Shear Strengthening Of RC Beams Research Articles

Shear strengthening of RC beams with NSM FRP. II: Assessment of strength models

The application of near-surface mounted (NSM) fiber-reinforced polymer (FRP) for shear strengthening of RC beams has attracted abundant research in the past few decades, and a number of strength models for predicting the contribution of NSM FRPs to the shear capacity of strengthened beam have been proposed. In the first of these two companion papers, a total of 12 strength models of NSM FRP shear strengthened RC beams collected from the existing literature have been comprehensively reviewed, while the present paper aims to provide an objective assessment of these models. To this end, the experimental results of 196 RC beams strengthened in shear with NSM FRP bars/strips are collected from the existing literature, as the database for the assessment. The comparisons between the experimental results and predictions by these strength models reveal that the existing strength models all fail to give accurate predictions. The reasons for the inaccurate predictions of these models are also analyzed.

An innovative technique of anchoring lacing bars with CFS sections for shear strengthening of RC beams

An innovative technique of anchoring lacing bars with CFS sections for shear strengthening of RC beams

Optimization of kenaf fibre reinforced polymer laminate for shear strengthening of RC beams using embedded connector

Kenaf fibre reinforced polymer (KFRP) laminate has gained its potentiality in shear strengthening of reinforced concrete beams recently, thus, method to obtain the minimal required dimension of KFRP shear strip is the utmost demand. The main aim of this research was to optimize the dimension of KFRP laminate for shear strengthening of RC beam. In experimental programme, high strength KFRP laminate and seven full scale RC beams were fabricated. The beams were shear strengthened using 7.5 mm thick and 20 mm, 30 mm and 35 mm widths of KFRP laminate, the dimensions of those shear strips were based on design strains of 0.007, 0.0045 and 0.004 respectively. Beams were also shear strengthened using CFRP laminates with similar widths of KFRP laminates for comparison. All beams were numerically analysed. Parametric study on design strain based on theoretical model was also conducted. Results showed that shear strengthened beam with 0.007 strain of KFRP laminate failed due to fracture of laminate. However, beams with laminate strains of 0.0045 and 0.004 did not show fracture or debonding of KFRP laminates, both beams had shown ductile flexural mode of failures with higher failure loads. In contrast, all CFRP laminate strengthened beams failed because of cover separation of laminates followed by shear. The failure loads of KFRP laminates strengthened beams were found to be higher as compared to those of CFRP laminates. The KFRP laminates were effectively enhanced shear capacity of strengthened beams without showing any premature failure even with the design strain of 0.0045, while, CFRP laminate showed premature cover separation failure with design strain of 0.002. Theoretical model showed that higher strength of concrete and length of laminate increased debonding or design strain of laminate. The numerical model predicted flexural and shear behaviour of shear strengthened beams. The flexural behaviour of strengthened beams based on numerical analysis were closely comparable with those of experimental findings. However, the model had limitation to predict local debonding failure of shear strip due to cracks and the effects of debonding on shear behaviour of strengthened beams.

Flexural and Shear Strengthening of RC Beams with Large Openings by Steel or CFRP Plates

Existence of transverse openings in the web of reinforced concrete beams is usually used to provide paths for required ducts and pipes which are necessary to accommodate essential services like water supply, sewage, air-conditioning, telephone and electricity. However providing an opening in the beam reduces its stiffness, which decreases the overall strength. The provision of openings through the beam depth, changes its simple mode of behavior to a more complex one depending on the size, shape and location of openings. Repair and strengthening of an existing structure may be essential in many cases such as increasing the stiffness of the beams due to making transverse openings in the web of beams after construction. An experimental test program of fourteen RC beams with large openings were strengthened by using additional layers of externally bonded steel plates or CFRP Plates with different techniques then tested by four-point bending test. The behaviors of the tested specimens were investigated with and without strengthening and compared to identify the effectiveness of each method and material of strengthening to increase the flexural and shear strength of beam with different opening location. The research shows that strengthening using CFRP Plates were more effective than using steel plates.

Flexural and shear strengthening of reinforced concrete beams with a hybrid CFRP solution

An experimental program was carried out for assessing the performance of a hybrid solution composed by CFRP systems for the simultaneous flexural and shear strengthening of RC beams. CFRP laminates, applied according to NSM technique, are used for the flexural strengthening, while U-shape CFRP discrete strips of wet lay-up sheet, applied according to the EBR technique, are adopted for the shear strengthening. An anchorage system was applied at the extremities of these CFRP strips in an attempt of avoiding their premature debonding. The experimental results showed the hybrid strengthening solution is very effective, 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. The performance of the hybrid CFRP configuration that included the anchorage system for the shear strengthening was significantly higher than the one assured by other shear strengthening solutions that were applied in similar RC beams and tested until failure using the same test system adopted in this experimental program. The predictive performance of the ACI formulations proposed for estimating the contribution of CFRP systems for the flexural and shear resistance of RC beams was appraised considering the obtained experimental results.

Experimental investigation of flexural and shear strengthening of RC beams using fiber-reinforced self-consolidating concrete jackets

The present study aims to investigate the efficiency of application of steel fiber-reinforced self-consolidating concrete (SFR-SCC) jackets for strengthening RC beams in flexure and shear. Accordingly, 10 beam specimens were constructed and categorized under two main groups. In the first group, the specimens were designed in a way that shear failure was dominant so that the effectiveness of SFR-SCC jacketing in shear strengthening could be evaluated. In contrast, specimens of the second group, designed with high amount of shear reinforcement, were strengthened with SFR-SCC jackets containing 2 GFRP rebars for the purpose of flexural strengthening. Parameters studied in this paper include the use of different steel fiber dosages, the effect of presence of shear reinforcement, utilization of GFRP rebars in the jackets, and behavior of specimens with different longitudinal reinforcement ratios. In the second group, failure mode of the strengthened specimens changed to flexure, while in the strengthened specimens reinforced with GFRP rebars, mode of failure changed to a combination of shear and compression.

An experimental approach for shear strengthening of RC beams using a proposed technique by embedded through-section FRP sheets

This article presents a new technique for enhancing the shear capacity of RC beams with FRP materials, which instead of bonding of FRP strips on the external face of element, involves perforating holes along the beam web, inserting FRP reinforcement inside these holes, and filling the holes with grout. Although according to technical literature, externally bonded and near-surface mounted FRP reinforcements are well known as effective solutions for increasing the shear capacity of RC elements, they are ill-suited for the cases where the concrete cover lacks sufficient bonding strength, and a debonding may allow the beam to fail before maximum capacity utilization. Furthermore, in the structures where the beam is connected to a floor, the FRP wrapping involves drilling holes in the floor to install the reinforcement, which creates shear vulnerability around the floor-beam contact area. Experimental results show that the beams reinforced with the proposed technique perform similar to or better than those with externally bonded FRP reinforcements. Also, the comparisons of the Applied Strengthening Material Index (ASMI) for specimens shows that the ratio of FRP shear contribution to the amount of FRP consumed is greater in the proposed technique than in the external bonding methods.

Shear Strengthening of RC Beams Using Polyester Rope

Shear Strengthening of RC Beams Using Polyester Rope

Shear strengthening of RC beams using near-surface mounted carbon fibre-reinforced polymers

ABSTRACTThis paper summarises the results of experimental work on reinforced concrete beams strengthened in shear using near-surface mounted carbon fibre-reinforced polymers (NSM-CFRP). Fourteen beams (150 × 200 × 1200 mm) in dimension, with insufficient shear reinforcement, were tested under four-point bending. The effects of side concrete cover depth, NSM-CFRP strip inclination angle and NSM-CFRP strip length on the behaviour of RC beams were studied. Six of the beams were cast with three different side concrete cover depths, 20, 30 and 40 mm, and strengthened in shear by NSM-CFRP, with inclination angles of 0° and 45°. Other beams with a side concrete cover depth of 30 mm were strengthened in shear by NSM-CFRP with different strip lengths, measured in terms of beam depth (full, 2/3, and 1/3) and inclinations of 0° and 45°. The results show that the concrete side cover depth enhances the behaviour of NSM-CFRP-strengthened beams. Beams with inclined NSM-CFRP strips experienced higher ultimate strengths than those with vertical NSM-CFRP. It was found that ultimate strength increases with longer strip length.

Applications of bolted steel plates to shear strengthening of RC beams

Many reinforced concrete beams have been found deficiencies in shear due to lack of shear reinforcement. Few researches have been done to investigate shear strengthening of low concrete strength of RC beams using bolted steel plates. This paper presents experimental results on the behaviour of RC beams strengthening using full steel plates along the shear span fixed with bolts. Nine RC beams having dimension of 150x200x1500mm were tested to failure on simply supports with four point loadings setup. The beams were reinforced with tension rebars area of 289.8 mm2 (2D10+1D13) and transvers reinforcement of Ø6-125. Two dial gauges were installed at the beam middle span to measure beam deflection during the test. The results show that the applications of steel plate and bolts as external reinforcement increase beam shear capacity, stiffness and delay the occurrence of first diagonal cracks. Beams stregnthened with U-shape plates gave better performances than the beams with two pieces of L-shape plates due to better achorages.

Embedded Connector in Severe Optimization of Steel Plate for Shear Strengthening of RC Beam: Experimental and Numerical Investigations

Environmental impact has become one of the major factors taken into consideration for recent civil engineering studies and projects. Thus, researchers have been concentrating on shear strengthening of existing reinforced concrete structure as an upgrade method instead of demolishing and reconstructing. In general, shear strengthening of RC beams using externally bonded steel plate has gained huge popularity. However, premature debonding of plates is the main drawback of the system, which could be mitigated using embedded connector; thus, the dimension of steel plate could be reduced significantly. Furthermore, numerical analysis on shear strengthening of beams using embedded connector would provide a great insight on the structural behavior. The aim of this research is to severely reduce the dimension of the steel plate using embedded connector for shear strengthening of RC beams and to investigate the performances of optimized shear-strengthened beams through experimental and numerical investigations. The results showed that the dimension of plate was reduced without debonding of the plate if the beam was designed for shear strengthening with the consideration of yield strength of steel plate and shear link. Experimental results showed a maximum increase in failure of 24%. The numerical results predicted accurately the structural performance of beams. The embedded connector had a great effect in deferring and minimizing the debonding failure and accordingly increasing the maximum load of shear failure between 14.5% and 24% compared to control beam.

Flexural and Shear strengthening of RC beams with NSM technique-manually made CFRP bars

In this paper, the efficiency of NSM method for both flexural and shear strengthening of RC beams were examined by applying an innovative manually made CFRP bar (MMFRP) as an alternative reinforcement composite material through experimental and numerical investigation. Experimental program was consisted of three inverted T-section RC flexural-dominated beams and three rectangular section RC shear-dominated beams with parameters of the length and anchoring of MMFRP bars and their inclination to the longitudinal axis of the beams. The structural performance of the tested beams and the Finite Element (FE) modeling approach including modes of failure, load-deflection response and ultimate load capacity are presented and discussed. Test results indicated that using proposed MMFRP bars significantly improved the flexural resistance and shear capacity of deficient concrete beams. Furthermore reduction of the crack width and increase in the quantity and propagation of new cracks was observed in strengthened beams compared to control beam.

State of research on shear strengthening of RC beams with FRCM composites

This paper summarizes the state of research on the topic of shear strengthening of RC beams using externally bonded FRCM composites. In the first part of this paper, a detailed bibliographical review of the literature on the shear strengthening of RC beams using FRCM composites is carried out, and a database of experimental tests is developed. Analysis of the database shows that FRCM composites are able to increase the shear strength of RC beams. The effectiveness of the strengthening system appears to be influenced by parameters including the wrapping configuration, matrix compressive strength relative to the concrete compressive strength, and axial rigidity of the fibers. Different failure modes have been reported, including fracture of the fibers, detachment of the FRCM jacket (with or without concrete attached), and slippage of the fibers through the mortar. A possible interaction between the internal transverse steel reinforcement and the FRCM system has also been observed. In the second part of this paper, four design models proposed to predict the contribution of the FRCM composite to the shear strength of RC beams are assessed using the database developed. Results show that the use of the properties of the FRCM composite in Models 3 and 4 instead of the fiber mechanical characteristics does not significantly increase the accuracy of the models. A simple formulation such as that proposed by Model 1, based on the bare fiber properties, is found to be more accurate for beams with or without composite detachment.

Experimental investigation of the use of CFRP grid for shear strengthening of RC beams

Experimental investigation of the use of CFRP grid for shear strengthening of RC beams

Shear strengthening of RC beams with NSM CFRP laminates: Experimental research and analytical formulation

The effectiveness of the NSM technique with CFRP laminates for the shear strengthening of RC beams with a certain percentage of steel stirrups was assessed by an extensive experimental research. In this context, the influence of the following parameters was investigated: concrete strength; percentage of existing steel stirrups; percentage and inclination of the CFRP laminates; existence of cracks when the RC beams are shear strengthened with NSM CFRP laminates. The results show that the higher is the concrete strength class the larger is the effectiveness of the NSM technique. The effectiveness of the CFRP laminates was higher in the beams with the lower percentage of steel stirrups. Inclined laminates were more effective than vertical laminates and the shear resistance of the beams has increased with the percentage of laminates. Pre-cracked RC beams shear strengthened with NSM CFRP laminates have presented a load carrying capacity similar to that of the homologous beams that were uncracked when strengthened. Taking the results obtained in the experimental research, an analytical formulation to predict the contribution of the possible distinct NSM shear strengthening configurations for the shear resistance of RC beams was developed. This analytical formulation is presented and its predictive performance is assessed.

Shear strengthening of RC beams using innovative manually made NSM FRP bars

This study evaluates the effectiveness of a Near Surface Mounted (NSM) technique using innovative manually made FRP rods (MMFRPs) for shear strengthening of RC beams. To delay the onset of MMFRP rod debonding, a new anchorage is also developed and tested. This paper reports the results of a series of tests on simply supported rectangular RC beams, strengthened in shear with MMFRP rods with or without the proposed anchors. The load–deflection response of all test beams is presented, in addition to selected strain measurements. Performance and the failure modes of the test beams are studied and discussed. The proposed MMFRP rods and end anchorage enhanced the shear capacity of the beams between 25% and 48% over the control specimen. Furthermore, the proposed end anchorage of MMFRP rods significantly enhanced the ductility of the test specimens.

Shear Strengthening of RC Beams Using Sprayed Glass Fiber Reinforced Polymer

The effectiveness of externally bonded sprayed glass fiber reinforced polymer (Sprayed GFRP) in shear strengthening of RC beams under quasi-static loading is investigated. Different techniques were utilized to enhance the bond between concrete and Sprayed GFRP, involving the use of through bolts and nuts paired with concrete surface preparation through sandblasting and through the use of a pneumatic chisel prior to Sprayed GFRP application. It was found that roughening the concrete surface using a pneumatic chisel and using through bolts and nuts were the most effective techniques. Also, Sprayed GFRP applied on 3 sides (U-shaped) was found to be more effective than 2-sided Sprayed GFRP in shear strengthening. Sprayed GFRP increased the shear load-carrying capacity and energy absorption capacities of RC beams. It was found that the load-carrying capacity of strengthened RC beams was related to an effective strain of applied Sprayed GFRP. This strain was related to Sprayed GFRP configuration and the technique used to enhance the concrete-FRP bond. Finally, an equation was proposed to calculate the contribution of Sprayed GFRP in the shear strength of an RC beam.

Efficacy of CFRP configurations for shear of RC beams: experimental and NLFE

This paper presents the results of an investigation on shear strengthening of RC beams externally reinforced with CFRP composite. A total of six full-scale beams of four CFRP strengthened and two unstrengthened were tested in the absence of internal stirrups in the shear span. The strengthening configurations contained two styles: discrete uniformly spaced strips and customized wide strips over B-regions. The composite systems provided an increase in ultimate strength as compared to the unstrengthened beams. Among the three layouts that had the same area of CFRP, the highest contribution was provided by the customized layout that targeted the B-regions. A comparative study of the experimental results with published empirical equations was conducted in order to evaluate the assumed effective strains. The empirical equations were found to be unconservative. Nonlinear finite element (NLFE) models were developed for the beams. The models agreed with test results that targeting the Bregion was more effective than distributing the same CFRP area in a discrete strip style over shear spans. Moreover, the numerical models predicted the contribution of different configurations better than the empirical equations.

Shear Strengthening of RC Beams with EB FRP: Influencing Factors and Conceptual Debonding Model

This paper deals with the shear strengthening of RC beams using externally bonded (EB) fiber-reinforced polymers (FRP). Current code provisions and design guidelines related to shear strengthening of RC beams with FRP are discussed in this paper. The findings of research studies, including recent work, have been collected and analyzed. The parameters that have the greatest influence on the shear behavior of RC members strengthened with EB FRP and the role of these parameters in current design codes are reviewed. This study reveals that the effect of transverse steel on the shear contribution of FRP is important and yet is not considered by any existing codes or guidelines. Therefore, a new design method is proposed to consider the effect of transverse steel in addition to other influencing factors on the shear contribution of FRP ( Vf ) . Separate design equations are proposed for U-wrap and side-bonded FRP configurations. The accuracy of the proposed equations has been verified by predicting the shear st...

Shear strengthening of RC beams with textile reinforced concrete (TRC) plate

Carbon–epoxy composite materials are of considerable interest for reinforcement, but they need to be improved and have constraints, particularly in terms of cost and criteria of sustainable development. Alternative materials like textile reinforced concrete (TRC) should be seriously considered as substitutes for traditional composite materials. This experimental study focuses on the mechanical feasibility of this type of solutions by comparing them with traditional solutions such as CFRP. The first comparative results are promising in terms of strength and stiffness. It can be established that, quantitatively, the materials have very similar behaviours, especially in the final stage. Finally, the Ritter–Mörsch truss model can be used with sufficient accuracy for the evaluation of the tensile strength, by considering a non-uniform stress distribution along the shear cracks that leads to failure.