Strengthening of Two-Way Slabs Using Fiber Reinforced Concrete, Near Surface Mounted and CFRP Layers under Impact Loading

Strengthening of Two-Way Slabs Using Fiber Reinforced Concrete, Near Surface Mounted and CFRP Layers under Impact Loading | 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 Strengthening of Two-Way Slabs Using Fiber Reinforced Concrete, Near Surface Mounted and CFRP Layers under Impact Loading Mehran Masoudiyan, mostafa Zinati, Ali Kargaran, Ali kheyroddin This is a preprint; it has not been peer reviewed by a journal. https://doi.org/ 10.21203/rs.3.rs-8078876/v1 This work is licensed under a CC BY 4.0 License Status: Under Review Version 1 posted 12 You are reading this latest preprint version Abstract This article investigates the effectiveness of five strengthening techniques for reinforced concrete (RC) two-way slabs subjected to impact loading. Fifteen square slabs were tested under drop-weight impacts to evaluate Fiber-Reinforced Concrete (FRC) with steel or polypropylene fibers, Externally Bonded Reinforcement (EBR) using Carbon Fiber Reinforced Polymer (CFRP), Near-Surface Mounted (NSM), and hybrid NSM-CFRP combinations. Results show improvements in impact resistance across all methods. FRC slabs with polypropylene fibers exhibited a 2.3 times increase in energy absorption compared to conventional RC slabs, while steel fibers reduced concrete scabbing by 35%. CFRP reinforced slabs (EBR) showed the highest strength, up to 34 impacts, almost triple the capacity of RC slabs. Hybrid techniques showed most effective, combining NSM and CFRP strips to reduce damage area by 28–59%. FRC offers a cost-effective solution for distributed reinforcement, EBR gives in localized protection, and hybrid methods result optimal performance for high-risk scenarios. Physical sciences/Engineering Physical sciences/Materials science Reinforced Concrete Two-Way Slab Impact Loading Fiber-Reinforced Concrete Near-Surface Mounted Carbon Fiber Reinforced Polymer 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 Figure 14 Figure 15 Figure 16 1 Introduction Two-way reinforced concrete slabs are critical structural elements that may require strengthening due to increased loading demands, structural defects, or damage from impact events. The strengthening of these slabs using Carbon Fiber Reinforced Polymer (CFRP) layers and fiber reinforced concrete has emerged as an effective rehabilitation technique, particularly for structures subjected to impact loading conditions 1 – 3 . The application of CFRP strengthening systems has gained significant attention due to their high strength-to-weight ratio, corrosion resistance, and ease of installation 4 . Under impact loading scenarios, these strengthening methods must address complex dynamic behaviors including stress wave propagation, energy absorption, and failure mode transitions 5 . Fiber-reinforced concrete (FRC) combines cementitious materials with randomly distributed fibers to create a composite material with enhanced tensile strength and ductility 6 . The discontinuous fibers dispersed throughout the concrete matrix significantly improve crack control, toughness, and impact resistance while maintaining structural flexibility. In modern construction, protecting concrete elements from external hazards like impact and blast loads has become critical for structural safety 7 – 16 . A structure's impact resistance, its ability to withstand sudden dynamic loads - serves as an important indicator of concrete quality and durability. The most commonly employed technique involves externally bonded CFRP sheets or strips applied to the tension surface of concrete slabs 1 – 3 . Research demonstrates that CFRP provides superior strengthening performance compared to other FRP materials, with strength enhancements of 34.5% compared to 11.2% for PET-FRP 1 . The application of CFRP strips to the tension surface significantly improves cracking loads by 97.73% and ultimate load capacity by 134.02% 2 . Advanced strengthening approaches utilize NSM CFRP bars inserted at specific depths from the tension face 17 . This method has shown effectiveness in controlling plastic deformation and improving punching strength of two-way slabs 17 . For more targeted reinforcement, the construction industry has perfected the near-surface mounted (NSM) technique. Workers carefully cut grooves into the concrete surface, then embed FRP bars that bond securely within the protective concrete layer. This method creates an incredibly durable connection that resists separation far better than surface-mounted alternatives. The latest breakthrough uses high-strength reinforcement (HSR) bars in these applications - a smart choice that saves materials, reduces environmental impact, and speeds up construction while maintaining top performance 18 – 27 . The EBROG technique has proven successful in postponing FRP debonding, with flexural strengthening achieving 77% increases in ultimate load capacity and combined flexural-punching shear strengthening systems providing 94% enhancement 28 . Innovative approaches combine CFRP with other materials, such as layered hybrid concrete composite slabs using reactive powder concrete (RPC) in the top layer and normal concrete in the bottom layer, reinforced with internal CFRP grids. These systems demonstrate 19% better impact resistance compared to steel-reinforced slabs 5 . CFRP strengthening alters failure patterns from concrete compression damage to CFRP anchorage stress concentrations, highlighting effective stress distribution and load-sharing synergy 3 . The strengthening systems demonstrate superior performance under high-velocity impact loads, with steel fiber and FRP combinations providing outstanding impact resistance 29 . The concrete compressive strength moderately influences ultimate load capacity in CFRP-strengthened slabs 1 , 30 . Increasing concrete strength from 20 MPa to 80 MPa results in predicted ultimate load increases from 15% to 62% for CFRP-strengthened slabs 1 , 30 . Higher concrete strength slabs (C70) show 23.3% greater ultimate loading capacity improvements 30 . Numerical results consistently demonstrate that increasing the strengthening ratio significantly impacts shear strength and damage percentage 2 , 17 , 31 . The relationship between CFRP plate stiffness and ultimate bond strength reduction has been established through experimental testing. CFRP strip spacing affects performance, with 200mm and 300mm center-to-center spacing showing different effectiveness levels. Strip strengthening locations near supports prove more effective than middle-of-slab applications 32 . The application of diagonally oriented CFRP strips reduces cracking zones compared to straight strips. Recent experimental studies report significant improvements in load-carrying capacity. CFRP strengthening systems achieve average ultimate loading capacity improvements of 16.2% for strengthening and 6.45% for repair applications 30 . More substantial improvements of up to 331% have been documented in specific configurations. CFRP strengthening reduces central deflection by 17.68% and crack width by 40% while maintaining structural integrity 2 . In situ testing reveals that CFRP-strengthened slabs with initial defects achieve nearly 50% increases in load-bearing capacity 3 . CFRP strengthening offers practical advantages including ease of installation and minimal structural modifications 3 . The technique allows for strengthening without significant increases in structural weight, making it suitable for existing buildings with load limitations. A critical limitation involves FRP debonding, which can compromise strengthening effectiveness 28 . Advanced techniques like EBROG have been developed to address this issue, though they require more complex installation procedures 28 , 33 . 2 Research significance The investigation and analysis of structures that are exposed to dynamic loads are generally very intricate. Despite a significant amount of research on the static and dynamic response of RC slabs and the static behavior of strengthened RC slabs with EBR and NSM methods, only a limited number of studies investigated the dynamic behavior of strengthened slabs under impact loading. Different strengthening methods must be examined and compared for performance considerations. These methods can be categorized into two general types: those used at the time of construction, such as fibers, and those applied after construction, such as FRP composites in the EBR and NSM methods. Also, previous investigations on the RC slabs have been performed using the new patterns of FRP layers. In this study, the performance of two-way slabs reinforced with steel and polypropylene fibers, four other EBR techniques using CFRP, two techniques of NSM and two hybrid methods were investigated for strengthening the slabs under low-velocity impact loading. Innovative techniques involving NSM and hybrid models were investigated through the use of steel reinforcing, a feature which distinguishes this research from prior studies. These new techniques were evaluated experimentally, with a focus on the load bearing capacity, energy dissipation, and failure patterns of the strengthened slabs. The objective of this investigation was to achieve a simultaneous increase in the mentioned parameters. 3 Experimental program 3.1 Material properties The fabricated concrete specimens achieved a mean compressive strength of 30 MPa at the 28-days. Their mix design is shown in Table 1 . In compliance with ACI 318–2019 34 , the slabs were reinforced using 8 mm diameter steel bars. To determine the average mechanical properties of 8 mm and 12 mm diameter steel rebar, axial tension tests were conducted on three samples according to American Society for Testing and Material (ASTM), demonstrated in Table 2 35 . Table 1 Concrete mix proportions. Cement (kg/m 3 ) Water (kg/m 3 ) Fine aggregate (kg/m 3 ) Coarse aggregate (kg/m 3 ) 350 175 700 900 Table 2 Mechanical properties of reinforcements. Type Grade Diameter (mm) Yield strength (MPa) Ultimate strength (MPa) #8 60 8 420 630 #12 80 12 560 790 The fiber content was calculated as a percentage of the cement's weight. Table 3 lists the fundamental characteristics of these fibers. Figure 1 provides a visual reference for the polypropylene fibers incorporated into the high-performance concrete. The specific mix designs for both the standard concrete and the fiber-reinforced concrete (FRC) can be found in Table 4 . The mechanical properties of the epoxy resins used are detailed in Table 5 . Table 3 Fibers mechanical properties. Type Tensile strength (MPa) Specific gravity (kg/m 3 ) L (mm) D (mm) L/D ratio polypropylene 570 910 55 steel 1220 7850 51 0.8 63.75 Table 4 Concrete mix design with fibers. Concrete Cement (kg) Water (kg) Sand (kg) Silica fume (kg) Polypropylene fibers (kg) Steel fibers (kg) Super plasticizer (kg) Fine aggregate (kg) Coarse aggregate (kg) polypropylene 28.25 8.47 38 2.825 0.315 0.282 - - steel 15.5 7 43.4 - 3.14 0.282 16 24.83 Table 5 CFRP and resin mechanical properties. Type Thickness of fiber/bar (mm) Tensile modulus (MPa) Modulus of elasticity (MPa) Ultimate tensile strength (%) Flexural modulus (MPa) CFRP layer 0.17 3500 230000 1.7 Epoxy resin (EBR) - 45 3500 - 3000 Epoxy resin (NSM) - 24.8 5200 - 6900 3.2 Test setup An impact load involves the sudden application of a shock force over a very short duration. For this experiment, the drop weight impact test, a widely recognized and practical method 36 , was employed. A mass of 46.7 kg was dropped onto the specimens to conduct this test. The configuration of the testing apparatus, shown in Fig. 2 , consisted of a primary frame and a tetrapod structure. The frame guides and releases the drop weight, while the tetrapod serves as a support for the test specimens. Each specimen was securely positioned within this rigid setup to undergo low-velocity impact loading, with the drop mass carefully aligned above its center. The weight was released from a height of 1,700 mm. To gather the concrete fragments produced by each impact strike for later measurement, a collection tray was positioned beneath the test setup. 4 Specimen details As shown in Fig. 3 , all specimens measured 900 mm in length, 900 mm in width, and 100 mm in thickness. The specimens were fabricated in three distinct types: a plain, unreinforced concrete slab (Plain), a weakly reinforced specimen (RC-210), and a standard specimen (RC-105). To better assess the effectiveness of the strengthening techniques, the weakly reinforced specimen (RC-210) was intentionally designed with a deficiency. The spacing of its transverse reinforcements was set at 175 mm for the longitudinal bars and 170 mm for the transverse bars, a configuration that deliberately violates the specifications of the relevant Code and guidelines 34 . The specific reinforcement layouts for all specimen types are detailed in Fig. 3 and Table 6 . Table 6 Specimen detail, reinforcement and strengthening methods. Groups Qty. Specimens Reinforcements Strengthening method CFRP layers Rebar near surface Fibers I 3 Plain × × × × × RC-105 φ8@105 × × × × RC-210 φ8@210 × × × × FRC (II) 4 Plain-PP × × × × Polypropylene Plain-S × × × × Steel RC-210-PP φ8@210 × × × Polypropylene RC-210-S φ8@210 × × × Steel EBR (III) 4 CF-Full φ8@210 2 layers CFRP full wrap CF-ST70 4 Strip layers (width 70) × × CF-ST280 1 Strip layers (width 280) × × CF-STX70 2 Strip layers diagonal (width 70) × × NSM (IV) 2 NSM-X950 φ8@210 Near surface method × 2φ12 diagonal L = 950mm × NSM-C550 × 2φ12 cross L = 550mm × Hybrid (V) 2 NSM-X950-CF φ8@210 Hybrid NSM + CFRP 2 layers CFRP diagonal strips L = 1200 mm 2φ12 diagonal L = 950mm × NSM-C550-CF 2 layers CFRP cross strips L = 700 mm 2φ12 cross L = 550mm × 4.1 Strengthening techniques Under impact loading, reinforced concrete (RC) slabs typically fail by punching shear, characterized by cracks that form closed polygonal patterns. In this experimental study, four such slab specimens were strengthened using the Externally Bonded Reinforcement (EBR) technique. Another four specimens were fortified by incorporating a mix of steel and polypropylene fibers into the concrete, creating fiber-reinforced concrete (FRC). Furthermore, four additional specimens were strengthened using two other methods: Near-Surface Mounted (NSM) and a hybrid technique. All strengthened specimens were based on the same design as the weak reference specimen, designated RC-210, with their specifications detailed in Fig. 4 . 4.1.1 The FRC group In this group, the concrete is reinforced with polypropylene (PP) and steel (S) fibers. The Plain-PP and Plain-S specimens are the same as the Plain unreinforced concrete specimens, reinforced with 1% PP and steel fibers, respectively. The RC-210-PP and RC-210-S specimens, which have steel rebars spaced 210 mm apart, also use PP and steel fibers for reinforcement. 4.1.2 The EBR group This group contained four specimens strengthened using the Externally Bonded Reinforcement (EBR) method with CFRP sheets and strips arranged in an orthogonal pattern on their bottom surfaces (Fig. 4 ). Different dimensions of CFRP sheets and strips were tested to evaluate the effectiveness of each configuration. All EBR strengthening was conducted in compliance with the ACI 440.2R-17 guidelines 37 . Among these, the CF-Full specimen was fully covered with two layers of CFRP sheets. While using CFRP strips is a more common practice for slab strengthening, the CF-ST70 specimen was reinforced with orthogonal, two-layer strips that were 70 mm wide. In contrast, the CF-ST280 specimen was strengthened with wider, two-layer orthogonal strips measuring 280 mm in width, applied to the middle surface. It is important to note that despite their different configurations, the total area of CFRP coverage was identical for the CF-ST70 and CF-ST280 specimens. A fourth specimen, CF-STX70, was strengthened with two diagonal CFRP strips, each 70 mm wide and 1200 mm long. 4.1.3 NSM group Based on the details provided in Fig. 5 , the NSM-X950 slab was strengthened using the Near-Surface Mounted (NSM) technique. This involved embedding two High-Strength Rods (HSRs), each 12 mm in diameter (as listed in Table 2 ) and 1000 mm long, diagonally in a crosswise “X” pattern within the slab. Also, in the NSM-X950 specimen, two grooves with width and depth of 25 mm and length of 950 mm on the cover of concrete have been created to hold the rebar. The NSM-C550 specimen contains two orthogonal transverse grooves with width and depth of 25 mm and length of 500 mm on the cover of concrete have been created. This specimen contains two HSRs with 12 mm diameter and 550 mm long crossed orthogonally. Since NSM technique does not require extensive surface preparation, the installation time can be less than other techniques. In these two specimens, grooves are cut in the desired direction into the cover of concrete surface. To install the NSM reinforcement, the grooves were first abraded on their inner surface. A layer of epoxy adhesive was applied, the bar was positioned inside, and the groove was then completely filled with more adhesive. Due to the geometric constraints of the specimens, an anchorage length had to be created. This was achieved by bending the ends of the High-Strength Rods (HSRs) at a 90-degree angle, creating a "staple" shape for mechanical interlock within the concrete. For both techniques, holes approximately 14 mm in diameter and 80 mm deep were drilled into the concrete. Approximately 60 mm of each HSR end (the bent "leg" of the staple) was then embedded and bonded into these holes using epoxy resin, as detailed in Fig. 5 and Table 6 . 4.1.4 The hybrid group This group contains two specimens from the NSM category that received additional strengthening. This was accomplished by applying CFRP strips in both diagonal and orthogonal patterns to their bottom surfaces, as illustrated in Fig. 5 . NSM-X950-CF and NSM-C550-CF specimens are strengthened by two CFRP strips with 1200 mm and 700 mm length, respectively. Width of strips is 100 mm. 5 Result and discussions 5.1 Failure modes Loading was stopped based on the following criteria: when the quantity of concrete debris and scabbing remained constant, and the diameter of the perforation showed no change after four to five successive impacts. This stability indicates the specimen had reached its maximum impact resistance.Throughout the testing, the progression of cracks and damage was monitored. This observed damage led to the debonding and rupture of the FRP sheets applied to the bottom surfaces of the slabs in both the EBR and hybrid specimen groups. At the end of the test, the FRP sheets are opened and the cracking pattern is visually observed. The Figs. 6 and 7 show the failure modes for different strengthening schemes. The overall observation for failure modes were, the cracks originate from the midpoint exactly where the drop weight hit the surface of the slabs. The cracks propagated transversely and diagonally towards the edges of the slab. As the number of impacts increased, the number and width of cracks increased, and ultimately the cracks were joined and formed closed polygons (similar circle or oval) on the bottom faces. The slabs in group (I) sustained the most severe damage on their top and bottom surfaces, which were struck directly by the impact. These specimens exhibited brittle fracture behavior when subjected to the impact loads. Furthermore, the rate of concrete fragmentation and the quantity of dislodged debris were significantly higher for this group than for all other specimens tested. In the Plain specimen, the limited wide cracks are created and propagated to the slab supports and the volume of scabbed concrete was more than the others. The failure mode for this specimen was brittle and the weight could penetrate to the slab more than the steel reinforced concrete. When the space between reabrs are changed from 210 mm to 105 mm the hole diameter is decreased as shown in Fig. 6 (RC-210 and RC-105). The behavior of specimens of the group (II), FRC, was more flexural deformation, spalling and scabbing in concrete and shattering to pieces. The conical separation in the bottom of fiber reinforced concrete was obvious and it was due to the fiber contribution in impact resistance of the specimen. In the steel reinforced concrete with fibers (RC-210-S and RC-210-PP) the area on the bottom surface is decreased and the number of cracks are more but with less width. Within the EBR group (III), the most significant damage was observed on the top surfaces of the slabs. This damage typically became apparent progressively; as more impacts were applied, the CFRP reinforcement ruptured or debonded layer by layer. There were no sudden failures or penetration at the arrival impacts or the separation of a large part of the specimen. It was observed that strengthening techniques was effective in the impact resistance. In the EBR groups, due to the strengthening and covering of the bottom face of specimens with CFRP, damages were observed in the form of concrete crushing, debonding and FRP rupture and concrete spalling. In start loading, the concrete crushing in the middle region of the specimen indicated the punching shear. The cracks propagated to the edges of the specimen and caused a debonding in CFRP strips. In group NSM (IV), the near surface rebars are detached from the groove at the good resistance because of the anchor effect of NSM rebars. With increasing the length of the rebars the impact resistance of the specimens is increased and the mass of scabbed concrete is decreased. For the NSM-C550 where the length of rebars is only 550 mm (almost half the dimension of the slab) the whole NSM are is detached and the impact number is also decreased. It is seems that in this method for preventing sudden failures, the length of the rebars should provide the whole dimension of the slab. The behavior of the Hybrid group (V) is much better than the NSM group, because of the hybrid action from the CFRP layers bonding and NSM rebars groove penetration. In comparison between NSM-X950 and NSM-X950-CF, it is evident that the damaged area is decreased and the failure is changed from brittle to a more reliable ones. When FRP rupture occurred at the corner in EBRD and NSM-X950-CF specimens due to the stress concentration, the resistance of the slab reduced. This indicates the positive effect of CFRP strips in sustaining the impact load. For NSM-X950-CF, the FRP rupture was observed under the 24th strike. This can be due to the stiffness and resistance of the hybrid techniques. One weakness of FRP strips under loading is the debonding from the concrete surface and the rupture. FRP rupture and debonding failure base on numbers of impacts are shown in Table 7 . Among the tested specimens, CF-ST70, reinforced with CFRP strips, failed after the fewest number of impacts. In contrast, specimens CF-ST280, NSM-X950-CF, and NSM-C550-CF withstood the highest number of strikes before failure. For the EBR group, a key indicator of an effective strengthening method was its ability to delay the debonding and rupture of the CFRP under repeated impact loading. Table 7 Number of impacts cause to debonding and rupture failures. Damage CF-Full CF-ST70 CF-ST280 CF-STX70 NSM-X950-CF NSM-C550-CF Debonding - 6 8 - - - Rupture 6, 18 3, 4, 9 15 8, 12 24 16 A comparison between an unretrofitted RC slab and one strengthened with CFRP sheets reveals that the CFRP application significantly inhibits the propagation of cracks on the slab's surface. Furthermore, the CFRP sheets are effective in delaying and mitigating the spalling of the concrete (the breaking away of pieces) from the punching shear cone that forms due to the impact load. Also, the CFRP sheet is peeled off around the punching shear cone and outside of this area no separation was observed. From these results, retrofitting slabs with CFRP sheets on the bottom surface changes the failure method from punching to punching-bending. 5.2 Energy In this section, total energy-absorption capacities of different slab specimens at first crack and at ultimate impact are presented. The energy absorption is obtained by using the Eq. ( 1 ). $$\:E=nWh$$ 1 The energy (E) is calculated as the product of the constant drop weight (W = 458.13 N), the constant drop height (h = 1700 mm), and the number of impacts (n). As detailed in Table 8 and Fig. 8 , within Group (I), specimen RC-105 absorbed the highest energy, a result attributed to its closely spaced reinforcement bars. This specimen's energy absorption was approximately 30% higher than that of specimen RC-210 and 117% higher than the plain (unreinforced) specimen. RC-210, which endured 7788 J, was the second most impact-resistant specimen in the group before failure. In the FRC group (Group II), the specimen with polypropylene fibers but no rebar (Plain-PP) exhibited the lowest energy absorption. The addition of fibers significantly improved performance: Specimens RC-210-PP (with rebar and PP fibers) and RC-210-S (with rebar and steel fibers) showed energy absorption increases of 230% and 170%, respectively, compared to the standard RC-210 specimen. Compared to the plain specimen, Plain-PP and Plain-S showed increases of 183% and 230%, respectively. Further comparisons within the FRC group highlight the effectiveness of the combined systems: RC-210-PP absorbed 98% more energy than Plain-PP. RC-210-S absorbed 35% more energy than Plain-S. Directly comparing fiber types, Plain-S (steel fibers) absorbed 18% more energy than Plain-PP (PP fibers), underscoring the superior role of steel fibers in enhancing the strength of slabs without steel rebar. It is important to note that the first impact caused initial cracking in all specimens from Groups I and II, meaning the energy required to produce the first crack was similar across these groups. Despite this, the RC-210-PP specimen ultimately demonstrated the highest total energy absorption capacity at failure within Group (II). Table 8 Energy for first crack and ultimate failure states. Group Specimen Energy at first crack (J) Energy at ultimate failure (J) I Plain 779 4673 RC-105 779 10125 RC-210 779 7788 FRC (II) Plain-PP 779 13240 RC-210-PP 779 25701 Plain-S 779 15576 RC-210-S 779 21028 EBR (III) CF-Full 1558 26480 CF-ST70 779 14019 CF-ST280 779 16355 CF-STX70 779 10903 NSM (IV) NSM-X950 779 13240 NSM-C550 779 8567 Hybrid (V) NSM-X950-CF 1558 21028 NSM-C550-CF 779 16355 In the samples with CFRP sheet for covering, EBR group, the highest energy is related to the CF-Full sample because the entire surface of the slab is covered with CFRP sheet. For this reason, the number of impacts that must occur to reach the final failure state is much higher. However, comparing the strip samples with a width of 70 mm, it can be seen that the energy of the CF-ST280 sample is higher than the other samples, as it covers the impact area to a greater width. The lowest energy tolerated in this group is related to the CF-STX70 sample, which is a cross-shaped case. It can be seen that in this case, only one cross-shaped cover is not enough, but the amount of fibers consumed in it is less than in other cases. For this reason, it can be a better option economically. In the NSM (IV) group, it can be seen that if the length of the bars is stretched sufficiently on both sides of the slab, it can have a significant effect in reducing damage and increasing the energy tolerated in the sample. The amount of energy tolerated by the 950 mm long NMS is approximately 1.5 times that of the 550 mm long sample. Among the hybrid specimens, NSM-X950-CF demonstrated the greatest bearing capacity and energy absorption. Its performance was 107% higher than that of the baseline specimen RC-210 and 28% higher than the other hybrid specimen, NSM-C550-CF. The results further indicate that adding the EBR method to the NSM techniques significantly enhanced their performance. Specifically, hybrid strengthening increased the bearing capacity by 59% and the energy absorption by 90% compared to the standard NSM-X950 and NSM-C550 specimens. This substantial improvement highlights the notable effectiveness of the hybrid strengthening approach. In the hybrid samples, it was found that for the initial crack in this group, the NSM-X950-CF sample required two impacts, which made its energy equivalent to the CF-Full sample. This indicates that if the slab is strengthened with the NSM method and then reinforced with CFRP fibers, it can perform on par with the full CFRP sheet. 5.3 Crack and failure impact number It is important to examine the number of impacts that the slab cracks and the slab reaches the final failure state, as it can provide a warning to the occupants before complete destruction. Table 9 and Fig. 9 show the number of impacts required for initial cracking and the impacts that the slab must receive to complete destruction. It can be seen that in Group I, the least impact, i.e. 6, is required to completely destroy the slab. This resistance value is due to the 100 mm thickness of the slab and the shear and impact strength of the concrete itself. The number of impacts equivalent to failure of the slab changes by only 3 impacts if the distance between the slab reinforcements is halved. However, the number of impacts required for failure is still twice as high as that of the Plain sample. In the FRC group, the number of impacts equivalent to failure has increased significantly compared to the samples without fibers. The number of impacts tolerated in the Plain-PP and Plain-S samples is 17 and 20, respectively, which is almost 3 times that of the Plain sample. However, the concrete sample with PP fibers shows higher impact resistance. Now, if the same sample is covered with steel bars at a distance of 210 mm, the failure mode impact value increases by about 5 times. The synergistic role of bars and fibers can play a very important role in increasing the impact resistance of concrete. Table 9 Impact numbers for first crack and ultimate failure. Group Specimen Number of impacts for first crack Number of impacts for ultimate failure I Plain 1 6 RC-105 1 13 RC-210 1 10 FRC (II) Plain-PP 1 17 RC-210-PP 1 33 Plain-S 1 20 RC-210-S 1 27 EBR (III) CF-Full 2 34 CF-ST70 1 18 CF-ST280 1 21 CF-STX70 1 14 NSM (IV) NSM-X950 1 17 NSM-C550 1 11 Hybrid (V) NSM-X950-CF 2 27 NSM-C550-CF 1 21 Also, in the EBR group, the highest impact capacity is related to the sample that is completely covered with CFRP sheet (CF-Full). It is interesting that this sample has withstood 34 impacts and the RC-210-PP sample has withstood 33. This means that the impact resistance of concrete can be greatly increased by distributing fibers in concrete even with 1% in mix design. In this group, the sample covered with a 280 mm wide sheet (CF-ST280) has withstood the highest impact. This value is almost equivalent to the impact resistance of the Plain-S sample. It shows that the role of fibers in the impact resistance of concrete is very high. The NSM group did not perform well in the number of impacts withstood. In the RC group, it had an effective role in increasing the impact load. However, if the same combination is combined with CFRP sheet, it can withstand a higher impact. If 950 mm long bars and CFRP sheet are used as a hybrid, it is possible to have a concrete in RC-210-S that is reinforced with steel fibers. According to the results of this section, it was seen that the combination of concrete with conventional rebar and PP or steel fibers can greatly increase the impact resistance of the slab. Even to the point where its role is equal to the complete coverage of the slab with CFRP sheets. Then it is seen that the strengthening method using CFRP sheets locally and at the impact site has a significant effect and can be used in hybrid form with CFRP sheets in cases where NSM is required. However, the NSM method alone is not reliable and has low reliability. 5.4 Damage area One measure of damage severity can be based on the diameters created on the surface of the concrete slab and below the concrete surface 31 . If the diameters created are not the same, two perpendicular diameters D 1 and D 2 are used, as shown in Fig. 10 . The damaged area on the surface of the slab or the underside of the slab is determined based on Eq. ( 2 ), which is an equivalent diameter, \(\:{D}_{eq}\) 26 . $$\:{D}_{eq}=\sqrt{{D}_{1}{D}_{2}}$$ 2 The area of scabbing zone on bottom face of slabs also has been calculated by Eq. ( 2 ). Table 10 shows the diameter of damage for the specimens on the slab and under the slab, as well as the number of impacts required to form the cracked and perforated area. In Group I, the diameter of damage in the Plain unreinforced specimen is greater than the other values in this group. The smaller the rebar spacing, the smaller the damaged area. This is due to the continuity of the high-density rebars that resist rupture. It is also observed that the number of impacts that cause this damage to occur is 2 and the number of impacts that cause holes in the specimens with steel reinforcement is twice that of the concrete without reinforcement. In the FRC group, the number of impacts corresponding to the formation of polygonal cracks and perforation is much higher than in the slab without reinforcement and the slab with steel reinforcement. It is also seen that in the Plain-PP and RC-210-PP specimens that contain PP fibers, the damaged radius is smaller than in the specimens with steel fibers (average 321 mm). But for the steel fiber specimens, the average damaged radius is 423 mm, which is a big difference from the PP fiber specimens. In the EBR group, because the CFRP sheets (CF-Full and CF-ST280) were covered under the impact area, the CFRP sheets prevented the concrete from separating and no specific cracks were formed, so the damaged radius was not calculated for them. The largest damaged radius is for the mesh strip specimen, which is 515 mm, followed by the diagonal strip specimen. It can be seen that the impact area must be completely covered with sheets to prevent penetration. Table 10 Diameter and damage area for specimens. Group Specimen Impacts for perforate Impacts for polygon cracks Bottom (mm) Top (mm) (D 1 ,D 2 ) D eq (D 1 ,D 2 ) D eq R Plain 2 2 495, 495 495 155, 160 157 RC-105 4 2 470, 470 470 150, 150 150 RC-210 4 2 380, 420 400 135, 135 135 FRC Plain-PP 10 3 410, 260 327 135, 135 135 RC-210-PP 18 10 300, 330 315 160, 160 160 Plain-S 5 4 490, 380 432 210, 210 210 RC-210-S 13 4 410, 420 415 160, 160 160 EBR CF-Full 25 --- --- --- 200, 200 200 CF-ST70 4 9 520, 510 515 175, 175 175 CF-ST280 9 --- --- --- 180, 190 185 CF-STX70 5 4 450, 380 414 155, 185 169 NSM NSM-X950 3 2 320, 280 299 165, 195 179 NSM-C550 3 3 510, 330 410 160, 180 170 Hybrid NSM-X950-CF 13 6 330, 310 320 170, 160 165 NSM-C550-CF 7 3 340, 315 327 190, 190 190 It is also observed in the NSM group that the number of impacts to form the cracked area is very low and also the radius of damage at this low number of impacts is 299 mm for X950 and 410 for C550. This shows that the length of the rebar placed at the near surface must have a large anchorage length in order to be able to withstand some resistance but still reach the final state in a lower number of impacts. By covering the same NSM group with CFRP sheets, which is in the hybrid group, the amount of impacts tolerated and also the diameter of the damaged area can be reduced. This trend is not so true for the X950 sample and the diameter of the damaged area has not changed much. However, in the case of the C550 sample, covering the grooved area with CFRP prevents damage to a large extent, which has reduced the radius of damage from 410 mm to 327 mm. In Fig. 11 , at each stage when the impact was applied to the slab, the equivalent radius was recorded based on the impact. The horizontal and vertical axes are considered the same for all graphs to allow for easy comparison. As can be seen, in the Plain, RC-105 and RC-210 samples, a smaller number of impacts led to extensive damage and it is seen that the equivalent damaged diameter is also less than the others. However, their impact load capacity is lower than the other samples. The load capacity of the samples and the damage caused is determined based on the equivalent diameter from approximately 100 mm onwards. However, in the FRC group samples, it is observed that the number of impacts tolerated has increased significantly. It is seen that the RC-210-PP sample has progressed even to 35 impacts and its equivalent diameter is less than 150 mm. The number of impacts for the samples that have both fibers and steel bars is higher than the samples without fibers in Group I. In the EBR group covered with CFRP sheets, only the CF-Full sample was able to withstand 35 impacts and the rest of the group members have been able to withstand up to about 20 impacts. In the NSM group, it is also seen that their behavior against impact and equivalent diameter is not suitable and they do not perform well, but if they are covered with CFRP sheet and also if the length of the rebar is equal to the diameter of the slab, they can be effective against impact load. Also, the number of impacts that cause the cracked area has also increased significantly in this sample. 5.5 Scabbing mass evaluation Data on the maximum and total weight of concrete scabbing for all specimens are provided in Table 11 and Figs. 12 and 13 . The extent of scabbing serves as a key indicator of damage, with less weight loss signifying better performance. Group I (Control Specimens): Specimens in this group exhibited brittle failure. RC-210 demonstrated the least amount of concrete scabbing overall. After 10 and 13 impacts, specimens RC-210 and RC-105 lost approximately 5% of their total weight, respectively. EBR Group: The performance of EBR specimens varied with the CFRP configuration. The highest single-instance scabbing (3.78 kg) occurred in specimen CF-STX70 on its 9th strike. In contrast, specimen CF-Full, which featured full-surface CFRP coverage on its bottom face, showed the best performance. Its lowest scabbing event was 1.32 kg on the 28th strike, demonstrating that more extensive coverage effectively contains damage and improves cohesion. FRC Group (Fiber-Reinforced Concrete): The addition of fibers significantly reduced weight loss and improved impact resistance. Polypropylene (PP) Fibers: Specimens Plain-PP and RC-210-PP lost only about 3.5% and 2.5% of their weight after enduring 17 and 33 strikes, respectively. RC-210-PP performed exceptionally well, sustaining numerous strikes with limited scabbing (4.49 kg total), highlighting the effectiveness of PP fibers. Steel (S) Fibers: Specimens Plain-S and RC-210-S lost about 7.8% and 3.8% of their weight after 20 and 27 strikes, respectively. When ranked by the lowest percentage of weight loss (a measure of damage tolerance), the best performers were: RC-210-PP (2.5% weight loss) Plain-PP (3.5% weight loss) RC-210-S (3.8% weight loss) Visual inspection of the bottom faces confirmed that the inclusion of either polypropylene or steel fibers effectively reduced crack propagation and the generation of concrete debris under impact loading. Table 11 Mass of scabbing for specimens. Group Specimen Number of impacts to cause ultimate failure Number of impacts to cause maximum mass Maximum mass of scabbing (kg) Total mass of scabbing (kg) R Plain 6 2 12.43 16.39 RC-105 13 3 7.46 9.67 RC-210 10 3 7 8.79 FRC Plain-PP 17 10 5.25 6.81 RC-210-PP 33 18 2.72 4.49 Plain-S 20 10 6.62 15.51 RC-210-S 27 20 2.87 10.28 EBR CF-Full 34 28 1.32 3.7 CF-ST70 18 10 1.64 8.24 CF-ST280 21 15 1.77 8.3 CF-STX70 14 9 3.78 13.26 NSM NSM-X950 17 9 1.09 9.18 NSM-C550 11 10 7.81 14.43 Hybrid NSM-X950-CF 27 15 1.11 6.9 NSM-C550-CF 21 20 2.27 7.57 A comparison of the EBR specimens—CF-ST70, CF-ST280, and CF-STX70—reveals a key finding. Since the impact load was applied to the center of the slabs, reinforcing a wider area around the expected failure zone (based on the equivalent diameter, Deq) is highly advantageous. This ability to provide extensive coverage is a major benefit of the EBR method, as it helps prevent sudden, catastrophic failure on the specimen's bottom surface. The performance data, measured by weight loss versus number of sustained impacts, clearly supports this: CF-Full (full coverage): ~1.8% weight loss after 34 strikes CF-ST280 (280mm wide strips): ~4% weight loss after 21 strikes CF-ST70 (70mm wide strips): ~4% weight loss after 18 strikes CF-STX70 (diagonal strips): ~6.6% weight loss after 14 strikes This data shows a direct correlation between the amount of CFRP coverage and the specimen's performance. The specimen with complete coverage (CF-Full) significantly outperformed all others, enduring nearly twice as many impacts while losing the least amount of material. In group NSM, the highest bearing capacity and energy absorption are related to specimen NSM-X950 which is equal to 70% compared to specimen RC-210 and equal to 55% compared to specimen NSM-C550. A clear performance difference is observed between the standard NSM and the hybrid (NSM + EBR) specimens. The hybrid technique, which adds CFRP coverage to the bottom surface, significantly enhanced impact resistance by increasing bearing capacity and reducing material loss. Weight Loss and Impact Resistance: Standard NSM Specimens: NSM-X950 lost ~ 4.5% of its weight after 17 strikes. NSM-C550 lost ~ 7% of its weight after 11 strikes. Hybrid Specimens (NSM + EBR): NSM-X950-CF lost ~ 3.5% of its weight after 27 strikes. NSM-C550-CF lost ~ 3.7% of its weight after 21 strikes. Concrete Scabbing: The hybrid method drastically reduced concrete scabbing: The total scabbing from NSM-C550 (14.43 kg) was 57% higher than from NSM-X950. The EBR coverage reduced total scabbing by 33% for the X950 design (compared to NSM-X950-CF) and by 90% for the C550 design (compared to NSM-C550-CF). The highest single scabbing event for NSM-C550-CF was 2.27 kg on its 20th strike. Its total scabbing was 7.57 kg, which is approximately 10% more than the total scabbing from NSM-X950-CF. It is important to note that the NSM and hybrid specimens themselves were heavier initially due to the added mass of high-strength rebar and adhesive. Consequently, any concrete fragments that broke away from these denser specimens also had a higher mass. 5.6 Punching angle Figure 14 demonstrates the calculation of punching cone in slabs. The angle was measured directly on the specimens in slabs that experienced punching failure. H is slab thickness and A is the horizontal distance between the edges of drop weight to the furthest edge of concrete-spalled region. At the end of the tests, the diameter of the spalling region at the bottom surface of the slab and A were measured. The angle of punching cone (α) is obtained by using Eq. ( 3 ): $$\:\alpha\:={\text{tan}}^{-1}(H/A)$$ 3 A lower α value indicates the area of failure and scabbing zone at the bottom face of the slabs is increased and the failure phenomenon fairly resembled that of punching shear. Generally, strengthening techniques such as fibers and a larger reinforcement ratio increased the angle of punching cone. Table 12 Punching cone angle for different strengthening methods. Group Specimen Impacts for polygon cracks Angle of punching cone (α o ) I Plain 2 11.4 o RC-105 2 12 o RC-210 2 14 o FRC Plain-PP 3 17 o RC-210-PP 10 17.6 o Plain-S 4 13 o RC-210-S 4 13.5 o EBR CF-Full --- --- CF-ST70 9 11 o CF-ST280 --- --- CF-STX70 4 13.6 o NSM NSM-X950 2 18.5 o NSM-C550 3 13.7 o Hybrid NSM-X950-CF 6 17.4 o NSM-C550-CF 3 17 o According to the values of punch shear angles (Table 12 ), it can be seen that in the samples of group I, this angle increases with increasing slab strength, but for the sample with rebar at a distance of 210 mm, it has increased significantly. In the samples with PP fibers, this angle is much higher than in the first group. In the failure modes, it was observed that a punched wedge protruded under the slab, causing an increase in the punch shear angle. In the samples with steel fibers, this value is lower. Also, in the NSM and hybrid groups, where a rebar is embedded inside the slab, the value of this angle is high. Because this rebar has given a two-dimensional function to the surface under the slab and causes an increase in the separated surface, for this reason the punch shear angle has increased in it. 5.7 Investigation of total crack length According to Fig. 16 , which details the total crack lengths on the top and bottom faces of the specimens, the extent of cracking varied significantly between groups and was recorded after each impact to analyze energy dissipation. In the FRC group, the bottom face of specimen RC-210-S exhibited the highest cumulative crack length of 3,210 mm, while RC-210-PP showed the best performance with only 583 mm. Similarly, for the EBR group, the bottom face of CF-STX70 had the most severe cracking at 4,210 mm, whereas the fully covered CF-Full specimen performed optimally with just 656 mm; notably, for CF-Full, no new cracks formed after the fifth strike, though existing cracks deepened with subsequent impacts. Within the NSM and hybrid groups, the highest total crack lengths were observed on the bottom face of NSM-C550 (2,490 mm in the second strike) and NSM-X950-CF (960 mm in the first strike). The longest single crack in each group was 360 mm for the Plain specimen, 900 mm for Plain-S, 2,570 mm for CF-STX70, 2,490 mm for NSM-C550, and 970 mm for NSM-X950-CF. To objectively evaluate the energy distribution capacity of the different materials, the correlation between top and bottom surface cracking was quantified using the Root Mean Square Error (RMSE) method, as defined in reference 38 . $$\:RMSE=\sqrt{\sum\:_{i=1}^{n}{\left({L}_{bottom,i}+{L}_{top,i}\right)}^{2}/n}$$ 4 The RMSE value, calculated from the total crack lengths on the top (L top ) and bottom (L bottom ) surfaces, measures the correlation in cracking between the two faces. A lower RMSE indicates a stronger correlation and superior performance, as it signifies the strengthening technique successfully distributed energy uniformly throughout the specimen, preventing localized failure. Performance by Group: EBR Group: CF-Full and CF-ST70 showed low RMSE (good correlation), while CF-STX70 had a high RMSE (poor correlation). FRC Group: RC-210-PP and RC-210-S had low RMSE values. The fibers created a homogenous composite that spread energy evenly, leading to correlated cracking on both surfaces. NSM Group: NSM-X950 had a lower RMSE than NSM-C550, indicating its configuration was more effective. Hybrid Group: These specimens achieved the lowest RMSE values overall, demonstrating that the combined techniques provided the most uniform energy distribution and optimal performance. A key explanation for a low RMSE is the formation of a more homogenous composite (from fibers or hybrid techniques) that ensures impact energy is dissipated evenly across all faces, rather than concentrating on one surface and causing a major disparity in cracking. 6 Conclusions The experimental study was conducted on fifteen RC two-way slabs under impact loads. Four specimens were reinforced by FRC techniques, two specimens were strengthened by EBR and NSM techniques and two specimens were strengthened by hybrid techniques. These conclusions are supported by experimental data including energy absorption measurements, crack pattern analysis, failure mode observations, and comparisons of damage metrics for all specimens. Results of this research are as follows: All strengthening methods demonstrated significant improvements in impact resistance, with each technique offering distinct advantages, FRC increased ductility and energy absorption, EBR with CFRP provided surface protection, NSM enhanced structural integrity, Hybrid methods combined the benefits of multiple approaches. Polypropylene fiber specimens absorbed 230% more energy than RC slabs, Steel fiber reinforcement reduced concrete scabbing by 35% compared to RC slab. FRC specimens showed more distributed cracking patterns rather than brittle failure. Fully wrapped slabs (CF-Full) withstood 34 impacts before failure, this represented nearly triple the impact capacity of RC slabs, CFRP wrapping effectively contained concrete spalling and debris. The technique showed particular effectiveness in preventing sudden punching shear failures. Hybrid NSM-CFRP techniques Combined benefits of embedded rebars and CFRP layers, reduced damage area by 28–59% compared to standalone methods. Also, delayed crack propagation through multiple mechanisms. NSM-X950-CF hybrid specimen showed 107% higher energy absorption than reference RC-210. Diagonal strengthening patterns showed 15–20% better performance than orthogonal. Specimens with longer NSM rebar embedment (950mm) performed better than shorter (550mm), and optimal CFRP strip width was found to be 280mm for impact zone coverage. Declarations CRediT authorship contribution statement Mehran Masoudiyan: Conceptualization, Formal analysis, Investigation, Resources, Visualization, Writing – original draft. Mostafa Zinati: Conceptualization, Formal analysis, Investigation, Resources, Visualization, Writing – original draft. Ali Kargaran: Conceptualization, Data curation, Investigation, Methodology, Project administration, Software, Supervision, Validation, Writing – review & editing. Ali Kheyroddin: Data curation, Investigation, Supervision, Validation, Writing – review & editing. 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. Data availability The datasets generated and/or analyzed during the current study are available from the corresponding author, Ali Kargaran ( [email protected] ), upon reasonable request. Funding This research received no funding. 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14:15:26","extension":"jpg","order_by":10,"title":"Figure 10","display":"","copyAsset":false,"role":"figure","size":156779,"visible":true,"origin":"","legend":"\u003cp\u003eDiameter of damaged area D\u003csub\u003eeq\u003c/sub\u003e (top and bottom face).\u003c/p\u003e","description":"","filename":"10.jpg","url":"https://assets-eu.researchsquare.com/files/rs-8078876/v1/d31fcf3f9c2142606cb5854a.jpg"},{"id":96888322,"identity":"b775a197-4144-4a59-b11c-11e689b9f8c5","added_by":"auto","created_at":"2025-11-27 08:50:52","extension":"jpg","order_by":11,"title":"Figure 11","display":"","copyAsset":false,"role":"figure","size":147922,"visible":true,"origin":"","legend":"\u003cp\u003eD\u003csub\u003eeq\u003c/sub\u003e for different group of strengthening.\u003c/p\u003e","description":"","filename":"11.jpg","url":"https://assets-eu.researchsquare.com/files/rs-8078876/v1/5a245cf292ad77e654ace823.jpg"},{"id":96888318,"identity":"b8ca4fd4-9da9-48fa-b491-c9f7aaa3301f","added_by":"auto","created_at":"2025-11-27 08:50:52","extension":"jpg","order_by":12,"title":"Figure 12","display":"","copyAsset":false,"role":"figure","size":101823,"visible":true,"origin":"","legend":"\u003cp\u003eThe impact number is required for maximum scabbing concrete weight.\u003c/p\u003e","description":"","filename":"12.jpg","url":"https://assets-eu.researchsquare.com/files/rs-8078876/v1/91385d7b4e2f1c6504869b7e.jpg"},{"id":96888329,"identity":"40ea6d91-ee6a-4197-b7b3-34a4c8cc9d9f","added_by":"auto","created_at":"2025-11-27 08:50:52","extension":"jpg","order_by":13,"title":"Figure 13","display":"","copyAsset":false,"role":"figure","size":107780,"visible":true,"origin":"","legend":"\u003cp\u003eTotal scabbing concrete weight.\u003c/p\u003e","description":"","filename":"13.jpg","url":"https://assets-eu.researchsquare.com/files/rs-8078876/v1/3c196ecf3eaaeaa194e7f83e.jpg"},{"id":96920356,"identity":"253ef017-b004-4dd2-896e-404d26c806bb","added_by":"auto","created_at":"2025-11-27 14:15:06","extension":"jpg","order_by":14,"title":"Figure 14","display":"","copyAsset":false,"role":"figure","size":28432,"visible":true,"origin":"","legend":"\u003cp\u003eThe punching cone in slab section due to impact load.\u003c/p\u003e","description":"","filename":"14.jpg","url":"https://assets-eu.researchsquare.com/files/rs-8078876/v1/980c5029e9626980e132127e.jpg"},{"id":96919279,"identity":"e40de53e-bc77-4f89-b68f-0ce77d93720d","added_by":"auto","created_at":"2025-11-27 14:13:31","extension":"jpg","order_by":15,"title":"Figure 15","display":"","copyAsset":false,"role":"figure","size":107914,"visible":true,"origin":"","legend":"\u003cp\u003ePunching cone angles.\u003c/p\u003e","description":"","filename":"15.jpg","url":"https://assets-eu.researchsquare.com/files/rs-8078876/v1/c373089fbece37ef0f260c89.jpg"},{"id":96919503,"identity":"1b7ed844-c061-412d-bfc4-ff4d8b8b131f","added_by":"auto","created_at":"2025-11-27 14:13:59","extension":"jpg","order_by":16,"title":"Figure 16","display":"","copyAsset":false,"role":"figure","size":102793,"visible":true,"origin":"","legend":"\u003cp\u003eRMSE of crack length for specimens.\u003c/p\u003e","description":"","filename":"16.jpg","url":"https://assets-eu.researchsquare.com/files/rs-8078876/v1/9910697e6a9f7e54237331f6.jpg"},{"id":97135442,"identity":"6384782c-105a-4791-b27c-4f5891436cd3","added_by":"auto","created_at":"2025-12-01 09:46:20","extension":"pdf","order_by":0,"title":"","display":"","copyAsset":false,"role":"manuscript-pdf","size":4212484,"visible":true,"origin":"","legend":"","description":"","filename":"manuscript.pdf","url":"https://assets-eu.researchsquare.com/files/rs-8078876/v1/d9774e54-20a3-4738-aacc-222449568bdc.pdf"}],"financialInterests":"No competing interests reported.","formattedTitle":"Strengthening of Two-Way Slabs Using Fiber Reinforced Concrete, Near Surface Mounted and CFRP Layers under Impact Loading","fulltext":[{"header":"1 Introduction","content":"\u003cp\u003eTwo-way reinforced concrete slabs are critical structural elements that may require strengthening due to increased loading demands, structural defects, or damage from impact events. The strengthening of these slabs using Carbon Fiber Reinforced Polymer (CFRP) layers and fiber reinforced concrete has emerged as an effective rehabilitation technique, particularly for structures subjected to impact loading conditions \u003csup\u003e\u003cspan additionalcitationids=\"CR2\" citationid=\"CR1\" class=\"CitationRef\"\u003e1\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR3\" class=\"CitationRef\"\u003e3\u003c/span\u003e\u003c/sup\u003e. The application of CFRP strengthening systems has gained significant attention due to their high strength-to-weight ratio, corrosion resistance, and ease of installation \u003csup\u003e\u003cspan citationid=\"CR4\" class=\"CitationRef\"\u003e4\u003c/span\u003e\u003c/sup\u003e. Under impact loading scenarios, these strengthening methods must address complex dynamic behaviors including stress wave propagation, energy absorption, and failure mode transitions \u003csup\u003e\u003cspan citationid=\"CR5\" class=\"CitationRef\"\u003e5\u003c/span\u003e\u003c/sup\u003e. Fiber-reinforced concrete (FRC) combines cementitious materials with randomly distributed fibers to create a composite material with enhanced tensile strength and ductility \u003csup\u003e\u003cspan citationid=\"CR6\" class=\"CitationRef\"\u003e6\u003c/span\u003e\u003c/sup\u003e. The discontinuous fibers dispersed throughout the concrete matrix significantly improve crack control, toughness, and impact resistance while maintaining structural flexibility. In modern construction, protecting concrete elements from external hazards like impact and blast loads has become critical for structural safety \u003csup\u003e\u003cspan additionalcitationids=\"CR8 CR9 CR10 CR11 CR12 CR13 CR14 CR15\" citationid=\"CR7\" class=\"CitationRef\"\u003e7\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR16\" class=\"CitationRef\"\u003e16\u003c/span\u003e\u003c/sup\u003e. A structure's impact resistance, its ability to withstand sudden dynamic loads - serves as an important indicator of concrete quality and durability. The most commonly employed technique involves externally bonded CFRP sheets or strips applied to the tension surface of concrete slabs \u003csup\u003e\u003cspan additionalcitationids=\"CR2\" citationid=\"CR1\" class=\"CitationRef\"\u003e1\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR3\" class=\"CitationRef\"\u003e3\u003c/span\u003e\u003c/sup\u003e. Research demonstrates that CFRP provides superior strengthening performance compared to other FRP materials, with strength enhancements of 34.5% compared to 11.2% for PET-FRP \u003csup\u003e\u003cspan citationid=\"CR1\" class=\"CitationRef\"\u003e1\u003c/span\u003e\u003c/sup\u003e. The application of CFRP strips to the tension surface significantly improves cracking loads by 97.73% and ultimate load capacity by 134.02% \u003csup\u003e2\u003c/sup\u003e. Advanced strengthening approaches utilize NSM CFRP bars inserted at specific depths from the tension face \u003csup\u003e\u003cspan citationid=\"CR17\" class=\"CitationRef\"\u003e17\u003c/span\u003e\u003c/sup\u003e. This method has shown effectiveness in controlling plastic deformation and improving punching strength of two-way slabs \u003csup\u003e\u003cspan citationid=\"CR17\" class=\"CitationRef\"\u003e17\u003c/span\u003e\u003c/sup\u003e. For more targeted reinforcement, the construction industry has perfected the near-surface mounted (NSM) technique. Workers carefully cut grooves into the concrete surface, then embed FRP bars that bond securely within the protective concrete layer. This method creates an incredibly durable connection that resists separation far better than surface-mounted alternatives. The latest breakthrough uses high-strength reinforcement (HSR) bars in these applications - a smart choice that saves materials, reduces environmental impact, and speeds up construction while maintaining top performance \u003csup\u003e\u003cspan additionalcitationids=\"CR19 CR20 CR21 CR22 CR23 CR24 CR25 CR26\" citationid=\"CR18\" class=\"CitationRef\"\u003e18\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR27\" class=\"CitationRef\"\u003e27\u003c/span\u003e\u003c/sup\u003e. The EBROG technique has proven successful in postponing FRP debonding, with flexural strengthening achieving 77% increases in ultimate load capacity and combined flexural-punching shear strengthening systems providing 94% enhancement \u003csup\u003e\u003cspan citationid=\"CR28\" class=\"CitationRef\"\u003e28\u003c/span\u003e\u003c/sup\u003e. Innovative approaches combine CFRP with other materials, such as layered hybrid concrete composite slabs using reactive powder concrete (RPC) in the top layer and normal concrete in the bottom layer, reinforced with internal CFRP grids. These systems demonstrate 19% better impact resistance compared to steel-reinforced slabs \u003csup\u003e\u003cspan citationid=\"CR5\" class=\"CitationRef\"\u003e5\u003c/span\u003e\u003c/sup\u003e. CFRP strengthening alters failure patterns from concrete compression damage to CFRP anchorage stress concentrations, highlighting effective stress distribution and load-sharing synergy \u003csup\u003e\u003cspan citationid=\"CR3\" class=\"CitationRef\"\u003e3\u003c/span\u003e\u003c/sup\u003e. The strengthening systems demonstrate superior performance under high-velocity impact loads, with steel fiber and FRP combinations providing outstanding impact resistance \u003csup\u003e\u003cspan citationid=\"CR29\" class=\"CitationRef\"\u003e29\u003c/span\u003e\u003c/sup\u003e. The concrete compressive strength moderately influences ultimate load capacity in CFRP-strengthened slabs \u003csup\u003e\u003cspan citationid=\"CR1\" class=\"CitationRef\"\u003e1\u003c/span\u003e,\u003cspan citationid=\"CR30\" class=\"CitationRef\"\u003e30\u003c/span\u003e\u003c/sup\u003e. Increasing concrete strength from 20 MPa to 80 MPa results in predicted ultimate load increases from 15% to 62% for CFRP-strengthened slabs \u003csup\u003e\u003cspan citationid=\"CR1\" class=\"CitationRef\"\u003e1\u003c/span\u003e,\u003cspan citationid=\"CR30\" class=\"CitationRef\"\u003e30\u003c/span\u003e\u003c/sup\u003e. Higher concrete strength slabs (C70) show 23.3% greater ultimate loading capacity improvements \u003csup\u003e\u003cspan citationid=\"CR30\" class=\"CitationRef\"\u003e30\u003c/span\u003e\u003c/sup\u003e. Numerical results consistently demonstrate that increasing the strengthening ratio significantly impacts shear strength and damage percentage \u003csup\u003e\u003cspan citationid=\"CR2\" class=\"CitationRef\"\u003e2\u003c/span\u003e,\u003cspan citationid=\"CR17\" class=\"CitationRef\"\u003e17\u003c/span\u003e,\u003cspan citationid=\"CR31\" class=\"CitationRef\"\u003e31\u003c/span\u003e\u003c/sup\u003e. The relationship between CFRP plate stiffness and ultimate bond strength reduction has been established through experimental testing. CFRP strip spacing affects performance, with 200mm and 300mm center-to-center spacing showing different effectiveness levels. Strip strengthening locations near supports prove more effective than middle-of-slab applications \u003csup\u003e\u003cspan citationid=\"CR32\" class=\"CitationRef\"\u003e32\u003c/span\u003e\u003c/sup\u003e. The application of diagonally oriented CFRP strips reduces cracking zones compared to straight strips. Recent experimental studies report significant improvements in load-carrying capacity. CFRP strengthening systems achieve average ultimate loading capacity improvements of 16.2% for strengthening and 6.45% for repair applications \u003csup\u003e\u003cspan citationid=\"CR30\" class=\"CitationRef\"\u003e30\u003c/span\u003e\u003c/sup\u003e. More substantial improvements of up to 331% have been documented in specific configurations. CFRP strengthening reduces central deflection by 17.68% and crack width by 40% while maintaining structural integrity \u003csup\u003e\u003cspan citationid=\"CR2\" class=\"CitationRef\"\u003e2\u003c/span\u003e\u003c/sup\u003e. In situ testing reveals that CFRP-strengthened slabs with initial defects achieve nearly 50% increases in load-bearing capacity \u003csup\u003e\u003cspan citationid=\"CR3\" class=\"CitationRef\"\u003e3\u003c/span\u003e\u003c/sup\u003e. CFRP strengthening offers practical advantages including ease of installation and minimal structural modifications \u003csup\u003e\u003cspan citationid=\"CR3\" class=\"CitationRef\"\u003e3\u003c/span\u003e\u003c/sup\u003e. The technique allows for strengthening without significant increases in structural weight, making it suitable for existing buildings with load limitations. A critical limitation involves FRP debonding, which can compromise strengthening effectiveness \u003csup\u003e\u003cspan citationid=\"CR28\" class=\"CitationRef\"\u003e28\u003c/span\u003e\u003c/sup\u003e. Advanced techniques like EBROG have been developed to address this issue, though they require more complex installation procedures \u003csup\u003e\u003cspan citationid=\"CR28\" class=\"CitationRef\"\u003e28\u003c/span\u003e,\u003cspan citationid=\"CR33\" class=\"CitationRef\"\u003e33\u003c/span\u003e\u003c/sup\u003e.\u003c/p\u003e"},{"header":"2 Research significance","content":"\u003cp\u003eThe investigation and analysis of structures that are exposed to dynamic loads are generally very intricate. Despite a significant amount of research on the static and dynamic response of RC slabs and the static behavior of strengthened RC slabs with EBR and NSM methods, only a limited number of studies investigated the dynamic behavior of strengthened slabs under impact loading. Different strengthening methods must be examined and compared for performance considerations. These methods can be categorized into two general types: those used at the time of construction, such as fibers, and those applied after construction, such as FRP composites in the EBR and NSM methods. Also, previous investigations on the RC slabs have been performed using the new patterns of FRP layers. In this study, the performance of two-way slabs reinforced with steel and polypropylene fibers, four other EBR techniques using CFRP, two techniques of NSM and two hybrid methods were investigated for strengthening the slabs under low-velocity impact loading. Innovative techniques involving NSM and hybrid models were investigated through the use of steel reinforcing, a feature which distinguishes this research from prior studies. These new techniques were evaluated experimentally, with a focus on the load bearing capacity, energy dissipation, and failure patterns of the strengthened slabs. The objective of this investigation was to achieve a simultaneous increase in the mentioned parameters.\u003c/p\u003e"},{"header":"3 Experimental program","content":"\u003cdiv id=\"Sec4\" class=\"Section2\"\u003e\u003ch2\u003e3.1 Material properties\u003c/h2\u003e\u003cp\u003eThe fabricated concrete specimens achieved a mean compressive strength of 30 MPa at the 28-days. Their mix design is shown in Table\u0026nbsp;\u003cspan refid=\"Tab1\" class=\"InternalRef\"\u003e1\u003c/span\u003e. In compliance with ACI 318\u0026ndash;2019 \u003csup\u003e34\u003c/sup\u003e, the slabs were reinforced using 8 mm diameter steel bars. To determine the average mechanical properties of 8 mm and 12 mm diameter steel rebar, axial tension tests were conducted on three samples according to American Society for Testing and Material (ASTM), demonstrated in Table\u0026nbsp;2 \u003csup\u003e35\u003c/sup\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\u003eConcrete mix proportions.\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\u003eCement (kg/m\u003csup\u003e3\u003c/sup\u003e)\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colname=\"c2\"\u003e\u003cp\u003eWater (kg/m\u003csup\u003e3\u003c/sup\u003e)\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colname=\"c3\"\u003e\u003cp\u003eFine aggregate (kg/m\u003csup\u003e3\u003c/sup\u003e)\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colname=\"c4\"\u003e\u003cp\u003eCoarse aggregate (kg/m\u003csup\u003e3\u003c/sup\u003e)\u003c/p\u003e\u003c/th\u003e\u003c/tr\u003e\u003c/thead\u003e\u003ctbody\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003e350\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003e175\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e\u003cp\u003e700\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c4\"\u003e\u003cp\u003e900\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\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\u003eMechanical properties of reinforcements.\u003c/p\u003e\u003c/div\u003e\u003c/caption\u003e\u003ccolgroup cols=\"5\"\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=\"char\" char=\".\" class=\"colspec\" colname=\"c5\" colnum=\"5\"\u003e\u003c/div\u003e\u003cthead\u003e\u003ctr\u003e\u003cth align=\"left\" colname=\"c1\"\u003e\u003cp\u003eType\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colname=\"c2\"\u003e\u003cp\u003eGrade\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colname=\"c3\"\u003e\u003cp\u003eDiameter (mm)\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colname=\"c4\"\u003e\u003cp\u003eYield strength (MPa)\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colname=\"c5\"\u003e\u003cp\u003eUltimate strength (MPa)\u003c/p\u003e\u003c/th\u003e\u003c/tr\u003e\u003c/thead\u003e\u003ctbody\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003e#8\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e\u003cp\u003e60\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e\u003cp\u003e8\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e\u003cp\u003e420\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e\u003cp\u003e630\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003e#12\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e\u003cp\u003e80\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e\u003cp\u003e12\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e\u003cp\u003e560\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e\u003cp\u003e790\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 fiber content was calculated as a percentage of the cement's weight. Table\u0026nbsp;\u003cspan refid=\"Tab3\" class=\"InternalRef\"\u003e3\u003c/span\u003e lists the fundamental characteristics of these fibers. Figure\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003e provides a visual reference for the polypropylene fibers incorporated into the high-performance concrete. The specific mix designs for both the standard concrete and the fiber-reinforced concrete (FRC) can be found in Table\u0026nbsp;\u003cspan refid=\"Tab4\" class=\"InternalRef\"\u003e4\u003c/span\u003e. The mechanical properties of the epoxy resins used are detailed in Table\u0026nbsp;\u003cspan refid=\"Tab5\" class=\"InternalRef\"\u003e5\u003c/span\u003e.\u003c/p\u003e\u003cp\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\u003eFibers mechanical properties.\u003c/p\u003e\u003c/div\u003e\u003c/caption\u003e\u003ccolgroup cols=\"6\"\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=\"char\" char=\".\" class=\"colspec\" colname=\"c5\" colnum=\"5\"\u003e\u003c/div\u003e\u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c6\" colnum=\"6\"\u003e\u003c/div\u003e\u003cthead\u003e\u003ctr\u003e\u003cth align=\"left\" colname=\"c1\"\u003e\u003cp\u003eType\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colname=\"c2\"\u003e\u003cp\u003eTensile strength (MPa)\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colname=\"c3\"\u003e\u003cp\u003eSpecific gravity (kg/m\u003csup\u003e3\u003c/sup\u003e)\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colname=\"c4\"\u003e\u003cp\u003eL (mm)\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colname=\"c5\"\u003e\u003cp\u003eD (mm)\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colname=\"c6\"\u003e\u003cp\u003eL/D ratio\u003c/p\u003e\u003c/th\u003e\u003c/tr\u003e\u003c/thead\u003e\u003ctbody\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003epolypropylene\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e\u003cp\u003e570\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e\u003cp\u003e910\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e\u003cp\u003e55\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c5\"\u003e\u0026nbsp;\u003c/td\u003e\u003ctd align=\"left\" colname=\"c6\"\u003e\u0026nbsp;\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003esteel\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e\u003cp\u003e1220\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e\u003cp\u003e7850\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e\u003cp\u003e51\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e\u003cp\u003e0.8\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c6\"\u003e\u003cp\u003e63.75\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\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\u003eConcrete mix design with fibers.\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=\"left\" class=\"colspec\" colname=\"c3\" colnum=\"3\"\u003e\u003c/div\u003e\u003cdiv align=\"left\" class=\"colspec\" colname=\"c4\" colnum=\"4\"\u003e\u003c/div\u003e\u003cdiv align=\"char\" char=\".\" 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=\"char\" char=\".\" 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\u003eConcrete\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colname=\"c2\"\u003e\u003cp\u003eCement (kg)\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colname=\"c3\"\u003e\u003cp\u003eWater (kg)\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colname=\"c4\"\u003e\u003cp\u003eSand (kg)\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colname=\"c5\"\u003e\u003cp\u003eSilica fume (kg)\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colname=\"c6\"\u003e\u003cp\u003ePolypropylene fibers (kg)\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colname=\"c7\"\u003e\u003cp\u003eSteel fibers (kg)\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colname=\"c8\"\u003e\u003cp\u003eSuper plasticizer (kg)\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colname=\"c9\"\u003e\u003cp\u003eFine aggregate (kg)\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colname=\"c10\"\u003e\u003cp\u003eCoarse 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\u003epolypropylene\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e\u003cp\u003e28.25\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e\u003cp\u003e8.47\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c4\"\u003e\u003cp\u003e38\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e\u003cp\u003e2.825\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c6\"\u003e\u003cp\u003e0.315\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c7\"\u003e\u0026nbsp;\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c8\"\u003e\u003cp\u003e0.282\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c9\"\u003e\u003cp\u003e-\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c10\"\u003e\u003cp\u003e-\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003esteel\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e\u003cp\u003e15.5\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e\u003cp\u003e7\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c4\"\u003e\u003cp\u003e43.4\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c5\"\u003e\u0026nbsp;\u003c/td\u003e\u003ctd align=\"left\" colname=\"c6\"\u003e\u003cp\u003e-\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c7\"\u003e\u003cp\u003e3.14\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c8\"\u003e\u003cp\u003e0.282\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c9\"\u003e\u003cp\u003e16\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c10\"\u003e\u003cp\u003e24.83\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\u003e\u003cdiv class=\"gridtable\"\u003e\u003ctable float=\"Yes\" id=\"Tab5\" border=\"1\"\u003e\u003ccaption language=\"En\"\u003e\u003cdiv class=\"CaptionNumber\"\u003eTable 5\u003c/div\u003e\u003cdiv class=\"CaptionContent\"\u003e\u003cp\u003eCFRP and resin mechanical properties.\u003c/p\u003e\u003c/div\u003e\u003c/caption\u003e\u003ccolgroup cols=\"6\"\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=\"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=\"char\" char=\".\" class=\"colspec\" colname=\"c6\" colnum=\"6\"\u003e\u003c/div\u003e\u003cthead\u003e\u003ctr\u003e\u003cth align=\"left\" colname=\"c1\"\u003e\u003cp\u003eType\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colname=\"c2\"\u003e\u003cp\u003eThickness of fiber/bar (mm)\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colname=\"c3\"\u003e\u003cp\u003eTensile modulus (MPa)\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colname=\"c4\"\u003e\u003cp\u003eModulus of elasticity (MPa)\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colname=\"c5\"\u003e\u003cp\u003eUltimate tensile strength (%)\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colname=\"c6\"\u003e\u003cp\u003eFlexural modulus (MPa)\u003c/p\u003e\u003c/th\u003e\u003c/tr\u003e\u003c/thead\u003e\u003ctbody\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003eCFRP layer\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003e0.17\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e\u003cp\u003e3500\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e\u003cp\u003e230000\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c5\"\u003e\u003cp\u003e1.7\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c6\"\u003e\u0026nbsp;\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003eEpoxy resin (EBR)\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003e-\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e\u003cp\u003e45\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e\u003cp\u003e3500\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c5\"\u003e\u003cp\u003e-\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c6\"\u003e\u003cp\u003e3000\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003eEpoxy resin (NSM)\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003e-\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e\u003cp\u003e24.8\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e\u003cp\u003e5200\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c5\"\u003e\u003cp\u003e-\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c6\"\u003e\u003cp\u003e6900\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\u003e3.2 Test setup\u003c/h2\u003e\u003cp\u003eAn impact load involves the sudden application of a shock force over a very short duration. For this experiment, the drop weight impact test, a widely recognized and practical method \u003csup\u003e\u003cspan citationid=\"CR36\" class=\"CitationRef\"\u003e36\u003c/span\u003e\u003c/sup\u003e, was employed. A mass of 46.7 kg was dropped onto the specimens to conduct this test. The configuration of the testing apparatus, shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003e, consisted of a primary frame and a tetrapod structure. The frame guides and releases the drop weight, while the tetrapod serves as a support for the test specimens. Each specimen was securely positioned within this rigid setup to undergo low-velocity impact loading, with the drop mass carefully aligned above its center. The weight was released from a height of 1,700 mm. To gather the concrete fragments produced by each impact strike for later measurement, a collection tray was positioned beneath the test setup.\u003c/p\u003e\u003cp\u003e\u003c/p\u003e\u003c/div\u003e"},{"header":"4 Specimen details","content":"\u003cp\u003eAs shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003e, all specimens measured 900 mm in length, 900 mm in width, and 100 mm in thickness. The specimens were fabricated in three distinct types: a plain, unreinforced concrete slab (Plain), a weakly reinforced specimen (RC-210), and a standard specimen (RC-105). To better assess the effectiveness of the strengthening techniques, the weakly reinforced specimen (RC-210) was intentionally designed with a deficiency. The spacing of its transverse reinforcements was set at 175 mm for the longitudinal bars and 170 mm for the transverse bars, a configuration that deliberately violates the specifications of the relevant Code and guidelines \u003csup\u003e\u003cspan citationid=\"CR34\" class=\"CitationRef\"\u003e34\u003c/span\u003e\u003c/sup\u003e. The specific reinforcement layouts for all specimen types are detailed in Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003e and Table\u0026nbsp;\u003cspan refid=\"Tab6\" class=\"InternalRef\"\u003e6\u003c/span\u003e.\u003c/p\u003e\u003cp\u003e\u003c/p\u003e\u003cp\u003e\u003cdiv class=\"gridtable\"\u003e\u003ctable float=\"Yes\" id=\"Tab6\" border=\"1\"\u003e\u003ccaption language=\"En\"\u003e\u003cdiv class=\"CaptionNumber\"\u003eTable 6\u003c/div\u003e\u003cdiv class=\"CaptionContent\"\u003e\u003cp\u003eSpecimen detail, reinforcement and strengthening methods.\u003c/p\u003e\u003c/div\u003e\u003c/caption\u003e\u003ccolgroup cols=\"8\"\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=\"left\" class=\"colspec\" colname=\"c3\" colnum=\"3\"\u003e\u003c/div\u003e\u003cdiv align=\"left\" 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=\"left\" class=\"colspec\" colname=\"c8\" colnum=\"8\"\u003e\u003c/div\u003e\u003cthead\u003e\u003ctr\u003e\u003cth align=\"left\" colname=\"c1\"\u003e\u003cp\u003eGroups\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colname=\"c2\"\u003e\u003cp\u003eQty.\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colname=\"c3\"\u003e\u003cp\u003eSpecimens\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colname=\"c4\"\u003e\u003cp\u003eReinforcements\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colname=\"c5\"\u003e\u003cp\u003eStrengthening method\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colname=\"c6\"\u003e\u003cp\u003eCFRP layers\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colname=\"c7\"\u003e\u003cp\u003eRebar near surface\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colname=\"c8\"\u003e\u003cp\u003eFibers\u003c/p\u003e\u003c/th\u003e\u003c/tr\u003e\u003c/thead\u003e\u003ctbody\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\" morerows=\"2\" rowspan=\"3\"\u003e\u003cp\u003eI\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c2\" morerows=\"2\" rowspan=\"3\"\u003e\u003cp\u003e3\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e\u003cp\u003ePlain\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c4\"\u003e\u003cp\u003e\u0026times;\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c5\"\u003e\u003cp\u003e\u0026times;\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c6\"\u003e\u003cp\u003e\u0026times;\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c7\"\u003e\u003cp\u003e\u0026times;\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c8\"\u003e\u003cp\u003e\u0026times;\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e\u003cp\u003eRC-105\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c4\"\u003e\u003cp\u003eφ8@105\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c5\"\u003e\u003cp\u003e\u0026times;\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c6\"\u003e\u003cp\u003e\u0026times;\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c7\"\u003e\u003cp\u003e\u0026times;\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c8\"\u003e\u003cp\u003e\u0026times;\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e\u003cp\u003eRC-210\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c4\"\u003e\u003cp\u003eφ8@210\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c5\"\u003e\u003cp\u003e\u0026times;\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c6\"\u003e\u003cp\u003e\u0026times;\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c7\"\u003e\u003cp\u003e\u0026times;\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c8\"\u003e\u003cp\u003e\u0026times;\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\" morerows=\"3\" rowspan=\"4\"\u003e\u003cp\u003eFRC (II)\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c2\" morerows=\"3\" rowspan=\"4\"\u003e\u003cp\u003e4\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e\u003cp\u003ePlain-PP\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c4\"\u003e\u003cp\u003e\u0026times;\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c5\"\u003e\u003cp\u003e\u0026times;\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c6\"\u003e\u003cp\u003e\u0026times;\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c7\"\u003e\u003cp\u003e\u0026times;\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c8\"\u003e\u003cp\u003ePolypropylene\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e\u003cp\u003ePlain-S\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c4\"\u003e\u003cp\u003e\u0026times;\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c5\"\u003e\u003cp\u003e\u0026times;\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c6\"\u003e\u003cp\u003e\u0026times;\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c7\"\u003e\u003cp\u003e\u0026times;\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c8\"\u003e\u003cp\u003eSteel\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e\u003cp\u003eRC-210-PP\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c4\"\u003e\u003cp\u003eφ8@210\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c5\"\u003e\u003cp\u003e\u0026times;\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c6\"\u003e\u003cp\u003e\u0026times;\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c7\"\u003e\u003cp\u003e\u0026times;\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c8\"\u003e\u003cp\u003ePolypropylene\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e\u003cp\u003eRC-210-S\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c4\"\u003e\u003cp\u003eφ8@210\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c5\"\u003e\u003cp\u003e\u0026times;\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c6\"\u003e\u003cp\u003e\u0026times;\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c7\"\u003e\u003cp\u003e\u0026times;\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c8\"\u003e\u003cp\u003eSteel\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\" morerows=\"3\" rowspan=\"4\"\u003e\u003cp\u003eEBR (III)\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c2\" morerows=\"3\" rowspan=\"4\"\u003e\u003cp\u003e4\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e\u003cp\u003eCF-Full\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c4\" morerows=\"3\" rowspan=\"4\"\u003e\u003cp\u003eφ8@210\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c5\" morerows=\"3\" rowspan=\"4\"\u003e\u003cp\u003e2 layers CFRP\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c6\"\u003e\u003cp\u003efull wrap\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c7\"\u003e\u0026nbsp;\u003c/td\u003e\u003ctd align=\"left\" colname=\"c8\"\u003e\u0026nbsp;\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e\u003cp\u003eCF-ST70\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c6\"\u003e\u003cp\u003e4 Strip layers (width 70)\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c7\"\u003e\u003cp\u003e\u0026times;\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c8\"\u003e\u003cp\u003e\u0026times;\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e\u003cp\u003eCF-ST280\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c6\"\u003e\u003cp\u003e1 Strip layers (width 280)\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c7\"\u003e\u003cp\u003e\u0026times;\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c8\"\u003e\u003cp\u003e\u0026times;\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e\u003cp\u003eCF-STX70\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c6\"\u003e\u003cp\u003e2 Strip layers diagonal (width 70)\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c7\"\u003e\u003cp\u003e\u0026times;\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c8\"\u003e\u003cp\u003e\u0026times;\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\" morerows=\"1\" rowspan=\"2\"\u003e\u003cp\u003eNSM (IV)\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c2\" morerows=\"1\" rowspan=\"2\"\u003e\u003cp\u003e2\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e\u003cp\u003eNSM-X950\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c4\" morerows=\"1\" rowspan=\"2\"\u003e\u003cp\u003eφ8@210\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c5\" morerows=\"1\" rowspan=\"2\"\u003e\u003cp\u003eNear surface method\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c6\"\u003e\u003cp\u003e\u0026times;\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c7\"\u003e\u003cp\u003e2φ12 diagonal L\u0026thinsp;=\u0026thinsp;950mm\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c8\"\u003e\u003cp\u003e\u0026times;\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e\u003cp\u003eNSM-C550\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c6\"\u003e\u003cp\u003e\u0026times;\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c7\"\u003e\u003cp\u003e2φ12 cross\u003c/p\u003e\u003cp\u003eL\u0026thinsp;=\u0026thinsp;550mm\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c8\"\u003e\u003cp\u003e\u0026times;\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\" morerows=\"1\" rowspan=\"2\"\u003e\u003cp\u003eHybrid (V)\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c2\" morerows=\"1\" rowspan=\"2\"\u003e\u003cp\u003e2\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e\u003cp\u003eNSM-X950-CF\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c4\" morerows=\"1\" rowspan=\"2\"\u003e\u003cp\u003eφ8@210\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c5\" morerows=\"1\" rowspan=\"2\"\u003e\u003cp\u003eHybrid NSM\u0026thinsp;+\u0026thinsp;CFRP\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c6\"\u003e\u003cp\u003e2 layers CFRP diagonal strips L\u0026thinsp;=\u0026thinsp;1200 mm\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c7\"\u003e\u003cp\u003e2φ12 diagonal L\u0026thinsp;=\u0026thinsp;950mm\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c8\"\u003e\u003cp\u003e\u0026times;\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e\u003cp\u003eNSM-C550-CF\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c6\"\u003e\u003cp\u003e2 layers CFRP cross strips L\u0026thinsp;=\u0026thinsp;700 mm\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c7\"\u003e\u003cp\u003e2φ12 cross\u003c/p\u003e\u003cp\u003eL\u0026thinsp;=\u0026thinsp;550mm\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c8\"\u003e\u003cp\u003e\u0026times;\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003c/tbody\u003e\u003c/colgroup\u003e\u003c/table\u003e\u003c/div\u003e\u003c/p\u003e\u003cdiv id=\"Sec7\" class=\"Section2\"\u003e\u003ch2\u003e4.1 Strengthening techniques\u003c/h2\u003e\u003cp\u003eUnder impact loading, reinforced concrete (RC) slabs typically fail by punching shear, characterized by cracks that form closed polygonal patterns. In this experimental study, four such slab specimens were strengthened using the Externally Bonded Reinforcement (EBR) technique. Another four specimens were fortified by incorporating a mix of steel and polypropylene fibers into the concrete, creating fiber-reinforced concrete (FRC). Furthermore, four additional specimens were strengthened using two other methods: Near-Surface Mounted (NSM) and a hybrid technique.\u003c/p\u003e\u003cp\u003eAll strengthened specimens were based on the same design as the weak reference specimen, designated RC-210, with their specifications detailed in Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003e.\u003c/p\u003e\u003cdiv id=\"Sec8\" class=\"Section3\"\u003e\u003ch2\u003e4.1.1 The FRC group\u003c/h2\u003e\u003cp\u003eIn this group, the concrete is reinforced with polypropylene (PP) and steel (S) fibers. The Plain-PP and Plain-S specimens are the same as the Plain unreinforced concrete specimens, reinforced with 1% PP and steel fibers, respectively. The RC-210-PP and RC-210-S specimens, which have steel rebars spaced 210 mm apart, also use PP and steel fibers for reinforcement.\u003c/p\u003e\u003c/div\u003e\u003cdiv id=\"Sec9\" class=\"Section3\"\u003e\u003ch2\u003e4.1.2 The EBR group\u003c/h2\u003e\u003cp\u003eThis group contained four specimens strengthened using the Externally Bonded Reinforcement (EBR) method with CFRP sheets and strips arranged in an orthogonal pattern on their bottom surfaces (Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003e). Different dimensions of CFRP sheets and strips were tested to evaluate the effectiveness of each configuration. All EBR strengthening was conducted in compliance with the ACI 440.2R-17 guidelines \u003csup\u003e\u003cspan citationid=\"CR37\" class=\"CitationRef\"\u003e37\u003c/span\u003e\u003c/sup\u003e. Among these, the CF-Full specimen was fully covered with two layers of CFRP sheets. While using CFRP strips is a more common practice for slab strengthening, the CF-ST70 specimen was reinforced with orthogonal, two-layer strips that were 70 mm wide. In contrast, the CF-ST280 specimen was strengthened with wider, two-layer orthogonal strips measuring 280 mm in width, applied to the middle surface. It is important to note that despite their different configurations, the total area of CFRP coverage was identical for the CF-ST70 and CF-ST280 specimens. A fourth specimen, CF-STX70, was strengthened with two diagonal CFRP strips, each 70 mm wide and 1200 mm long.\u003c/p\u003e\u003cp\u003e\u003c/p\u003e\u003c/div\u003e\u003cdiv id=\"Sec10\" class=\"Section3\"\u003e\u003ch2\u003e4.1.3 NSM group\u003c/h2\u003e\u003cp\u003eBased on the details provided in Fig.\u0026nbsp;\u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e5\u003c/span\u003e, the NSM-X950 slab was strengthened using the Near-Surface Mounted (NSM) technique. This involved embedding two High-Strength Rods (HSRs), each 12 mm in diameter (as listed in Table\u0026nbsp;\u003cspan refid=\"Tab2\" class=\"InternalRef\"\u003e2\u003c/span\u003e) and 1000 mm long, diagonally in a crosswise \u0026ldquo;X\u0026rdquo; pattern within the slab. Also, in the NSM-X950 specimen, two grooves with width and depth of 25 mm and length of 950 mm on the cover of concrete have been created to hold the rebar. The NSM-C550 specimen contains two orthogonal transverse grooves with width and depth of 25 mm and length of 500 mm on the cover of concrete have been created. This specimen contains two HSRs with 12 mm diameter and 550 mm long crossed orthogonally. Since NSM technique does not require extensive surface preparation, the installation time can be less than other techniques. In these two specimens, grooves are cut in the desired direction into the cover of concrete surface. To install the NSM reinforcement, the grooves were first abraded on their inner surface. A layer of epoxy adhesive was applied, the bar was positioned inside, and the groove was then completely filled with more adhesive. Due to the geometric constraints of the specimens, an anchorage length had to be created. This was achieved by bending the ends of the High-Strength Rods (HSRs) at a 90-degree angle, creating a \"staple\" shape for mechanical interlock within the concrete. For both techniques, holes approximately 14 mm in diameter and 80 mm deep were drilled into the concrete. Approximately 60 mm of each HSR end (the bent \"leg\" of the staple) was then embedded and bonded into these holes using epoxy resin, as detailed in Fig.\u0026nbsp;\u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e5\u003c/span\u003e and Table\u0026nbsp;\u003cspan refid=\"Tab6\" class=\"InternalRef\"\u003e6\u003c/span\u003e.\u003c/p\u003e\u003c/div\u003e\u003cdiv id=\"Sec11\" class=\"Section3\"\u003e\u003ch2\u003e4.1.4 The hybrid group\u003c/h2\u003e\u003cp\u003eThis group contains two specimens from the NSM category that received additional strengthening. This was accomplished by applying CFRP strips in both diagonal and orthogonal patterns to their bottom surfaces, as illustrated in Fig.\u0026nbsp;\u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e5\u003c/span\u003e. NSM-X950-CF and NSM-C550-CF specimens are strengthened by two CFRP strips with 1200 mm and 700 mm length, respectively. Width of strips is 100 mm.\u003c/p\u003e\u003cp\u003e\u003c/p\u003e\u003c/div\u003e\u003c/div\u003e"},{"header":"5 Result and discussions","content":"\u003cdiv id=\"Sec13\" class=\"Section2\"\u003e\u003ch2\u003e5.1 Failure modes\u003c/h2\u003e\u003cp\u003eLoading was stopped based on the following criteria: when the quantity of concrete debris and scabbing remained constant, and the diameter of the perforation showed no change after four to five successive impacts. This stability indicates the specimen had reached its maximum impact resistance.Throughout the testing, the progression of cracks and damage was monitored. This observed damage led to the debonding and rupture of the FRP sheets applied to the bottom surfaces of the slabs in both the EBR and hybrid specimen groups. At the end of the test, the FRP sheets are opened and the cracking pattern is visually observed. The Figs.\u0026nbsp;\u003cspan refid=\"Fig6\" class=\"InternalRef\"\u003e6\u003c/span\u003e and \u003cspan refid=\"Fig7\" class=\"InternalRef\"\u003e7\u003c/span\u003e show the failure modes for different strengthening schemes. The overall observation for failure modes were, the cracks originate from the midpoint exactly where the drop weight hit the surface of the slabs. The cracks propagated transversely and diagonally towards the edges of the slab. As the number of impacts increased, the number and width of cracks increased, and ultimately the cracks were joined and formed closed polygons (similar circle or oval) on the bottom faces.\u003c/p\u003e\u003cp\u003e\u003c/p\u003e\u003cp\u003e\u003c/p\u003e\u003cp\u003eThe slabs in group (I) sustained the most severe damage on their top and bottom surfaces, which were struck directly by the impact. These specimens exhibited brittle fracture behavior when subjected to the impact loads. Furthermore, the rate of concrete fragmentation and the quantity of dislodged debris were significantly higher for this group than for all other specimens tested. In the Plain specimen, the limited wide cracks are created and propagated to the slab supports and the volume of scabbed concrete was more than the others. The failure mode for this specimen was brittle and the weight could penetrate to the slab more than the steel reinforced concrete. When the space between reabrs are changed from 210 mm to 105 mm the hole diameter is decreased as shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig6\" class=\"InternalRef\"\u003e6\u003c/span\u003e (RC-210 and RC-105). The behavior of specimens of the group (II), FRC, was more flexural deformation, spalling and scabbing in concrete and shattering to pieces. The conical separation in the bottom of fiber reinforced concrete was obvious and it was due to the fiber contribution in impact resistance of the specimen. In the steel reinforced concrete with fibers (RC-210-S and RC-210-PP) the area on the bottom surface is decreased and the number of cracks are more but with less width. Within the EBR group (III), the most significant damage was observed on the top surfaces of the slabs. This damage typically became apparent progressively; as more impacts were applied, the CFRP reinforcement ruptured or debonded layer by layer. There were no sudden failures or penetration at the arrival impacts or the separation of a large part of the specimen. It was observed that strengthening techniques was effective in the impact resistance. In the EBR groups, due to the strengthening and covering of the bottom face of specimens with CFRP, damages were observed in the form of concrete crushing, debonding and FRP rupture and concrete spalling. In start loading, the concrete crushing in the middle region of the specimen indicated the punching shear. The cracks propagated to the edges of the specimen and caused a debonding in CFRP strips. In group NSM (IV), the near surface rebars are detached from the groove at the good resistance because of the anchor effect of NSM rebars. With increasing the length of the rebars the impact resistance of the specimens is increased and the mass of scabbed concrete is decreased. For the NSM-C550 where the length of rebars is only 550 mm (almost half the dimension of the slab) the whole NSM are is detached and the impact number is also decreased. It is seems that in this method for preventing sudden failures, the length of the rebars should provide the whole dimension of the slab. The behavior of the Hybrid group (V) is much better than the NSM group, because of the hybrid action from the CFRP layers bonding and NSM rebars groove penetration. In comparison between NSM-X950 and NSM-X950-CF, it is evident that the damaged area is decreased and the failure is changed from brittle to a more reliable ones. When FRP rupture occurred at the corner in EBRD and NSM-X950-CF specimens due to the stress concentration, the resistance of the slab reduced. This indicates the positive effect of CFRP strips in sustaining the impact load. For NSM-X950-CF, the FRP rupture was observed under the 24th strike. This can be due to the stiffness and resistance of the hybrid techniques. One weakness of FRP strips under loading is the debonding from the concrete surface and the rupture. FRP rupture and debonding failure base on numbers of impacts are shown in Table\u0026nbsp;\u003cspan refid=\"Tab7\" class=\"InternalRef\"\u003e7\u003c/span\u003e. Among the tested specimens, CF-ST70, reinforced with CFRP strips, failed after the fewest number of impacts. In contrast, specimens CF-ST280, NSM-X950-CF, and NSM-C550-CF withstood the highest number of strikes before failure. For the EBR group, a key indicator of an effective strengthening method was its ability to delay the debonding and rupture of the CFRP under repeated impact loading.\u003c/p\u003e\u003cp\u003e\u003cdiv class=\"gridtable\"\u003e\u003ctable float=\"Yes\" id=\"Tab7\" border=\"1\"\u003e\u003ccaption language=\"En\"\u003e\u003cdiv class=\"CaptionNumber\"\u003eTable 7\u003c/div\u003e\u003cdiv class=\"CaptionContent\"\u003e\u003cp\u003eNumber of impacts cause to debonding and rupture failures.\u003c/p\u003e\u003c/div\u003e\u003c/caption\u003e\u003ccolgroup cols=\"7\"\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=\"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\u003cthead\u003e\u003ctr\u003e\u003cth align=\"left\" colname=\"c1\"\u003e\u003cp\u003eDamage\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colname=\"c2\"\u003e\u003cp\u003eCF-Full\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colname=\"c3\"\u003e\u003cp\u003eCF-ST70\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colname=\"c4\"\u003e\u003cp\u003eCF-ST280\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colname=\"c5\"\u003e\u003cp\u003eCF-STX70\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colname=\"c6\"\u003e\u003cp\u003eNSM-X950-CF\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colname=\"c7\"\u003e\u003cp\u003eNSM-C550-CF\u003c/p\u003e\u003c/th\u003e\u003c/tr\u003e\u003c/thead\u003e\u003ctbody\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003eDebonding\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003e-\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e\u003cp\u003e6\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e\u003cp\u003e8\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\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003eRupture\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003e6, 18\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e\u003cp\u003e3, 4, 9\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e\u003cp\u003e15\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c5\"\u003e\u003cp\u003e8, 12\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c6\"\u003e\u003cp\u003e24\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c7\"\u003e\u003cp\u003e16\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\u003eA comparison between an unretrofitted RC slab and one strengthened with CFRP sheets reveals that the CFRP application significantly inhibits the propagation of cracks on the slab's surface. Furthermore, the CFRP sheets are effective in delaying and mitigating the spalling of the concrete (the breaking away of pieces) from the punching shear cone that forms due to the impact load. Also, the CFRP sheet is peeled off around the punching shear cone and outside of this area no separation was observed. From these results, retrofitting slabs with CFRP sheets on the bottom surface changes the failure method from punching to punching-bending.\u003c/p\u003e\u003c/div\u003e\u003cdiv id=\"Sec14\" class=\"Section2\"\u003e\u003ch2\u003e5.2 Energy\u003c/h2\u003e\u003cp\u003eIn this section, total energy-absorption capacities of different slab specimens at first crack and at ultimate impact are presented. The energy absorption is obtained by using the Eq.\u0026nbsp;(\u003cspan refid=\"Equ1\" class=\"InternalRef\"\u003e1\u003c/span\u003e).\u003cdiv id=\"Equ1\" class=\"Equation\"\u003e\u003cdiv format=\"TEX\" class=\"mathdisplay\" id=\"FileID_Equ1\" name=\"EquationSource\"\u003e\n$$\\:E=nWh$$\u003c/div\u003e\u003cdiv class=\"EquationNumber\"\u003e1\u003c/div\u003e\u003c/div\u003e\u003c/p\u003e\u003cp\u003eThe energy (E) is calculated as the product of the constant drop weight (W\u0026thinsp;=\u0026thinsp;458.13 N), the constant drop height (h\u0026thinsp;=\u0026thinsp;1700 mm), and the number of impacts (n). As detailed in Table\u0026nbsp;\u003cspan refid=\"Tab8\" class=\"InternalRef\"\u003e8\u003c/span\u003e and Fig.\u0026nbsp;\u003cspan refid=\"Fig8\" class=\"InternalRef\"\u003e8\u003c/span\u003e, within Group (I), specimen RC-105 absorbed the highest energy, a result attributed to its closely spaced reinforcement bars. This specimen's energy absorption was approximately 30% higher than that of specimen RC-210 and 117% higher than the plain (unreinforced) specimen. RC-210, which endured 7788 J, was the second most impact-resistant specimen in the group before failure. In the FRC group (Group II), the specimen with polypropylene fibers but no rebar (Plain-PP) exhibited the lowest energy absorption. The addition of fibers significantly improved performance: Specimens RC-210-PP (with rebar and PP fibers) and RC-210-S (with rebar and steel fibers) showed energy absorption increases of 230% and 170%, respectively, compared to the standard RC-210 specimen. Compared to the plain specimen, Plain-PP and Plain-S showed increases of 183% and 230%, respectively. Further comparisons within the FRC group highlight the effectiveness of the combined systems: RC-210-PP absorbed 98% more energy than Plain-PP. RC-210-S absorbed 35% more energy than Plain-S. Directly comparing fiber types, Plain-S (steel fibers) absorbed 18% more energy than Plain-PP (PP fibers), underscoring the superior role of steel fibers in enhancing the strength of slabs without steel rebar. It is important to note that the first impact caused initial cracking in all specimens from Groups I and II, meaning the energy required to produce the first crack was similar across these groups. Despite this, the RC-210-PP specimen ultimately demonstrated the highest total energy absorption capacity at failure within Group (II).\u003c/p\u003e\u003cp\u003e\u003cdiv class=\"gridtable\"\u003e\u003ctable float=\"Yes\" id=\"Tab8\" border=\"1\"\u003e\u003ccaption language=\"En\"\u003e\u003cdiv class=\"CaptionNumber\"\u003eTable 8\u003c/div\u003e\u003cdiv class=\"CaptionContent\"\u003e\u003cp\u003eEnergy for first crack and ultimate failure states.\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=\"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\u003cthead\u003e\u003ctr\u003e\u003cth align=\"left\" colname=\"c1\"\u003e\u003cp\u003eGroup\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colname=\"c2\"\u003e\u003cp\u003eSpecimen\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colname=\"c3\"\u003e\u003cp\u003eEnergy at first crack (J)\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colname=\"c4\"\u003e\u003cp\u003eEnergy at ultimate failure (J)\u003c/p\u003e\u003c/th\u003e\u003c/tr\u003e\u003c/thead\u003e\u003ctbody\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\" morerows=\"2\" rowspan=\"3\"\u003e\u003cp\u003eI\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003ePlain\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e\u003cp\u003e779\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e\u003cp\u003e4673\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003eRC-105\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e\u003cp\u003e779\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e\u003cp\u003e10125\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003eRC-210\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e\u003cp\u003e779\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e\u003cp\u003e7788\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\" morerows=\"3\" rowspan=\"4\"\u003e\u003cp\u003eFRC (II)\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003ePlain-PP\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e\u003cp\u003e779\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e\u003cp\u003e13240\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003eRC-210-PP\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e\u003cp\u003e779\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e\u003cp\u003e\u003cb\u003e25701\u003c/b\u003e\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003ePlain-S\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e\u003cp\u003e779\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e\u003cp\u003e15576\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003eRC-210-S\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e\u003cp\u003e779\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e\u003cp\u003e21028\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\" morerows=\"3\" rowspan=\"4\"\u003e\u003cp\u003eEBR (III)\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003eCF-Full\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e\u003cp\u003e\u003cb\u003e1558\u003c/b\u003e\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e\u003cp\u003e\u003cb\u003e26480\u003c/b\u003e\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003eCF-ST70\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e\u003cp\u003e779\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e\u003cp\u003e14019\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003eCF-ST280\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e\u003cp\u003e779\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e\u003cp\u003e16355\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003eCF-STX70\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e\u003cp\u003e779\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e\u003cp\u003e10903\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\" morerows=\"1\" rowspan=\"2\"\u003e\u003cp\u003eNSM (IV)\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003eNSM-X950\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e\u003cp\u003e779\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e\u003cp\u003e13240\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003eNSM-C550\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e\u003cp\u003e779\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e\u003cp\u003e8567\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\" morerows=\"1\" rowspan=\"2\"\u003e\u003cp\u003eHybrid (V)\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003eNSM-X950-CF\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e\u003cp\u003e\u003cb\u003e1558\u003c/b\u003e\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e\u003cp\u003e21028\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003eNSM-C550-CF\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e\u003cp\u003e779\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e\u003cp\u003e16355\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\u003e\u003c/p\u003e\u003cp\u003eIn the samples with CFRP sheet for covering, EBR group, the highest energy is related to the CF-Full sample because the entire surface of the slab is covered with CFRP sheet. For this reason, the number of impacts that must occur to reach the final failure state is much higher. However, comparing the strip samples with a width of 70 mm, it can be seen that the energy of the CF-ST280 sample is higher than the other samples, as it covers the impact area to a greater width. The lowest energy tolerated in this group is related to the CF-STX70 sample, which is a cross-shaped case. It can be seen that in this case, only one cross-shaped cover is not enough, but the amount of fibers consumed in it is less than in other cases. For this reason, it can be a better option economically. In the NSM (IV) group, it can be seen that if the length of the bars is stretched sufficiently on both sides of the slab, it can have a significant effect in reducing damage and increasing the energy tolerated in the sample. The amount of energy tolerated by the 950 mm long NMS is approximately 1.5 times that of the 550 mm long sample. Among the hybrid specimens, NSM-X950-CF demonstrated the greatest bearing capacity and energy absorption. Its performance was 107% higher than that of the baseline specimen RC-210 and 28% higher than the other hybrid specimen, NSM-C550-CF. The results further indicate that adding the EBR method to the NSM techniques significantly enhanced their performance. Specifically, hybrid strengthening increased the bearing capacity by 59% and the energy absorption by 90% compared to the standard NSM-X950 and NSM-C550 specimens. This substantial improvement highlights the notable effectiveness of the hybrid strengthening approach. In the hybrid samples, it was found that for the initial crack in this group, the NSM-X950-CF sample required two impacts, which made its energy equivalent to the CF-Full sample. This indicates that if the slab is strengthened with the NSM method and then reinforced with CFRP fibers, it can perform on par with the full CFRP sheet.\u003c/p\u003e\u003c/div\u003e\u003cdiv id=\"Sec15\" class=\"Section2\"\u003e\u003ch2\u003e5.3 Crack and failure impact number\u003c/h2\u003e\u003cp\u003eIt is important to examine the number of impacts that the slab cracks and the slab reaches the final failure state, as it can provide a warning to the occupants before complete destruction. Table\u0026nbsp;\u003cspan refid=\"Tab9\" class=\"InternalRef\"\u003e9\u003c/span\u003e and Fig.\u0026nbsp;\u003cspan refid=\"Fig9\" class=\"InternalRef\"\u003e9\u003c/span\u003e show the number of impacts required for initial cracking and the impacts that the slab must receive to complete destruction. It can be seen that in Group I, the least impact, i.e. 6, is required to completely destroy the slab. This resistance value is due to the 100 mm thickness of the slab and the shear and impact strength of the concrete itself. The number of impacts equivalent to failure of the slab changes by only 3 impacts if the distance between the slab reinforcements is halved. However, the number of impacts required for failure is still twice as high as that of the Plain sample. In the FRC group, the number of impacts equivalent to failure has increased significantly compared to the samples without fibers. The number of impacts tolerated in the Plain-PP and Plain-S samples is 17 and 20, respectively, which is almost 3 times that of the Plain sample. However, the concrete sample with PP fibers shows higher impact resistance. Now, if the same sample is covered with steel bars at a distance of 210 mm, the failure mode impact value increases by about 5 times. The synergistic role of bars and fibers can play a very important role in increasing the impact resistance of concrete.\u003c/p\u003e\u003cp\u003e\u003cdiv class=\"gridtable\"\u003e\u003ctable float=\"Yes\" id=\"Tab9\" border=\"1\"\u003e\u003ccaption language=\"En\"\u003e\u003cdiv class=\"CaptionNumber\"\u003eTable 9\u003c/div\u003e\u003cdiv class=\"CaptionContent\"\u003e\u003cp\u003eImpact numbers for first crack and ultimate failure.\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=\"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\u003cthead\u003e\u003ctr\u003e\u003cth align=\"left\" colname=\"c1\"\u003e\u003cp\u003eGroup\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colname=\"c2\"\u003e\u003cp\u003eSpecimen\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colname=\"c3\"\u003e\u003cp\u003eNumber of impacts for first crack\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colname=\"c4\"\u003e\u003cp\u003eNumber of impacts for ultimate failure\u003c/p\u003e\u003c/th\u003e\u003c/tr\u003e\u003c/thead\u003e\u003ctbody\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\" morerows=\"2\" rowspan=\"3\"\u003e\u003cp\u003eI\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003ePlain\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e\u003cp\u003e1\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e\u003cp\u003e6\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003eRC-105\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e\u003cp\u003e1\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e\u003cp\u003e13\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003eRC-210\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e\u003cp\u003e1\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e\u003cp\u003e10\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\" morerows=\"3\" rowspan=\"4\"\u003e\u003cp\u003eFRC (II)\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003ePlain-PP\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e\u003cp\u003e1\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e\u003cp\u003e17\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003eRC-210-PP\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e\u003cp\u003e1\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e\u003cp\u003e33\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003ePlain-S\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e\u003cp\u003e1\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e\u003cp\u003e20\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003eRC-210-S\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e\u003cp\u003e1\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e\u003cp\u003e27\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\" morerows=\"3\" rowspan=\"4\"\u003e\u003cp\u003eEBR (III)\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003eCF-Full\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e\u003cp\u003e\u003cb\u003e2\u003c/b\u003e\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e\u003cp\u003e34\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003eCF-ST70\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e\u003cp\u003e1\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e\u003cp\u003e18\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003eCF-ST280\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e\u003cp\u003e1\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e\u003cp\u003e21\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003eCF-STX70\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e\u003cp\u003e1\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e\u003cp\u003e14\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\" morerows=\"1\" rowspan=\"2\"\u003e\u003cp\u003eNSM (IV)\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003eNSM-X950\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e\u003cp\u003e1\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e\u003cp\u003e17\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003eNSM-C550\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e\u003cp\u003e1\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e\u003cp\u003e11\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\" morerows=\"1\" rowspan=\"2\"\u003e\u003cp\u003eHybrid (V)\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003eNSM-X950-CF\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e\u003cp\u003e\u003cb\u003e2\u003c/b\u003e\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e\u003cp\u003e27\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003eNSM-C550-CF\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e\u003cp\u003e1\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e\u003cp\u003e21\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\u003eAlso, in the EBR group, the highest impact capacity is related to the sample that is completely covered with CFRP sheet (CF-Full). It is interesting that this sample has withstood 34 impacts and the RC-210-PP sample has withstood 33. This means that the impact resistance of concrete can be greatly increased by distributing fibers in concrete even with 1% in mix design. In this group, the sample covered with a 280 mm wide sheet (CF-ST280) has withstood the highest impact. This value is almost equivalent to the impact resistance of the Plain-S sample. It shows that the role of fibers in the impact resistance of concrete is very high. The NSM group did not perform well in the number of impacts withstood. In the RC group, it had an effective role in increasing the impact load. However, if the same combination is combined with CFRP sheet, it can withstand a higher impact. If 950 mm long bars and CFRP sheet are used as a hybrid, it is possible to have a concrete in RC-210-S that is reinforced with steel fibers.\u003c/p\u003e\u003cp\u003e\u003c/p\u003e\u003cp\u003eAccording to the results of this section, it was seen that the combination of concrete with conventional rebar and PP or steel fibers can greatly increase the impact resistance of the slab. Even to the point where its role is equal to the complete coverage of the slab with CFRP sheets. Then it is seen that the strengthening method using CFRP sheets locally and at the impact site has a significant effect and can be used in hybrid form with CFRP sheets in cases where NSM is required. However, the NSM method alone is not reliable and has low reliability.\u003c/p\u003e\u003c/div\u003e\u003cdiv id=\"Sec16\" class=\"Section2\"\u003e\u003ch2\u003e5.4 Damage area\u003c/h2\u003e\u003cp\u003eOne measure of damage severity can be based on the diameters created on the surface of the concrete slab and below the concrete surface \u003csup\u003e\u003cspan citationid=\"CR31\" class=\"CitationRef\"\u003e31\u003c/span\u003e\u003c/sup\u003e. If the diameters created are not the same, two perpendicular diameters D\u003csub\u003e1\u003c/sub\u003e and D\u003csub\u003e2\u003c/sub\u003e are used, as shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig10\" class=\"InternalRef\"\u003e10\u003c/span\u003e. The damaged area on the surface of the slab or the underside of the slab is determined based on Eq.\u0026nbsp;(\u003cspan refid=\"Equ2\" class=\"InternalRef\"\u003e2\u003c/span\u003e), which is an equivalent diameter, \u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\(\\:{D}_{eq}\\)\u003c/span\u003e\u003c/span\u003e \u003csup\u003e26\u003c/sup\u003e.\u003cdiv id=\"Equ2\" class=\"Equation\"\u003e\u003cdiv format=\"TEX\" class=\"mathdisplay\" id=\"FileID_Equ2\" name=\"EquationSource\"\u003e\n$$\\:{D}_{eq}=\\sqrt{{D}_{1}{D}_{2}}$$\u003c/div\u003e\u003cdiv class=\"EquationNumber\"\u003e2\u003c/div\u003e\u003c/div\u003e\u003c/p\u003e\u003cp\u003eThe area of scabbing zone on bottom face of slabs also has been calculated by Eq.\u0026nbsp;(\u003cspan refid=\"Equ2\" class=\"InternalRef\"\u003e2\u003c/span\u003e).\u003c/p\u003e\u003cp\u003e\u003c/p\u003e\u003cp\u003eTable\u0026nbsp;\u003cspan refid=\"Tab10\" class=\"InternalRef\"\u003e10\u003c/span\u003e shows the diameter of damage for the specimens on the slab and under the slab, as well as the number of impacts required to form the cracked and perforated area. In Group I, the diameter of damage in the Plain unreinforced specimen is greater than the other values in this group. The smaller the rebar spacing, the smaller the damaged area. This is due to the continuity of the high-density rebars that resist rupture. It is also observed that the number of impacts that cause this damage to occur is 2 and the number of impacts that cause holes in the specimens with steel reinforcement is twice that of the concrete without reinforcement. In the FRC group, the number of impacts corresponding to the formation of polygonal cracks and perforation is much higher than in the slab without reinforcement and the slab with steel reinforcement. It is also seen that in the Plain-PP and RC-210-PP specimens that contain PP fibers, the damaged radius is smaller than in the specimens with steel fibers (average 321 mm). But for the steel fiber specimens, the average damaged radius is 423 mm, which is a big difference from the PP fiber specimens. In the EBR group, because the CFRP sheets (CF-Full and CF-ST280) were covered under the impact area, the CFRP sheets prevented the concrete from separating and no specific cracks were formed, so the damaged radius was not calculated for them. The largest damaged radius is for the mesh strip specimen, which is 515 mm, followed by the diagonal strip specimen. It can be seen that the impact area must be completely covered with sheets to prevent penetration.\u003c/p\u003e\u003cp\u003e\u003cdiv class=\"gridtable\"\u003e\u003ctable float=\"Yes\" id=\"Tab10\" border=\"1\"\u003e\u003ccaption language=\"En\"\u003e\u003cdiv class=\"CaptionNumber\"\u003eTable 10\u003c/div\u003e\u003cdiv class=\"CaptionContent\"\u003e\u003cp\u003eDiameter and damage area for specimens.\u003c/p\u003e\u003c/div\u003e\u003c/caption\u003e\u003ccolgroup cols=\"8\"\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\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=\"left\" class=\"colspec\" colname=\"c8\" colnum=\"8\"\u003e\u003c/div\u003e\u003ctbody\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\" morerows=\"1\" rowspan=\"2\"\u003e\u003cp\u003eGroup\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\" morerows=\"1\" rowspan=\"2\"\u003e\u003cp\u003eSpecimen\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c3\" morerows=\"1\" rowspan=\"2\"\u003e\u003cp\u003eImpacts for perforate\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c4\" morerows=\"1\" rowspan=\"2\"\u003e\u003cp\u003eImpacts for polygon cracks\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colspan=\"2\" nameend=\"c6\" namest=\"c5\"\u003e\u003cp\u003eBottom (mm)\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colspan=\"2\" nameend=\"c8\" namest=\"c7\"\u003e\u003cp\u003eTop (mm)\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c5\"\u003e\u003cp\u003e(D\u003csub\u003e1\u003c/sub\u003e,D\u003csub\u003e2\u003c/sub\u003e)\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c6\"\u003e\u003cp\u003eD\u003csub\u003eeq\u003c/sub\u003e\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c7\"\u003e\u003cp\u003e(D\u003csub\u003e1\u003c/sub\u003e,D\u003csub\u003e2\u003c/sub\u003e)\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c8\"\u003e\u003cp\u003eD\u003csub\u003eeq\u003c/sub\u003e\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\" morerows=\"2\" rowspan=\"3\"\u003e\u003cp\u003eR\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003ePlain\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e\u003cp\u003e2\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c4\"\u003e\u003cp\u003e2\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c5\"\u003e\u003cp\u003e495, 495\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c6\"\u003e\u003cp\u003e\u003cb\u003e495\u003c/b\u003e\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c7\"\u003e\u003cp\u003e155, 160\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c8\"\u003e\u003cp\u003e157\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003eRC-105\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e\u003cp\u003e4\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c4\"\u003e\u003cp\u003e2\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c5\"\u003e\u003cp\u003e470, 470\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c6\"\u003e\u003cp\u003e\u003cb\u003e470\u003c/b\u003e\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c7\"\u003e\u003cp\u003e150, 150\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c8\"\u003e\u003cp\u003e150\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003eRC-210\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e\u003cp\u003e4\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c4\"\u003e\u003cp\u003e2\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c5\"\u003e\u003cp\u003e380, 420\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c6\"\u003e\u003cp\u003e\u003cb\u003e400\u003c/b\u003e\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c7\"\u003e\u003cp\u003e135, 135\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c8\"\u003e\u003cp\u003e135\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\" morerows=\"3\" rowspan=\"4\"\u003e\u003cp\u003eFRC\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003ePlain-PP\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e\u003cp\u003e10\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c4\"\u003e\u003cp\u003e3\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c5\"\u003e\u003cp\u003e410, 260\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c6\"\u003e\u003cp\u003e\u003cb\u003e327\u003c/b\u003e\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c7\"\u003e\u003cp\u003e135, 135\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c8\"\u003e\u003cp\u003e135\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003eRC-210-PP\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e\u003cp\u003e18\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c4\"\u003e\u003cp\u003e10\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c5\"\u003e\u003cp\u003e300, 330\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c6\"\u003e\u003cp\u003e\u003cb\u003e315\u003c/b\u003e\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c7\"\u003e\u003cp\u003e160, 160\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c8\"\u003e\u003cp\u003e160\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003ePlain-S\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e\u003cp\u003e5\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c4\"\u003e\u003cp\u003e4\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c5\"\u003e\u003cp\u003e490, 380\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c6\"\u003e\u003cp\u003e\u003cb\u003e432\u003c/b\u003e\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c7\"\u003e\u003cp\u003e210, 210\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c8\"\u003e\u003cp\u003e210\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003eRC-210-S\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e\u003cp\u003e13\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c4\"\u003e\u003cp\u003e4\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c5\"\u003e\u003cp\u003e410, 420\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c6\"\u003e\u003cp\u003e\u003cb\u003e415\u003c/b\u003e\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c7\"\u003e\u003cp\u003e160, 160\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c8\"\u003e\u003cp\u003e160\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\" morerows=\"3\" rowspan=\"4\"\u003e\u003cp\u003eEBR\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003eCF-Full\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e\u003cp\u003e25\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c4\"\u003e\u003cp\u003e---\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\u003cb\u003e---\u003c/b\u003e\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c7\"\u003e\u003cp\u003e200, 200\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c8\"\u003e\u003cp\u003e200\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003eCF-ST70\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e\u003cp\u003e4\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c4\"\u003e\u003cp\u003e9\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c5\"\u003e\u003cp\u003e520, 510\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c6\"\u003e\u003cp\u003e\u003cb\u003e515\u003c/b\u003e\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c7\"\u003e\u003cp\u003e175, 175\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c8\"\u003e\u003cp\u003e175\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003eCF-ST280\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e\u003cp\u003e9\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c4\"\u003e\u003cp\u003e---\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\u003cb\u003e---\u003c/b\u003e\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c7\"\u003e\u003cp\u003e180, 190\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c8\"\u003e\u003cp\u003e185\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003eCF-STX70\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e\u003cp\u003e5\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c4\"\u003e\u003cp\u003e4\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c5\"\u003e\u003cp\u003e450, 380\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c6\"\u003e\u003cp\u003e\u003cb\u003e414\u003c/b\u003e\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c7\"\u003e\u003cp\u003e155, 185\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c8\"\u003e\u003cp\u003e169\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\" morerows=\"1\" rowspan=\"2\"\u003e\u003cp\u003eNSM\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003eNSM-X950\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e\u003cp\u003e3\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c4\"\u003e\u003cp\u003e2\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c5\"\u003e\u003cp\u003e320, 280\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c6\"\u003e\u003cp\u003e\u003cb\u003e299\u003c/b\u003e\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c7\"\u003e\u003cp\u003e165, 195\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c8\"\u003e\u003cp\u003e179\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003eNSM-C550\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e\u003cp\u003e3\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c4\"\u003e\u003cp\u003e3\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c5\"\u003e\u003cp\u003e510, 330\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c6\"\u003e\u003cp\u003e\u003cb\u003e410\u003c/b\u003e\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c7\"\u003e\u003cp\u003e160, 180\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c8\"\u003e\u003cp\u003e170\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\" morerows=\"1\" rowspan=\"2\"\u003e\u003cp\u003eHybrid\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003eNSM-X950-CF\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e\u003cp\u003e13\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c4\"\u003e\u003cp\u003e6\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c5\"\u003e\u003cp\u003e330, 310\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c6\"\u003e\u003cp\u003e\u003cb\u003e320\u003c/b\u003e\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c7\"\u003e\u003cp\u003e170, 160\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c8\"\u003e\u003cp\u003e165\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003eNSM-C550-CF\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e\u003cp\u003e7\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c4\"\u003e\u003cp\u003e3\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c5\"\u003e\u003cp\u003e340, 315\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c6\"\u003e\u003cp\u003e\u003cb\u003e327\u003c/b\u003e\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c7\"\u003e\u003cp\u003e190, 190\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c8\"\u003e\u003cp\u003e190\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\u003eIt is also observed in the NSM group that the number of impacts to form the cracked area is very low and also the radius of damage at this low number of impacts is 299 mm for X950 and 410 for C550. This shows that the length of the rebar placed at the near surface must have a large anchorage length in order to be able to withstand some resistance but still reach the final state in a lower number of impacts. By covering the same NSM group with CFRP sheets, which is in the hybrid group, the amount of impacts tolerated and also the diameter of the damaged area can be reduced. This trend is not so true for the X950 sample and the diameter of the damaged area has not changed much. However, in the case of the C550 sample, covering the grooved area with CFRP prevents damage to a large extent, which has reduced the radius of damage from 410 mm to 327 mm. In Fig.\u0026nbsp;\u003cspan refid=\"Fig11\" class=\"InternalRef\"\u003e11\u003c/span\u003e, at each stage when the impact was applied to the slab, the equivalent radius was recorded based on the impact. The horizontal and vertical axes are considered the same for all graphs to allow for easy comparison.\u003c/p\u003e\u003cp\u003e\u003c/p\u003e\u003cp\u003eAs can be seen, in the Plain, RC-105 and RC-210 samples, a smaller number of impacts led to extensive damage and it is seen that the equivalent damaged diameter is also less than the others. However, their impact load capacity is lower than the other samples. The load capacity of the samples and the damage caused is determined based on the equivalent diameter from approximately 100 mm onwards. However, in the FRC group samples, it is observed that the number of impacts tolerated has increased significantly. It is seen that the RC-210-PP sample has progressed even to 35 impacts and its equivalent diameter is less than 150 mm. The number of impacts for the samples that have both fibers and steel bars is higher than the samples without fibers in Group I. In the EBR group covered with CFRP sheets, only the CF-Full sample was able to withstand 35 impacts and the rest of the group members have been able to withstand up to about 20 impacts. In the NSM group, it is also seen that their behavior against impact and equivalent diameter is not suitable and they do not perform well, but if they are covered with CFRP sheet and also if the length of the rebar is equal to the diameter of the slab, they can be effective against impact load. Also, the number of impacts that cause the cracked area has also increased significantly in this sample.\u003c/p\u003e\u003c/div\u003e\u003cdiv id=\"Sec17\" class=\"Section2\"\u003e\u003ch2\u003e5.5 Scabbing mass evaluation\u003c/h2\u003e\u003cp\u003eData on the maximum and total weight of concrete scabbing for all specimens are provided in Table\u0026nbsp;\u003cspan refid=\"Tab11\" class=\"InternalRef\"\u003e11\u003c/span\u003e and Figs.\u0026nbsp;\u003cspan refid=\"Fig12\" class=\"InternalRef\"\u003e12\u003c/span\u003e and \u003cspan refid=\"Fig13\" class=\"InternalRef\"\u003e13\u003c/span\u003e. The extent of scabbing serves as a key indicator of damage, with less weight loss signifying better performance.\u003c/p\u003e\u003cp\u003e\u003cul\u003e\u003cli\u003e\u003cp\u003eGroup I (Control Specimens):\u003c/p\u003e\u003c/li\u003e\u003c/ul\u003e\u003c/p\u003e\u003cp\u003eSpecimens in this group exhibited brittle failure. RC-210 demonstrated the least amount of concrete scabbing overall. After 10 and 13 impacts, specimens RC-210 and RC-105 lost approximately 5% of their total weight, respectively.\u003c/p\u003e\u003cp\u003e\u003cul\u003e\u003cli\u003e\u003cp\u003eEBR Group:\u003c/p\u003e\u003c/li\u003e\u003c/ul\u003e\u003c/p\u003e\u003cp\u003eThe performance of EBR specimens varied with the CFRP configuration. The highest single-instance scabbing (3.78 kg) occurred in specimen CF-STX70 on its 9th strike. In contrast, specimen CF-Full, which featured full-surface CFRP coverage on its bottom face, showed the best performance. Its lowest scabbing event was 1.32 kg on the 28th strike, demonstrating that more extensive coverage effectively contains damage and improves cohesion.\u003c/p\u003e\u003cp\u003e\u003cul\u003e\u003cli\u003e\u003cp\u003eFRC Group (Fiber-Reinforced Concrete):\u003c/p\u003e\u003c/li\u003e\u003c/ul\u003e\u003c/p\u003e\u003cp\u003eThe addition of fibers significantly reduced weight loss and improved impact resistance. Polypropylene (PP) Fibers: Specimens Plain-PP and RC-210-PP lost only about 3.5% and 2.5% of their weight after enduring 17 and 33 strikes, respectively. RC-210-PP performed exceptionally well, sustaining numerous strikes with limited scabbing (4.49 kg total), highlighting the effectiveness of PP fibers. Steel (S) Fibers: Specimens Plain-S and RC-210-S lost about 7.8% and 3.8% of their weight after 20 and 27 strikes, respectively. When ranked by the lowest percentage of weight loss (a measure of damage tolerance), the best performers were:\u003c/p\u003e\u003cp\u003e\u003cul\u003e\u003cli\u003e\u003cp\u003eRC-210-PP (2.5% weight loss)\u003c/p\u003e\u003c/li\u003e\u003cli\u003e\u003cp\u003ePlain-PP (3.5% weight loss)\u003c/p\u003e\u003c/li\u003e\u003cli\u003e\u003cp\u003eRC-210-S (3.8% weight loss)\u003c/p\u003e\u003c/li\u003e\u003c/ul\u003e\u003c/p\u003e\u003cp\u003eVisual inspection of the bottom faces confirmed that the inclusion of either polypropylene or steel fibers effectively reduced crack propagation and the generation of concrete debris under impact loading.\u003c/p\u003e\u003cp\u003e\u003cdiv class=\"gridtable\"\u003e\u003ctable float=\"Yes\" id=\"Tab11\" border=\"1\"\u003e\u003ccaption language=\"En\"\u003e\u003cdiv class=\"CaptionNumber\"\u003eTable 11\u003c/div\u003e\u003cdiv class=\"CaptionContent\"\u003e\u003cp\u003eMass of scabbing for specimens.\u003c/p\u003e\u003c/div\u003e\u003c/caption\u003e\u003ccolgroup cols=\"6\"\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=\"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=\"char\" char=\".\" class=\"colspec\" colname=\"c6\" colnum=\"6\"\u003e\u003c/div\u003e\u003cthead\u003e\u003ctr\u003e\u003cth align=\"left\" colname=\"c1\"\u003e\u003cp\u003eGroup\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colname=\"c2\"\u003e\u003cp\u003eSpecimen\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colname=\"c3\"\u003e\u003cp\u003eNumber of impacts to cause ultimate failure\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colname=\"c4\"\u003e\u003cp\u003eNumber of impacts to cause maximum mass\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colname=\"c5\"\u003e\u003cp\u003eMaximum mass of scabbing\u003c/p\u003e\u003cp\u003e(kg)\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colname=\"c6\"\u003e\u003cp\u003eTotal mass of scabbing\u003c/p\u003e\u003cp\u003e(kg)\u003c/p\u003e\u003c/th\u003e\u003c/tr\u003e\u003c/thead\u003e\u003ctbody\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003eR\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003ePlain\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e\u003cp\u003e6\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e\u003cp\u003e2\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c5\"\u003e\u003cp\u003e12.43\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c6\"\u003e\u003cp\u003e16.39\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u0026nbsp;\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003eRC-105\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e\u003cp\u003e13\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e\u003cp\u003e3\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c5\"\u003e\u003cp\u003e7.46\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c6\"\u003e\u003cp\u003e9.67\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u0026nbsp;\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003eRC-210\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e\u003cp\u003e10\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e\u003cp\u003e3\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c5\"\u003e\u003cp\u003e7\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c6\"\u003e\u003cp\u003e8.79\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003eFRC\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003ePlain-PP\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e\u003cp\u003e17\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e\u003cp\u003e10\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c5\"\u003e\u003cp\u003e5.25\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c6\"\u003e\u003cp\u003e6.81\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u0026nbsp;\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003eRC-210-PP\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e\u003cp\u003e33\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e\u003cp\u003e18\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c5\"\u003e\u003cp\u003e2.72\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c6\"\u003e\u003cp\u003e4.49\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u0026nbsp;\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003ePlain-S\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e\u003cp\u003e20\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e\u003cp\u003e10\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c5\"\u003e\u003cp\u003e6.62\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c6\"\u003e\u003cp\u003e15.51\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u0026nbsp;\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003eRC-210-S\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e\u003cp\u003e27\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e\u003cp\u003e20\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c5\"\u003e\u003cp\u003e2.87\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c6\"\u003e\u003cp\u003e10.28\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003eEBR\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003eCF-Full\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e\u003cp\u003e34\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e\u003cp\u003e28\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c5\"\u003e\u003cp\u003e1.32\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c6\"\u003e\u003cp\u003e3.7\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u0026nbsp;\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003eCF-ST70\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e\u003cp\u003e18\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e\u003cp\u003e10\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c5\"\u003e\u003cp\u003e1.64\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c6\"\u003e\u003cp\u003e8.24\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u0026nbsp;\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003eCF-ST280\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e\u003cp\u003e21\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e\u003cp\u003e15\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c5\"\u003e\u003cp\u003e1.77\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c6\"\u003e\u003cp\u003e8.3\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u0026nbsp;\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003eCF-STX70\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e\u003cp\u003e14\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e\u003cp\u003e9\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c5\"\u003e\u003cp\u003e3.78\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c6\"\u003e\u003cp\u003e13.26\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003eNSM\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003eNSM-X950\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e\u003cp\u003e17\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e\u003cp\u003e9\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c5\"\u003e\u003cp\u003e1.09\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c6\"\u003e\u003cp\u003e9.18\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u0026nbsp;\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003eNSM-C550\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e\u003cp\u003e11\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e\u003cp\u003e10\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c5\"\u003e\u003cp\u003e7.81\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c6\"\u003e\u003cp\u003e14.43\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003eHybrid\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003eNSM-X950-CF\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e\u003cp\u003e27\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e\u003cp\u003e15\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c5\"\u003e\u003cp\u003e1.11\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c6\"\u003e\u003cp\u003e6.9\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u0026nbsp;\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003eNSM-C550-CF\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e\u003cp\u003e21\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e\u003cp\u003e20\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c5\"\u003e\u003cp\u003e2.27\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c6\"\u003e\u003cp\u003e7.57\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\u003eA comparison of the EBR specimens\u0026mdash;CF-ST70, CF-ST280, and CF-STX70\u0026mdash;reveals a key finding. Since the impact load was applied to the center of the slabs, reinforcing a wider area around the expected failure zone (based on the equivalent diameter, Deq) is highly advantageous. This ability to provide extensive coverage is a major benefit of the EBR method, as it helps prevent sudden, catastrophic failure on the specimen's bottom surface. The performance data, measured by weight loss versus number of sustained impacts, clearly supports this:\u003c/p\u003e\u003cp\u003e\u003cul\u003e\u003cli\u003e\u003cp\u003eCF-Full (full coverage): ~1.8% weight loss after 34 strikes\u003c/p\u003e\u003c/li\u003e\u003cli\u003e\u003cp\u003eCF-ST280 (280mm wide strips): ~4% weight loss after 21 strikes\u003c/p\u003e\u003c/li\u003e\u003cli\u003e\u003cp\u003eCF-ST70 (70mm wide strips): ~4% weight loss after 18 strikes\u003c/p\u003e\u003c/li\u003e\u003cli\u003e\u003cp\u003eCF-STX70 (diagonal strips): ~6.6% weight loss after 14 strikes\u003c/p\u003e\u003c/li\u003e\u003c/ul\u003e\u003c/p\u003e\u003cp\u003eThis data shows a direct correlation between the amount of CFRP coverage and the specimen's performance. The specimen with complete coverage (CF-Full) significantly outperformed all others, enduring nearly twice as many impacts while losing the least amount of material.\u003c/p\u003e\u003cp\u003e\u003c/p\u003e\u003cp\u003e\u003c/p\u003e\u003cp\u003eIn group NSM, the highest bearing capacity and energy absorption are related to specimen NSM-X950 which is equal to 70% compared to specimen RC-210 and equal to 55% compared to specimen NSM-C550. A clear performance difference is observed between the standard NSM and the hybrid (NSM\u0026thinsp;+\u0026thinsp;EBR) specimens. The hybrid technique, which adds CFRP coverage to the bottom surface, significantly enhanced impact resistance by increasing bearing capacity and reducing material loss. Weight Loss and Impact Resistance:\u003c/p\u003e\u003cp\u003eStandard NSM Specimens:\u003c/p\u003e\u003cp\u003e\u003cul\u003e\u003cli\u003e\u003cp\u003eNSM-X950 lost\u0026thinsp;~\u0026thinsp;4.5% of its weight after 17 strikes.\u003c/p\u003e\u003c/li\u003e\u003cli\u003e\u003cp\u003eNSM-C550 lost\u0026thinsp;~\u0026thinsp;7% of its weight after 11 strikes.\u003c/p\u003e\u003c/li\u003e\u003c/ul\u003e\u003c/p\u003e\u003cp\u003eHybrid Specimens (NSM\u0026thinsp;+\u0026thinsp;EBR):\u003c/p\u003e\u003cp\u003e\u003cul\u003e\u003cli\u003e\u003cp\u003eNSM-X950-CF lost\u0026thinsp;~\u0026thinsp;3.5% of its weight after 27 strikes.\u003c/p\u003e\u003c/li\u003e\u003cli\u003e\u003cp\u003eNSM-C550-CF lost\u0026thinsp;~\u0026thinsp;3.7% of its weight after 21 strikes.\u003c/p\u003e\u003c/li\u003e\u003c/ul\u003e\u003c/p\u003e\u003cp\u003eConcrete Scabbing:\u003c/p\u003e\u003cp\u003e\u003cul\u003e\u003cli\u003e\u003cp\u003eThe hybrid method drastically reduced concrete scabbing:\u003c/p\u003e\u003c/li\u003e\u003cli\u003e\u003cp\u003eThe total scabbing from NSM-C550 (14.43 kg) was 57% higher than from NSM-X950.\u003c/p\u003e\u003c/li\u003e\u003cli\u003e\u003cp\u003eThe EBR coverage reduced total scabbing by 33% for the X950 design (compared to NSM-X950-CF) and by 90% for the C550 design (compared to NSM-C550-CF).\u003c/p\u003e\u003c/li\u003e\u003cli\u003e\u003cp\u003eThe highest single scabbing event for NSM-C550-CF was 2.27 kg on its 20th strike. Its total scabbing was 7.57 kg, which is approximately 10% more than the total scabbing from NSM-X950-CF.\u003c/p\u003e\u003c/li\u003e\u003c/ul\u003e\u003c/p\u003e\u003cp\u003eIt is important to note that the NSM and hybrid specimens themselves were heavier initially due to the added mass of high-strength rebar and adhesive. Consequently, any concrete fragments that broke away from these denser specimens also had a higher mass.\u003c/p\u003e\u003c/div\u003e\u003cdiv id=\"Sec18\" class=\"Section2\"\u003e\u003ch2\u003e5.6 Punching angle\u003c/h2\u003e\u003cp\u003eFigure\u0026nbsp;\u003cspan refid=\"Fig14\" class=\"InternalRef\"\u003e14\u003c/span\u003e demonstrates the calculation of punching cone in slabs. The angle was measured directly on the specimens in slabs that experienced punching failure. H is slab thickness and A is the horizontal distance between the edges of drop weight to the furthest edge of concrete-spalled region. At the end of the tests, the diameter of the spalling region at the bottom surface of the slab and A were measured. The angle of punching cone (α) is obtained by using Eq.\u0026nbsp;(\u003cspan refid=\"Equ3\" class=\"InternalRef\"\u003e3\u003c/span\u003e):\u003cdiv id=\"Equ3\" class=\"Equation\"\u003e\u003cdiv format=\"TEX\" class=\"mathdisplay\" id=\"FileID_Equ3\" name=\"EquationSource\"\u003e\n$$\\:\\alpha\\:={\\text{tan}}^{-1}(H/A)$$\u003c/div\u003e\u003cdiv class=\"EquationNumber\"\u003e3\u003c/div\u003e\u003c/div\u003e\u003c/p\u003e\u003cp\u003eA lower α value indicates the area of failure and scabbing zone at the bottom face of the slabs is increased and the failure phenomenon fairly resembled that of punching shear. Generally, strengthening techniques such as fibers and a larger reinforcement ratio increased the angle of punching cone.\u003c/p\u003e\u003cp\u003e\u003c/p\u003e\u003cp\u003e\u003cdiv class=\"gridtable\"\u003e\u003ctable float=\"Yes\" id=\"Tab12\" border=\"1\"\u003e\u003ccaption language=\"En\"\u003e\u003cdiv class=\"CaptionNumber\"\u003eTable 12\u003c/div\u003e\u003cdiv class=\"CaptionContent\"\u003e\u003cp\u003ePunching cone angle for different strengthening methods.\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\u003eGroup\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colname=\"c2\"\u003e\u003cp\u003eSpecimen\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colname=\"c3\"\u003e\u003cp\u003eImpacts for polygon cracks\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colname=\"c4\"\u003e\u003cp\u003eAngle of punching cone\u003c/p\u003e\u003cp\u003e(α\u003csup\u003eo\u003c/sup\u003e)\u003c/p\u003e\u003c/th\u003e\u003c/tr\u003e\u003c/thead\u003e\u003ctbody\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\" morerows=\"2\" rowspan=\"3\"\u003e\u003cp\u003eI\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003ePlain\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e\u003cp\u003e2\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c4\"\u003e\u003cp\u003e11.4\u003csup\u003eo\u003c/sup\u003e\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003eRC-105\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e\u003cp\u003e2\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c4\"\u003e\u003cp\u003e12\u003csup\u003eo\u003c/sup\u003e\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003eRC-210\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e\u003cp\u003e2\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c4\"\u003e\u003cp\u003e14\u003csup\u003eo\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\u003eFRC\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003ePlain-PP\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e\u003cp\u003e3\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c4\"\u003e\u003cp\u003e17\u003csup\u003eo\u003c/sup\u003e\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003eRC-210-PP\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e\u003cp\u003e10\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c4\"\u003e\u003cp\u003e17.6\u003csup\u003eo\u003c/sup\u003e\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003ePlain-S\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e\u003cp\u003e4\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c4\"\u003e\u003cp\u003e13\u003csup\u003eo\u003c/sup\u003e\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003eRC-210-S\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e\u003cp\u003e4\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c4\"\u003e\u003cp\u003e13.5\u003csup\u003eo\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\u003eEBR\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003eCF-Full\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e\u003cp\u003e---\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c4\"\u003e\u003cp\u003e---\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003eCF-ST70\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e\u003cp\u003e9\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c4\"\u003e\u003cp\u003e11\u003csup\u003eo\u003c/sup\u003e\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003eCF-ST280\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e\u003cp\u003e---\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c4\"\u003e\u003cp\u003e---\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003eCF-STX70\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e\u003cp\u003e4\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c4\"\u003e\u003cp\u003e13.6\u003csup\u003eo\u003c/sup\u003e\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\" morerows=\"1\" rowspan=\"2\"\u003e\u003cp\u003eNSM\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003eNSM-X950\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e\u003cp\u003e2\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c4\"\u003e\u003cp\u003e18.5\u003csup\u003eo\u003c/sup\u003e\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003eNSM-C550\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e\u003cp\u003e3\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c4\"\u003e\u003cp\u003e13.7\u003csup\u003eo\u003c/sup\u003e\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\" morerows=\"1\" rowspan=\"2\"\u003e\u003cp\u003eHybrid\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003eNSM-X950-CF\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e\u003cp\u003e6\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c4\"\u003e\u003cp\u003e17.4\u003csup\u003eo\u003c/sup\u003e\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003eNSM-C550-CF\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e\u003cp\u003e3\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c4\"\u003e\u003cp\u003e17\u003csup\u003eo\u003c/sup\u003e\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\u003eAccording to the values of punch shear angles (Table\u0026nbsp;\u003cspan refid=\"Tab12\" class=\"InternalRef\"\u003e12\u003c/span\u003e), it can be seen that in the samples of group I, this angle increases with increasing slab strength, but for the sample with rebar at a distance of 210 mm, it has increased significantly. In the samples with PP fibers, this angle is much higher than in the first group. In the failure modes, it was observed that a punched wedge protruded under the slab, causing an increase in the punch shear angle. In the samples with steel fibers, this value is lower. Also, in the NSM and hybrid groups, where a rebar is embedded inside the slab, the value of this angle is high. Because this rebar has given a two-dimensional function to the surface under the slab and causes an increase in the separated surface, for this reason the punch shear angle has increased in it.\u003c/p\u003e\u003cp\u003e\u003c/p\u003e\u003c/div\u003e\u003cdiv id=\"Sec19\" class=\"Section2\"\u003e\u003ch2\u003e5.7 Investigation of total crack length\u003c/h2\u003e\u003cp\u003eAccording to Fig.\u0026nbsp;\u003cspan refid=\"Fig16\" class=\"InternalRef\"\u003e16\u003c/span\u003e, which details the total crack lengths on the top and bottom faces of the specimens, the extent of cracking varied significantly between groups and was recorded after each impact to analyze energy dissipation. In the FRC group, the bottom face of specimen RC-210-S exhibited the highest cumulative crack length of 3,210 mm, while RC-210-PP showed the best performance with only 583 mm. Similarly, for the EBR group, the bottom face of CF-STX70 had the most severe cracking at 4,210 mm, whereas the fully covered CF-Full specimen performed optimally with just 656 mm; notably, for CF-Full, no new cracks formed after the fifth strike, though existing cracks deepened with subsequent impacts. Within the NSM and hybrid groups, the highest total crack lengths were observed on the bottom face of NSM-C550 (2,490 mm in the second strike) and NSM-X950-CF (960 mm in the first strike). The longest single crack in each group was 360 mm for the Plain specimen, 900 mm for Plain-S, 2,570 mm for CF-STX70, 2,490 mm for NSM-C550, and 970 mm for NSM-X950-CF. To objectively evaluate the energy distribution capacity of the different materials, the correlation between top and bottom surface cracking was quantified using the Root Mean Square Error (RMSE) method, as defined in reference \u003csup\u003e\u003cspan citationid=\"CR38\" class=\"CitationRef\"\u003e38\u003c/span\u003e\u003c/sup\u003e.\u003cdiv id=\"Equ4\" class=\"Equation\"\u003e\u003cdiv format=\"TEX\" class=\"mathdisplay\" id=\"FileID_Equ4\" name=\"EquationSource\"\u003e\n$$\\:RMSE=\\sqrt{\\sum\\:_{i=1}^{n}{\\left({L}_{bottom,i}+{L}_{top,i}\\right)}^{2}/n}$$\u003c/div\u003e\u003cdiv class=\"EquationNumber\"\u003e4\u003c/div\u003e\u003c/div\u003e\u003c/p\u003e\u003cp\u003eThe RMSE value, calculated from the total crack lengths on the top (L\u003csub\u003etop\u003c/sub\u003e) and bottom (L\u003csub\u003ebottom\u003c/sub\u003e) surfaces, measures the correlation in cracking between the two faces. A lower RMSE indicates a stronger correlation and superior performance, as it signifies the strengthening technique successfully distributed energy uniformly throughout the specimen, preventing localized failure.\u003c/p\u003e\u003cp\u003ePerformance by Group:\u003c/p\u003e\u003cp\u003e\u003cul\u003e\u003cli\u003e\u003cp\u003eEBR Group: CF-Full and CF-ST70 showed low RMSE (good correlation), while CF-STX70 had a high RMSE (poor correlation).\u003c/p\u003e\u003c/li\u003e\u003cli\u003e\u003cp\u003eFRC Group: RC-210-PP and RC-210-S had low RMSE values. The fibers created a homogenous composite that spread energy evenly, leading to correlated cracking on both surfaces.\u003c/p\u003e\u003c/li\u003e\u003cli\u003e\u003cp\u003eNSM Group: NSM-X950 had a lower RMSE than NSM-C550, indicating its configuration was more effective.\u003c/p\u003e\u003c/li\u003e\u003cli\u003e\u003cp\u003eHybrid Group: These specimens achieved the lowest RMSE values overall, demonstrating that the combined techniques provided the most uniform energy distribution and optimal performance.\u003c/p\u003e\u003c/li\u003e\u003c/ul\u003e\u003c/p\u003e\u003cp\u003eA key explanation for a low RMSE is the formation of a more homogenous composite (from fibers or hybrid techniques) that ensures impact energy is dissipated evenly across all faces, rather than concentrating on one surface and causing a major disparity in cracking.\u003c/p\u003e\u003cp\u003e\u003c/p\u003e\u003c/div\u003e"},{"header":"6 Conclusions","content":"\u003cp\u003eThe experimental study was conducted on fifteen RC two-way slabs under impact loads. Four specimens were reinforced by FRC techniques, two specimens were strengthened by EBR and NSM techniques and two specimens were strengthened by hybrid techniques. These conclusions are supported by experimental data including energy absorption measurements, crack pattern analysis, failure mode observations, and comparisons of damage metrics for all specimens. Results of this research are as follows:\u003c/p\u003e\u003cp\u003e\u003cul\u003e\u003cli\u003e\u003cp\u003eAll strengthening methods demonstrated significant improvements in impact resistance, with each technique offering distinct advantages, FRC increased ductility and energy absorption, EBR with CFRP provided surface protection, NSM enhanced structural integrity, Hybrid methods combined the benefits of multiple approaches.\u003c/p\u003e\u003c/li\u003e\u003cli\u003e\u003cp\u003ePolypropylene fiber specimens absorbed 230% more energy than RC slabs, Steel fiber reinforcement reduced concrete scabbing by 35% compared to RC slab. FRC specimens showed more distributed cracking patterns rather than brittle failure.\u003c/p\u003e\u003c/li\u003e\u003cli\u003e\u003cp\u003eFully wrapped slabs (CF-Full) withstood 34 impacts before failure, this represented nearly triple the impact capacity of RC slabs, CFRP wrapping effectively contained concrete spalling and debris. The technique showed particular effectiveness in preventing sudden punching shear failures.\u003c/p\u003e\u003c/li\u003e\u003cli\u003e\u003cp\u003eHybrid NSM-CFRP techniques Combined benefits of embedded rebars and CFRP layers, reduced damage area by 28\u0026ndash;59% compared to standalone methods. Also, delayed crack propagation through multiple mechanisms. NSM-X950-CF hybrid specimen showed 107% higher energy absorption than reference RC-210.\u003c/p\u003e\u003c/li\u003e\u003cli\u003e\u003cp\u003eDiagonal strengthening patterns showed 15\u0026ndash;20% better performance than orthogonal. Specimens with longer NSM rebar embedment (950mm) performed better than shorter (550mm), and optimal CFRP strip width was found to be 280mm for impact zone coverage.\u003c/p\u003e\u003c/li\u003e\u003c/ul\u003e"},{"header":"Declarations","content":"\u003cp\u003eCRediT authorship contribution statement\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eMehran Masoudiyan:\u003c/strong\u003e Conceptualization, Formal analysis, Investigation, Resources, Visualization, Writing \u0026ndash; original draft.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eMostafa Zinati:\u003c/strong\u003e Conceptualization, Formal analysis, Investigation, Resources, Visualization, Writing \u0026ndash; original draft.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eAli Kargaran:\u003c/strong\u003e Conceptualization, Data curation, Investigation, Methodology, Project administration, Software, Supervision, Validation, Writing \u0026ndash; review \u0026amp; editing.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eAli Kheyroddin:\u003c/strong\u003e Data curation, Investigation, Supervision, Validation, Writing \u0026ndash; review \u0026amp; editing.\u003c/p\u003e\n\u003cp\u003eDeclaration of competing interest\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\u003cp\u003eData\u0026nbsp;availability\u003c/p\u003e\n\u003cp\u003eThe datasets generated and/or analyzed during the current study are available from the corresponding author, Ali Kargaran ([email protected]), upon reasonable request.\u003c/p\u003e\n\u003cp\u003eFunding\u003c/p\u003e\n\u003cp\u003eThis research received no funding.\u003c/p\u003e\u003ch2\u003eAuthor Contribution\u003c/h2\u003e\u003cp\u003eMehran Masoudiyan: Conceptualization, Formal analysis, Investigation, Resources, Visualization, Writing \u0026ndash; original draft.Mostafa Zinati: Conceptualization, Formal analysis, Investigation, Resources, Visualization, Writing \u0026ndash; original draft.Ali Kargaran: Conceptualization, Data curation, Investigation, Methodology, Project administration, Software, Supervision, Validation, Writing \u0026ndash; review \u0026amp; editing.Ali Kheyroddin: Data curation, Investigation, Supervision, Validation, Writing \u0026ndash; review \u0026amp; editing.\u003c/p\u003e"},{"header":"References","content":"\u003col\u003e\u003cli\u003e\u003cspan\u003eQsymah, A. \u0026amp; Ayasrah, M. Finite Element Analysis of Two-Way Reinforced Concrete Slabs Strengthened with FRP Under Flexural Loading. \u003cem\u003eBuildings\u003c/em\u003e \u003cb\u003e14\u003c/b\u003e, 3389 (2024).\u003c/span\u003e\u003c/li\u003e\u003cli\u003e\u003cspan\u003eSharhan, Z. S., Cucuzza, R., Domaneschi, M. \u0026amp; Ghodousian, O. Movahedi Rad, M. Reinforcement of RC Two-Way Slabs with CFRP Laminates: Plastic Limit Method for Carbon Emissions and Deformation Control. \u003cem\u003eBuildings\u003c/em\u003e \u003cb\u003e14\u003c/b\u003e, 3873 (2024).\u003c/span\u003e\u003c/li\u003e\u003cli\u003e\u003cspan\u003eSheng, Y. \u0026amp; Gong, Y. In Situ Testing Evaluation and Numerical Simulation of CFRP-Strengthened Reinforced Concrete Two-Way Slab with Initial Defect. \u003cem\u003eBuildings\u003c/em\u003e \u003cb\u003e15\u003c/b\u003e, 82 (2024).\u003c/span\u003e\u003c/li\u003e\u003cli\u003e\u003cspan\u003eMtashar, S. H. \u0026amp; Al-Azzawi, A. A. 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Eng.\u003c/em\u003e \u003cb\u003e48\u003c/b\u003e, 2449\u0026ndash;2478 (2024).\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":"Reinforced Concrete, Two-Way Slab, Impact Loading, Fiber-Reinforced Concrete, Near-Surface Mounted, Carbon Fiber Reinforced Polymer","lastPublishedDoi":"10.21203/rs.3.rs-8078876/v1","lastPublishedDoiUrl":"https://doi.org/10.21203/rs.3.rs-8078876/v1","license":{"name":"CC BY 4.0","url":"https://creativecommons.org/licenses/by/4.0/"},"manuscriptAbstract":"\u003cp\u003eThis article investigates the effectiveness of five strengthening techniques for reinforced concrete (RC) two-way slabs subjected to impact loading. Fifteen square slabs were tested under drop-weight impacts to evaluate Fiber-Reinforced Concrete (FRC) with steel or polypropylene fibers, Externally Bonded Reinforcement (EBR) using Carbon Fiber Reinforced Polymer (CFRP), Near-Surface Mounted (NSM), and hybrid NSM-CFRP combinations. Results show improvements in impact resistance across all methods. FRC slabs with polypropylene fibers exhibited a 2.3 times increase in energy absorption compared to conventional RC slabs, while steel fibers reduced concrete scabbing by 35%. CFRP reinforced slabs (EBR) showed the highest strength, up to 34 impacts, almost triple the capacity of RC slabs. Hybrid techniques showed most effective, combining NSM and CFRP strips to reduce damage area by 28\u0026ndash;59%. FRC offers a cost-effective solution for distributed reinforcement, EBR gives in localized protection, and hybrid methods result optimal performance for high-risk scenarios.\u003c/p\u003e","manuscriptTitle":"Strengthening of Two-Way Slabs Using Fiber Reinforced Concrete, Near Surface Mounted and CFRP Layers under Impact Loading","msid":"","msnumber":"","nonDraftVersions":[{"code":1,"date":"2025-11-27 08:50:47","doi":"10.21203/rs.3.rs-8078876/v1","editorialEvents":[{"type":"communityComments","content":0},{"type":"decision","content":"Revision requested","date":"2025-12-15T15:15:41+00:00","index":"","fulltext":""},{"type":"editorInvitedReview","content":"","date":"2025-12-12T10:11:59+00:00","index":"hide","fulltext":""},{"type":"editorInvitedReview","content":"","date":"2025-12-02T16:58:31+00:00","index":"hide","fulltext":""},{"type":"editorInvitedReview","content":"","date":"2025-12-01T20:26:50+00:00","index":"hide","fulltext":""},{"type":"reviewerAgreed","content":"59897059981756967636437075689724466059","date":"2025-11-25T08:10:56+00:00","index":"hide","fulltext":""},{"type":"reviewerAgreed","content":"282741207569018416045504405580963969207","date":"2025-11-21T15:14:30+00:00","index":"hide","fulltext":""},{"type":"reviewerAgreed","content":"83183535667862590346518194158400277334","date":"2025-11-19T15:19:27+00:00","index":"hide","fulltext":""},{"type":"reviewersInvited","content":"","date":"2025-11-19T14:22:56+00:00","index":"","fulltext":""},{"type":"editorInvited","content":"","date":"2025-11-19T13:50:21+00:00","index":"","fulltext":""},{"type":"editorAssigned","content":"","date":"2025-11-17T08:11:23+00:00","index":"","fulltext":""},{"type":"checksComplete","content":"","date":"2025-11-17T08:10:31+00:00","index":"","fulltext":""},{"type":"submitted","content":"Scientific Reports","date":"2025-11-10T15:46:26+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":"ee39592b-5042-4f28-8171-9156c66ea520","owner":[],"postedDate":"November 27th, 2025","published":true,"recentEditorialEvents":[],"rejectedJournal":[],"revision":"","amendment":"","status":"under-review","subjectAreas":[{"id":58563758,"name":"Physical sciences/Engineering"},{"id":58563759,"name":"Physical sciences/Materials science"}],"tags":[],"updatedAt":"2026-04-21T14:38:37+00:00","versionOfRecord":[],"versionCreatedAt":"2025-11-27 08:50:47","video":"","vorDoi":"","vorDoiUrl":"","workflowStages":[]},"version":"v1","identity":"rs-8078876","journalConfig":"researchsquare"},"__N_SSP":true},"page":"/article/[identity]/[[...version]]","query":{"redirect":"/article/rs-8078876","identity":"rs-8078876","version":["v1"]},"buildId":"8U1c8b4HqxoKbykW_rLl7","isFallback":false,"isExperimentalCompile":false,"dynamicIds":[84888],"gssp":true,"scriptLoader":[]}