FEA were compared with the values calculated from design equations. The results revealed that the robustness of multi-story buildings having RC load bearing wall systems decrease considerably with the creation of cut-out openings. However, owing to the initial robustness of the buildings, large cut-outopenings could be created under normal service conditions without strengthening of the building structure. Furthermore, design equations provided very conservative predictions of the ultimate capacity characterizing the solid walls and walls with small openings, whereas similar FEA and analytically predicted capacities were obtained for walls with large openings.

  • 23.
    Stehn, Lars
    et al.
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Structural and Construction Engineering.
    Börjes, K.
    Mitthögskolan, Östersund.
    The influence of nail ductility on the load capacity of a glulam truss structure2004In: Engineering structures, ISSN 0141-0296, E-ISSN 1873-7323, Vol. 26, no 6, p. 809-816Article in journal (Refereed)
    Abstract [en]

    When considering the design of load-carrying structures, brittle behaviour at failure should be avoided in order to attain a higher level of safety. In wood structures, the way to achieve high ductility is to take advantage of the plasticity of mechanical connectors (nails, dowels, bolts, etc.). In this paper the influence of ductile connections, slotted-in nailed wood to steel joints, on the total load-carrying capacity and deformability of a glulam truss is investigated. Experimental and finite element parametric studies are carried out to observe how different shapes of the nail load-displacement curve affect the load-carrying capacity. The results clearly show that consideration of the true elasto-plastic load-displacement behaviour of the nails results in a higher capacity of the truss compared to using linear elastic nail properties.

  • 24.
    Turesson, Jonas
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Wood Science and Engineering.
    Berg, Sven
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Wood Science and Engineering.
    Ekevad, Mats
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Wood Science and Engineering.
    Impact of board width on in-plane shear stiffness of cross-laminated timber2019In: Engineering structures, ISSN 0141-0296, E-ISSN 1873-7323, Vol. 196, article id 109249Article in journal (Refereed)
    Abstract [en]

    Board width-to-thickness ratios in non-edge-glued cross laminated timber (CLT) panels influence the in-plane shear stiffness of the panel. The objective is to show the impact of board width-to-thickness ratios for 3- and 5-layer CLT panels. Shear stiffnesses were calculated using finite element analysis and are shown as reduction factors relative to the shear stiffnesses of edge-glued CLT panels. Board width-to-thickness ratios were independently varied for outer and inner layers. Results show that the reduction factor lies in the interval of 0.6 to 0.9 for most width-to-thickness ratios. Results show also that using boards with low width-to-thickness ratios give low reduction factors. The calculated result differed by 2.9% compared to existing experimental data.

  • 25.
    Vessby, Johan
    et al.
    Linnaeus University, Växjö, Linnéuniversitetet.
    Källsner, Bo
    School of Engineering, Linnæus University, Växjö, Linnéuniversitetet, Linnaeus University, Växjö.
    Girhammar, Ulf Arne
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Structural and Construction Engineering.
    Olsson, Anders
    Faculty of Technology, Linnaeus University.
    Evaluation of softening behaviour of timber light-frame walls subjected to in-plane forces using simple FE models2014In: Engineering structures, ISSN 0141-0296, E-ISSN 1873-7323, Vol. 81, p. 464-479Article in journal (Refereed)
    Abstract [en]

    The present investigation focuses on evaluating the entire load–displacement relationship, especially the softening part, of light-frame wall segments subjected to in-plane monotonic forces when the load-slip curves of the individual sheathing-to-framing fasteners are considered. Different sheathing-to-framing joint characteristics, including unloading behaviour, and stud-to-rail joint characteristics are incorporated in the analyses. Two loading cases are investigated: Horizontal loading resulting in uplift of the leading stud and diagonal loading representing a fully anchored wall.Two common types of finite element (FE) models for the sheathing-to-framing joints are used for the analyses: A single spring model and a spring pair model, where the joint characteristics valid for the timber properties perpendicular and parallel to the grain are used. The maximum capacity of the wall segments is somewhat overestimated when using the spring pair model compared to that of the single spring model. The softening parts of the load–displacement curves are significantly affected, regardless of whether the perpendicular or parallel characteristics of the joints are used.The results from FE simulations using models with perpendicular and parallel characteristics are compared with full scale test results for walls with a single segment loaded horizontally and diagonally. The behaviour of the wall segments subjected to horizontal loading is dominated by fastener displacements perpendicular to the bottom rail. Hence, FE models including perpendicular characteristics should be used. For diagonal loading the behaviour of the wall segments is dominated by displacements parallel to the framing members, and FE models including parallel characteristics should therefore be used.The analyses were extended to multiple segment walls resulting in the same type of behaviour as single segment walls.

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