Search Results (29)

FRCM (Fabric-Reinforced Cementitious Matrix) composites, while providing an effective alternative to FRP (Fiber-Reinforced Polymer) strengthening systems when epoxy resins cannot be used, typically fail to achieve their full strengthening potential. Research indicates that appropriate mesh anchorage systems can minimize some of the undesirable effects that limit FRCM composite performance. This study investigates the effectiveness of different anchorage systems for PBO (p-Phenylene Benzobis Oxazole) fibers in FRCM composites used for strengthening reinforced concrete slabs. A series of unidirectionally bent RC slabs were tested under four-point bending: an unstrengthened control element, slabs strengthened with PBO-FRCM without anchorage, with bar anchorage (GFRP bar in a groove), and with cord anchorage (PBO cord through the slab). The research focused on analyzing the load–deflection behavior and key strain mechanisms that influence structural performance. The findings indicate that a single layer of PBO-FRCM increases bending capacity, raises yield load, and delays initial cracking. Most significantly, the research reveals substantial differences in composite mesh utilization efficiency. This study confirms that mechanical anchorage, particularly bar anchorage, significantly enhances the effectiveness of PBO-FRCM strengthening systems by delaying composite detachment and allowing for greater utilization of the high-strength fiber material. These results contribute valuable insights for RC slabs using FRCM composite systems and the anchorage of their mesh. Full article

The use of fiber-reinforced polymer (FRP) composites in retrofitting and strengthening reinforced concrete (RC) slabs has gained substantial attention due to their durability, high strength-to-weight ratio, and ease of application. The objective of this study was to theoretically investigate the flexural behavior of RC slabs strengthened with carbon fiber-reinforced polymer (CFRP) plates applied in different percentages and patterns using finite element methods (FEMs) in comparison with the experiment outcomes available in the literature using the ABAQUS software (version 2020). This study focused on understanding the influence of the CFRP configuration on the structural behavior, including the load-carrying capacity, flexural performance, crack patterns, and failure modes, under static loading on seventeen RC slabs of 1800 × 1800 mm and 150 mm thickness. A comprehensive program was adopted, where RC slabs were strengthened using CFRP plates with different coverage percentages (0.044, 0.088, 0.133, 0.178, and 0.223) and arrangements (unidirectional, cross-hatched, and grid patterns) to evaluate the slabs’ performance under realistic service conditions. After comparison, the results validate that the percentage and pattern of CFRP plates influence the performance of RC slabs. Higher CFRP plate percentages yielded greater strength enhancement, while optimized patterns guaranteed a uniform stress distribution and delayed crack initiation. This study hypothesizes that the flexural strength, stiffness, and failure behavior of RC slabs are significantly affected by the percentage and arrangement of CFRP strengthening, with certain configurations providing superior structural performance. The use of CFRP cross-hatched plates improved the load–deflection behavior, increasing the ultimate loads by 35% (452 kN) while reducing ultimate deflection, with the cross-hatched CFRP specimen showing the highest deflection among all the CFRP specimens. This study provides engineers and practitioners with valuable information on choosing appropriate strengthening plans for RC slabs using CFRP plates, leading to more cost-effective and ecologically friendly structural rehabilitation methods. Full article

While fiber-reinforced polymer (FRP) sheets effectively enhance the flexural strength of reinforced concrete (RC) slabs, excessive flexural strengthening can reduce ductility and lead to brittle failure. This study provides an overview of the failure limits for the end spans of continuous RC slabs, considering the relationship between moment and shear capacities. A design approach for maximizing the strength contribution and amount of carbon FRP (CFRP) while ensuring ductile failure in strengthened slabs was developed and refined based on ACI standard recommendations. The failure mode of the strengthened slab was validated through numerical analysis using Abaqus software by further investigating the stress distribution of flexural members. Analytical results indicated that a 0.15 mm thick CFRP layer could enhance the nominal failure load by 148% while preserving desirable ductile failure behavior, demonstrating the effectiveness and feasibility of the proposed approach. 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

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

The fiber-reinforced polymer (FRP) strengthening of reinforced concrete (RC) elements with torsional deficiencies has not yet been extensively studied. Existing studies have primarily focused on rectangular RC beams. The few studies on L or T-shaped beams have used open-form retrofitting methods. However, premature debonding of the retrofitting from concrete surfaces often leads to detachment before achieving enhanced torsional capacity. This study introduces an innovative application of closed-form FRP retrofitting for RC T-beams against torsion. Two novel closed-form torsional upgrading methods were proposed and investigated through a comprehensive experimental program involving eight large-scale T-beams. One method employs FRP ropes embedded in transverse grooves near the surface, while the other combines U-shaped EB-FRP strips with FRP ropes. Additionally, two configurations were examined replicating scenarios where the upper part of the slab is accessible or inaccessible. The results demonstrate that the closed-form methods improve torsional strength by 9% to 25% and twist at failure by 92% to 536% compared to unstrengthened beams, with beams retrofitting through the slab exhibiting superior performance. Step-by-step technical guidelines of the proposed methods are presented to minimize construction defects and ensure effective implementation in real RC structures. Full article

This article explores the punching shear behavior of GFRP-RC interior slab–column connections. The parameters tested included the column–aspect ratio (1.0, 2.0, 3.0, 4.0, and 5.0), perimeter-to-depth ratio for square column stubs with side lengths of 0.3, 0.4, 0.5, 0.6, and 0.7 m, and span-to-depth ratios of 4, 6, 8, 10, and 12. A review of the literature revealed that no previous study has investigated the effect of these parameters or their interactions on this type of connection. Numerically, twenty-five slabs were created using finite element (FE) software (V3), each with square dimensions of 2.5 m and a constant thickness of 0.2 m. The central column extended 0.3 m from the top and bottom of the slab. All four sides of the slabs were supported, and the specimens underwent pure static shear load testing. The test results demonstrated that all slabs failed due to punching shear. Increasing any parameter value reduced the punching shear stresses. Additionally, the results indicated that Canadian (CSA-S806-12) and Japanese (JSCE-97) standards for FRP-RC materials generally provided the closest predictions of punching shear capacity compared to the American guideline, ACI 440.1R-22. However, all standards exhibited shortcomings and require enhancement and modifications, particularly to consider the impact of the span-to-depth ratio. Therefore, three equations were developed to predict the shear strength of the connections, yielding better results than those prescribed by the North American and Japanese standards. Full article

Several design standards have been developed in the last two decades to estimate the punching capacity of two-way reinforced concrete (RC) slabs reinforced with fiber-reinforced polymer (FRP) reinforcement. FRP-RC design standards include the recently published ACI 440.11-22, CSA/S806-12, and JSCE-2007. These models are either based on empirical data or semi-empirical methods and calibrated using different databases. Additionally, these standards do not have provisions for connections with shear reinforcement. Therefore, a reliable worldwide database for developing and assessing the applicability of such provisions with test results is vital. This study presents a worldwide and up-to-date database for punching shear of FRP-RC slabs. The database includes 197 tested connections, comprising interior and edge connections, with and without shear reinforcement, and a wide range of materials and cross-sectional properties. The database was used to evaluate the accuracy of the mentioned standards in predicting the punching shear capacity. For connections without shear reinforcement, it was determined that the three design standards yielded similar performance with different conservatism levels. ACI 440.11-22 yielded the most conservative results, with average V_exp/V_pred ratios of 2.04 compared to 1.28 and 1.3 for other models. For connection with shear reinforcement, specimens with E_vf> 100 GPa resulted in V_exp/V_pred ratios less than 1.0 for ACI and CSA standards. Full article

Fiber-Reinforced Polymer (FRP) composites have emerged as a promising alternative to conventional steel reinforcements in concrete structures owing to their benefits of corrosion resistance, higher strength-to-weight ratio, reduced maintenance cost, extended service life, and superior durability. However, there has been limited research on non-destructive testing (NDT) methods applicable for identifying damage in FRP-reinforced concrete (FRP-RC) elements. This knowledge gap has often limited its application in the construction industry. Engineers and owners often lack confidence in utilizing this relatively new construction material due to the challenge of assessing its condition. Thus, the main objective of this study is to determine the applicability of two of the most common NDT methods: the Ground-Penetrating Radar (GPR) and Phased Array Ultrasonic (PAU) methods for the detection of damage in FRP-RC elements. Three slab specimens with variations in FRP type (glass-, carbon- and basalt-FRP, i.e., GFRP, CFRP, and BFRP, respectively), bar diameter, bar depths, and defect types were investigated to determine the limitations and detection capabilities of these two NDT methods. The results show that GPR could detect damage in GFRP bars and CFRP strands, but PAU was limited to damage detection in CFRP strands. The findings of this study show the applicability of conventional NDT methods to FRP-RC and at the same time identify the areas with a need for further research. Full article

Sustainable solutions in the building construction industry have emerged as a new method for retrofitting applications in the last two decades. Fiber-reinforced polymers (FRPs) have garnered much attention among researchers for improving reinforced concrete (RC) structures. The existing design guidelines for FRP-strengthened RC members were developed using empirical methods that are based on specific databases, limiting the accuracy of the predicted results. Therefore, the use of innovative and efficient prediction tools to predict the behavior of FRP-strengthened RC members has become essential. During the last few years, efforts have been progressively focused on the use of machine learning (ML) as a feasible and effective technique for solving various structural engineering problems. Its capability to predict the behavior of complex nonlinear structural systems while considering a wide range of parameters offers a distinctive opportunity to make the behavior of RC members more predictable and accurate. This paper aims to evaluate the current state of using various ML algorithms in RC members strengthened with FRP to enable researchers to determine the capabilities of current solutions as well as to find research gaps to carry out more research to bridge revealed knowledge and practice gaps. Scopus databases were searched using predefined standards. The search revealed ninety-six articles published between 2016 and 2023. Consequently, these articles were analyzed for ML applications in the field of FRP retrofitting, including flexural and shear strengthening of RC beams, flexural strengthening of slabs, confinement and compressive strength of columns, and FRP bond strength. The results reveal that 32% of the reviewed studies focused on the application of ML techniques to the flexural and shear strengthening of RC beams, 32% on the confinement and compressive strength of columns, 6.5% on the flexural strengthening of slabs, 22% on FRP bond strength, 6.5% on materials, and 1% on beam–column joints. This research also revealed that the application of various ML algorithms has shown a significant improvement in resistance prediction accuracy as compared with the existing empirical solutions. Supervised learning techniques were the most favorable learning method due to their good generalization, interpretability, adaptability, and predictive efficiency. In addition, the selection of suitable ML algorithms and optimization techniques is found to be mainly dictated by the nature of the problem and the characteristics of the dataset. Nonetheless, selecting the most appropriate ML model and optimization algorithm for each specific application remains a challenge, given that each algorithm is developed with different principles and methodologies. Full article

Reinforced concrete (RC) one-way ribbed slabs serve as a prevalent flooring solution in the Middle East. In this region, the occurrence of openings within these slabs is frequent, particularly when making modifications to existing buildings. However, these openings compromise the stiffness and load-bearing capacity of the slabs, necessitating strengthening measures. All of the available investigations were carried out on strengthening RC one- and two-way solid slabs with openings. However, a noticeable research gap exists, as none of these studies have delved into the strengthening of RC one-way ribbed slabs with openings. This gap was bridged in this study by conducting a comprehensive experimental inquiry into the effectiveness of utilizing fiber-reinforced polymer (FRP) laminates to restore the flexural capacity of RC one-way ribbed slabs featuring flexure openings. The experimental program comprised four half-scale one-way ribbed slabs (having three ribs) divided into one unstrengthened specimen without openings to act as a reference, one unstrengthened specimen with a single opening located in the peak-moment region, and two FRP-strengthened slabs each having a single opening located in the peak-moment region. The dimensions of each slab were 2600 mm (length) × 825 mm (width) × 175 mm (thickness). The openings were square (side length = 400 mm), which included cutting the middle rib. The slabs were tested under four-point flexure until failure. It was revealed that strengthening slabs using FRP sheets fully restored the flexural capacity, which was even exceeded by up to 8%. However, the secant stiffness and dissipated energy were partially restored compared with the unstrengthened slab without opening, and these response parameters were reduced by up to 19% and 32%, respectively. Moreover, the displacement ductility for strengthened specimens was moderately reduced compared with the unstrengthened specimen without opening. Furthermore, an analytical procedure was suggested based on section analysis for quick and reasonable assessment of the peak load for both unstrengthened and strengthened one-way ribbed slabs with and without flexure openings. Full article

Predicting the punching shear strength (PSS) of fiber-reinforced polymer reinforced concrete (FRP-RC) beams is a critical task in the design and assessment of reinforced concrete structures. This study utilized three meta-heuristic optimization algorithms, namely ant lion optimizer (ALO), moth flame optimizer (MFO), and salp swarm algorithm (SSA), to select the optimal hyperparameters of the random forest (RF) model for predicting the punching shear strength (PSS) of FRP-RC beams. Seven features of FRP-RC beams were considered as inputs parameters, including types of column section (TCS), cross-sectional area of the column (CAC), slab’s effective depth (SED), span–depth ratio (SDR), compressive strength of concrete (CSC), yield strength of reinforcement (YSR), and reinforcement ratio (RR). The results indicate that the ALO-RF model with a population size of 100 has the best prediction performance among all models, with MAE of 25.0525, MAPE of 6.5696, R² of 0.9820, and RMSE of 59.9677 in the training phase, and MAE of 52.5601, MAPE of 15.5083, R² of 0.941, and RMSE of 101.6494 in the testing phase. The slab’s effective depth (SED) has the largest contribution to predicting the PSS, which means that adjusting SED can effectively control the PSS. Furthermore, the hybrid machine learning model optimized by metaheuristic algorithms outperforms traditional models in terms of prediction accuracy and error control. Full article

The service environment of civil air defense engineering structures is relatively harsh, and the corrosion of steel bars is the main reason for reducing the durability of concrete structures in civil air defense engineering. A hybrid FRP–steel-reinforced concrete (hybrid-RC) structure has excellent durability. Therefore, it is a good choice to apply hybrid-RC to civil air defense engineering structures. In order to study the blast resistance of hybrid-RC structures, close blast and contact blast experiments were carried out on hybrid-RC slabs, steel-reinforced concrete (SRC) slabs and GFRP-reinforced concrete (GRC) slabs. For the close blast experiment, the steel reinforcement in the SRC slab first entered the plasticity stage, whereas the GFRP reinforcement in the hybrid-RC slab was in the elastic stage under the close blast. Therefore, the capacity to dissipate energy through the vibration in the hybrid-RC slab was better than that of the SRC slab. The residual deformation in the hybrid-RC slab after the close blast experiment was smaller than that of the SRC slab. The Blast Recovery Index (BRI) was introduced to evaluate the recovery capacity of the concrete slab after the close blast, and damage assessment criteria for the hybrid-RC slabs were proposed according to the maximum support rotation θ_m and BRI. There was little difference in the size of the local damage in the hybrid-RC slab and the SRC slab under the contact blast. However, since the GFRP reinforcement was still in the elastic stage and the steel reinforcement was plastic after the contact blast, the ratio of the residual bearing capacity to the original bearing capacity in the hybrid-RC concrete slab would be larger than that of the SRC slab. The prediction formula for the top face diameter D and blasting depth L of the hybrid-RC slab was obtained through dimensionless analysis. This research can provide a reference for the anti-blast design of hybrid-RC slabs. Full article

Bar splicing is considered an essential part of the construction process of reinforced concrete (RC) due to the ease of installation in construction, transportation constraints, and restricted length of reinforcing bars. Splices serve the primary role of joining reinforcement bars in standard RC elements such as columns, walls, beams, slabs, and joints. Bond behavior between the bars and the concrete is one of the fundamental qualities required for appropriate RC structure design and analysis, as it affects serviceability and ultimate limit states. The most common failure found in lap splice locations is debonding, which occurs at the splice region and insufficient lapped length is considered as the primary cause because of design or construction mistakes, design by outmoded code, and natural catastrophes. As a result, strengthening existing substandard splices in RC structures is critical. The purpose of this research is to analyze and summarize experimental strengthening solutions for inadequate splices. The most common methods are confining spirals, confining with internal or external steel stirrups or carbon fiber reinforced polymer (CFRP), concrete jacketing, fiber reinforced polymers (FRP), post-tensioning prestressed RC, external confining with CFRP, near surface mounted (NSM) techniques, ultra-high-performance concrete (UHPC), fiber reinforced concrete (FRC) and combinations of two methods. Each method of strengthening is evaluated based on its performance, benefits, drawbacks, application-specific elements, and variables influencing the design and scope of applicability. A comparison of the key methodologies was also carried out. The most recent studies and recommendations for improving inadequate lapped splices are provided. Full article

This paper presents a numerical study to evaluate the fire resistance of concrete beams and slabs incorporating natural fiber-reinforced polymers (FRP). A validated finite element model was applied to carry out a series of numerical studies on fire-exposed reinforced concrete (RC) beams and slabs strengthened with conventional and bio-based FRP composites. The model calculates the temperature-dependent moment–curvature relationship for various segments of the member at each time step, which are then used to calculate the moment capacity and deflection of the member. The variables in the beams and slabs include different strengthening techniques (externally bonded FRP and near-surface mounted FRP), different fiber composites, and fire insulation schemes (uninsulated and insulated). The results from the study indicate that the bio-based FRP-strengthened RC members undergo a faster degradation in moment capacity and also experience higher deflections under fire exposure. This leads to a lower fire resistance in RC members with bio-based FRP composites compared to beams and slabs with conventional FRP-strengthened concrete members. The addition of fire insulation to the bio-based FRP-strengthened members can enhance their fire performance and help achieve the required fire resistance ratings for use in building applications. In this study, the NSM CFRP-strengthened RC beams were found to have a fire resistance of 3 h without any fire insulation; however, the bio-based FRP-strengthened beams required a layer of vermiculite–gypsum-based fire insulation material (of about 25 mm) to achieve similar fire resistance. Full article