References of "Mihaylov, Boyan"
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See detailModelling the Effect of FRP Sheets on the Complete Behaviour of Shear-Critical Coupling Beams
Mihaylov, Boyan ULiege; Liu, Jian; Garcia, Claudia

in Concrete Structures for Resilient Society, Design and Structures (2020, December 23)

Detailed reference viewed: 37 (2 ULiège)
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See detailKinematics-Based Approach for Shear Strength of Prestressed Concrete Deep Beams
Mihaylov, Boyan ULiege; Liu, Jian; Ozkan, Muhammed

in Concrete Structures for Resilient Society, Design and Structures (2020, November 23)

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See detailModeling the Effect of FRP Sheets on the Behavior of Short Coupling Beams Exhibiting Diagonal Tension Failure
Mihaylov, Boyan ULiege; Liu, Jian; Carretero Garcia, Claudia

in Journal of Composites for Construction (2020), 24(5),

Reinforced concrete (RC) coupling beams in pre-1970s coupled wall structures often feature small amounts of stirrups, and thus are susceptible to shear failure along inclined cracks. In short beams with ... [more ▼]

Reinforced concrete (RC) coupling beams in pre-1970s coupled wall structures often feature small amounts of stirrups, and thus are susceptible to shear failure along inclined cracks. In short beams with span-to-depth ratio smaller than about 2.5, the failure occurs along diagonal cracks and can limit the ductility of the member, which in turn limits the seismic performance of the entire coupled wall system. To suppress diagonal tension failure, the coupling beams can be strengthened with externally-bonded fiber-reinforced polymer (FRP) sheets. However, as the FRP sheets exhibit debonding and rupture, their contribution to the shear resistance cannot be evaluated without an explicit consideration of the compatibility of deformations with the existing beam. Therefore, this paper proposes a mechanical model based on deformations which predicts the complete behavior of FRP-strengthened short coupling beams exhibiting diagonal tension failure, including the effects of debonding and rupture of the FRP. The model is an extension of a two-parameter kinematic theory (2PKT) for RC coupling beams and uses two degrees of freedom to evaluate the deformations of the beam. The extended 2PKT is validated with tests from the literature and is used to study the effect of FRP sheets. The model predicts the influence of existing diagonal cracks as well as the effect of the preparation of the beam edges prior to the application of the FRP sheets. According to the model, the effectiveness of FRP sheets to increase the shear resistance increases with the span-to-depth ratio of the beam. Furthermore, for the relatively very short beams studied in the paper, it is predicted that U-sheets and side sheets are nearly as effective as fully-wrapped FRP sheets. [less ▲]

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See detailModeling the Effect of Prestressing on the Ultimate Behavior of Deep-to-Slender Concrete Beams
Mihaylov, Boyan ULiege; Liu, Jian; Ozkan, Muhammed

in ACI Structural Journal (2020), accepted paper

Deep concrete beams with shear-span-to-depth ratios a/d≤2.5 are used to resist large shear forces due to their ability to develop arch action. In high-rise buildings, deep transfer girders are typically ... [more ▼]

Deep concrete beams with shear-span-to-depth ratios a/d≤2.5 are used to resist large shear forces due to their ability to develop arch action. In high-rise buildings, deep transfer girders are typically loaded by discontinuous columns from multiple floors, while in bridges deep pier caps support the girders of the superstructure. In these situations, prestressing is typically applied to limit the opening of cracks under service loads, but its favorable effect on the shear strength is either neglected or underestimated. This paper examines experimental evidence for the shear behavior of prestressed beams and proposes a kinematics-based model for predicting their strength and deformations at failure. It is shown that prestressing alters the crack patterns of concrete beams, and consequently results in the development of arch action in beams with shear-span-to-depth ratios reaching 6 or 7. Therefore the proposed model, which stems from a two-parameter kinematic theory for deep reinforced concrete beams, is extended and applied to prestressed test specimens with a/d varying from 0.55 to 6.73 producing adequate predictions of strength and deformations. [less ▲]

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See detailA simplified kinematic approach for the shear strength of fibre-reinforced concrete deep beams
Mihaylov, Boyan ULiege; Rajapakse Mudiyanselage, Chathura Madushanka ULiege

in Structural Concrete (2020), doi.org/10.1002/suco.201900461

Deep beams with shear span-to-depth ratios a/d ≤ 2.5 are used to resist large shear forces due to their ability to develop direct strut action. To further enhance the shear strength and crack control of ... [more ▼]

Deep beams with shear span-to-depth ratios a/d ≤ 2.5 are used to resist large shear forces due to their ability to develop direct strut action. To further enhance the shear strength and crack control of such members, researchers have studied the use of fibre-reinforced concrete (FRC). However, while this solution is promising, there is a need for rational mechanical models capable of predicting the shear strength of FRC deep beams in a sufficiently simple manner. This paper proposes such a mod-el based on first principles: kinematics, equilibrium and consti-tutive relationships. The proposed model simplifies an earlier two-parameter kinematic theory (2PKT) for the complete shear behavior of FRC deep beams, to predict the shear strength and components of shear resistance in a straightforward manner. The new simplified method (S2PKT) is validated by compar-ing the predicted results to 22 tests from the literature, as well as to FEM and 2PKT predictions. It is shown that the proposed simplified kinematic approach predicts well the shear strength with an average experimental-to-predicted shear strength ratio of 1.12 and a coefficient of variation of 12.9%. Furthermore, the model is used to discuss the effect of shear span-to-depth ratio and fibre volumetric ratio on the shear strength of FRC deep beams. [less ▲]

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See detailAssessment of Failure Along Re-Entrant Corner Cracks in Existing RC Dapped-End Connections
Rajapakse Mudiyanselage, Chathura Madushanka ULiege; Degée, Hervé; Mihaylov, Boyan ULiege

in Structural Engineering International (2020), in review

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See detailEvaluating the Shear Resistance of Deep Beams Loaded or Supported by Wide Elements
Proestos, Giorgio; Palipana, Dhanushka; Mihaylov, Boyan ULiege

in Engineering Structures (2020), doi.org/10.1016/j.engstruct.2020.111368

It is common in concrete structures to encounter deep beams that are loaded or supported by wide elements such as shear walls in buildings and large piers in bridges. This type of boundary condition ... [more ▼]

It is common in concrete structures to encounter deep beams that are loaded or supported by wide elements such as shear walls in buildings and large piers in bridges. This type of boundary condition results in stress concentrations at the edges of the loading/supporting elements, and this in turn results in steep diagonal cracks and concentrated diagonal struts. In this study the shear strength of deep beams affected by stress concentrations is studied in detail with two methods: a two-parameter kinematic theory (2PKT) and nonlinear finite element models (FEM). It is shown that, with appropriate simple modifications to account for the loading/support conditions and the dowel action of the longitudinal web reinforcement, the 2PKT captures well the shear strength of 10 tests specimens from the literature. In addition to similarly adequate shear strength predictions, the more complex FEM also captures the strain concentrations measured in the tests. It is recognized that FEM analyses and detailed experimental measurements need to be used to ultimately develop a rational approach for evaluating the stress concentrations for the needs of both kinematic and strut-and-tie modelling. [less ▲]

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See detailEffect of Axial Restraint and Loading History on the Behavior of Short RC Coupling Beams
Mihaylov, Boyan ULiege; Trandafir, Alexandru ULiege; Palios, Xenofontas et al

in ACI Structural Journal (2020), in review

Short reinforced concrete (RC) coupling beams are key for the adequate behavior of coupled-wall structures, while at the same time they are susceptible to brittle shear failures. Particularly vulnerable ... [more ▼]

Short reinforced concrete (RC) coupling beams are key for the adequate behavior of coupled-wall structures, while at the same time they are susceptible to brittle shear failures. Particularly vulnerable are existing pre-1970s coupling beams in seismic zones that feature orthogonal reinforcement with low amounts of stirrups. However, while the shear behavior of such members is influenced by the axial restraint provided by the stiff shear walls, lab tests have neglected this effect. In addition, lab tests typically feature a symmetrical cyclic loading history, while in reality large inelastic pulses in one direction may affect the behavior of the beam in the opposite loading direction. Therefore, this paper presents an experimental program consisting of four large-scale coupling beams with variable level of axial restraint and different types of loading. Load-displacement curves, crack diagrams, deformed shapes, steel strain measurements, photographs, and an advanced strut-and-tie model are used to establish a comprehensive picture of the behavior of the beams. It is shown that the axial restraint generates large compression in the beams and significantly alters their crack pattern and shear strength. Large inelastic pulses have a limited effect on the strength, but significantly influence the drift capacity of coupling beams. [less ▲]

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See detailNumerical Modelling Approach for UHPFRC Members Including Crack Spacing Formulations
Franssen, Renaud ULiege; Guner, Serhan ULiege; Courard, Luc ULiege et al

in Engineering Structures (2020), in review

Ultra-high performance fiber-reinforced concrete (UHPFRC) possesses excellent mechanical properties and durability. The steel fibers in the concrete result in significant post-cracking tensile resistance ... [more ▼]

Ultra-high performance fiber-reinforced concrete (UHPFRC) possesses excellent mechanical properties and durability. The steel fibers in the concrete result in significant post-cracking tensile resistance and enhanced crack control. However, while UHPFRC is a promising material for the construction of new (and repair of existing) infrastructure, its application is still limited—in part due to the lack of numerical models with the capacity to simulate its complex behavior. To help overcome this challenge, this study proposes a numerical material modeling approach for the nonlinear finite element analysis of UHPFRC. The approach aims to provide a general applicability to model both shear- and flexure-critical members made from strain-softening or -hardening UHPFRC, while still using simple equations. This objective can be achieved by establishing a comprehensive set of crack spacing formulations and modeling recommendations to capture the unique behavior of UHPFRC. The crack spacing estimates are used together with the Diverse Embedment Model for FRC, which is extended here for the modeling of UHPFRC. When applied to 29 flexure- and shear-critical specimens, the proposed modeling approach accurately simulates the experimental responses with an average of 1.04 and a coefficient of variation of 10.2% for the experimental-to-predicted strength ratios. [less ▲]

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See detailAnalysis of the Behaviour of Bridge Piers Retrofitted with UHPFRC Jackets
Franssen, Renaud ULiege; Langer, Mathias; Courard, Luc ULiege et al

in Middendorf, Bernhard; Fehling, Ekkehard; Wetzel, A (Eds.) Proceedings of HiPerMat 2020 5th International Symposium on Ultra-High Performance Concrete and High Performance Construction Materials (2020)

Detailed reference viewed: 35 (4 ULiège)
See detailModelling the Nonlinear Shear Behavior of Short FRC Coupling Beams
Mihaylov, Boyan ULiege

Conference (2019, December 13)

Detailed reference viewed: 27 (1 ULiège)
See detailMonitoring, Assessment and Retrofit of Concrete Structures Based on First Principles
Mihaylov, Boyan ULiege

Conference (2019, December 13)

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See detailRenforcement en cisaillement de piles de pont de type voile avec chemisage en BFUP
Franssen, Renaud ULiege; Courard, Luc ULiege; Mihaylov, Boyan ULiege

in Brühwiler, Eugen; Oesterlee, Cornelius; Redaelli, Dario (Eds.) 3ème Journée d'étude, 24 octobre 2019 BÉTON FIBRÉ ULTRA-PERFORMANT concevoir, dimensionner, construire (2019, October 24)

La maintenance des structures vieillissantes pose de sérieux défis partout dans le monde. Parmi les matériaux utilisés pour des méthodes de réhabilitation durables, les bétons fibrés ultra-performants ... [more ▼]

La maintenance des structures vieillissantes pose de sérieux défis partout dans le monde. Parmi les matériaux utilisés pour des méthodes de réhabilitation durables, les bétons fibrés ultra-performants (BFUP) présentent des propriétés mécaniques exceptionnelles ainsi qu’une très bonne durabilité. Ce projet s’intéresse à une méthode de réparation et de renforcement des piles de pont par chemisage en BFUP. Ces piles sont souvent soumises à des environnements agressifs et peuvent être sensibles, en cas de séisme, à des ruptures fragiles par cisaillement. Cet article présente les résultats d’une campagne de quatre essais à rupture réalisés sur des piles de pont à section rectangulaire de 1.50 x 0.23 m² et 2.3 m de hauteur. Le spécimen de référence présente un faible nombre d’étriers tandis que les trois autres piles, en addition aux étriers, ont subi une préparation de surface puis ont été renforcées avec un chemisage en BFUP dont l’épaisseur et la liaison avec le béton variaient d’une pile à l’autre. Les résultats montrent l’influence de la couche de BFUP et de la préparation de surface en termes de comportement global et de contrôle des fissures. [less ▲]

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See detailShear Strength of RC Deep Beams with Web Openings based on Two-Parameter Kinematic Theory
Liu, Jian ULiege; Mihaylov, Boyan ULiege

in Structural Concrete (2019)

Deep concrete beams often feature web openings that disrupt the flow of forces from the loads to the supports and reduce the shear strength of the member. While such openings can significantly impact the ... [more ▼]

Deep concrete beams often feature web openings that disrupt the flow of forces from the loads to the supports and reduce the shear strength of the member. While such openings can significantly impact the safety level of the structure, the research on deep beams has been focused mostly on the shear behaviour of solid members. To address this issue, this paper proposes a new model for deep beams with rectangular openings that stems from a two-parameter kinematic theory (2PKT) for solid beams. The model is established based on an analysis of the shear behaviour and failure modes of test speci-mens using nonlinear finite element and strut-and-tie models. In the new model, a deep shear span with an opening is repre-sented by two solid shear spans, one above and one below the opening. By linking the two sub-models, the proposed kinemat-ics-based approach describes the complete deformed shape of the shear span with four degrees of freedom (DOFs). These DOFs are predicted by combining the kinematic conditions with equilibrium conditions and constitutive relationships for the mechanisms of shear resistance across the critical shear cracks. The model is validated with 27 tests from the literature showing adequate shear strength predictions. [less ▲]

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See detailEffect of Member Size and Tendon Layout on the Shear Behavior of Post-Tensioned Beams
Mihaylov, Boyan ULiege; Liu, Jian ULiege; Simionopoulos, Konstantine et al

in ACI Structural Journal (2019), 116(4), 265-274

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See detailMixed-Type Modeling of Structures with Slender and Deep Beam Elements
Liu, Jian ULiege; Guner, Serhan; Mihaylov, Boyan ULiege

in ACI Structural Journal (2019), 116(4), 253-264

The nonlinear analysis of reinforced concrete frame structures with slender members can be performed accurately and efficiently with 1D elements based on the plane-sections-remain-plane hypothesis ... [more ▼]

The nonlinear analysis of reinforced concrete frame structures with slender members can be performed accurately and efficiently with 1D elements based on the plane-sections-remain-plane hypothesis. However, if the frame also includes deep beams which require 2D high-fidelity finite element procedures, the analysis of large structures can become very costly. To address this challenge, this paper proposes a mixed-type modeling framework which integrates 1D slender beam elements with a novel 1D macroelement for deep beams. The framework is implemented in an existing nonlinear analysis procedure and is used to model 18 deep beam tests and a 20-story frame. It is shown that the proposed framework provides similarly accurate predictions to the 2D high fidelity procedures but requires a fraction of the time for modeling and analysis. Furthermore, the macroelement improves the post-peak predictions, and therefore the framework is suitable for evaluating the resilience of structures under extreme loading. [less ▲]

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See detailKinematic-based Approach for Complete Shear Behaviour of Deep FRC Beams
Mihaylov, Boyan ULiege; Liu, Jian ULiege; Tvrznikova, Karolina

in Concrete – Innovations in Materials, Design and Structures (2019, May 27)

While tests of deep fibre-reinforced concrete (FRC) beams have shown that steel fibres enhance the crack control and shear strength, the modelling of these effects in a simple and rational manner remains ... [more ▼]

While tests of deep fibre-reinforced concrete (FRC) beams have shown that steel fibres enhance the crack control and shear strength, the modelling of these effects in a simple and rational manner remains a challenging problem. Because FRC features enhanced tension behaviour, it is not well suited for the traditional strut-and-tie approach which neglects the tension in the concrete. Therefore, this paper proposes an alternative approach which focuses on the displacements in the critical shear cracks. The displacements are described with a kinematic model with two degrees of freedom, and are used with appropriate constitutive relationships to estimate the shear contribution of the fibres. This kinematics-based approach is validated with experimental data, and it is shown to capture adequately the complete pre- and post-peak behaviour of deep FRC beams. [less ▲]

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See detailModelling the Ultimate Shear Behaviour of Deep Beams with Web Openings
Liu, Jian ULiege; Mihaylov, Boyan ULiege

in Concrete – Innovations in Materials, Design and Structures (2019, May 27)

Web openings are inevitably installed in deep beams in practice, while most of the research is focused on the shear behaviour of solid deep beams. The existence of web openings can reduce significantly ... [more ▼]

Web openings are inevitably installed in deep beams in practice, while most of the research is focused on the shear behaviour of solid deep beams. The existence of web openings can reduce significantly the shear capacity of deep beams and therefore cause safety problems. In this study, the typical shear failure modes and load transfer mechanisms of deep beams with web openings are firstly investigated, and based on the investigation a kinematic model is proposed for the shear capacity prediction. This kinematic model stems from the existing two parameter kinematic theory (2PKT), which was shown to provide satisfying predictions on shear capacity of solid deep beams. In the proposed model, one shear span is divided into two sub shear spans below and above the web opening, respectively. The steel layout at beam end beyond the web opening is crucial for resisting shear transferred above the web opening. Twenty seven deep beam specimens with web openings are used for the validation. The proposed kinematic model provides satisfying results, i.e. Vexp/Vpre: Avg=1.14 and COV=7.8%. [less ▲]

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See detailTwo-Parameter Kinematic Approach for complete Shear Behaviour of Deep FRC Beams
Mihaylov, Boyan ULiege; Liu, Jian ULiege; Tvrznikova, Karolina

in Structural Concrete (2019)

While tests of deep fiber-reinforced 1 concrete (FRC) beams have shown that steel fibers enhance the crack control and shear strength, the modeling of these effects in a simple and rational manner remains ... [more ▼]

While tests of deep fiber-reinforced 1 concrete (FRC) beams have shown that steel fibers enhance the crack control and shear strength, the modeling of these effects in a simple and rational manner remains a challenging problem. Because FRC features enhanced tension behavior, it is not well suited for the traditional strut-and-tie approach which neglects the tension in the concrete. Therefore, this paper proposes an alternative approach which focuses on the displacements in the critical shear cracks. The displacements are described with a kinematic model with two degrees of freedom, and are used with appropriate constitutive relationships to estimate the shear contribution of the fibers. This kinematics-based approach is validated with experimental data, and it is shown to capture adequately the complete pre- and post-peak behavior of deep FRC beams. It is also shown that the model predicts well the effect of beam aspect ratio, fiber volume ratio, longitudinal reinforcement ratio and concrete strength on the shear strength of deep FRC beams. [less ▲]

Detailed reference viewed: 111 (18 ULiège)
See detailMonitoring, Assessment and Retrofit of Concrete Structures based on First Principles
Mihaylov, Boyan ULiege

Scientific conference (2019, March 22)

Detailed reference viewed: 31 (1 ULiège)