Flexural Fatigue Performance Analysis of Bridge T-Beam Members Strengthened with Prestressed CFRP Plates

Flexural Fatigue Performance Analysis of Bridge T-Beam Members Strengthened with Prestressed CFRP Plates | Research Square window.SnipcartSettings = { analytics: { enabled: false } }; (function() { var accessVector = localStorage.getItem('access_vector') || ''; window.dataLayer = window.dataLayer || []; if (accessVector) { window.dataLayer.push({ user: { profile: { profileInfo: { snid: accessVector } } } }); } })(); (function(w,d,s,l,i){w[l]=w[l]||[];w[l].push({'gtm.start':new Date().getTime(),event:'gtm.js'});var f=d.getElementsByTagName(s)[0],j=d.createElement(s),dl=l!='dataLayer'?'&l='+l:'';j.async=true;j.src='https://www.googletagmanager.com/gtm.js?id='+i+dl;f.parentNode.insertBefore(j,f);})(window,document,'script','dataLayer','GTM-K279D39R'); Browse Preprints In Review Journals COVID-19 Preprints AJE Video Bytes Research Tools Research Promotion AJE Professional Editing AJE Rubriq About Preprint Platform In Review Editorial Policies Our Team Advisory Board Help Center Sign In Submit a Preprint Cite Share Download PDF Article Flexural Fatigue Performance Analysis of Bridge T-Beam Members Strengthened with Prestressed CFRP Plates Qiang Lu, Fengbing Zhao, Bolin Jiang, Shanshan Wu This is a preprint; it has not been peer reviewed by a journal. https://doi.org/ 10.21203/rs.3.rs-8931617/v1 This work is licensed under a CC BY 4.0 License Status: Under Review Version 1 posted 7 You are reading this latest preprint version Abstract Prestressed carbon fiber–reinforced polymer (CFRP) plate strengthening has been widely applied in the rehabilitation of flexural bridge members due to its advantages of low self-weight, convenient construction, and excellent durability. However, existing studies have mainly focused on the static behavior of prestressed CFRP-strengthened beams, while the flexural fatigue performance of prestressed CFRP plate–strengthened bridge girders remains insufficiently understood. To address this gap, this study investigates bridge T-beam members through a series of flexural fatigue tests, including unstrengthened beams, beams strengthened with non-prestressed CFRP plates, and beams strengthened with prestressed CFRP plates. The evolution of mid-span deflection, stiffness degradation, strain responses of tensile reinforcement and CFRP plates, as well as the interfacial bond behavior under different strengthening schemes were systematically analyzed. In addition, the effects of fatigue damage accumulation on the residual static performance and ultimate load-carrying capacity of prestressed CFRP-strengthened beams were further examined. The experimental results indicate that, compared with unstrengthened beams and non-prestressed CFRP-strengthened beams, prestressed CFRP plate–strengthened beams exhibited smaller mid-span deflections, more stable stiffness degradation characteristics, and lower strain amplitudes in tensile reinforcement during fatigue loading, demonstrating a significant improvement in flexural fatigue performance. In contrast, beams strengthened with non-prestressed CFRP plates were prone to CFRP–concrete interfacial debonding under cyclic loading, which led to stress redistribution between the steel reinforcement and CFRP plates, resulting in a rapid increase in reinforcement strain amplitude and premature fatigue failure. Post-fatigue monotonic loading tests further revealed that moderate fatigue damage had a limited influence on the static load capacity of prestressed CFRP-strengthened beams, whereas more pronounced degradation in stiffness and load-bearing performance occurred under higher fatigue load levels. Overall, the results demonstrate that prestressed CFRP plates can effectively reduce the stress level of tensile reinforcement while maintaining favorable interfacial bonding performance, thereby significantly enhancing the flexural fatigue resistance of bridge girder members. This study provides experimental evidence to support fatigue strengthening strategies for existing bridges. Physical sciences/Engineering Physical sciences/Materials science Prestressed CFRP plates girder bridges flexural fatigue structural performance analysis Figures Figure 1 Figure 2 Figure 3 Figure 4 Figure 5 Figure 6 Figure 7 Figure 8 Figure 9 Figure 10 Figure 11 Figure 12 Figure 13 1. Introduction With the continuous increase in traffic load levels and the growing service life of bridges, girder bridges are prone to fatigue damage accumulation under repeated vehicular loading. This is typically manifested by stiffness degradation, increased deflection, and crack propagation, which severely compromise the service performance and durability of bridge structures. For existing small- and medium-span girder bridges, effectively enhancing their flexural fatigue resistance under the premise of maintaining traffic operation or minimizing interruptions has become an urgent issue in the field of bridge maintenance and strengthening [ 1 – 2 ]. Fiber-reinforced polymer (FRP) composites, characterized by high strength, low self-weight, and excellent corrosion resistance, have been widely employed in the flexural strengthening of concrete girder bridges. Among various techniques, externally bonded carbon fiber–reinforced polymer (CFRP) plate strengthening has gained extensive application in engineering practice due to its convenient installation and well-defined load-transfer mechanism [ 3 – 4 ]. Numerous studies have investigated the mechanical performance of reinforced concrete beams strengthened with externally bonded CFRP plates. The research conducted by Li et al. [ 5 ], Wang et al. [ 6 ], and Zhang et al. [ 7 ] demonstrated that non-prestressed CFRP plates can enhance the load-carrying capacity and improve the deformation behavior of beams to a certain extent; however, their strengthening effectiveness remains limited under service conditions. This limitation is mainly attributed to the relatively low elastic modulus of CFRP materials, which prevents their high-strength advantage from being fully mobilized during the deformation-restricted service stage. To overcome the restricted efficiency of non-prestressed CFRP strengthening, prestressed CFRP plate systems have gradually attracted increasing attention. Studies by El-Sayed [ 8 ], Zhou [ 9 ], and Wang [ 10 ] indicated that applying prestress to CFRP plates prior to bonding can significantly reduce the tensile stress level in reinforcing steel under service conditions and improve the strength utilization efficiency of CFRP materials. Experimental results have confirmed that prestressed CFRP plates outperform non-prestressed CFRP plates in terms of enhancing cracking resistance, reducing deflection, and increasing static load capacity. Regarding fatigue performance, existing studies generally agree that fatigue failure of reinforced concrete beams is primarily governed by the stress level of tensile reinforcement. After conducting fatigue tests on multiple reinforced concrete T-beams, Alam et al. [ 11 ] reported that strengthening with non-prestressed CFRP plates can extend the fatigue life of beams; nevertheless, the fatigue behavior is still mainly controlled by the fatigue performance of steel reinforcement, and the strengthening effectiveness is largely constrained by the bond quality at the CFRP–concrete interface. Corte et al. [ 12 ] observed in high-amplitude fatigue loading tests that some CFRP-strengthened beams experienced interfacial degradation and debonding failure before reaching the designed number of fatigue cycles. Furthermore, studies by Abdel [ 13 ] and Kueres [ 14 ] showed that stiffness degradation of CFRP-strengthened beams becomes more pronounced under the combined effects of fatigue loading and long-term adverse environmental conditions. The aforementioned studies have, to some extent, revealed the fatigue behavior of beams strengthened with non-prestressed CFRP plates; however, research on the fatigue performance of prestressed CFRP plate–strengthened members remains relatively limited. Yuan et al. [ 15 ] conducted cyclic loading tests on RC slabs strengthened with prestressed CFRP plates and reported that fatigue failure is generally initiated by fracture of the tensile reinforcement, followed by interfacial debonding of the CFRP plate. Ghafoori [ 16 ] demonstrated that after two million fatigue cycles, the post-fatigue load-carrying capacity of prestressed CFRP-strengthened beams exhibited only a slight reduction, confirming the effectiveness of prestressing measures. Experimental results from Almassri [ 17 ] and Zhang [ 18 ] further indicated that, compared with non-prestressed CFRP systems, prestressed CFRP can more effectively reduce steel strain, concrete creep strain, and beam deflection, thereby significantly extending the fatigue life. Ye et al. [ 19 ] also found in fatigue strengthening studies of steel beams that the application of prestressed CFRP plates could increase the fatigue life by several times. It should be noted, however, that prestressed CFRP plate strengthening systems face additional challenges under fatigue loading, particularly with respect to end anchorage and the complex interfacial stress state. Al-Fakih [ 20 ] and Zhu [ 21 ] pointed out that increasing the prestress level leads to a substantial rise in interfacial stresses near the CFRP plate ends, making interfacial degradation more likely under cyclic loading. Moreover, since epoxy adhesives alone are often unable to sustain the large force transfer associated with prestressing, permanent anchorage devices are typically required in practice. The presence of such anchorage systems further complicates the stress distribution among concrete, steel reinforcement, and CFRP plates. These factors collectively indicate that the fatigue behavior of prestressed CFRP plate–strengthened beams differs fundamentally from that of non-prestressed systems, highlighting the necessity for systematic and targeted investigations. Based on the above research background, this study investigates bridge T-beam members through a comprehensive flexural fatigue experimental program, including unstrengthened beams, beams strengthened with non-prestressed CFRP plates, and beams strengthened with prestressed CFRP plates. By systematically monitoring the mid-span deflection, stiffness degradation, strain responses of tensile reinforcement and CFRP plates, as well as the CFRP–concrete interfacial behavior, the fatigue response characteristics and failure modes of beams under different strengthening schemes are analyzed. Furthermore, post-fatigue monotonic loading tests are conducted to evaluate the effects of fatigue damage accumulation on the static performance and residual load-carrying capacity of prestressed CFRP-strengthened beams. The findings are expected to provide experimental evidence for the flexural fatigue performance assessment and practical application of prestressed CFRP plate strengthening in existing girder bridge members. 2. Flexural Fatigue Tests of Beams 2.1 Specimen Design and Test Conditions The beam specimens had an overall length of 5.0 m with a calculated span of 4.8 m. The beam depth was 600 mm, while the flange width and thickness were 600 mm and 100 mm, respectively, and the web thickness was 200 mm. The geometric dimensions and reinforcement arrangement of the specimens are illustrated in Fig. 1 . To investigate the flexural fatigue performance of reinforced concrete T-beam members strengthened with prestressed CFRP plates, a total of three RC T-beam specimens were fabricated in this study. The corresponding test conditions are summarized in Table 1 . Table 1 Test conditions Specimen number Strengthening condition Prestressing stress/MPa 1 Not strengthened - 2 Strengthened 0 3 Strengthened 1000 2.2 Material Properties The concrete used for the beam specimens was designed with a target strength grade of C40, and the corresponding mix proportions are provided in Table 2 . All concrete specimens were cast simultaneously, and the measured 28-day cubic compressive strength was 41.2 MPa. Table 2 Mix proportions of concrete P.O 42.5 Cement/kg Water/kg Medium Sand/kg Stone (5–20 mm continuously graded aggregate)/kg 440 170 680 1100 The longitudinal reinforcement and stirrups used in the beam specimens were of strength grades HRB400 and HPB235, respectively, and their measured mechanical properties are summarized in Table 3 . Table 3 Material properties Material Parameter Value Concrete cubic compressive strength 41.2 MPa elastic modulus 33.1 GPa Poisson’s ratio 0.19 density 2409 kg/m 3 Rebar yield strength (HRB400) 421 MPa yield strength (HPB235) 265 MPa tensile strength (HRB400) 573 MPa tensile strength (HPB235) 384 MPa CFRP plate width 100 mm thickness (single layer) 2 mm tensile strength 2900 MPa elastic modulus 170 GPa Epoxy resin adhesive bonding strength 13.5 MPa 2.3 Installation of Prestressed CFRP Plates The CFRP plates were bonded to the soffit of the beam specimens, centrally aligned along the longitudinal axis, with a bonded length of 3.6 m. The prestressed CFRP plates were connected to the end anchorage devices through corrugated clamping plates, as shown in Fig. 2 . The end anchorage systems were fixed to the beam ends using chemical anchor bolts. The anchorage devices were selected from a commonly used commercial product available in the domestic market, as illustrated in Fig. 2 . The CFRP plates were first tensioned to the target prestressing level using a hydraulic jack, and then bonded to the concrete surface. During the bonding process, the target prestress level was maintained. For the non-prestressed CFRP plate–strengthened beam (Specimen 2), anchorage devices were installed at both ends of the CFRP plate to provide mechanical fixation and to prevent interfacial debonding between the CFRP plate and the concrete surface [ 7 – 8 ]. To ensure reliable prestress transfer and stable bond performance, the installation of the prestressed CFRP plates followed a controlled and standardized procedure. Prior to bonding, the concrete soffit within the designated bond length was mechanically roughened to remove laitance and contaminants, and the surface was cleaned to ensure adequate adhesion. Any local surface defects were repaired to obtain a sound bonding substrate. Prestressing was applied using a hydraulic jack connected to the active-end anchorage system, while the opposite end was fixed by a passive anchorage. A dual-control method was adopted, in which both the applied jack force and the measured CFRP strain were monitored to achieve the target prestress level (1000 MPa). The prestress was applied incrementally to minimize seating losses and anchorage slip. After reaching the target level, the prestress was maintained for a stabilization period to ensure stress uniformity before bonding operations were finalized. The epoxy adhesive was prepared according to the manufacturer’s specified mixing ratio and applied uniformly to the prepared concrete surface. The CFRP plate was bonded while maintaining the target prestress level to ensure effective stress transfer. During curing, the bonded region was protected from external disturbances, and sufficient curing time was allowed under ambient laboratory conditions before removing the prestressing equipment. The end anchorage system consisted of steel clamping plates and chemical anchor bolts installed at the beam ends. High-strength bolts were tightened in a symmetric sequence to ensure uniform clamping pressure. This configuration enhanced force transfer efficiency and mitigated stress concentration near the laminate ends under fatigue loading. 2.4 Test Loading and Measurements As shown in Fig. 1 , the flexural fatigue tests were conducted under a four-point bending configuration. The loading span was 4800 mm, and the shear span length was 2100 mm. The loading setup and reaction frame are illustrated in Fig. 3 . A constant-amplitude sinusoidal cyclic load was applied with the mean load as the reference level. The minimum and maximum loads were set to 10 kN and 50 kN, respectively, and the loading frequency was 5 Hz. The applied load was monitored and controlled using a load cell installed between the hydraulic jack and the loading beam. According to relevant studies, a total of seven dial gauges were installed to measure the beam deflections, as shown in Fig. 4 . Electrical resistance strain gauges with a gauge length of 5 mm were attached at the mid-span of the longitudinal reinforcement to monitor the steel strain. In addition, twenty-five electrical resistance strain gauges, each with a gauge length of 5 mm, were bonded to the surface of the CFRP plate to measure the strain distribution along the tensile direction, as illustrated in Fig. 4 . In addition, four and six electrical resistance strain gauges with a gauge length of 100 mm were bonded to the compression zone and the side surfaces of the beam specimens, respectively, to measure the concrete compressive strain and to analyze the strain distribution along the beam depth. 3. Experimental Results The experimental results are summarized in Table 4 . Table 4 Test results Specimen number ε max,rebar /10 − 6 ε min,rebar /10 − 6 Δ ε rebar /10 − 6 ε max,CFRP /10 − 6 ε min,CFRP /10 − 6 Δ ε CFRP /10 − 6 δ 1 /mm Max cycle Failure mode 1 1029 50 979 - - - 7.6 22.7×10 4 reinforcement fracture 2 964 254 710 771 138 633 5.7 70.2×10 4 reinforcement fracture after CFRP debonding 3 531 75 456 708 134 574 4.5 10 6 monotonically loaded to failure after 200×10 4 cycles Note: In Table 4 , ε max,rebar and ε min,rebar denote the maximum and minimum strains of the tensile reinforcement, respectively, and Δ ε rebar represents the strain range of the reinforcement. Similarly, ε max,CFRP and ε min,CFRP denote the maximum and minimum strains of the CFRP plate, respectively, and Δ ε CFRP represents the strain range of the CFRP plate. In addition, δ 1 refers to the beam deflection corresponding to the maximum load in the first loading cycle. 3.1 Fatigue Behavior Figure 5 presents the variation of mid-span deflection with the number of loading cycles for Specimen 1 (the unstrengthened control beam) during the fatigue test. As shown in Fig. 5 , the mid-span deflection of Specimen 1 increased significantly within the first 10 4 loading cycles, indicating the accumulation of internal damage in the beam under cyclic loading. During the subsequent range of (1–2)×10 4 cycles, a slight reduction in deflection was observed. Thereafter, the deflection exhibited a continuous increasing trend over the cycle range of (2–10)×10 4 . When the number of cycles reached 22.7×10 4 , fracture of the longitudinal tensile reinforcement occurred, leading to the failure of Specimen 1. The variation of mid-span deflection with the number of cycles for Specimen 2 (the beam strengthened with a non-prestressed CFRP plate) is shown in Fig. 7 . The mid-span deflection continuously increased as the fatigue cycles progressed. During the first loading cycle, the maximum strain of the longitudinal tensile reinforcement in Specimen 2 under the peak load reached 964 µε, which was 79.8% of that recorded in Specimen 1. After 50×10 4 cycles, debonding between the CFRP plate and the concrete surface was observed near the loading point, as illustrated in Fig. 8 . With further increase in the number of cycles, the debonded region propagated toward both supports and eventually developed into overall debonding of the CFRP plate from the soffit concrete surface. At this stage, the CFRP plate was only mechanically retained by the steel anchorage devices. When the number of cycles reached 70.2×10 4 , fatigue fracture of the longitudinal tensile reinforcement occurred at the beam bottom, leading to the failure of Specimen 2. Specimen 3 (the beam strengthened with a prestressed CFRP plate) was initially prestressed to a level of 1000 MPa. The growth curve of mid-span deflection with increasing fatigue cycles is presented in Fig. 7 . Within the first 10 4 loading cycles, the mid-span deflection of Specimen 3 increased rapidly, indicating significant internal damage accumulation in the beam under cyclic loading [ 5 , 17 , 22 ]. Thereafter, the mid-span deflection exhibited a gradual growth up to 160×10 4 cycles. During the subsequent cycle range of (160–200)×10 4 , the deflection growth rate increased noticeably, showing a pronounced rise. 3.2 Deformation Analysis By comparing the curves of Specimens 2 and 3 in Fig. 7 , it can be observed that the beam strengthened with a prestressed CFRP plate (Specimen 3) exhibited a significant advantage in flexural fatigue resistance. For Specimen 2, the mid-span deflection under the maximum load of the first loading cycle (𝛿1) was 5.7 mm, and the deflection continued to increase with the number of cycles until failure occurred. In contrast, under the same fatigue loading conditions, Specimen 3 showed a markedly lower deflection level during the first 150×10 4 cycles. Moreover, it should be emphasized that after the rapid increase in mid-span deflection during the initial 10 3 cycles, the deflection of Specimen 3 remained relatively stable, whereas the mid-span deflection of Specimen 2 exhibited a continuous growth trend throughout the fatigue loading process. Figure 9 illustrates the variation of stiffness with the number of fatigue cycles for Specimens 2 and 3. It can be seen that the stiffness of Specimen 2 decreased significantly after the first 10 5 loading cycles, and it continued to decline throughout the subsequent fatigue loading process until failure occurred. This indicates that cyclic fatigue loading induces pronounced damage accumulation in beams strengthened with non-prestressed CFRP plates (Specimen 2) [ 9 , 12 ]. Similarly, the stiffness of Specimen 3 initially increased and then decreased rapidly within the first 10 5 loading cycles, which is consistent with the observed variation in mid-span deflection. After the rapid reduction stage, the stiffness of Specimen 3 exhibited a gradual decline up to 160×10 4 cycles, while remaining at a relatively stable level. This suggests that cyclic fatigue loading did not induce pronounced damage accumulation within the beam during this stage. However, during the subsequent cycle range of (160–200)×10 4 , a sudden stiffness drop was observed. This phenomenon agrees well with the corresponding deflection development, reflecting the structural performance degradation of the prestressed CFRP plate–strengthened beam (Specimen 3) under fatigue loading [ 1 – 2 , 4 , 23 ]. 3.3 Strain Analysis Figure 10 presents the variation of the strain range of the bottom tensile reinforcement (Δ ε rebar ) and the strain range of the CFRP plate (Δ ε CFRP ) with increasing fatigue cycles for Specimens 2 and 3. As shown in Fig. 10 (a), the strain range of the tensile reinforcement in Specimen 2 increased significantly with the number of cycles, which can be attributed to CFRP–concrete interfacial debonding and the associated stress redistribution. In contrast, as indicated in Fig. 10 (b), throughout the entire fatigue loading process, the evolution trend of the CFRP plate strain range in Specimen 3 remained consistent with that of the tensile reinforcement. This suggests that the CFRP plate maintained a favorable bonding condition with the soffit concrete surface during fatigue loading [ 6 , 16 ]. Figure 10 (c) compares the evolution of the strain range of the bottom tensile reinforcement with the number of fatigue cycles for Specimens 2 and 3. It can be observed that throughout the entire fatigue loading process, the tensile reinforcement strain range of Specimen 3 remained consistently lower than that of Specimen 2. At 50×10 4 cycles, the strain range of Specimen 2 was approximately 1.6 times that of Specimen 3. Specimen 2 failed after 70.2×10 4 cycles due to fatigue fracture of the tensile reinforcement, whereas Specimen 3 did not exhibit failure even after 200×10 4 cycles. These results indicate that prestressed CFRP plate strengthening can effectively reduce the stress level of tensile reinforcement and significantly enhance the flexural fatigue resistance of reinforced concrete T-beams [ 3 , 7 – 8 ]. In contrast, non-prestressed CFRP plates tend to lose their bond with the concrete surface under cyclic fatigue loading, and therefore cannot provide effective strengthening for T-beam members [ 5 , 24 ]. To further elucidate the underlying mechanism governing the different strain evolution behaviors between prestressed and non-prestressed CFRP strengthening systems, the interfacial stress transfer mechanism and bond–slip interaction should be considered. According to bond mechanics principles, the interfacial shear stress between the CFRP plate and concrete substrate can be approximately expressed as: $$\:\tau\:\left(x\right)=\frac{{E}_{f}{t}_{f}}{{b}_{f}}\bullet\:\frac{d{\epsilon\:}_{f}\left(x\right)}{dx}$$ where E f and t f denote the elastic modulus and thickness of the CFRP plate, respectively, bf is the plate width, and d ε f /d x represents the strain gradient along the bonded length. This relationship indicates that local interfacial shear stress is directly governed by the spatial variation of CFRP strain. For the non-prestressed CFRP-strengthened beam, the initial interfacial stress is negligible prior to loading. Under cyclic bending, tensile force transfer from concrete to CFRP leads to progressive strain localization near the loading region, resulting in high shear stress concentration at the interface. As fatigue cycles accumulate, microcracking and interfacial slip initiate and propagate, eventually causing partial debonding. Once debonding occurs, the tensile force previously carried by the CFRP plate is redistributed to the steel reinforcement, leading to a sharp increase in reinforcement strain range and accelerating fatigue fracture. In contrast, the prestressed CFRP system introduces an initial compressive stress state in the concrete and an initial tensile stress in the CFRP plate before external loading is applied. This prestress reduces the effective tensile stress amplitude experienced by the reinforcement under cyclic loading and modifies the strain gradient distribution along the bonded length. As a result, interfacial shear stress peaks are mitigated and more uniformly distributed. From a bond–slip perspective, prestressing delays the development of relative slip between the CFRP plate and concrete substrate, thereby restraining damage evolution within the interfacial transition zone. The schematic comparison of interfacial stress distribution and bond–slip behavior between the two strengthening systems is illustrated in Fig. 11 . It can be inferred that prestressing effectively stabilizes the load transfer mechanism, alleviates stress redistribution triggered by local debonding, and maintains coordinated deformation between CFRP and reinforcement. This mechanism explains why the prestressed CFRP-strengthened beam exhibited a consistently lower reinforcement strain range and a significantly extended fatigue life. From the perspective of interfacial mechanics, the different fatigue responses between non-prestressed and prestressed CFRP systems can be further explained by bond deterioration and stress redistribution mechanisms. In the non-prestressed configuration, the interface initially carries no prestress, and cyclic loading promotes progressive slip accumulation near high-moment regions. Once partial debonding initiates, tensile force previously transferred to the CFRP plate is redistributed to the steel reinforcement, resulting in a rapid increase in reinforcement strain range and accelerated fatigue crack propagation. In contrast, prestressing introduces an initial tensile stress in the CFRP plate and a compressive state in the concrete substrate, which reduces the effective tensile stress amplitude in the reinforcement and mitigates interfacial shear stress concentration. Consequently, slip development and debonding are delayed, stabilizing the load transfer mechanism and contributing to the improved fatigue resistance of the prestressed strengthening system. 3.4 Failure Loading After undergoing 200×10 4 fatigue loading cycles, no debonding cracks were observed between the CFRP plate and the soffit concrete surface, nor was any fracture of the bottom longitudinal tensile reinforcement detected. Subsequently, to further investigate the influence of fatigue damage accumulation on the static performance and residual load-carrying capacity of the prestressed CFRP plate–strengthened T-beam, Specimen 3 was subjected to monotonic loading until failure. The corresponding response curves are presented in Fig. 12 . For Specimen 3, yielding of the bottom longitudinal tensile reinforcement occurred when the applied load reached 175 kN. As the load increased to 205 kN, debonding between the CFRP plate and the soffit concrete surface initiated at the mid-span region. The debonding crack then rapidly propagated toward the steel anchorage devices at both beam ends and extended throughout the entire bonded length. At this stage, the CFRP plate was connected to the beam only through the end steel anchorages, which carried the total tensile force in the CFRP plate. Similar to Specimen 2, after CFRP plate debonding occurred, both the mid-span deflection and the CFRP plate strain of Specimen 3 increased significantly. When the load further increased to 215 kN, failure took place due to tensile rupture of the anchorage bolts at one end, causing the steel anchorage device to be pulled out from the beam. The corresponding failure pattern is shown in Fig. 13 . As mentioned above, Specimen 3 exhibited damage accumulation during the cycle range of (16–20)×10 4 . Figure 12 indicates that the existing accumulated damage had a noticeable influence on the static behavior of Specimen 3 [ 11 , 14 ]. 4. Conclusions Based on the flexural fatigue experimental investigation of unstrengthened reinforced concrete T-beams, T-beams strengthened with non-prestressed CFRP plates, and T-beams strengthened with prestressed CFRP plates under constant-amplitude cyclic loading, the effects of different strengthening schemes on the evolution of mid-span deflection, stiffness degradation characteristics, strain responses of tensile reinforcement and CFRP plates, as well as interfacial bonding performance were systematically analyzed. In addition, monotonic loading tests were conducted on the prestressed CFRP-strengthened beams after fatigue loading to further evaluate the influence of fatigue damage accumulation on the static performance and residual load-carrying capacity of the members. On this basis, combined with the observed fatigue failure modes and the evolution of key mechanical parameters, the enhancement mechanisms of flexural fatigue performance provided by prestressed CFRP plate strengthening were comprehensively discussed. The main conclusions can be drawn as follows: (1) Compared with the unstrengthened beam and the beam strengthened with a non-prestressed CFRP plate, the prestressed CFRP plate–strengthened beam exhibited smaller mid-span deflections, more stable stiffness degradation behavior, and lower tensile reinforcement strain levels during fatigue loading. Under comparable or even higher fatigue load levels, the fatigue life of the prestressed CFRP-strengthened beam was significantly extended, whereas the non-prestressed CFRP-strengthened beam failed due to fatigue fracture of the tensile reinforcement after approximately 70.2×10 4 cycles. (2) The experimental results showed that throughout the fatigue loading process, the strain range of the CFRP plate in the prestressed CFRP-strengthened beam evolved consistently with that of the tensile reinforcement, and no significant interfacial debonding was observed. In contrast, the non-prestressed CFRP-strengthened beam experienced progressive CFRP–concrete interfacial debonding under cyclic loading, which induced stress redistribution from the CFRP plate to the steel reinforcement. This redistribution led to a pronounced increase in reinforcement strain range and accelerated fatigue crack propagation in the steel bars. The introduction of prestress effectively reduced the tensile stress amplitude in the reinforcement and delayed the development of interfacial slip and debonding, thereby stabilizing the load transfer mechanism and enhancing the flexural fatigue resistance of the strengthened beam. (3) Post-fatigue monotonic loading tests indicated that the prestressed CFRP plate–strengthened beam exhibited a load–carrying behavior prior to steel yielding that was generally consistent with that of the corresponding beam subjected to monotonic loading only, suggesting that moderate fatigue damage had a limited influence on its overall load capacity. However, under higher fatigue load levels and larger load amplitudes, the yielding load and the interfacial debonding load were significantly reduced, accompanied by accelerated stiffness degradation. Overall, prestressed CFRP plate strengthening demonstrates good engineering applicability for enhancing the flexural fatigue performance of existing girder bridge members. Declarations Funding Declaration This research was supported by the Science and Technology Research Program of Chongqing Municipal Education Commission (Grant No.KJZD-K202503402, KJZD-K202505801), sponsored by Natural Science Foundation of Chongqing,China (Grant No.CSTB2025NSCQ-GPX0797). Author Contributions Qiang Lu: Supervision; Validation; Writing – Review & Editing. Fengbing Zhao: Conceptualization; Methodology; Investigation; Data Curation; Writing – Original Draft. Bolin Jiang: Resources; Visualization; Formal Analysis. Shanshan Wu: Software; Experimental Setup; Data Processing. All authors have read and approved the final version of this manuscript. Data availability Data will be made available on request. Declaration of Competing Interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper. Ethical approval Not applicable Consent to publish Not applicable Clinical trial Not applicable References Wang, H. T. et al. Flexural strengthening of damaged steel beams with prestressed CFRP plates using a novel prestressing system. Eng. Struct. 284 , 115953 (2023). Li, A., Wang, H., Li, H., Kong, D. & Xu, S. Stress concentration analysis of the corroded steel plate strengthened with carbon fiber reinforced polymer (CFRP) plates. Polymers 14 , 3845 (2022). Abdel Havez, A. & Al-Mayah, A. Flexural strengthening of concrete structures using externally bonded and unbonded prestressed CFRP laminates: A literature review. J. Compos. Constr. 27 , (2023). Zhou, C., Wang, L., Wang, Y. & Fang, Z. Experimental study on the flexural strengthening of one-way RC slabs with end-buckled and/or externally bonded CFRP sheets. Eng. Struct. 282 , 115832 (2023). Li, J., Zhu, M. & Deng, J. Flexural behaviour of notched steel beams strengthened with a prestressed CFRP plate subjected to fatigue damage and wetting/drying cycles. Eng. Struct. 250 , 113430 (2022). Wang, H. T. et al. Structural performance of steel beams strengthened with prestressed CFRP plates: Steel beam-CFRP plate string systems. Thin-Walled Struct. 220 , 114251 (2026). Zhang, W., Kang, S., Liu, X., Lin, B. & Huang, Y. Experimental study of a composite beam externally bonded with a carbon fiber-reinforced plastic plate. J. Building Eng. 71 , 106522 (2023). El-Sayed, A. K., Al-Zaid, R. A., Al-Negheimish, A. I., Shuraim, A. B. & Alhozaimy, A. M. Long-term behavior of wide shallow RC beams strengthened with externally bonded CFRP plates. Constr. Build. Mater. 51 , 473–483 (2014). Zhou, C. Y., Yu, Y. N. & Xie, E. L. Strengthening RC beams using externally bonded CFRP sheets with end self-locking. Compos. Struct. 241 , 112070 (2020). Wang, Q. et al. Fatigue performance of CFRP reinforced pretensioned prestressed beams. Constr. Build. Mater. 324 , 126509 (2022). Alam, M. A., Onik, S. A. A. & Mustapha, K. N. B. Crack-based bond strength model of externally bonded steel plate and CFRP laminate to predict debonding failure of shear-strengthened RC beams. J. Building Eng. 27 , 100943 (2020). De Corte, W. & Van Bogaert, P. Evaluation of an experimental CFRP prestressed beam and slab road bridge. Compos. Part. B . 36 , 91–98 (2005). Abdel Havez, A. & Al-Mayah, A. High prestressing of externally mounted CFRP plates for prestressed hollow-core slabs strengthening. Structures 75 , 108698 (2025). Kueres, S. & Hegger, J. Reliability analysis of footbridges pre-tensioned with carbon fiber reinforced polymer tendons under flexural loading. Eng. Struct. 203 , 109546 (2020). Yuan, X., Zhu, C., Zheng, W., Hu, J. & Tang, B. Flexure performance of externally bonded CFRP plate-strengthened reinforced concrete members. Mathematical Problems in Engineering 2604024 (2020). (2020). Ghafoori, E. et al. Finite element analysis for fatigue damage reduction in metallic riveted bridges using prestressed CFRP plates. Polymers 6 , 1096–1118 (2014). Almassri, B., Halahla, A. M. & Corroded RC beam repaired in flexure using NSM CFRP rod and an external steel plate. Structures 27 , 343–351 (2020). Zhang, Z. J. et al. Entire mechanical analysis of prestressed CFRP strengthened RC beams under different prestress introduction methods. Adv. Bridge Eng. 5 , 13 (2024). Ye, H. et al. Fatigue performance analysis of damaged steel beams strengthened with prestressed unbonded CFRP plates. J. Bridge Eng. 23 , 04018040 (2018). Al-Fakih, A. et al. Cracking behavior of sea sand RC beam bonded externally with CFRP plate. Structures 33 , 1578–1589 (2021). Zhu, K. Research on prestressed CFRP plate in the reinforcement of composite box girder bridge. Journal of Physics: Conference Series 2920, 012013 (2024). Cheng, X. et al. Seismic response of a box bridge after reinforcement with prestressed CFRP textile. Australian J. Civil Eng. 18 , 29–45 (2019). Hu, L., Li, W. & Feng, P. Long-term behavior of CFRP plates under sustained loads. Adv. Struct. Eng. 25 , 939–953 (2022). Wang, H. T. & Wu, G. Bond-slip models for CFRP plates externally bonded to steel substrates. Compos. Struct. 184 , 1204–1214 (2018). Additional Declarations No competing interests reported. Cite Share Download PDF Status: Under Review Version 1 posted Reviewers agreed at journal 23 Apr, 2026 Reviewers agreed at journal 28 Feb, 2026 Reviewers invited by journal 26 Feb, 2026 Editor invited by journal 26 Feb, 2026 Editor assigned by journal 24 Feb, 2026 Submission checks completed at journal 24 Feb, 2026 First submitted to journal 21 Feb, 2026 You are reading this latest preprint version Research Square lets you share your work early, gain feedback from the community, and start making changes to your manuscript prior to peer review in a journal. As a division of Research Square Company, we’re committed to making research communication faster, fairer, and more useful. We do this by developing innovative software and high quality services for the global research community. Our growing team is made up of researchers and industry professionals working together to solve the most critical problems facing scientific publishing. Also discoverable on Platform About Our Team In Review Editorial Policies Advisory Board Help Center Resources Author Services Accessibility API Access RSS feed Manage Cookie Preferences © Research Square 2026 | ISSN 2693-5015 (online) Privacy Policy Terms of Service Do Not Sell My Personal Information {"props":{"pageProps":{"initialData":{"identity":"rs-8931617","acceptedTermsAndConditions":true,"allowDirectSubmit":false,"archivedVersions":[],"articleType":"Article","associatedPublications":[],"authors":[{"id":598667459,"identity":"93d58bbe-8e53-4818-a72c-02816d301a84","order_by":0,"name":"Qiang Lu","email":"","orcid":"","institution":"School of Civil Engineering, Chongqing Vocational Institute of Engineering","correspondingAuthor":false,"prefix":"","firstName":"Qiang","middleName":"","lastName":"Lu","suffix":""},{"id":598667466,"identity":"60596cd0-7c80-4a3b-be85-4486915224fa","order_by":1,"name":"Fengbing Zhao","email":"data:image/png;base64,iVBORw0KGgoAAAANSUhEUgAAAZAAAAAyAQMAAABI0h/eAAAABlBMVEX///8AAABVwtN+AAAACXBIWXMAAA7EAAAOxAGVKw4bAAAA+UlEQVRIiWNgGAWjYDACCRBhA2IwNjAwVEjIyROnJQ2m5YyFsWED8VqAmLGtIpHhAAEd8rObHz5gSLDJk49ubnv4dZ5EAmMD88NHN/BoYZxzzNiAISGt2PDOwXZj2W0SeewMbMbGOXi0MEskmEkw/jicuHFGYpu05DaJYsYGHjZpfFrYJNK/STAk/IdqmSOR2HCAgBYeiRwzoJYDifMlEtskPzYQoUVCIqfYICEhOXGDzME2aYZjEsaGzQT8Ij8jfeODDwl2ifNntz+T/FFTJyfP3vzwMT4tYJAAxAYHgGHBA+IxE1IOt64BGOI/iFU9CkbBKBgFIwoAAJhISbdPRF16AAAAAElFTkSuQmCC","orcid":"","institution":"School of Civil Engineering, Guizhou University of Engineering Science","correspondingAuthor":true,"prefix":"","firstName":"Fengbing","middleName":"","lastName":"Zhao","suffix":""},{"id":598667469,"identity":"b3264cf0-00bf-4c9a-bdc9-68bcb13486d4","order_by":2,"name":"Bolin Jiang","email":"","orcid":"","institution":"School of Civil Engineering, Chongqing Vocational Institute of Engineering","correspondingAuthor":false,"prefix":"","firstName":"Bolin","middleName":"","lastName":"Jiang","suffix":""},{"id":598667471,"identity":"0b200211-33f7-4541-a0de-69edc7021df7","order_by":3,"name":"Shanshan Wu","email":"","orcid":"","institution":"School of Railways and Architecture, Chongqing Vocational College of Public Transportation","correspondingAuthor":false,"prefix":"","firstName":"Shanshan","middleName":"","lastName":"Wu","suffix":""}],"badges":[],"createdAt":"2026-02-21 07:53:35","currentVersionCode":1,"declarations":"","doi":"10.21203/rs.3.rs-8931617/v1","doiUrl":"https://doi.org/10.21203/rs.3.rs-8931617/v1","draftVersion":[],"editorialEvents":[],"editorialNote":"","failedWorkflow":false,"files":[{"id":103856984,"identity":"c913a633-4af9-4968-84d1-f37fc232cb04","added_by":"auto","created_at":"2026-03-03 18:31:29","extension":"png","order_by":1,"title":"Figure 1","display":"","copyAsset":false,"role":"figure","size":149768,"visible":true,"origin":"","legend":"\u003cp\u003eDiagram of beam specimens\u003c/p\u003e","description":"","filename":"floatimage1.png","url":"https://assets-eu.researchsquare.com/files/rs-8931617/v1/43c95f02b21c1b1b0b6827a2.png"},{"id":104400839,"identity":"6d5bd09a-e51f-4c1f-ad04-c6f73e6682aa","added_by":"auto","created_at":"2026-03-11 12:11:14","extension":"png","order_by":2,"title":"Figure 2","display":"","copyAsset":false,"role":"figure","size":2367424,"visible":true,"origin":"","legend":"\u003cp\u003eEnd anchorage: (a) corrugated clamping plate, (b) fix-end anchorage, (c) prestressing-end anchorage and (d) prestressed CFRP plate\u003c/p\u003e","description":"","filename":"floatimage2.png","url":"https://assets-eu.researchsquare.com/files/rs-8931617/v1/51198628d4d4ccd055d59560.png"},{"id":104401329,"identity":"c330a789-78b7-4e82-b65d-5fd455f33082","added_by":"auto","created_at":"2026-03-11 12:12:25","extension":"png","order_by":3,"title":"Figure 3","display":"","copyAsset":false,"role":"figure","size":514614,"visible":true,"origin":"","legend":"\u003cp\u003eTest loading device\u003c/p\u003e","description":"","filename":"floatimage3.png","url":"https://assets-eu.researchsquare.com/files/rs-8931617/v1/dbef40f903af40848ec6e548.png"},{"id":103856985,"identity":"cdec63b1-b8ae-40d8-a6c6-522825996fc4","added_by":"auto","created_at":"2026-03-03 18:31:29","extension":"png","order_by":4,"title":"Figure 4","display":"","copyAsset":false,"role":"figure","size":168699,"visible":true,"origin":"","legend":"\u003cp\u003eMeasurement layout\u003c/p\u003e","description":"","filename":"floatimage4.png","url":"https://assets-eu.researchsquare.com/files/rs-8931617/v1/2dfa57cedf10e4478e6f4c92.png"},{"id":103856988,"identity":"b35c8374-549c-4d04-9c9f-194d735af455","added_by":"auto","created_at":"2026-03-03 18:31:29","extension":"png","order_by":5,"title":"Figure 5","display":"","copyAsset":false,"role":"figure","size":141609,"visible":true,"origin":"","legend":"\u003cp\u003eMid-span deflection versus number of loading cycles for Specimen 1\u003c/p\u003e","description":"","filename":"floatimage5.png","url":"https://assets-eu.researchsquare.com/files/rs-8931617/v1/d5434cca0104642ce2db8d48.png"},{"id":103856990,"identity":"82eeea86-f7b1-42af-8087-f8b9d31d2869","added_by":"auto","created_at":"2026-03-03 18:31:29","extension":"png","order_by":6,"title":"Figure 6","display":"","copyAsset":false,"role":"figure","size":571709,"visible":true,"origin":"","legend":"\u003cp\u003eFailure for Specimen 1\u003c/p\u003e","description":"","filename":"floatimage6.png","url":"https://assets-eu.researchsquare.com/files/rs-8931617/v1/361867f0cf0f6d556334aa4d.png"},{"id":103856987,"identity":"229e91c3-05da-4aee-8431-37c4fbd332a0","added_by":"auto","created_at":"2026-03-03 18:31:29","extension":"png","order_by":7,"title":"Figure 7","display":"","copyAsset":false,"role":"figure","size":156439,"visible":true,"origin":"","legend":"\u003cp\u003eMid-span deflection versus number of loading cycles for Specimen 2 and Specimen 3\u003c/p\u003e","description":"","filename":"floatimage7.png","url":"https://assets-eu.researchsquare.com/files/rs-8931617/v1/29e17e9de56805136ec6a925.png"},{"id":103856989,"identity":"92fefbf3-fa45-44ba-af66-ada143f8426e","added_by":"auto","created_at":"2026-03-03 18:31:29","extension":"png","order_by":8,"title":"Figure 8","display":"","copyAsset":false,"role":"figure","size":803519,"visible":true,"origin":"","legend":"\u003cp\u003ePeeling of CFRP plate\u003c/p\u003e","description":"","filename":"floatimage8.png","url":"https://assets-eu.researchsquare.com/files/rs-8931617/v1/76d82f3e7cac1023f8c07bcb.png"},{"id":103856996,"identity":"d48a3c8f-96ef-41b1-b490-c99c16c3f142","added_by":"auto","created_at":"2026-03-03 18:31:29","extension":"png","order_by":9,"title":"Figure 9","display":"","copyAsset":false,"role":"figure","size":160986,"visible":true,"origin":"","legend":"\u003cp\u003eStiffness versus number of loading cycles\u003c/p\u003e","description":"","filename":"floatimage9.png","url":"https://assets-eu.researchsquare.com/files/rs-8931617/v1/1cbd270c297dc46b6c066425.png"},{"id":104401424,"identity":"13a9824c-cd1c-4c9b-9475-4698b42213cb","added_by":"auto","created_at":"2026-03-11 12:12:40","extension":"png","order_by":10,"title":"Figure 10","display":"","copyAsset":false,"role":"figure","size":1197737,"visible":true,"origin":"","legend":"\u003cp\u003eStrain of marterials versus number of loading cycles: (a) Specimen 2, (b) Specimen 3 and (c) comparison between Specimen 2 and 3\u003c/p\u003e","description":"","filename":"floatimage10.png","url":"https://assets-eu.researchsquare.com/files/rs-8931617/v1/0adb8d4842d65c12b2d0d383.png"},{"id":104401209,"identity":"eda2895d-3a4a-4e8c-89fa-91c979731142","added_by":"auto","created_at":"2026-03-11 12:12:06","extension":"png","order_by":11,"title":"Figure 11","display":"","copyAsset":false,"role":"figure","size":468333,"visible":true,"origin":"","legend":"\u003cp\u003eIllustration of fatigue damage evolution mechanisms in non-prestressed and prestressed CFRP strengthening systems\u003c/p\u003e","description":"","filename":"floatimage11.png","url":"https://assets-eu.researchsquare.com/files/rs-8931617/v1/57f2a66f153bffb00afb12ae.png"},{"id":104401485,"identity":"527960ec-382d-4076-9ce5-5571514fa843","added_by":"auto","created_at":"2026-03-11 12:12:49","extension":"png","order_by":12,"title":"Figure 12","display":"","copyAsset":false,"role":"figure","size":1161651,"visible":true,"origin":"","legend":"\u003cp\u003eVariation of parameters during monotonic loading: (a) mid-span deflection, (b) concrete compressive strain, (c) rebar tensile strain and (d) CFRP plate strain\u003c/p\u003e","description":"","filename":"floatimage12.png","url":"https://assets-eu.researchsquare.com/files/rs-8931617/v1/148d520d7b62cb6bb6897935.png"},{"id":103856993,"identity":"b9b73bda-c6f0-4200-b6ed-7c7dcdefe63b","added_by":"auto","created_at":"2026-03-03 18:31:29","extension":"png","order_by":13,"title":"Figure 13","display":"","copyAsset":false,"role":"figure","size":341188,"visible":true,"origin":"","legend":"\u003cp\u003eFlexural rupture of the CFRP plate\u003c/p\u003e","description":"","filename":"floatimage13.png","url":"https://assets-eu.researchsquare.com/files/rs-8931617/v1/063763ec407cc09c0ccb9a94.png"},{"id":104408068,"identity":"17bbda3e-54ec-42e8-9e40-4c6941ffdc96","added_by":"auto","created_at":"2026-03-11 12:41:23","extension":"pdf","order_by":0,"title":"","display":"","copyAsset":false,"role":"manuscript-pdf","size":9351179,"visible":true,"origin":"","legend":"","description":"","filename":"manuscript.pdf","url":"https://assets-eu.researchsquare.com/files/rs-8931617/v1/3713d8a6-5b5d-46a4-9af9-1228f35b290f.pdf"}],"financialInterests":"No competing interests reported.","formattedTitle":"Flexural Fatigue Performance Analysis of Bridge T-Beam Members Strengthened with Prestressed CFRP Plates","fulltext":[{"header":"1. Introduction","content":"\u003cp\u003eWith the continuous increase in traffic load levels and the growing service life of bridges, girder bridges are prone to fatigue damage accumulation under repeated vehicular loading. This is typically manifested by stiffness degradation, increased deflection, and crack propagation, which severely compromise the service performance and durability of bridge structures. For existing small- and medium-span girder bridges, effectively enhancing their flexural fatigue resistance under the premise of maintaining traffic operation or minimizing interruptions has become an urgent issue in the field of bridge maintenance and strengthening [\u003cspan citationid=\"CR1\" class=\"CitationRef\"\u003e1\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR2\" class=\"CitationRef\"\u003e2\u003c/span\u003e].\u003c/p\u003e \u003cp\u003eFiber-reinforced polymer (FRP) composites, characterized by high strength, low self-weight, and excellent corrosion resistance, have been widely employed in the flexural strengthening of concrete girder bridges. Among various techniques, externally bonded carbon fiber\u0026ndash;reinforced polymer (CFRP) plate strengthening has gained extensive application in engineering practice due to its convenient installation and well-defined load-transfer mechanism [\u003cspan citationid=\"CR3\" class=\"CitationRef\"\u003e3\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR4\" class=\"CitationRef\"\u003e4\u003c/span\u003e]. Numerous studies have investigated the mechanical performance of reinforced concrete beams strengthened with externally bonded CFRP plates. The research conducted by Li et al. [\u003cspan citationid=\"CR5\" class=\"CitationRef\"\u003e5\u003c/span\u003e], Wang et al. [\u003cspan citationid=\"CR6\" class=\"CitationRef\"\u003e6\u003c/span\u003e], and Zhang et al. [\u003cspan citationid=\"CR7\" class=\"CitationRef\"\u003e7\u003c/span\u003e] demonstrated that non-prestressed CFRP plates can enhance the load-carrying capacity and improve the deformation behavior of beams to a certain extent; however, their strengthening effectiveness remains limited under service conditions. This limitation is mainly attributed to the relatively low elastic modulus of CFRP materials, which prevents their high-strength advantage from being fully mobilized during the deformation-restricted service stage. To overcome the restricted efficiency of non-prestressed CFRP strengthening, prestressed CFRP plate systems have gradually attracted increasing attention. Studies by El-Sayed [\u003cspan citationid=\"CR8\" class=\"CitationRef\"\u003e8\u003c/span\u003e], Zhou [\u003cspan citationid=\"CR9\" class=\"CitationRef\"\u003e9\u003c/span\u003e], and Wang [\u003cspan citationid=\"CR10\" class=\"CitationRef\"\u003e10\u003c/span\u003e] indicated that applying prestress to CFRP plates prior to bonding can significantly reduce the tensile stress level in reinforcing steel under service conditions and improve the strength utilization efficiency of CFRP materials. Experimental results have confirmed that prestressed CFRP plates outperform non-prestressed CFRP plates in terms of enhancing cracking resistance, reducing deflection, and increasing static load capacity. Regarding fatigue performance, existing studies generally agree that fatigue failure of reinforced concrete beams is primarily governed by the stress level of tensile reinforcement. After conducting fatigue tests on multiple reinforced concrete T-beams, Alam et al. [\u003cspan citationid=\"CR11\" class=\"CitationRef\"\u003e11\u003c/span\u003e] reported that strengthening with non-prestressed CFRP plates can extend the fatigue life of beams; nevertheless, the fatigue behavior is still mainly controlled by the fatigue performance of steel reinforcement, and the strengthening effectiveness is largely constrained by the bond quality at the CFRP\u0026ndash;concrete interface. Corte et al. [\u003cspan citationid=\"CR12\" class=\"CitationRef\"\u003e12\u003c/span\u003e] observed in high-amplitude fatigue loading tests that some CFRP-strengthened beams experienced interfacial degradation and debonding failure before reaching the designed number of fatigue cycles. Furthermore, studies by Abdel [\u003cspan citationid=\"CR13\" class=\"CitationRef\"\u003e13\u003c/span\u003e] and Kueres [\u003cspan citationid=\"CR14\" class=\"CitationRef\"\u003e14\u003c/span\u003e] showed that stiffness degradation of CFRP-strengthened beams becomes more pronounced under the combined effects of fatigue loading and long-term adverse environmental conditions.\u003c/p\u003e \u003cp\u003eThe aforementioned studies have, to some extent, revealed the fatigue behavior of beams strengthened with non-prestressed CFRP plates; however, research on the fatigue performance of prestressed CFRP plate\u0026ndash;strengthened members remains relatively limited. Yuan et al. [\u003cspan citationid=\"CR15\" class=\"CitationRef\"\u003e15\u003c/span\u003e] conducted cyclic loading tests on RC slabs strengthened with prestressed CFRP plates and reported that fatigue failure is generally initiated by fracture of the tensile reinforcement, followed by interfacial debonding of the CFRP plate. Ghafoori [\u003cspan citationid=\"CR16\" class=\"CitationRef\"\u003e16\u003c/span\u003e] demonstrated that after two million fatigue cycles, the post-fatigue load-carrying capacity of prestressed CFRP-strengthened beams exhibited only a slight reduction, confirming the effectiveness of prestressing measures. Experimental results from Almassri [\u003cspan citationid=\"CR17\" class=\"CitationRef\"\u003e17\u003c/span\u003e] and Zhang [\u003cspan citationid=\"CR18\" class=\"CitationRef\"\u003e18\u003c/span\u003e] further indicated that, compared with non-prestressed CFRP systems, prestressed CFRP can more effectively reduce steel strain, concrete creep strain, and beam deflection, thereby significantly extending the fatigue life. Ye et al. [\u003cspan citationid=\"CR19\" class=\"CitationRef\"\u003e19\u003c/span\u003e] also found in fatigue strengthening studies of steel beams that the application of prestressed CFRP plates could increase the fatigue life by several times. It should be noted, however, that prestressed CFRP plate strengthening systems face additional challenges under fatigue loading, particularly with respect to end anchorage and the complex interfacial stress state. Al-Fakih [\u003cspan citationid=\"CR20\" class=\"CitationRef\"\u003e20\u003c/span\u003e] and Zhu [\u003cspan citationid=\"CR21\" class=\"CitationRef\"\u003e21\u003c/span\u003e] pointed out that increasing the prestress level leads to a substantial rise in interfacial stresses near the CFRP plate ends, making interfacial degradation more likely under cyclic loading. Moreover, since epoxy adhesives alone are often unable to sustain the large force transfer associated with prestressing, permanent anchorage devices are typically required in practice. The presence of such anchorage systems further complicates the stress distribution among concrete, steel reinforcement, and CFRP plates. These factors collectively indicate that the fatigue behavior of prestressed CFRP plate\u0026ndash;strengthened beams differs fundamentally from that of non-prestressed systems, highlighting the necessity for systematic and targeted investigations.\u003c/p\u003e \u003cp\u003eBased on the above research background, this study investigates bridge T-beam members through a comprehensive flexural fatigue experimental program, including unstrengthened beams, beams strengthened with non-prestressed CFRP plates, and beams strengthened with prestressed CFRP plates. By systematically monitoring the mid-span deflection, stiffness degradation, strain responses of tensile reinforcement and CFRP plates, as well as the CFRP\u0026ndash;concrete interfacial behavior, the fatigue response characteristics and failure modes of beams under different strengthening schemes are analyzed. Furthermore, post-fatigue monotonic loading tests are conducted to evaluate the effects of fatigue damage accumulation on the static performance and residual load-carrying capacity of prestressed CFRP-strengthened beams. The findings are expected to provide experimental evidence for the flexural fatigue performance assessment and practical application of prestressed CFRP plate strengthening in existing girder bridge members.\u003c/p\u003e"},{"header":"2. Flexural Fatigue Tests of Beams","content":"\u003cdiv id=\"Sec3\" class=\"Section2\"\u003e \u003ch2\u003e2.1 Specimen Design and Test Conditions\u003c/h2\u003e \u003cp\u003eThe beam specimens had an overall length of 5.0 m with a calculated span of 4.8 m. The beam depth was 600 mm, while the flange width and thickness were 600 mm and 100 mm, respectively, and the web thickness was 200 mm. The geometric dimensions and reinforcement arrangement of the specimens are illustrated in Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003e.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eTo investigate the flexural fatigue performance of reinforced concrete T-beam members strengthened with prestressed CFRP plates, a total of three RC T-beam specimens were fabricated in this study. The corresponding test conditions are summarized in Table\u0026nbsp;\u003cspan refid=\"Tab1\" class=\"InternalRef\"\u003e1\u003c/span\u003e.\u003c/p\u003e \u003cp\u003e \u003cdiv class=\"gridtable\"\u003e\u003ctable float=\"Yes\" id=\"Tab1\" border=\"1\"\u003e \u003ccaption language=\"En\"\u003e \u003cdiv class=\"CaptionNumber\"\u003eTable 1\u003c/div\u003e \u003cdiv class=\"CaptionContent\"\u003e \u003cp\u003eTest conditions\u003c/p\u003e \u003c/div\u003e \u003c/caption\u003e \u003ccolgroup cols=\"3\"\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c1\" colnum=\"1\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c2\" colnum=\"2\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c3\" colnum=\"3\"\u003e\u003c/div\u003e \u003cthead\u003e \u003ctr\u003e \u003cth align=\"left\" colname=\"c1\"\u003e \u003cp\u003eSpecimen number\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c2\"\u003e \u003cp\u003eStrengthening condition\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c3\"\u003e \u003cp\u003ePrestressing stress/MPa\u003c/p\u003e \u003c/th\u003e \u003c/tr\u003e \u003c/thead\u003e \u003ctbody\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e1\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eNot strengthened\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e-\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e2\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eStrengthened\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e0\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e3\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eStrengthened\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e1000\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003c/tbody\u003e \u003c/colgroup\u003e \u003c/table\u003e\u003c/div\u003e \u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec4\" class=\"Section2\"\u003e \u003ch2\u003e2.2 Material Properties\u003c/h2\u003e \u003cp\u003eThe concrete used for the beam specimens was designed with a target strength grade of C40, and the corresponding mix proportions are provided in Table\u0026nbsp;\u003cspan refid=\"Tab2\" class=\"InternalRef\"\u003e2\u003c/span\u003e. All concrete specimens were cast simultaneously, and the measured 28-day cubic compressive strength was 41.2 MPa.\u003c/p\u003e \u003cp\u003e \u003cdiv class=\"gridtable\"\u003e\u003ctable float=\"Yes\" id=\"Tab2\" border=\"1\"\u003e \u003ccaption language=\"En\"\u003e \u003cdiv class=\"CaptionNumber\"\u003eTable 2\u003c/div\u003e \u003cdiv class=\"CaptionContent\"\u003e \u003cp\u003eMix proportions of concrete\u003c/p\u003e \u003c/div\u003e \u003c/caption\u003e \u003ccolgroup cols=\"4\"\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c1\" colnum=\"1\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c2\" colnum=\"2\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c3\" colnum=\"3\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c4\" colnum=\"4\"\u003e\u003c/div\u003e \u003cthead\u003e \u003ctr\u003e \u003cth align=\"left\" colname=\"c1\"\u003e \u003cp\u003eP.O 42.5 Cement/kg\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c2\"\u003e \u003cp\u003eWater/kg\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c3\"\u003e \u003cp\u003eMedium Sand/kg\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c4\"\u003e \u003cp\u003eStone (5\u0026ndash;20 mm continuously graded aggregate)/kg\u003c/p\u003e \u003c/th\u003e \u003c/tr\u003e \u003c/thead\u003e \u003ctbody\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e440\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e170\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e680\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e1100\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003c/tbody\u003e \u003c/colgroup\u003e \u003c/table\u003e\u003c/div\u003e \u003c/p\u003e \u003cp\u003eThe longitudinal reinforcement and stirrups used in the beam specimens were of strength grades HRB400 and HPB235, respectively, and their measured mechanical properties are summarized in Table\u0026nbsp;\u003cspan refid=\"Tab3\" class=\"InternalRef\"\u003e3\u003c/span\u003e.\u003c/p\u003e \u003cp\u003e \u003cdiv class=\"gridtable\"\u003e\u003ctable float=\"Yes\" id=\"Tab3\" border=\"1\"\u003e \u003ccaption language=\"En\"\u003e \u003cdiv class=\"CaptionNumber\"\u003eTable 3\u003c/div\u003e \u003cdiv class=\"CaptionContent\"\u003e \u003cp\u003eMaterial properties\u003c/p\u003e \u003c/div\u003e \u003c/caption\u003e \u003ccolgroup cols=\"3\"\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c1\" colnum=\"1\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c2\" colnum=\"2\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c3\" colnum=\"3\"\u003e\u003c/div\u003e \u003cthead\u003e \u003ctr\u003e \u003cth align=\"left\" colname=\"c1\"\u003e \u003cp\u003eMaterial\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c2\"\u003e \u003cp\u003eParameter\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c3\"\u003e \u003cp\u003eValue\u003c/p\u003e \u003c/th\u003e \u003c/tr\u003e \u003c/thead\u003e \u003ctbody\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\" morerows=\"3\" rowspan=\"4\"\u003e \u003cp\u003eConcrete\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003ecubic compressive strength\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e41.2 MPa\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eelastic modulus\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e33.1 GPa\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003ePoisson\u0026rsquo;s ratio\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e0.19\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003edensity\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e2409 kg/m\u003csup\u003e3\u003c/sup\u003e\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\" morerows=\"3\" rowspan=\"4\"\u003e \u003cp\u003eRebar\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eyield strength (HRB400)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e421 MPa\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eyield strength (HPB235)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e265 MPa\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003etensile strength (HRB400)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e573 MPa\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003etensile strength (HPB235)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e384 MPa\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\" morerows=\"3\" rowspan=\"4\"\u003e \u003cp\u003eCFRP plate\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003ewidth\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e100 mm\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003ethickness (single layer)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e2 mm\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003etensile strength\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e2900 MPa\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eelastic modulus\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e170 GPa\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eEpoxy resin adhesive\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003ebonding strength\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e13.5 MPa\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003c/tbody\u003e \u003c/colgroup\u003e \u003c/table\u003e\u003c/div\u003e \u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec5\" class=\"Section2\"\u003e \u003ch2\u003e2.3 Installation of Prestressed CFRP Plates\u003c/h2\u003e \u003cp\u003eThe CFRP plates were bonded to the soffit of the beam specimens, centrally aligned along the longitudinal axis, with a bonded length of 3.6 m. The prestressed CFRP plates were connected to the end anchorage devices through corrugated clamping plates, as shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003e. The end anchorage systems were fixed to the beam ends using chemical anchor bolts. The anchorage devices were selected from a commonly used commercial product available in the domestic market, as illustrated in Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003e. The CFRP plates were first tensioned to the target prestressing level using a hydraulic jack, and then bonded to the concrete surface. During the bonding process, the target prestress level was maintained.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eFor the non-prestressed CFRP plate\u0026ndash;strengthened beam (Specimen 2), anchorage devices were installed at both ends of the CFRP plate to provide mechanical fixation and to prevent interfacial debonding between the CFRP plate and the concrete surface [\u003cspan citationid=\"CR7\" class=\"CitationRef\"\u003e7\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR8\" class=\"CitationRef\"\u003e8\u003c/span\u003e].\u003c/p\u003e \u003cp\u003eTo ensure reliable prestress transfer and stable bond performance, the installation of the prestressed CFRP plates followed a controlled and standardized procedure. Prior to bonding, the concrete soffit within the designated bond length was mechanically roughened to remove laitance and contaminants, and the surface was cleaned to ensure adequate adhesion. Any local surface defects were repaired to obtain a sound bonding substrate. Prestressing was applied using a hydraulic jack connected to the active-end anchorage system, while the opposite end was fixed by a passive anchorage. A dual-control method was adopted, in which both the applied jack force and the measured CFRP strain were monitored to achieve the target prestress level (1000 MPa). The prestress was applied incrementally to minimize seating losses and anchorage slip. After reaching the target level, the prestress was maintained for a stabilization period to ensure stress uniformity before bonding operations were finalized. The epoxy adhesive was prepared according to the manufacturer\u0026rsquo;s specified mixing ratio and applied uniformly to the prepared concrete surface. The CFRP plate was bonded while maintaining the target prestress level to ensure effective stress transfer. During curing, the bonded region was protected from external disturbances, and sufficient curing time was allowed under ambient laboratory conditions before removing the prestressing equipment. The end anchorage system consisted of steel clamping plates and chemical anchor bolts installed at the beam ends. High-strength bolts were tightened in a symmetric sequence to ensure uniform clamping pressure. This configuration enhanced force transfer efficiency and mitigated stress concentration near the laminate ends under fatigue loading.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec6\" class=\"Section2\"\u003e \u003ch2\u003e2.4 Test Loading and Measurements\u003c/h2\u003e \u003cp\u003eAs shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003e, the flexural fatigue tests were conducted under a four-point bending configuration. The loading span was 4800 mm, and the shear span length was 2100 mm. The loading setup and reaction frame are illustrated in Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003e.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eA constant-amplitude sinusoidal cyclic load was applied with the mean load as the reference level. The minimum and maximum loads were set to 10 kN and 50 kN, respectively, and the loading frequency was 5 Hz. The applied load was monitored and controlled using a load cell installed between the hydraulic jack and the loading beam.\u003c/p\u003e \u003cp\u003eAccording to relevant studies, a total of seven dial gauges were installed to measure the beam deflections, as shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003e. Electrical resistance strain gauges with a gauge length of 5 mm were attached at the mid-span of the longitudinal reinforcement to monitor the steel strain. In addition, twenty-five electrical resistance strain gauges, each with a gauge length of 5 mm, were bonded to the surface of the CFRP plate to measure the strain distribution along the tensile direction, as illustrated in Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003e.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eIn addition, four and six electrical resistance strain gauges with a gauge length of 100 mm were bonded to the compression zone and the side surfaces of the beam specimens, respectively, to measure the concrete compressive strain and to analyze the strain distribution along the beam depth.\u003c/p\u003e \u003c/div\u003e"},{"header":"3. Experimental Results","content":"\u003cp\u003eThe experimental results are summarized in Table\u0026nbsp;\u003cspan refid=\"Tab4\" class=\"InternalRef\"\u003e4\u003c/span\u003e.\u003c/p\u003e \u003cp\u003e \u003cdiv class=\"gridtable\"\u003e\u003ctable float=\"Yes\" id=\"Tab4\" border=\"1\"\u003e \u003ccaption language=\"En\"\u003e \u003cdiv class=\"CaptionNumber\"\u003eTable 4\u003c/div\u003e \u003cdiv class=\"CaptionContent\"\u003e \u003cp\u003eTest results\u003c/p\u003e \u003c/div\u003e \u003c/caption\u003e \u003ccolgroup cols=\"10\"\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c1\" colnum=\"1\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c2\" colnum=\"2\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c3\" colnum=\"3\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c4\" colnum=\"4\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c5\" colnum=\"5\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c6\" colnum=\"6\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c7\" colnum=\"7\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c8\" colnum=\"8\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c9\" colnum=\"9\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c10\" colnum=\"10\"\u003e\u003c/div\u003e \u003cthead\u003e \u003ctr\u003e \u003cth align=\"left\" colname=\"c1\"\u003e \u003cp\u003eSpecimen number\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c2\"\u003e \u003cp\u003e\u003cem\u003eε\u003c/em\u003e\u003csub\u003emax,rebar\u003c/sub\u003e/10\u003csup\u003e\u0026minus;\u0026thinsp;6\u003c/sup\u003e\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c3\"\u003e \u003cp\u003e\u003cem\u003eε\u003c/em\u003e\u003csub\u003emin,rebar\u003c/sub\u003e/10\u003csup\u003e\u0026minus;\u0026thinsp;6\u003c/sup\u003e\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c4\"\u003e \u003cp\u003eΔ\u003cem\u003eε\u003c/em\u003e\u003csub\u003erebar\u003c/sub\u003e/10\u003csup\u003e\u0026minus;\u0026thinsp;6\u003c/sup\u003e\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c5\"\u003e \u003cp\u003e\u003cem\u003eε\u003c/em\u003e\u003csub\u003emax,CFRP\u003c/sub\u003e/10\u003csup\u003e\u0026minus;\u0026thinsp;6\u003c/sup\u003e\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c6\"\u003e \u003cp\u003e\u003cem\u003eε\u003c/em\u003e\u003csub\u003emin,CFRP\u003c/sub\u003e/10\u003csup\u003e\u0026minus;\u0026thinsp;6\u003c/sup\u003e\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c7\"\u003e \u003cp\u003eΔ\u003cem\u003eε\u003c/em\u003e\u003csub\u003eCFRP\u003c/sub\u003e/10\u003csup\u003e\u0026minus;\u0026thinsp;6\u003c/sup\u003e\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c8\"\u003e \u003cp\u003e\u003cem\u003eδ\u003c/em\u003e\u003csub\u003e1\u003c/sub\u003e/mm\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c9\"\u003e \u003cp\u003eMax cycle\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c10\"\u003e \u003cp\u003eFailure mode\u003c/p\u003e \u003c/th\u003e \u003c/tr\u003e \u003c/thead\u003e \u003ctbody\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e1\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e1029\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e50\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e979\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e-\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003e-\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c7\"\u003e \u003cp\u003e-\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c8\"\u003e \u003cp\u003e7.6\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c9\"\u003e \u003cp\u003e22.7\u0026times;10\u003csup\u003e4\u003c/sup\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c10\"\u003e \u003cp\u003ereinforcement fracture\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e2\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e964\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e254\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e710\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e771\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003e138\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c7\"\u003e \u003cp\u003e633\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c8\"\u003e \u003cp\u003e5.7\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c9\"\u003e \u003cp\u003e70.2\u0026times;10\u003csup\u003e4\u003c/sup\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c10\"\u003e \u003cp\u003ereinforcement fracture after CFRP debonding\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e3\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e531\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e75\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e456\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e708\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003e134\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c7\"\u003e \u003cp\u003e574\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c8\"\u003e \u003cp\u003e4.5\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c9\"\u003e \u003cp\u003e10\u003csup\u003e6\u003c/sup\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c10\"\u003e \u003cp\u003emonotonically loaded to failure after 200\u0026times;10\u003csup\u003e4\u003c/sup\u003e cycles\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003c/tbody\u003e \u003c/colgroup\u003e \u003ctfoot\u003e \u003ctr\u003e\u003ctd colspan=\"10\"\u003eNote: In Table\u0026nbsp;\u003cspan refid=\"Tab4\" class=\"InternalRef\"\u003e4\u003c/span\u003e, \u003cem\u003eε\u003c/em\u003e\u003csub\u003emax,rebar\u003c/sub\u003e and \u003cem\u003eε\u003c/em\u003e\u003csub\u003emin,rebar\u003c/sub\u003e denote the maximum and minimum strains of the tensile reinforcement, respectively, and Δ\u003cem\u003eε\u003c/em\u003e\u003csub\u003erebar\u003c/sub\u003e represents the strain range of the reinforcement. Similarly, \u003cem\u003eε\u003c/em\u003e\u003csub\u003emax,CFRP\u003c/sub\u003e and \u003cem\u003eε\u003c/em\u003e\u003csub\u003emin,CFRP\u003c/sub\u003e denote the maximum and minimum strains of the CFRP plate, respectively, and Δ\u003cem\u003eε\u003c/em\u003e\u003csub\u003eCFRP\u003c/sub\u003e represents the strain range of the CFRP plate. In addition, \u003cem\u003eδ\u003c/em\u003e\u003csub\u003e1\u003c/sub\u003e refers to the beam deflection corresponding to the maximum load in the first loading cycle.\u003c/td\u003e\u003c/tr\u003e \u003c/tfoot\u003e \u003c/table\u003e\u003c/div\u003e \u003c/p\u003e \u003cdiv id=\"Sec8\" class=\"Section2\"\u003e \u003ch2\u003e3.1 Fatigue Behavior\u003c/h2\u003e \u003cp\u003eFigure\u0026nbsp;\u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e5\u003c/span\u003e presents the variation of mid-span deflection with the number of loading cycles for Specimen 1 (the unstrengthened control beam) during the fatigue test.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eAs shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e5\u003c/span\u003e, the mid-span deflection of Specimen 1 increased significantly within the first 10\u003csup\u003e4\u003c/sup\u003e loading cycles, indicating the accumulation of internal damage in the beam under cyclic loading. During the subsequent range of (1\u0026ndash;2)\u0026times;10\u003csup\u003e4\u003c/sup\u003e cycles, a slight reduction in deflection was observed. Thereafter, the deflection exhibited a continuous increasing trend over the cycle range of (2\u0026ndash;10)\u0026times;10\u003csup\u003e4\u003c/sup\u003e. When the number of cycles reached 22.7\u0026times;10\u003csup\u003e4\u003c/sup\u003e, fracture of the longitudinal tensile reinforcement occurred, leading to the failure of Specimen 1.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eThe variation of mid-span deflection with the number of cycles for Specimen 2 (the beam strengthened with a non-prestressed CFRP plate) is shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig7\" class=\"InternalRef\"\u003e7\u003c/span\u003e. The mid-span deflection continuously increased as the fatigue cycles progressed. During the first loading cycle, the maximum strain of the longitudinal tensile reinforcement in Specimen 2 under the peak load reached 964 \u0026micro;ε, which was 79.8% of that recorded in Specimen 1. After 50\u0026times;10\u003csup\u003e4\u003c/sup\u003e cycles, debonding between the CFRP plate and the concrete surface was observed near the loading point, as illustrated in Fig.\u0026nbsp;\u003cspan refid=\"Fig8\" class=\"InternalRef\"\u003e8\u003c/span\u003e. With further increase in the number of cycles, the debonded region propagated toward both supports and eventually developed into overall debonding of the CFRP plate from the soffit concrete surface. At this stage, the CFRP plate was only mechanically retained by the steel anchorage devices. When the number of cycles reached 70.2\u0026times;10\u003csup\u003e4\u003c/sup\u003e, fatigue fracture of the longitudinal tensile reinforcement occurred at the beam bottom, leading to the failure of Specimen 2.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eSpecimen 3 (the beam strengthened with a prestressed CFRP plate) was initially prestressed to a level of 1000 MPa. The growth curve of mid-span deflection with increasing fatigue cycles is presented in Fig.\u0026nbsp;\u003cspan refid=\"Fig7\" class=\"InternalRef\"\u003e7\u003c/span\u003e. Within the first 10\u003csup\u003e4\u003c/sup\u003e loading cycles, the mid-span deflection of Specimen 3 increased rapidly, indicating significant internal damage accumulation in the beam under cyclic loading [\u003cspan citationid=\"CR5\" class=\"CitationRef\"\u003e5\u003c/span\u003e, \u003cspan citationid=\"CR17\" class=\"CitationRef\"\u003e17\u003c/span\u003e, \u003cspan citationid=\"CR22\" class=\"CitationRef\"\u003e22\u003c/span\u003e]. Thereafter, the mid-span deflection exhibited a gradual growth up to 160\u0026times;10\u003csup\u003e4\u003c/sup\u003e cycles. During the subsequent cycle range of (160\u0026ndash;200)\u0026times;10\u003csup\u003e4\u003c/sup\u003e, the deflection growth rate increased noticeably, showing a pronounced rise.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec9\" class=\"Section2\"\u003e \u003ch2\u003e3.2 Deformation Analysis\u003c/h2\u003e \u003cp\u003eBy comparing the curves of Specimens 2 and 3 in Fig.\u0026nbsp;\u003cspan refid=\"Fig7\" class=\"InternalRef\"\u003e7\u003c/span\u003e, it can be observed that the beam strengthened with a prestressed CFRP plate (Specimen 3) exhibited a significant advantage in flexural fatigue resistance. For Specimen 2, the mid-span deflection under the maximum load of the first loading cycle (\u0026#120575;1) was 5.7 mm, and the deflection continued to increase with the number of cycles until failure occurred. In contrast, under the same fatigue loading conditions, Specimen 3 showed a markedly lower deflection level during the first 150\u0026times;10\u003csup\u003e4\u003c/sup\u003e cycles. Moreover, it should be emphasized that after the rapid increase in mid-span deflection during the initial 10\u003csup\u003e3\u003c/sup\u003e cycles, the deflection of Specimen 3 remained relatively stable, whereas the mid-span deflection of Specimen 2 exhibited a continuous growth trend throughout the fatigue loading process.\u003c/p\u003e \u003cp\u003eFigure\u0026nbsp;\u003cspan refid=\"Fig9\" class=\"InternalRef\"\u003e9\u003c/span\u003e illustrates the variation of stiffness with the number of fatigue cycles for Specimens 2 and 3. It can be seen that the stiffness of Specimen 2 decreased significantly after the first 10\u003csup\u003e5\u003c/sup\u003e loading cycles, and it continued to decline throughout the subsequent fatigue loading process until failure occurred. This indicates that cyclic fatigue loading induces pronounced damage accumulation in beams strengthened with non-prestressed CFRP plates (Specimen 2) [\u003cspan citationid=\"CR9\" class=\"CitationRef\"\u003e9\u003c/span\u003e, \u003cspan citationid=\"CR12\" class=\"CitationRef\"\u003e12\u003c/span\u003e].\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eSimilarly, the stiffness of Specimen 3 initially increased and then decreased rapidly within the first 10\u003csup\u003e5\u003c/sup\u003e loading cycles, which is consistent with the observed variation in mid-span deflection. After the rapid reduction stage, the stiffness of Specimen 3 exhibited a gradual decline up to 160\u0026times;10\u003csup\u003e4\u003c/sup\u003e cycles, while remaining at a relatively stable level. This suggests that cyclic fatigue loading did not induce pronounced damage accumulation within the beam during this stage. However, during the subsequent cycle range of (160\u0026ndash;200)\u0026times;10\u003csup\u003e4\u003c/sup\u003e, a sudden stiffness drop was observed. This phenomenon agrees well with the corresponding deflection development, reflecting the structural performance degradation of the prestressed CFRP plate\u0026ndash;strengthened beam (Specimen 3) under fatigue loading [\u003cspan citationid=\"CR1\" class=\"CitationRef\"\u003e1\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR2\" class=\"CitationRef\"\u003e2\u003c/span\u003e, \u003cspan citationid=\"CR4\" class=\"CitationRef\"\u003e4\u003c/span\u003e, \u003cspan citationid=\"CR23\" class=\"CitationRef\"\u003e23\u003c/span\u003e].\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec10\" class=\"Section2\"\u003e \u003ch2\u003e3.3 Strain Analysis\u003c/h2\u003e \u003cp\u003eFigure\u0026nbsp;\u003cspan refid=\"Fig10\" class=\"InternalRef\"\u003e10\u003c/span\u003e presents the variation of the strain range of the bottom tensile reinforcement (Δ\u003cem\u003eε\u003c/em\u003e\u003csub\u003erebar\u003c/sub\u003e) and the strain range of the CFRP plate (Δ\u003cem\u003eε\u003c/em\u003e\u003csub\u003eCFRP\u003c/sub\u003e) with increasing fatigue cycles for Specimens 2 and 3. As shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig10\" class=\"InternalRef\"\u003e10\u003c/span\u003e(a), the strain range of the tensile reinforcement in Specimen 2 increased significantly with the number of cycles, which can be attributed to CFRP\u0026ndash;concrete interfacial debonding and the associated stress redistribution. In contrast, as indicated in Fig.\u0026nbsp;\u003cspan refid=\"Fig10\" class=\"InternalRef\"\u003e10\u003c/span\u003e(b), throughout the entire fatigue loading process, the evolution trend of the CFRP plate strain range in Specimen 3 remained consistent with that of the tensile reinforcement. This suggests that the CFRP plate maintained a favorable bonding condition with the soffit concrete surface during fatigue loading [\u003cspan citationid=\"CR6\" class=\"CitationRef\"\u003e6\u003c/span\u003e, \u003cspan citationid=\"CR16\" class=\"CitationRef\"\u003e16\u003c/span\u003e].\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eFigure\u0026nbsp;\u003cspan refid=\"Fig10\" class=\"InternalRef\"\u003e10\u003c/span\u003e(c) compares the evolution of the strain range of the bottom tensile reinforcement with the number of fatigue cycles for Specimens 2 and 3. It can be observed that throughout the entire fatigue loading process, the tensile reinforcement strain range of Specimen 3 remained consistently lower than that of Specimen 2. At 50\u0026times;10\u003csup\u003e4\u003c/sup\u003e cycles, the strain range of Specimen 2 was approximately 1.6 times that of Specimen 3. Specimen 2 failed after 70.2\u0026times;10\u003csup\u003e4\u003c/sup\u003e cycles due to fatigue fracture of the tensile reinforcement, whereas Specimen 3 did not exhibit failure even after 200\u0026times;10\u003csup\u003e4\u003c/sup\u003e cycles. These results indicate that prestressed CFRP plate strengthening can effectively reduce the stress level of tensile reinforcement and significantly enhance the flexural fatigue resistance of reinforced concrete T-beams [\u003cspan citationid=\"CR3\" class=\"CitationRef\"\u003e3\u003c/span\u003e, \u003cspan citationid=\"CR7\" class=\"CitationRef\"\u003e7\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR8\" class=\"CitationRef\"\u003e8\u003c/span\u003e]. In contrast, non-prestressed CFRP plates tend to lose their bond with the concrete surface under cyclic fatigue loading, and therefore cannot provide effective strengthening for T-beam members [\u003cspan citationid=\"CR5\" class=\"CitationRef\"\u003e5\u003c/span\u003e, \u003cspan citationid=\"CR24\" class=\"CitationRef\"\u003e24\u003c/span\u003e].\u003c/p\u003e \u003cp\u003eTo further elucidate the underlying mechanism governing the different strain evolution behaviors between prestressed and non-prestressed CFRP strengthening systems, the interfacial stress transfer mechanism and bond\u0026ndash;slip interaction should be considered. According to bond mechanics principles, the interfacial shear stress between the CFRP plate and concrete substrate can be approximately expressed as:\u003cdiv id=\"Equa\" class=\"Equation\"\u003e\u003cdiv format=\"TEX\" class=\"mathdisplay\" id=\"FileID_Equa\" name=\"EquationSource\"\u003e\n$$\\:\\tau\\:\\left(x\\right)=\\frac{{E}_{f}{t}_{f}}{{b}_{f}}\\bullet\\:\\frac{d{\\epsilon\\:}_{f}\\left(x\\right)}{dx}$$\u003c/div\u003e\u003c/div\u003e\u003c/p\u003e \u003cp\u003ewhere \u003cem\u003eE\u003c/em\u003e\u003csub\u003e\u003cem\u003ef\u003c/em\u003e\u003c/sub\u003e and \u003cem\u003et\u003c/em\u003e\u003csub\u003e\u003cem\u003ef\u003c/em\u003e\u003c/sub\u003e denote the elastic modulus and thickness of the CFRP plate, respectively, bf is the plate width, and d\u003cem\u003eε\u003c/em\u003e\u003csub\u003e\u003cem\u003ef\u003c/em\u003e\u003c/sub\u003e/d\u003cem\u003ex\u003c/em\u003e represents the strain gradient along the bonded length. This relationship indicates that local interfacial shear stress is directly governed by the spatial variation of CFRP strain.\u003c/p\u003e \u003cp\u003eFor the non-prestressed CFRP-strengthened beam, the initial interfacial stress is negligible prior to loading. Under cyclic bending, tensile force transfer from concrete to CFRP leads to progressive strain localization near the loading region, resulting in high shear stress concentration at the interface. As fatigue cycles accumulate, microcracking and interfacial slip initiate and propagate, eventually causing partial debonding. Once debonding occurs, the tensile force previously carried by the CFRP plate is redistributed to the steel reinforcement, leading to a sharp increase in reinforcement strain range and accelerating fatigue fracture.\u003c/p\u003e \u003cp\u003eIn contrast, the prestressed CFRP system introduces an initial compressive stress state in the concrete and an initial tensile stress in the CFRP plate before external loading is applied. This prestress reduces the effective tensile stress amplitude experienced by the reinforcement under cyclic loading and modifies the strain gradient distribution along the bonded length. As a result, interfacial shear stress peaks are mitigated and more uniformly distributed. From a bond\u0026ndash;slip perspective, prestressing delays the development of relative slip between the CFRP plate and concrete substrate, thereby restraining damage evolution within the interfacial transition zone.\u003c/p\u003e \u003cp\u003eThe schematic comparison of interfacial stress distribution and bond\u0026ndash;slip behavior between the two strengthening systems is illustrated in Fig.\u0026nbsp;\u003cspan refid=\"Fig11\" class=\"InternalRef\"\u003e11\u003c/span\u003e. It can be inferred that prestressing effectively stabilizes the load transfer mechanism, alleviates stress redistribution triggered by local debonding, and maintains coordinated deformation between CFRP and reinforcement. This mechanism explains why the prestressed CFRP-strengthened beam exhibited a consistently lower reinforcement strain range and a significantly extended fatigue life.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eFrom the perspective of interfacial mechanics, the different fatigue responses between non-prestressed and prestressed CFRP systems can be further explained by bond deterioration and stress redistribution mechanisms. In the non-prestressed configuration, the interface initially carries no prestress, and cyclic loading promotes progressive slip accumulation near high-moment regions. Once partial debonding initiates, tensile force previously transferred to the CFRP plate is redistributed to the steel reinforcement, resulting in a rapid increase in reinforcement strain range and accelerated fatigue crack propagation. In contrast, prestressing introduces an initial tensile stress in the CFRP plate and a compressive state in the concrete substrate, which reduces the effective tensile stress amplitude in the reinforcement and mitigates interfacial shear stress concentration. Consequently, slip development and debonding are delayed, stabilizing the load transfer mechanism and contributing to the improved fatigue resistance of the prestressed strengthening system.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec11\" class=\"Section2\"\u003e \u003ch2\u003e3.4 Failure Loading\u003c/h2\u003e \u003cp\u003eAfter undergoing 200\u0026times;10\u003csup\u003e4\u003c/sup\u003e fatigue loading cycles, no debonding cracks were observed between the CFRP plate and the soffit concrete surface, nor was any fracture of the bottom longitudinal tensile reinforcement detected. Subsequently, to further investigate the influence of fatigue damage accumulation on the static performance and residual load-carrying capacity of the prestressed CFRP plate\u0026ndash;strengthened T-beam, Specimen 3 was subjected to monotonic loading until failure. The corresponding response curves are presented in Fig.\u0026nbsp;\u003cspan refid=\"Fig12\" class=\"InternalRef\"\u003e12\u003c/span\u003e.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eFor Specimen 3, yielding of the bottom longitudinal tensile reinforcement occurred when the applied load reached 175 kN. As the load increased to 205 kN, debonding between the CFRP plate and the soffit concrete surface initiated at the mid-span region. The debonding crack then rapidly propagated toward the steel anchorage devices at both beam ends and extended throughout the entire bonded length. At this stage, the CFRP plate was connected to the beam only through the end steel anchorages, which carried the total tensile force in the CFRP plate. Similar to Specimen 2, after CFRP plate debonding occurred, both the mid-span deflection and the CFRP plate strain of Specimen 3 increased significantly. When the load further increased to 215 kN, failure took place due to tensile rupture of the anchorage bolts at one end, causing the steel anchorage device to be pulled out from the beam. The corresponding failure pattern is shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig13\" class=\"InternalRef\"\u003e13\u003c/span\u003e.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eAs mentioned above, Specimen 3 exhibited damage accumulation during the cycle range of (16\u0026ndash;20)\u0026times;10\u003csup\u003e4\u003c/sup\u003e. Figure\u0026nbsp;\u003cspan refid=\"Fig12\" class=\"InternalRef\"\u003e12\u003c/span\u003e indicates that the existing accumulated damage had a noticeable influence on the static behavior of Specimen 3 [\u003cspan citationid=\"CR11\" class=\"CitationRef\"\u003e11\u003c/span\u003e, \u003cspan citationid=\"CR14\" class=\"CitationRef\"\u003e14\u003c/span\u003e].\u003c/p\u003e \u003c/div\u003e"},{"header":"4. Conclusions","content":"\u003cp\u003eBased on the flexural fatigue experimental investigation of unstrengthened reinforced concrete T-beams, T-beams strengthened with non-prestressed CFRP plates, and T-beams strengthened with prestressed CFRP plates under constant-amplitude cyclic loading, the effects of different strengthening schemes on the evolution of mid-span deflection, stiffness degradation characteristics, strain responses of tensile reinforcement and CFRP plates, as well as interfacial bonding performance were systematically analyzed. In addition, monotonic loading tests were conducted on the prestressed CFRP-strengthened beams after fatigue loading to further evaluate the influence of fatigue damage accumulation on the static performance and residual load-carrying capacity of the members. On this basis, combined with the observed fatigue failure modes and the evolution of key mechanical parameters, the enhancement mechanisms of flexural fatigue performance provided by prestressed CFRP plate strengthening were comprehensively discussed. The main conclusions can be drawn as follows:\u003c/p\u003e \u003cp\u003e(1) Compared with the unstrengthened beam and the beam strengthened with a non-prestressed CFRP plate, the prestressed CFRP plate\u0026ndash;strengthened beam exhibited smaller mid-span deflections, more stable stiffness degradation behavior, and lower tensile reinforcement strain levels during fatigue loading. Under comparable or even higher fatigue load levels, the fatigue life of the prestressed CFRP-strengthened beam was significantly extended, whereas the non-prestressed CFRP-strengthened beam failed due to fatigue fracture of the tensile reinforcement after approximately 70.2\u0026times;10\u003csup\u003e4\u003c/sup\u003e cycles.\u003c/p\u003e \u003cp\u003e(2) The experimental results showed that throughout the fatigue loading process, the strain range of the CFRP plate in the prestressed CFRP-strengthened beam evolved consistently with that of the tensile reinforcement, and no significant interfacial debonding was observed. In contrast, the non-prestressed CFRP-strengthened beam experienced progressive CFRP\u0026ndash;concrete interfacial debonding under cyclic loading, which induced stress redistribution from the CFRP plate to the steel reinforcement. This redistribution led to a pronounced increase in reinforcement strain range and accelerated fatigue crack propagation in the steel bars. The introduction of prestress effectively reduced the tensile stress amplitude in the reinforcement and delayed the development of interfacial slip and debonding, thereby stabilizing the load transfer mechanism and enhancing the flexural fatigue resistance of the strengthened beam.\u003c/p\u003e \u003cp\u003e(3) Post-fatigue monotonic loading tests indicated that the prestressed CFRP plate\u0026ndash;strengthened beam exhibited a load\u0026ndash;carrying behavior prior to steel yielding that was generally consistent with that of the corresponding beam subjected to monotonic loading only, suggesting that moderate fatigue damage had a limited influence on its overall load capacity. However, under higher fatigue load levels and larger load amplitudes, the yielding load and the interfacial debonding load were significantly reduced, accompanied by accelerated stiffness degradation. Overall, prestressed CFRP plate strengthening demonstrates good engineering applicability for enhancing the flexural fatigue performance of existing girder bridge members.\u003c/p\u003e"},{"header":"Declarations","content":"\u003cp\u003e\u003cstrong\u003eFunding Declaration\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThis research was supported by the Science and Technology Research Program of Chongqing Municipal Education Commission (Grant No.KJZD-K202503402, KJZD-K202505801), sponsored by Natural Science Foundation of Chongqing,China (Grant No.CSTB2025NSCQ-GPX0797).\u003c/p\u003e\n\n\u003cp\u003e\u003cstrong\u003eAuthor Contributions\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eQiang Lu: Supervision; Validation; Writing \u0026ndash; Review \u0026amp; Editing.\u003c/p\u003e\n\u003cp\u003eFengbing Zhao: Conceptualization; Methodology; Investigation; Data Curation; Writing \u0026ndash; Original Draft.\u003c/p\u003e\n\u003cp\u003eBolin Jiang: Resources; Visualization; Formal Analysis.\u003c/p\u003e\n\u003cp\u003eShanshan Wu: Software; Experimental Setup; Data Processing.\u003c/p\u003e\n\u003cp\u003eAll authors have read and approved the final version of this manuscript.\u003c/p\u003e\n\n\u003cp\u003e\u003cstrong\u003eData availability \u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eData will be made available on request.\u003c/p\u003e\n\n\u003cp\u003e\u003cstrong\u003eDeclaration of Competing Interest\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThe authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.\u003c/p\u003e\n\n\u003cp\u003e\u003cstrong\u003eEthical approval\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eNot applicable\u003c/p\u003e\n\n\u003cp\u003e\u003cstrong\u003eConsent to publish\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eNot applicable\u003c/p\u003e\n\n\u003cp\u003e\u003cstrong\u003eClinical trial\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eNot applicable\u003c/p\u003e"},{"header":"References","content":"\u003col\u003e\u003cli\u003e\u003cspan\u003eWang, H. T. et al. Flexural strengthening of damaged steel beams with prestressed CFRP plates using a novel prestressing system. \u003cem\u003eEng. Struct.\u003c/em\u003e \u003cb\u003e284\u003c/b\u003e, 115953 (2023).\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eLi, A., Wang, H., Li, H., Kong, D. \u0026amp; Xu, S. Stress concentration analysis of the corroded steel plate strengthened with carbon fiber reinforced polymer (CFRP) plates. \u003cem\u003ePolymers\u003c/em\u003e \u003cb\u003e14\u003c/b\u003e, 3845 (2022).\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eAbdel Havez, A. \u0026amp; Al-Mayah, A. Flexural strengthening of concrete structures using externally bonded and unbonded prestressed CFRP laminates: A literature review. \u003cem\u003eJ. Compos. Constr.\u003c/em\u003e \u003cb\u003e27\u003c/b\u003e, (2023).\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eZhou, C., Wang, L., Wang, Y. \u0026amp; Fang, Z. Experimental study on the flexural strengthening of one-way RC slabs with end-buckled and/or externally bonded CFRP sheets. \u003cem\u003eEng. Struct.\u003c/em\u003e \u003cb\u003e282\u003c/b\u003e, 115832 (2023).\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eLi, J., Zhu, M. \u0026amp; Deng, J. Flexural behaviour of notched steel beams strengthened with a prestressed CFRP plate subjected to fatigue damage and wetting/drying cycles. \u003cem\u003eEng. Struct.\u003c/em\u003e \u003cb\u003e250\u003c/b\u003e, 113430 (2022).\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eWang, H. T. et al. Structural performance of steel beams strengthened with prestressed CFRP plates: Steel beam-CFRP plate string systems. \u003cem\u003eThin-Walled Struct.\u003c/em\u003e \u003cb\u003e220\u003c/b\u003e, 114251 (2026).\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eZhang, W., Kang, S., Liu, X., Lin, B. \u0026amp; Huang, Y. Experimental study of a composite beam externally bonded with a carbon fiber-reinforced plastic plate. \u003cem\u003eJ. Building Eng.\u003c/em\u003e \u003cb\u003e71\u003c/b\u003e, 106522 (2023).\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eEl-Sayed, A. K., Al-Zaid, R. A., Al-Negheimish, A. I., Shuraim, A. B. \u0026amp; Alhozaimy, A. M. Long-term behavior of wide shallow RC beams strengthened with externally bonded CFRP plates. \u003cem\u003eConstr. Build. Mater.\u003c/em\u003e \u003cb\u003e51\u003c/b\u003e, 473\u0026ndash;483 (2014).\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eZhou, C. Y., Yu, Y. N. \u0026amp; Xie, E. L. Strengthening RC beams using externally bonded CFRP sheets with end self-locking. \u003cem\u003eCompos. Struct.\u003c/em\u003e \u003cb\u003e241\u003c/b\u003e, 112070 (2020).\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eWang, Q. et al. Fatigue performance of CFRP reinforced pretensioned prestressed beams. \u003cem\u003eConstr. Build. Mater.\u003c/em\u003e \u003cb\u003e324\u003c/b\u003e, 126509 (2022).\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eAlam, M. A., Onik, S. A. A. \u0026amp; Mustapha, K. N. B. Crack-based bond strength model of externally bonded steel plate and CFRP laminate to predict debonding failure of shear-strengthened RC beams. \u003cem\u003eJ. Building Eng.\u003c/em\u003e \u003cb\u003e27\u003c/b\u003e, 100943 (2020).\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eDe Corte, W. \u0026amp; Van Bogaert, P. Evaluation of an experimental CFRP prestressed beam and slab road bridge. \u003cem\u003eCompos. Part. B\u003c/em\u003e. \u003cb\u003e36\u003c/b\u003e, 91\u0026ndash;98 (2005).\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eAbdel Havez, A. \u0026amp; Al-Mayah, A. High prestressing of externally mounted CFRP plates for prestressed hollow-core slabs strengthening. \u003cem\u003eStructures\u003c/em\u003e \u003cb\u003e75\u003c/b\u003e, 108698 (2025).\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eKueres, S. \u0026amp; Hegger, J. Reliability analysis of footbridges pre-tensioned with carbon fiber reinforced polymer tendons under flexural loading. \u003cem\u003eEng. Struct.\u003c/em\u003e \u003cb\u003e203\u003c/b\u003e, 109546 (2020).\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eYuan, X., Zhu, C., Zheng, W., Hu, J. \u0026amp; Tang, B. Flexure performance of externally bonded CFRP plate-strengthened reinforced concrete members. Mathematical Problems in Engineering 2604024 (2020). (2020).\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eGhafoori, E. et al. Finite element analysis for fatigue damage reduction in metallic riveted bridges using prestressed CFRP plates. \u003cem\u003ePolymers\u003c/em\u003e \u003cb\u003e6\u003c/b\u003e, 1096\u0026ndash;1118 (2014).\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eAlmassri, B., Halahla, A. M. \u0026amp; Corroded RC beam repaired in flexure using NSM CFRP rod and an external steel plate. \u003cem\u003eStructures\u003c/em\u003e \u003cb\u003e27\u003c/b\u003e, 343\u0026ndash;351 (2020).\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eZhang, Z. J. et al. Entire mechanical analysis of prestressed CFRP strengthened RC beams under different prestress introduction methods. \u003cem\u003eAdv. Bridge Eng.\u003c/em\u003e \u003cb\u003e5\u003c/b\u003e, 13 (2024).\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eYe, H. et al. Fatigue performance analysis of damaged steel beams strengthened with prestressed unbonded CFRP plates. \u003cem\u003eJ. Bridge Eng.\u003c/em\u003e \u003cb\u003e23\u003c/b\u003e, 04018040 (2018).\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eAl-Fakih, A. et al. Cracking behavior of sea sand RC beam bonded externally with CFRP plate. \u003cem\u003eStructures\u003c/em\u003e \u003cb\u003e33\u003c/b\u003e, 1578\u0026ndash;1589 (2021).\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eZhu, K. Research on prestressed CFRP plate in the reinforcement of composite box girder bridge. Journal of Physics: Conference Series 2920, 012013 (2024).\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eCheng, X. et al. Seismic response of a box bridge after reinforcement with prestressed CFRP textile. \u003cem\u003eAustralian J. Civil Eng.\u003c/em\u003e \u003cb\u003e18\u003c/b\u003e, 29\u0026ndash;45 (2019).\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eHu, L., Li, W. \u0026amp; Feng, P. Long-term behavior of CFRP plates under sustained loads. \u003cem\u003eAdv. Struct. Eng.\u003c/em\u003e \u003cb\u003e25\u003c/b\u003e, 939\u0026ndash;953 (2022).\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eWang, H. T. \u0026amp; Wu, G. Bond-slip models for CFRP plates externally bonded to steel substrates. \u003cem\u003eCompos. Struct.\u003c/em\u003e \u003cb\u003e184\u003c/b\u003e, 1204\u0026ndash;1214 (2018).\u003c/span\u003e\u003c/li\u003e\u003c/ol\u003e"}],"fulltextSource":"","fullText":"","funders":[],"hasAdminPriorityOnWorkflow":false,"hasManuscriptDocX":true,"hasOptedInToPreprint":true,"hasPassedJournalQc":"","hasAnyPriority":false,"hideJournal":false,"highlight":"","institution":"","isAcceptedByJournal":false,"isAuthorSuppliedPdf":false,"isDeskRejected":"","isHiddenFromSearch":false,"isInQc":false,"isInWorkflow":false,"isPdf":false,"isPdfUpToDate":true,"isWithdrawnOrRetracted":false,"journal":{"display":true,"email":"[email protected]","identity":"scientific-reports","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":false,"externalIdentity":"scirep","sideBox":"Learn more about [Scientific Reports](http://www.nature.com/srep/)","snPcode":"","submissionUrl":"","title":"Scientific Reports","twitterHandle":"","acdcEnabled":true,"dfaEnabled":true,"editorialSystem":"stoa","reportingPortfolio":"Scientific Reports","inReviewEnabled":true,"inReviewRevisionsEnabled":true},"keywords":"Prestressed CFRP plates, girder bridges, flexural fatigue, structural performance analysis","lastPublishedDoi":"10.21203/rs.3.rs-8931617/v1","lastPublishedDoiUrl":"https://doi.org/10.21203/rs.3.rs-8931617/v1","license":{"name":"CC BY 4.0","url":"https://creativecommons.org/licenses/by/4.0/"},"manuscriptAbstract":"\u003cp\u003ePrestressed carbon fiber\u0026ndash;reinforced polymer (CFRP) plate strengthening has been widely applied in the rehabilitation of flexural bridge members due to its advantages of low self-weight, convenient construction, and excellent durability. However, existing studies have mainly focused on the static behavior of prestressed CFRP-strengthened beams, while the flexural fatigue performance of prestressed CFRP plate\u0026ndash;strengthened bridge girders remains insufficiently understood. To address this gap, this study investigates bridge T-beam members through a series of flexural fatigue tests, including unstrengthened beams, beams strengthened with non-prestressed CFRP plates, and beams strengthened with prestressed CFRP plates. The evolution of mid-span deflection, stiffness degradation, strain responses of tensile reinforcement and CFRP plates, as well as the interfacial bond behavior under different strengthening schemes were systematically analyzed. In addition, the effects of fatigue damage accumulation on the residual static performance and ultimate load-carrying capacity of prestressed CFRP-strengthened beams were further examined. The experimental results indicate that, compared with unstrengthened beams and non-prestressed CFRP-strengthened beams, prestressed CFRP plate\u0026ndash;strengthened beams exhibited smaller mid-span deflections, more stable stiffness degradation characteristics, and lower strain amplitudes in tensile reinforcement during fatigue loading, demonstrating a significant improvement in flexural fatigue performance. In contrast, beams strengthened with non-prestressed CFRP plates were prone to CFRP\u0026ndash;concrete interfacial debonding under cyclic loading, which led to stress redistribution between the steel reinforcement and CFRP plates, resulting in a rapid increase in reinforcement strain amplitude and premature fatigue failure. Post-fatigue monotonic loading tests further revealed that moderate fatigue damage had a limited influence on the static load capacity of prestressed CFRP-strengthened beams, whereas more pronounced degradation in stiffness and load-bearing performance occurred under higher fatigue load levels. Overall, the results demonstrate that prestressed CFRP plates can effectively reduce the stress level of tensile reinforcement while maintaining favorable interfacial bonding performance, thereby significantly enhancing the flexural fatigue resistance of bridge girder members. This study provides experimental evidence to support fatigue strengthening strategies for existing bridges.\u003c/p\u003e","manuscriptTitle":"Flexural Fatigue Performance Analysis of Bridge T-Beam Members Strengthened with Prestressed CFRP Plates","msid":"","msnumber":"","nonDraftVersions":[{"code":1,"date":"2026-03-03 18:31:24","doi":"10.21203/rs.3.rs-8931617/v1","editorialEvents":[{"type":"communityComments","content":0},{"type":"reviewerAgreed","content":"163188950344744724427958463999598502929","date":"2026-04-24T02:05:42+00:00","index":"hide","fulltext":""},{"type":"reviewerAgreed","content":"336285778645290217005275584484114902138","date":"2026-03-01T00:02:56+00:00","index":"hide","fulltext":""},{"type":"reviewersInvited","content":"","date":"2026-02-26T15:43:47+00:00","index":"","fulltext":""},{"type":"editorInvited","content":"","date":"2026-02-26T15:31:26+00:00","index":"","fulltext":""},{"type":"editorAssigned","content":"","date":"2026-02-24T09:30:21+00:00","index":"","fulltext":""},{"type":"checksComplete","content":"","date":"2026-02-24T09:26:12+00:00","index":"","fulltext":""},{"type":"submitted","content":"Scientific Reports","date":"2026-02-21T07:45:37+00:00","index":"","fulltext":""}],"status":"published","journal":{"display":true,"email":"[email protected]","identity":"scientific-reports","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":false,"externalIdentity":"scirep","sideBox":"Learn more about [Scientific Reports](http://www.nature.com/srep/)","snPcode":"","submissionUrl":"","title":"Scientific Reports","twitterHandle":"","acdcEnabled":true,"dfaEnabled":true,"editorialSystem":"stoa","reportingPortfolio":"Scientific Reports","inReviewEnabled":true,"inReviewRevisionsEnabled":true}}],"origin":"","ownerIdentity":"6ae22222-2773-4531-98fb-0ae67ebd8807","owner":[],"postedDate":"March 3rd, 2026","published":true,"recentEditorialEvents":[],"rejectedJournal":[],"revision":"","amendment":"","status":"under-review","subjectAreas":[{"id":63709095,"name":"Physical sciences/Engineering"},{"id":63709096,"name":"Physical sciences/Materials science"}],"tags":[],"updatedAt":"2026-03-03T18:31:24+00:00","versionOfRecord":[],"versionCreatedAt":"2026-03-03 18:31:24","video":"","vorDoi":"","vorDoiUrl":"","workflowStages":[]},"version":"v1","identity":"rs-8931617","journalConfig":"researchsquare"},"__N_SSP":true},"page":"/article/[identity]/[[...version]]","query":{"redirect":"/article/rs-8931617","identity":"rs-8931617","version":["v1"]},"buildId":"XKTyCvWXoU3ODBz1xrDgd","isFallback":false,"isExperimentalCompile":false,"dynamicIds":[84888],"gssp":true,"scriptLoader":[]}