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Experimental procedures used for the study of reinforcement to concrete bond have been hampered for a long time by inconsistencies and large differences in the obtained behavior, such as bond strength and mode of failure, depending on the specimen form and setup used in the test. Bond is controlled by the mechanics of the interface between reinforcement and concrete, and is sensitive to the influences of extraneous factors, several of which underlie, but are not accounted for, in conventional pullout test setups. To understand and illustrate the importance of specimen form and testing arrangement, a series of computational simulations are used in the present work on eight distinct variants of conventional bar pullout test setups that are used routinely in experimental literature for the characterization of bond-slip laws. The resulting bond strength increase generated by unaccounted confining stress fields that arise around the bar because of the boundary conditions of the test setup is used to classify the tests with respect to their relevance with the intended use of the results. Of the pullout setups examined, the direct tension pullout test produced the most conservative bond strength results, completely eliminating the contributions from eccentricity and passive confinement.

Understanding the bond behavior of steel rebar in concrete is important in order to determine the performance of a reinforced concrete structure. Although numerous studies have been carried out by many researchers to develop a robust model for numerical analysis, no consensus has been reached as the bond behavior depends on hysteresis. In this study, the bond behavior of a steel bar in concrete with pre-existing damage is investigated under low-level cyclic loading. Based on the experimental bond stress and slip curve, a numerical model for finite element analysis to simulate the effect of low-level cyclic loading is proposed. The results from the numerical analysis show good agreement with the experimental data, including accumulated damage on stiffness and strength throughout entire load cycles.

The existing non-ductile RC structures built prior to the 1960s–1970s were mainly conceived to carry only vertical loads. As a result, the columns of these structures demonstrate poor overall hysteresis behavior during strong earthquakes, dominated by brittle shear or/and premature excessive slipping of the inadequately lap-spliced reinforcement. In the present study, the effectiveness of two different strengthening systems (including either the wrapping of the columns by carbon-fiber-reinforced polymer textile or the use of thin high-strength reinforced concrete jackets), was experimentally and analytically investigated. The main variables examined were the strengthening material, the length of the lap splices and the amount of confinement provided by the jackets. Three cantilever column specimens were constructed without incorporating modern design code requirements for preserving seismic safety and structural integrity. Subsequently, the specimens were strengthened and subjected to earthquake-type loading. Their hysteresis performances were compared, while also evaluated with respect to the response of two similar original specimens and the behavior of a control one with continuous reinforcement, tested in a previous study. The predictions of the proposed analytical formulation for the hysteresis behavior of the strengthened specimens were satisfactorily verified by the experimental results.

UIDB/EMS/00667/2020 Nowadays, the use of the Digital Image Correlation (DIC) technique has spread and it is being used in several engineering areas to measure displacements. The available data obtained from the DIC measurement to evaluate the bond performance between a Carbon fibre Reinforced Polymer (CFRP) externally bonded to a timber substrate is scarce. From the existing data obtained with other materials, this contactless technique revealed to be quite useful but its accuracy with other well-established techniques, such as the use of electric strain gauges is not well understood yet. Therefore, the current work aims to study the accuracy of 2D DIC measurements with the measurements obtained from the use of strain gauges within a low-cost perspective. To that end, several CFRP-to-timber bonded joints were tested under the single-lap shear test and different bonding techniques were considered as well. Some flaws intrinsically derived from the DIC measurements that complicate the bond assessment, such as the fluctuations in the generated displacements field, are identified, and to bypass this problem a new methodology is proposed. This new methodology is based on two different closed-form solutions that, after defining the local and global bond behaviours of different CFRP-to-timber bonded joints, allowed to eliminate the fluctuations found from the DIC measurements, facilitating the estimation and the comprehension of the full debonding process of the CFRP-to-timber joints, which was achieved with a good proximity to the homologous debonding process derived from the strain gauge measurements. publishersversion published

As a composite material, the damping energy consumption mechanism of fiber reinforced polymer-confined reinforced concrete (FRP-C RC) structure is very complex. In previous dynamic calculation models, the bond-slip effect for steel bars was often ignored, which would lead to a considerable error in the response of the FRP-C RC structures. In this paper, a new numerical model of FRP-C RC columns considering the bond-slip for steel bars is established using a zero-length element and nonlinear beam-column elements in the OpenSees software, and the results of the model are verified by experimental results. Based on the complex damping theory, the loss factor expression and nonlinear damping model of FRP-C RC columns with the bond slip effect are proposed. Finally, the dynamic response of FRP-C RC columns with nonlinear damping under harmonic load is calculated and compared with the results available in literature. The results show that the proposed model considering steel bars’ bond-slip can provide better prediction for dynamic response of FRP-C RC columns and make the future seismic design of FRP-C RC columns safer.

This paper presents a detailed finite element modeling scheme to simulate the cyclic response of RC columns considering low-cycle fatigue and bond-slip of reinforcement. The modeling scheme includes a triaxial constitutive model recently proposed in the literature to simulate concrete failure under cyclic loading. For steel, a commonly used uniaxial model is enhanced to account for bar rupture using a new low-cycle fatigue criterion, which has been validated with data from fatigue tests on reinforcing bars. The bond-slip behavior of vertical reinforcing bars is modeled using a zero-thickness concrete-steel interface element. The interface element has a bond stress-slip constitutive law that predicts bond deterioration caused by generalized slip demands, tensile yielding of steel, and compression damage in concrete. The finite element models are validated with experimental data from cyclic tests on large-scale column and pile specimens which exhibited flexure-dominated responses. The models accurately simulate the lateral force–displacement response and failure of the specimens, and provide peak tensile strain demands along longitudinal bars which are similar to those measured experimentally. Sensitivity analyses are also conducted to study the effect of modeling assumptions related to low-cycle fatigue and bond-slip behavior.

Nonlinear finite element (FE) analysis of reinforced concrete (RC) structures is characterized by numerous modeling options and input parameters. To accurately model the nonlinear RC behavior involving concrete cracking in tension and crushing in compression, practitioners make different choices regarding the critical modeling issues, e.g., defining the concrete constitutive relations, assigning the bond between the concrete and the steel reinforcement, and solving problems related to convergence difficulties and mesh sensitivities. Thus, it is imperative to review the common modeling choices critically and develop a robust modeling strategy with consistency, reliability, and comparability. This paper proposes a modeling strategy and practical recommendations for the nonlinear FE analysis of RC structures based on parametric studies of critical modeling choices. The proposed modeling strategy aims at providing reliable predictions of flexural responses of RC members with a focus on concrete cracking behavior and crushing failure, which serve as the foundation for more complex modeling cases, e.g., RC beams bonded with fiber reinforced polymer (FRP) laminates. Additionally, herein, the implementation procedure for the proposed modeling strategy is comprehensively described with a focus on the critical modeling issues for RC structures. The proposed strategy is demonstrated through FE analyses of RC beams tested in four-point bending&mdash, one RC beam as reference and one beam externally bonded with a carbon-FRP (CFRP) laminate in its soffit. The simulated results agree well with experimental measurements regarding load-deformation relationship, cracking, flexural failure due to concrete crushing, and CFRP debonding initiated by intermediate cracks. The modeling strategy and recommendations presented herein are applicable to the nonlinear FE analysis of RC structures in general.

Recent earthquakes have shown that the seismic behavior of noncode‐conforming reinforced concrete buildings are in several cases strongly affected by the nonlinear response and possible failure of the beam‐column joints. Beam‐column joint inelasticity is typically due to either shear cracking and failure of the central concrete panel or bond‐slip of the longitudinal steel bars. This paper proposes a new Joint with Hinges macro‐element capable of simulating the most important sources of nonlinearities in the joints. It consists of a quadrilateral central panel whose rigid edges are connected to the beams’ and columns’ end nodes through nonlinear finite‐length interfaces that represent the plastic hinge zones. The central panel deforms in shear only. The joint macro‐element accounts for the nonlinear shear response of the central panel, for the bond‐slip of the longitudinal rebars crossing the joint and for the nonlinear shear and flexural behavior of the plastic hinge zones of the beams and columns connected to the joint. The resulting model of the reinforced concrete frame is the assembly of nonlinear Joint with Hinges macro‐elements connected by elastic frame elements. The proposed formulation is applied in this paper to plane frames. Validation studies with results from available experimental tests on beam‐column joint subassemblages show the proposed model capability to predict the hysteretic responses and the failure mechanisms of connections with unreinforced joints and different beam reinforcement ratios.

Historical masonry arch bridges are a fundamental part of the road and railway networks in Europe. Very often, due to factors such as lack of maintenance, increase of traffic loads, etc., these structures need interventions in order to guarantee their adequate structural performance. For this reason, an important research effort has been devoted in previous decades to study the behavior of masonry arches and to identify innovative techniques able to increase their ultimate capacity, such as fiber reinforced polymer (FRP) composites. In this paper, the results of an experimental campaign carried out on masonry arches strengthened with one FRP layer applied at the structure intrados are used to calibrate a numerical analysis model. Then, the model is used to predict the contribution that this type of strengthening would have had on the well-known Prestwood Bridge. The numerical results show that the hypothetical intervention of the Prestwood Bridge would imply an increase in the ultimate load of the structure, although it would be significantly lower than that usually obtained for the case of arches tested in laboratory.

Bond-slip is an important interaction between steel and concrete in reinforced concrete (RC) structures and other civil engineering constructions. It is essential to understand and to characterize, at local level, this stress transference mechanism. In particular its behavior for monotonic and cyclic demands, the parameters that influence this mechanism, and how it is affected by different deterioration factors. Therefore, characterizing and monitoring the bond-slip mechanism is essential for the safety assessment of RC structures, more specifically determining the reinforcing bars slippage inside the concrete, and therefore the stress and strain distribution in RC members. In this work, two optical fiber sensors are presented, based on silica and polymer fiber Bragg gratings (FBGs), which were implanted inside a concrete block specimen and subjected to a pull-out test. After 6 days of curing, the pull-out test was recorded and the displacement incurred during the test was also monitored with a traditional electric sensor; for comparison with the data acquired with the two optical sensors. The results obtained confirm the viability and advantages of the optical sensors, evidenced by their higher resolution and far lower dimensions (allowing them to be embedded into the concrete) when compared with their electronic counterparts. The straightforward implementation and use of the optical sensors show very promising results when used in civil engineering structures.

Made available in DSpace on 2018-12-11T16:54:14Z (GMT). No. of bitstreams: 0 Previous issue date: 2018-09-15 Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP) Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq) Australian Research Council University of Sydney This paper presents an alternative methodology to represent rebars and their bond-slip behavior against concrete based on coupling finite elements. Among the main features and advantages of the proposed technique are: (i) the coupling between the two independent meshes for concrete and reinforcement does not introduce any additional degree of freedom in the global problem; (ii) both rigid and non-rigid coupling can be used to represent the particular cases of perfect adherence and general bond-slip behavior, respectively; (iii) rebars of arbitrary geometry and orientation can be modeled; (iv) the methodology can be applied to 2D and 3D problems and (v) the formulation can be adapted to other type of finite elements and implemented easily in any existing FEM code. Constitutive models based on continuum damage mechanics are used to represent the concrete behavior and concrete-rebar interaction. A number of numerical analyses are performed and the results obtained show the versatility and accuracy of the proposed methodology. University of São Paulo, Av. Prof. Luciano Gualberto, Trav. 3 n. 380 - CEP São Paulo State University UNESP/Bauru, Av. Eng. Luiz Edmundo C, Coube 14-01 - CEP The University of Sydney School of Civil Engineering Faculty of Engineering & Information Technologies, J05 Civil Engineering Building São Paulo State University UNESP/Bauru, Av. Eng. Luiz Edmundo C, Coube 14-01 - CEP FAPESP: 2009/07451-2 FAPESP: 2012/05430-0 CNPq: 429552/2016-5 Australian Research Council: DE150101703

In order to improve the longitudinal shear resistance between foam concrete and C-Channels, an investigation is carried out on the shear connectors in foam concrete with cold-formed steel double C-Channels embedment. Twenty-four tests have been carried out in two groups. Two types of connectors: flange connectors and web connectors are installed using self-drilling screws for a rapid construction. The experimental results show that they can effectively improve the longitudinal shear-resist capacity of the concrete. After the experiment, the specimens are dismantled for an interior observation. Based on the observation, the form of damage, the failure mechanism was discovered, and the equation of longitudinal shear capacity was developed. It is concluded that the failure involves independent slippage between two C-Channels and the shear connection fractures. Since the composite structure requires sufficient slip between the two materials, these types of shear connectors will have good enhancement for this type of composite structures subjected to dynamic loads.

The work refers to the seismic behaviour of existing reinforced concrete (RC) frame buildings reinforced with plain rebar. A focus on the modelling of their flexural response is proposed, to explicitly consider the effect of smooth reinforcement slip on the structural performance. Analytical stress-slip relationships for different plain rebar anchorage shape are presented, their implementation in a structural model is then suggested. The element non-linear behaviour is lumped at the element end, based on its expected rocking-like behaviour; nevertheless, the model is able to account for the deformation contribution spread along the rebar embedded length, both in the element and in the joint or foundation side. The cyclic behaviour of an anchored plain rebar is also analytically treated; however, to facilitate the representation in a numerical environment, simplified rules are proposed to simulate the effects of reversal and repeated loading. The effectiveness of the model in predicting the response of such type of buildings is proved by simulating tests on columns, beam-column joints, and an entire frame, taken from literature. The structural elastic response is well captured, as well as the energy dissipation during cycling loading. The assessed secant stiffness at yielding is found to be significantly lower with respect to the prediction obtained without the consideration of smooth bar slip; in other words, with respect to the stiffness assessed for an element with deformed reinforcement. The results are particularly significant for range of drift demand within 1.50% and help a comprehensive design and assessment of seismic retrofit of existing buildings, since the modelling approach allow a reliable prediction of the triggering of brittle mechanisms.

This paper is concerned with examining the complete bond-slip behaviour between deformed reinforcement bars and concrete incorporating rubber particles from recycled tyres as a partial replacement for mineral aggregates. An experimental study consisting of fifty-four pull-out tests on cylindrical rubberised and normal concrete specimens, in conjunction with two reinforcement sizes with short embedment lengths, is described. In addition to a detailed assessment of the full bond-slip relationship, the test results offer a direct interpretation of bond behaviour under practical levels of confinement and its influence on the failure modes. Particular emphasis is given to the characteristic bond behaviour of rubberised concrete in terms of maximum bond strength and splitting strength as well bond stiffness and slip parameters. The detailed test measurements and observations provided in this study enable the definition of key bond parameters depicting the interfacial behaviour between rubberised concrete and deformed bars. The findings also permit the development of modified approaches for reliable representation of the failure modes and bond capacities for the concrete materials considered in this investigation.

This paper formulates an analytical calculation model for predicting the cracking behavior of reinforced concrete ties to provide more consistent crack width calculation methods for large-scale concrete structures in which large bar diameters and covers are used. The calculation model was derived based on the physical behavior of reinforced concrete ties reported from experiments and finite-element analyses in the literature. The derivations led to a second order differential equation for the slip that accounts for the three-dimensional effects of internal cracking by using a proper bond-slip law. The second order differential equation for the slip was solved completely analytically, resulting in a closed-form solution in the case of lightly loaded members and in a non-closed-form solution in the case of heavily loaded members. Finally, the paper provides a solution strategy to facilitate a practical and applicable method for predicting the complete cracking response. Comparison with experimental and finite-element results in the literature demonstrated the ability of the calculation model to predict crack widths and crack spacing consistently and on the conservative side regardless of the bar diameter and cover. © 2020. This is the authors' accepted and refereed manuscript to the article. The final authenticated version is available online at: http://dx.doi.org/10.1061/(ASCE)ST.1943-541X.0002510

In this study, based on the concrete damaged plasticity (CDP) model in the ABAQUS software, various plastic damage factor calculation methods were introduced to obtain CDP parameters suitable for reactive powder concrete (RPC) materials. Combined with the existing tests for the bending performance of steel-reinforced RPC beams, the CDP parameters of the RPC material were input into ABAQUS to establish a finite element model considering the bond and slip between the steel and RPC for numerical simulation. The load-deflection curve obtained by the simulation was compared with the measured curve in the experiment. The results indicated that on the basis of the experimentally measured RPC material eigenvalue parameters, combined with the appropriate RPC constitutive relationship and the calculation method of the plastic damage factor, the numerical simulation results considering the bond-slip were in good agreement with the experimental results with a deviation of less than 10%. Thus, it is recommended to select a gentle compressive stress-strain curve in the descending section, an approximate strengthening model of the tensile stress-strain curve, and to use the energy loss method and Sidoroff’s energy equivalence principle to calculate the RPC plastic damage parameters.

The cyclic performance of non-seismically designed reinforced concrete (RC) columns, strengthened with carbon fiber reinforced polymer (CFRP) jackets, was analytically and experimentally investigated herein. Three cantilever column specimens were constructed, incorporating design parameters of the period 1950s&ndash, 1970s, namely with concrete of a low compressive strength, plain steel bars, widely-spaced ties and inadequate lap splices of reinforcement. The specimens were strengthened using CFRP jackets and were subsequently subjected to cyclic inelastic lateral displacements. The main parameters examined were the length of the lap splices, the acceptable relative bar slipping value and the width of the jackets. The hysteresis behaviors of the enhanced columns were compared, while also being evaluated with respect to those of two original columns and to the seismic performance of a control specimen with continuous reinforcement, tested in a previous work. An analytical formulation was proposed for accurately predicting the seismic responses of the column specimens, comparing the actual shear stress value with the ultimate shear capacity of the concrete in the lap splice region. The test results verified the predictions of the analytical model, regarding the seismic performance of the strengthened columns. Moreover, the influences of the examined parameters in securing the ductile hysteresis performance were evaluated.

Here we present a multi-scale model to carry out the computation of brittle composite materials reinforced with fibers, and we show its application to standard reinforced concrete. The computation is carried out within an operator-split framework on the macro-scale, which allows for different failure mechanisms to develop in separate phases, as both the concrete and the bond-slip exhibit non-linear behavior. The computations on the micro-scale are performed for each constituent separately. The reinforcement is taken to be linear elastic, and the bond-slip is handled as a plastic deformation. The standard elastoplastic procedure is used to compute the bond stresses, combined with the X-FEM methodology to give the global representation of slip. The crack development in concrete, on the other hand, is described with a damage model with exponential softening, where ED-FEM is used to represent localized failure. A numerical example is shown to test the developed methodology.

An improved numerical model that can simulate the nonlinear behavior of reinforced concrete beams subjected to blast and impact loadings is introduced in this paper. The layered section approach is based in the formulation, and the dynamic material behaviors of concrete and steel are defined with the use of the dynamic increase factor. Unlike the classical layered section approach that usually gives conservative structural responses because of no consideration of the bond-slip effect, the introduced numerical model takes into account the bond-slip between reinforcing steel and surrounding concrete by changing the bending stiffness EI of elements placed within the plastic hinge length. Since the bond-slip developed after yielding of reinforcing steel is dominant and accompanies fixed-end rotation, the equivalent bending stiffness to be used in the critical region can be evaluated on the basis of the compatibility condition. In advance, the consideration of the unloading and reloading histories of reinforcing steel and concrete makes it possible to exactly trace the structural behavior even after reaching the maximum structural response. Finally, correlation studies between analytical results and experimental data are conducted to establish the validity of the introduced numerical model, and the obtained results show that it is important to consider the bond-slip effect and the loading history of constituent materials.

In this research, nonlinear dynamic analysis of concrete shear wall using a new nonlinear model based on damage mechanics approach and considering bond slip effects is presented. Nonlinear behavior of concrete is modeled by a rotational smeared crack model using damage mechanics approach. The proposed model considers major characteristics of the concrete subjected to two and three dimensional loading conditions. These characteristics are pre-softening behavior, softening initiation criteria and fracture energy conservation. The model was used in current research analysis after verification by some available numerical tests. Reinforcements are modeled by a bilinear relationship using two models: Discrete truss steel element and Smeared model. In Discrete model the effects of bond-slide between concrete and rebar is mentioned using the bond-link element model concept. Based on the presented algorithms and methodology, an FEM code is developed in FORTRAN. The validity of the proposed models and numerical algorithms has been checked using the available experimental results. Finally, numerical simulation of CAMUS I and CAMUS III reinforced concrete shear walls is carried out. Comparisons of deduced results confirm the validity of proposed models. The obtained results, both in the expected displacements and crack profiles for the walls, show a good accuracy with respect to the experimental results. Also, using discrete truss element model with respect to the smeared steel model leads to increasing the accuracy of maximum displacement response to 7% in analysis.

[EN] Forty-eight tests have been carried out to find of the failure mode of a new type of the foam concrete using C-Channels as embedements. Four groups of foam concrete specimens with various embedment depths of the steel in the concrete. The modes of failure of this new type of structure are summarized, which include the independent failure of the C-Channels with and without a concrete block inside the channel as well as the combined failure of the two channels, and the failure of the extrusion block. It is concluded that the failure involves independent slippage between two C-Channels, and the steel and the foam concrete blocks inside the C-Channels., The authors gratefully acknowledge funding from the National Natural Science Foundation of China. Project name: Failure mechanism research for lightweight steel and foam concrete composite structure Approval number: 51378238.

The seismic response of older R/C frames can be particularly sensitive to interaction with masonry infills, poor section detailing and smooth reinforcing bars. These aspects are quite often neglected in design and assessment both with linear and nonlinear models due to the modelling complexity and inherent increase in computational effort. This work presents a review of practical nonlinear models available in literature and quantifies, at the system performance level, the influence of bond-slip in critical plastic hinge locations and interaction effects with infill panels and shear deficient columns. Bond-slip effects are directly incorporated into the nonlinear fiber section models through a simplified approach and nonlinear shear behavior of columns is aggregated at the element level in conjunction to the common diagonal infill strut scheme. Three different infilled frame configurations are analyzed: a) bare frame, b) partially infilled frame (pilotis frame) and c) uniformly infilled frame. Static pushover analyses and Incremental Dynamic Nonlinear Response History Analyses (IDA) are performed spanning a wide range of hazard levels. Comparative analysis with concurrent incorporation of infill-induced shear damage and bond-slip quantify the loss of strength for the uniformly infilled configuration and the increased deformations for the bare frame and partially infilled configurations in terms of seismic performance parameters.

The effect of bond-slip in the assessment of reinforced concrete structures under static or dynamic cyclic loads with numerical models may be significant. Its relevance is discussed in this paper, by analysis of the correlation of experimental and analytical results. The latter were obtained with a perfect bond-based model and with a fiber-section beam-column model which makes it possible to consider the effect of bond-slip in the vicinity of exterior as well of interior joints of reinforced concrete frame structures. The experimental results consist of a shaking table test of a reinforced concrete frame, with predominant flexural condition, in agreement with the premisses of this research. The model with bond-slip was capable of predicting the structural behaviour in a very satisfactory manner. Furthermore, the results of the assessment including bond-slip are significantly more accurate than those assuming perfect bond.

Textile Reinforced Concrete (TRC) has emerged as a promising novel alternative offering corrosion resistance and both thinner and light-weight structures. Although TRC has been extensively researched, the formalization of experimental methods and design standards is still in progress. The aim of this work was to extract local-bond behaviour from pull-out tests of basalt and carbon TRC and utilize these in both simple (1D) and advanced models (3D) to yield the global structural behaviour. The simulation results from the 1D and 3D models are able to simulate the complex behaviour of TRC with a reasonable level of correlation. (C) 2014 Elsevier Ltd. All rights reserved.

Grouted dowel connections are used extensively in precast load bearing walls owing to their simple construction and forgiving tolerances. Current design guidelines do not adequately consider the composite nature of such connections. Moreover, robust numerical models for these connections are yet to be developed. Therefore, a finite element model of grouted dowel connections was developed in this paper. The model adopts a phenomenological bond&ndash, slip constitutive law to predict the load versus slip response of grouted bars and considers tensile yielding of the reinforcement. The local bond&ndash, slip law used was generated from carefully designed experiments to eliminate spurious effects associated with bond testing. The model was validated using experimental results on grouted connections, as well as data retrieved from the open literature. Excellent agreement between experimental and numerical results was observed, highlighting the accuracy of the model in depicting interfacial stresses of the assembly. The model requires simple calibration, is computationally efficient, and can accurately simulate the failure behavior of bars embedded in grouted connections.

The behavior of reinforced concrete elements is complex due to the nature of the concrete that is weak in tension. Among these complex issues are the initial cracking and crack propagation of concrete, and the bond-slip phenomenon between the concrete and reinforcing steel. Laboratory tested specimens are not only costly, but are limited in number. Therefore a finite element analysis is favored in combination to experimental data. The finite element technique involving the cracks inserting is one of the approaches to study the behavior of reinforced concrete structures through numerical simulation. In finite element modeling, the cracks can be represented by either smeared or discrete crack. The discrete crack method has its potential to include strain discontinuity within the structure. A finite element model (FEM) including the concrete cracking and the bond-slip was developed to simulate the nonlinear response of reinforced concrete structures.

Existing reinforced concrete (RC) structures often need to be repaired, strengthened and upgraded to satisfy current code requirements. In recent years many interventions have been done bonding composite materials to the surface of existing RC elements. The structural effectiveness of these interventions strongly depends on the bond between the strengthening material and the concrete and on the mechanical properties of the concrete cover. In this paper the bond between fiber reinforced cementitious matrix (FRCM) materials made out of a poliparafenilenbenzobisoxazole (PBO) net embedded in a cement based matrix and the concrete is analytically analyzed with reference to the approach generally adopted for the fiber reinforced polymers (FRP) materials, which is based on the local bond-slip relation between the strengthening fibers and the supporting concrete. A local bond-slip relation is calibrated on the base of the results of an experimental investigation previously performed by the authors. The bond-slip relation is essential in the modeling of the structural behavior of RC elements strengthened with PBO-FRCM, in that it allows to calculate the force that can be transferred to the concrete, the effective anchorage length, the concrete cracks distance and opening.

This is the post-print version of the final paper published in Engineering Structures. The published article is available from the link below. Changes resulting from the publishing process, such as peer review, editing, corrections, structural formatting, and other quality control mechanisms may not be reflected in this document. Changes may have been made to this work since it was submitted for publication. Copyright @ 2010 Elsevier B.V. This paper is concerned with the ultimate behaviour of lightly reinforced concrete members under extreme loading conditions. Although the consideration given to the assessment of ductility is of general relevance to various applications, it is of particular importance to conditions resembling those occurring during severe building fires. The main purpose of the investigation is to examine the failure of idealised members representing isolated strips within composite floor slabs which become lightly reinforced in a simulated fire situation due to the early loss of the steel deck. An experimental study, focusing on the failure state associated with rupture of the reinforcement in idealised concrete members, is presented. The tests enable direct assessment of the influence of a number of important parameters such as the reinforcement type, properties and ratio on the ultimate response. The results of several tests also facilitate a detailed examination of the distribution of bond stresses along the length. After describing the experimental arrangements and discussing the main test results, the paper introduces a simplified analytical model that can be used to represent the member response up to failure. The model is validated and calibrated through comparisons against the test results as well as more detailed nonlinear finite element simulations. The results and observations from this investigation offer an insight into the key factors that govern the ultimate behaviour. More importantly, the analytical model permits the development of simple expressions which capture the influence of salient parameters such as bond characteristics and reinforcement properties, for predicting the ductility of this type of member. With due consideration of the findings from other complementary experimental and analytical studies on full slab elements under ambient and elevated temperatures, this work represents a proposed basis for developing quantified failure criteria. Engineering and Physical Sciences Research Council (EPSRC)

Made available in DSpace on 2021-07-14T10:35:12Z (GMT). No. of bitstreams: 0 Previous issue date: 2015. Added 1 bitstream(s) on 2021-07-14T11:33:38Z : No. of bitstreams: 1 S1983-41952015000600787.pdf: 2779795 bytes, checksum: 79a8fb4ee721769cf8d8707eb3dc85f8 (MD5) Fundação de Amparo à Pesquisa de Minas Gerais Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP) Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq) A modelagem de estruturas de concreto armado tem tido um crescente progresso na Mecânica Computacional, de modo que os fenômenos complexos, tais como fissuração e esmagamento, fluência, escoamento da armadura, perda da aderência aço-concreto, podem ser modelados de forma razoavelmente realista, usando um conjunto apropriado de recursos numéricos e computacionais. Entre as diversas opções, os baseados no Método dos Elementos Finitos (MEF) permitem simulações complexas de análises de estruturas de concreto armado, incluindo a interação de diferentes efeitos não lineares. Este artigo lida com a análise não linear em elementos finitos, da perda de aderência entre a armadura de aço e o concreto, levando em consideração um estudo experimental anteriormente realizado. A análise via MEF apresentada usa uma combinação de recursos onde o comportamento do concreto é descrito pelo Modelo Constitutivo de Microplanos, e um Modelo de Armadura Embutida é usado para representar o aço inserido no concreto e levar em conta o efeito da perda de aderência. Os modelos do MEF foram criados usando o sistema computacional INSANE (Interactive Structural Analysis Environment), software de código aberto que possui um conjunto de ferramentas para análise não linear de estruturas em concreto armado. As correlações entre os resultados numérico-experimentais e os vários parâmetros validam a combinação de recursos proposta e identificam o significado de vários efeitos sobre a resposta. The modeling of reinforced concrete structures has taken advantage of the increasing progress on Computational Mechanics, in such way that complex phenomena, such as cracking and crushing, creep, reinforcement yielding, steel-concrete bond loss, can be modeled in a reasonable realistic way, using the proper set of numerical and computational resources. Among several options, the ones based on the Finite Element Method (FEM) allow complex analysis simulations of reinforced concrete structures, including the interaction of different nonlinear effects. This paper deals with the nonlinear finite element analysis of the bond-slip between reinforcing steel and concrete, taking into account an experimental study previously performed. The FEM analysis presented uses a combination of resources where the material behavior of concrete is described by the Microplane Constitutive Model, and an embedded reinforcement model is used to represent steel inside the concrete and take into account the effect of bond-slip. The FEM models were created using the INSANE (INteractive Structural ANalysis Environment) computational system, open source software that has a set of FEM tools for nonlinear analysis of reinforced concrete structures. The correlations between numerical-experimentals results and several parameters validate the proposed combination of resources and identifies the significance of various effects on the response. Universidade Federal de Minas Gerais Universidade do Extremo Sul Catarinense, Departamento de Engenharia Civil Univesidade Estadual Paulista, Departamento de Engenharia Civil Fundação de Amparo à Pesquisa de Minas Gerais: PPM-00310-13; 08/57743-7; 308785/2014-2 FAPESP: PPM-00310-13; 08/57743-7; 308785/2014-2 CNPq: PPM-00310-13; 08/57743-7; 308785/2014-2

Refined non-linear static or dynamic analyses of reinforced concrete structures require the knowledge of the actual force-displacement or bending moment-rotation curves of each structural member, which depend on the crack widths and on the crack pattern, and after all on the slip between concrete and reinforcing steel. For this reason the definition of improved local models taking into account all these local aspects is a fundamental prerequisite for advanced assessment of r.c. structures. A numerical procedure which allows to predict the relative displacement between steel reinforcement and the surrounding concrete in a reinforced concrete element, once assigned the stress in the naked steel bar and the bond-slip law is discussed. The method provides as final outcomes the sequence of crack openings and the individual crack widths, regardless of the particular bond-slip correlation adopted. The proposed procedure is implemented referring to two relevant experimental case studies, demonstrating that it is able to predict satisfactorily actual strain fields and slips along the investigated reinforced concrete elements.