Shear Reinforcement In Concrete Beams Research Articles

Shear Reinforcement of Concrete Beams Using Iraqi Bamboo

Steel rebars require significant energy to produce and are prone to corrosion when exposed to ambient air. Therefore, Iraqi bamboo replaces steel stirrups and steel rebars in this research. Five reinforced concrete beams are tested using four-point load testing. The first beam was cast without stirrups to achieve shear failure and is labeled a control specimen. Three other beams had Iraqi bamboo instead of steel at the critical sections. The last beam had steel stirrups spaced at a distance half of the effective depth of the beam. It is found that the Iraqi bamboo can increase the load-carrying capacity of the beam by up to 15% if compared with the beam with no stirrups. Also, the ductility of the beam has increased by 17%. However, the maximum load-carrying capacity of the steel stirrup beam was larger than that of the bamboo stirrups by at least 21%. The main reason is the spacing of the stirrups, which is the main factor influencing the beams' behavior prone to shear failure.

A novel design model for predicting the shear resistance of reinforced concrete beams strengthened with EBR-CFRP systems

Shear resistance prediction of reinforced concrete (RC) beams strengthened with externally bonded reinforcements (EBR) is a challenging task due to the complex nature of shear resisting mechanisms and their intricate interaction. Existing design models often overlook these dependencies, leading to significant variations in prediction accuracy. In this paper, a design model is proposed by integrating the most relevant shear resisting mechanisms based on the evidence demonstrated by a large database of experimental results from RC beams shear strengthened with wet layup carbon fibre reinforced (CFRP) sheets applied according to the EBR technique. The developed approach integrates the simplified modified compression field theory (SMCFT) with a regression-based model. A global sensitivity analysis was conducted according to which closed form equations were derived to obtain the tensile stress factor in cracked concrete and the inclination angle of the critical diagonal crack. A reliability analysis is carried out, and resistance reduction factors are achieved for different levels of reliability index. The database, composed of 284 RC beams shear strengthened with EBR-CFRP technique, is utilized to validate the proposed model, and compare its performance against some well-established existing design models. The results show that the proposed model, with an adequate framework for its use on design practice, outperforms the other considered models.

Experimental study and analysis of RC beams shear strengthened with FRP/SMA composites

In practice, the prestressing is difficult to apply to achieve shear reinforcement of reinforced concrete (RC) beams due to the limited operating space used for installing mechanical tensioning equipment. So, how to efficiently introduce prestressing into RC beams is a practical problem. In this study, the authors utilized the recovery effect of shape memory alloys (SMA) wires to successfully introduce prestressing into RC beams and externally bonded with fiber reinforced polymer (FRP) sheets, forming a FRP/SMA composite shear reinforcement technology. After that, shear behavior of RC beams strengthened with FRP/SMA composites was investigated by a series of experiments. In order to further illustrate the effect of FRP/SMA composite shear reinforcement on RC beams, other reinforcement materials, such as SMA wires and FRP sheets, have also been separately applied in shear reinforcement experiments. Moreover, carbon fiber reinforced polymer (CFRP) and basalt fiber reinforced polymer (BFRP) are respectively applied to prepare FRP/SMA composites. For beams strengthened with FRP/SMA composites, the prestressing generated by the recovery effect of SMA wires can effectively suppress the formation of diagonal cracks in RC beams. The ultimate load and the corresponding displacement of strengthened beams significantly increased due to the constraint effect of FRP on the propagation of shear cracks. The shear capacity of CFRP/SMA composites strengthening beams was higher than that of BFRP/SMA composites strengthening beams, as CFRP/SMA composites better limited the propagation of cracks. Based on the test results, an analytical model has been proposed to predict the shear capacity of strengthened beams, and its effectiveness has been confirmed through comparison with experimental results.

Investigation of the use of textile carbon yarns as sustainable shear reinforcement in concrete beams

In recent years, textile reinforcement has been widely researched and used in reinforced concrete beams, slabs, and thin plates. However, the design for bending is completely different from that of the shear case. The use of textile carbon yarns in place of or in addition to traditional steel stirrups to reinforce the shear has been investigated. Eight beams with dimensions of 200 mm × 300 mm × 1500 mm were used in this investigation. These beams were tested in shear under four load points. Two specimens were used with and without steel stirrups as reference specimens, while the other six beams used textile carbon yarns instead of steel stirrups. The variables of this study were the length of overlap, which was 30%, 60%, and 100%, the spacing was 90 mm and 130 mm, while inclination was 45° and 90°, and bonding with or without steel fibers. The results showed that using 100% overlap length, 90 mm spacing, a 45° angle, and adding steel fibers increased the shear capacity, increased the deflection, and made the cracking behavior better.

Alternatives to Enhance the Structural Performance of PET-Modified Reinforced Concrete Beams

Numerous studies investigated the possibility of incorporating plastic wastes in concrete mixtures, thus contributing to efficient management and sustainable development of the construction industry. This paper investigates the possibility of reducing the water-to-cement ratio and/or incorporating steel fibers or polymeric latexes to mitigate the drop in structural properties of reinforced concrete (RC) beams containing polyethylene terephthalate (PET) additions. The PET was derived from waste plastic bottles that were shredded into small pieces and added during concrete batching at 1.5% to 4.5%, by total volume. Test results showed that the concrete plain and structural properties degrade with PET additions, given their lightweight nature and poor characteristic strength compared to aggregate particles. The reduction of w/c from 0.55 to 0.46 proved efficient to refine the matrix porosity and reinstate the shear and flexural strengths of RC beams. Moreso, the incorporation of 0.8% steel fibers (by volume) or 15% styrene-butadiene rubber latexes (by mixing water) were efficient to enhance the bridging phenomenon and reduce the propagation of cracks during beam testing.

Shear Strengthening of High Strength Concrete Beams That Contain Hooked-End Steel Fiber

Steel fiber has been used successfully in concrete mixtures to control volumetric changes, including shrinkage. However, the feasibility of the use of steel fiber has been restricted to nonstructural construction, such as ‘slab on ground’. Recently, researchers have attempted to expand the applications of steel fiber to replace structural reinforcement (rebar) and have shown promising results in its substitution for shear reinforcement. Few studies have been conducted to ensure the feasibility of using steel fiber in structural components, however. This experimental study was designed to investigate the shear performance of steel fiber-reinforced concrete beams using the tensile strength of steel fiber and the shear span-to-depth ratio as variables. The experimental results indicate that the tensile strength of steel fiber significantly affects the shear strength of steel fiber-reinforced concrete beams, regardless of the shear span-to-depth ratio, and that steel fiber can play a role in shear reinforcement of concrete beams.

Characteristics of Restrained Drying Shrinkage on Arched Steel Fiber-Reinforced Concrete

The volumetric changes of concrete, including drying shrinkage, are effectively controlled in steel fiber-reinforced concrete (SFRC) mixtures due to the action of the included steel fiber. The current code provision in ANSI/SDI C-2017 allows a minimum steel fiber content of 0.2% of the volume fraction of concrete to control drying shrinkage and to manage cracking in the slab. Limited research has addressed replacing the shear reinforcement in concrete beams with steel fiber. In this study, we used newly developed arched steel fiber to evaluate shrinkage characteristics, including free-drying shrinkage and restrained drying shrinkage, of SFRC and scaled-down deck slab elements. We compared the measured drying shrinkage test results to predicted results obtained from models found in the literature. We confirmed that, overall, the number, width, and length of cracks were reduced significantly at the surface of SFRC slabs when arched steel fiber at 0.2% volume fraction was included in the mixture.

Experimental study on the shear behavior of RC beams reinforced by natural composite materials (flax fibers)

The context of this study is the shear strengthening analysis of a concrete beam using a new natural material. This paper presents the experimental results of the shear reinforcement of concrete beams with a flax fiber reinforced polymer (FFRP) using the External Bonding method (EB) and the Near Surface Mounted method (NSM). A total of 16 beams were tested with three point bending tests. The beams had rectangular sections and a 2-meter span and a T sections with a 2.5 m span. The following parameters were investigated: (i) the percentage of flax reinforcement (continuous vs non continuous), (ii) the percentage of transversal steel (stirrups), (iii) the method of reinforcement (EB vs NSM), (iv) and the interaction between the FFRP and the stirrups.The results obtained showed that the ultimate load increased by 10% to 35% for these reinforced beams; however, this type of reinforcement did not contribute to a modification of the type of failure or the behavior of post failure. The results also showed that the NSM method is more efficient than the EB method. In addition, the presence of transversal reinforcement reduces the contribution of flax fibers in the shear resistance of the beam. Finally, the experimental results obtained are compared succefully to different design code equations.

Properties of Steel Fiber Reinforced Concrete Using Either Industrial or Recycled Fibers from Waste Tires

Currently, more than 2.5 million tires are discarded each year in Bogota, Colombia, and 1.2 million of them are not properly disposed, producing a huge environmental problem. As a possible solution, previous studies have assessed the performance of steel fibers recovered from recycled post-consumer tires as reinforcement of concrete. However, engineers in Colombia are still uncertain to use this type of recycled material, since the concrete and the dosages used in reported studies were obtained mostly from different construction practices and materials in countries other than Colombia. The aim of this paper is to show and discuss the results of a research intended at evaluating the mechanical response of concrete reinforced using recycled steel fibers from waste tires in Bogota, Colombia. The testing campaign of the study comprised 45 axial compression and splitting tension tests on cylinders, and 14 bending tests on concrete slabs reinforced using nominal fiber dosages of 15, 30 and 60 kg/m3 of steel fibers obtained from used tires. For comparative purposes, the study included also the test on 21 cylinders and 12 beams made of concrete reinforced using industrial steel fibers, with the same nominal dosages used for the recycled steel fibers. Based on measured response, preliminary design equations are proposed to estimate the mechanical properties of concrete reinforced using recycled steel fibers. It is also checked whether the obtained results fulfil the requirements specified by ACI-318 and NSR-10 building codes when steel fibers are used as minimum shear reinforcement of concrete beams.

Experimental investigation and numerical analysis of RC beams shear strengthened with FRP/ECC composite layer

Five Reinforced Concrete (RC) beams strengthened with Basalt Fiber Reinforced Polymer (BFRP) grid in conjunction with Engineered Cementitious Composite (ECC) were tested along with one conventional RC beam for reference to investigate their performance improvement, particularly in shear capacity, due to strengthening. The test results highlighted that the failure modes of the tested beams were dominated with shear-compression failure in the shear/bending moment regions and concrete crushing in the compression part of the pure bending zone. A good bonding performance between the BFRP-ECC composite and concrete substrate was exhibited during the testing process, which can effectively suppress the propagation of diagonal cracks in the shear/bending moment regions. The shear capacity of strengthened RC beams was greatly improved with the increase of BFRP grid reinforcement ratio. Moreover, the reinforcement effect of this strengthening technique was much more effective with the increase of shear-span ratio of the tested RC beams. Furthermore, finite element analyses based on ABAQUS/Standard software were conducted to provide analytical estimations of the shear capacity of the strengthened RC beams. The analytical results revealed that the predicted values agree very well with the test data, which can effectively predict the shear capacity of RC beams strengthened with BFRP-ECC composite.

Shear Behavior of Concrete Beams Reinforced With A New Type of Glass Fiber Reinforced Polymer Reinforcement: Experimental Study.

The article presents experimental tests of a new type of composite bar that has been used as shear reinforcement for concrete beams. In the case of shearing concrete beams reinforced with steel stirrups, according to the theory of plasticity, the plastic deformation of stirrups and stress redistribution in stirrups cut by a diagonal crack are permitted. Tensile composite reinforcement is characterized by linear-elastic behavior throughout the entire strength range. The most popular type of shear reinforcement is closed frame stirrups, and this type of Fiber Reinforced Polymer (FRP) shear reinforcement was the subject of research by other authors. In the case of FRP stirrups, rupture occurs rapidly without the shear reinforcement being able to redistribute stress. An attempt was made to introduce a quasi-plastic character into the mechanisms transferring shear by appropriately shaping the shear reinforcement. Experimental material tests covered the determination of the strength and deformability of straight Glass Fiber Reinforced Polymer (GFRP) bars and GFRP headed bars. Experimental studies of shear reinforced beams with GFRP stirrups and GFRP headed bars were carried out. This allowed a direct comparison of the shear behavior of beams reinforced with standard GFRP stirrups and a new type of shear reinforcement: GFRP headed bars. Experimental studies demonstrated that GFRP headed bars could be used as shear reinforcement in concrete beams. Unlike GFRP stirrups, these bars allow stress redistribution in bars cut by a diagonal crack.

Time-dependent reliability analysis of RC beams shear and flexural strengthened with CFRP subjected to harsh environmental deteriorations

Time-dependent reliability analysis of existing reinforced concrete (RC) beams strengthened with externally bonded carbon fiber reinforced polymer (CFRP) wraps is conducted. Corrosion effect in terms of remaining cross sectional area of steel reinforcement is modelled as a non-stationary Gaussian process and the probability of failure is estimated as a solution to the first passage probability from the safe domain. Moreover, flexural and shear limit states are modeled in a series system formulation. It was found that the steel stirrup ratio strongly influenced the reliability of beams subject to harsh environments and in some cases beam may experience brittle fracture during its service life. Furthermore, it is found that the upper bound of the system probability of failure is significantly higher than its corresponding individual limit states due to correlation between flexural and shear failure modes.

Influence of Steel Fiber on the Shear Strength of a Concrete Beam

The shear failure in a concrete beam is a brittle type of failure. The addition of steel fibers in a plain concrete mix helps to bridge and restrict the cracks formed in the brittle concrete under applied loads, and enhances the ductility of the concrete. In this research an attempt was made to investigate the behavior and the ultimate shear strength of hooked end steel fiber reinforced concrete beams without traditional shear reinforcement. Four simply-supported reinforced concrete beams with a shear span-to-depth ratio of about 3.0 were tested under two-point loading up to failure. Steel fibers volumetric fractions that used were 0.0, 0.5, 0.75 and 1.0%. Test results indicated that using 1.0% volume fraction of hooked steel fiber led to exclude shear failure and enhanced the use of steel fibers as shear reinforcement in concrete beams. The results also showed that a concrete beam with hooked steel fiber provided higher post-flexural-cracking stiffness, an increase in the shear capacity and energy absorption and an increase in the maximum concrete and steel reinforcement strains.

NSM shear strengthening technique with CFRP laminates applied in high T cross section RC beams

Abstract The effectiveness of the Near Surface Mounted (NSM) technique with Carbon Fiber Reinforced Polymer (CFRP) laminates for the shear strengthening of relatively high T cross section (h = 600 mm) Reinforced Concrete (RC) beams was assessed by experimental research. Two inclinations of the laminates were tested (52° and 90°) and, for each one, two percentages of CFRP were adopted. The RC beams shear strengthened with NSM laminates had a percentage of steel stirrups of 0.09%. The experimental results showed that NSM shear strengthening technique with CFRP laminates is very effective in RC beams of relatively high cross section height, not only in terms of increasing the load carrying capacity of the beams, but also in assuring higher mobilization of the tensile capacity of the CFRP. Furthermore, inclined laminates were more effective than vertical laminates and the shear capacity of the beams increased with the percentage of laminates. Taking into account available experimental results obtained with the same test setup, but using RC beams of lower depth of T cross section (h = 400 mm), it can be concluded that the effectiveness of the NSM technique with CFRP laminates increase with the increase of the depth of the cross section. The formulations provided by Nanni et al. (2004) and Dias and Barros (2013) for the NSM shear strengthening technique predicted a CFRP contribution around 51% and 67%, respectively, of the experimentally registered values.

Effect of fiber dosage and prestress level on shear behavior of hybrid GFRP-steel reinforced concrete I-shape beams without stirrups

Abstract Corrosion of steel reinforcements embedded in concrete elements is generally known as one of the most common reasons that shorten the service life of the structures. The present study aims to contribute in overcoming this problem by replacing steel stirrups as shear reinforcement of concrete beams using a steel fiber reinforced self-compacting concrete (SFRSCC). In the present research the potential of SFRSCC for improving the shear resistance of the beams without stirrups is explored. In order to further reduce the risk of corrosion in this type of beams, a hybrid system of flexural reinforcement composed of a steel strand and GFRP rebars is applied and properly arranged in order to assure a relatively thick concrete cover for the steel reinforcement. The GFRP bars are placed with the minimum cover thickness for providing the maximum internal arm and, consequently, mobilizing efficiently their relatively high tensile strength. The effectiveness of applying different dosages of steel fibers and varying the prestress force to improve the shear behavior of the designed beam are evaluated. By considering the obtained experimental results, the predictive performance of a constitutive model (plastic-damage multidirectional fixed smeared crack model) implemented in a FEM-based computer program, as well as the one from three analytical formulations for estimating shear resistance of the developed beams were assessed. The FEM-based simulations have provided a good prediction of the deformational response and cracking behavior of the tested beams. All the analytical formulations demonstrated acceptable accuracy for design purposes, but the one proposed by CEB-FIP Modal Code 2010 predicts more conservative shear resistance.

Nonlinear finite element study on the improvement of shear capacity in reinforced concrete T-Section beams by an alternative diagonal shear reinforcement

In the study a new shear reinforcement configuration named as diagonal shear reinforcement (DSR) is proposed as an easily applicable, economical and alternative technique to improve the shear capacity and ductility of shear critical reinforced concrete (RC) beams under monotonic and cyclic loadings. For this objective a numerical nonlinear finite element (FE) study is performed by considering two tested beams with flexural and shear failure modes. These two tests results are first verified numerically then DSR is included to existing FE model to start a parametric study for highlighting the efficiency of proposed DSR shear reinforcement configuration.The numerical results demonstrate that there is a significant increase in shear and ductility capacity of RC beams when proposed DSR is included. Moreover, with an increase in diameter and yield strength of DSR, the shear capacity further improves and failure mechanism shifts from shear to flexure. Thus, more ductile behavior for shear critical RC beams is achieved by the proposed DSR reinforcement configuration.

Flexural and shear behaviour of concrete beams reinforced with bamboo

The performance of bamboo as reinforcement in concrete structures can be successful if safety limit conditions are considered. The aim of this paper is to evaluate the feasibility of bamboo strips application as a flexure and shear reinforcement in concrete beams. Culms from Dendrocalamus giganteus were split and employed as reinforcement using rectangular sections of 20 mm width × natural length of the bamboo. Experimental analysis of six simply supported bamboo-reinforced concrete beams subjected to two point loads was carried out up to collapse. The ultimate test loads for the different beams were compared to the loads predicted according to ACI 318 (steel reinforced concrete beams regulation). Finally, a recommendation based on the analysis of the results for the design of such beams is proposed.

An Appraisal of Steel Fibers as Minimum Shear Reinforcement in Concrete Beams

An Appraisal of Steel Fibers as Minimum Shear Reinforcement in Concrete Beams

Bond efficiency of EBR and EBROG methods in different flexural failure mechanisms of FRP strengthened RC beams

In recent years, using FRP sheets for strengthening and rehabilitation of reinforced concrete beams has been considered as an effective, convenient and practical method. Preventing surface debonding phenomenon is one of the issues facing the use of FRP sheets as external flexural and shear reinforcement of concrete beams. Premature debonding is caused by the lack of appropriate bonding between concrete surface and composite sheet. Externally Bonded Reinforcement (EBR) is a common method for mounting the sheet that uses conventional surface preparation. In addition, in recent years, Grooving method (GM) in its special form of Externally Bonded Reinforcement On Grooves (EBROG) has been proposed as an alternative to conventional method of surface preparation in EBR method. Although the capability of GM in preventing the premature debonding of FRP sheets from concrete substrate has been discussed in the literature, however, its efficiency compared to EBR technique in different flexural failure modes has not been investigated. In this paper, 12 reinforced concrete (RC) beams with dimension of 1000×140×120mm were strengthened with FRP sheets and were tested. Specimens with different tensile steel and FRP reinforcement ratios were designed in a way under which the EBR and EBROG methods can be compared in two failure mechanisms of concrete crushing and FRP sheet rupture after tensile steel yielding. The results clearly showed that using the method of grooving compared with surface preparation method leads to increased ultimate load carrying capacity and ductility, and absorbing the energy in the beams by preventing the premature debonding mechanism. The results also showed that the efficiency of grooving method compared to conventional surface preparation is more highlighted in the beams with FRP rupture mechanism.

A FEM-based model to predict the behaviour of RC beams shear strengthened according to the NSM technique

Experimental research has demonstrated the excellent performance of the near surface mounted (NSM) technique with carbon fibre reinforced polymer (CFRP) laminates for the shear strengthening of reinforced concrete (RC) beams. This paper presents a finite element analysis to evaluate the behaviour of RC beams shear strengthened with NSM CFRP laminates. To predict correctly the deformational and the cracking behaviour of RC elements failing in shear using a smeared crack approach, the strategy adopted to simulate the crack shear stress transfer is crucial. For this purpose, a strategy for modelling the fracture mode II was implemented in a smeared crack model already existing in the FEM-based computer program, FEMIX. This strategy is mainly based on a softening shear stress-shear strain diagram adopted for modelling the crack shear stress transfer.To assess the predictive performance of the developed model, the experimental tests carried out with a series of T cross section RC beams shear strengthened according to the NSM technique by using CFRP laminates were simulated. In this series of beams, three different percentages of CFRP laminates and, for each CFRP percentage, three inclinations for the laminates were tested: 90°, 60° and 45°. By using the properties obtained from the experimental program for the characterization of the relevant properties of the intervening materials, and deriving from inverse analysis the data for the crack shear softening diagram, the simulations carried out have fitted with high accuracy the deformational and cracking behaviour of the tested beams, as well as the strain fields in the reinforcements. The constitutive model is briefly described, and the simulations are presented and analyzed.