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This study investigates the mechanical behavior of steel fiber-reinforced concrete (SFRC) beams internally reinforced with steel bars and externally bonded with carbon fiber-reinforced polymer (CFRP) sheets fixed by adhesive and hybrid jointing techniques. In particular, attention is paid to the load resistance and failure modes of composite beams....
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The axial load capacity and the stiffness of a rectangular hollow structural section (HSS) can be increased by adhesively bonding carbon fiber reinforced polymer (CFRP) plates to the outer surface of the steel tube. Experimental studies showed that two different failure modes generally occur for such a strengthened tube, the first mode was debondin...
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... Concrete reinforced with carbon fiber can optimize the mechanical or physical properties of concrete. However, it can make structures durable enough because it can expand the lifespan of infrastructures by preventing corrosion and improving crack propagation [24], [25], [26]. CFRC reduces porosity and water absorption, preventing freeze-thaw damage in cold climate. ...
Concrete is a widely used material in construction due to its ability to withstand compressive forces. However, it is weak in resisting tensile forces, typically bearing only about ten percent of its compressive strength under tension. This limitation has become a significant concern in modern construction and infrastructure development. While the concept of prestressing concrete has been introduced, it remains a costly solution. To address this challenge more cost-effectively, researchers have increasingly focused on the incorporation of fibers into concrete, although it cannot match the strength provided by prestressing. Fiber reinforcement enhances the tensile strength of concrete by exploiting its various beneficial characteristics such as the bridging effect, reduction of shrinkage cracks, and improved ductility. Various types of fibers, including natural fibers, synthetic fibers, glass fibers, and steel fibers, can be incorporated into concrete to improve its mechanical performance. This paper exhibits a comprehensive overview of the various types of fibers used as additives in concrete, evaluating their effects on concrete behavior. Fiber-reinforced concrete (FRC) offers a potential solution to enhance the mechanical properties of concrete in a cost-effective way.
... These materials, known as fiber-reinforced polymers (FRPs), have already seen widespread use in enhancing the performance of deficient RC structural members [9]. FRPs (sheets, strips, laminates, bars, and ropes) are commonly employed as additional external reinforcement to improve the flexural or shear capacity of these structures, utilized in the repair and strengthening of various RC components, including beam-column joints [10], columns [11], frames [12], beams [13][14][15], deep beams [16], corroded beams [17], and slabs [18][19][20]. ...
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.
... Various anchoring methods have been developed to delay or address the premature debonding issue and improve the overall performance of the EB-CFRP strengthening systems (Gribniak et al., 2017(Gribniak et al., , 2023Godat et al., 2020;Aksoylu, 2021). Among these, spike anchors, typically CFRP ropes, gained traction as a practical solution, anchoring the EB-CFRP sheets to the concrete substrate (Godat et al., 2020). ...
Existing reinforced concrete buildings frequently require shear-strengthening to ensure structural integrity, and externally bonded carbon fiber-reinforced polymers (EB-CFRP) have become a wide-applicable approach. However, slabs and geometric restrictions impede wrapping the element, necessitating incomplete U-shaped applications vulnerable to debonding failures. This experimental study introduces a novel approach for shear strengthening nine full-scale T-beams using near-surface mounted CFRP ropes forming closed stirrups. Their
effectiveness as shear reinforcement is investigated compared to an alternative method incorporating EB-CFRP sheets with CFRP rope anchorage. Test results indicate that both techniques enhance the beams’ strength and performance. The load capacity increased 2 times for the reference specimen and 1.4-1.9 times for the strengthened beam with FRP sheets. The displacement at the maximum load increased 5.2-7.8 and 6.6-7.5 times, respectively. The rope stirrup arrangement outperforms the rope anchorage system in mechanical and construction efficiency. A thorough protocol for executing these processes to mitigate construction-related defects is introduced.
... Normally, FRP sheets are externally bonded along tensile surfaces or vertical sections of concrete flexural members to enhance their bending capacity or shear resistance [3][4][5][6]. It is easier to bond reasonable layers and numbers of FRP sheets on the surface of concrete with an adhesive, while rational measures, including fiber nails, fiber/steel depression strips and fiber/steel stirrups, can be used to ensure the bond of FRP sheets to the surface of concrete with deformation under load [3,[7][8][9][10][11]. Another approach utilizes near-surface-mounted FRP strips by placing the FRP strips in the cutting grooves of the concrete surface with epoxy paste, which can help prevent the FRP from debonding from the concrete and improve the bearing capacity of strengthened reinforced concrete beams compared with those of externally bonded FRP in the case of an equal amount of reinforcement being used [12][13][14]. ...
... I 0 = (0.0833 + 0.1α Es ρ)bh 3 (11) y 0 = (0.5 + 0.42α Es ρ)h ...
Because researchers are aiming to restore the deformation and minimize the crack width of existing concrete structures, the strengthening technology of prestressed carbon-fiber-reinforced plastic (CFRP) is currently the focus of many studies and applications. In terms of the strengthening of a prestressed CFRP sheet on the flexural performance of cracked reinforced concrete beams under repeated loads, a four-point bending test of 12 beams was conducted considering the prestress degree reflected by the amount and the prestress force of the CFRP sheet. The longitudinal strengthened CFRP sheet was bonded on the bottom surface of the test beam and fixed by U-jacket CFRP sheets at the ends after tensioning. The strains of concrete, longitudinal tensile steel bars and CFRP sheets were measured at the pure bending segment of test beams, while the cracks, midspan deflection and failure pattern were recorded. The results show that the normal strain on the mid-span section of the strengthened beams by the prestress CFRP sheets was fitted for the assumption of plane section, the cracks and mid-span deflection decreased with the prestress degree of the CFRP sheets to provide better serviceability for the strengthened beams, the load capacity could be increased by 41.0–88.8% at the yield of longitudinal tensile steel bars and increased by 41.9–74.8% at the ultimate state and the ductility at the failure state was sharply reduced by 54.9–186%. The peeling off of broken CFRP sheets played a role in controlling the failure pattern of the strengthened beams under repeated loads. Finally, methods for predicting the bending performance of reinforced concrete beams strengthened by prestressed CFRP sheets were proposed. This study enriches the knowledge about damaged reinforced concrete beams that were strengthened with prestressed CFRP sheets.
... A significant number of experimental studies have also been conducted on RC beams strengthened in flexure with NSM FRP circular or rectangular rods [21][22][23][24][25][26][27]. The existing experimental studies on RC beams strengthened with NSM FRP usually show a significant improvement in flexural capacity with high utilization of the tensile capacity of the FRP compared with the EB-strengthening technique [28,29]. Furthermore, numerous research in the literature has shown how ultimate loading capacities and the associated bond mechanisms of strengthened beams with NSM FRP are deeply influenced by the thickness of the concrete cover, geometry and percentage of FRP strengthening, and amount of longitudinal steel reinforcement and compressive concrete strength [30][31][32][33]. ...
This paper intends to deepen the topic of damage detection based on non-destructive tests (NDT) for the assessment of the dynamic behavior of RC beams damaged and strengthened both with near-surface mounted (NSM) Carbon and GlassFRP rods. The NSM strengthening with fiber-reinforced polymer (FRP) rods of damaged reinforced concrete (RC) beams is a viable alternative to the traditional strengthening with externally bonded (EB) FRP strips or sheets. In this paper, static tests were foreseen on RC beams to create cracking, and successively, the RC beams strengthened with NSM CFRP and GFRP rods were still investigated using free vibration tests at different loading levels until failure. The purpose of this research is to compare the response of two different types of strengthening of damaged RC beams based on the strength of CFRP and GFRP rods until failure modes. At different steps of loading, the behavior of beams under experimental vibrations has been monitored by frequency response function (FRF) diagrams. Finally, a discussion of the results is presented.
... This similarity results from the bar reinforcement effect and well agree with the experimental deformation analysis principles formulated in the dissertation [55]. • The fibers improve the flexural resistance of SFRC elements with bar reinforcement in the post-cracking stage, ensuring the development of efficient composite systems, e.g., [56,57]. ...
... Fig. 11b presents the smoothed stress-strain diagram averaging five inverse simulations of stochastically selected moment-curvature data points, generating individual scatterplots. The moving average of all five stress-strain sets described the averaged constitutive model in the studies [29,37,[54][55][56]59]. The thesis [55] describes the inverse analysis procedure in detail and presents the corresponding MATLAB code. ...
Fiber reinforcement is a promising solution to cracking problems and improving the concrete's structural performance. The residual strength of the cracked concrete can characterize the reinforcement efficiency. However, quantifying the residual performance of steel fiber-reinforced concrete (SFRC) is challenging. The existing methodologies provide empirical formulas for estimating the residual strength using test results of SFRC elements in which a predominant crack governs the mechanical resistance. For instance, the 0.5 mm crack width determines the minimum value considered in the RILEM standard formulas. Thus, the SFRC strength evolution at earlier cracking stages remains unknown. At the same time, such a crack approximation is irrelevant to structural cases when reinforcement bars stimulate the formation of multiple cracks, and the 0.1-0.2 mm crack typically corresponds to the yielding of the steel bars. This study describes an alternative approach for quantifying the average residual stresses in SFRC elements with multiple cracks. It hypothesizes the possibility of separating the mechanical resistance components, corresponding to tension stiffening and fiber bridging effects characteristic of SFRC elements with bar reinforcement, using standardized small-scale specimens to estimate the fiber contribution. The laboratory tests of the plain concrete and SFRC beams with bar reinforcement illustrate the proposed technique. The RILEM standard three-point bending tests and the numerical simulation of full-scale beams verify the analysis's adequacy. The developed model is suitable for finite element simulations (employing the smeared crack model); the capability of separating the tension stiffening and fiber bridging effects ensures its versatility.
... This effect under the service limit condition might have a significant impact on deflections, rigidity, and crack widths. SFs may considerably increase residual stiffness and decrease control crack splitting in concrete since they can withstand tensile loads along fractures [74][75][76][77][78]. But the very limited use of SFRC in beams is roughly due to the challenges in identifying rational and precise methods which depict and predict the behavior of the material in both the service and ultimate limit states. ...
This article assess the precise estimation of the hysteresis loop of reinforced concrete (RC) beams in distinct failure cases to verify inelastic seismic beam function. Any test failure in RC frame columns is able to produce hysteresis curves in low cyclic repeat load that follows the analysis of the hysteretic behavior of the frame columns. In this case, the application of fibers as a mass enhancement to improve the post-cracking of RC beams, strength, and delay cracking has been investigated. In this research, the hysteretic response of deep and slender SFRC beams enhanced with SF using ten beams under the reversal cyclic load was studied through innovative ANN hysteresis. Shear and flexural strength of SFRC beams were analyzed using a diverse number of fibers with content from 0.1 to 5% per volume, closed stirrups (from 0 to 0.5%), and steel reinforcing bars (0.50% and 1.50%). The innovative artificial neural network hysteresis model has been utilized to define the accuracy prediction of the parameters and determine the hysteresis loop of RC columns failing in different modes. Comparing the experimental findings properly indicated the accuracy of the model to capture the main features of the response, such as the load versus deformation cyclic envelope, SFRC tension softening effect, and the impact of the fibers on the hysteretic energy. The results revealed that SFRC beams represented developed cyclic efficiency in case of deformation, load-bearing capacity, residual stiffness, cracking and energy dissipation ability while generating their integrity within the imposed reversal cyclic experiments.
... The proper combination of advanced composite materials can also enhance impact resistance [12] and ensure structural integrity [13] and efficiency in utilizing the reinforcement components [14]. The latter investigation exemplifies the structural steel design alteration, extending it to the post-yielding stage when deformations but not the strength condition governs the structural solution. ...
... Unfortunately, the mechanical performance of polymeric composites is an aging and long-term deterioration subject [15][16][17][18] and requires further extensive investigation. In addition, the advanced composites raise the internal structure and component optimization problems, e.g., [3,8,13,14], requiring innovative design solutions and concepts. ...
... The research already identified that combining steel fibers and fiber-reinforced polymer (FRP) sheets with mechanical fastening resulted in structurally efficient and sustainable reinforcement systems for cement-based composite elements [13,19]. It was shown that the failure of the ordinary concrete beams was due to the splitting of the concrete cover at the level of the longitudinal reinforcement. ...
The modern industry allows producing composite materials with a broad spectrum of mechanical properties applicable in medicine, aviation, and automotive industries. However, the building industry generates a substantial part of budgets worldwide and utilizes vast material amounts. At the same time, the engineering practice has revealed that innovative technologies require new design concepts related to developing materials with mechanical properties tailored for structural purposes. It is the opposite of the current design philosophy when design solutions allow applying only the existing typical materials, the physical characteristics of which, in general, are imperfectly suiting the technical requirements, leading to an inefficient increase of the material amounts for safety’s sake. Moreover, some structural solutions are barely possible using standardized approaches. This work illustrates the implementation of the proposed adaptive design concept and discusses the design perspectives.
... The EBR-FRP is one of the popular methods used to strengthen RC members with insufficient ductility and strength [12,13]. The most important advantages are lightness and high strength (high strength-toweight ratio), resistance to corrosion, resistance to environmental influences and ease of application. ...
In this study, the behavioral changes of reinforced concrete T-beams with insufficient shear strength under vertical loads as a result of strengthening with glass fiber reinforced polymer composites (GFRP) in various configurations was investigated comparatively. Nine reinforced concrete T-section shear-critical beams were produced. One of the beams is a reference and the other eight are wrapped with different GFRP methods. GFRP composites were applied along the shear spans of the beams in different wrapping styles, with or without anchorage. The effect of each GFRP application on the load-bearing, ductility and energy dissipation capacity of beams was investigated. As a result of the experiments, it was seen that shear failure was prevented by increasing the bonding surface between the GFRP and the concrete surface. In addition, it was observed that the anchored specimens strengthened with GFRP strips with a lower bonding surface were more effective in terms of ductility than all other non-anchor strengthening types. The shear capacity of beams having shear failure despite being strengthened was also compared with the approach of four different codes. It has been observed that the codes give different results from the experimental studies, especially due to the conservative acceptance of GFRP's deformation limits.
... In this research, changes in the behavior of the mechanical system were used to solve problems in defect identification. Lee (2004), Li (2000), Viktor (Gribniak, et al., 2017), and Yan (2007) summarized various approaches to defect diagnosis based on changes in structural features. The diagnostic methods for defects that have been developed thus far can be divided into two categories (Oskar Skoglund, et al., 2020): traditional methods and modern methods. ...
Using power-spectral density (PSD) analysis for structures, we evaluated defects following a widespread research trend. During the structure’s operation, PSD not only demonstrated its structural integrity at the time of surveying but also predicted future changes in the structure. The present research used changes in PSD as a key feature for monitoring a beam structure’s shearing patterns. Two shearing models—side shearing and shearing under the beam—revealed changes in the shape of PSD images that corresponded to degrees of defect in the different shearing models. We applied these results to the monitoring of simple actual span structures over a long period of time. We monitored the structure’s operational status over time to examine the increased influence of structural defects based on significant changes in the PSD regarding spectral amplitude and spectral width. The frequencies initially found in the high-frequency region of PSD tended to shift toward the lower-frequency regions before disappearing entirely. In the future, the results of this research may improve the evaluation of structural integrity through variations of PSD in vibrational spectral shapes.
