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  • 51.
    Sabau, Cristian
    et al.
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Structural and Construction 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.
    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.
    Monitoring structural behavior of reinforced concrete walls with openings using digital image correlation2016In: IABSE CONGRESS, STOCKHOLM, 2016: Challenges in Design and Construction of an Innovative and Sustainable Built Environment / [ed] ennart Elfgren, Johan Jonsson, Mats Karlsson, Lahja Rydberg-Forssbeck and Britt Sigfrid, CH - 8093 Zürich, Switzerland: International Association for Bridge and Structural Engineering, 2016, p. 1803-1811Conference paper (Refereed)
    Abstract [en]

    Several measuring techniques based on digital image correlation (DIC) are nowadays used in many fields. DIC measurements can facilitate documentation of crack patterns on specimens subject to loading, valuable information, which would otherwise be hard to obtain, especially in the case of reinforced concrete elements. This can not only give a better insight into the failure mechanism of the element, but also evaluate cracking as measure of serviceability.This article discusses existing serviceability limits and failure modes of reinforced concrete walls in buildings in light of results obtained using DIC on two half-scale reinforced concrete walls with openings tested to failure. Results suggest that cracks induced by a load level equivalent to 70% of ultimate load bearing capacity, do not exceed limits indicated in relevant guidelines.The failure mode of two way walls with openings was found to be similar to that of two way slabs with openings, however differences were identified in the development of the failure mechanism. Finally, two strengthening strategies of reinforced concrete walls are discussed.

  • 52.
    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.
    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.
    Review of FRCM strengthening solutions for structural wall panelsIn: American Concrete Institute. Publication SP, ISSN 0193-2527, E-ISSN 1094-8120Article in journal (Refereed)
    Abstract [en]

    This paper summarizes the state-of-the-art on the topic of structural wall panels strengthened using fabric reinforced cementitious matrix composites (FRCM) composites. A systematic review of the literature is carried out to identify gaps in the available literature. A database of experimental tests, relevant for structural panels, was created and used to assess the influence of parameters such as test method, fiber type and material compressive strength, on the performance of FRCM strengthening. Since experimental investigations on walls strengthened with FRCM composites is still limited and mostly focused on shear, further investigations on walls as compression members can be considered timely, especially walls with openings, which have been overlooked. Experimental tests performed by the authors on reinforced concrete walls with openings are presented and assessed relative to the complete database. It was shown that FRCM composites are suitable repair solutions when new openings need to be created in existing walls.

  • 53.
    Sabau, Cristian
    et al.
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Structural and Fire Engineering.
    Popescu, Cosmin
    Northern Research Institute – NORUT.
    Sas, Gabriel
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Structural and Fire Engineering.
    Schmidt, Jacob W.
    echnical University of Denmark, Department of Civil 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.
    Strengthening of RC beams using bottom and side NSM reinforcement2018In: Composites Part B: Engineering, ISSN 1359-8368, E-ISSN 1879-1069, Vol. 149, p. 82-91Article in journal (Refereed)
    Abstract [en]

    The allowable strain in fibre reinforced polymers reinforcement is limited by design codes to avoid debonding. The near-surface mounted (NSM) reinforcement technique has been proven to produce better anchorage behaviour compared to externally bonded reinforcement solutions. However, NSM solutions do not always eliminate debonding issues, with concrete cover detachment (CCD) typically occurring in RC beams strengthened for flexure. This experimental study investigated the efficiency of side mounted (S) compared to bottom mounted (B) NSM bars to prevent CCD. The experimental results were compared to models available in the literature that predict the observed failure modes and the crack spacing in the NSM anchorage zone. Compared to B-NSM, the S-NSM solution was successful in avoiding brittle CCD failure and showed increased rotational capacity and energy dissipation at failure. Existing CCD debonding models were found to be conservative.

  • 54.
    Sas, Gabriel
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Structural and Construction Engineering.
    FRP shear strengthening of RC beams and walls2008Licentiate thesis, comprehensive summary (Other academic)
    Abstract [en]

    The shear failure of Fibre Reinforced Polymers (FRP) strengthened reinforced concrete (RC) beams has not been studied to the same extent as the bending failure mechanism in the past decade. The complex nature of the shear failure mechanism just for reinforced concrete beams is still under debate among scientists and not solved yet. If we add the FRP strengthening to the already existing unknown issues, it is quite clear why attention was not focused on the shear failure of strengthened beam. In other words an extra uncertainty to the already existing ones is complicating more the problem of shear in concrete. It is of utmost importance to understand the shear failure mechanism of reinforced concrete beams and for this all the known theories for designing reinforced concrete beams subjected to shear are presented: truss analogy, theory of plasticity for concrete and modified compression field theory. The use of these theories in two of the most used standards is also exemplified. Further on, a design model for the shear strengthening of concrete beams by using fibre-reinforced polymers (FRP) is presented in Appendix I, and the limitations of the truss model analogy are highlighted. The fracture mechanics approach is used in analyzing the bond behaviour between the FRP composites and concrete. The fracture energy of concrete and the axial rigidity of the FRP are considered to be the most important parameters. The effective strain in the FRP when the debonding occurs is determined. The limitations of the anchorage length over the cross section are analyzed. A simple iterative design method for the shear debonding is finally proposed. Since the model's predictions are found satisfactory but not really precise, a deep literature review has been performed (Paper I). All the significant theoretical models for predicting the shear capacity of FRP strengthened RC beams developed during the years are analyzed, commented and compared with an extensive experimental database. The database contains the results from more than 200 tests performed in different research institutions across the world. The results of the comparison are not very promising and the use of the additional principle in the actual shear design equations should be questioned. The large scatter between the predicted values of different models and experimental results is of real concern bearing in mind that some of the models are used in present design codes. Further on, the influence of the FRP composites on the openings of shear (squat) walls is analyzed. In the same manner as for RC beams the current design methods existing in ACI (2005) and Eurocode (2004 a, b) are presented. Since the strengthening of shear walls was studied even less than FRP strengthened beams RC beam an up to date literature review of the experimental and theoretical work is presented. A concept, developed in collaboration with the Civil Engineering Department from "Politehnica" University of Timisoara, is presented for testing RC walls with openings subjected to lateral and gravitational loads (Appendix III). From a matrix of 50 different practical configurations of openings are selected 12 walls which are the subject of an ongoing experimental program. 8 walls with different opening configurations are subjected to cyclic lateral loading under constant gravitational load to simulate the seismic behaviour of FRP strengthened walls with openings. 4 walls with different opening configurations are tested to monotonic gravitational loading up to failure.

  • 55.
    Sas, Gabriel
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Structural and Construction Engineering.
    FRP shear strengthening of reinforced concrete beams2011Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    The shear failure mechanisms of flexural reinforced concrete (RC) members is highly complex; its precise details cannot be explained with simple analytical relationships, and are the topic of considerable scientific debate. The studies described and examined the three most used shear theories in the world – the fixed angle truss model (45°TM), the variable angle truss model (VAT), and modified compression field theory (MCFT). These three theories rest on the assumption that a beam loaded in shear behaves as a truss. However, this assumption is applied in different ways in various codes. In this thesis, three major standards, each of which uses a different implementation of these theories (CEN, 2005; ACI-318, 2008; CSA-A23.3, 2009), were used to predict the shear force capacity of a RC railway bridge that was strengthened in flexure with near surface mounted (NSM) carbon fibre reinforced polymers (CFRP) and then tested to failure. The data obtained in this test indicated that the codes underestimated the real shear behaviour of the bridge. There are some accepted reasons for such inaccuracies, namely the use of empirically derived equations in the ACI (2008) and CSA (2009) standards and the omission of the concrete contribution in CEN (2005). Moreover, the NSM reinforcement material used exhibits elastic behaviour until the point of failure; it was found that the use of such materials introduces further decreases the accuracy of the models’ predictions. The strains that developed in the area of the bridge where shear failure was expected were monitored throughout the test using a specially-developed photographic method. The results obtained with this method were promising, especially for research purposes, since it generated reliable data using relatively affordable tools.The use of FRP for shear strengthening introduces further complications to the problem of shear in reinforced concrete members because introduces two new failure modes: debonding at the concrete interface and fibre rupture of the FRP. Extensive research has been carried out on FRP shear strengthening around the world. Much of the data gathered in these studies has been compiled in a database. By analysing this large database, it was found that the effectiveness of FRP shear strengthening is influenced by many factors, including the properties of the FRPs, the FRP strengthening configuration used, the nature of the beam’s cross-section, the shear span to depth ratio, the presence of stirrups, and the nature of the tensile reinforcement. Analysis of this database also demonstrated that most of the studies reported in the literature had focused on investigating the influence of the properties of the FRPs and the different configuration systems, and that the other factors mentioned above have been sparsely investigated if not totally ignored. The strengthening configuration and the amount of fibres influence the failure mode of the FRP and the shear force that it can carry. It appears that the side-bonded and the U-wrapped configurations are most prone to failure by debonding. This is consistent with the findings of various small experimental programs, and was confirmed by analysis of the larger dataset. These findings are relevant because failure of the FRP by debonding is more complex mechanism than is the rupture of the fibres mechanism. As is shown in this thesis, the extent to which the FRP variables (properties and strengthening configuration) can affect the point at which failure occurs and the mode by which it happens is dependent on the quantity of stirrups and tensile reinforcement in the beam, to the position of the load in relation to the size of the cross section (shear span to depth ratio), the type of strengthening configuration, the concrete and FRP properties. For design purposes, it is important to predict the shear failure of FRP shear strengthened beams with as much accuracy as possible. Therefore, a design model for debonding of the shear strengthening of concrete beams with FRP was developed and the limitations of the truss model analogy were highlighted. The fracture mechanics approach was used to analyse the behaviour of the bond between the FRP composites and the concrete. In this model, of the parameters examined, the fracture energy of concrete and the axial rigidity of the FRP are considered to be the most important. The effective strain in the FRP when debonding occurs was determined and the limitations of the anchorage length over the cross section were analysed; ultimately, a simple iterative method for shear debonding was proposed. Since the model’s predictions were considered satisfactory but not really precise, an extensive review of the literature was conducted. All of the significant theoretical models for predicting the shear capacity of FRP strengthened RC beams that have been reported over the years were analysed and commented on, and their predictions were compared to the results recorded in a preliminary experimental database. The predictions of the models that are most widely used in design were compared to the experimental results reported in the database; the model developed by the author was evaluated alongside these more established models. All of the models, including that presented in this thesis, were found to generate inaccurate predictions, but two models have been calibrated so as to provide safe estimates of the FRP shear capacity. Finally a new model for FRP shear strengthening was proposed for use in engineering. The new model was developed on the basis of an analysis of the contents of the database of experimental findings. The model incorporates several design equations adopted from various models and is set up for engineering use. The predictions of the shear force carried by the FRP strengthening material are found to be conservative.

  • 56.
    Sas, Gabriel
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Structural and Fire Engineering.
    Project: endure2014Other (Other (popular science, discussion, etc.))
  • 57.
    Sas, Gabriel
    et al.
    Norut Northern Research Institute, Narvik.
    Bagge, Niklas
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Structural and Construction Engineering.
    Häggström, Jens
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Structural and Construction Engineering.
    Nilimaa, Jonny
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Structural and Construction Engineering.
    Puurula, Arto
    Blanksvärd, Thomas
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Structural and Construction Engineering.
    Täljsten, Björn
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Structural and Construction Engineering.
    Elfgren, Lennart
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Structural and Construction Engineering.
    Carolin, Anders
    Trafikverket, Trafikverket, Luleå.
    Paulsson, Björn
    Trafikverket, UIC, Banverket.
    Tested versus code capacity of existing bridges: Three examples2015In: IABSE Conference Geneva 2015: Structural Engineering: Providing Solutions to Global Challenges, Geneva: International Association for Bridge and Structural Engineering, 2015, p. 727-734Conference paper (Other academic)
    Abstract [en]

    This paper presents the results from three tests to failure of different types of bridges: a two span reinforced concrete railway trough bridge; a five-span prestessed concrete beam bridge; and a one span metal railway truss bridge. The results show that the capacity of the structures are underestimated by current standards, while numerical analysis combined with material testing can provide more accurate results. Some examples are also presented on how deficiencies incapacity can be mitigated using fiber reinforced polymer strengthening systems.

  • 58.
    Sas, Gabriel
    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.
    Enochsson, Ola
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Structural and Construction Engineering.
    Emborg, Mats
    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.
    Puurula, Arto
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Structural and Construction Engineering.
    Elfgren, Lennart
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Structural and Construction Engineering.
    Flexural-shear failure of a full scale tested RC bridge strengthened with NSM CFRP: Shear capacity analysis2011In: Nordic Concrete Research, ISSN 0800-6377, Vol. 2/2011, no 44, p. 189-206Article in journal (Refereed)
  • 59.
    Sas, Gabriel
    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.
    Enochsson, Ola
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Structural and Construction Engineering.
    Täljsten, Björn
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Structural and Construction Engineering.
    Elfgren, Lennart
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Structural and Construction Engineering.
    Full scale failure testing of a reinforced concrete bridge: photographic strain monitoring2012In: Proceedings of The 6th International Conference on FRP Composites in Civil Engineering: CICE 2012, 2012Conference paper (Refereed)
    Abstract [en]

    Full-scale failure tests are rarely performed on structures, primarily due to their high costs and the lack of suitable test objects. The main aim of this test was to study shear failure of the bridge, which is a less understood and more difficult to predict mode of failure in RC structures than is bending. In order to prevent bending failure, it was necessary to strengthen the bridge using near surface mounted (NSM) reinforcements made of carbon fibre reinforced polymer (CFRP) bars. The bridge was heavily monitored during the test, using both traditional sensors such as electrical strain gauges and linear variable differential transducers (LVDTs) alongside new monitoring systems such as fibre optic sensors, strain rosette LVDTs, and a novel photographic monitoring system. This paper presents the results obtained from the photographic strain measurements and describes the use of the photographic tools in monitoring and characterising the behaviour of the failure zone during the full scale test. The strains measured using this method were found to agree well with those measured using classical strain gauges. In addition, the strain contour plots generated using the photographic method provided important insights into the strains within the bridge’s failure zone.

  • 60.
    Sas, Gabriel
    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.
    Enochsson, Ola
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Structural and Construction Engineering.
    Täljsten, Björn
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Structural and Construction Engineering.
    Elfgren, Lennart
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Structural and Construction Engineering.
    Photographic strain monitoring during full-scale failure testing of Örnsköldsvik Bridge2012In: Structural Health Monitoring, ISSN 1475-9217, E-ISSN 1741-3168, Vol. 11, no 4, p. 489-498Article in journal (Refereed)
    Abstract [en]

    Full-scale failure tests are rarely performed on structures, primarily due to their high costs and the lack of suitable test objects. This article reports the results of a ‘test-to-failure’ performed using a real bridge. The results obtained in such tests are valuable for assessing analytical models, updating finite element models and investigating the real behaviour of structures. The specific intention in these experiments was to study the shear failure of the bridge, which is a less well-understood mode of failure than is bending. To this end, it was necessary to strengthen the bridge using near-surface-mounted reinforcements made of carbon fibre–reinforced polymer bars in order to prevent bending failure. The bridge was heavily monitored during the test, using both traditional sensors such as electrical strain gauges and linear variable differential transducers alongside new monitoring systems such as fibre-optic sensors, strain rosette linear variable differential transducers and a novel photographic monitoring system. This article presents the photographic strain measurements and describes the use of the photographic tools in monitoring and characterizing the behaviour of the failure zone during the full-scale test. The strains measured using the photographic method were found to agree well with those measured using classical strain gauges. In addition, the strain contour plots generated using the photographic method provided crucial insights into the strains within the bridge’s failure zone. This study was conducted under the remit of the EU ‘Sustainable Bridges’ Project.

  • 61.
    Sas, Gabriel
    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.
    Nilimaa, Jonny
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Structural and Construction Engineering.
    Täljsten, Björn
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Structural and Construction Engineering.
    Elfgren, Lennart
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Structural and Construction Engineering.
    Bennitz, Anders
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Structural and Construction Engineering.
    Carolin, Anders
    Trafikverket.
    Strengthening of concrete structures with carbon fibre reinforced polymers (CFRP): case studies2012In: Concrete Structures for Sustainable Community: proceedings of the International FIB Symposium 2012, Stockholm, Sweden, 11 - 14 June 2012 / [ed] Dirch H. Bager; Johan Silfwerbrand, Stockholm: Swedish Concrete Association , 2012, p. 423-426Conference paper (Refereed)
    Abstract [en]

    Carbon Fibre Reinforced Polymers (CFRP) has found an increased application in strengthening of concrete structures. Mostly the CFRP is used as externally bonded reinforcement. However, prestressing of it gives a possibility to increase the capacity and stiffness of existing concrete structures. A number of tests in the laboratory as well as field case studies have been carried out. The paper describes some of them.

  • 62.
    Sas, Gabriel
    et al.
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Structural and Construction Engineering.
    Carolin, Anders
    Täljsten, Björn
    A model for predicting the shear bearing capacity of FRP-strengthened beams2008In: Mechanics of composite materials, ISSN 0191-5665, E-ISSN 1573-8922, Vol. 44, no 3, p. 245-256Article in journal (Refereed)
    Abstract [en]

    The shear failure of reinforced concrete beams needs more attention than the bending failure since no or only small warning precedes the failure. For this reason, it is of utmost importance to understand the shear bearing capacity and also to be able to undertake significant rehabilitation work if necessary. In this paper, a design model for the shear strengthening of concrete beams by using fiber-reinforced polymers (FRP) is presented, and the limitations of the truss model analogy are highlighted. The fracture mechanics approach is used in analyzing the bond behavior between the FRP composites and concrete. The fracture energy of concrete and the axial rigidity of the FRP are considered to be the most important parameters. The effective strain in the FRP when the debonding occurs is determined. The limitations of the anchorage length over the cross section are analyzed. A simple iterative design method for the shear debonding is finally proposed.

  • 63.
    Sas, Gabriel
    et al.
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Structural and Construction Engineering.
    Carolin, Anders
    Täljsten, Björn
    Barros, Joaquim
    University of Minho.
    Lima, Joao
    University of Minho.
    Arifovic, Fedja
    Technical University of Denmark.
    How reliable are the available models for predicting the FRP contribution for the shear resistance of RC beams?2008In: Proceedings of CCC 2008 - Challenges for Civil Construction / [ed] Torres Marques, FEUP edições (Faculdade de Engenharia da Universidade do Porto Edicoes), 2008Conference paper (Refereed)
    Abstract [en]

    The most well-known models for prediction of the contribution of externally bonded FRP for shear strengthening of reinforced concrete beams are compared on this paper. The comparison is based on experimental results from approximately 200 strengthened concrete beams with various strengthening configurations and geometric dimensions. The results are not promising and a large scatter between the considered models was obtained. In addition, none of these models predict the ultimate shear capacity very accurately, which is of serious concern considering that some of the models are used in various design codes.

  • 64.
    Sas, Gabriel
    et al.
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Structural and Construction Engineering.
    Demeter, Istvan
    Politechnica University of Timisoara.
    Nagy-György, Tamas
    Politechnica University of Timisoara.
    Stoian, Valeriu
    Politechnica University of Timisoara.
    Carolin, Anders
    Täljsten, Björn
    FRP strengthened RC panels with cut-out openings2008In: Proceedings of CCC 2008 - Challenges for Civil Construction / [ed] Torres Marques, FEUP edições (Faculdade de Engenharia da Universidade do Porto Edicoes), 2008Conference paper (Refereed)
    Abstract [en]

    A strengthening solution for multi-storey buildings in seismically active regions is considered. The Precast Reinforced Concrete Large Panel (PRCLP) structural system is described. Besides earthquakes, different problems during the last decades were identified in the PRCLP structural behaviour: design mistakes, neglected health monitoring, construction problems, change of use for example cut-out openings. The presented study is a part of an ongoing research program which deals with the influence of the Fibre Reinforced Polymer (FRP) strengthening on the behaviour of Precast RC Wall Panels (PRCWP) with cut out openings subjected to cyclic (seismic) and normal (gravity) loading. In this paper a brief literature survey concerning RC walls strengthened by FRP is presented and the experimental tests setup is discussed. The wall specimens were designed according to the 1981 Romanian code. Tests are described and a discussion based on previous experimental work on shear walls is undertaken and future research is suggested.

  • 65.
    Sas, Gabriel
    et al.
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Structural and Construction Engineering. NORUT, Department of Infrastructure Structures and Materials.
    Dăescu, Cosmin
    Politechnica University of Timisoara.
    Popescu, Cosmin
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Structural and Construction Engineering.
    Tamás, Nagy-György
    Politechnica University of Timisoara.
    Numerical optimization of strengthening disturbed regions of dapped-end beams using NSM and EBR CFRP2014In: Composites Part B: Engineering, ISSN 1359-8368, E-ISSN 1879-1069, Vol. 67, p. 381-390Article in journal (Refereed)
    Abstract [en]

    This paper presents a parametric investigation, based on non-linear finite element modeling, to identify the most effective configuration of carbon fiber reinforced polymers (CFRP) for strengthening reinforced concrete (RC) dapped end beams. Following a field application and laboratory tests, it focuses on effects of 24 externally bonded (EBR) and near surface mounted reinforcement (NSMR) configurations on yield strain in steel and the capacity and failure mode of dapped-end beams. The investigated parameters were the mechanical properties of the CFRP, the strengthening procedure and the inclination of the fibers with respect to the longitudinal axis. Two failure scenarios were considered: rupture and debonding of the FRP. The results indicate that high-strength NSM FRPs can considerably increase the capacity of dapped-end beams and the yielding strains in reinforcement can be substantially reduced by using high modulus fibers.

  • 66. Sas, Gabriel
    et al.
    Hansen, Christian
    Technical University of Denmark.
    Täljsten, Björn
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Structural and Construction Engineering.
    FRP strengthening of RC walls with openings2009In: Advanced Composites in Construction (ACIC) 2009 Conference Proceedings / [ed] Sue Halliwell; Claire Whysall; Tim Stratford, ACIC , 2009, p. 202-213Conference paper (Refereed)
    Abstract [en]

    Strengthening reinforced concrete (RC) walls with openings using fibre reinforced polymers (FRP) has been proved experimentally to be a viable rehabilitation method. However, very few theoretical investigations are reported. In this paper two methods of analysis are presented. Since openings vary in size, the analysis of a strengthened wall can be divided into frame idealization method for large openings, and combined disk and frame analysis for smaller openings. The first method provides an easy to use tool in practical engineering, where the latter describes the principles of a ductile strengthening method, relying on dislocation of yield lines and creation of a new yield mechanism. The frame idealization method can be considered as a safe guideline for real strengthening projects based on commonly used principles. The principles in the latter are new and promising, and need experimental verification before use in strengthening projects.

  • 67.
    Sas, Gabriel
    et al.
    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.
    Vasa pontoon: crack mapping and finite element analysis2009Report (Other academic)
  • 68.
    Sas, Gabriel
    et al.
    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.
    Barros, Joaquim
    University of Minho, School of Engineering, Department of Civil Engineering.
    Lima, Joao
    University of Minho, School of Engineering, Department of Civil Engineering.
    Carolin, Anders
    Are available models reliable for predicting the FRP contribution to the shear resistance of RC beams?2009In: Journal of composites for construction, ISSN 1090-0268, E-ISSN 1943-5614, Vol. 13, no 6, p. 514-534Article in journal (Refereed)
    Abstract [en]

    In this paper the trustworthiness of the existing theory for predicting the fiber-reinforced plastic contribution to the shear resistance of reinforced concrete beams is discussed. The most well-known shear models for external bonded reinforcement are presented, commented on, and compared with an extensive experimental database. The database contains the results from more than 200 tests performed in different research institutions across the world. The results of the comparison are not very promising and the use of the additional principle in the actual shear design equations should be questioned. The large scatter between the predicted values of different models and experimental results is of real concern bearing in mind that some of the models are used in present design codes.

  • 69.
    Song, Shoutan
    et al.
    Southeast University, Nanjing.
    Yang, Dong
    Southeast University, Nanjing.
    Tu, Yongming
    Southeast University, Nanjing.
    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.
    Elfgren, Lennart
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Structural and Fire Engineering.
    Analysis of the shear strength of joints in segmental prestressed concrete bridges2016In: 19th IABSE Congress Strockholm 21-23 September 2016: Challenges in Design and Construction of an Innovative and Sustainable Built Environment / [ed] Lennart Elfgren, Johan Jonsson, Mats Karlsson, Lahja Rydberg-Forssbeck and Britt Sigfrid, CH - 8093 Zürich, Switzerland, 2016, p. 573-579Conference paper (Refereed)
    Abstract [en]

    Joints in segmental prestressed concrete bridge (SPCB) are weak links and shear failures are likely to take place under loads. Determining the shear strength is an important part in the design of a SPCB. The shear strength in the joint relates closely to the joint form (as dry joints, epoxy joints, flat joints and keyed joints). The strength can be divided into three main parts: (1) The strength of the dry plane connection, known mainly as concrete surface friction; (2) The strength of the epoxy plane connection; and (3) The strength of the shear key root. This paper analyzes the failure mechanism and shear strength of these three parts .It also considers the influences of the shear key size and the seam height to shear strength, and establishes calculation formulas of the joint section strength in a united form. This provides a guide for the joint design in precast segmental bridges

  • 70.
    Stoian, V.
    et al.
    Politechnica University of Timisoara.
    Nagy-György, T.
    Politechnica University of Timisoara.
    Daescu, A.C.
    Politechnica University of Timisoara.
    Diaconu, D.
    Politechnica University of Timisoara.
    Sas, Gabriel
    Theoretical and experimental study on prestressed concrete beam support zone strengthened with composites2006In: Proceedings of the 2nd FIB Congress: June 5-8, 2006, Naples, Italy, Naples: FIB Italia , 2006Conference paper (Refereed)
  • 71.
    Täljsten, Björn
    et al.
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Structural and Construction Engineering.
    Blanksvärd, Thomas
    Sas, Gabriel
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Structural and Construction Engineering.
    Handbok för dimensionering och utförande i samband med förstärkning av betongkonstruktioner med pålimmade fiberkompositer2012Book (Other academic)
  • 72.
    Täljsten, Björn
    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 Fire Engineering.
    Sas, Gabriel
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Structural and Construction Engineering.
    Kompositförstärkning av betong2016Book (Other academic)
  • 73.
    Täljsten, Björn
    et al.
    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.
    Sas, Gabriel
    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. WSP.
    Nilimaa, Jonny
    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.
    Elfgren, Lennart
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Structural and Fire Engineering.
    Carolin, Anders
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering. Trafikverket.
    Häggström, Jens
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Structural and Fire Engineering. Trafikverket.
    Bridges tested to failure in Sweden2018In: IABSE Conference 2018 – Engineering the Past, to Meet the Needs of the FutureJune 25-27 2018, Copenhagen, Denmark, 2018Conference paper (Refereed)
    Abstract [en]

    Five bridges of different types have been tested to failure and the results have been compared to analyses of the load-carrying capacity using standard code models and advanced numerical methods. The results may help to make accurate assessments of similar existing bridges. There it is necessary to know the real behaviour, weak points, and to be able to model the load-carrying capacity in a correct way.The five bridges were: (1) a strengthened one span concrete road bridge - Stora Höga ; (2) a one span concrete rail trough bridge loaded in fatigue – Lautajokk; (3) a two span strengthened concrete trough railway bridge - Övik; (4) a one span railway steel truss bridge -Åby; and (5) a five span prestressed concrete road bridge - Kiruna. The unique results in the paper are the experiences of the real failure types, the robustness/weakness of the bridges, and the accuracy and shortcomings/potentials of different codes and models for safety assessment of existing structures

  • 74.
    Täljsten, Björn
    et al.
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Structural and Construction Engineering.
    Nilimaa, Jonny
    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.
    Sas, Gabriel
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Structural and Construction Engineering.
    Flexural-shear failure of a full scale tested RC bridge strengthened with NSM CFRP2011Conference paper (Other academic)
  • 75.
    Täljsten, Björn
    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.
    Strengthening of concrete structures with FRP: a guideline2014In: Nordic Concrete Research, ISSN 0800-6377, Vol. 49, p. 113-126Article in journal (Refereed)
    Abstract [en]

    There is a need to retrofit existing concrete structures. There are many different ways to increase the performance of a concrete structure, FRP (Fiber Reinforced Polymer) strengthening being one. This method is commonly used across the world to improve the load carrying capacity of concrete structures. In this paper, an overview of a Swedish guideline for the FRP strengthening of concrete structures is presented. The guideline covers designing for bending and shear as well as for confinement, and there is also a discussion of the need to proper workmanship and the choice of the right material for strengthening.

  • 76.
    Täljsten, Björn
    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.
    Blanksvärd, Thomas
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Structural and Construction Engineering.
    Strengthening of concrete structures with FRP: a guideline2014In: Nordic Concrete Research, ISSN 0800-6377, Vol. 50, p. 289-292Article in journal (Refereed)
12 51 - 76 of 76
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