Search Results (132)

This study investigates strengthening reinforced concrete (RC) beams using fiber-reinforced polymers (FRPs). Nine samples were cast and strengthened with varying parameters, including the width, number of laminates, use of anchors, and application of prestressing. A novel device—the easy prestressing machine (EPM)—was developed to apply prestress. The EPM is lightweight and operable manually, enabling up to 10% prestressing. All specimens were tested under three-point bending until failure, and load-displacement curves were recorded. An analytical method based on curvature increment and incorporating material nonlinearities is also proposed to estimate the load-displacement response of RC beams with and without FRP strengthening. Both experimental and analytical results are presented and compared. The analytical model strongly agreed with the experimental results, showing Pearson correlation coefficients exceeding 90% for most specimens. According to the experimental findings, applying FRP, particularly when combined with anchorage and prestressing, increased the load-bearing capacity by up to 45%. Anchorage and prestressing effectively mitigate premature debonding, with prestressing showing a more pronounced impact on enhancing bond performance and load capacity. Based on the results, conclusions regarding the analytical model, structural behavior, and optimal strengthening strategies are discussed. Full article

To address the existing challenges of lacking a unified and reliable shear capacity prediction model for fiber-reinforced polymer (FRP)-strengthened reinforced concrete beams (FRP-SRCB) and the excessive experimental workload, this study establishes a shear capacity prediction model for FRP-SRCB based on machine learning (ML). First, the correlation between input and output parameters was analyzed by the Pearson correlation coefficient method. Then, representative single model (ANN) and integrated model (XGBoost) algorithms were selected to predict the dataset, and their performance was evaluated based on three commonly used regression evaluation metrics. Finally, the prediction accuracy of the ML model was further verified by comparing it with the domestic and foreign design codes. The results manifest that the shear capacity exhibits a strong positive correlation with the beam width and effective height. Compared to the ANN model, the XGBoost-based prediction model achieves determination coefficients (R²) of 0.999 and 0.879 for the training and test sets, respectively, indicating superior predictive accuracy. Furthermore, the shear capacity calculations from design codes show significant variability, demonstrating the superior predictive capability of ML algorithms. These findings offer a guideline for the design and implementation of FRP reinforcement in actual bridge engineering. Full article

In order to deeply investigate the effects of various factors on the shear behavior of RC beams strengthened with fiber-reinforced polymer (FRP) grid–polymer cement mortar (PCM) composite, and to construct a more accurate formula for the shear behavior of reinforced concrete beams, the following work is carried out in this investigation: Firstly, the finite element numerical simulation of FRP grid–PCM composite RC beams model is carried out using ABAQUS and compared with the test results to verify the correctness of the model; then, the effects of the amount of FRP grid reinforcement, the elastic modulus of the FRP grid, the shear span ratio of the beam, the concrete strength, and the shear reinforcement ratio on the shear performance of the strengthened beams are analyzed; finally, based on the effective strain of the FRP grid to quantify its actual shear contribution, a calculation formula of the shear behavior Capacity of RC Beams Strengthened with an FRP grid–PCM composite is proposed. The results show that the model established in this paper can effectively simulate the shear behavior of the beams in the test; additionally, the effects of the amount of FRP grid reinforcement, the shear span ratio, and the concrete strength are more significant. Finally, the theoretical results of the calculation formula fit well with the collected experimental ones. Full article

Currently, there are many infrastructures for which these design service lives are expired. These lifespans have been extended through retrofitting and strengthening. Usually, the existing reinforced concrete (RC) structures are strengthened by applying steel plate bonding and concrete enlargement methods. However, since fiber-reinforced polymer (FRP) composite materials have properties that are better than those of steel and concrete materials, i.e., being light weight, with anticorrosive material, a high ratio of strength to weight, and better workability, FRP sheet bonding methods for RC members have been developed, and practical applications have been gradually increased worldwide, statically. The methods may also have some potential to strengthen the members under impact and blast loading. In this paper, to rationally improve the impact resistance of RC beams under flexure, beams were strengthened by bonding an FRP sheet to the bottom tension side. Then, low-velocity impact loading tests (hereafter referred to as impact loading tests) using a 300 kg steel weight were carried out on the beams strengthened with carbon FRP (CFRP) sheets of different areal masses to investigate the failure mode at the ultimate state of the beams, in which the areal mass is physically similar to the amount of the sheet reinforcing RC beams and hereafter referred to as the sheet volume. Two sheet volumes (one is an areal mass of 300 g/m² having a 0.17 mm thickness and the other is of 600 g/m² having a 0.33 mm thickness) were compared, and two static failure modes, concrete crushing-intermediate crack (IC) debonding and premature IC debonding, were observed. The following results were obtained from this study: taking a static calculated moment ratio M_y/M_u of the rebar yield-moment M_y to the ultimate moment M_u for each beam, in the case of the beams having an M_y/M_u (=0.67) larger than 0.65 that went through static failure in the concrete crushing-IC debonding mode, the beams failed in sheet rupturing mode subjected to an impact load. When the sheet volume was comparatively large and a static calculated moment ratio M_y/M_u (=0.6) was less than 0.65, the beams collapsed in the premature IC debonding mode under not only static but also impact loading, and the impact resistance of the beams was enhanced with an increasing sheet volume; this increase was greater in the impact loading case than in the static loading case. Full article

This study evaluates the performance of lightweight aggregate deep beams strengthened with low-cost glass fiber-reinforced polymer composite (Lo-G) wraps as an alternative to expensive synthetic fiber-reinforced polymers (FRPs). The investigation includes side-bonded and fully wrapped configurations of Lo-G wraps, alongside carbon FRP (CFRP) strips for comparison. The experimental results show that epoxy-based anchors provided significantly better resistance against de-bonding than mechanical anchors, improving beam performance. Strengthening with Lo-G wraps resulted in a peak capacity increase of 17.0% to 46.9% for side-bonded beams in Group 2, 10.5% to 41.4% for fully wrapped beams in the strip configuration in Group 3, and 15.4% to 42.7% for CFRP strips in Group 4. The ultimate deflection and dissipated energy were also improved, with dissipated energy increases of up to 264.6%, 322.3%, and 222.7% for side-bonded and fully wrapped Lo-G wraps and CFRP strips, respectively. The side-bonded configuration with two or three Lo-G wraps, supplemented by epoxy wraps, outperformed fully wrapped 250 mm strips in peak capacity, with peak capacity improvements of up to 46.9%. However, beams with mechanical anchors showed poor performance due to premature debonding. They rely on friction and expansion within the concrete to resist pull-out forces. If the surrounding concrete is not strong enough or if the anchor is not properly installed, it can lead to failure. Additionally, reducing strip spacing negatively impacted performance. Lo-G wraps showed an 8.5% higher peak capacity and 32.8% greater dissipated energy compared to CFRP strips. Despite these improvements, while Lo-G wraps are a cost-effective alternative, their long-term performance remains to be investigated. None of the existing models accurately predicted the shear strength contribution of Lo-G wraps, as the lower elastic modulus and tensile strength led to high deviations in prediction-to-experimental ratios, underscoring the need for new models to assess shear strength. Full article

Structural deflection is a critical factor used for evaluating the effectiveness of reinforcement. This study proposes a method for generating FRP layouts with a local displacement constraint to strengthen damaged structures. A local displacement constraint strategy is developed using the Lagrange multiplier method, integrating the constraint into the objective function and transforming the problem into an unconstrained optimization framework. The design sensitivity formula for strengthening damaged structures is derived based on this displacement-constrained strategy. Additionally, an automatic adjustment strategy of the Lagrange multiplier is given based on the bisection method. Finally, the effectiveness and applicability of the proposed method are illustrated through case studies on damaged RC beams, slabs, and arches. The FRP configurations under various constraints are discussed and compared with the results generated by the BESO method. Results demonstrate that the proposed method can effectively generate FRP configurations for damaged RC structures. Full article

In recent years, civil engineering has increasingly focused on utilizing fiber-reinforced polymers (FRPs) to retrofit and strengthen reinforced concrete (RC) structures. This paper explores advancements in FRP retrofitting techniques, with a particular focus on their application to beam–column joints in RC structures. The introduction outlines the evolution of FRP materials and their optimization for seismic retrofitting applications. A critical review of existing research highlights the effectiveness of FRP reinforcement in improving seismic resilience. The study examines three distinct cases from post-earthquake assessments in Albania, addressing the impact of poor concrete quality and inadequate detailing on structural performance. To capture the behavior of FRP-strengthened RC structures comprehensively, nonlinear finite element analysis (NLFEA) was employed for localized analysis to observe the influence of FRP strengthening on critical joints, while finite element modeling (FEM) was used for global analysis to demonstrate the behavior at the structural level. The combined approach evaluates the effectiveness of FRP reinforcement in mitigating vulnerabilities, such as shear deficiencies and brittle failure modes, across varying scenarios of material quality and detailing. Key findings indicate that FRP retrofitting strategies result in a 25% increase in peak shear force and a 20% improvement in displacement capacity, showcasing enhanced ductility and seismic resilience. The finite element analysis demonstrated strong prediction accuracy, with error margins below 5% when compared to experimental results. These results emphasize the critical role of tailored FRP retrofitting strategies in enhancing seismic resilience, offering valuable insights for future retrofitting practices in seismic-prone regions. Full article

This paper establishes fatigue life prediction models using the soft computing method to address insufficient parameter consideration and limited computational accuracy in predicting the fatigue life of fiber-reinforced polymer (FRP) strengthened concrete beams. Five different input forms were proposed by collecting 117 sets of fatigue test data of FRP-strengthened concrete beams from the existing literature and integrating the outcomes from Pearson correlation analysis and significance testing. Using Gene Expression Programming (GEP), the effects of various input configurations on the accuracy of model predictions were examined. The model prediction results were also evaluated using five statistical indicators. The GEP model used concrete compressive strength, the steel reinforcement stress range ratio to the yield strength, and the stiffness factor as input parameters. Subsequently, using the same input parameters, the Multi-Objective Genetic Algorithm Evolutionary Polynomial Regression (MOGA-EPR) method was then employed to develop a fatigue life prediction model. Sensitivity analyses of the GEP and MOGA-EPR models revealed that both could precisely capture the fundamental connections between fatigue life and multiple contributing variables. Compared to existing models, the proposed ones have higher prediction accuracy with a coefficient of determination reaching 0.8, significantly enhancing the accuracy of fatigue life predictions for FRP-strengthened concrete beams. Full article

FRP (fiber-reinforced composite) is generally regarded as the repair and enhancement material for existing concrete structures in extreme service environments such as high temperatures or fire exposure. In order to reveal the effect of high temperatures (i.e., thermal load) on the interfacial debonding behavior of a FRP-strengthened concrete beam, the novel closed-form analytical model was established and validated while considering the interfacial bond-slip constitutive. Based on the analytical model, solutions to the distributions of interfacial slip, interfacial shear stress, and debonding load were derived. Moreover, the effects of temperature variations and the FRP’s bonded thickness and length on interfacial bond behavior were also evaluated. The results indicated that the increase in temperature variations accelerated the development trends of interfacial slip and shear stress, where the affected range was mainly concentrated in the bonded plate end. The relationship between temperature variations and debonding loads presented a changing linear trend, and a prediction model for the debonding load was also proposed. Meanwhile, the increase in the FRP’s bonded thickness decreased the bond performance and accelerated the degradation trend of the debonding load. However, the increase in FRP’s bonded length improved the bearing capacity of the FRP-strengthened concrete beam. This paper provides meaningful guidelines for the sustainable design and construction of FRP-strengthened concrete structures in high-temperature environments. Full article

The need to strengthen the existing reinforced concrete (RC) elements is becoming increasingly crucial for modern cities as they strive to develop resilient and sustainable structures and infrastructures. In recent years, various solutions have been proposed to limit the undesirable effects of corrosion in RC elements. While C-FRP has shown promise in corrosion-prone environments, its use in structural applications is limited by cost, bonding, and anchorage challenges with concrete. To address these, the present research investigates the structural performance of RC beams reinforced with C-FRP bars under static loading using Structural Health Monitoring (SHM) with an Electro-Mechanical Impedance (EMI) system employing Lead Zirconate Titanate (PZT) piezoelectric transducers which are applied to detect damage development and enhance the protection of RC elements and overall, RC structures. This study underscores the potential of C-FRP bars for durable tensile reinforcement in RC structures, particularly in hybrid designs that leverage steel for compression strength. The study focuses on critical factors such as stiffness, maximum load capacity, deflection at each loading stage, and the development of crack widths, all analyzed through voltage responses recorded by the PZT sensors. Particular emphasis is placed on the bond conditions and anchorage lengths of the tensile C-FRP bars, exploring how local confinement conditions along the anchorage length influence the overall behavior of the beams. Full article

Reinforced concrete beam bridges are usually retrofitted by a steel plate or FRP. However, these two methods tend to result in disadvantages, e.g., construction complexity and debonding failure, owing to the corresponding material properties. In this study, a steel- and CFRP-based method is proposed to achieve the merits of typical retrofitting methods by combining a CFRP plate, a steel plate, and angle steel. To investigate the effect of the cooperative strengthening, six full-scale beam specimens were designed and are evaluated through a monotonic four-point bending test. The failure mode, load–deflection relationship, critical parameters, and crack development are systematically and sequentially analyzed. Finally, a predicting method is proposed to calculate the flexural capacity. The retrofitted beam is characterized by an acceptable load-bearing capacity and deformation capacity. With continuous retrofitting, the crack load and ultimate load can be improved up to 84.9% and 4.41 times, respectively. The steel plate and angle steel function in both the load bearing and the anchorage to the CFRP plate contributes more to the ultimate bearing capacity after the steel components yield. Finally, a calculating model is shown to accurately predict the ultimate bearing capacity after retrofitting, with an average error of 4.03%. Full article

Because of their improved properties, FRP composites are vastly used in the strengthening of aged concrete infrastructures. However, it has been observed that their performance is highly compromised when exposed to high temperatures, as expected during fire incidents, which critically affects FRP–concrete bond behavior, hence affecting the overall efficiency of the strengthening system. This paper critically presents the available literature concerning the degradation of bond strength between FRP systems with concrete substrates due to increased temperatures. Both analytical and numerical bond–slip models developed for the prediction of bond strength degradation under such conditions are reviewed. A generally confirmed fact is that exposure to high temperatures, especially those reaching glass transition temperature (T_g) for epoxy adhesives, leads to bond degradation. Therefore, cement mortar-bonded CFRP textiles display better performance in fire endurance. This present paper also utilizes machine learning algorithms for the prediction of bond strength under elevated temperatures based on an experimental database of 37 beams. The nonlinear relationships and variable interactions in the developed model provide a reliable method for the estimation of bond strength with reduced extensive experimental testing, where the critical role of temperature in bond behavior is identified. This paper emphasizes the use of advanced predictive models to ensure the durability and safety of FRP-strengthened concrete structures in thermally challenging environments. Full article

To study the flexural performance of fiber-reinforced polymer (FRP) grid–polymer cement mortar (PCM)-composite-strengthened RC beams, the finite element numerical simulation of FRP grid–PCM composite RC beams is carried out using ABAQUS to analyze the effects of the amount of FRP grid reinforcement, the type of FRP grid material, and the geometry of FRP grid on the flexural performance of reinforced concrete beams and to establish the flexural capacity calculation formula of FRP grid–PCM-reinforced RC beams in case of debonding failure, based on analysis of the influencing factors. The results show that increasing the reinforcement of the FRP grid and increasing the stiffness of the FRP grid can improve the flexural bearing capacity of RC beams, and the change of FRP grid geometry has little effect on the flexural bearing capacity of RC beams. The established formula for calculating the flexural bearing capacity of FRP grid-reinforced concrete beams can better predict the flexural capacity of reinforced concrete beams under peeling failure. Full article

Fatigue is a common issue in steel elements, leading to microstructural fractures and causing failure below the yield point of the material due to cyclic loading. High fatigue loads in steel building structures can cause brittle failure at the joints and supports, potentially leading to partial or total damage. The present study deals with accurate prediction of the fatigue life and stress intensity factor (SIF) of pre-cracked steel beams, which is crucial for ensuring their structural integrity and durability under cyclic loading. A computationally efficient adaptive meshing tool, known as Separative Morphing Adaptive Remeshing Technology (SMART), in ANSYS APDL is employed to create a reliable three-dimensional finite element model (FEM) that simulates fatigue crack growth with a stress ratio of “R = 0”. The objective of this research is to examine the feasibility of using a non-linear FE model with an adaptive meshing technique, SMART, to predict the crack growth, fatigue life, and SIF on pre-cracked steel beams strengthened with FRP. Through a comprehensive parametric analysis, the effects of different types of FRPs (carbon and glass) and fiber orientations (θ = 0° to 90°) on both the SIF and fatigue life are evaluated. The results reveal that the use of longitudinally oriented FRP (θ = 0°) significantly reduces the SIF, resulting in substantial improvements in the fatigue life of up to 15 times with CFRP and 4.5 times with GFRP. The results of this study demonstrate that FRP strengthening significantly extends the fatigue life of pre-cracked steel beams, and the developed FE model is a reliable tool for predicting crack growth, SIF, and fatigue life. Full article

This paper discusses the iteration of a seismic retrofit solution for shear-deficient end regions of 19 reinforced concrete (RC) moment-resisting frame (MRF) T-beams located in a 12-story RC MRF building in downtown Los Angeles, California. Local strengthening with externally bonded (EB) fiber-reinforced polymer (FRP) fabric was chosen as the preferred retrofit strategy due to its cost-effectiveness and proven performance. The FRP-shear-strengthening scheme for the deficient end-hinging regions of the MRF beams was designed and evaluated through large-scale cyclic testing of three replica specimens. The specimens were constructed at 4/5 scale and cantilever T-beam configurations with lengths of 3.40 m or 3.17 m. The cross-sectional geometry was 0.98 × 0.61 m with a top slab of 1.59 m in width and 0.12 m in thickness. Applied to these specimens were three different retrofit configurations, tested sequentially, namely: (a) unanchored continuous U-wrap; (b) anchored continuous U-wrap with conventional FRP-embedded anchors at the ends; and (c) fully closed external FRP hoops made of discrete FRP U-wrap strips and FRP through-anchors that penetrate the top slab and connect both ends of the FRP strips, combined with intermediate crack-control joints. The strengthening concept with FRP hoops precluded the premature debonding and anchor pullout issues of the two more conventional retrofit solutions and, despite a more challenging and labor-intensive installation, was selected for the in-situ implementation. The proposed hooplike EB-FRP shear-strengthening scheme enabled the deficient MRF beams to overcome a 30% shear overstress at the end-yielding region and to develop high-end rotations (e.g., 0.034 rad [3.4% drift] at peak and 0.038 rad [3.8% drift]) at strength loss for a beam that, otherwise, would have prematurely failed in shear. These values are about 30% larger than the ASCE 41 prescriptive value for the Life Safety (LS) performance objective. Energy dissipation achieved with the fully closed scheme was 108% higher than that of the unanchored FRP U-wrap and 45% higher than that of the FRP U-wrap with traditional embedded anchors. The intermediate saw-cut grooves successfully attracted crack formation between the strips and away from the FRP reinforcement, which contributed to not having any discernable debonding of the strips up to 3% drift. This paper presents the experimental evaluation of the three large-scale laboratory specimens that were used as the design basis for the final retrofit solution. Full article