A Equipa - Investigadores
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    Ali Edalat Behbahani

    Aluno de Doutoramento

    Tese: Development of nonlinear material models to simulate behavior of cement based materials

    Orientador: Joaquim António Oliveira de Barros
    Co-orientador: António Ventura Gouveia

    Generally, Finite element code is often modular in structure, whether it is a commercial code or a written in house. An important module is the one related to the material behavior or constitutive stress response of the material given prescribed condition of deformation.
    In this research elasto-plastic framework was chosen and challenges were detected through simulation of constitutive behavior of various cement based materials.
    In implementing plasticity models into finite element formulation, it is necessary to integrate a set of constitutive equations. A mathematical basis algorithm, Return mapping algorithm, will be adopted to update the stresses by implicitly integrating of the elasto-plastic constitutive equation.
    A yield criterion is also required to fulfill system of nonlinear equations. Various criteria are proposed to capture intrinsic characteristic of plain concrete. In the case of FRC, usually the criteria are devised by modified tensile meridian. Research will be followed by implementing various criteria and showing their potentialities into aforementioned materials.
    To produce hardening/softening regimes the yield criterion can be known as a function of the scalar valued hardening parameter. Dependent on the strain history the hardening parameter is integrated along the loading path. To produce multi-axial hardening/softening regimes implementation of two hardening parameters, one for tension and another for compression, can be adopted. Another alternative can be placed on implementation of damage models.

    Keywords: elasto-plastic, Constitutive equation, yield criterion, concrete, hardening-softening, return mapping algorithm

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    Amin Abrishambaf

    Aluno de Doutoramento

    Tese: An integral approach to simulate the creep behaviour of steel fibre reinforced self-compacting concrete (SFRSCC) laminar structures

    ABSTRACT
    Fibre reinforcement is only effective after concrete cracking initiation, so creep of cracked steel fibre reinforced self-compacting concrete (SFRSCC) can be a concern for accomplishing the requirements of long-term deformability imposed by serviceability limit state. Therefore, a formulation to predict the long-term deflection of cracked SFRSCC laminar structures will be developed. Using advanced image analysis techniques, the fibre effectiveness index (FEI) that represents the distribution and orientation of the fibres is determined. An innovative fibre pull-out creep test is executed to obtain the time-dependent force-slip relationship (F - s(t)), with fibres preliminary subjected to distinct slip levels in order to induce different bond damage conditions (i.e. distinct grades of fibre’s reinforcement mobilization). From the FEI and F - s(t), a stress-crack width relationship that integrates the creep effects is developed. Monotonic and cyclic four-point notched beam (4PNB) creep bending tests are also executed, as well as creep tests with prototypes of SFRSCC laminar structures.

    Keywords: Steel fibre reinforced self compacting concrete; creep test; fibre pull-out creep test; fibre orientation and dispersion; tensile behaviour.

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    Christoph Sousa

    Aluno de Doutoramento

    Tese: SHRINKAGE CRACKING OF RC STRUCURES CONTAINING FIBRE REINFORCED CONCRETE

    The work focuses on the synergetic effect of the use of steel fibre reinforcement and conventional reinforcement (rebars) in regard to shrinkage crack control, aiming the possibility of partial replacement of conventional rebars by discrete steel fibres. In the pursuit of such goal, one of the most important tools is the experimental study of cracking tendency of restrained concrete elements (with emphasis on the interaction between shrinkage and creep), through passive and active restraint testing, but also through the study of tension stiffening effects in reinforced concrete ties (containing both conventional reinforcement and fibres). Analytical and numerical studies are also envisaged, with specific regard to phenomena such as shrinkage, creep and cracking/bond.

    Keywords: steel fibre reinforced concrete; combined reinforcement (fibres + rebars); cracking; self-induced stress; restrained shrinkage; creep/shrinkage interaction

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    Cristina Frazão

    Investigadora

    Cristina Frazão is a researcher in Civil Engineering at ISISE - Institute for Sustainability and Innovation in Structural Engineering, Engineering School of University of Minho. She is also a MSc student at this University and her thesis title is "Durability of Steel Fiber Reinforced Self-Compacting Concrete".
    Her research interests include the study of the long-term behavior of steel fiber reinforced self-compacting concrete (SFRSCC) under the influence of aggressive agents, in particular the chlorides. The main objectives of this topic are to identify and characterize the parameters that control the initiation and propagation of steel fibers corrosion and to quantify the corrosion influence on the mechanical performance of cracked SFRSCC structures. For achieving these goals, a variety of experimental tests are going to be carried out, such as compressive, bending and durability tests to evaluate material properties of SFRSCC, electrochemical tests to evaluate the steel fiber corrosion process in corrosive environments and flexural pullout creep test in cracked SFRSCC specimens with distinct crack width and subjected to accelerated conditions of aggressive exposure. The results contribute to a better understanding of the mechanisms involved in SFRSCC durability. This information will be integrated into constitutive models for evaluation of long-term behavior of SFRSCC structures under specific aggressive environmental conditions. The purpose of this research is the contribution to the optimal performance of the sandwich panel made with SFRSCC, which is developed under the project entitled "LEGOUSE –Development of cost competitive pre-fabricated modular buildings".

    Keywords: SFRSCC, chlorides, steel fiber corrosion, durability, LEGOUSE

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    Esmaeel Esmaeeli

    Aluno de Doutoramento

    Tese: HYBRID COMPOSITE PANELS FOR STRENGHETENING AND INCREASING THE ENERGY DISSIPATION CAPACITY OF RC MEMBERS

    Summary
    The potential of a hybrid composite plate (HCP) for the strengthening of reinforced concrete (RC) members is evaluated. HCP is composed of a CFRP sheet that is glued to the external surface of a thin plate made of strain hardening cementitious composite (SHCC). These panels are attached to the faces of RC members. The main objective of covering the CFRP with the SHCC plate, in the durability perspective, is to provide a protective layer for the CFRP systems, adding an extra safety against the detrimental effects of vandalism, and cycles of relatively high humidity and temperature. In terms of mechanical behavior, the SHCC plate brings the potential of using the mechanical anchorages, which means higher inter-laminar shear stresses can be developed between the strengthening layer and the substrate. During this project, a self compacting SHCC is developed and its mechanical properties, mainly tensile behavior, are characterized. The bond-slip of the HCP is evaluated for the panel, which is attached to the substrate by means of using adhesive only or the combination of the adhesive and mechanical anchors. Afterward, the applications of the HCP as the strengthening system for determinate beams and indeterminate ones with the dominant failure in flexure or shear are experimentally studied. Also the capacity of the energy dissipation of this innovative strengthening scheme for the beam-column joints will be assessed. Eventually, having these experimental results, the numerical simulations using the finite element approach will be developed and according to the parametric studies the analytical formulations for the design purpose will be proposed.

    Keywords: strain hardening cementitious composite, RC Beam and Beam-column joint, FRP, strengthening

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    Fatemeh Soltanzadeh

    Aluna de Doutoramento

    Tese: HIGH PERFORMANCE FIBER REINFORCED CONCRETE FOR THE REPLACEMENT OF SHEAR STIRRUPS

    Projeto: DURCOST

    Orientador: Joaquim António Oliveira De Barros

    In order to increase both flexural and shear resistance property of pre-fabricated concrete beam, a High Performance Fiber Reinforced Concrete (HPFRC) will be developed. The stirrups which are the most susceptible elements to corrosion due to locating close to the surface of the beams will be replaced by steel fibers.
    The beams contain longitudinal reinforcement with a hybrid system composed of Fiber Reinforced Polymer (FRP) and steel bars with the certain level of prestressing. The combination of these two groups of bar helps to utilize the durable and sustainable Reinforced Concrete (RC) beam.


    The main objective of the present research program can be expressed as the development of a design guideline for shear strengthening of the present structural system. Thus, the research is included an experimental and numerical program. The experimental program is composed of the following sub-programs:

    1 – Development and characterization of the mechanical properties of the High Performance Fiber Reinforced Concrete (HPFRC),
    2 – Assessment of the effectiveness of using HPFRC to eliminate the stirrups in pre-fabricated and pre-stressed hybrid reinforced beams, and
    3- Assessment of mechanical characterization and the relative durability properties of pre-stressed HPFRC beam under monotonic and cyclic loads.

    Furthermore, the durability properties of the beams, the shrinkage behavior of HPFRC and its shear behavior under the thermal loads will be discussed. The size effects on the beams failing in shear will be taken into account. The applicability of available models to simulate the shrinkage and size effect will be analyzed. The monotonic and fatigue tests will be performed for HPFRC beams having a certain level of damage.
    A design guideline will be proposed and parametric studies will be carried out with a FEM-based computer program capable of simulating the relevant aspects of the nonlinear behavior of HPFRC, in order to calibrate the governing parameters of this design guideline. The predictive performance of this guideline will be assessed taking the experimental results for basis of comparison.

    Keywords: High Performance Fiber Reinforced Concrete (HPFRC); prestressed hybrid reinforced system; durable shear resistance beam; monotonic and fatigue loading.

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    Hadi Baghi

    Aluno de Doutoramento

    Tese: The effectiveness of SHCC-FRC panels for the shear resistance of RC beams

    Summary
    In the present research program, to increase the shear strength of RC beams a new technique based on the use of prefabricated thin plate of Strain Hardening Cement Composites (SHCC) with Fibre-reinforced polymer (FRP) sheet will be used. The SHCC with unique mechanical characteristics such as multiple micro cracks before localization, casting in a thin layer due to the self-levelling property, and high strain capacity could be one of the suggestions for producing the prefabricated plate. To produce the hybrid system, plate and FRP, several configurations are used. As an example the FRP could be glued in the inner surface of the prefabricated plate to form a hybrid system prior to installation on the structure to strengthen. As another alternative of hybrid plate is composed of SHCC reinforced with FRP grids that are placed inside the plate during the moulding like ordinary steel reinforcement. This technique is called textile reinforced composite (TRC). Using an adhesive and bolts (if necessary – optional) this plate is fixed to the structural element to strengthen. The SHCC provides extra fire protection to the structure, vandalism acts and can enhance the durability performance of the strengthened structure. The SHCC plate can also increase the shear and flexural stiffness of the structure to be strengthened. Due to the relatively high post-cracking tensile resistance of the SHCC, mechanical bolts can be used to apply the hybrid plate to the structure to strengthen, avoiding an eventual premature peeling failure of the plate that can occur.

    Keywords: strain hardening cementitious composite, RC Beam and, FRP, strengthening

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    Hadi Mazaheripour

    Aluno de Doutoramento

    Tese: Flexural behavior of hybrid GFRP and steel reinforced FRC prestressed beams

    Orientador: Joaquim António Oliveira de Barros
    Co-orientador: José Manuel Sena Cruz

    ABSTRACT
    The present work proposes a new reinforcing system that combines Glass Fiber Reinforced Polymer (GFRP) and steel bars for the development of durable and sustainable reinforced concrete (RC) structures; the GFRP bars due to their corrosion immunity and high tensile strength, and the steel bars derived from their high ductility. The GFRP bars are placed with the minimum concrete cover required by bond and steel stirrups will be replaced by discrete steel fibers, by the use of high ductile and high shear strength Fiber Reinforced Concrete (HPFRC). The steel reinforcement ratio is also designed in order to assure the safety of the structure in case of a fire occurrence and the consequent loss of GFRP reinforcing capacities. The GFRP and steel bars are applied with a certain pre-stress level for the optimization of their reinforcing capabilities and to overcome the lower elasticity modulus of GFRP bars. An extensive experimental program encompasses the pre-fabricated hybrid reinforced pre-stressed beams will be carried out, and analytical/numerical models will be developed for the establishment of a guideline for the design and construction of this type of structures. The constitutive models available in FEMIX, FEM-based computer program, will be used and calibrated to simulate the behavior of these elements from their very early age up to their working conditions.

    Keywords: GFRP bars, Pre-stressed beam, FRC, Flexural

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    Hamidreza Salehian

    Aluno de Doutoramento

    Tese: A novel inverse analysis approach to determine post-cracking response of FRC

    Orientador: Professor Barros

    Acquiring tensile characterization of FRC is the most important step for taking benefit
    of this material in structural application, in particular for the case distinct fibres are
    considered to be an exclusive reinforcement of the system, such as in FRC elevated slab
    systems, in which traditional steel reinforcements are removed.
    Despite the importance of tensile characteristics of FRC, a uniform and well accepted
    test instruction with enough integrity has not been represented so far. Tensile property
    of FRC can be obtained directly in uniaxial tensile test (UTT). However, due to inherent
    difficulties of UTT, some other alternatives, such as flexural tests, have proposed in
    literatures to extract indirectly tensile properties of FRC. In these indirect approaches a
    convertor should be developed, to extract the tensile behaviour of FRC from results of
    the alternative tests, in so-called inverse approach.
    In the actual study, a novel inverse approach is presented based on moment-rotation
    behaviour of FRC beam subjected to three point bending test (3PBT).

    Keyword: tensile behaviour, FRC, three point bending test, inverse analysis.

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    Hassan Abdolpour

    Aluno de Doutoramento

    Tese: Improving Performance of composite sandwich panels by using corrugated GFRP ribs and SHCC material

    The main aim of this research is to demonstrate the feasibility of employing light weight composite sandwich panels for the domestic area. For this goal different materials are going to be carried out by comprising glass fiber reinforcement polymer (GFRP) for the skins to carry out tensile stress and internal ribs inside the foam to increase the shear capacity of the core materials. In addition Strain Hardening Cementations base Composite material (SHCC) on the top skin of the composite specimens is utilized by the means of decreasing middle span deflection of the structure and increasing the flexural stiffness and loading capacity. Deferent sorts of filling materials such as Polyethylene, Polyurethane (PUR) will be used to increase stiffness and strength of the core. This research comprises experimental and analytical investigations.
    For the analytical assessment typical finite element methods are utilised to evaluate these structure behaviour. For this achievement finite element softwares such as FEMIX, ABAQUS, DOCROS, DEFDOCROS and SECTION are utilized. The purpose of this analysing is to evaluate the effective elastic modulus, shear modules, degree of composite interaction of the panels and thickness of the components to resist in one way bending behaviour. In addition in these analysing different failure modes such as skin wrinkling, core compression and shear failure will be investigated.
    The experimental stage is conducted in two phases to investigate the mechanical material properties and one-way bending test on full scale of sandwich panel slab. For the material testing, variety of tests such as tensile test on GFRP coupon; tensile and compressive test on SHCC material; compressive test, tensile and shear test on the foam are going to be carried out. Consequently for the full scale composite sandwich slab four point bending tests, cyclic tests will be done.

    Keywords: Sandwich structure, Foam, FEM-software, SHCC material, GFRP, four-point bending test

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    Inês Costa

    Aluna de Doutoramento

    Tese: Prestressed Carbon Fibre Laminates applied according to Near Surface Mounted technique to increase the flexural resistance of Reinforced Concrete beams

    Abstract
    This technique is expected to increase the flexural capacity of the beams to strengthen and to recover part of its existing deformation, reducing or even closing existing cracks, resulting in benefits in terms of structural durability and integrity. For the design of RC elements strengthened according to this technique, an analytical formulation will be developed, as well as a predictive methodology to estimate the associated prestress losses. The predictive performance of this formulation will be assessed from the experimental results obtained, simulating the behaviour of the experimental tests with reliable FEM-based models.

    Keywords: Prestressed CFRP, NSM, Analytical formulation, Presress losses.

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    Jacinto Silva

    Aluno de Doutoramento

    Tese: Continuous monitoring of deformability of stabilized soils based on modal identification.

    Abstract
    Quality control of stabilized soil layers is usually made by means of in-situ tests performed at reference ages (e.g.28 days), through the assessment of a performance criterion, such as stiffness. This means that a relatively large time lag exists between the actual compaction of the layer and the instant at which conformity is checked, with significant costs of reallocation of equipment/staff in case of rejection. For this reason, it is desirable for contractors to have information about rejection/acceptance within a short period after compaction. In view of this requirement, the aim of this PhD thesis is to devise a methodology that allows evaluation of the stiffness evolution of stabilized soils right since the instant of placement. For such purpose, the work will be based on adaptations and improvements of a methodology that has been recently developed for concrete and cement paste, which allows the continuous monitoring of stiffness since the fresh state of the cement-based material. The methodology is termed EMM-ARM (Elasticity Modulus Measurement through Ambient Response Method) and consists of placing the tested material inside an acrylic mould, which is in turn setup as a simply supported beam. By monitoring the accelerations of the composite beam at mid-span, it is possible to perform output-only modal identification, thus obtaining a continuous record of the first flexural resonant frequency of the beam. The corresponding E-modulus (E) of the studied material can be continuously and quantitatively assessed by applying the dynamic equation of motion. In order to adapt and improve the EMM-ARM methodology to the use with stabilized soils in the scope of this PhD work, the planned tasks include: application and comparison of methodologies to determine the stabilized soil stiffness; study and implementation of different modal analysis techniques on EMM-ARM methodology; development of in-situ sampling methodology to get undisturbed specimens for EMM-ARM purposes; stiffness prediction at reference ages (e.g. at 28 or 90 days) based on data collected with EMM-ARM at relatively early ages (e.g., 3 to 5 days).

    Key words: Soil, Stabilization, Cement, E-Modulus, Modal Identification

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    José Granja

    Aluno de Doutoramento

    Tese: CONTINUOUS CHARACTERIZATION OF STIFFNESS OF CEMENT‐BASED MATERIALS: EXPERIMENTAL ANALYSIS AND MICRO-MECHANICS MODELING

    This work focuses on the optimization of the methodology termed “Elasticity Modulus Monitoring through Ambient Response Method” (EMM-ARM), which has been recently devised by Prof. Miguel Azenha for continuous monitoring of the modulus of elasticity of cementitious materials. This technique is based on modal identification of a composite beam acrylic/concrete, since right after casting. The variation of the resonant frequency of the beam allows inferring the evolution of the elastic modulus.
    In this work we intend to make a comprehensive validation of the EMM-ARM as well as improvements for overcoming the current limitations and establish an integrated methodology for systematic application in laboratory and in-situ.
    The aim of this work is also to make a foray into the microstructural modeling of the stiffness evolution of cementitious materials by taking advantage of unprecedented quantitative experimental data that it will be possible to accumulate through the application of the EMM-ARM methodology.

    Keywords: Concrete E-Modulus; Non-Destructive Methods; EMM-ARM; Continuous Monitoring of Stiffness; Modal Analysis; Microstructural Modelling

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    Mahsa Taheri

    Aluna de Doutoramento

    Tese: Development of new closed form solution to determine load caring capacity of reinforced FRC beams

    Orientador: Professor Barros

    Abstract
    Taking benefit of moment-curvature approach to determine load caring capacity of RC beams is based on Bernoulli’s linear strain profiles. For the case of reinforced concrete members, linearity of strain profile necessitates considering an equal strain for both reinforcement and its surrounding concrete. This means to adopt the moment-curvature method for RC members, a full-interaction (perfect bond) between concrete and reinforcement should be assumed, which can be a too rudimental assumption, mainly if crack width, deflection and load carrying capacity for service limit states needs to be accurately predicted. The main aim of the study actually being finalized is development of a model to determine load-carrying capacity of FRC members based on moment-rotation approach, in which internal moment of the cracked section in each step of loading can be correlated to the rotation of section. This model is capable to simulate the partial bond between reinforcement and the surrounding concrete, the crack propagation (crack width and crack spacing) with a stress-crack width law.

    Keyword: moment rotation approach, partial bond, crack width, crack spacing, stress-crack width law.

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    Mário Coelho

    Aluno de Doutoramento

    Tese: Bond behavior of FRP systems inserted in the cover concrete

    Abstract
    The main objective of the research work foreseen for this thesis is to develop a design methodology of the bond of reinforced concrete structures strengthened with fiber reinforced polymers (FRP) systems inserted into the cover concrete. For that purpose, the bond between FRP and concrete will be studied in four complementary strands: bibliographic, analytic, experimental and numerical.
    A database compiling results of bond tests published in the field literature will be developed in order to ease the refinement of the existent bond laws. The results of the experimental campaign that will be done in this thesis will also be added to the database.
    The analysis of this database will constitute an important calibration tool, not only for the existent bond laws, but also for one bond law to be proposed. This will be proposed in accordance to the safety design philosophy of the Eurocode and will be dedicated to design. Thereby it will allow obtain design values of the bond strength using characteristic values of the mechanical properties of each involved material, as well as partial safety coefficients, calibrated using structural reliability analyses.
    This law will be twofold validated, through a complementary experimental program and through numerical simulation of the phenomenon using available finite elements software (®FEMIX). In this, a tridimensional constitutive law to simulate the existent interfaces will be implemented given that this is an eminently tridimensional problem. This law will be based on the theory of plasticity taking into account the interaction between the normal and shear stresses, as experimentally observed, through a proper selection of the yield surface, flow laws and the hardening/softening laws.

    Keywords
    FRP; NSM; Experimental; Analytical; Numerical; Design.

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    Matteo Breveglieri

    Aluno de Doutoramento

    Tese: Shear Strengthening of RC Elements with ETS Technique

    Abstract
    This experimental program deals with the shear strengthening of RC elements and is focused on the assessment of the influence of the percentage of existing steel stirrups on the performance of the ETS shear strengthening technique using conventional steel bars. According to this technique, holes are drilled through the beam section with a desired inclination, and bars of steel or composite material are introduced into these holes and bonded to the concrete with adhesive materials. As already demonstrated for the EBR and NSM techniques, the internal existing steel stirrups can significantly influence the effectiveness of the strengthening system. Reinforced concrete (RC) T-cross section beams are used in the test program. The test carried out is an asymmetric three-point bending test characterized by an a/d ratio of 2.5. The ETS bars are placed between the stirrups to increase the efficiency of the system. This experimental program is composed of a series of beams with varying percentages of existing steel stirrups strengthened with different percentages and inclinations (90° and 45°) of ETS steel bars. The main objective of these tests is to assess the efficiency of the ETS technique for shear strengthening of RC beams with different existing shear reinforcement, and evaluate the increase of strength with an analytical model.

    Keywords: Shear, ETS Technique, Strengthening

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    Mhoammadreza Hosseini

    Aluno de Doutoramento

    Tese: Behaviour of RC slabs flexurally strengthened with pre-stressed NSM CFRP laminates

    ABSTRACT
    The efficacy of the near surface mounted (NSM) strengthening technique with passive carbon fiber reinforced polymer (CFRP) laminates to increase the flexural resistance of reinforced concrete (RC) slabs was already well assessed. In fact, NSM CFRP laminates without any pre-stress level can increase significantly the ultimate load carrying capacity of RC slabs. However, for the deflection levels corresponding to the serviceability limit states this increase is of small relevance. To obtain a significant increment in terms of load carrying capacity for these deflection levels, pre-stressing the CFRP is a suitable solution. By pre-stressing the CFRP, a greater portion of material tensile capacity is used, which contributes to increase the load carrying capacity of the strengthened elements under both service and ultimate conditions. The pre-stress can also contribute to close eventual existing cracks and to increase the
    shear capacity of these elements.
    In order to investigate the effect of the pre-stressed NSM CFRP laminates on the behavior of RC slabs a research work is being done. This work is part of a research program under the general title of “PRELAMI - Performance of reinforced concrete structures strengthened in flexural with an innovative system using prestressed NSM CFRP laminates”.

    Keywords:CFRP laminates, Near surface mounted (NSM), Pre-stressed, Flexural strengthening, RC slabs

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    Mohammad Ali Rezazadeh

    Aluno de Doutoramento

    Tese: Pre-stress CFRP laminates applied according to the NMS technique for the flexural strengthening of RC beams

    Orientador: Prof. Joaquim António Oliveira de Barros

    Abstract
    In the present research project, the flexural performance of Reinforced Concrete (RC) beams strengthened with prestressed CFRP laminates by Near Surface Mounted (NSM) technique, based on the installation of CFRP laminates with a certain prestress level into thin slits opened on the concrete cover of the elements, is investigated both experimentally and analytically. The influence of different parameters on the strengthening effectiveness is assessed by experimental programs, such as: prestress level, percentage longitudinal steel reinforcement, performance under Serviceability Limit State (SLS), transfer length of prestress and bond between CFRP laminate and surrounding concrete. Proposing of the numerical model to simulate the experimental results such as: flexural behavior of the RC beams strengthened with Prestressed NSM CFRP laminates, transfer length, prestress losses, is also another part of the project.

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    Mohammad Mastali

    Aluno de Doutoramento

    Tese: Rehabilitation of Building Floors with Lightweight High Performance GFRP Sandwich Panels

    Abstract
    This study refers to generate a new generation of composite slab in rehabilitation of old buildings which categorized in the sandwich panel structures. In these new slabs, the DFRCC (Ductile Fiber Reinforced Cement based Composites) are used as the top layer. Using these materials leads to increase loading capacity and ductility of structure.
    The efficiency of proposed slabs will be investigated by performing various tests on the manufactured prototypes. By designing of slabs, reasonable values for thicknesses of structural components will be obtained. In this direction, parametric studies under linear and nonlinear behavior of structures are undertaken and some criteria in order to select the best solution will be used. By obtaining suitable thickness for each component the materials which are supposed to be used in the specimens, have to be tested in order to obtain their mechanical properties. Hence, by evaluating obtained data about the materials which are supposed to be used and getting satisfied results, specimens are authorizing to be manufactured.
    After preparing specimens, for assessing the proposed slabs some tests in small scale have been planned to be carried out on the prototypes which include shear, bending and localized loading. By analyzing slabs in small scale, weak points of proposed slab would be able to manifest and will be modified and compensated in the full scale specimens. The final destination is assessing proposed slab in full scale under uniform loading. Tested specimens will be simulated in the FEM software and its results will be calibrated with the experimental results. Consequently, some simplified formula and practical rules will be extracted for using these kinds of slabs in engineering society.

    Key word: GFRP sandwich panel, DFRCC material, Slab, Rehabilitation.

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    Patrícia Silva

    Aluna de Doutoramento

    Tese: Long-term behavior and durability of reinforced concrete slabs flexurally strengthened with NSM CFRP strips

    Abstract
    The main objective of present research project is to contribute to the knowledge on durability performance of the NSM technique with CFRP laminates under various specific application environments, load conditions and chemical degradation. In the context of the project, long term performance concept of member or structure strengthened using the NSM technique is defined as its ability to resist cracking, oxidation, chemical degradation, delamination, ageing, creep, fatigue and/or the effects of foreign object damage for a specified period of time, under the appropriate load condition, under specified environmental conditions.
    The specimens will be submitted a different effects like chlorides, pure water, freeze-thaw, wet/dry cycles, thermal cycles, fatigue and creep. The experimental program is supported by accelerated ageing tests using flexural tests with slabs of quasi-real scale. The test results obtained from the experimental programs will be used for predicting the service life of NSM technique supported in some numerical models. These numerical models will be implemented in the FEMIX program, which is a general purpose 2D and 3D models will be used in the simulation of the structural elements finite element software system.

    Keywords: durability; NSM; CFRP; creep; fatigue; FEMIX.

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    Pedro Fernandes

    Aluno de Doutoramento

    Tese: Long-term and durability performance of bond between concrete elements and CFRP laminates according to the NSM technique

    In the last years, the near-surface mounted (NSM) technique has been adopted to increase the load carrying capacity of concrete members. Up to now, research was mainly focused on the structural aspects of NSM strengthening of concrete structures. The present work has the main objective to contribute to the knowledge on durability performance of the NSM technique with CFRP laminates under various specific application environments, load conditions and chemical degradation. The work involves three components: an experimental program, a numerical simulation and design recommendations.
    The experimental program will be supported by accelerated ageing tests using bond tests specimens (mesoscale) to study the bond performance. The specimens will be submitted to different effects like chlorides, freeze-thaw, wet/dry cycles, thermal cycles, fatigue and creep.
    Digital image correlation method will be used, as a complementary tool for monitoring the NSM pullout tests. The test results obtained from the experimental programs will be used for predicting the service life of NSM technique supported in some numerical models. These numerical models will be implemented in the FEMIX program, which is a general purpose finite element software system.

    Keywords: CFRP laminates; NSM technique; Bond performance; durability; numerical models; design recommendations.

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    Pedro Mendes

    Investigador

    Msc Thesis: Design and analysis of a pedestrian bridge with GFRP profiles and SFRSCC deck

    In recent years, the pedestrian bridges built from composites materials have notably increased. This growth is due to the durability problems of traditional materials, as well as the need for fastest construction times. Thus, the use of fibre reinforced polymers (FRP) along with fibre reinforced concretes (FRC) begin to play a part more and more important in this type of structures, since the ductility, high post-cracking tensile strength, high compressive stiffness and strength of FRC can be combined with the benefits derived from the use of FRP profiles to obtain high performance structural systems.
    In this dissertation a 12 m length single span pedestrian bridge with two composite I-profiles was designed. It was evaluated the influence of the height and thickness of GFRP (Glass fibre reinforced polymer) profiles as well as the addition of a thin layer of carbon fibre prestressed sheet in the bottom flange of the GFRP profile. Using the finite element method, the structural behaviour of the developed structural systems was analysed. Furthermore, two prototypes of this structural system were built and monitored in order to assess their long-term deformational behaviour when subjected to a loading configuration correspondent to the load combination for the deflection serviceability limit stats. The main results are presented and discussed.

    Keywords: Pedestrian bridge; Composites; Pultruded profiles; Creep; Finite element method.

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    Rajendra Varma

    Aluno de Doutoramento

    Tese: Numerical models for the simulation of the cyclic behaviour of RC structures incorporating new advanced materials

    Abstract
    Various advanced materials have been developed with specific purposes, like fibre reinforced concrete (FRC) to improve the resistance to cracking and crack propagation, carbon fibre reinforced polymer (CFRP) for strengthening and retrofitting. The post cracking behaviour of FRC can range from strain-softening to strain-hardening. A parametric study was undertaken to study the effect of post-cracking behaviour of FRC sections, with the aim of proposing design methodology using DOCROS, software for design of cross-sections. In the ambit of parametric study, DOCROS and post-processing software to estimate force-deflection relationship of the beams failing in flexure were developed further. To improve the confinement of RC columns, embracing them with wet lay-up CFRP sheets is one of the modern and superior techniques. The analytical relationship was proposed for uniaxial constitutive model of CFRP confined concrete under monotonic and cyclic loading. For this analytical approach, an extensive database derived from experiments carried out by various researchers was used, and the proposed cyclic constitutive law was implemented in FEMIX and validated with experimental tests carried by independent research.
    The uniaxial constitutive laws of concrete, steel and CFRP confined concrete were implemented in FEMIX under fibre model, which is based on Timoshenko beam theory. The fibre model assumes that the cross-section can be divided into longitudinal fibres of steel, concrete, CFRP confined concrete etc, and perfect bind exist among fibres. However, perfect bond between concrete and steel cannot be guaranteed always, hence to idealize such material interface, bond-slip laws are developed. Special procedure is followed to simulate interface behaviour in combination with fibre approach, which is critical to simulate bar-slippage and pinching of columns. A biaxial concrete model under the framework of the fracture mechanics was developed, to simulate the RC elements under plane stress field. The concrete response is described by a nonlinear orthotropic model, whose axes of orthotropy are parallel to the principal strain directions. Equivalent uniaxial stress-strain relationships of the concrete are used in orthogonal direction in scope of rotating crack model. To supplement it, a smeared reinforcement model for steel bars is also developed, in context of plane stress elements/Mindlin shells. All the implemented models were validated with experimental results.

    Keywords: Rotating crack models, Fiber element models, Constitutive model

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    Rodrigo Lameiras

    Aluno de Doutoramento

    Tese: Sandwich structural panels comprising thin-walled Steel Fibre Reinforced Self-Compacting Concrete (SFRSCC) and Fibre Reinforced Polymer (FRP) connectors: from material features to structural behaviour.

    Abstract
    A durable, flexible, resistant and thermally efficient sandwich structural panel composed of two exterior SFRSCC thin layers and a lightweight thermal insulating core material will be developed for the walls of a pre-fabricated housing system. The stress transfer between the two SFRSCC layers will be assured by non-metallic connectors, in order to improve the thermal performance of wall panel system. Different arrangements of panels and production methods will be explored. The SFRSCC parameters related to stresses associated to environmental actions will be experimentally determined. The mechanical behaviour of thin-walled SFRSCC under compressive and tensile monotonic loading will be assessed through deformation-controlled uniaxial tests. Based on the results, constitutive laws will be proposed to characterize the SFRSCC mechanical behaviour. To explore the adoption of embedded and adhesively bonded FRP connectors, tests for determining the bond behaviour between SFRSCC and FRP connectors will be performed with the final aim of proposing bond-slip rational models for different types of connectors. The sandwich behaviour of elements composed by proposed connections and SFRSCC will be evaluated and compared. The actual mechanical behaviour of the proposed structural solutions will be investigated through an extensive experimental program with prototypes. Finally, a thermo-mechanical model will be implemented and used for the conduction of parametric studies of several panel solutions. As a final output, it is intended to issue guidelines for the design of this type of structure.

    Keywords:
    sandwich structural panels, Steel Fibre Reinforced Self-Compacting Concrete (SFRSCC), Fibre Reinforced Polymers (FRP) connectors, embedded connections, adhesively bonded connections.

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    Ziaaddin Zamanzadeh

    Aluno de Doutoramento

    Tese: Investigating the physical, chemical and mechanical performance of concretes made out of recycled components.

    This subject is of topical interest in the fields of both buildings technology and structural engineering.
    Although several researches have already done to enhance the knowledge of both environmental compatibility and sustainability of concrete production in building industry, further research is still needed for addressing various issues related to the compatibility of recycled materials with the traditional ones employed in the common concrete production. This research focuses on the three following objectives. Both experimental and theoretical activities are needed and actually planned for achieving the main goals undermentioned.
    Objective 1) Physical and mechanical behaviour of concrete with recycled aggregates including investigating the performance of concretes made out of RCA employed as fine to-coarse aggregate and assessing the feasibility and quantifying the relevant physical and mechanical properties of concretes with aggregates obtained by recycling demolition rubbles and comparing the above results with those corresponding to standard concretes and with the one obtained on concretes with recycled glass or bricks employed as aggregates.
    Objective 2) investigating the possible contribution of recycled fibers on concretes with recycled concrete aggregates. The main goal of the activities planned within the Objective 2 of the research is to investigate the behaviour of FRC with steel fibers obtained by recycling the reinforcement of rubber tyres and
    investigating the behaviour of concrete reinforced with fibers obtained by plastic wastes (i.e., PVC, PET, and so on so forth) and the possible effect of rubber particles as aggregates on the toughness of the above mentioned fiber-reinforced concretes.
    Objective 3) Feasibility and possible applications of concrete with natural fibers including investigating the production and quality control of the natural fibers for fiber reinforced concrete and the behaviour of FRC with natural fibers in the fresh state and hardened state.

    Keywords: Recycled Fiber, Recycled Aggregate, Reinforced Concrete

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