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See detailKinematics-Based Modelling of Deep Transfer Girders in Reinforced Concrete Frame Structures
Liu, Jian ULiege

Doctoral thesis (2019)

Reinforced concrete deep beams often carry heavy loads as transfer girders in high-rise buildings, pile caps in bridges or other important structural members. Due to their small slenderness, they exhibit ... [more ▼]

Reinforced concrete deep beams often carry heavy loads as transfer girders in high-rise buildings, pile caps in bridges or other important structural members. Due to their small slenderness, they exhibit shear failure with disturbed deformation patterns differently from slender beams. Many experiments have revealed the complexity of the shear mechanisms of deep beams, and a number of formulations and models have been proposed attempting to explain their behaviour. However, up to the present, the accurate prediction of the shear response of deep beams remains a challenge. Considering the importance of such kind of structural element, this thesis is dedicated to make a further investigation on the shear mechanisms and provide a useful tool to predict the entire shear response of deep beams. More than seventy models for deep beams are firstly summarized and classified into different categories according to their main characteristics. Detailed evaluation is made on ten models among them, with the help of a database of 574 deep beam tests. It is found that a semi-empirical strut-and-tie model (STM) and a two-parameter kinematic theory (2PKT) for deep beams produce the least scattered predictions in terms of shear strength experimental-to-predicted ratio Vexp/Vpred. Further studies are conducted to explore the effect of various important parameters, e.g. shear-to-span-depth ratio (a/d), size effect, and other. While the 2PKT produces uniform Vexp/Vpred across the entire range of experimental data and captures well the effects of all studied parameters, the semi-empirical STM exhibits certain bias with respect to the beam slenderness and does not account for the important size effect in shear. In order to evaluate the serviceability, safety and resilience of deep beams, the thesis continues with the development of a 1D macroelement based on a three-parameter kinematic theory (3PKT) which is an extension of the 2PKT method to continuous deep beams. This macroelement aims at capturing the entire response of deep beams including both the pre- and post-peak regimes. One macroelement represents a deep shear span by using only two nodes with two degrees of freedom per node. Both simply-supported and continuous deep beams are modelled with the proposed 1D macroelement. It is shown that the macroelement captures well the force redistribution between shear spans in continuous members, and in this way predicts their enhanced ductility as compared to simply supported deep beams. It is also shown that the model captures the opening of the critical shear cracks under increased loading. The crack predictions can be compared with field measurements to accurately evaluate the safety of the structure, and in this way to avoid potential costly strengthening measures. As a result of the compatibility between the proposed 1D macroelement and classical 1D slender beam elements, a mixed-type modelling framework is proposed to overcome the high cost of analysis on large frame structures including deep transfer girders modelled with 2D high-fidelity finite element procedures. The framework is implemented in an existing nonlinear analysis procedure and is used to model eighteen deep beam tests and a twenty-story frame. It is shown that the proposed framework provides similarly accurate predictions to 2D high-fidelity procedures but requires a fraction of the time for modelling and analysis. Furthermore, the macroelement improves the post-peak predictions, and therefore the proposed framework is suitable for evaluating the resilience of structures under extreme loading. Although the full shear response of solid deep beams can be well captured with the proposed macroelements, it is still an open issue to understand the behaviour of deep beams with web openings. In practice, web openings are inevitably installed in deep transfer girders to allow for windows, doors and different conduits. They may disrupt the flow of forces from the loads to the supports and significantly reduce the shear strength of deep members. To address this issue, a new model for deep beams with rectangular openings is proposed based on the 2PKT method for solid beams. It is established based on an analysis of the shear behaviour and failure modes of test specimens using nonlinear finite element and strut-and-tie models. In the new model, two sub deep beams form above and below the web opening. Each sub shear span is modelled with two kinematic parameters as in solid shear spans, and the deformation pattern of the entire shear span can be described by these four degrees of freedoms (DOFs). The model is validated with 27 tests from the literature showing adequate shear strength predictions. It is shown that shear strength of deep beams with web openings is more affected by the depth of the opening than by its horizontal dimension. Also, the transition from deep to slender beam behaviour in members with openings occurs at smaller aspect ratios than in solid members. These experimental observations are well captured by the 2PKT approach. [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

Conference (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

Conference (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 ▲]

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

in ACI Structural Journal (2019)

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

in ACI Structural Journal (2019)

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 detailA Kinematic Approach for the Complete Shear Behavior of Short FRC Coupling Beams
Mihaylov, Boyan ULiege; Liu, Jian ULiege; Lobet, Rémy

in ACI Structural Journal (2018), 328

Short coupling beams are susceptible to brittle shear failures that need to be suppressed with dense transverse and diagonal reinforcement. To reduce the amount of shear reinforcement and improve the ... [more ▼]

Short coupling beams are susceptible to brittle shear failures that need to be suppressed with dense transverse and diagonal reinforcement. To reduce the amount of shear reinforcement and improve the service behavior, researchers have proposed a solution with steel fiber-reinforced concrete (FRC). However, while this solution is promising, there are no sufficiently simple mechanical models capable of describing the complete shear behavior of short FRC coupling beams. This paper proposes such a model based on first principles: kinematics, equilibrium, and constitutive relationships for the mechanism of shear resistance. The model is compared with tests from the literature and with a significantly more complex finite element model (FEM). It is shown that, while the proposed kinematic approach requires a straightforward input and negligible time for computations, it also provides a similar (or better) accuracy as the FEM with excellent shear strength predictions. [less ▲]

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See detailMacroelement for Complete Shear Behaviour of Continuous Deep Girders
Liu, Jian ULiege; Mihaylov, Boyan ULiege

in ACI Structural Journal (2018), 115(4), 1089-1100

The evaluation of the serviceability, safety, and resilience of deep girders in bridges and buildings requires accurate models for their pre- and post-peak shear behavior. This paper purposes such a model ... [more ▼]

The evaluation of the serviceability, safety, and resilience of deep girders in bridges and buildings requires accurate models for their pre- and post-peak shear behavior. This paper purposes such a model formulated as a macroelement for deep shear spans under single and double curvature. The element has two nodes with two degrees of freedom per node (translation and rotation). The paper discusses the formulation of the macroelement based on a threeparameter kinematic theory and provides comparisons with tests. It is shown that the macroelement captures the redistribution of forces in continuous members, and in this way predicts their enhanced ductility as compared to simply supported beams. It is also shown that the model captures the opening of the critical shear cracks under loading. The crack predictions can be compared with field measurements to accurately evaluate the safety of the structure, and in this way to avoid potential costly strengthening measures. [less ▲]

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See detailTowards Mixed-Type Modelling of Structures with Slender and Deep Beam Elements
Liu, Jian ULiege; Mihaylov, Boyan ULiege

Conference (2017, June 12)

Concrete frame structures often include both slender and deep beams. Deep beams possess a large shear capacity, and thus are typically used as transfer girders to carry heavy loads over large spans. The ... [more ▼]

Concrete frame structures often include both slender and deep beams. Deep beams possess a large shear capacity, and thus are typically used as transfer girders to carry heavy loads over large spans. The overloading of such members due to extreme events such as earthquakes may result in the collapse of the entire structure. To evaluate the resilience of large frame structures under extreme loading, it is necessary to model the interaction between the deep girders and the rest of the structure in an accurate and computationally effective manner. To address this issue, this paper proposes a mixed-type modelling framework by formulating an innovative 1D macro deep-beam element and coupling it with 1D slender elements. The new macro element aims to combine the accuracy of 2D micro finite elements with the simplicity of 1D macro elements. The paper summarizes the formulations of this element, based on the three-parameter kinematic theory, and integrates it into an existing global nonlinear analysis procedure to create a mixed-type modeling framework. The verification study, including a frame structure with a deep transfer girder, has shown that this approach captures the response of the frame with an accuracy similar to that of 2D micro finite elements, while requiring approx. 20% of the analysis time. [less ▲]

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See detailSplenic microRNA expression profiles and integration analyses involved in host responses to Salmonella enteritidis infection in chickens
Li, P.; Fan, W.; Li, Q. et al

in Frontiers in Cellular and Infection Microbiology (2017), 7(AUG),

To understand the role of miRNAs in regulating genes involved in the host response to Salmonella enteritidis (SE) infection, next generation sequencing was applied to explore the altered splenic ... [more ▼]

To understand the role of miRNAs in regulating genes involved in the host response to Salmonella enteritidis (SE) infection, next generation sequencing was applied to explore the altered splenic expression of microRNAs (miRNAs) and deregulated genes in specific-pathogen-free chickens. Birds were either infected or not (controls, C) and those challenged with SE were evaluated 24 h later and separated into two groups on the basis of the severity of clinical symptoms and blood load of SE: resistant (R, SE challenged-slight clinical symptoms and <10 5 cfu / 10 μL), and susceptible (S, SE challenged-severe clinical symptoms and >10 7 cfu/10 μL). Thirty-two differentially expressed (DE) miRNAs were identified in spleen, including 16 miRNAs between S and C, 13 between R and C, and 13 between S and R. Through integration analysis of DE miRNAs and mRNA, a total of 273 miRNA-target genes were identified. Functional annotation analysis showed that Apoptosis and NOD-like receptor signaling pathway and adaptive immune response were significantly enriched (P < 0.05). Interestingly, apoptosis pathway was significantly enriched in S vs. C, while NOD-like receptor pathway was enriched in R vs. C (P < 0.05). Two miRNAs, gga-miR-101-3p and gga-miR-155, in the hub positions of the miRNA-mRNA regulatory network, were identified as candidates potentially associated with SE infection. These 2 miRNAs directly repressed luciferase reporter gene activity via binding to 3'-untranslated regions of immune-related genes IRF4 and LRRC59; over-expressed gga-miR-155 and interference gga-miR-101-3p in chicken HD11 macrophage cells significantly altered expression of their target genes and decreased the production of pro-inflammatory cytokines. These findings facilitate better understanding of the mechanisms of host resistance and susceptibility to SE infection in chickens. © 2017 Li, Fan, Li, Wang, Liu, Everaert, Liu, Zhang, Zheng, Cui, Zhao and Wen. [less ▲]

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See detailA MACRO-ELEMENT FOR THE NONLINEAR ANALYSIS OF DEEP BEAMS BASED ON A THREE-PARAMETER KINEMATIC MODEL
Liu, Jian ULiege; Mihaylov, Boyan ULiege

Conference (2016, November 22)

This paper presents a computationally-effective macro element for predicting the complete shear response of RC deep beams. The element stems from a three-parameter kinematic theory (3PKT) for the shear ... [more ▼]

This paper presents a computationally-effective macro element for predicting the complete shear response of RC deep beams. The element stems from a three-parameter kinematic theory (3PKT) for the shear strength and deformation capacity of deep beams under double curvature. The macro element consists of two rotational springs and one transverse spring to simulate the nonlinear flexural and shear behaviour of deep shear spans. The element is applied to two deep beams tested to shear failure under three-point bending. The results are used to study the effect of unsymmetrical shear failures on the pre- and post-peak behaviour of nominally symmetrical members. It is found that the post-peak response is sensitive to the unloading path of the shear resisting mechanisms as well as to the global roughness of the critical diagonal cracks. Based on these analyses, modifications to the constitutive relationships of the shear mechanisms are proposed, and the macro element is applied to a continuous deep beam. It is shown that the model adequately captures the complete behaviour of the beam, including the redistribution of forces following the shear failure in the critical shear span. [less ▲]

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See detailA Macro-Element Formulation and Solution Procedure for Shear Analysis of RC Deep Beams
Liu, Jian ULiege; Mihaylov, Boyan ULiege

in the 11th fib International PhD Symposium in Civil Engineering (2016, August 30)

This paper presents a computationally-effective macro element capable of predicting the complete shear response of RC deep beams in analogy with beam elements for slender beams. The element stems from a ... [more ▼]

This paper presents a computationally-effective macro element capable of predicting the complete shear response of RC deep beams in analogy with beam elements for slender beams. The element stems from a three-parameter kinematic theory (3PKT) for the shear strength and deformation capacity of deep beams subjected to double curvature. The macro element is composed of two rotational springs and one transverse spring to simulate the nonlinear flexural and shear behaviour of the shear span. The element has two nodes (end sections) with two DOFs per node, which enables it to be easily connected to other elements of the same or different types to model structures with deep beams. The numerical implementation of the element is based on the secant stiffness approach which provides robust convergence properties. Validation studies are performed by using thirteen tests from the literature showing excellent results for the complete shear response. The obtained peak load experimental-to-predicted ratios have an average of 1.10 with a coefficient of variation of 14.2%, while these values for the mid-span deflection are 1.16 and 17.0%. [less ▲]

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See detailA comparative study of models for shear strength of reinforced concrete deep beams
Liu, Jian ULiege; Mihaylov, Boyan ULiege

in Engineering Structures (2016), 112(April), 81-89

Since the 1960s, researchers have proposed different empirical formulas and analytical models for the shear strength of deep reinforced concrete beams. Some of these approaches have shown adequate ... [more ▼]

Since the 1960s, researchers have proposed different empirical formulas and analytical models for the shear strength of deep reinforced concrete beams. Some of these approaches have shown adequate accuracy when applied to small sets of beam tests, while their ability to predict the effect of a large range of test variables remains unknown. This paper presents a summary of models for deep beams from 73 publications, and focuses on a detailed evaluation of ten more recent models by using a database of 574 deep beam tests. It is found that a semi-empirical strut-and-tie model (STM) and a two-parameter kinematic theory (2PKT) for deep beams produce the least scattered predictions. The former model produced an average shear strength experimental-to-predicted ratio Vexp/Vpred of 1.00 with a coefficient of variation (COV) of 19.8%, while the latter resulted in an average of 1.08 with a COV of 15.4%. The two models are also compared by plotting the Vexp/Vpred ratios against different tests variables, and by performing parametric studies with individual test series. It is shown that the semi-empirical STM exhibits certain bias with respect to the shear-span-to-depth ratio, while the 2PKT produces uniform results across the entire range of experimental data. It is also noted that the semi-empirical STM requires somewhat less computational effort than the 2PKT approach. [less ▲]

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See detailA Comparative Study of Models for Shear Strength of Reinforced Concrete Deep Beams
Liu, Jian ULiege; Mihaylov, Boyan ULiege

in Civil-Comp Proceedings (2015, September 03)

The shear behaviour of deep reinforced concrete beams has been a focus of experimental and analytical studies since the early 1950s, resulting in different approaches for predicting the shear strength of ... [more ▼]

The shear behaviour of deep reinforced concrete beams has been a focus of experimental and analytical studies since the early 1950s, resulting in different approaches for predicting the shear strength of deep beams. This paper compares the main modelling assumptions of these approaches and summarizes the results from validation studies available in the literature. Based on these comparisons, a two-parameter kinematic theory (2PKT) and a mechanical model by Zararis are selected for further evaluation with the help of test series with different experimental variables. It is shown that both approaches predict the trends in beam series with varying shear-span-to-depth ratios, even though the mechanical model overestimates the shear strength of beams without web reinforcement. It is also shown that the two models differ significantly in capturing the effect of transverse reinforcement and the size effect in shear. While the 2PKT accounts for sliding shear failures which limit the effectiveness of transverse reinforcement beyond a certain reinforcement ratio, the mechanical model predicts a monotonic increase of shear strength with the ratio. The 2PKT is also shown to capture the size effect in shear observed in two series of tests well, while the mechanical model neglects this effect. [less ▲]

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