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This research systematically compares the effectiveness of Carbon Fiber-Reinforced Polymer (FRP) and Fabric-Reinforced Cementitious Matrix (FRCM) in shear strengthening of reinforced concrete (RC) deep beams featuring web openings. Through a comprehensive experimental program, six RC beams were subjected to shear tests, considering variations in the number of layers for both FRCM and FRP, employing a U-wrapping configuration. Recorded parameters include load-deflection curves, ultimate strength, cracking patterns, failure modes, and strains in steel bars, allowing a comprehensive comparison between strengthened and un-strengthened RC beams. The study compares observed shear strengths from experiments with shear capacities predicted by proposed models for RC beams strengthened with FRCM and FRP, following codes such as ACI 440.2R-17, CSA S806-12, Eurocode 2, and ACI 549.4R-20. Increasing layers enhanced shear strengths and post-elastic stiffness. The presence of substantial openings led to early shear cracks and reduced strength. CFRP improved shear strength by 13.99% (1-layer) and 18.12% (2-layer), while FRCM strengthened layers by 20.2% (1 layer) and 29.3% (2 layers). FRCM outperformed in strength and stiffness, while FRP excelled in ductility and concrete confinement. Experimental and calculated results varied based on ACI, CSA, and Eurocode, with ACI providing consistent and accurate results. CSA's calculation surpassed experiments, emphasizing its consideration of effective fabric design strain. [ABSTRACT FROM AUTHOR]

This study presents an experimental investigation on the contribution of carbon fiber-reinforced polymer (CFRP) sheets in shear-strengthened beams with different strengthening schemes. Three different reinforcement types and strengthening schemes are applied (U-shaped, U-shaped with additional anchorage and fully-wrapped). The strength contribution of FRP sheets, internal stirrups, and concrete are estimated based on experimental data. Two different anchoring strategies to prevent the FRP strengthening from debonding were also present, using horizontal strips of FRP and rebars on grooves on the web of the beams. The behavior of each of the beams is discussed in terms of loaddisplacement, failure mode, strains distribution, cracking pattern, and shear force contribution. The influence of the strengthening configuration and FRP anchorage on the FRP shear contribution and total shear resistance is discussed based on the experimental. The individual contribution of FRP, stirrups and concrete are estimated based on strain data from the tests. Finally, the experimental shear capacity is compared to the recommendations of ACI 440.2R, and fib Bulletins 14 and 90. [ABSTRACT FROM AUTHOR]

This paper presents the results of a study that investigates the mechanisms of shear resistance in reinforced concrete (RC) beams that are shear-strengthened with engineered cementitious composites (ECCs) and fiber-reinforced polymer (FRP). The ECC FRP utilizes ECC as the bonding agent between the FRP and concrete and the FRP as the high-strength reinforcement. The test program was divided into three groups: (1) 15 dog-bone shaped ECC FRP coupons; (2) 27 ECC FRP push-off blocks; and (3) two ECC FRP shear-strengthened RC beams 125 mm wide, 300 mm high, and 2,640 mm long. Groups 1 and 2 aimed at investigating the uniaxial tension and push-off behavior, respectively, by simulating the crack separation and sliding mechanisms. These mechanisms are fundamental to understanding the shear resistance of the ECC FRP and are characterized by the applicable tensile stress–strain and shear stress–sliding laws. The embedded FRP mesh in the ECC FRP composites significantly enhances the crack sliding that is required for shear strength development, with a minimal impact on the tensile and shear strengths. In addition, the precrack width reduced the shear strength of the ECC FRP. Group 3 aimed to investigate the shear behavior of the ECC FRP beams. The crack width and sliding were monitored during loading, which provides insights into the shear contributions from the concrete, steel stirrups, and ECC FRP. The results reveal a major shift in the shear capacity contribution from the concrete to the ECC FRP in the strengthened beams, which led to a substantial shear improvement. The contributions of the ECC FRP to shear resistance by crack separation and sliding were comparable throughout the loading process. The FRP meshes in the ECC FRP composites effectively limited deformation, maintained structural integrity, and redistributed the shear capacity from the ECC FRP to concrete. [ABSTRACT FROM AUTHOR]

AbstractThis paper showcases shear testing conducted on seven reinforced concrete deep beams featuring square openings, aimed at demonstrating the efficacy of a shear strengthening approach utilizing textile-reinforced concrete (TRC). This experimental program researches two types of openings of 150 × 150 mm and 200 × 200 mm at the centre of the shear spans. The solid beam undergoes testing for comparison with both the unstrengthened and strengthened beams containing openings. The study evaluates the effectiveness of TRC through a comparison of load-displacement curves, cracking patterns, and strains in reinforcements between the strengthened and un-strengthened beams. The experimental results indicate that the TRC strengthening technique effectively boosts the shear-carrying capacity of beams. Examination of the tested beams reveals a significant enhancement in stiffness at the point of maximum force, with improvements ranging from 22% to 86%, depending on the opening size and the number of reinforced textile layers. Rupture in TRC and crushing in the concrete strut are observed in the strengthened beams, whereas the un-strengthened beams show severe crushing in concrete at failure. The test results are compared with calculations based on code provisions, revealing that the prediction model consistently yields values 11 to 44% higher than the experimental results. [ABSTRACT FROM AUTHOR]

The hybridisation of fibre-reinforced polymers (FRPs), particularly with the combination of natural and synthetic fibres, is a prominent option for their development. In the context of the construction industry, there is a notable gap in research on the use of jute and glass fibres for the strengthening of concrete structures. This paper presents comprehensive experimental results from tests on seven reinforced concrete (RC) beams strengthened for shear using synthetic, natural, and hybrid jute–glass FRP composites. The beams were reinforced using the externally bonded reinforcement (EBR) technique with U-wrap bonding. A beam without any strengthening was tested and set as a reference for the other beams. Two beams were tested with synthetic FRP shear strengthenings, one with carbon fibre-reinforced polymer (CFRP) and another with glass fibre-reinforced polymer (GFRP). The remaining tests were on RC beams strengthened with natural jute fibre-reinforced polymer (JFRP) and hybrid jute–glass FRP. The paper discusses the experimental behaviour of the tested beams in terms of vertical displacements, crack widths, and strains on steel bars, concrete, and FRP. The experimental strengths are also compared with theoretical estimates obtained using ACI 440.2R and fib Bulletin 90. The tests confirm the effectiveness of natural jute FRP and jute–glass hybrid FRP as an option for the shear strengthening of reinforced concrete beams. [ABSTRACT FROM AUTHOR]

This paper presents an experimental investigation of the use of composite polymer mortar (CPM) and steel strands wire mesh (SSWM) to strengthen reinforced concrete (RC) beams in shear. In order to maximize the shear resistance of the steel strands, a new type of anchor device called wedge‐shaped steel plate hoops (WSSPHs) was developed. And the study aimed to examine the effect of shear‐to‐span ratio and prestressing level on the mechanical properties of the beams. A total of nine beams were constructed and tested under four‐point bending monotonic load, comprising three control beams and six strengthened beams. The study analyzed the damage modes, load‐deflection curves, strength, stiffness, and ductility of the beams. The test results indicated that (1) the mechanical properties of the strengthened beams were improved, with the shear capacity improving by 38.47%–71.37% after strengthening. (2) It was observed that SSWM could be utilized more effectively in high shear‐to‐span ratio beams among the strengthened beams with the same prestressing level. (3) Additionally, the larger prestressing level was found to change the design damage mode of the test beams, with RB‐2.5‐0.5 failing in bending. Finally, a model was proposed to predict the shear capacity of the test beams based on the specification GB 50011‐2010. The model considered the effect of the initial prestressing of the steel strands. [ABSTRACT FROM AUTHOR]

This research studies shear strengthening performance for Normal Concrete (NC) beams employing Engineered Cementitious Composite (ECC) reinforced with Galvanized Welded Wire Mesh (GWWM) in conjunction with/without a prestressing system. Six full‐scale Reinforced Concrete (RC) beams were experimented under static monotonic loading at critical shear span zone up to collapse. The investigated factors were: the type and technique of strengthening, materials used for strengthening, and size and configuration of shear reinforcement. Two techniques were introduced: ECC layer reinforced with GWWM and pretensioned steel bars recovered by ECC with one GWWM. GWWM with and without pretensioned steel bars were delivered as shear reinforcement for strengthening. Vertical and inclined steel bars were the two configurations selected for the prestressing technique for suppressing shear stress. The study was discussed through the experimented beams' crack load and pattern, collapse mode, elastic stiffness, absorbed energy, initial cracking load, and ultimate load, along with the corresponding defection. Experimental results showed that both exploited techniques could govern crack patterns, enhance the failure mode, and upgrade ultimate loading capacity up to 52%. Finite element models were built up, simulating those strengthened with an ECC covering layer augmented with GWWM extracting a model with an error of about 3%. [ABSTRACT FROM AUTHOR]

This paper presents an experimental shear test performed to investigate the web‐shear capacity of composite hollow‐core slabs (HCS) with cast‐in‐place (CIP) concrete. Five HCS specimens are fabricated, and the presence of a topping slab and number of cores strengthened by core‐filling concrete are set as key test variables. The shear force–displacement responses of the specimens, patterns of cracks occurring in the HCS and filled cores, strain behavior of stirrups, and composite action between the HCS and CIP concrete are measured and analyzed comprehensively. In addition, the web‐shear capacity of the composite HCS with CIP concrete is calculated based on elasticity theory and the transformed area method, in which the residual stress ratio factor is introduced to reflect the shear contribution of the core‐filling concrete after its shear cracking. Moreover, a practical equation is proposed to allow structural engineers to easily perform the shear‐strengthening design of HCS via the core‐filling method. The detailed model and the simplified equation accurately evaluate the web‐shear capacities of the HCS specimens. [ABSTRACT FROM AUTHOR]

Predicting the shear resistance of reinforced concrete (RC) beams strengthened with externally bonded reinforcement using carbon fiber–reinforced polymer (CFRP) materials poses a significant challenge due to the complex nonlinear relationship with beam features and the inherent randomness in shear failure events, driven by their brittle nature. This paper proposes a model employing a multiobjective optimization technique that both, enhances the accuracy and ensures unbiased predictions. To highlight the achieved improvement, a comparison is made between the performance of the proposed model and a series of well-established models in the literature. The proposed model presents superior predictive performance and a smaller coefficient of variation in the model error distribution than the models in the literature. In addition, it exhibits unbiased predictions, highlighting the advantages of incorporating multiobjective optimization. Furthermore, a modified demerit point classification is introduced and applied to all models, highlighting the superiority of the proposed model in producing more reliable and cost-effective predictions. [ABSTRACT FROM AUTHOR]

The potential for recovering the shear capacity of heat-damaged beams using carbon-fibre-reinforced polymer (CFRP) ropes was investigated using 12 concrete beams (150 × 250 × 1450 mm3) with shear reinforcement deficiency. Six beams were heated for 2 h at a temperature of 400°C; the others were not heated. All the beams were retrofitted with near-surface mounted CFRP ropes as external U-shaped stirrups, inserted in vertical holes (embedded through reinforcement) or implemented as a hybrid system of both. Lateral dowels were implanted in concrete along with schemes involving U-shaped stirrups to improve resistance against cover separation and shear failure, respectively. The mechanical behaviour of the beams was evaluated under three-point loading, with data collected and analysed to characterise the load–deflection relationships. Cracking and failure modes were analysed. For the heat-damaged beams, the adopted schemes restored load capacity and improved toughness and ductility, but not flexural stiffness. Moreover, implementing ropes as U-shaped external stirrups, terminating 20 mm below the top surface of the beams, helped avert side-cover separation, yet resulted in horizontal shear failure at the level of the upper concrete cover of the damaged beams. The residual strain induced in the U-shaped external stirrups was 14–40%, which is compatible with those reported in other works adopting similar repair methodologies. [ABSTRACT FROM AUTHOR]

A novel cost-effective secondary hardening ultrahigh-strength steel, strengthened by the co-precipitation of M2C and NiAl, was developed. The present study systematically investigated the co-precipitation evolution, austenite reversion, and mechanisms of strengthening and toughening at different ageing temperatures. As the ageing temperature increased, the quenched microstructure underwent various transformations, including precipitation and dissolution of cementite, nucleation and coarsening of M2C and NiAl nanoparticles, as well as reversion of austenite. At ageing temperatures of 427 °C and 454 °C, a small amount of cementite was present in the martensite matrix, and M2C and NiAl precipitates started to form, resulting in low strength and poor toughness. At 482 °C, the peak-ageing stage was reached, achieving a maximum yield strength of 1875 ± 4 MPa and an ultimate tensile strength of 2185 ± 3 MPa. This strength is primarily attributed to shear strengthening of NiAl particles and Orowan strengthening of M2C carbides. Additionally, the complete dissolution of cementite at this stage improved toughness. As the ageing temperature increased to 510 °C and 538 °C, the strength decreased due to coarsening of M2C, while the toughness improved as a result of film austenite reversion and enhanced dislocations bypassing around the M2C carbides.

I-shaped concrete girders are widely used in precast bridge and roof construction, making them a common structural component in existing infrastructure. Despite well-established strengthening techniques using various innovative materials, such as externally bonded carbon fibre reinforced polymer (CFRP) reinforcement, the shear strengthening of an I-shaped concrete girder is not straightforward. Several research studies have shown that externally bonded CFRP reinforcement might exhibit early debonding at the concave corners of the I-shape, resulting in a marginal increase in shear capacity. This research study aims to assess the performance of two different CFRP shear strengthening strategies for I-shaped concrete cross-sections. In the first strategy, CFRP was bonded along the I-shape of the cross-section with the provision of additional anchorage. In the second strategy, the I-shape was transformed into a rectangular shape by using in-fill blocks over which the CFRP was bonded in a U-configuration. In addition to the strengthening strategies, the investigated parameters included two different materials for the in-fill blocks (conventional and aerated concrete) and two different anchoring schemes (bolted steel plate anchor and CFRP spike anchor). To avoid testing on large-scale girders, a new test methodology has been implemented on concrete I-sections. The test results demonstrate the feasibility of comparing different shear strengthening configurations dedicated to I-sections. Among other findings, the results showed that the local transformation of the I-shape to an equivalent rectangular shape could be a viable solution, resulting in shear strength enhancement of 12% to 53% without and with the anchorages, respectively. [ABSTRACT FROM AUTHOR]

The aversion of sudden shear failure in reinforced concrete (RC) beams and structures requires effective strengthening methods. This study investigated the efficacy of precast ultra-high-performance fiber-reinforced concrete (UHPFRC) panels for shear strengthening of RC beams. The focus was on the effect of concrete surface preparation on strengthening. The grooving method (GM), specifically the externally bonded reinforcement on grooves (EBROG) technique, has been proposed as an alternative to the EBR method. Experimental results from four-point loading tests on five RC beams revealed that the EBROG method significantly increased the load-carrying capacity and energy dissipation over that of the EBR method. Optimized groove classes and appropriate groove angles further improved its performance, transitioning failure modes and debonding mechanisms. The EBROG method increased the beam ultimate load 1.78-fold and energy dissipation 11.36-fold compared to the control specimens. The failure modes transitioned from shear to flexure-shear, and the debonding modes shifted from surface to deep debonding. An analytical approach is developed to predict the shear capacity, incorporating panel properties and installation methods. This research underscores the potential of UHPFRC panels and the EBROG technique for effective shear strengthening of RC structures.

This study investigates the behavior of deep reinforced concrete beams with openings strengthened using galvanized corrugated steel sheets (GCSS) and galvanized flat steel sheets (GFSS). An experimental program was conducted on ten deep beam specimens with different opening configurations, strengthened by externally bonded GCSS and GFSS around the openings. The key test parameters are different types of galvanized steel sheets (corrugated and flat) and different opening configurations (circular and square) with different opening sizes. It is found that the application of galvanized steel alters the mode of failure of the strengthened beams compared to the unstrengthened beam which failed due to premature shear failure. The deep beams strengthened with galvanized steel sheets exhibited higher initial stiffness, energy absorption capacity, and ultimate loads compared to the control beam. Finite element modeling (FEM) using ABAQUS software was performed to simulate their experimental behavior and the prediction accuracy is examined against the test results. A parametric study using the validated FEM is carried out to examine the influence of the thickness of the galvanized plates and opening size ratio on the shear strength of the deep beams. The findings reveal that shear strength increases with the increase of the plate thickness and an opening ratio of 0.33 is recommended for practical applications of deep beams strengthened with galvanized steel sheets.

This paper presents an experimental investigation of the shear improvement of defected reinforced concrete (RC) beams using sustainable aluminum boxes filled with high performance concretes (HPCs). The study compares the performance of eleven RC beams with different configurations of aluminum boxes, filling materials, and inclination angles. Additionally, it examines the effect of reinforcing the ultra-high-performance concrete (UHPC) used to fill these boxes with glass fiber reinforced polymer (GFRP) bars. The results show that the proposed technique can effectively restore and enhance the load-deflection behavior, ultimate capacity, stiffness, and energy absorption of the beams. Inclining aluminum boxes within beams at a 45-degree angle and filling them with strain-hardening cementitious composites (SHCCs) partially restores performance. A beam with three boxes showed significant improvements over the defected beam, achieving 65 % higher stiffness, 44 % higher cracking load, and 33 % higher ultimate load. The optimal configuration was found to be 60-degree inclined aluminum boxes filled with UHPC and embedded GFRP bars. This configuration achieved a near-identical performance to the non-defected control beam and surpassed it in some respects. Furthermore, a two-pronged approach was employed. Firstly, finite element models (FEMs) were developed and carefully validated against experimental results. These validated models then became the foundation for a parametric study, allowing researchers to investigate the influence of various parameters on the beam's performance. The parametric study indicates that with a fixed thickness of the aluminum boxes used, beams strengthened with boxes filled with UHPC have higher shear capacity compared to those strengthened with boxes filled with SHCC. Secondly, a theoretical formula was proposed to predict the total shear capacity of the strengthened beams. This formula exhibited excellent agreement with both the experimental data and the finite element (FE) results, solidifying its potential as a practical tool for engineers in design and analysis.

This paper investigates the shear strengthening of simply supported deep beams using welded wire mesh and glass fiber mesh filled with strain-hardening cementitious composites (SHCC) concrete. Nine reinforced concrete (RC) deep beams were tested in this study to investigate different shear-strengthening techniques including the type of mesh (glass fiber mesh and welded steel wire mesh), number of layers (single and double), and the effects of additional anchor using high-strength bolts on the shear performance of RC deep beams. The results showed the SHCC-mesh jackets increased the ultimate load of the deep beams by up to 82 %, cracking load by up to 73 %, elastic stiffness by up to 457 %, and energy absorption by up to 380 % compared to the unstrengthen control beam. Furthermore, the welded wire mesh provided greater enhancements of strength, stiffness, and energy absorption than the glass fiber mesh. In addition, anchoring the jackets further improved the strengthening efficiency. Advanced nonlinear three-dimensional finite element models were also simulated to capture the structural responses of the RC deep beams strengthened using welded wire mesh and glass fiber mesh. It was found that the numerical models accurately predicted the behavior of the beams upon validation against the experimental results.

To investigate the reinforcing effect of externally prestressed carbon-fiber-reinforced polymer (CFRP) tendons on the shear performance of reinforced concrete beams, a set of model tests was designed. Static load comparative tests were conducted on one original beam and four reinforced beams to experimentally investigate the impacts of the prestress level and damage in the shear zone on the shear reinforcement effect and analyze the reinforcement mechanism of CFRP tendons. The results show that in the beams reinforced with CFRP, the CFRP tendons could work collaboratively with the stirrups to reduce the strain on the stirrups; the increasing rate in the yield load was 28–70%. After the stirrups yielded, the CFRP tendons did not yet reach their ultimate tensile strength and could still withstand increased shear forces, resulting in an increasing rate of the ultimate load for the reinforced beams with a CFRP content of 56–78%. The enhancements in both the yield load and the ultimate load were positively correlated with the level of prestress in the CFRP tendons. This reinforcement technique efficiently restricts the growth and delays the first appearance of diagonal cracks. The prestress can close the pre-existing diagonal cracks and provide a reserve of shear capacity for the beams. The initial damage in the shear zone decreases the initial shear stiffness and increases the width of the initial diagonal cracks. However, this effect gradually diminishes as the load increases and does not significantly impact the shear capacity. Prestressing can significantly improve the strength utilization rate of the CFRP reinforcement when the reinforced beams fail. The deformation of the CFRP tendon is directly related to the shear deformation. By combining this relationship with the truss–arch model, the shear capacity for the reinforced beam can be predicted. The predicted results exhibit an error of less than 10% when compared to the test results, offering valuable design guidance for reinforced engineering composites. [ABSTRACT FROM AUTHOR]

The open mesh textile reinforcements used today in textile-reinforced mortar (TRM) strengthening applications are composed of identical fiber rovings in both orthogonal directions, regardless of the type of application. However, for reinforced concrete (RC) members, such as beams and columns, where fibers are utilized in one main direction, such textile geometry can lead to ineffective and excessive use of raw materials and, therefore, uneconomic design. This paper experimentally investigates the use of hybrid textile reinforcement for flexural and shear strengthening in 22 RC beams. Four types of hybrid textiles were designed and manufactured to allow for the environmentally friendly and cost-efficient use of the fibers. Expensive high-strength carbon and weaker glass fibers were used in the main and secondary directions, respectively. Hybrid carbon–glass textiles, which are composed of weaker glass fiber rovings with larger spacings in the secondary direction, showed similar effectiveness with the standard carbon textiles with 50%–50% weight distribution per direction. A cost estimation revealed that massive savings on raw materials can be achieved when hybrid layouts are used instead of conventional textiles. Therefore, the results of this paper could provide a new scope for the optimization of current TRM systems for various retrofitting applications and might assist in the development of a more economical, environmentally friendly, and balanced design of textile reinforcements. [ABSTRACT FROM AUTHOR]

The shear behavior of simply supported RC beams strengthened with polyethylene terephthalate (PET) fiber-reinforced polymer (FRP) was studied in this paper. The test variables include strengthening schemes (i.e., U-wrapping and full-wrapping) and FRP reinforcement ratios. A comprehensive and meticulous investigation was conducted on the failure mode of RC beams, shear force-deflection curves, the development process of shear cracks, the evolution of FRP strain, and the interaction between FRP and concrete. The shear capacity and deformation were increased by 42.5–123.2% and −16.34–96.89% using the fully wrapped scheme, respectively. The improvement in shear capacity was 42.5–72.55% when the U-wrapped scheme was adopted. The PET FRP fully wrapped beams exhibited a type of ductile shear failure. The strain of PET FRP in the fully wrapped specimen exceeded 4% without fracture, ensuring the deformation capacity after the peak load. The shear deformation caused the increase in post-peak mid-span deflection. The U-wrapped specimens showed debonding failure, with the debonding strain of PET FRP being more than that of conventional FRP. Finally, six design guidelines for PET FRP shear contribution were evaluated for both U-wrapped and fully wrapped schemes.

This article compromises a three-dimensional numerical study employing the Abaqus program to investigate the behavior of reinforced concrete (RC) beams externally strengthened in shear using aluminum alloy (AA) plates bonded utilizing steel anchors. Based on previous experimental tests, a numerical validation study was conducted in two parts. The first part modeled the interaction behavior using different bonding methods between steel plates and the surface of the RC beams, whether utilizing epoxy adhesive only, steel anchors only, or a dual system between them. The second part modeled the performance of shear-defected RC beams that externally strengthened by the AA plates using epoxy adhesive. To take into account debonding collapse due to epoxy adhesive bonding, the interaction between the AA plates and beam surface was simulated with a cohesive-damage interaction. Comparing the numerical results with previous experimental studies shows the success of the numerical model in simulating the performance of different bonding methods, as well as the behavior of the RC beams defected in shear and strengthened by the AA plates, which qualified it to study some additional variables. From the study it was found that by utilizing only epoxy adhesive, the strengthening technique using the AA plate over the entire shear span zone (AASP method) was capable of increasing the ultimate capacity of the defected beam by 104%, which represents 77% of the load of the non-defected beam. It was also demonstrated that the AA plates were susceptible to collapse by the out-of-plane buckling when bonded using the steel anchors only. By utilizing a dual system for bonding the AA plates consisting of epoxy adhesive and steel anchors, the AASP method was capable of enhancing the ultimate capacity of the defected beam by 164% and changing its failure pattern to the preferred ductile bending pattern.

In this study, the shear strengthening of reinforced concrete (RC) beams by externally web-side bonded carbon fiber-reinforced polymer (CFRP) strips is investigated experimentally. The current study regards the problems associated with shear strengthening of RC beams without stirrups by using externally bonded CFRP strips on two opposing web sides of the beam and four ratios of longitudinal reinforcements were used as the test variables. To investigate the shear capacity of RC beams, a total of eight 130 mm x 250 mm x 2,400 mm RC beams without shear reinforcement were used. Parameters varied in the tests and included a ratio of longitudinal reinforcement (1.24%, 1.86%, 2.47%, and 3.09%) and vertical application of CFRP strips. Considering the experiment's findings, the capacity of RC beams strengthened in shear with externally bonded web-sided CFRP strips is 1.88-1.95 times greater than that of control beams. It was revealed that the longitudinal reinforcement ratio significantly influences the failure type and crack patterns in the shear span zone. With an increasing longitudinal reinforcement ratio, the shear capacity of the beam increased slightly.

The hybridisation of fibre-reinforced polymers (FRPs), particularly with the combination of natural and synthetic fibres, is a prominent option for their development. In the context of the construction industry, there is a notable gap in research on the use of jute and glass fibres for the strengthening of concrete structures. This paper presents comprehensive experimental results from tests on seven reinforced concrete (RC) beams strengthened for shear using synthetic, natural, and hybrid jute–glass FRP composites. The beams were reinforced using the externally bonded reinforcement (EBR) technique with U-wrap bonding. A beam without any strengthening was tested and set as a reference for the other beams. Two beams were tested with synthetic FRP shear strengthenings, one with carbon fibre-reinforced polymer (CFRP) and another with glass fibre-reinforced polymer (GFRP). The remaining tests were on RC beams strengthened with natural jute fibre-reinforced polymer (JFRP) and hybrid jute–glass FRP. The paper discusses the experimental behaviour of the tested beams in terms of vertical displacements, crack widths, and strains on steel bars, concrete, and FRP. The experimental strengths are also compared with theoretical estimates obtained using ACI 440.2R and fib Bulletin 90. The tests confirm the effectiveness of natural jute FRP and jute–glass hybrid FRP as an option for the shear strengthening of reinforced concrete beams.

The reinforced concrete (RC) beams could be upgraded in shear using steel and fiber‐reinforced polymer (FRP) having several shapes (bars, strips, or sheets). Using near‐surface mounted (NSM) Glass FRP (GFRP) bars is still limited compared to carbon FRP (CFRP) elements as shear reinforcement. Moreover, using reinforced high‐strength concrete layers (HSCL) as NSM shear strengthening for the RC beams is still limited. Herein, three RC beams internally reinforced in shear using different shear areas (without, 100 mm stirrups apart, and 200 mm stirrups apart) were experimentally tested as reference beams (CB). Other eight beams strengthened in shear using NSM HSCL, and bars were experimentally tested. Moreover, an extended finite element (FE) simulation was implemented through a verified FE model to study the effect of other NSM aspects on shear‐strengthened beam response. The results explained that, regardless of the internal stirrups area and external NSM characteristics, the shear‐strengthened beams showed higher load efficiency than the corresponding CB. The NSM upgraded shear beam had slightly higher load efficiency than the un‐strengthened beam having the same steel area as internally shear stirrups. Moreover, increasing the internal shear stirrups decreased the total efficiency of the NSM shear strengthening and the internal stirrups regardless of the NSM characteristics. Furthermore, the NSM HSCL was more efficient than the corresponding NSM bars in increasing the load capacity and stiffness of the shear‐strengthened beams. The reported analytical model predicted well the shear capacity of the tested beams. [ABSTRACT FROM AUTHOR]

This article compares the shear performance of reinforced concrete (RC) beams strengthened with textile-reinforced mortar (TRM) and fiber-reinforced polymers (FRPs). The investigated parameters included strengthening material, i.e., TRM or FRP; two different (light and heavy) carbon meshes in the TRM strengthening method; anchor type (fan type and mechanical) and wrapping type (U-shape and side bonding). Thirteen fabricated reinforced concrete beams were strengthened and exposed to a three-point bending test. Two beams, one with insufficient shear strength (without stirrups) and the other with sufficient shear strength (with stirrups), were produced as control specimens. Eight beams were strengthened with TRM, and the remaining three beams were strengthened with FRP. The main findings from the study are as follows: (a) FRP was more successful than TRM by 5–45% in increasing the shear capacity of reinforced concrete beams depending on the parameters studied, (b) TRM with heavy carbon increased the shear capacity of beam specimens approximately 1.10 times compared to TRM with light carbon, (c) among the wrapping styles, side bonding was from 8 to 31% more effective, (d) the mechanical anchor increased the shear capacity against the fan-type anchor with a ratio ranging from 1.05 to 1.18 in U-shaped wrapping; however, the same ratio was between 0.91 and 0.94 for side bonding, and (e) the energy dissipation capacities in TRM and FRP strengthening were increased up to 3.62 and 4.13 times, respectively. Finally, the experimental study was verified with an analytical model, and reasonable results were obtained. [ABSTRACT FROM AUTHOR]

This study evaluates the performance of Reinforced Concrete (RC) beams enhanced in shear using Engineered Cementitious Composites (ECCs) and Carbon Fiber-Reinforced Polymers (CFRPs). The experimental study encompasses fifteen RC beams. This set includes one control specimen and fourteen beams fortified in shear with Externally Bonded (EB) composites. Two of these specimens were enhanced with ECC layers, while the remaining were augmented with combined CFRP-ECC layers. Variables in the test included the ECC layer thickness, matrix type, number of CFRP layers, and strengthening configurations such as full wrapping, vertical strips, and inclined strips. The results indicated that the shear capacity of the fortified beams increased by 61.1% to 160.1% compared to the control specimen. The most effective structural performance was observed in the full wrapping method, which utilized a single CFRP layer combined with either 20 mm or 40 mm ECC thickness, outperforming other techniques. However, the inclined strip method demonstrated a notably higher load-bearing capacity than the full wrapping approach for beams with double CFRP layers paired with 20 mm and 40 mm ECC thicknesses. This configuration also exhibited superior ductility compared to the rest. Furthermore, the experimental shear capacities obtained were juxtaposed with theoretical values from prevailing design standards. [ABSTRACT FROM AUTHOR]

As part of the experiments, 4-point-bending tests to investigate the shear capacity of strengthened T-beams were carried out. Thereby, 5 reference beams and 25 T-beams with carbon reinforced concrete strengthening were tested. Two different impregnated carbon grids in various strengthening configurations at the beams' webs were checked. The number of strengthening layers was varied as well as the orientation of the grid in the strengthening layer. Furthermore, the influence of pre-damage of the RC beam before strengthening and two different shear slendernesses were investigated. A load increase of 25% to 42% compared to the unstrengthened reference specimens demonstrates the capability of carbon concrete for shear strengthening. In addition to the presentation of tested large-scale specimens, a test analysis will also be conducted, along with the derivation of a limit value for the maximum possible strengthening ratio using carbon-reinforced concrete based on the observed failure modes. [ABSTRACT FROM AUTHOR]

This paper investigates the effectiveness of local strengthening using textile reinforced mortar (TRM) jackets on the global response of reinforced concrete (RC) frames under gravity and lateral cyclic loadings. Finite element analysis (FEA) was employed to develop and validate an RC bare frame model against an experimental study in the literature. Consequently, four TRM strengthening configurations were applied considering the column's confinement and strengthening of joints and beams. With the aim to attain a ductile behavior of the frame, the selection of each configuration was based on the predicted failure of the preceding strengthening arrangement. A parametric study was performed to investigate the effect of the number of layers, length of TRM jackets, textile orientation, and distributed load values. Finally, the FEA models were compared with traditionally and noninteracting masonry infilled frames from the literature. By evaluating the local retrofitting influence on the global response of the frames, the strength and stiffness enhancements were marginal as compared to the control model. Local measures were more effective in the frame's post-peak response, hence, enhancing the ductility of RC frames. The TRM application to the beam-column joints resulted in substantially higher energy dissipation as compared to the model with no joint upgrading. When comparing the TRM local strengthening method to the global technique using infilled walls, the TRM retrofitted models showed similar energy dissipation to that of noninteracting masonry infilled specimen and lower values than those of the traditionally infilled frame. [ABSTRACT FROM AUTHOR]

Existing reinforced concrete buildings frequently require shear-strengthening to ensure structural integrity, and externally bonded carbon fiber-reinforced polymers (EB-CFRP) have become a wide-applicable approach. However, slabs and geometric restrictions impede wrapping the element, necessitating incomplete U-shaped applications vulnerable to debonding failures. This experimental study introduces a novel approach for shear-strengthening nine full-scale T-beams using near-surface mounted CFRP ropes forming closed stirrups. Their effectiveness as shear reinforcement is investigated compared to an alternative method incorporating EB-CFRP sheets with CFRP rope anchorage. Test results indicate that both techniques enhance the beams’ strength and performance. The load capacity increased 2 times for the reference specimen and 1.4-1.9 times for the strengthened beam with FRP sheets. The displacement at the maximum load increased 5.2-7.8 and 6.6-7.5 times, respectively. The rope stirrup arrangement outperforms the rope anchorage system in mechanical and construction efficiency. A thorough protocol for executing these processes to mitigate construction-related defects is introduced.

I-shaped concrete girders are widely used in precast bridge and roof construction, making them a common structural component in existing infrastructure. Despite well-established strengthening techniques using various innovative materials, such as externally bonded carbon fibre reinforced polymer (CFRP) reinforcement, the shear strengthening of an I-shaped concrete girder is not straightforward. Several research studies have shown that externally bonded CFRP reinforcement might exhibit early debonding at the concave corners of the I-shape, resulting in a marginal increase in shear capacity. This research study aims to assess the performance of two different CFRP shear strengthening strategies for I-shaped concrete cross-sections. In the first strategy, CFRP was bonded along the I-shape of the cross-section with the provision of additional anchorage. In the second strategy, the I-shape was transformed into a rectangular shape by using in-fill blocks over which the CFRP was bonded in a U-configuration. In addition to the strengthening strategies, the investigated parameters included two different materials for the in-fill blocks (conventional and aerated concrete) and two different anchoring schemes (bolted steel plate anchor and CFRP spike anchor). To avoid testing on large-scale girders, a new test methodology has been implemented on concrete I-sections. The test results demonstrate the feasibility of comparing different shear strengthening configurations dedicated to I-sections. Among other findings, the results showed that the local transformation of the I-shape to an equivalent rectangular shape could be a viable solution, resulting in shear strength enhancement of 12% to 53% without and with the anchorages, respectively.

Ultra-high performance fiber reinforced concrete (UHPFRC) is an advanced cementitious composite with high compressive strength and low permeability. Due to its excellent mechanical properties and superior durability, UHPFRC is considered promising for strengthening of the existing concrete bridges. In order to examine its strengthening efficiency for shear capacity, an experimental study is carried out on shear-deficient beams without stirrups. Strengthening method comprising precast UHPFRC laminates being glued with epoxy resin on two lateral sides of the reinforced concrete beams, is examined. To investigate the robustness of the system under severe exposure conditions, some beams are subjected to freeze-thaw (FT) cycles. Beams are tested to failure under three-point bending configuration. Test results show that for epoxy resin bonding, UHPFRC shear strengthening is a promising method to increase the load and deformational capacity, and to limit the crack openings. The load capacity is doubled, and the deformational capacity is increased by around 60%. After exposure to 30 FT cycles, the strengthening efficiency and fracture behaviour of UHPFRC composite beams seem not to be affected. It seems that the interfacial bond strength is sufficient to prevent premature debonding between UHPFRC and NC, which under combined action of environmental exposure (e.g. FT) and mechanical loading might become a challenge. Finally, a finite element model is developed to predict and understand the shear behaviour of the reference and strengthened beams. In general numerical results show good agreement with the experimental results in terms of failure pattern and peak load prediction once the perfect bond model is used for the interface between UHPFRC and NC. In order to better understand the role of governing parameters on the shear capacity of the composite member, parametric studies are conducted focusing on the role of varying UHPFRC softening behaviour and UHPFRC-concrete interface properties.

High-strength jute fibre-reinforced polymer (JFRP) laminates have recently been introduced to strengthen RC beams against shear. In contrast to synthetic-based composites, JFRP laminates would be more ductile, compatible with steel shear rebar and effective in reducing debonding due to their lower modulus of elasticity. The prime objective of this research was providing an optimal solution to strengthen a severely deficient RC beam against shear using an externally bonded JFRP laminate with anchor. Fabrication of the JFRP laminate was carried out with the maximum fibre content of 37.5% to obtain high tensile strength. Five full-scale RC beam specimens were cast. Shear strengthening was done by an externally bonded JFRP laminate with double connector, multiple connector and embedded-bar anchor systems. The dimensions of JFRP laminate were obtained based on proposed guidelines. Based on the experimental test, the average tensile strength of the fabricated JFRP laminate was found to be 162 MPa. Results also showed that the JFRP laminate with multi-connector anchor increased the maximum shear capacity of deficient RC beams by 89% and the beams had failed by the fracture of laminate. Beams strengthened with embedded-bar anchor had shown flexural ductile failure. Both beams failed after yielding of flexural bar. The proposed guidelines could be used for shear strengthening of severely deficient beams to enhance the maximum shear capacity using full strength of JFRP laminate with anchor. [ABSTRACT FROM AUTHOR]

As worldwide infrastructure is ageing, significant efforts have been paid to the development of strengthening techniques that will restore or increase the initial capacity of existing structures. Considering that it is expected that shear failure happens in a less ductile mode than that observed under bending actions, special attention has been devoted to shear strengthening methods. These methods included externally bonded fiber reinforced polymers (EB‐FRP), near‐surface mounted (NSM‐FRP) method, and the embedded trough‐section (ETS) technique, among others. In this paper, ETS method is used for the strengthening in shear of a reinforced concrete railway bridge located in Finland. The ETS method consists in the embedment of FRP or steel bars through predrilled holes into the concrete core. The bars are bonded to the concrete using adhesives. The paper includes a brief review of recent advances in the use of ETS and comparison with other available techniques, the description of the case study, instrumentation of the bars using fiber optic sensors (FOS) for strain monitoring, the procedure used for the installation of the bars in the field, and a preliminary analysis of the data collected. [ABSTRACT FROM AUTHOR]

Most of the infrastructure structures in Central Europe were erected between 1960 and 1990 and are therefore now between 30 and 60 years old. As recalculations of bridges show, frequently deficits in load‐bearing capacity arise due to aging of the structures, the increasing loads on these structures and the changes in the design codes. Often, a complete replacement of these structures is planned, which leads to high investment costs but also to massive traffic disruptions due to the complete or partial closure of the structure. Investigations show clearly that strengthening of existing structures is far more sustainable than building a new bridge. Therefore, in the last decade, research has been conducted at the University of Innsbruck on new, efficient post‐installed reinforcement systems with the help of which the lifetime of existing infrastructure buildings can be significantly extended. These new systems have to be installed in the existing structure as quickly as possible and with a minimum disruption of the traffic. This is the only way to keep traffic disruption and thus environmental impact to a minimum. The development of new systems for the strengthening of existing structures is shown and the positive effects to the environmental impact are figured out at some project examples. [ABSTRACT FROM AUTHOR]

This paper investigates the shear behavior of unidirectional hybrid slabs made of a normal-strength concrete (NSC) substrate and an ultrahigh-performance concrete (UHPC) overlay on the tensile side. The impacts of two important aspects on the shear behavior were studied. First, various strengthening configurations (thickness, with or without NSC substitution, with existing and/or new rebars) were investigated, specifically two configurations scarcely studied in the scientific literature. Second, the state of damage of the NSC slab prior to the overlay application was examined for the first time. The hybrid slabs tested behaved monolithically until the establishment of a composite mechanical action occurring at up to 1.66 times the reference shear resistance. The composite mechanical action offered structural hardening with significant increase of shear resistance up to 2.50 times the reference shear resistance. Strain distribution and reorganization was monitored on the slabs using digital image correlation technology, and showed creation of a strut and tie system in four successive steps. Both the UHPC thickness and the total area of longitudinal rebar had a significant impact on the ultimate shear resistance. The effect of the load history on the ultimate shear resistance was limited, and partly masked by the combined effect of the type of NSC-UHPC interface and the overlay configuration influencing the crack pattern. [ABSTRACT FROM AUTHOR]

To investigate the reinforcing effect of externally prestressed carbon-fiber-reinforced polymer (CFRP) tendons on the shear performance of reinforced concrete beams, a set of model tests was designed. Static load comparative tests were conducted on one original beam and four reinforced beams to experimentally investigate the impacts of the prestress level and damage in the shear zone on the shear reinforcement effect and analyze the reinforcement mechanism of CFRP tendons. The results show that in the beams reinforced with CFRP, the CFRP tendons could work collaboratively with the stirrups to reduce the strain on the stirrups; the increasing rate in the yield load was 28–70%. After the stirrups yielded, the CFRP tendons did not yet reach their ultimate tensile strength and could still withstand increased shear forces, resulting in an increasing rate of the ultimate load for the reinforced beams with a CFRP content of 56–78%. The enhancements in both the yield load and the ultimate load were positively correlated with the level of prestress in the CFRP tendons. This reinforcement technique efficiently restricts the growth and delays the first appearance of diagonal cracks. The prestress can close the pre-existing diagonal cracks and provide a reserve of shear capacity for the beams. The initial damage in the shear zone decreases the initial shear stiffness and increases the width of the initial diagonal cracks. However, this effect gradually diminishes as the load increases and does not significantly impact the shear capacity. Prestressing can significantly improve the strength utilization rate of the CFRP reinforcement when the reinforced beams fail. The deformation of the CFRP tendon is directly related to the shear deformation. By combining this relationship with the truss–arch model, the shear capacity for the reinforced beam can be predicted. The predicted results exhibit an error of less than 10% when compared to the test results, offering valuable design guidance for reinforced engineering composites.

The performance of a new fiber-reinforced cementitious matrix (FRCM) system developed using custom-designed mortar and fabrics is investigated in this study. The behavior of this system is evaluated in terms of both the flexural and shear strengthening of reinforced concrete beams. Eight beams are designed to assess the effectiveness of the FRCM system in terms of flexural strengthening, and four specimens are designed to investigate their shear behavior. The parameters investigated for flexural strengthening are the number of layers, span/depth ratio, and the strengthening method. Unlike previous studies, custom fabrics with similar axial stiffness are used in all strengthening methods in this study. In the shear-strengthened specimens, the effects of the span/depth ratio and strengthening system type (fiber-reinforced polymer (FRP) or FRCM) are investigated. The proposed FRCM system exhibits desirable flexural and shear strengthening for enhancing the load capacity, provides sufficient bonding with the substrate, and prevents premature failure modes. Considering the similar axial stiffness of fabrics used in both FRCM and FRP systems and the higher load capacity of specimens strengthened by the former, cement-based mortar performs better than epoxy. [ABSTRACT FROM AUTHOR]

Many bridges suffer from aging and deterioration problems and need to be strengthened. PSWR-PUC is an emerging structural strengthening technology that enhances the load-bearing capacity of concrete bridges by embedding prestressed steel wire ropes into polyurethane cement. This paper focuses on investigating the shear reinforcement effectiveness of PSWR-PUC. Firstly, the composition of PSWR-PUC is introduced. Subsequently, two T-beam bridges in similar service condition are selected, and shear strengthening schemes involving PSWR-PUC and externally bonded steel plates are devised. Lastly, static loading tests are conducted, and the deflection and strain data of the two bridges before and after reinforcement intervention are analyzed. The results indicate that both strengthening methods improve the bridge load-carrying capacity. However, compared to the bridge strengthened with the externally bonded steel plate method, the deflections in the bridge strengthened with PSWR-PUC decreased by 36.8% and 42.1%, the strains decreased by 18% and 23%, and the shear stiffness was improved to a greater extent. These results verified that the PSWR-PUC strengthening method is effective for improving structural capacity and performance. This study will contribute to an in-depth understanding of the performance characteristics and application scope of PSWR-PUC shear strengthening technology, and it provides a scientific basis and guidance for practical engineering applications. [ABSTRACT FROM AUTHOR]

Although fiber reinforced polymers (FRPs) have become the most widely used material to strengthened existing concrete structures in shear, premature debonding of externally bonded FRP remains a significant cause of material under-utilisation. In an effort to suppress debonding failure, research has shown that the use of ±45° bidirectional fabric patch anchors can delay the occurrence of FRP debonding. However, most research to date on patch anchors has been based on joint-level tests and the data available on full-scale beam applications has been very limited. One means by which additional data can be generated on the performance of patch anchors when applied to full-scale beams is using finite element simulations. This paper presents a 2D and 3D non-linear finite element model calibrated using available data on prestressed T-beams strengthened in shear with FRP laminates and patch anchors. The models captured the failure modes, strains in the FRP and crack patterns of the specimens very well and predicted the failure load for the control, strengthened and anchored specimens within a margin of difference of 6–9%, 4–13% and 1–2%, respectively. Parametric studies involving variation of concrete strength and FRP thickness were conducted to generate additional data and the research findings are presented. [ABSTRACT FROM AUTHOR]