Search

A few research studies are available on the behavior of reinforced concrete (RC) box section beams with fiber‐reinforced polymer bars (FRP) and FRP stirrups. Consequently, the behavior of these beams needs to be investigated. This article studies experimentally, numerically, and analytically the effect of some variables on the behavior of RC box section beams. This article investigates many variables, such as the shear span‐to‐total depth ratio, the flexural FRP reinforcement ratio, and the FRP vertical and horizontal web reinforcement ratio. The experimental program consists of nine simply supported reinforced concrete box section beams. The numerical models using the nonlinear finite element program ANSYS V.15 are carried out. The results are compared to the experimental results using load‐deflection curves, crack patterns, failure loads, and failure modes. The shear capacities based on Egyptian ECP 208‐2019 and ACI 440‐2015 codes are compared to each other and to the experimental results. The findings show an adequate agreement between the experimental, numerical, and analytical results for the range of the studied parameters. The results reveal that increasing the shear span‐to‐depth ratio by 50% decreases the carrying capacity, toughness, and displacement ductility by 2%, 28%, and 12%, respectively. The increase in main FRP reinforcement rebars by 20% increases the carrying capacity and toughness by 59% and 62%, respectively. Increasing vertical FRP stirrups by 79% increases the failure load and toughness by 26% and 15%, respectively, and displacement ductility increases only by 0.8%. The increase in horizontal FRP stirrups by 79% increases the failure load, toughness, and displacement ductility by 33%, 8%, and 4%, respectively. Both Egyptian and American codes are conservative in some cases and unconservative in others, while the numerical results are unconservative. [ABSTRACT FROM AUTHOR]

Cranes are employed to lift precast concrete girders during their construction. Presently, there is no recommendation for operational velocities during girder assemblage, particularly for long elements; simultaneously, several accidents have been reported during the transitory phase of girder motion. Since this mechanical problem has been examined in technical literature using a static approach, the present research study aims to investigate the dynamical behavior of a long, prestressed concrete girder by determining critical operational velocities according to crane movements. Prestressing cables' eccentricity and lifting loop position deviation were accounted for in 3D finite element simulations of a 40 m span precast prestressed concrete girder. Transient nonlinear analyses to obtain stresses and deflections were performed, so as to account for the large deformation behavior of the motion. A frequency domain approach was employed to analyze the time history results using the girder's natural frequencies obtained by modal analysis. The finite element model was developed to simulate upward, downward, and lateral girder movements. The most significant displacements and stresses were observed in the highest girder acceleration peaks, amplified by eccentricities. Safety against cracking and subsequent failure during vertical and lateral movements was ensured for crane operating accelerations of 0.02 g (v = 20 cm/s) and 0.007 g (v = 7 cm/s), respectively. Compared with the usual static analysis, for the critical case investigated, the inertial effect intensified the tensile stresses by 27 times, increased the compressive stresses by 11%, and increased the girder deflection by 3 times. [ABSTRACT FROM AUTHOR]

This paper presents the experimental study and finite element modeling of the flexural behavior of concrete beams reinforced with reused steel bars as longitudinal reinforcements. The experimental program and results of eight reinforced concrete (RC) beams constructed with and without reused steel bars are described in detail. The replacement percentages of brand‐new bars with reused steel bars in the tested beams were 50% and 100%. The reused steel bars were coated with and without epoxy. Steel fibers with fractions of 0.5% and 1.0% of the concrete volume were added to the concrete mixes. The load‐deflection relationship, ductility index, toughness, and failure modes of the tested beams are presented and discussed. It is shown that utilizing reused steel bars decreases the ultimate load of RC beams but increases their deflection at the ultimate load compared with the control beam. Increasing the steel fiber ratio increases the ultimate load and the deflection at the ultimate load of RC beams incorporating reused steel bars. However, the zinc‐rich epoxy used to coat the reused steel bars does not affect the behavior of the beams. Three‐dimensional nonlinear finite element (FE) models of the tested beams were developed using ABAQUS and validated against the test results. The developed FE models are capable of accurately simulating the experimentally observed behavior of RC beams with reused steel bars. [ABSTRACT FROM AUTHOR]

The positive effect of fiber‐reinforced concrete (FRC) on shear capacity of reinforced concrete beams is well presented in many experimental studies since 1970s. However, as the main effect of fibers is in the cracking stage, it increases the complexity to analyze such structures numerically. With the increased availability of nonlinear finite element analysis software, structural designers are encouraged to use them to solve complex structural problems. In such cases, understanding and correct definition of material laws in cracked stage of FRC structures are crucial. A blind competition was organized by fib WG 2.4.2 to address this issue. It revealed that the numerical predictions of almost all of the participants overestimated the shear capacity of a T‐beam subjected to bending. The aim of the current study is to demonstrate critical aspects in the definition of input parameters of FRC analysis. A comprehensive parametric analysis is performed considering tensile softening law, shear stiffness, and shear strength definition in cracked stage as well as shrinkage effects. The results suggest that most important aspect is the correct definition of tensile softening law, which should correspond to the lower bound of residual strength obtained by standard notched prisms tests according to EN 14651 or even smaller. [ABSTRACT FROM AUTHOR]

Most of the Italian infrastructures have been built since the mid‐twentieth century. Prestressed concrete (PC) has been widely used, especially for bridges and viaducts. These structures have proved effective over time, but their performance could be affected by degradation phenomena (i.e., corrosion of the tendons and residual prestressing) or construction defects (i.e., grouting of the ducts), which need to be accurately modeled. This paper focuses on the flexural response of two reduced‐scale, posttensioned, PC bridge girders, prestressed with two different jacking forces and tested under four‐point bending configuration. Four multidimensional numerical models were developed to simulate the experimental behaviors of the selected specimens, using two alternative computational strategies, namely, the finite element method (FEM) and applied element method (AEM). Three FEM modeling were considered, ranging from one‐dimensional lumped‐plasticity models to two‐dimensional and three‐dimensional (3D) spread‐plasticity models. Besides, 3D AEM models were developed into another software package. The accuracy and the computational costs of the two numerical strategies are discussed in this paper. Also, the main features of each numerical modeling technique are addressed, including comparisons between numerical and experimental global response data as well as the statistical characterization of the model error. Based on these different features, the authors also suggest the most suitable numerical strategy for future studies on PC girders. [ABSTRACT FROM AUTHOR]

Ultra‐high performance concrete (UHPC) prefabricated beams are competitive in accelerated bridge construction. However, their broader application has been hindered by limited large‐scale tests and inaccurate design methods. To fill this gap, the authors conducted an experimental investigation on the shear and flexural performance of UHPC pi‐beams using two full‐scale specimens. One specimen was a precast UHPC beam, while the other was a composite beam with a normal concrete slab on the UHPC beam. The primary focus was on crack propagation, ultimate capacities, and failure modes. To complement the experimental findings, the extended finite element method (XFEM) was developed as a numerical approach. Nevertheless, relying solely on XFEM to understand real structural behavior is prone to misinterpretations. Moreover, the shear and flexural capacities were evaluated using existing codes and compared with the experimental results. The comparisons revealed that the predictions of shear capacities were at least 15% lower than the experimental values, whereas the flexural capacities showed acceptable agreement. To address this, the authors introduced the limit equilibrium method, leading to a more accurate prediction of shear capacity for UHPC beams with a deviation of <2%. [ABSTRACT FROM AUTHOR]

A novel posttensioning technique using nickel‐titanium‐niobium (NiTiNb) shape memory alloy (SMA) wires for the repair of reinforced concrete beams was evaluated numerically. A finite element model of a reinforced concrete beam was developed within a damage mechanics framework to simulate concrete cracking and subsequent posttensioning. The predicted yield and ultimate moment capacities of the simulated posttensioned beams were up to 14% less than the corresponding experimental results. Cumulative discrepancies in the assumed material models led to the conservative model results. The effects of concrete tensile damage, SMA reinforcement ratio, SMA‐concrete interaction (bonded vs. unbonded), and the effective prestress on the service and ultimate behavior of the posttensioned beam were evaluated. Partial loss of prestress in the SMA due to elastic shortening of the concrete was insignificant (<3%) because of the relatively low elastic modulus of the SMA. Increasing the SMA reinforcement ratio by three times increased the yield moment of the posttensioned beam by 99%. Reducing the effective SMA prestress to 80% of the initial prestress to account for the possible losses resulted in a decrease in the yield moment by up to 7.8%. [ABSTRACT FROM AUTHOR]

In topology optimization with discrete model finite element analysis (FEA), feasible reinforcement domain determines to a large extent the result, and the trade‐off between accuracy and efficiency of optimization as well. Therefore, a cantilever reinforced concrete short beam was comparatively optimized based on five feasible reinforcement domains with complexity at different levels, respectively. The outcomes exhibit that, it is reasonable to evolve reinforcement layout by topology optimization with discrete model FEA. The orientation of diagonal reinforcement in optimal topologies from complex feasible reinforcement domains would correspond more to the orientation of the principal tensile stress than that using simple ones, since complex ones have rebar distribution with high density or diagonal reinforcement with various orientations. After optimization, the global stress level of the reinforcement decreases, and then utilization rate of the reinforcement strength increases. Additionally, the consumption of rebar and the workload of reinforcement engineering only slightly increased, although such optimal reinforcement topologies are relatively complex. Consequently, the mechanical properties of concrete members can be substantially improved by using a more complex feasible reinforcement domain for optimizing rebar distribution. A complex domain should be chosen on the premise of completing the optimization within a reasonable time in engineering applications. [ABSTRACT FROM AUTHOR]

A joint system was proposed to connect square thin‐walled concrete‐filled steel tube (CFST) columns and reinforced concrete (RC) beams. In the system, longitudinal beam reinforcing bars are continuous through the joint zone by passing the rectangular holes in the steel tube, aiming to achieve direct load‐transfer of the beam and joint integrity; and the square thin‐walled steel tube with holes is strengthened by internal diaphragms. Previous cyclic tests showed that the proposed joint system satisfied the requirements of strong‐joint weak‐component, namely the shear capacity of the joint zone was larger than that provided by CFST columns and RC beams. However, further research was necessary to evaluate the behavior under axial compression, as the discontinuous diagonal ribs and holes in the joint steel tube weakened the load capacity. In this investigation, the effect of internal diaphragms was first evaluated based on the axial compression tests on six square CFST stub columns. The test results showed that the internal diaphragms effectively improved the strength and ductility. The finite element analyses (FEA) on square CFST columns and RC beam to CFST column joints stiffened by internal diaphragms were then carried out based on the verified FEA models. The analysis results showed that thicker internal diaphragms increased the strength, and changed the failure mode from the column‐center failure to column‐end failure for columns and from the joint failure to column failure for joints, respectively. Finally, the mechanics‐based models and axial strength equations of square CFST columns and RC beam to CFST column joints stiffened by internal diaphragms were proposed, and the predictions agreed well with the test and analysis results. [ABSTRACT FROM AUTHOR]

This paper investigates the shear strengthening of reinforced concrete (RC) beams incorporating engineered cementitious composite (ECC) and stainless steel plates (SSPs). The use of ECC, characterized by strain‐hardening in conjunction with SSPs, was investigated in this study to improve the shear performance of RC beams. Total 10 RC beams were tested under static loading up to failure to investigate a few key parameters, namely: material of strengthening (ECC and SSPs), the thickness of ECC, and shape and configuration of SSPs. Experimental findings showed that the proposed strengthening methods can significantly improve the failure pattern and increase the ultimate shear capacity of the studied RC beams by 36%–97% compared to the unstrengthened beam. Experimental results were compared against the predicted ultimate shear strength of RC beams using design equations specified by various design codes. Nonlinear three‐dimensional finite element modeling was developed for beams strengthened with ECC layer and validated against the test results and found to be accurate. Based on the experimental and numerical results, new shear capacity formulae were proposed considering the ratio of ECC‐to‐concrete beam cross‐section (ρECC) and then verified against the numerical predictions. [ABSTRACT FROM AUTHOR]

Infrastructures (viaducts, bridges, tunnels, railways, and roads) are fundamental to allow people and goods move around a country. In particular, in Italy, due to its orographic and morphological complexity, the ratio between the number of viaducts and the national geographical extension is the largest in Europe. This kind of structure constitutes a weakness of the road networks, especially those over 50 years old, and among these, prestressed concrete structures are the most vulnerable. Therefore, the study of the robustness of an infrastructure network is a quite useful topic for modern societies and public mobility managers. The aim of the present work is to develop a reliable and fast analysis tool capable of processing many structures in a relatively short time. In order to calibrate the most suitable instrument, starting from the study of an experimental campaign on six prototypes of artificially corroded posttensioned concrete beams, the reliability of concentrated plasticity models was investigated to reproduce force‐displacement diagrams and in particular, the effect of corrosion on the moment‐curvature relationship. In fact, this method could provide a well‐defined nonlinear analysis of prestressed elements, especially in the case of grillage decks where external girders could be more affected by corrosion damage in opposition to internal girders or diaphragms. A numerical model by FEM analysis is also presented to reproduce a vulnerability study on an actual structure. [ABSTRACT FROM AUTHOR]

This research has investigated the effect of reinforcement corrosion on the flexural response of reinforced concrete beams subjected to blast loading. Five beams, with and without corrosion, were tested under blast loads using a shock‐tube. The corroded specimens were subjected to an accelerated corrosion regime prior to testing, with a mass loss of up to 22% in the longitudinal steel reinforcement over the mid‐span or full‐span regions. A companion set of two beams was tested under quasi‐static four‐point bending. The results from the static tests show that corrosion of the longitudinal reinforcement decreased the strength and ductility, and ultimately changed the failure mode from ductile to brittle. Under blast loading, the steel corrosion increased maximum displacements and support rotations, reduced blast capacity, increased damage and fragmentation, and led to more brittle failure as the % mass loss increased. The effects of corrosion on blast response were moderate when the steel was corroded over the full‐span region. Furthermore, the blast response of the beams was predicted using dynamic inelastic single‐degree‐of‐freedom (SDOF) analysis, with the resistance functions developed using 2D finite element modeling, while accounting for the reduction in steel stress–strain properties and corrosion‐induced cracking. The SDOF analysis showed acceptable results in terms of ability to predict maximum displacements of the flexural‐governed beams (corroded and un‐corroded). [ABSTRACT FROM AUTHOR]

The present investigation deals with the flexural behavior of a new type of Hybrid steel, polypropylene Engineered Cementitious Composite (Hf‐ECC) ‐ Lightweight Aggregate Concrete (LWAC) encased Hybrid Steel Truss Composite (HSTC) beams and detailed parametric study of HSTC beams using Abaqus. Eight simply supported beams fabricated with identical hybrid steel truss, but with varying depths and layer arrangement of Hf‐ECC and LWAC were experimentally tested to investigate the effects of Hf‐ECC depth of HSTC beam on the ultimate load‐carrying capacities and failure modes. Test results show that cracking, yield, ultimate moments, and the ductility of HSTC beams are improved by increasing the depth of Hf‐ECC due to the excellent tensile properties of Hf‐ECC. In addition to the above enhancement, it is also found that the combined use of Hf‐ ECC and LWAC could improve the beams' general ductility and considerable energy dissipation capacity due to Hf‐ECC's excellent deformation ability besides reducing beams' weight. In addition to experimental work, a finite element model is used to predict the load‐deflection behavior of Hf‐ECC and LWAC‐encased HSTC beams. [ABSTRACT FROM AUTHOR]

Nineteen 2D nonlinear finite element analysis (NLFEA) solution strategies were benchmarked against a wide variety of 101 experiments on reinforced concrete beams failing in bending, flexural shear, or shear compression. The relatively high number of solution strategies was motivated by the conviction that choices for the constitutive models, the finite element kinematics and equilibrium settings will interact, and must therefore be tested in conjunction. Modeling uncertainty distribution parameters are presented for the 19 solution strategies, using all beams, and using beams with and without stirrups separately. The resulting statistics are discussed against the correctness of the simulated failure modes and failure loads, revealing that rotating crack models perform well for the relatively ductile failures in beams with stirrups, while fixed crack models perform better for the more brittle failures in beams without stirrups. The tailored solution strategies that predict failure modes correctly, imply a log‐normal distribution of the modeling uncertainty with relatively low coefficients of variation. The outlook is that these estimates of the statistical properties of the modeling uncertainties could serve as a basis within safety formats. [ABSTRACT FROM AUTHOR]

Precast concrete structures have been widely applied in the construction industry worldwide. However, the current construction method for the reinforced concrete frame–shear wall structure (FSWS) is semi‐precast because the shear wall is commonly cast‐in‐place. This paper proposes a full precast FSWS and investigates three new vertical joints with different lap splices that can facilitate on‐site construction. Push‐off tests are conducted to investigate the shear performance on the aspect of cracking and failure patterns, the evolution of deformation, stiffness reduction, and energy dissipation. A finite element model with delicate consideration of the contact is developed and validated against experimental data. A further parametric study is conducted. This study shows that the lap splice with a more uniformly distributed reinforcement layout yields the crack distribution more uniformly and increases the ductility of the joints. The proposed three vertical joints exhibit an improvement in ductility compared to the monolithic one. Furthermore, the shear keys change the failure mechanism of the precast joints into the multi‐struts failure mechanism thus increasing the shear strength. The parametric study shows that the decreasing of the splice lap length could increase the shear capacity of the vertical joints but decreases the ductility. However, the ductility reduction depends on the variation of lap splices. [ABSTRACT FROM AUTHOR]

To investigate the mechanical behavior of composite beams under pure torsion, considering the torsional contribution of the steel beam flanges, we established finite element models of I‐steel–concrete composite beams. The nonlinear material constitutive relationship of concrete and steel was adopted in the model, and we validated the relationship by tests. Afterward, parametric analyses were carried out to study the main factors affecting the torsional performance of the composite beam. Our primary investigation focused on the composite effects and load sharing ratio of the steel beam and the concrete slab under pure torsion. We established the formulas for obtaining the maximum shear stresses in the concrete slab and the steel beam based on the composite effects and superposition principle. From these tests and our calculations, we proposed a model defining the torsional bearing capacity and the torsional stiffness of the I‐steel–concrete composite beam; thus, the torsional contribution of the concrete slab and the steel beam were a primary concern in this research. Bearing capacity formulas are also proposed herein and are comparable with those in the literature, demonstrating that our formulas, with simple forms, are highly reliable when predicting the torsional behavior of the composite beam. [ABSTRACT FROM AUTHOR]

Modeling and assessing the load‐carrying capacity of reinforced concrete (RC) structures that are cracked is important because the condition of an RC structure changes due to natural aging and accumulated damage. The current approach to determining the residual capacity of a cracked RC structure is time‐consuming and error‐prone due to a limited capacity to obtain and process structural information. In this study, an automated approach was proposed to determining residual capacity by performing finite element (FE) analysis of an RC structure using point cloud three dimensional modeling. Two simply supported RC beams were subjected to bending tests to provide validation data. The initial activity was to extract dimensional data from laser‐scanned point cloud data of a beam. The information obtained was used to automatically generate nonlinear FE models of the beam that was used for nonlinear FE analyses in Abaqus. An initial crack was added to the beam to model a cracked beam in real conditions. Three different models were used to simulate initial cracks, a weakened element model, a cohesive zone model, and an extended FE model. The results indicate that the proposed method of automating the combination of point cloud data with nonlinear FE analysis provides a novel practical approach to modeling and assessing cracked RC beams. [ABSTRACT FROM AUTHOR]

In this study, the efficiency of using high strain hardening ultra high performance concrete (HSH‐UHPC) on strengthening existing reinforced concrete beams was investigated by experimental and analytical means. First, the HSH‐UHPC constitutive relation was obtained using "Dog‐bone" specimen under uniaxial tensile test. Then three reinforced concrete beams strengthened with HSH‐UHPC layers and one control beam were tested under flexural loading. The midspan deflection, strain distribution, crack propagation and failure mode of the tested beams were described in detail. The tests verified that the middle section of UHPC‐NC composite beam basically conforms to the assumption of plane section. The flexural resistance of composite structure can be greatly improved by installing proper longitudinal reinforcement in UHPC layer. Meanwhile, numerical studies have been conducted on the tested beams using the experimentally obtained constitutive relations. The result shows that the finite element analysis results are consistent with the test results. Finally, a contribution factor for the HSH‐UHPC layer on the flexural resistance of the composite beam was proposed. At the same time, it is found that the contribution efficiency of the HSH‐UHPC to the flexural resistance increases with longitudinal reinforcement ratios in the HSH‐UHPC. [ABSTRACT FROM AUTHOR]

In this research, the influence of using steel fibers on the shear action of reinforced concrete beams, made of recycled concrete aggregate (RCA), was investigated through experiment and finite element analysis (FEA). First, 12 reinforced concrete beams were tested with varying amounts of steel fibers. These beams contained normal concrete aggregate (NCA) as reference beams besides RCA beams. All beam models had the same 150 mm x 250 mm cross‐section and 2000 mm length. The beams had three bars of 16 mm reinforcement and two bars of 12 mm reinforcement at its bottom and top, respectively. Three replacement ratios of recycled aggregate (RA) were considered; 0%, 30%, and 70%. Moreover, steel fibers were introduced in the beams at 0%, 0.5%, 1%, and 1.5% content by volume. The beams were evaluated under a four‐point bending test while the load‐deflection diagram and failure load for all beams were considered as the criteria for comparing the shear response of different beams. A thorough FEA was carried out using ANSYS to model these beams. The FEA results were compared with the outcomes of the experimental tests, and a clear agreement was obtained. The results showed that using steel fibers improved the shear strength of the beams by 2.94%, 15.88%, and 34.71% for NAC beams, 1.39%, 11.11%, and 16.67% for 30% RCA beams, and 24.53%, 40.57%, and 59.44% for 70% RCA beams, respectively by using steel fibers with ratios of 0.5%, 1%, and 1.5%, respectively. [ABSTRACT FROM AUTHOR]

Ultra‐high performance concrete‐normal strength concrete (UHPC‐NC) composite beam is a brand‐new composite structure. UHPC‐NC composite beam not only has the interfacial problem of the two materials, but its shear resistance should be investigated, which directly determines the mechanical performance and engineering value. In this article, the finite element analysis (FEA) method combined with the UHPC‐NC composite beam shear experiment are used to analyze the shear resistance of the composite beam and the influence of the interfacial zone on the shear behavior. The shear span‐to‐depth ratio, UHPC layer, and longitudinal reinforcement of specimens are designed to study the shear mechanism. Then the FEA model is used to simulate the cooperative working properties of the concrete beam and the UHPC layer, which includes two conditions—slip and no‐slip. The shear resistance, load‐span deflection curve and the strain of longitudinal reinforcement of the UHPC‐NC composite beams are analyzed and studied in combination with the results of shear experiment. The results show that the UHPC‐NC composite beam can effectively improve the ultimate shear resistance and ductility of the beam. At the same time, the interfacial zone of UHPC‐NC composite beam at the ultimate stage is a weak area, the cracking of that will has adverse effects on the mechanical properties of the composite beam, which needs to be paid attention to in the structural design. [ABSTRACT FROM AUTHOR]

The deformation characteristics of cracked reinforced concrete beams are largely dependent on the tension stiffening effect. As one of the serviceability analysis approaches, the employment of a concrete tensile stress block that reflects the flexural tension stiffening behavior is useful for evaluation of beam deflections. In many practical applications, however, beams have to withstand a small degree of axial compression. There has been little research on axial load effects on tension stiffening, and tensile stress block for beams subject to compressive axial load has not been developed. In this study, finite element method is employed to analyze beams under different levels of compressive axial load. The numerical results reveal that the tensile stress block is considerably influenced by the presence of axial load. Using the tension stress fields obtained, values of stress block parameters under different levels of axial load are determined. Adequacy of the proposed model was verified using the test data reported in the literature. [ABSTRACT FROM AUTHOR]

Most of the Dutch bridges were built around middle of the last century and it is vital for designers to find out if these bridges can still be considered safe for the traffic of modern times. The capacity in shear is especially critical as it was not considered in design recommendations before 1976. Therefore, experiments on a 1:2 scale model of a transversely prestressed concrete bridge deck cast between concrete girders were carried out to investigate the bearing (punching shear) capacity. The scale was selected based on the space available in the laboratory and the expected failure loads that would have to be applied. Also, a three‐dimensional, solid, nonlinear finite element model was developed in the Finite Element Analysis software package TNO DIANA to study the structural behavior of deck slabs and is the focus of this paper. The results of the experimental and numerical analyses leads to the conclusion that existing bridges still have significant residual strength due to the presence of transverse prestressing and the membrane forces, and nonlinear finite element models can predict the load carrying capacity quite accurately. [ABSTRACT FROM AUTHOR]

This paper presents the efficiency of using prefabricated ultra‐high performance fiber reinforced concrete (UHPFRC) plates in shear strengthening of reinforced concrete (RC) beams experimentally and numerically using finite element method. In order to ensure high quality and facilitate the strengthening process on site applications, it has been considered to apply UHPFRC as a plate pasted on concrete surface using epoxy. Tested specimens included four strengthened beams besides three control beams. Strengthening the RC beams was based on the use of two different techniques; (a) one longitudinal side strengthening (b) two longitudinal sides strengthening. Moreover, strengthening RC beams with reinforced or non‐reinforced prefabricated UHPFRC plates was also investigated. Results show that UHPFRC plates significantly increased the maximum load capacity, ductility and mid span reinforcement strain of the strengthened RC beams comparing with reference beam failed in shear. Also, steel connectors used in reinforcement of UHPFRC plates prevented debonding failure mode. A three‐dimensional (3D) finite element model (FEM) of the tested beams was also developed to predict the behavior of these specimens strengthened in shear. The adhesive layer was simulated using cohesive surface model to consider the slippage between concrete surface and UHPFRC plates. Results of the FEM showed good agreement with experimental results, as they were able to predict the behavior of the beams with high accuracy. [ABSTRACT FROM AUTHOR]

In order to develop a calculation method for the ultimate flexural capacity of high strain‐hardening ultra‐high performance concrete (UHPC) T‐beams, four‐point loading tests on five specimens were carried out. The design parameters were the ratio and the strength of reinforcement. Based on the assumption of plane section, a linear regression analysis was carried out and the ultimate tensile strain of high strain‐hardening UHPC was obtained. The analysis results proved that the bond between reinforcement and UHPC is reliable and these two materials can maintain strain consistency before the reinforcement reaches its yield strain. A finite element model of the specimens was established using ANSYS and distributed reinforcement was added to simulate the behavior of UHPC after cracking. Considering the tensile contribution of the high strain‐hardening UHPC after cracking, the calculation method for flexural capacity of high strain‐hardening UHPC T‐beams was derived. The finite element simulation method and the theoretical formula calculation method proposed in this paper are in good agreement with the experimental values, and they can be applied for the theoretical analysis and the design of high strain‐hardening UHPC beams. The theoretical calculation method proposed in this paper is compared with calculation methods proposed by standards. The study shows that the proposed calculation method is accurate and generally applicable. [ABSTRACT FROM AUTHOR]

This computational investigation focused on numerical modeling of the shear behavior of ultra‐high‐performance concrete (UHPC) beams reinforced longitudinally with high‐strength rebars and ordinary‐strength steel (stirrups). Nonlinear three‐dimensional finite element model, using the concrete damaged plasticity model and material properties obtained from uniaxial compressive and tensile laboratory tests, was conducted to simulate UHPC concrete beams within a commercial finite element software package ABAQUS 6.13. This investigation included the effects of various parameters; shear span‐to‐effective depth ratio (a/d), volume fraction of steel fibers, Vf, longitudinal reinforcement ratio, ρ, and stirrups spacing, s, on shear behavior of UHPC beams. Numerical results compared with previously obtained experimental results in terms of shear force–midspan deflection and cracking‐propagation behaviors. The results showed that finite element analysis predicted the shear behavior of UHPC beams in good agreement with the experimental data and predicted the response of the beam with variation in various parameters with a good accuracy. [ABSTRACT FROM AUTHOR]

Rotation capacity of reinforced concrete ( RC) beams is a vital property for its relationships with moment redistribution, energy absorbability, and so on. Evaluation of the rotation capacity has been one of the classic and intractable problems in structural engineering over the past decades. The precise prediction about rotational behavior of a RC beam is the primary basis of quantifying its rotation capacity. In this paper a displacement-based finite layer element method considering the factors of flexural cracks, concrete crushing, and pre-and postyield behavior of bond is presented to predict the rotational behavior. In conclusion, it shows good agreement between simulation results, implemented by the proposed method, and the test results in the literature. [ABSTRACT FROM AUTHOR]

This paper presents a critical comparison of the existing code provisions for the shear strength of concrete beams. The comparison is based on the computerized filtering-out of the inevitable statistical bias from the available multivariate database on shear strength, on an examination of the predicted size effects on shear strength and their underlying hypotheses and on the results of recent high-fidelity numerical simulations of shear failure. In addition to examining the existing models, the present comparison also provides several key considerations for testing the scientific soundness of any model of shear failure in concrete beams, which is necessary for future revisions to the design code provisions. [ABSTRACT FROM AUTHOR]

The dynamic response of a cracked beam subjected to moving loads has been studied extensively in the past decades. However, very little is known about the dynamic impact factors and crack propagation when vehicles move along the cracked beam. It can be reasonably postulated that a crack extension may occur when the vehicle loads cross the cracked bridge at a high speed. As a result, the dynamic response will be enlarged significantly due to the flexural rigidity reduction induced by cracks, which may result in a dangerous effect on structures. To address this problem, a three-dimensional vehicle-bridge model was developed to investigate the dynamic response of cracked bridges with crack breathing. Crack breathing is simulated at the crack surface using contact elements. The modified crack closure method is adopted to calculate the stress intensity factors. The results showed that the impact factors for the damaged bridge under a moving load could be notably larger than those for the intact bridge, and could exceed the value specified in the AASHTO bridge design code. Meanwhile, crack propagation may occur when the vehicles move along the cracked bridge at a high speed. So, it is very necessary to limit the velocity and transverse position of the vehicles to avoid further damage to the cracked bridge. [ABSTRACT FROM AUTHOR]

This article presents an experimental programme on reinforced concrete beams retrofitted with steel angles and pre-stressed stainless steel ribbons to increase their flexural strength and ductility. Two different configurations of the steel ribbon were designed, and two companion specimens for each type considered were subjected to a four-point bending test to facilitate a direct comparison in the analysis of the effectiveness of the retrofitting technique. The influence of longitudinal steel angles and transverse stainless steel ribbons is analysed, and the concrete confinement due to stainless steel ribbons examined. The strengthened beams show remarkable increments in flexural strength and ductility with respect to the as-built beam. Moreover, a simple cross-sectional model was adopted to calculate the flexural strength; then sophisticated numerical tools were used to reproduce both the experimental load-displacement curve and crack pattern for each specimen. [ABSTRACT FROM AUTHOR]

Some experimental research studies have reported that longitudinal reinforcement in beams and columns exhibits larger strains inside the joint than at the joint periphery (defined as the intersection of the outer surfaces of beam and column). This may explain why several technical specifications and state-of-the-art programs recommend basing the design of beams and columns on internal force values larger than those at the joint periphery. These results and procedures are questionable and are investigated in this paper. The non-linear finite element analysis presented here for reinforced concrete frames under gravity and quasi-static monotonic lateral loads examines (i) the stress fields in reinforcement inside interior, exterior and roof exterior joints, and (ii) the load-carrying capacity of representative sub-frame models incorporating such joints. The results prove that it is actually safe, with respect to the joint load capacity, to base the design of longitudinal reinforcement in beams and columns on the internal force values at the joint periphery. This result also contributes to the recommendation to use real-size beam-column joint models in the analysis procedure. [ABSTRACT FROM AUTHOR]

The design shear resistance of an existing structure can be evaluated with analytical design procedures and numerical procedures provided by non-linear finite element analyses. The new fib Model Code 2010 proposes different calculation methods that fall into four different levels of approximation. As the level of approximation rises, so the complexity and the accuracy of the calculated shear resistance increases. Non-linear finite element analyses belong to the highest level of approximation, but although they are more and more becoming a customary tool in the daily design process, building codes do not provide guidance on how to perform these analyses. This paper describes non-linear finite element analyses performed on prestressed beams, which underwent shear failure during experimental loading, in order to assess and criticize the finite element approaches. The aim of this work is to propose guidelines for numerical simulations in order to reduce model and user factors. The results obtained from the non-linear finite element analyses have been compared with the analytical results using different levels of approximation. The design shear resistance obtained with the highest level of approximation, level IV, derived from non-linear finite element analyses, turned out to be higher than the design shear resistance obtained with analytical procedures (levels I/II/III). [ABSTRACT FROM AUTHOR]

The article lists topics within the journal including shear tests on continuous prestressed concrete beams, non-linear finite element analyses of large reinforced concrete structures and blast resistance characteristics of concrete.