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This paper presents the experimental study on the reinforced concrete (RC) beam strengthened with externally bonded carbon fiber reinforced polymer (EB-CFRP) laminate and engineered cementitious composites (ECC) material. A total of six beams were tested under the four-point bending test to investigate the influence of strengthening scheme, type of CFRP laminate and the width of CFRP plate on the flexural response. The results revealed that hybrid strengthened beam with the technical of EB-CFRP and ECC transition layer significantly enhanced the crack load (29.0%–133.3%), yield load (50.9%–96.5%) and ultimate load (50.0%–81.9%) of the beams relative to the control beam. The employment of ECC material was an ideal transition layer for delaying the interfacial debonding of CFRP laminate, where the ultimate tensile strain of CFRP plate in hybrid strengthened beams was 13.2%–33.33% higher than that of beam merely strengthened with EB-CFRP plate. Beams strengthened with CFRP sheet had the greater flexural performance and higher utilization of CFRP than its counterparts strengthened with CFRP plate. Moreover, the predicted model associated with ultimate bearing capacity of the hybrid beams was provided based on ACI 440.2R-08, which was relatively conservative with a margin for the ultimate load of the hybrid strengthened beams. [ABSTRACT FROM AUTHOR]

Despite the advantages of using lightweight and non-corrosive carbon fiber reinforced polymer (CFRP) reinforcements in concrete structures, their widespread adoption has been limited due to concerns regarding the brittle failure of CFRP rupture and its relatively softer load-deflection stiffness. This work offers logical solutions to these two crucial problems: using aggregate coating to strengthen the CFRP-concrete bond and ultimately the load-deflection stiffness, and using CFRP-concrete debonding propagation to create pseudo-ductile behavior. Subsequently, the concrete cracking behavior, the apparent CFRP modulus with aggregates, and the post-peak capacity and deflection of three-dimensional (3D) CFRP-reinforced concrete are all described by equations derived from experiments. These formulas will be helpful in the future design of non-prismatic concrete components for low-impact building projects. The potential of this innovative design scheme in terms of increased capacity and deflections with less concrete material is demonstrated through comparisons between non-prismatic CFRP-reinforced concrete and measured steel reinforced equivalency. [ABSTRACT FROM AUTHOR]

This research provides a study for an experimental program using sand‐perlite‐lightweight reinforced concrete (RC) beams strengthened and anchored with carbon fiber reinforced polymer (CFRP) materials. The main objective of this work is to showcase the efficiency of using U‐wrap anchors to secure the externally applied CFRP sheets on lightweight RC beams. A series of six full‐scale T‐beams with an increasing number of CFRP U‐wraps per shear span was prepared and tested. The use of U‐wrap anchorage enhanced the flexural performance of the sand‐lightweight concrete beams by progressively delaying the premature debonding of CFRP sheets as a direct function of the number of U‐wraps used per shear span. The beam flexural capacity gradually improved from 116 kN without the use of U‐wrap anchors to 182 kN when using six U‐wraps per shear span, which reflects a significant enhancement. Similarly, the ultimate deflection gradually improved from 56 mm for the beam without U‐wrap anchors to 94 mm when applying six U‐wraps per shear span. A design model established earlier, for normal weight concrete, has been successfully qualified to yield accurate findings against the experimental results. Also, the outcome of this study interestingly showed that the ultimate strength results of the anchored beams were close to their counterparts of normal weight concrete conducted on identical beams. This finding shows that U‐wrap anchors performed efficiently despite the lack of coarse aggregate interlock in the concrete mix. [ABSTRACT FROM AUTHOR]

Recently, a new proposed technique named; Externally Bonded Reinforcement on Grooves (EBROG) has been presented as a strengthening method to postpone or eliminate the undesirable debonding failure mode that is accompanying to Externally Bonded Reinforcement (EBR) method. This paper introduces an experimental and analytical study to evaluate the validity and accuracy of the formulas that were introduced by the standard codes and researchers, in estimating the ultimate load of RC continuous beams strengthened with carbon fiber reinforced polymer (CFRP) sheets in flexure. The experimental program includes testing of ten RC beams with cross section of (200×130) mm and two equal spans, each span has a 1050 mm length. The comparison between the ultimate load collected from the test results and that predicted using ten different analytical models is conducted. It is found that the ACI 440.2R-17 and most of other analytical models well predicted the ultimate load of RC beams strengthening with one layer of CFRP sheets using EBR, but most of these models significantly underestimate the ultimate load of tested beams that were strengthened using EBROG method. ACI, Shehata el. al., and Teng et al. models give close predicted load to the experimental results in case of EBR beams strengthened with two layers. [ABSTRACT FROM AUTHOR]

The need to develop the concrete industry has increased with the increase in environmental damage resulting from building and construction operations. In the present research, the Numerical study of shear behavior of geopolymer concrete beams without stirrups by using the ANSYS program. It also includes concrete modelling to study the behavior of geopolymer concrete (GPC). The longitudinal reinforcements of beams (without stirrups) were "basalt fiber reinforced polymer bars". In order to enhance the shear behavior of the specimens, various types of fibers were added to geopolymer concrete (GPC): "steel fibers (SF), synthetic polypropylene fibers (PF), polyvinyl alcohol fibers (PVF), and carbon fibers (CF)". A numerical analysis was performed by the ANSYS version 15 program to study many parameters affecting the shear behavior of geopolymer concrete, such as longitudinal reinforcements,, and the inclusion of the opening. The results indicated that using steel fibers (SF) in geopolymer concrete increased the load failure of the tested specimens. On the other hand, using carbon fibers (CF) in the geopolymer concrete enhanced the ductility factor of these beams. The load capacity of the geopolymer concrete specimen is enhanced with longitudinal reinforcement by the CFRP bar compared to those reinforcements by BFRP bars. While the use of GFRP bars was less efficient than BFRP bars. Using FRP bars, and steel bars in strengthening geopolymer concrete beams with openings enhanced the failure load of these specimens. [ABSTRACT FROM AUTHOR]

Precast segmental beams with prestressed external tendons have become increasingly common in bridge constructions owing to the merits of high-quality control and fast onsite construction with minimum environmental impact. Due to the nonlinear characteristics of the dynamic behavior of these segmental beams associated to the joint opening, the traditional condition monitoring and damage assessment methods based on vibration parameters either in time or frequency domain using the linear theory are unsuitable. To overcome this challenge, this paper proposes a damage assessment method through analyzing nonlinear structural dynamic responses for monitoring the conditions of segmental beams with different joint types and prestressed external tendons. Two damage indices are proposed to identify the occurrence of damage and to qualitatively indicate the damage severity. In the proposed approach, the measured dynamic responses of the segmental concrete beams under hammer impact are first adaptively decomposed into a finite number of mono-components by using variational mode decomposition (VMD) technique. Then, the instantaneous frequencies of the decomposed mono-components from the dynamic responses are obtained by conducting the Hilbert transform. Two damage indicators are defined for the damage assessment and for the identification of the damage location, respectively. Three four-span segmental beams with different types of joints (i.e. dry joints or epoxy joints) and prestressing tendon types (i.e. steel and carbon fiber reinforced polymer tendons) were constructed and tested under five loading levels with different damage severities. The feasibility and accuracy of the proposed approach are verified by comparing the identification results with the secant and initial stiffness extracted from the load–deflection curves at different loading levels. The effectiveness of these two damage indicators is also validated with the structural conditions observed in the tests. The results show that the proposed approach can successfully identify damage in segmental concrete beams. [ABSTRACT FROM AUTHOR]

Corrosion of conventional steel reinforcement is responsible for numerous structurally deficient bridges, which is a multi-billion-dollar challenge that creates a vicious cycle of maintenance, repair, and replacement of infrastructure. Repair of existing structures with fiber-reinforced polymer (FRP) has become widespread due to multiple advantages. Carbon FRP's superior tensile strength and stiffness make it particularly effective in shear and flexural strengthening of reinforced concrete (RC) beams. This experimental study incorporates carbon fiber polymer composite bars and wraps to study and report on the flexural behavior of RC beams. By employing a combination of CFRP bar and wrap for strengthening RC beams, this study observed an approximate 95% improvement in flexural load capacity relative to control RC beams without strengthening. This substantial enhancement highlights the effectiveness of integrating CFRP in structural applications. Nevertheless, the key observation is the failure mode due to this combination providing significant insights into the changes facilitated by this combination approach. [ABSTRACT FROM AUTHOR]

The dual‐function retrofitting system that uses the carbon‐fabric reinforced cementitious matrix (C‐FRCM) as both the anode of impressed current cathodic protection (ICCP) system and the structural strengthening (SS) material, that is, an ICCP‐SS system, is investigated. The experimental program mainly focused on the shear behavior of C‐FRCM strengthened reinforced concrete (RC) continuous beam under the dual‐function retrofitting system. The influence of anode polarization on the shear strengthening of RC continuous beams is analyzed. Shear tests were conducted on a total of 14 corroded RC continuous beams to investigate the influence of key parameters, including anode polarization degree of prefabricated C‐FRCM plate, layer of carbon fiber mesh and side‐wrapping. The failure modes, shear capacities, and load‐deflection curves of the shear‐strengthened RC continuous beams are reported. Based on the test results, the applicability of relevant design codes was evaluated and found to provide rather conservative predictions for the shear capacity of the examined C‐FRCM strengthened RC continuous beams. [ABSTRACT FROM AUTHOR]

This study investigates the effect of strengthening self-compacted concrete (SCC) beams using CFRP sheets on flexural behaviour subjected to repeated loads. During the experiment, six rectangular reinforced SCC beams were evaluated; two were reference beams without strengthening, while the remaining four were strengthened with CFRP sheets. The beam's length, depth, and width are 2100 mm, 300 mm, and 200 mm, respectively. A monotonic load was applied to one of the reference beams, while repeated loads were applied to the remaining (compression cyclic loads). The main parameters studied in this experimental work were the type of loading (monotonic and repeated), the positions of strengthening and the dimensions of CFRP sheets. The flexural behaviour of these beams was investigated through experimental examination by recording the ultimate load and maximum deflection. Meanwhile, the cracks' pattern and failure modes were observed. The findings of the present study demonstrated that the limited cycles of repeated loads have marginal effect on the flexural behaviour of the beams. This results in an ultimate load reduction of no more than 11%. It was also noted that SCC beams strengthened using CFRP sheets subjected to repeated loads significantly affected the flexural behaviour of these beams. Consequently, the ultimate load of the strengthened beams was improved by up to 18%. Besides, the maximum deflection of the strengthened SCC beams was reduced by 45% compared to those without strengthening. Using strengthening throughout the beams' entire width and length that are subjected to repeated loads improved their ultimate load to surpass that of non-strengthened beams under monotonic loads by as much as 7%. [ABSTRACT FROM AUTHOR]

The bearing capacity of reinforced concrete (RC) beam will be weakened by fire. It is necessary to strengthen RC beams after fire. The carbon fiber mesh (CFM) can be used to reinforce RC beams. In this paper, RC beams were exposed to varying temperatures, followed by reinforcement with varying layers of CFM. The influence of the heating temperature and the number of CFM layers on the flexural performance of RC beams was investigated. The results indicated that the cracking loads of RC beams were 18.2, 16.4, 16.3, and 15.5 kN when the RC beams were subjected to room temperatures, 150, 350, and 550 °C. Compared to the unreinforced beams at room temperature, the cracking loads of the RC beams were reduced by 9.89%, 10.44%, and 14.84%. As the quantity of CFM reinforcement layers rises, so does the ultimate bearing capacity. For example, when the temperature was 150 °C, the ultimate loads of the beams with one and three layers of CFM were increased by 20% and 31.76% compared to the reference beam. When the temperature was 350 °C, the ultimate loads of the beams with one and three layers of CFM were increased by 19.51% and 28.04% compared to the RC beam without CFM. When the temperature was 550 °C, the ultimate loads of the beams with one and three layers of CFM were increased by 20% and 26.67% compared to the RC beam without CFM. Fire-damaged RC beams can be strengthened by one layer of CFM and mortar if the temperature was below 350 °C. Fire-damaged RC beams can be strengthened by three layers of CFM and mortar if the temperature was below 550 °C. The mechanical properties can be obviously enhanced. [ABSTRACT FROM AUTHOR]

For earthquake-damaged reinforced concrete structures, the static loading test method is adopted to carry out loading tests under cyclic loading on reinforced concrete beams with different reinforcement rates and columns with different axial compression ratios, and the effect of reinforcing and repairing the damaged reinforced concrete structure by using adhesive steel plates and carbon fiber cloth is investigated. Through comparative studies of structural hysteresis curves and skeleton curves under different reinforcement methods, it is concluded that reinforcement has significantly improved the hysteresis characteristics and ductility of members, and the seismic performance of the carbon fiber reinforcement method is better than that of the steel plate reinforcement. This study provides valuable references and suggestions for practical earthquake-damaged building reinforcement and repair works and seismic reinforcement works. [ABSTRACT FROM AUTHOR]

This study aimed to evaluate the static response of prestressed reinforced concrete beams strengthened in their flexure and shear properties using different strengthening techniques, steel plates, and externally bonded woven carbon fiber fabric (WCFF). The experimental work involved testing twenty large-scale prestressed reinforced concrete beams with a length of 3000 mm, and cross-sections measuring 400 mm in height and 200 mm in breadth were cast in the factory and tested in the laboratory. Four beams without prestressing served as the reference beams; two unbonded pre-tensioned beams served as the control beams, and the remaining fourteen beams were strengthened with steel plates and externally bonded woven carbon fiber fabric (WCFF). Eight of the beams were strengthened with 4 mm thick steel plates and tested under a monotonically increasing load with manual readings recorded. The remaining six beams were strengthened with 0.5 mm thick WCFF and tested under a monotonically increasing load with manual readings recorded. The variables considered included the strengthening techniques (FRP composite sheets, steel plates), the types of strengthening (slices, U-shaped), and the flexural and shear capacities of the strengthened beams. All the implemented strengthening techniques yielded enhancements in both the flexural and shear strength outcomes of the beams compared to their respective controls. The most significant increase in load capacity, whether in terms of ultimate load or first crack load, for the prestressed concrete beams' flexure properties occurred when strengthening with U-shaped steel plates. Additionally, the greatest reduction in deflection at the point of reaching the maximum load for the prestressed concrete beams, in terms of their flexure properties, was observed when strengthening with U-shaped steel plates. Similarly, the maximum load increase for the prestressed concrete beams, in terms of their shear properties, was achieved through strengthening with U-shaped woven carbon fiber fabric wrapping. Furthermore, a finite element model was created to simulate various experimental specimens. The finite element model's results exhibited harmony with the experimental results, affirming the efficacy of the presented finite element model. [ABSTRACT FROM AUTHOR]

The use of engineered cementitious composites (ECC) can greatly reduce or even entirely prevent premature debonding of externally bonded (EB) fiber-reinforced polymers (FRP). This study examined the flexural behavior of pre-damaged reinforced concrete (RC) beams reinforced by carbon fiber reinforced polymer (CFRP) sheets. Ten beams were created and constructed for four-point bending test. The main testing parameters were the degree of pre-damage, the thickness of the ECC layer, and the reinforcing method. According to the test results, CFRP rupture occurred in the undamaged specimens, while CFRP debonding occurred in all of the pre-damaged specimens. The pre-damaged specimens' flexural stiffness and load-carrying capability can be effectively increased. Best flexural performance and a maximum CFRP utilization of 83.2 % can be achieved by pre-damaged concrete beams when the thickness of the ECC layer entirely surrounds the longitudinal tensile reinforcement. For pre-damage specimens, the increased ECC layer thickness contributed to increased ductility and had little effect on the ultimate load. A mathematical model based on the plane section assumption is proposed to predict the flexural capacity of ECC-CFRP jointly reinforced beams, and the effect of different failure modes is taken into account. The error between the predicted and measured values is within ± 10 %. • We investigated the flexural performance of pre-damaged concrete beams reinforced with ECC-CFRP. • We examined the impact of three factors: the degree of pre-damage, the thickness of the ECC layer, and the reinforcing method. • Better flexural performance can be achieved when the thickness of the ECC layer entirely surrounds the longitudinal tensile reinforcement. • The increased ECC layer thickness at 45 % damage mainly contributed to increase ductility and had little effect on the ultimate load. • A mathematical model based on the plane section assumption is proposed to predict the flexural capacity. [ABSTRACT FROM AUTHOR]

• The behavior of externally bonded CFRP strips in compression is investigated through an experimental study. • The behavior of CFRP strips mounted on concrete elements under pure compressive stress is assessed. • The behavior of CFRP sheets under compressive stress due to bending moment is evaluated. • The CFRP strips may exhibit debonding failure mode and buckling in compression. • The type of adhesive and the thickness of CFRP sheets have a significant effect on the behavior of CFRP strips under compression. Although the compressive strength of Fiber Reinforced Polymer (FRP) sheets is neglected in the design of FRP-retrofitted Reinforced Concrete (RC) elements, they may be subjected to compressive stress in some load combinations. In the present study, an experimental study is conducted to investigate the behavior of externally bonded Carbon Fiber Reinforced Polymer (CFRP) sheets in compression. The experimental program is carried out in two phases. First, the behavior of CFRP strips bonded on concrete cylinders and subjected to pure compressive load is assessed. At this stage, the influence of concrete compressive strength, the dimensions of CFRP strips (thickness, width, and free length), and the type of adhesive used for bonding CFRP strips on the concrete surface, on the behavior of CFRP strips in compression are investigated. According to the test results, the FRP strips bonded with weak resin exhibit debonding failure and simultaneously buckle at a relatively low compressive strain, while CFRP strips bonded with stronger adhesive do not exhibit debonding failure in compression until concrete crushing. The behavior of CFRP strips bonded on reinforced concrete (RC) beams subjected to compressive stress due to bending moment is investigated in the second phase of this study. For this purpose, nine RC beams with the same dimensions and reinforcement detailing are fabricated and retrofitted using CFRP strips with different configurations. Four-point bending test is conducted at this stage of the experimental program. The results of the bending tests show that debonding failure and buckling of CFRP strips are observed in specimens with relatively thick CFRP sheets (3 and 4-layer) and larger free lengths. [ABSTRACT FROM AUTHOR]

This study presented the development of a new method for strengthening of Reinforced Concrete (RC) slabs using Carbon Fiber Reinforced Polymer rods (CFRP) and an Ultra-High Performance Fiber Reinforcement Concrete (UHPFRC) external jacket with a Mechanical Anchorage System (MAS). The mechanical anchorage system includes two components: high-carbon steel plates and the Mechanical Expansion Anchorage Bolt System (MEABS), and it's employed to prevent any premature de-bonding between the existing concrete surface and the externally strengthening layers (CFRP rods and UHPFRC jacket). The efficiency of the proposed strengthening method was evaluated through conducting an experimental test on a few fortified slabs by applying cyclic loads using a dynamic actuator. For this purpose, three distinct concrete slabs were tested to assess various design parameters, including a control slab, a strengthened slab with the UHPFRC jacket only, and a strengthened slab with CFRP bars at the bottom of the slab with an external UHPFRC jacket. The results of experimental tests reveal that the proposed strengthening system significantly enhanced the load capacity of the slab and prevented premature debonding failures between the old concrete of the slab and the new UHPFRC layer until the stage of slab failure. Accordingly, the new proposed strengthening system played a crucial role in enhancing the tension zone of the slabs and delaying the occurrence of diagonal crack loads. On the other hand, embedding CFRP bars within the UHPFRC jacket in the strengthened slab led to a notable enhancement of 82 % in the ultimate load capacity of the slab. The FE and analytical models were developed to predict the behavior of the specimens. The models' outcomes were in good agreement with the experimental data. Consequently, the new proposed strengthening system emerges as a reliable technique for enhancing the performance of reinforced concrete slabs, eliminating the risk of debonding between old and new parts. • A new method for strengthening of RC slabs using CFRP rods and UHPFRC external jacket with a Mechanical Anchorage System. • Application of the new proposed system to strengthening two casted slab specimens and test them under cyclic load. • Assessing the effectiveness of the proposed strengthening technique by comparing the performance with the benchmark slab. • The numerical and theoretical model is evaluated based on the experimental results. [ABSTRACT FROM AUTHOR]

The prestressed CFRP (carbon fiber reinforced polymer) strengthening technique has significant superiority over the ordinary externally bonded CFRP technique in increasing the strengthening efficiency and strength utilization of the CFRP. However, as a key to the prestressing technique, the field- applicable prestressed CFRP system without requiring end access is still very scarce. In this study, a novel prestressed CFRP plate system was developed for strengthening reinforced concrete (RC) beams, and with this system no operation space is required at the RC beam end. The anchorage performance of the anchors was first examined by the pull-out tests of the anchor-CFRP plate assemblies, and then large-scale RC beams were strengthened using this system to evaluate its construction feasibility and strengthening efficiency. The test results showed that the developed prestressing system could effectively anchor a 50 mm×3.0 mm CFRP plate with rupture failure of the CFRP plate, and the flexural performance of RC beams was effectively enhanced by both the bonded and unbonded strengthening. Compared with the unstrengthened beam, the increase ratios of the strengthened beams reached 150 %-225 % for cracking load, 33.0 %-48.8 % for yielding load, and 46.1 %-49.5 % for ultimate load. Under the same prestress, the unbonded and bonded methods provided a rather close ultimate load but the bonded strengthening gained an advantage in enhancing the cracking and yielding loads. The study proves the feasibility and effectiveness of this system for flexural strengthening application of RC beams with a width of no less than 250 mm, and provides a foundation for further studies (e.g., long-term durability and fatigue behavior) and practical applications of this system. • A practical prestressed CFRP plate system was developed for strengthening RC beams. • The anchorage behavior was evaluated by pull-out tests of anchor-CFRP plate assemblies. • Large-scale RC beams were strengthened using this system to evaluate its feasibility. • Effects of the prestress and adhesive layer on the flexural strengthening were investigated. [ABSTRACT FROM AUTHOR]

An experimental program was conducted to examine the seismic performance of flexural beam members strengthened with carbon fiber-reinforced polymer (CFRP) sheet and anchored using carbon fiber splay anchors. This research study extends the use of carbon fiber anchors to secure the top and bottom CFRP flexural sheets under cyclic loading. In this study, low strength concrete is examined, with lightly reinforced steel ratio (0.0034) to test full-scale rectangular beams. Five reinforced concrete beams were cast, strengthened, and tested under reversed cycles of four-point bending to failure. The beams were categorized into a control specimen, strengthened specimens with thin sheets with and without fiber anchors, and strengthened specimens with thick sheets with and without fiber anchors. They were tested cyclically under displacement control according to the AC 125 loading protocol. The failure modes ranged from classical ultimate failure for the control beam to rupture and intermediate crack (IC) debonding for the beam with unanchored thin CFRP sheets. On the other hand, debonding took place for the thicker sheets with no anchors, while the thicker sheets with fiber anchors underwent cover delamination failure mode despite the fact that the sheets were extended very close to the simple supports. The hysteresis response loops were compared for the different specimens and the analytical envelop curves were predicted resulting in a close agreement to the experimental finding. • Seismic performance of flexural beams CFRP strengthened with and without carbon fiber anchors is successfully examined. • Thicker CFRP sheets yield lower energy dissipation, ductility, but higher strength and seismic pinching. • Failure modes varied from sheet debonding to CFRP rupture and cover delamination. • The use of anchors at sheet ends was not very effective in extending the hysteretic cycles beyond those without anchors. • The need to apply fiber anchors along the entire shear span to harness improved behavior is clearly evident. [ABSTRACT FROM AUTHOR]

• A 3D meso-scale numerical simulation method of CFRP strengthened RC beams is established. • The coupling effect between shear-span ratio and CFRP fiber ratio is explored. • The quantitative relationship between the contribution of CFRP and shear-span ratio is analyzed. • The effect of shear-span ratio and CFRP fiber ratio on the size effect is investigated. • The shear strength size effect law of CFRP strengthened RC beams is proposed. In this study, a 3D meso-scale numerical simulation method is established for analyzing the shear failure of carbon fiber reinforced polymer (CFRP) strengthened RC beams without stirrups. The inhomogeneity of concrete, the bond-slip relationship between steel bars and concrete, and the interaction between CFRP and concrete are considered. Based on this method, effects of shear-span ratio and CFRP fiber ratio on the shear performance and nominal shear strength size effect of CFRP strengthened RC beams are investigated. Results indicate that the size effect of CFRP strengthened RC beams is obvious, however, the shear-span ratio has little impact on the size effect of nominal shear strength of RC beams. The CFRP fiber ratio enhances the shear strength of RC beams on the one hand, while weakens the shear size effect of RC beams on the other hand. However, its influence on the shear performance of RC beams remains basically unchanged with varying shear-span ratios, indicating that there is no coupling effect between the shear-span ratio and CFRP fiber ratio. The shear-span ratio significantly influences both the shear bearing capacity of RC beams and the shear contribution of CFRP sheets, with the increase in the shear-span ratio, the shear bearing capacity of RC beams decreases to varying degrees, and the shear contribution of CFRP sheets increases initially and then decreases. Finally, the shear strength size effect law (SEL) of CFRP strengthened RC beams is proposed, which can quantitatively describe the effects of the shear-span ratio and the CFRP fiber ratio. [Display omitted] [ABSTRACT FROM AUTHOR]

Plate end debonding is a common failure mode for fiber reinforced polymer (FRP) strengthened beams. FRP sheets and shape memory alloy (SMA) composites can effectively slow down plate end debonding and improve beam ductility owing to the anchorage effect of SMA wires on the FRP ends. This work aims to comprehensively study the anchorage performance of FRP/SMA composite strengthened beams through both model analysis and experimental investigation. The plate end debonding strength models of existing FRP strengthened beams were initially summarized and analyzed, and an improved model was proposed to predict the debonding strength of FRP/SMA composite strengthened beams at the plate end. Moreover, the anchorage performance and flexural behavior of beams strengthened with carbon fiber reinforced polymer (CFRP) and SMA composites were studied through experiments. The failure mode of the FRP sheet strengthened beams was plate end debonding failure, while the plate end debonding failure of the CFRP/SMA composite strengthened beams occurred at the strengthening zone end, and the peeling failure was delayed owing to the anchorage effect of SMA wires on the ends of the strengthening CFRP sheets. The recovery effect of SMA wires could successfully introduce prestress into CFRP sheets. Moreover, the CFRP strain corresponding to plate end debonding increased because of the anchorage of SMA wires on the CFRP sheet in the strengthening zone. The strength and ductility of the CFRP/SMA composite strengthened beam significantly improved. The proposed model for predicting the plate end debonding strength of FRP/SMA composite strengthened beams was validated through experiments. • An improved model is proposed to predict the debonding strength of beams strengthened with FRP/SMA composites at the plate ends. • The debonding failure was delayed due to the anchorage effect of SMA wires on CFRP sheets in the strengthening zone. • The strength and ductility of the beam strengthened with CFRP/SMA composites have been significantly improved. • The proposed model for predicting the plate end debonding strength of FRP/SMA composite strengthened beams was validated through experiments. [ABSTRACT FROM AUTHOR]

This work attempted to investigate the on-site application of ohmic heating curing method on the structural concrete with steel reinforcement. The steel reinforced carbon fiber concrete beams were cured by ohmic heating method in the realistic severely cold weather. It was found that steel rebars disturbed the electrically conductive network formed by carbon fibers, resulting in a reduced curing duration of 48 h and an abnormal temperature distribution with high corner temperature and low core temperature. Electrical insulation treatments (epoxy resin coating and heat-shrink tubing) were taken and evaluated based on the ohmic heating features and mechanical properties. The results showed that the epoxy resin coating had a limited insulation effect, with an electrical resistance of 3.9 Ω, which displayed a similar temperature distribution with the uninsulated beam. On the contrary, the heat-shrink tubing had a significant insulation effect with an electrical resistance of 36.5 Ω, leading to an average core temperature of 23.6 ℃ during 7 days of curing period. The average rebound strength of beams with epoxy resin coating and heat-shrink tubing was 34.0 MPa and 41.6 MPa, respectively, and the ultimate deflection of beams was 34.37 mm and 49.18 mm, respectively, which was in correspondence with the temperature distribution. Besides, the heat-shrink tubing increased crack spacing width of beam, while the epoxy resin had little influence on crack pattern. This work emphasized the importance of electrically conductive path of concrete for ohmic heating curing method and gained practical experience of this method on the structural concrete. • Effect of steel rebar on ohmic heating curing of carbon fiber concrete beams was revealed. • Insulation treatments could reduce the steel rebars' interference to carbon fiber conductive network. • Carbon fiber concrete beams with insulated steel rebars were successfully cured under realistic cold weather by ohmic heating. • Mechanical properties were investigated together with the electrical and thermal performance. [ABSTRACT FROM AUTHOR]

Low-cost iron-based shape memory alloys (Fe-SMA) are recently proving to be favorable alternatives for strengthening reinforced concrete (RC) members. Unlike carbon fiber reinforced polymers (CFRP), Fe-SMAs eliminate the need for labor-intensive anchorages and exhibit plastic behavior similar to reinforcing steel, rendering them especially promising for prestressed near-surface mounted (NSM) applications. However, due to their recent development, not many long-term experimental studies have been yet available and thus the long-term durability of Fe-SMA-strengthened RC members remains relatively unexplored. To this end, the structural behavior of two RC beams strengthened with NSM Fe-SMA were investigated, exposed to a natural environmental conditions and sustained loading above their cracking load level for 8 years, followed by four-point bending until failure. Results were compared with a previous investigation of identical beams and Fe-SMA strips without exposure to environmental factors or sustained loading. Additionally, a comprehensive cross-section analysis (CSA) was conducted for both long-term exposure and four-point bending. Despite notable creep effects caused by the 8 years of sustained loading that accounted to approximately 55% of the total mid-span deflections, no significant differences were observed in terms of load-carrying capacity, ultimate deflections, or strains, compared to the unexposed beams. The employed CSA effectively captured the long-term and bending behavior. Additionally, a parameter study and global sensitivity analysis were conducted to identify influential parameters affecting structural performance, concrete compressive strength was found as the most dominant influencing parameter. • Eight-year environmental exposure and sustained loading of RC beams with Fe-SMA NSM. • Time-dependent material models with CSA for diagnosis and condition prognosis. • Ultimate capacity unaffected despite notable deflections during sustained loading. • Global sensitivity analysis reveal concrete strength as most influential parameter. [ABSTRACT FROM AUTHOR]

An innovative prestressing system was developed in this study, which can effectively anchor the prestressed carbon fiber sheets as well as conveniently apply prestress to the carbon fiber sheets. Tensioning tests of the carbon fiber sheet-anchor assemblies were first conducted to verify the anchorage behavior of anchors. Then this prestressing system was used for strengthening reinforced concrete (RC) beams to further verify its feasibility and investigate the effect of the impregnation and curing conditions of the carbon fiber sheets on the flexural strengthening efficiency. The results indicated that the tested ultimate capacity of the carbon fiber sheet-anchor assembly reached 72.1∼97.9% of the theoretical ultimate capacity of the carbon fiber sheet based on different impregnation and curing conditions. The concrete crushing failure and rupture failure of prestressed carbon fiber sheets occurred in the strengthened RC beams. The cracking and yielding loads of the RC beams with prestressed sheets were increased by 56.7∼68.5% and 21.7∼30%, respectively, while those with non-prestressed sheets were increased by 27.3% and 13.7%, respectively. The ultimate load was significantly affected by the impregnation and curing conditions. The prestressed carbon fiber sheets with the uncured full impregnation condition were not superior to the non-prestressed sheets in terms of the ultimate load, whereas the cured full impregnation and partial impregnation conditions were more effective than the uncured full impregnation condition. Finally, theoretical equations were used to calculate the cracking, yielding, and ultimate moments of RC beams strengthened with prestressed carbon fiber sheets. • A new and practical prestressing system of the carbon fiber sheets was developed for strengthening RC beams. • The anchorage behavior was verified by the tensioning tests of the carbon fiber sheet-anchor assemblies. • Three impregnation and curing conditions of the carbon fiber sheets were designed and compared. • Impregnation and curing conditions significantly affected the ultimate load and failure mode. [ABSTRACT FROM AUTHOR]