Search Results (232)

In practical engineering, buildings are predominantly subjected to combined forces, and reinforced concrete (RC) beams serve as the primary load-bearing components of buildings. However, there is a paucity of research on the torsional effects of RC beams, particularly concerning the torsional failure mechanisms of large-size beams. To address this gap, this paper establishes a meso-scale numerical analysis model for RC beams reinforced with Carbon Fiber Reinforced Polymer (CFRP) sheets under combined bending and torsion pressures. The research analyzes how the fiber ratio and torsion-bending ratio govern torsion-induced failure characteristics and size effects in CFRP-strengthened RC beams. The results indicate that an increase in the fiber ratio leads to accumulated damage distribution in the RC beam, a gradual decrease in CFRP sheet strain, and an increase in peak load and peak torque, albeit with diminishing amplitudes; as the torsion-bending ratio increases, crack distribution becomes more concentrated, the angle between cracks and the horizontal direction decreases, overall peak load decreases, peak torque increases, and CFRP sheet strain increases; and the nominal torsional capacity of CFRP-strengthened RC beams declines with increasing size, exhibiting a reduction of 24.1% to 35.6%, which distinctly demonstrates the torsional size effect under bending–torsion coupling conditions. A modified Torque Size Effect Law is formulated, characterizing in quantitative terms the dependence of the fiber ratio and the torsion-bending ratio. Full article

The growing application of carbon fiber-reinforced polymers (CFRPs) in construction opens new possibilities for replacing traditional materials such as steel, particularly in strengthening and retrofitting concrete structures. CFRP materials offer notable advantages, including high tensile strength, low self-weight, corrosion resistance, and the ability to be tailored to complex geometries. This paper provides a comprehensive review of current technologies used to strengthen concrete columns, with a particular focus on the application of fiber-reinforced polymer (FRP) tubes in composite column systems. The manufacturing processes of FRP composites are discussed, emphasizing the influence of resin types and fabrication methods on the mechanical properties and durability of composite elements. This review also analyzes how factors such as fiber type, orientation, thickness, and application method affect the load-bearing capacity of both newly constructed and retrofitted damaged concrete elements. Furthermore, the paper identifies research gaps concerning the use of perforated CFRP tubes as internal reinforcement components. Considering the increasing interest in innovative column strengthening methods, this paper highlights future research directions, particularly the application of perforated CFRP tubes combined with external composite strengthening and self-compacting concrete (SCC). Full article

The use of a carbon-fiber-reinforced polymer (CFRP) for structural strengthening has been widely adopted in recent decades. Early studies focused on externally bonded (EB) techniques, but premature delamination of CFRP from concrete surfaces often limited their efficiency. To address this, alternative methods, such as Externally Bonded Reinforcement Over Grooves (EBROG) and Externally Bonded Reinforcement Inside Grooves (EBRIG), were developed to enhance the bond strength and delay delamination. While most research has examined longitudinal groove layouts, this study investigates a hybrid system combining a CFRP fabric bonded inside transverse grooves (EBRITG) with externally bonded layers over the grooves (EBROTG). The system leverages the grooves’ surface area to anchor the CFRP and improve the bonding strength. Seven RC beams were tested in two stages: five beams with varied strengthening methods (EBROG, EBRIG, and hybrid) in the first stage and two beams with a hybrid system and concrete cover anchorage in the second stage. Results demonstrated significant flexural capacity improvement—57% and 72.5% increase with two and three CFRP layers, respectively—compared to the EBROG method, confirming the hybrid system’s superior bonding efficiency. Full article

The use of both structural steel and reinforced concrete is common in civil and military infrastructure projects. Anchorage plays a crucial role in these systems, serving as the key element that connects structural components and secures attachments within complex composite structures. This research focuses on evaluating the performance of steel–concrete column connections under the combined effects of lateral loading and fire exposure. Additionally, the study investigates the use of carbon fiber-reinforced polymers (CFRP) for strengthening and repairing these connections. The research methodology combines experimental testing and finite-element modeling to achieve its objectives. First, experimental investigation was carried out to test two groups of steel-reinforced concrete column specimens, each group made of three specimens. The first group specimens were designed based on special moment frame (SMF) detailing, and the other group specimens were designed based on intermediate moment frame (IMF) detailing. These two types of design were selected based on seismic demands, with SMFs offering high ductility and resilience for severe earthquakes and IMFs providing a cost-effective solution for moderate seismic zones, both benefiting from ongoing innovations in connection detailing and design approaches. Then, finite-element analysis was conducted to model the test specimens. High-fidelity finite-element modeling was conducted using ANSYS program, which included three-dimensional coupled thermal-stress analyses for the six tested specimens and incorporated nonlinear temperature-dependent materials characteristics of each component and the interfaces. Both the experimental and numerical results of this study show that fire has a more noticeable effect on displacement compared to the peak capacities of both types of specimens. Fire exposure results in a larger reduction in the initial residual lateral stiffness of the SMF specimens when compared to IMF specimens. While the effect of CFRP wraps on initial residual lateral stiffness was consistent for all specimens, it caused more improvement for the IMF specimen in terms of post-fire ductility when compared to SMF specimens. This exploratory study confirms the need for further research on the effect of fire on the concrete–steel anchorage zones. Full article

To study the flexural performance of damaged reinforced concrete beams reinforced with carbon fiber nets (CFNs), seven beams were designed for a flexural test. The physical parameters, such as damage phenomena, characteristic load, deflection variation, concrete strain, reinforcement strain, and CFRP mesh strain, were analyzed using different forms of U-hoops and the preload amplitude as variables. The results show that the magnitude of the preload and the different U-hoop forms affect the ultimate load capacity, crack distribution, and deflection of the beams. Compared with the unreinforced beams, the yield load, ultimate load, and cracking load of the reinforced beams were significantly increased; CFNs reinforcement could significantly improve the flexural load-carrying capacity of the beams. Under the same preload amplitude, the X-shaped diagonal U-hoop has better diagonal crack suppression capability than the vertical U-hoop. Under secondary stress conditions, CFNs reinforcement inhibits the appearance and development of cracks and increases the flexural load capacity, which can effectively alleviate the stiffness degradation caused by the preload. The simulation of the test results using the ANSYS (v2023 R1) 2016 platform produced good agreement, with an error of about 10%, which verifies the feasibility of using the finite element method to simulate the test beam. Full article

The work presents and examines a fiber anchoring system of NSM CFRP strips proposed for strengthening RC beams. The study included 11 beams: 3 unstrengthened beams, 3 beams strengthened with NSM CFRP strip without anchorage, and 5 beams strengthened with NSM CFRP strips with additional anchorage in two variants (the fiber anchor wrapped around the CFRP strip end and fan-folded on the beam surface; the fiber anchor connected with a 20 cm overlap to the strip). All beams were loaded until failure with two concentrated forces (four-point loading test). The measurements were carried out using digital image correlation (DIC). The obtained ultimate load values reached an average of 43.5 kN for unstrengthened beams, while for strengthened beams, they ranged between 56.6 kN and 60.2 kN. The strengthening efficiency was comparable for all beams regardless of the anchorage used and ranged from 29% to 37%. All strengthened beams failed due to strip debonding. The obtained results did not allow confirmation of the effectiveness of the proposed anchoring system. Detailed analysis showed that the lack of anchoring effectiveness was related to the debonding initiating factor, i.e., vertical crack opening displacement, which has not been described in proper detail by the researchers. Full article

Deep learning approaches based on autoencoders have been widely used for structural monitoring. Traditional approaches of autoencoders based on reconstruction errors involve limitations, since they do not exploit their hierarchical nature, and only healthy data are used for training. In this work, some health indicators, based on manifold invariance through the encoding procedure, were built for the monitoring of concrete structures strengthened with carbon fiber-reinforced polymers by directly exploring the latent space representation of the input data to a deep autoencoder. Latent representations of experimental observations of different classes were used for the learning of the network, delimiting areas in a low-dimensional space. New synthetic data with their variations, generated with a variational autoencoder, were encompassed to the trained autoencoder. The proposed method was verified on raw electromechanical impedance spectra obtained from lead zirconate titanate sensors bonded on a specimen subjected to different loading stages. The results of this research demonstrate the efficiency of the proposed approach. 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

Türkiye, a country that suffers significant structural damage from earthquakes, was struck by two major quakes on 6 February 2023, centered in Pazarcık (M_w = 7.7) and Elbistan (M_w = 7.6) in Kahramanmaraş. These earthquakes caused extensive damage and destruction to urban concrete structures, significantly contributing to the loss of life. Inadequate designs in columns, which are meant to maintain structural integrity and transfer forces, were a primary cause of the structural damage. This study provides information about these catastrophic earthquakes, focusing on the detailed examination of damages in reinforced-concrete (RC) columns. Structural analyses were conducted on a selected RC building, taking into account the primary causes of column damage: low-strength concrete and insufficient transverse reinforcement. Five different concrete classes and two transverse reinforcement spacing options were considered to analyze the impact of concrete strength. To address the exceeded shear forces in the columns, a fiber-reinforced polymer (FRP) wrapping method was employed for strengthening. Initially, a reinforcement analysis was performed on a single column that exceeded shear force limits, followed by strengthening applications on all columns exceeding the limit shear force. The results demonstrated that carbon fibers have a significant impact on the shear forces in columns. The conclusion of the research is that FRP increases the ductility of concrete columns, enabling them to withstand seismic forces more effectively. This is vital in ensuring the integrity of structures in earthquake-prone areas. Using FRP materials can also significantly reduce the carbon footprint associated with concrete construction by minimizing the need for maintenance and extending the lifespan of structures. FRP presents a sustainable and effective solution for addressing failures in reinforced concrete columns. Its unique properties not only enhance strength and durability but also significantly improve the resilience of structures against corrosion, seismic events, and overload conditions. Full article

In the case of load increases and the refurbishment of existing buildings, it is often necessary to carry out strengthening measures on existing timber beams. When timber concrete composite (TCC) ceilings cannot be used, it is possible to reinforce the undersides of the beams with structural steel or fiber composites (aramid or carbon-fiber-reinforced polymer). This work investigates how significant effects on the load-bearing and deformation behavior can be achieved with these materials in terms of construction practice. The article is intended to show structural engineers which reinforcement measures lead to which forces, deformations, etc., and how these are utilized. This should form the basis for the planning of reinforcement measures, as it is not clear from the beginning whether AFRP, CFRP, or steel is the most suitable material. For this purpose, a comparative parameter study was carried out under practical conditions and with a variable degree of reinforcement using the corresponding formulas. The internal forces in the timber and reinforcement cross-sections, the deflection behavior, and the failure loads at the strength and design levels were calculated. It was demonstrated that, particularly for steel and carbon-fiber-reinforced polymer (CFRP) reinforcements, significant increases in the ultimate load can be achieved and the often-important deformation behavior can be significantly improved. Especially the steel variant leads to high improvements in deflection and breaking load behavior, with the base material (wood) also being utilized more economically as a result. A comparative ecological study in the form of the global warming potential showed that reinforcement methods are also advantageous from the point of view of sustainability compared to renovations with timber concrete composite slabs or new concrete slabs. Full article

To investigate the strengthening effectiveness of Fabric-Reinforced Cementitious Matrix (FRCM) composites on shield tunnel segments, this study conducted four-point bending tests on FRCM composite panels. The influence of different cementitious matrices (engineered cementitious composite, ECC; ultra-high-performance concrete, UHPC) on the flexural behavior of FRCM panels was systematically analyzed. Numerical simulations were additionally conducted to analyze deformation behavior, damage progression, and stress variations in steel reinforcements within standard structural segments strengthened with FRCM composite panels. A parametric analysis was performed to assess the effects of cementitious matrix type, panel thickness, and carbon fiber-reinforced polymer (CFRP) grid layers on the reinforcement efficiency. The experimental results demonstrated that FRCM composite panels exhibit superior flexural performance. Specimens with UHPC matrices exhibited higher cracking stresses and enhanced flexural stiffness during the elastic phase, while those with ECC matrices demonstrated advantages in post-peak hardening behavior and energy dissipation capacity. Both matrix types achieved similar cracking strains and comparable ultimate flexural strengths. Numerical simulations revealed that FRCM strengthening significantly improves the ultimate flexural bearing capacity of segments while effectively controlling deformation. For UHPC-based FRCM reinforced segments, the ultimate bearing capacity increased with both UHPC thickness and CFRP layer quantity. In contrast, ECC-based FRCM reinforced segments exhibited capacity enhancement primarily correlated with CFRP layer addition, with negligible sensitivity to ECC thickness variations. 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

The combination of fiber reinforced polymer (FRP) and engineered cementitious composite (ECC) has emerged as a promising method for strengthening reinforced concrete (RC) structures. By embedding FRP within an ECC to form a composite reinforcement layer, the advantages of both materials can be effectively harnessed, and the dense ECC matrix can be employed to safeguard FRP from adverse environments. Significantly, the interface bonding property constitutes the key for the two materials to collaborate effectively. In light of the research gap related to the bonding performance of embedded FRP strips in ECC joints, this study conducted a bench-scale investigation into the pull-out behavior of carbon FRP (CFRP) strips within an ECC. The relationship between the average bonding strength (2.84 MPa~4.77 MPa) and the embedded length of FRP strips was established. Additionally, the pull-out mechanism of FRP strips within an ECC matrix was utilized to elucidate the influence of the embedded length on the distinct behavior of FRP strips within an ECC. An analytical method for predicting the full-range behavior of embedded FRP strip–ECC joints by using a trilinear bond–slip relationship was introduced. Four key parameters of the trilinear bond–slip relationship for embedded FRP strip–ECC joints were provided to meet the requirements of future engineering applications. Full article

The inefficiency of unreinforced concrete beams as flexural members poses a challenge because concrete’s tensile strength is significantly lower than its compressive strength. In response to this challenge, reinforcement bars are commonly employed near the tension zone of reinforced concrete (RC) beams. Nonetheless, structures constructed with RC face challenges such as reduced live load capacity, concrete deterioration, and the corrosion of reinforcement bars over time. To address this, ongoing research is exploring maintenance and retrofitting techniques using high-strength, lightweight fiber-reinforced polymer (FRP) composite materials such as carbon fiber-reinforced polymer (CFRP) and glass fiber-reinforced polymer (GFRP). In this study, the flexural performance of corroded RC beams was enhanced through retrofitting with CFRP plates and sheets. The corroded RC beams were fabricated using an applied-current method with a 5% NaCl solution to induce a 10% target corrosion level under controlled laboratory conditions. Flexural tests were conducted to evaluate the structural performance, failure modes, load–displacement relationships, and energy dissipation capacities. The results showed that CFRP reinforcement mitigates the adverse effects of corrosion-induced reduction in rebar cross-sectional areas, leading to increased stiffness and improved load-carrying capacity. In particular, CFRP reinforcement increased the yield load by up to 36.5% and the peak load by up to 90% in corroded specimens. The accumulated energy dissipation capacity also increased by 92%. These enhancements are attributed to the effective load-sharing behavior between the corroded rebar and the CFRP reinforcement. Full article

Fiber-reinforced polymers (FRPs) are effective for strengthening masonry walls. Debonding at the polymer–masonry interface is a major concern, requiring further investigation into interface behavior. This study utilizes detailed micro-modeling finite element (FE) analysis to predict failure mechanisms and analyze the behavior of brick masonry walls strengthened with externally bonded carbon fiber-reinforced polymer (CFRP) under in-plane loading. The research investigates three CFRP strengthening configurations (X, I, and H). The FE model incorporates the nonlinear behavior of brick masonry components using the Concrete Damage Plasticity (CDP) model and uses a cohesive interface approach to model unit–mortar interfaces and the bond joints between masonry and CFRPs. The results demonstrate that diagonal CFRP reinforcement enhances the ductility and capacity of masonry wall systems. The FE model accurately captures the crack propagation, fracture mechanisms, and shear strength of both unreinforced and reinforced walls. The study confirms that the model can reliably predict the structural behavior of these composite systems. Furthermore, the study compares predicted shear strengths with established design equations, highlighting the ACI 440.7R-10 and CNR-DT 200/2013 models as providing the most accurate predictions when compared to experimental results. Full article