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Estimating the stress of reinforcing bars and its variations in service conditions can be useful to determine the reserve capacity of structures or to assess the risk of fatigue in the reinforcement. This paper investigates the use crack width measurements to estimate the stress in the bars. In existing structures, crack width formulations can be used to estimate the stress in the reinforcement from crack width measurements, profiting from additional information that can be measured in‐situ, such as the crack spacing. Recent experimental results show that the values of the mean bond stress typically considered in code formulations overestimate the actual bond stresses activated in cracked concrete specimens. This paper presents the results of an experimental program consisting of reinforced concrete ties and beams instrumented with Digital Image Correlation and fiber optical measurements. The results confirm the differences with typically assumed bond stresses. A formulation to estimate the bond stresses in service conditions is derived from the results of the numerical integration of a previously developed local bond–slip relationship. Their pertinence for the estimation of the stress in the reinforcement from the measured crack width is evaluated with satisfactory results for monotonic loading and for the maximum force in cyclic tests. [ABSTRACT FROM AUTHOR]

Bond–slip is an important characteristic that determines the stiffness, displacement, and load-bearing capacity of a reinforced concrete (RC) beam. It is essential for performing a precise numerical analysis of the beam. In most cases, bond–slip models can define the bond–slip curve only when there are experimental data. However, many bond test data have been obtained from pull-out tests, and the dominant view is that the bond–slip behavior observed in the pull-out test is quite different from that in an actual RC beam. Therefore, a mapping function that makes it possible to estimate the bond–slip behaviors of beam specimens using those of pull-out specimens was developed in this study. A total of 255 pull-out specimen data and 75 beam specimen data were collected from previous studies, and the importance and influence of each feature of the two groups were analyzed using random forest and K-means clustering. The mapping function was derived using genetic programming, and its accuracy was verified through a comparison with existing models. The proposed model exhibits a high degree of accuracy in estimating bond–slip and bond strength in beam specimens and can provide useful information for understanding the difference in bond–slip behaviors between the two groups. [ABSTRACT FROM AUTHOR]

In this paper, 3D finite element simulations were conducted for lap-spliced ultra-high-performance concrete (UHPC) beams using ABAQUS software. Based on the concrete damaged plasticity (CDP) model, the plastic damage factor was introduced to simulate the material properties of UHPC. The nonlinear characteristics of the steel bar and UHPC were considered, and the bond–slip constitutive relationship was selected to evaluate the bond–slip between the lap-spliced steel bar and UHPC. The simulated load–deflection curve, peak load, bond strength, and failure mode were in good agreement with the experimental results. The verified finite element model was used to analyze the parameters of the lap-spliced UHPC beam. The effects of lap-spliced steel bar diameter, stirrup spacing of non-lap segment, and shear span ratio on the mechanical properties and bond properties of the lap-spliced UHPC beam were studied. This study can provide a reference for the future simulation and design of lap-spliced UHPC beams. [ABSTRACT FROM AUTHOR]

This paper presents a comprehensive investigation of the bond characteristics of steel bar reinforced geopolymer concrete (GPC). The ASTM A944 beam end tests were conducted on GPC beams reinforced with plain or ribbed bars. The bond–slip curves and the bond strength of GPC beams were obtained. The relationship between the bond stress and relative slip in plain and ribbed bar reinforced GPC has been represented by empirical formulae. The bond testing results were compared with those of corresponding ordinary Portland cement concrete (OPC) using statistical hypothesis tests. The results of hypothesis testing showed that GPC was significantly superior to OPC in terms of bond capability with plain bars and bond stiffness with ribbed bars. The statistical analysis indicated that the bond–slip relations derived for OPC are inapplicable to GPC; thus, new bond–slip relations are suggested to estimate the development of bond stress and relative slip between GPC and steel bars. [ABSTRACT FROM AUTHOR]

A hybrid strengthening system, comprising a carbon fiber reinforced polymer (CFRP) sheet combined with fiber reinforced concrete (FRC) layer is proposed in this study as a mitigatory solution to brittle debonding problems. Five reinforced concrete (RC) beams, comprising both control cases and those strengthened with the hybrid CFRP-FRC system at various FRP reinforcement ratios, were fabricated and tested to assess the system's effectiveness. A comprehensive finite element (FE) model was also developed to complement the experimental campaign and extend it into a parametric investigation on the effects of FRP reinforcement ratio (ρ f), fiber percentage in FRC (v f), and FRC layer thickness (t FRC). Compared with beams strengthened with FRP alone, using the FRC layer increased the ultimate load (P ult.) of FRP-strengthened beams by 29–59%, depending on ρ f and v f. The ductility of the hybrid FRP-FRC strengthened beams also increased by more than twice compared to the beams strengthened with only FRP. For the FRP reinforcement ratio (ρ f) of 0.18%, use of an FRC layer with v f = 2% yields the highest increase in P ult. and ductility for the hybrid system. Ultimately, the brittle FRP debonding failure was successfully eliminated using the FRC layer, leading to desirable FRP rupture. Built with capabilities to capture material nonlinearity, contact, and debonding phenomena, the FE model predictions excellently matched those of the test results in terms of the beam's capacity, failure modes as well as load-deflection and load-strain responses. • A hybrid strengthening using CFRP sheets combined with FRC layer is proposed. • Performance was evaluated using tests on RC beams at various FRP reinforcement ratios. • A comprehensive finite element model was developed to complement the experiment. • FRC layer serves as a mitigatory solution to brittle FRP debonding and leads to desirable FRP rupture. • Compared with FRP only strengthening, FRC layer increased the capacity by 29–59% along with up to twice the ductility realized by using FRP alone. [ABSTRACT FROM AUTHOR]

Externally bonded carbon fiber-reinforced polymer (CFRP) composites are an effective method for flexural and shear strengthening and repair of reinforced concrete (RC) beams. In externally bonded CFRP strengthening, epoxy-based CFRP wet layup systems are predominately used. CFRP composites pre-impregnated with polyurethane (PU) resin and PU primers were demonstrated as an effective alternative in previous studies yet have seen limited applications. Due to the broad range of PU primer and laminate properties, bond between PU-CFRP system and concrete substrate can be potentially promoted. This paper experimentally characterizes the performance of six different PU-CFRP systems for external flexural strengthening of RC beams and investigates the relationship between bond-slip properties and the target flexural responses. Twenty-one lap shear specimens, 30 concrete flexural beams, and seven RC flexural girders were tested and compared with a conventional epoxy-based wet layup system and non-CFRP control specimens. Results indicated that PU adhesive and laminate can be tailored to obtain desired flexural performance, with bond cohesive energy and shear slip being the parameters that best predict the flexural beam strength, deformability, and failure modes. Comparable flexural capacity improvement was also observed between the PU-CFRP and the epoxy-based CFRP wet layup systems. [ABSTRACT FROM AUTHOR]

This study presents the development of a nonlinear finite element (FE) model that is capable of simulating the response and predicting the shear strength of concrete beams reinforced with carbon fiber-reinforced polymer (CFRP) bars. More specifically, this paper investigates the effect of unsymmetrical loading that creates two shear span-to-depth (a/d) ratios within the beam specimen and further complicates shear response. It is observed that the predicted FE results are in close agreement with the measured experimental results. Thus, it can be concluded that the developed models can be used to simulate the behavior of concrete beams reinforced with CFRP bars. [ABSTRACT FROM AUTHOR]

• Bond behavior between SFCB and ECC is comprehensively investigated by spliced beam tests. • A bond-slip constitutive model of SFCB in ECC is devised to estimate the bond-slip behavior. • The bond stress distribution of splicing SFCB in the splice region of ECC beams is discussed through FE analysis. The collaborative utilization of steel-FRP composite bar (SFCB) and engineered cementitious composites (ECC) represents a favorable choice for engineering structures exposed to aggressive environments, offering benefits involving both mechanical behavior and durability. This paper primarily studies the bond performance of SFCB embedded in ECC through spliced beam tests coupled with finite element analysis. The findings demonstrate that with an appropriate cover thickness or transverse confinement, spliced ECC beams exhibit failure modes characterized by splitting and pull-out. Under such conditions, the bond-slip response demonstrates limited sensitivity to changes in cover thickness and transverse confinement. Conversely, increasing the cover thickness or introducing transverse confinement in spliced concrete beams, which exhibit splitting failure, significantly enhances the bond strength. Furthermore, in contrast to spliced concrete beams, spliced ECC beams are observed to demonstrate a bond toughness that is 3.85–12.10 times greater. The discrepancy in bond toughness between ECC and concrete diminishes as the cover thickness and transverse confinement increase. Notably, the uniform distribution of bond stress in the splice region of ECC beams remains unaffected by variations in splice length. To incorporate the impact of bond stress distribution when calculating the splice length of SFCB in ECC beams, a coefficient of 0.85 is introduced. [ABSTRACT FROM AUTHOR]

• The unbonded ratio is the main factor affecting the performance of an RC beam. • The friction coefficient between the rebar and concrete is related to the load stage. Hybrid aggregates, comprising normal-weight and lightweight aggregates, offer an effective means to enhance the physical and mechanical properties of concrete. However, the comprehensive effect of hybrid aggregate concrete on the flexural performance of reinforced concrete (RC) beams remains largely unexplored. In this study, utilizing LC30 lightweight concrete, LC40 gravel lightweight concrete, hybrid aggregate lightweight concrete, and hybrid aggregate concrete with reduced ceramsite content as matrix materials, RC ordinary beams and RC bond-slip beams with dimensions of 150 mm × 300 mm × 2400 mm were meticulously designed and fabricated. Employing a four-point bending test, the effects of the concrete matrix, the unbonded ratio, and the reinforcement ratio of the bottom longitudinal rebar on the flexural behavior of the two types of beams were scrutinized. Furthermore, the load–deflection and load–slip responses were subjected to numerical simulation using the finite element method. The findings demonstrate that hybrid aggregates exert a substantial influence on adjusting the dry apparent density, strength, and elastic modulus of concrete to align with design specifications. While the physical and mechanical characteristics of both beam types are primarily governed by the reinforcement ratio and unbonded ratio, the concrete matrix, despite its distinct properties, exhibits minimal effect on these attributes. Nevertheless, it significantly affects beam stiffness and the relative slip between the rebar and the concrete matrix. Both beam categories adhere to the plane section assumption and reveal that optimal collaborative performance between the rebar and concrete matrix occurs at a bottom longitudinal reinforcement ratio of 1%, albeit diminishing with escalating unbonded ratios. The failure progression of both beam types can be categorized into three stages: elastic phase, crack propagation phase, and compressive failure phase. The process of crack advancement, the load–deflection profile, and the load–slip behavior of the beams manifest similarities, albeit subject to variations attributable to the concrete matrix, bottom longitudinal reinforcement ratio, and unbonded ratio. The Menetrey–Willam constitutive model effectively replicates the load–deflection and load–slip characteristics of both beam types. However, its simulation precision is influenced by the friction coefficient existing between the rebar and the concrete matrix. Notably, this friction coefficient undergoes alteration in consonance with the concrete failure process, thereby reflecting the gradual degradation of bonding performance between the rebar and the concrete matrix. [ABSTRACT FROM AUTHOR]

Bonding capacity of the interface between FRP plate and concrete can be evaluated by FRP-concrete interface slippage curve. In order to find a relatively accurate interface bond-slip model, the interface performance of concrete beam strengthened with externally bonded CFRP plate was studied. Strengthened wide-notch concrete beam models were fabricated and tested, where the concrete cover at the pure bending section of models was partly removed to form the wide-notch on the side surface, externally bonded CFRP plates were used to strengthen the beams and the four-point bending test was accomplished. External measuring devices were mounted on the beam models to accurately measure the slippage of certain beam sections along the beam span. Results show that the test and its testing system are suitable to study the bonding shear stress and the slip properties at the interface of concrete and CFRP plate. The designated beam section movement is easy to measure. The stress distribution is clear and the average shear stress of CFRP plate is convenient to obtain. The slippage and bond-slip curve are accurate. Strain gauges are not necessary for the measurement of slippage. Thus the testing system and calculation method for slippage reported in this paper can provide help with other researches on the interface properties of CFRP and concrete. [ABSTRACT FROM AUTHOR]

An experimental study was performed to investigate the effects of polypropylene fibers on uncorroded and corroded reinforced concrete beams. Three different volume fractions of polypropylene fibers having 0, 0.5, and 1.5%, were tested at four corrosion levels of 0% and approximately 5, 7, and 9%. A full scale of an accelerated corrosion pool was used for the accelerated corrosion process. Reinforced concrete beams were used for an under monotonic bending test. The contribution of the actual corrosion levels of transverse and longitudinal reinforcement bars to the total corrosion levels were obtained from reinforcement bars fully extracted from concrete. Flexural strength, bond-slip, and moment-curvature relationships were examined for uncorroded and corroded reinforced concrete beams. A new model was developed to predict the flexural strength of corroded reinforced concrete beams. The proposed model for predicting the residual flexural strength of corroded beams was compared with test data published in previous studies. Furthermore, a novel model is presented for improved predictions between the actual and theoretically estimated corrosion mass losses, based on Faraday’s law, with the aid of fully extracted reinforcement bars. The model used to predict the flexural strength of corroded reinforced concrete beams with large sizes demonstrated good agreement with current and previously published literature data. In the case of corroded beams comprising differing amounts of polypropylene fibers, the performance of the corroded beams was limited by a fiber volume fraction of 1.5% at low corrosion levels. [ABSTRACT FROM AUTHOR]

The strengthening of reinforced concrete members with prestressed fibre-reinforced polymer laminates has been investigated by researchers due to major improvements in member serviceability characteristics. Currently, analytical models generally employ mostly empirical procedures in predicting member behaviour, and as a result, the analytical results exhibit poor correlation to experimental investigations. In this article, an analytical model is developed using new and existing theoretical techniques to critically analyse strengthened reinforced concrete beams for a range of loading scenarios to generate moment–rotation and load–deflection relationships. The prestress level and the intermediate crack debonding strain of the prestressed fibre-reinforced polymer laminate with the inclusion of mechanical end anchorage were highlighted as key parameters within the model. The proposed model adopts closed-form solutions to allow for a wide range of beams with varying steel and fibre-reinforced polymer reinforcement ratios and dimensions. The model incorporates calibrated crack spacing theory to predict the crack width and spacing as well as the length of the cracked region in the beam. The models have good correlation with collected experimental data and thus can be used for the analysis of reinforced concrete beams strengthened with prestressed fibre-reinforced polymer, throughout all stages of loading from serviceability to failure. [ABSTRACT FROM AUTHOR]

Under cyclic loading, the shear strength of reinforced concrete (RC) beam-column joints is decreased by diagonal cracking and beam bar-slip, as the inelastic deformation increases. In the present study, a joint shear strength model was developed for the performance-based design of interior beam-column joints. As the primary design parameter, the bar bond parameters were used to define the joint shear deformation and shear strength. All possible failure mechanisms of beams and joints were considered: flexural yielding of the beam end (bar fracture or concrete crushing), diagonal cracking and concrete crushing in the joint panel, bar bond-slip, and bar elongation. For verification, the proposed model was applied to 50 existing beam-column joint specimens. The prediction results of joint shear capacity and deformation capacity were compared with the existing test results. The results showed that the predictions generally agreed with the test results. [ABSTRACT FROM AUTHOR]

This paper investigates the structural behavior of fiber reinforced polymer (FRP) strengthened reinforced concrete (RC) beams by developing a new simple, efficient and accurate finite element model (FEM-B). In addition to the FRP, concrete and steel rebars, the adhesive and stirrups which have been generally ignored in the reported models from literatures are considered in the new models. At first, a finite element model (FEM-P) is developed assuming perfect bond between concrete, FRP and adhesive interfaces. Then the FEM-P model is expanded to form the FEM-B model by including the bond-slip effect between concrete, FRP and adhesive interfaces. The developed new finite element models (FEM-B and FEM-P) are validated against experimental results and demonstrate to be effective for the structural analysis of FRP strengthened RC beams. Furthermore, parametric studies are carried out to learn the effects of types and thickness of FRP on the structural behavior of FRP strengthened RC beams based on the FEM-B model. The research findings are summarized finally. [ABSTRACT FROM AUTHOR]

Fibre reinforced polymer (FRP) is used extensively nowadays in construction industry to reinforce and strengthen reinforced concrete (RC) structures to enhance the structural performance of the structures under various loading conditions. Finite element analysis is an efficient and accurate method for modelling the structural behavior of FRP strengthened RC structures especially under extreme loadings such as cyclic loading. For accurate numerical modelling of the structural behavior of FRP strengthened RC beams, appropriate material models of each component and bond behavior are essential. In this chapter, the developed materials models for concrete, FRP, steel rebar and adhesive and the bond stress-slip models for FRP/adhesive/concrete interfaces are reviewed. In addition the developed finite element models for analysis of FRP strengthened RC beams under static and cyclic load are also reviewed. [ABSTRACT FROM AUTHOR]

This paper describes a numerically efficient approach to describe reinforcing bars bond-slip in the vicinity of interior beam–column joints, which is an effect that significantly influences frames behavior regarding stiffness and hysteretic energy dissipation capacity. The fiber-section model proposed here allows for the accurate analysis of those critical regions, taking into account the factors most relevant to the determination of its behavior, without the computational disadvantages of other more complex formulations. The methodology is defined by the fiber model based on continuous anchored bars and by its implementation into a fiber force-based finite element. The behavior of the fiber model based on anchored bars is discussed and then the fiber-section finite element is evaluated by comparison with an experimental test of a beam–column subassemblage subjected to cyclic loading. The proposed beam–column finite element is capable of predicting anchorage slip and the analytical results of the structural subassemblage agree well with the experimental results. [ABSTRACT FROM AUTHOR]

• Bond-slip durability of GFRP reinforced concrete beams under wet-dry and freeze-thaw cycles were studied. • Flexural pull-out beam test was used. • Normal, self-compacting, and fibre-reinforced concretes were studied. • Steel and GFRP reinforced beams were compared. In this experimental study, the bond-slip performance between glass fibre reinforced polymer (GFRP) bars and three different concrete types, namely normal, self-compacting, and fibre-reinforced concrete under freeze-thaw and wet-dry cycles have been studied. Steel reinforced concrete beams were also tested for comparison purposes. In total, 54 GFRP and steel reinforced concrete beams were prepared, conditioned, and tested using RILEM recommendations. 18 specimens were subjected to 200 wet-dry cycles between ambient and 60 ˚C and another 18 specimens were subjected to 200 freeze-thaw cycles between -18 ˚C and 4 ˚C for 150 days. The results showed the bond strength reductions of 12, 3 and 9 % between steel bars and beam specimens cast with normal, self-compacting, and fibre-reinforced concrete, respectively after exposure to 200 wet-dry cycles. However, the corresponding values for GFRP reinforced concrete beams under the same conditioning environment were 1, 1, and 16 % respectively. With respect to freeze-thaw cycles, bond strength of steel reinforced normal, self-compacting, and fibre-reinforced concretes experienced only about 5, 2, and 4 % reductions, respectively, after 200 cycles. The corresponding reduction values for GFRP reinforced beams were insignificant and about 2, 1, and 4%. Steel reinforced beams fail due to the concrete crushing, while GFRP reinforced beams fail due to GFRP surface peeling-off. Generally, GFRP reinforced beams experienced fewer bond strength reductions compared to steel reinforced beams. Also, regardless of concrete type, due to their corrosion vulnerability, steel reinforced beams experienced greater stiffness reductions than that of GFRP reinforced beams when subjected to seawater wet-dry cycles. However, such a difference was not drastic. [ABSTRACT FROM AUTHOR]

Highlights: [•] This paper presents experimental results of RC beam-column connections. [•] We proposed a simple model to predict moment–rotation behavior of the connections. [•] The model is evaluated by comparing predicted and experimental results. [•] Comparisons showed that the model is able to predict the effects of slippage of bars. [Copyright &y& Elsevier]

Highlights: [•] Efficiency of FRP composites in restoring shear strength of sulfate-damage beams. [•] Evaluating anchorage of FRP strips using FRP sheets. [•] Analytical predictions of shear capacity of beams matched experimental results. [•] Use of FRP strips and sheets helped restoring original mechanical properties. [•] FRP composite enhanced crack resistance, and delayed the onset of initial cracking. [Copyright &y& Elsevier]

The paper presents quasi-static numerical simulations of the behaviour of short reinforced concrete beams without shear reinforcement under mixed shear-tension failure using the FEM and four various constitutive continuum models for concrete. First, an isotropic elasto-plastic model with a Drucker-Prager criterion defined in compression and with a Rankine criterion defined in tension was used. Next, an anisotropic smeared crack and isotropic damage model were applied. Finally, an elasto-plastic-damage model was used. To ensure mesh-independent FE results, to describe strain localization in concrete and to capture a deterministic size effect, all models were enhanced in a softening regime by a characteristic length of micro-structure by means of a non-local theory. Bond-slip between concrete and reinforcement was considered. The numerical results were directly compared with the corresponding laboratory tests performed by Walraven and Lehwalter (1994). The advantages and disadvantages of enhanced models to model the reinforced concrete behaviour were outlined. [ABSTRACT FROM AUTHOR]

Highlights: [•] Experimental study of flexural and bond–slip behaviour of FRP concrete beams. [•] Bond–slip behaviour is detected under standard beam test rather than pull-out test. [•] Numerical modelling of the flexural and bond–slip behaviour using new elements. [•] Further validation of the recently developed elements by the experimental results. [•] Parametric study to investigate the structural behaviours with varying parameters. [Copyright &y& Elsevier]

Abstract: A new beam–column model is developed for the seismic analysis of reinforced concrete (R/C) structures. This finite element consists of two interacting, gradual spread inelasticity sub-elements representing inelastic flexural and shear response and two rotational springs at the ends of the member to model anchorage slip effects. The flexural sub-element is able to capture gradual spread of flexural yielding in plastic hinge regions of R/C members. The shear sub-element interacts throughout the analysis with the flexural sub-element, in the location of the plastic hinge regions, in order to capture gradual spread of inelastic shear deformations as well as degradation of shear strength with curvature ductility demand based on an analytical procedure proposed herein. The skeleton curves and hysteretic behaviour in all three deformation mechanisms are determined on the basis of analytical procedures and hysteretic models found to match adequately the experimental results. Empirical formulae are proposed for the shear distortion at onset of stirrup yielding and onset of shear failure. The proposed element is implemented in the general finite element code for damage analysis of R/C structures IDARC and is validated against experimental results involving R/C column and frame specimens failing in shear subsequent to yielding in flexure. It is shown that the model can capture well the hysteretic response and predict reliably the type of failure of these specimens. [Copyright &y& Elsevier]

Abstract: The introduction of Near Surface Mounted (NSM) strengthening technique to retrofit reinforced concrete (RC) members in flexure using Carbon Fiber-Reinforced Polymer (CFRP) rods is becoming more attractive to both researchers and designers in recent years. Although NSM strengthening systems has been used extensively, still further experimental, analytical, and numerical research is warranted to understand the effect of the several strengthening parameters on the flexural performance of RC members. This paper presents the development of a detailed 3D nonlinear finite element (FE) numerical model that can accurately predict the load-carrying capacity and response of RC beams strengthened with NSM FRP rods subjected to four-point bending loading. The developed FE model considers the nonlinear constitutive material properties of concrete, yielding of steel reinforcement, cracking of the filler bonding materials, bond slip of the steel and NSM reinforcements with the adjacent concrete surfaces, and bond at the interface between the filling materials and concrete. The numerical FE simulations were compared with experimental measurement tested by other investigators comprising of seven specimen strengthened with NSM CFRP rods in addition to one un-strengthened control specimen. Overall, the predicted FE mid-span deflection responses agreed very well with the corresponding measured experimental tested data at all stages of flexural loading. Furthermore, the developed models were also capable of predicting the failure mode of the strengthened tested specimen such as NSM rod debonding (peeling off) and concrete cover separation. The validated FE models are then used to study the effect of different NSM material bar types and sizes to provide further information over the limited available experimental data. It is concluded that the developed FE model is suitable as a practical and economical tool especially in design-oriented parametric studies for accurate modeling and analysis of flexural strengthening of RC members with NSM reinforcement. [Copyright &y& Elsevier]

The objective of this study was to experimentally investigate the bond-related tension stiffening behavior of flexural reinforced concrete (RC) beams made with lightweight aggregate concrete (LWAC) under various high-cycle fatigue loading conditions. Based on strain measurements of tensile steel in the RC beams, fatigue-induced degradation of tension stiffening effects was evaluated and was, compared to reinforced normal weight concrete (NWC) beams with equal concrete compressive strengths (40 MPa). According to applied load-mean steel strain relationships, the mean steel strain that developed under loading cycles was divided into elastic and plastic strain components. The experimental results showed that, in the high-cycle fatigue regime, the tension stiffening behavior of LWAC beams was different from that of NWC beams; LWAC beams had a lesser reduction in tension stiffening due to a better bond between steel and concrete. This was reflected in the stability of the elastic mean steel strains and in the higher degree of local plasticity that developed at the primary flexural cracks. [ABSTRACT FROM AUTHOR]

Abstract: This paper presents an analytical study on the modeling of exterior reinforced concrete (RC) beam-column connections strengthened using carbon fiber reinforced polymer (CFRP) composites subjected to lateral loading. To simulate the overall connection behavior reasonably well, the developed analytical model takes into account joint shear behavior, bond slip of longitudinal beam reinforcement, and effects of various configurations of CFRP sheets. In particular, effects of anchorage at the ends of the attached CFRP sheets, which have never been modeled in previous analytical studies to date, were incorporated into the developed model. The results from analytical and experimental studies for seven beam-column connection specimens tested by the authors were compared in terms of initial stiffness, maximum strength, stiffness degradation, strength degradation, and energy dissipation. The comparison indicates that the analytical results showed a good agreement with the experimental results. Therefore, the developed connection model, which is a macro-scale model with a few elements, can be used for performance assessments of RC structures having CFRP-strengthened beam-column connections with an adequate accuracy and simplicity. [Copyright &y& Elsevier]

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. [ABSTRACT FROM AUTHOR]

• Pull-out tests of bundled steel/FRP bars embedded in concrete were performed. • The influence of bond-slip effect of bundled bars in RC beams was investigated. • Equivalent bond-slip model of bundled steel/FRP bars was theoretically derived and validated. • High-fidelity FE model incorporating bond-slip effect by cohesive elements is developed. Due to the controllable bond performance and high-efficiency construction of bundled hybrid reinforcements, the seismic performance and accelerated construction of a precast concrete structure can be guaranteed. Eighteen pullout specimens of bundled deformed steel bars and basalt fiber reinforced polymer (BFRP) bars (single, double, three-bundle) were tested under monotonic loading. The peak bond strength decreased by 40.7% as the reinforcement bundles increased from one to three. The corresponding experimental investigations on five concrete beams reinforced by different types of bundled reinforcement showed that, compared to a beam with ordinary distributed reinforcement (control beam), the ultimate displacement of the beams with three bundles and six bundles increased by 60% and 90%, respectively. The load bearing capacity of the six-bundle beam was 9.6% larger than that of the control beam. A simplified bond-slip model based on the concept of equivalent bond area was proposed and showed good agreement with the test results. In addition, finite element analysis considering the bond-slip between the reinforcement and concrete was conducted to predict the load–deflection relationships of the new composite beam. A comparison of the analytical and experimental results showed that the analytical model could accurately predict the failure modes, load–deflection relationships and strain developments of bundled hybrid reinforced beams. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

A new one-dimensional two-node layered composite beam element that accounts for the bond-slip between reinforcing bars and surrounding concrete is presented for nonlinear analysis of steel/fiber-reinforced polymer (FRP) concrete beams. A layered approach is used not only to represent the nonlinear material property accurately but also to model the bond-slip effect between the reinforcing bars and the concrete. In addition to the typical transverse displacement and rotation at the two nodes of the beam element, additional nodal degrees of freedom are introduced to represent the axial displacements of the reinforcements to account for bond-slip effect. Timoshenko's beam functions are employed for the displacement shape functions, and shear locking is avoided naturally. The element is validated against numerical examples and demonstrated to be accurate and computationally efficient for the analysis of steel/FRP-reinforced concrete beams with bond-slip. [ABSTRACT FROM AUTHOR]