To enhance the strengthening effectiveness of existing reinforced concrete (RC) beams and fully utilize the material properties of ultra-high performance concrete (UHPC), this study systematically investigates the flexural strengthening mechanism of UHPC layers through mechanical property tests, four-point bending experiments, and refined finite element simulations. The research first calibrated the constitutive model of UHPC via uniaxial tension and compression tests. Subsequently, flexural tests were conducted on RC beams strengthened with a 40 mm thick UHPC layer, and the crack propagation process was observed using digital image correlation (DIC) technology. Based on experimental results, a finite element model considering material nonlinearity and interfacial bond-slip behavior was established. Parameters such as the thickness of the strengthening layer, material strength, and reinforcement ratio were analyzed. The results demonstrate that the UHPC strengthening layer significantly improves the flexural capacity, stiffness, and crack resistance of RC beams. The reinforced UHPC strengthening layer exhibited even more pronounced enhancements, with the cracking load and ultimate load increasing by up to 145.2% and 67.9%, respectively. DIC results revealed that cracks initiated in the UHPC layer and propagated across the interface into the RC beam. Surface roughening treatment ensured effective composite action without debonding failure. Finite element analysis further indicated that unreinforced strengthening layers led to stress concentration at the beam bottom, exhibiting brittle failure characteristics. In contrast, reinforced strengthening layers significantly improved stress distribution, resulting in more uniform and delayed crack development. The load–displacement curves displayed a distinct plateau after the peak load, indicating enhanced structural ductility and controlled failure. This study provides experimental evidence and theoretical support for the optimal design and engineering application of UHPC in flexural strengthening of RC beams.

Abstract With escalating traffic demands and environmental impacts, the mechanical performance of reinforced concrete (RC) beams faces increasing challenges, necessitating safe and economical enhancement solutions. This study develops and validates a prefabricated prestressed variable truss system (PPVTS) for RC beam rehabilitation, supported by physics‐based predictive models. Four RC beam specimens underwent experimental four‐point bending tests to evaluate strengthening efficacy. Complementary finite element (FE) simulations incorporated precise material constitutive relationships, while theoretical derivations established a simplified mechanical equilibrium‐based model for flexural capacity. Results demonstrate exceptional agreement between experimental and numerical ultimate strength predictions (≤5% deviation). Sensitivity analysis confirms that increasing truss member thickness or prestressed strand diameter further enhances structural bending resistance. The theoretical model achieved <4% average error relative to experimental data. This work advances RC beam maintenance through composite strengthening and provides a robust theoretical framework for predicting flexural capacity in strengthened beams.

Experimental evaluation of sustainable jute\u2013basalt hybrid FRP systems for flexural strengthening of RC beams with variable wrapping and light-weight aggregate replacement

It is proven that beam openings have an inverse effect on the beam's strength. To enhance the beams' overall resistance to applied loads and to improve their ductility, failure mode, and first cracking load, strengthening is necessary. This study investigates the effects of using heavy-duty metal straps (HDMS) to strengthen reinforced concrete (RC) beams with openings. Seven RC beams with dimensions of 250 mm high and 150 mm wide and a clear span of 1200 mm were tested. Six of them had an opening in the middle of the RC beams' span, while one of them was a solid control specimen. The shape of the opening and the method of HDMS application were the main variables. The circular opening had a diameter of 110 mm, while the square opening was 100 mm × 100 mm, which yields approximately equal areas. The HDMS was applied vertically or horizontally around the openings. The horizontal HDMS strengthening can increase the load-carrying capacity by 110% and 115% compared to the solid control beams for circular and square openings, respectively. The strengthened beams with vertical HDMS deflected by up to 179% and 160% compared to the solid beams, respectively. Finally, vertical strengthening delays the first cracking load of the tested specimens by 116% and 105% for circular and square openings, respectively, compared to a non-strengthened opening beam.

The near-surface mounted (NSM) technique with carbon fibre-reinforced polymer (CFRP) composites has been proven to be one of the most effective alternatives for the flexural strengthening of existing reinforced concrete (RC) members. However, several issues remain unresolved, including the effects of elevated temperatures on the performance of these strengthened RC elements. This study experimentally investigates the mechanical performance of RC slabs strengthened with NSM-CFRP systems under elevated temperatures, using both (i) steady-state and (ii) transient heating under applied loads. The steady-state tests were conducted at 20, 40, 50, 70, and 80 °C, while the transient tests were performed at 20 and 80 °C. Deflections, strains, temperatures and loads were registered during the heating phase and during the flexural tests up to failure. These measurements were used to analyse the system response in terms of load-deflection curves, evolution of concrete and CFRP strains, and bond stresses between the epoxy adhesive and CFRP. At 80 °C, the NSM-CFRP-strengthened RC slabs exhibited an average reduction of 12.1% (steady-state) and 2.3% (transient) in ultimate strength. Moreover, the concrete crushing failure mode governed up to 70 °C, despite passing the epoxy's glass transition temperature (54 °C), while cohesive failure of the adhesive governed the failure at 80 °C.

This study is an experimental study on flexural strengthening of reinforced concrete beam where three types of epoxy-bonded jacketing systems are used (glass fiber-reinforced composite (GFRC, S1), jute fiber-reinforced composite (JFRC, S2), and hybrid fiber-reinforced composite (HFRC, S3)) and an unjacketed control beam (S0). All the specimens were subjected to displacement-controlled three-point bending to measure the enhancement of strength, stiffness, and energy absorption using mass-normalized (TPM) and synthetic-content-normalized (TSM) performance indices. Jacketing compared to control also raised the maximum load from 11.80 N to 17.10 N for GFRC (+44.9%), to 14.64 N for JFRC (+24.1%), and to 14.89 N of HFRC (+26.2%). The energy taken up rose from 38.44 J (S0), 152.50 J (S1, +297%), 95.32 J (S2, +148%), and 132.79 J (S3, +245%). Flexural strength was also increased to 56.26 MPa (S1), 43.54 MPa (S2), and 51.38 MPa (S3) and yield strength was raised from 10.43 MPa (S0) to 26.40 MPa (S1), 16.84 Mpa (S2), and 23.05 Mpa (S3). The increase of flexural modulus between S0 (4871.33 MPa) and S1 (12,322.34 MPa), S2 (7862.61 MPa), and S3 (10,759.57 MPa) showed the enhancement of the stiffness. Mass-normalized performance showed great overall efficiency in the case of GFRC and HFRC, with TPM = 3.70 and 3.60 J/kg, respectively, and synthetic-content efficiency was higher in the case of JFRC, with TSM = 9.66 J/kg, which is the advantage of low-synthetic reinforcement in energy-based performance. In general, the suggested jacketing systems have a great influence on flexural responsiveness and power absorption, whereby GFRC and JFRC offer maximum capacity and stiffness, respectively, and the greatest efficiency per unit synthetic material, respectively. In terms of novelty, the paper is one of the first to measure the sustainability-based performance of an epoxy-bonded GFRC, HFRC, and bio-based JFRC jacketing, comparing the results in terms of synthetic-content efficiency (TSM) and mass-normalized indices, which reflect the energy absorption benefits per unit of synthetic material.

While steel sheets are an effective strengthening technique for existing structures, experimental evidence on galvanised steel sheets is limited, necessitating their evaluation as a durable and cost-effective solution for the flexural strengthening of reinforced concrete (RC) beams. This study analyses the influence of external reinforcement using galvanised steel sheets applied to RC beams. The structural behaviour of the specimens was assessed through flexural tests, with monotonic loading applied at one-third and two-thirds of the effective span, in accordance with ASTM C78 guidelines. In addition, an analytical model was formulated to capture the non-linear behaviour of concrete, reinforcing steel, and galvanised steel sheets. The results indicate that beams strengthened with external reinforcement exhibit an increase in load-bearing capacity of up to 69% in the elastic range, together with significant improvements in ductility of up to 22%. Moreover, the use of vertical U-wrap sheets and anchor bolts enhances the bond between the sheets and the concrete, thereby reducing the risk of premature debonding. Overall, the findings confirm that the use of galvanised steel sheets is an effective and practical strengthening technique for improving the flexural performance of RC beams.

This study introduces a novel, modular approach for the flexural strengthening of large-span prestressed reinforced concrete (PRC) I-beams using segmented precast layers of ultra-high-performance concrete (UHPC) reinforced with glass fibre reinforced polymer (GFRP) bars. This methodology addresses key constructability challenges associated with continuous, in situ strengthening of long bridge girders. The primary aim was to evaluate the effectiveness of this segmentation by considering parameters such as layer continuity and reinforcement overlap. Experimental findings from seven PRC beams demonstrated exceptional structural performance. The external precast UHPC layers yielded a substantial enhancement in load-carrying capacity (82%–112%) and initial stiffness (49%–61%). While the introduction of a joint caused only a marginal load reduction (4%–14%), it crucially provided a mechanism for controlled failure localisation, acting effectively as a plastic hinge. Furthermore, the study confirmed excellent bond integrity between the UHPC overlay and the concrete substrate, with no observed separation. These results validate the segmented precast UHPC overlay as a highly viable, efficient, accelerated and economically advantageous solution for the rehabilitation and performance upgrade of large-span structural members.

This study investigates the flexural behavior of RC beams strengthened with Basalt Textile Reinforced Mortar (BTRM), focusing on the influence of the number of textile layers, mesh size, and anchorage techniques. Six full-scale RC beams were tested under four-point bending, comprising one unstrengthened control specimen and five beams strengthened using different BTRM configurations. The experimental results demonstrated that increasing the number of BTRM layers from three to five enhanced the ultimate load capacity by up to 18% compared to the control beam. Nevertheless, debonding was identified as the predominant failure mode across most strengthened specimens. The influence of mesh size was examined by comparing an eight-layer specimen using 5mm mesh size with a three-layer specimen using 34mm mesh size; both configurations exhibited comparable flexural performance. Variations in mesh size (34 versus 5mm) had a negligible effect on load capacity. The incorporation of basalt bars resulted in a marginal improvement in flexural strength, whereas mechanical anchorage provided limited enhancement in overall performance. These findings highlight the critical need to improve bond behavior and anchorage efficiency in order to fully benefit from the strengthening potential of BTRM systems. In addition, an analytical study was conducted to assess the accuracy of existing predictive models, including those proposed in current design guidelines and previously published analytical approaches, against the experimental results. A modified predictive equation derived from an existing analytical model demonstrated good agreement with both the experimental data and results reported in the literature.

The structural integrity of reinforced concrete (RC) bridges is critical to the safety and functionality of transportation infrastructure. This paper presents a field investigation of steel-based strengthening methods for rehabilitating deteriorated RC T-beam bridges, encompassing transverse, shear, and flexural enhancements. Static load testing using four dump trucks was conducted to evaluate the performance of strengthening methods. Finite element (FE) models were developed to analyze structural behavior and complement the experimental investigation. The results show that the transverse strengthening successfully improved transverse load distribution across the beams. A detailed investigation was conducted on three flexural strengthening methods designed to reduce deflection. The steel channel strengthening (SCS) method proved to be the most effective in improving stiffness of the beams, compared to the cover plate strengthening (CPS) and the steel truss strengthening (STS) methods. The SCS method reduced the maximum mid-span deflection by up to 50.7% compared with the unreinforced condition, outperforming the CPS (17.5%) and SCS (19.5%) methods. Strain distribution analysis confirmed effective composite action for the CPS and SCS approaches, whereas the STS method exhibited incomplete composite behavior. The results highlight that achieving effective composite behavior between the strengthening system and the existing concrete member is a governing factor for strengthening performance. Parameter analysis demonstrates that the 16B channel used in SCS practical application provides a cost-effective option. The findings validate the steel-based strengthening methods for deteriorated RC bridges and provide practical guidance for field applications.

This review aims to carefully analyze how Carbon Fiber Reinforced Polymer (CFRP) bars and sheets are used in reinforced concrete, focusing on their strength, durability and ability to support a structure. The analysis compiles recent research to look into the positives and negatives of using CFRP rather than steel as a reinforcement for structures. The main parts of this field are bonding ways, extra costs, effects on the environment and how CFRP performs in various situations. The summary points out that CFRP can considerably increase flexural and shear strength in concrete, resist corrosion and create objects that are both durable and light in weight. Despite the expensive cost, limited information about durability and some bonding-related issues, CFRP systems exhibit encouraging effects in applications like flexural strengthening, shear reinforcement and confining concrete columns. Research and new technologies will likely allow CFRP to be more widely used in the future, solving many infrastructure problems

A fiber-reinforced polymer (FRP) sheet bonding method for the flexural strengthening of existing RC members under impact loading has not yet been established because the strengthening effects of the sheet and the impact resistance behavior of the members have not been sufficiently clarified. In this study, a numerical analysis method is proposed to better evaluate the impact resistance behavior, such as sheet debonding and rupturing, of RC beams flexurally strengthened with carbon fiber-reinforced polymer (CFRP) sheets subjected to a low-velocity impact load; moreover, its applicability is investigated, and the results from the experiments, the continuous surface cap (CSC) model and the Karagozian & Case model (KCC model), which were already implemented in a commercial software package as a constitutive model for concrete, were compared. The crack width needs to be sufficiently decreased to follow the actual behavior of the beams and to accurately estimate the strengthening effect of the sheet. In the proposed method, to decrease the element size of the concrete, the tensile stress in the concrete element is assumed to be completely released upon reaching its strength, and an adapted tensile strength of concrete was introduced on the basis of the equivalent tensile fracture energy concept. The results obtained from this study were as follows: (1) the impact resistance behaviors, including sheet debonding and rupturing, were appropriately evaluated by using the proposed method, and the element size of the concrete was set to approximately 6 mm; (2) the CSC model was able to effectively evaluate the behavior of the beams with sheet rupturing but not with sheet debonding; and (3) the KCC model was not able to appropriately evaluate the strengthening effect of the sheet.

Investigating the flexural fatigue performance of rubberized concrete is essential for advancing its application in dynamic load environments, which aligns with the green and low-carbon objectives of modern building materials. In this study, comprehensive mechanical and fatigue tests-including assessments of static strength, fatigue life, and flexural fatigue strength-were conducted to clarify the mechanisms by which crumb rubber influences the fatigue resistance of concrete. Increasing the rubber content markedly improved fatigue life, although a reduction in compressive strength was observed. Specifically, compared to the reference concrete, concrete incorporating 10% pretreated crumb rubber by volume of fine aggregate exhibited a 21.2% increase in fatigue life. Furthermore, pretreatment of crumb rubber not only further enhanced the fatigue resistance of concrete but also partially mitigated the decline in strength. Additionally, the compressive strength of concrete with 7.5% pretreated crumb rubber was 15.0% higher than that of concrete with the same amount of untreated crumb rubber. Pretreated crumb rubber further augmented the energy dissipation capability of concrete, thereby enhancing its fatigue performance. Consequently, rubberized concrete emerges as a promising alternative material for fatigue-critical applications, and the pretreatment of crumb rubber is recommended as an effective auxiliary measure to optimize performance.

This study investigates the flexural performance of reinforced concrete (RC) beams with longitudinal openings (holes) of different shapes and sizes, strengthened using carbon fiber-reinforced polymer (CFRP) sheets. Openings were circular, square, or rectangular and placed at different heights along the beam depth. These openings reduced the beam’s load capacity by 1% to 22%, depending on their size, shape, and location. Two CFRP strengthening techniques were used: bottom longitudinal strips and transverse ring strips. The study was performed using both experimental tests and nonlinear finite element analysis (NLFEA). The NLFEA models, created in ABAQUS, showed strong agreement with the test results with close prediction of the ultimate loads, deflections, and failure modes. A parametric study was then developed using the model to investigate the effect of varying concrete grades, tensile and compression reinforcement ratios, and using a steel anchor system on the beam’s strength. The results show that the use of longitudinal CFRP succeeded in restoring the solid beam capacity with an additional increment range between 2 and 16%. Beams having square holes strengthened with ring strips achieved the ultimate capacity of the solid beams with an increment of 4%. The different concrete grades, tensile and compression steel ratios, CFRP thickness, and anchoring system are critical factors in designing hollow beams. Furthermore, the addition of steel anchors has a significant contribution in delaying debonding and enhancing the bond between CFRP and concrete. Overall, the results confirm that CFRP sheets are effective in improving the structural performance of RC beams with openings.

Strengthening reinforced-concrete (RC) members using near-surface-mounted (NSM) titanium-alloy bars (TiABs) has become an emerging method to extend the service life of RC structures. Current design and construction guidance for strengthening existing RC structures with this method is limited to the usage of TiAB with hooked ends, which can be challenging for structures where accommodating hooks is impractical. To evaluate an alternative mounting method, experimental work was performed in this study to investigate the flexural behavior of RC beams strengthened with NSM straight TiAB (without end hooks) and determine their bond strength for development length calculations. Five RC beams strengthened with NSM TiAB having TiAB bonded lengths were tested and compared against an unstrengthened control specimen. The test results indicate that beams strengthened with straight TiABs can achieve increased load capacity, provided that sufficient bond length is provided. Specimens with sufficient bond length demonstrated performance comparable to those strengthened with hooked TiABs, achieving yielding in both the steel reinforcement and the TiAB. An average bond strength of 0.5 ksi for straight TiABs is recommended when performing development length calculations. Additionally, this study presents guidelines and construction procedures for the practical application of NSM straight TiABs.

This study introduces a hybrid framework combining an Artificial Neural Network (ANN) with the Jaya optimization algorithm to predict the minimum Carbon Fiber Reinforced Polymer (CFRP) area required for flexural strengthening of reinforced concrete (RC) cantilever walls. A multilayer perceptron (MLP) network was trained on 500 Jaya-optimized design scenarios incorporating twelve design variables, including geometry, loads, and material properties. The ANN achieved high predictive accuracy, with R-values near 1.0 across training, validation, and testing phases. Five independent test cases yielded an average error of 3.69%, and 10-fold cross-validation confirmed model robustness (R = 0.9996). A global perturbation-based sensitivity analysis was also conducted to quantify the influence of each input parameter, highlighting wall length, moment demand, and concrete strength as the most significant features. This integrated ANN–Jaya model enables rapid, code-compliant CFRP design in accordance with ACI 318 and ACI 440.2R-17, minimizing material usage and ensuring economic and sustainable retrofitting. The proposed approach offers a practical, data-driven alternative to traditional iterative methods, suitable for application in modern performance-based structural engineering.

Abstract Many reinforced concrete (RC) members, such as bridge slabs, are periodically subjected to repeated loads and therefore require strengthening to extend their service life. The near-surface mounted (NSM) technique has recently emerged as one of the most effective methods for flexural strengthening. This study investigates the fatigue behaviour and flexural load-carrying capacity of one-way RC slabs strengthened with NSM steel, CFRP, GFRP, and BFRP bars. A total of ten slabs were tested: five under static loading and five under cyclic loading. The fatigue group was subjected to one million cycles at 50% of the ultimate static load of their respective controls, followed by static loading to failure. Performance parameters examined included crack development, failure modes, ultimate load, mid-span deflection, residual strength, ductility, energy absorption, and deformability. The results demonstrated that NSM strengthening significantly improved slab performance. The slabs were strengthened using carbon fibre-reinforced polymer (CFRP), glass fibre-reinforced polymer (GFRP), basalt fibre-reinforced polymer (BFRP), and steel bars, designated as FCR, FGR, FBR, and SR, respectively. The maximum load-carrying capacities increased by 122.5%, 49.1%, 61.35%, and 21.77%, respectively, compared to their corresponding control slabs. Residual bearing capacity also improved, with CFRP- and BFRP-strengthened slabs (FCR and FBR) achieving 11.26% and 8.17% gains over their static counterparts. These findings confirm the effectiveness of the NSM technique in enhancing fatigue resistance and post-fatigue serviceability of RC slabs, with CFRP bars providing the greatest strength improvement among FRP options, while steel bars offered a balanced combination of strength and ductility.

Purpose This research explores the potential of employing DIC method to assess the load-deflection behavior of lightweight reinforced concrete (LWRC) beams enhanced with near-surface-mounted (NSM) glass fiber-reinforced polymer (GFRP) bars. Design/methodology/approach This research explores the potential of employing DIC method to assess the load-deflection behavior of LWRC beams enhanced with NSM GFRP bars. An experimental study was presented to investigate the behavior of the strengthened LWRC beams. The lightweight expanded clay aggregate (LECA) was utilized to substitute the natural coarse aggregate (NCA) in concrete mixture to produce LWRC beams. The experimental program comprised 14 LWRC beams subjected to four-point loading until a failure. The beams are classified into two groups: the first group comprised of seven LWRC beams reinforced to fail by flexural mode, while the second group included seven LWRC beams reinforced to fail by shear mode. Within each group, one beam served as the control, lacking any reinforcement, while the remaining samples were strengthened using NSM GFRP bars arranged and configurated in various patterns. In addition, this study uses the DIC method to capture the strain profile and load-displacement behavior of the NSM strengthened beam specimens with deferent locations, numbers, diameters, bond lengths, spacings, angle of inclinations and materials of the NSM GFRP rods. The experimental results showed improvements in the load-carrying capacity of the LWRC beams when NSM GFRP bars are used for flexural and shear strengthening, compared to that of control specimens. Further, the DIC results were compared with those obtained experimentally, revealing that the DIC method offers higher accuracy compared to visual inspection, particularly in the analysis of cracking loads. This DIC capability enables early detection of potential issues before cracks happen in the specimen. Findings The experimental results showed improvements in the load-carrying capacity of the LWRC beams when NSM GFRP bars are used for flexural and shear strengthening, compared to that of control specimens. Further, the DIC results were compared with those obtained experimentally, revealing that the DIC method offers higher accuracy compared to visual inspection, particularly in the analysis of cracking loads. Research limitations/implications The study is applied on simply reinforced concrete beams under two-points loads. Practical implications This DIC capability enables early detection of potential issues before cracks happen in the specimen. Social implications The study helps in sustainable using of reinforced concrete building. Originality/value The study employed the DIC method to assess the load-deflection behavior of LWRC beams enhanced with NSM GFRP bars.

TRM versus FRP: Can cement-based matrices replace organic binders in the flexural strengthening of reinforced low-grade concrete beams?

Abstract Over the past few decades, utilizing fiber-reinforced polymer in strengthening or rehabilitation of structural members has become a highly promising technique to extend reinforced concrete (RC) structures' lifespan and enhance their structural integrity. Rehabilitation of old structures is necessary due to various factors, including harsh environments, earthquakes, increased loads, corrosion in reinforcement, and inadequate design. Numerous studies have examined the strengthening of RC beams in shear and flexure using carbon fiber reinforced polymer (CFRP) composites with different schemes, including bonding CFRP externally, through experimental and theoretical investigations. In this study, a series of eight RC beams was cast with low-strength concrete. The beams were designed to be weak in flexural. Flexural critical RC beams were strengthened with different CFRP application schemes. The experimental findings were validated through both numerical and analytical analyses, demonstrating close agreement. The results indicate that the application of CFRP laminate or fabric increased the ultimate load in flexural strengthening applications by approximately 40–60%, particularly when CFRP was bonded to the bottom soffit with CFRP U-jacketing placed at both ends. Furthermore, placing a 50 cm CFRP U-jacket at both ends of RC beams, critical in flexural and strengthened using a CFRP laminate at the soffit of the section, led to a 120% increase in load capacity with elastic behavior.