11 results on '"Sas, Gabriel"'
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2. Failure of a RC Bridge initiated by debonding : 3-D Non-Linear Finite Element Analysis of Near Surface Mounted Fibre Reinforced Polymer Bars (NSM FRPB)
- Author
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Puurula, Arto M., Enochsson, Ola, Sas, Gabriel, Täljsten, Björn, and Elfgren, Lennart
- Subjects
Torsion ,3D non-linear finite element analysis (NL FEA) ,Infrastrukturteknik ,Bending ,Ultimate load carrying capacity ,Full scale test ,Shear ,Carbon Fibre Reinforced Polymer (CFRP) ,Bridges ,Infrastructure Engineering ,Failure Analysis ,Strengthening ,Near Surface Mounted Reinforcement (NSMR) ,Bond - Abstract
The bond failure is studied of a reinforced concrete trough bridge strengthened with near surface mounted reinforcement of carbon fibre reinforced polymer (CFRP) bars. The bars were embedded in epoxy resin in pre-sawed groves in the soffit of the bridge edge beams. The failure was modelled with 3D nonlinear finite elements, and it was possible to study the process from initiation to final collapse. A local bond failure in the interface between the concrete and the epoxy resin initiated a redistribution of forces in the bridge leading to yielding in the longitudinal and vertical steel reinforcement, rupture of stirrups and finally a full failure of the bridge. The bridge was a 50-year-old typical concrete railway trough bridge in Örnsköldsvik, in northern Sweden. It was going to be dismantled due to a relocation of the railway line. The aim of the loading test was to get detailed information of the bridge behaviour all the way up to the final failure. The test was a part of the European Research Project “Sustainable Bridges” regarding assessment and strengthening of existing bridges. The bridge was strengthened in bending before the loading test to avoid an uninteresting flexural failure. Failure was reached for an applied load of 11,7 MN by pulling downwards a steel beam placed in the middle of one of the two spans. The FE calculations presented here show the effect of the strengthening with CFRP, the effect of the epoxy when using the Near Surface Mounted Reinforcement (NSMR) strengthening method and the high load-carrying capacity of this bridge type Forskningsfinansiär: European Union 6th Framewok Program; The Federal Institute for Materials Research and Testing (BAM); Botniabanan; Cervenka Consulting; Nordisk Spännarmering; Savonia University of Applied Sciences; University of Oulu; Skanska Sverige AB; STO Skandinavia AB; Örnsköldsviks kommun; University of Minho (UMINHO) Sustainable Bridges
- Published
- 2021
3. Assessment of prestressed concrete bridges - challenges
- Author
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Täljsten, Björn, Paulsson, Björn, Popescu, Cosmin, Bagge, Niklas, Nilforoush, Rasoul, Emborg, Mats, Blanksvärd, Thomas, Sas, Gabriel, and Elfgren, Lennart
- Subjects
Corrosion ,Annan samhällsbyggnadsteknik ,Annan materialteknik ,Monitoring ,Strengthening ,Other Materials Engineering ,Prestressed Concrete Bridges ,Challenges ,Safety ,Assessment ,Other Civil Engineering ,Fatigue ,Repair - Abstract
Prestressed concrete bridges are important parts of our infrastructure. They are susceptible to different kinds of deterioration processes. Examples of damages and deficiencies are cracking, corrosion, voids, bond loss, reduction of cover layer, delamination, fatigue and loss of stiffness and strength. This necessitates methods to continuously assess their condition in order to avoid problems that might lead to shorter service life or reduction of structural integrity. Many of the existing prestressed bridges in Europe are now approaching their design life length. However, with proper and continuous inspection, monitoring and assessment, we may plan proactive maintenance and the structural safety can be assured or – if necessary - increased. This will save both money and decrease the environmental impact of the structure. ISBN för värdpublikation: 978-3-85748-169-7
- Published
- 2020
4. Full-Scale Test to Failure of a Prestressed Concrete Bridge in Kiruna
- Author
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Bagge, Niklas, Blanksvärd, Thomas, Sas, Gabriel, Bernspång, Lars, Täljsten, Björn, Carolin, Anders, and Elfgren, Lennart
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Infrastrukturteknik ,Shear Resistance ,Testing ,Civil engineering and architecture - Building engineering ,Strengthening ,Fibres ,Assessment ,Pre-stress ,Structural Design ,Infrastructure Engineering ,Repair ,Samhällsbyggnadsteknik och arkitektur - Byggnadsteknik ,Reinforcement - Abstract
To calibrate methods for condition assessment of prestressed concrete (PC) bridges, tests are planned for a 50 year old five-span bridge with a length of 121 m in Kiruna in northern Sweden. Both non-destructive and destructive full-scale tests will be performed. This paper summarises the test programme, which comprises evaluation of the structural behaviour of the bridge, the residual forces in the prestressed steel, methods for strengthening using carbon fibre reinforced polymers (CFRP) and the shear resistance of the bridge slab. To calibrate methods for condition assessment of prestressed concrete (PC) bridges, tests are planned for a 50 year old five-span bridge with a length of 121 m in Kiruna in northern Sweden. Both non-destructive and destructive full-scale tests will be performed. This paper summarises the test programme, which comprises evaluation of the structural behaviour of the bridge, the residual forces in the prestressed steel, methods for strengthening using carbon fibre reinforced polymers (CFRP) and the punching capacity of the bridge slab. Godkänd; 2014; 20140829 (nikbag); Konferensartikel i tidskrift
- Published
- 2014
5. Strengthening Concrete Structures using Mineral Based Composites
- Author
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Blanksvärd, Thomas, Sas, Gabriel, and Täljsten, Björn
- Subjects
Mortar ,Infrastrukturteknik ,Beams ,Strengthening ,Shear ,Engineering mechanics - Construction engineering ,Teknisk mekanik - Konstruktionsteknik ,CFRP ,Grid ,Infrastructure Engineering ,Concrete - Abstract
During the last two decades, strengthening concrete structures with epoxy bonded carbon fiber reinforced polymers (CFRP) has shown excellent results in increasing bearing capacity. However, there are some limitations with epoxy coated concrete surfaces, e.g.; low permeability which may provoke freeze/thaw problems, poor thermal compatibility to the concrete substrate which makes epoxy coating more sensitive to the surrounding temperature and regulations when it comes to the security and health (allergic reactions) of applicators and third party users. In this respect, using mineral based composites (MBC) may overcome some of these challenges associated with epoxy bonded strengthening systems. MBC, in this context, refers to high strength fibers bonded to the surface using a mineral based bonding agent. This study examines the cracking behavior and strain development of shear MBC strengthened RC beams. The results show that using MBC as shear strengthening postpones the formation of macro-cracks and that a considerable strengthening effect is achieved by using MBC. Godkänd; 2013; 20131113 (gabsas)
- Published
- 2013
6. FRP shear strengthening of reinforced concrete beams
- Author
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Sas, Gabriel
- Subjects
model ,Infrastrukturteknik ,comparison ,literature review ,strengthening ,fiber reinforced polymers ,shear ,reinforced concrete ,Infrastructure Engineering - Abstract
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. Godkänd; 2011; 20110328 (gabsas); DISPUTATION Ämnesområde: Konstruktionsteknik/Structural Engineering Opponent: Professor Giorgio Monti, University of Rome, Italy Ordförande: Professor Björn Täljsten, Institutionen för samhällsbyggnad och naturresurser, Luleå tekniska universitet Tid: Fredag den 29 april 2011, kl 13.00 Plats: F1031, Luleå tekniska universitet
- Published
- 2011
7. FRP strengthened RC panels with cut-out openings
- Author
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Sas, Gabriel, Demeter, Istvan, Nagy-György, Tamas, Stoian, Valeriu, Carolin, Anders, and Täljsten, Björn
- Subjects
Technology - Civil engineering and architecture ,Cut-out Openings ,Infrastrukturteknik ,Strengthening ,Teknikvetenskap - Samhällsbyggnadsteknik och arkitektur ,Shear Walls ,Infrastructure Engineering ,Reinforced Concrete ,FRP - Abstract
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. Godkänd; 2008; 20091216 (gabsas)
- Published
- 2008
8. Concrete walls weakened by openings as compression members: A review.
- Author
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Popescu, Cosmin, Sas, Gabriel, Blanksvärd, Thomas, and Täljsten, Björn
- Subjects
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CONCRETE walls , *MATERIALS compression testing , *AXIAL loads , *RELIABILITY in engineering , *ENGINEERING design , *BOUNDARY value problems - Abstract
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. [ABSTRACT FROM AUTHOR]
- Published
- 2015
- Full Text
- View/download PDF
9. Loading to failure and 3D nonlinear FE modelling of a strengthened RC bridge.
- Author
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Puurula, Arto M., Enochsson, Ola, Sas, Gabriel, Blanksvärd, Thomas, Ohlsson, Ulf, Bernspång, Lars, Täljsten, Björn, and Elfgren, Lennart
- Subjects
REINFORCED concrete ,RAILROAD bridges ,CONCRETE bridges ,STRENGTH of building materials ,CARBON fibers ,GIRDERS - Abstract
A reinforced concrete railway trough bridge in Örnsköldsvik, Sweden, was strengthened in bending with rods of carbon-fibre-reinforced polymer and loaded to failure. The aim was to test and calibrate methods developed in the European Research Project ‘Sustainable Bridges’ regarding assessment and strengthening of existing bridges. A steel beam was placed in the middle of one of the two spans and was pulled downwards. Failure was reached at an applied load of 11.7 MN. It was initiated by a bond failure caused by a combined action of shear, torsion as well as bending after yielding in the longitudinal steel reinforcement and the stirrups. The bond failure led to a redistribution of the internal forces from the tensile reinforcement to the stirrups, causing the final failure. The computer models developed to simulate the loading process were improved step by step from linear shell models to more detailed models. The most developed model, a three-dimensional nonlinear finite element model with discrete reinforcement, gave accurate accounts of the response of the bridge. [ABSTRACT FROM PUBLISHER]
- Published
- 2014
- Full Text
- View/download PDF
10. Assessment of the Strengthening of an RC Railway Bridge with CFRP Utilizing a Full-Scale Failure Test and Finite-Element Analysis.
- Author
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Puurula, Arto M., Enochsson, Ola, Sas, Gabriel, Blanksvärd, Thomas, Ohlsson, Ulf, Bernspång, Lars, Täljsten, Björn, Carolin, Anders, Paulsson, Björn, and Elfgren, Lennart
- Subjects
REINFORCED concrete construction ,RAILROAD bridges ,FINITE element method ,FAILURE analysis ,MECHANICAL loads ,CARBON fiber-reinforced plastics ,SHEAR strength ,BRIDGES ,SAFETY - Abstract
A finite element (FE) model was calibrated using the data obtained from a full-scale test to failure of a 50 year old reinforced concrete (RC) railway bridge. The model was then used to assess the effectiveness of various strengthening schemes to increase the load-carrying capacity of the bridge. The bridge was a two-span continuous single-track trough bridge with a total length of 30 m, situated in Örnsköldsvik in northern Sweden. It was tested in situ as the bridge had been closed following the construction of a new section of the railway line. The test was planned to evaluate and calibrate models to predict the load-carrying capacity of the bridge and assess the strengthening schemes originally developed by the European research project called Sustainable bridges. The objective of the test was to investigate shear failure, rather than bending failure for which good calibrated models are already available. To that end, the bridge was strengthened in flexure before the test using near-surface mounted square section carbon fiber reinforced polymer (CFRP) bars. The ultimate failure mechanism turned into an interesting combination of bending, shear, torsion, and bond failures at an applied load of 11.7 MN (2,630 kips). A computer model was developed using specialized software to represent the response of the bridge during the test. It was calibrated using data from the test and was then used to calculate the actual capacity of the bridge in terms of train loading using the current Swedish load model which specifies a 330 kN (74 kips) axle weight. These calculations show that the unstrengthened bridge could sustain a load 4.7 times greater than the current load requirements (which is over six times the original design loading), whilst the strengthened bridge could sustain a load 6.5 times greater than currently required. Comparisons are also made with calculations using codes from Canada, Europe, and the United States. [ABSTRACT FROM AUTHOR]
- Published
- 2015
- Full Text
- View/download PDF
11. Assessment of RC walls with cut-out openings strengthened by FRP composites using a rigid-plastic approach.
- Author
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Popescu, Cosmin, Schmidt, Jacob W., Goltermann, Per, and Sas, Gabriel
- Subjects
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CONCRETE walls , *FIBER-reinforced plastics , *CARBON fiber-reinforced plastics , *BEARINGS (Machinery) , *PEAK load - Abstract
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. [ABSTRACT FROM AUTHOR]
- Published
- 2017
- Full Text
- View/download PDF
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