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This study evaluated the effectiveness of carbon fiber–reinforced polymer (CFRP) composites in strengthening RC beams for a simple span overhanging from both ends and subjected to equal concentrated forces at each end. This innovative loading configuration allows for investigating the performance of CFRP composites under pure moment within the middle span and ensuring continuity of the moment over the supports, which cannot be captured using the classical simple span with four-point loading configuration. A nonlinear finite-element analysis (NLFEA) using Abaqus software was carried out to accomplish the objectives of this study. The NLFEA models were verified initially based on independent experimental results from the literature to calibrate the NLFEA models in terms of the material constitutive models, boundary conditions, and meshing. Then 12 NLFEA models were created with different strengthening schemes of CFRP strips, varying in terms of length and number of layers, in addition to a control beam. All the evaluated RC beams were similar in terms of length and cross-sectional dimensions, material properties, and steel reinforcement. The results revealed that the developed NLFEA models can reasonably simulate the flexural behavior and failure mode of the studied RC beams, which are significantly affected by the configuration and length of the CFRP strips. The results also indicated that it is essential to extend the CFRP strips from the middle span toward the overhanging span to provide continuity and allow the CFRP strips to contribute effectively to the flexural strength. [ABSTRACT FROM AUTHOR]

In this paper the fatigue performance of strengthened steel plate girders with CFRP strips was investigated using numerical models. The cracked plate girders were strengthened by different reinforcement configurations at high damage level of web plate. The research confirmed that the strengthening by CFRP strips leads to a significant increase of the fatigue life and reduction of the crack propagation, especially the strengthening for both flange and web. Moreover, the study proposed V-Shape strengthening system by CFRP strips around the crack in the web plate. Consequently, the results demonstrated that U-shape strengthening system with prestressed CFRP has the best efficiency for fatigue strengthening. On the other hand, the fatigue analysis based on stress life method was performed by using S-N curve to predict the actual total fatigue life for the steel plate girder without initial damage. Therefore, the results showed that the fatigue damage of plate girders starts to appear at maximum loading (0.5P_y). Furthermore, the load capacity and the age at which the strengthening should start were studied as parameters. Finally, the results concluded that an early repair for plate girders is more efficient in improving the fatigue performance, especially when the bridge is subjected to heavy loads.

Currently, there is not much research on strengthening structural elements with hollows. This manuscript presents the test results from twelve circular reinforced concrete column specimens strengthened with CFRP strips. This study focuses on the strain behavior of longitudinal reinforcement and CFRP strips due to high shear force intensity. Hollows in the cross-section are used to see the effect of voids on the column strain distribution. Nine specimens have a hollow cross-section with hollow diameters of 1.5", 2.5", and 3.5" for each of the three specimens. Meanwhile, the other three specimens have a solid crosssection. All specimens do not use stirrups to determine the contribution of concrete and CFRP strips to resist shear. Strain gauges are placed in certain positions to read the strain on the longitudinal reinforcement and CFRP strips. The test results are in the form of tensile forces and are then analyzed to obtain the movement pattern of tensile forces in the longitudinal reinforcement and CFRP strips. Numerical analysis using a fiber element model is used to obtain the strain in each reinforcement layer. The numerical analysis results were then compared with the test results and showed close results. Then, an equation for calculating the tensile force in CFRP strips is proposed. The proposed equation approximates the test results with an accuracy level of 90%.

Copyright of Tikrit Journal of Engineering Sciences is the property of Republic of Iraq Ministry of Higher Education & Scientific Research (MOHESR) and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Concrete corbels are short cantilevers subjected to monotonic and repeated loads. Repeated loads generally negatively affect the concrete structural members' strength as they decrease the resistance to external loads. To increase these loads, strengthening with carbon fiber reinforced polymer (CFRP) strips as an externally bounded technique is used. This paper studies the behavior and strength of strengthened corbels subjected to monotonic and repeated (constant and incremental) loads. The experimental program included the casting and testing of twelve double-concrete corbels. All specimens have been kept constant for corbel dimensions and main and secondary reinforcement. Nine were strengthened with CFRP strips using different patterns, while the others were left un-strengthened as control corbels. The results showed that both repeated loads' types, i.e., constant and incremental, affected the ultimate load capacity of corbels. Compared to monotonic loading, a reduction occurred in ultimate load and ultimate deflection for corbels subjected to five repeated loading cycles. For corbels strengthened by externally bounded CFRP strips under any applied loads, the ultimate load significantly increased, while the ultimate deflection decreased compared to un-strengthened at the same applied load. All corbels failed by de-bonding the CFRP strips.

This study investigated the influence of CFRP composite wrapping techniques on the load–deflection and strain relationships of non-prismatic RC beams. A total of twelve non-prismatic beams with and without openings were tested in the present study. The length of the non-prismatic section was also varied to assess the effect on the behavior and load capacity of non-prismatic beams. The strengthening of beams was performed by using carbon fiber-reinforced polymer (CFRP) composites in the form of individual strips or full wraps. The linear variable differential transducers and strain gauges were installed at the steel bars to observe the load–deflection and strain responses of non-prismatic RC beams, respectively. The cracking behavior of unstrengthened beams was accompanied by excessive flexural and shear cracks. The influence of CFRP strips and full wraps was primarily observed in solid section beams without shear cracks, resulting in enhanced performance. In contrast, hollow section strengthened beams exhibited minor shear cracks alongside the primary flexural cracks within the constant moment region. The absence of shear cracks was reflected in the load–deflection curves of strengthened beams, which demonstrated a ductile behavior. The strengthened beams demonstrated 40% to 70% higher peak loads than control beams, whereas the ultimate deflection was increased up to 524.87% compared to that of the control beams. The improvement in the peak load was more prominent as the length of the non-prismatic section increased. A better improvement in ductility was achieved for the case of CFRP strips in the case of short non-prismatic lengths, whereas the efficiency of CFRP strips was reduced as the length of the non-prismatic section increased. Moreover, the load–strain capacity of CFRP-strengthened non-prismatic RC beams was higher than the control beams. [ABSTRACT FROM AUTHOR]

This paper presents the theoretical behaviors of concrete beams with and without stirrups under drop weight testing. The main objective of this work is to investigate numerically the influence of different types of longitudinal steel reinforcement (steel bars and FRP bars) on the impact behavior of concrete beams in terms of peak load, and deflection. In addition, the effect of drop height, the presence of stirrups, the concrete compressive strength of the concrete beams, and strengthening concrete beams by FRP strips have been involved in investigating their contribution to the behavior of the impact response. The analytical work has been carried out using ABAQUS/CAE 2019. Firstly, the model has been validated against four beams tested experimentally with various impact heights. Then, four groups of beams with different parameters have been simulated and tested under the same impact loading conditions. The first group has consisted of four beams with normal concrete strength reinforced by FRP bars. The second group has been strengthened externally by CFRP strips. The third and the fourth groups are with stirrups and higher grade of concrete, respectively. It has been found out that the current simulation could be an effective tool for predicting the dynamic performance of beams with and without stirrups subjected to impact loading. Furthermore, the improvements done to the available experimental specimens have led to increase the peak impact load and decrease the ultimate deflection. [ABSTRACT FROM AUTHOR]

In the last few decades, several contributions have used the Fiber Reinforced Polymer (FRP) for reinforcing slabs. However, previous studies disregarded the effect of spacing between the bands of the Carbon Fiber Reinforced Polymer (CFRP), which appears scientifically to be of great importance for enriching the literature. The principal objective of this paper is to ascertain the experimental data and results on the strengthened concrete slabs’ behavior when changing the spacing between the CFRP bands. To meet this objective, six slabs with 600 mm length, 500 mm width, and 50 mm thickness have been utilized. To begin with, we have put to test one reference slab without strengthening while the other slabs were strengthened with CFRP strips. Secondly, the strengthened slabs have been reinforced with three CFRP bands of 50 mm wide by varying either the spacing between them among 50 mm, 100 mm, and 150 mm, or the number of the CFRP layers. This research paper casts light on several points describing the strengthened concrete slabs’ behavior. It is worth mentioning that the slab breaking load increased when the spacing between the CFRP strips was small; and the bands were distributed close to the center.

Copyright of Journal of Engineering (17264073) is the property of Republic of Iraq Ministry of Higher Education & Scientific Research (MOHESR) and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

This work presented some selected results of laboratory tests and FEM analysis study of simple supported RC beams strengthened using carbon strips. The beams were examined to establish the effectiveness of this method of strengthening in terms of increasing their load-carrying capacity as well as flexural stiffness at different preloading states. A set of beams was divided into five groups, which differ in the level of the load applied before application of the composite strips on their bottom surfaces. Laboratory tests were supplemented with numerical analyses based on the finite-element method (FEM) using Abaqus software. The created numerical models were validated, and good agreement of the experimental results with the results obtained in the numerical analyses was observed. The deformation state existing in the main reinforcing bars, in concrete as well as in the strengthening composite strip, and its influence on the failure mechanism of the beams were analyzed. In the stiffness analysis, it was assumed that the stiffness of a beam strengthened with composite material after the elastic range (concrete and reinforcement steel) can be represented by the relation between the stiffness of the noncracked section B and beam curvature κ. The curvature–bending moment diagram as well as bending moment–stiffness diagram were prepared on the basis of laboratory and numerical results. Based on the results, it can be stated that the preload on the beam before strengthening affects the levels of deformation and the utilization rates of the composite material as well as reinforcing bars. The curvature and stiffness of the beams depend on the load level at which the CFRP strip strengthening is realized. The results of the analysis of preloaded beams before strengthening indicate that totally relieving them prior to strip application turns out to be the most beneficial solution. [ABSTRACT FROM AUTHOR]

This paper presents an experimental and numerical study into the shear response of brick masonry triplet prisms under different levels of precompression, as well as samples reinforced with carbon fiber-reinforced polymer (CFRP) strips. Masonry triplets were constructed with two different mortar mix ratios (1:1:3 and 1:1:5). In this study, finite element models for the analysis of shear triplets are developed using detailed micro-modelling (DMM) approach and validated with the experimental data. The failure mechanisms observed in the masonry triplets were simulated using a coupled XFEM-cohesive behaviour approach in ABAQUS finite element software. The nonlinear behaviour of mortar and brick was simulated using the concrete damaged plasticity (CDP) constitutive laws. The cohesive element with zero thicknesses was employed to simulate the behaviour of the unit–mortar interfaces. The extended finite element method (XFEM) was employed to simulate the crack propagation in the mortar layer without an initial definition of crack location. CFRP strips were simulated by 3D shell elements and connected to masonry elements by an interface model. The changes in failure mechanism and shear strength are calculated for varying types of mortar and fiber orientation of CFRP composite. Based on this study, it was concluded that the ultimate shear strength of masonry triplets is increased due to the external bonding of CFRP strips. The performance of masonry specimens strengthened with CFRP strips is assessed in terms of gain in shear strength and post-peak behaviour for all configurations and types of mortar considered. The comparison of FE and experimental results proved that the models have the potential to be used in practice to accurately predict the shear strength and reflect damage progression in unreinforced and CFRP-reinforced masonry triplets under in-plane loading, including the debonding of the CFRP reinforcement. Additionally, XFEM was found to be a powerful technique to be used for the location of crack initiation and crack propagation in the mortar layer. [ABSTRACT FROM AUTHOR]

This study investigated the influence of CFRP composite wrapping techniques on the load–deflection and strain relationships of non-prismatic RC beams. A total of twelve non-prismatic beams with and without openings were tested in the present study. The length of the non-prismatic section was also varied to assess the effect on the behavior and load capacity of non-prismatic beams. The strengthening of beams was performed by using carbon fiber-reinforced polymer (CFRP) composites in the form of individual strips or full wraps. The linear variable differential transducers and strain gauges were installed at the steel bars to observe the load–deflection and strain responses of non-prismatic RC beams, respectively. The cracking behavior of unstrengthened beams was accompanied by excessive flexural and shear cracks. The influence of CFRP strips and full wraps was primarily observed in solid section beams without shear cracks, resulting in enhanced performance. In contrast, hollow section strengthened beams exhibited minor shear cracks alongside the primary flexural cracks within the constant moment region. The absence of shear cracks was reflected in the load–deflection curves of strengthened beams, which demonstrated a ductile behavior. The strengthened beams demonstrated 40% to 70% higher peak loads than control beams, whereas the ultimate deflection was increased up to 524.87% compared to that of the control beams. The improvement in the peak load was more prominent as the length of the non-prismatic section increased. A better improvement in ductility was achieved for the case of CFRP strips in the case of short non-prismatic lengths, whereas the efficiency of CFRP strips was reduced as the length of the non-prismatic section increased. Moreover, the load–strain capacity of CFRP-strengthened non-prismatic RC beams was higher than the control beams.

To research the axial compression behavior of steel reinforced recycled concrete (SRRC) short columns confined by carbon fiber reinforced plastics (CFRP) strips, nine scaled specimens of SRRC short columns were fabricated and tested under axial compression loading. Subsequently, the failure process and failure modes were observed, and load-displacement curves as well as the strain of various materials were analyzed. The effects on the substitution percentage of recycled coarse aggregate (RCA), width of CFRP strips, spacing of CFRP strips and strength of recycled aggregate concrete (RAC) on the axial compression properties of columns were also analyzed in the experimental investigation. Furthermore, the finite element model of columns which can consider the adverse influence of RCA and the constraint effect of CFRP strips was founded by ABAQUS software and the nonlinear parameter analysis of columns was also implemented in this study. The results show that the first to reach the yield state was the profile steel in the columns, then the longitudinal rebars and stirrups yielded successively, and finally RAC was crushed as well as the CFRP strips was also broken. The replacement rate of RCA has little effect on the columns, and with the substitution rate of RCA from 0 to 100%, the bearing capacity of columns decreased by only 4.8%. Increasing the CFRP strips width or decreasing the CFRP strips spacing could enhance the axial bearing capacity of columns, the maximum increase was 10.5% or 11.4%, and the ductility of columns was significantly enhanced. Obviously, CFRP strips are conducive to enhance the axial bearing capacity and deformation capacity of columns. On this basis, considering the restraint effect of CFRP strips and the adverse effects of RCA, the revised formulas for calculating the axial bearing capacity of SRRC short columns confined by CFRP strips were proposed. [ABSTRACT FROM AUTHOR]

The potential of recovering the flexural performance of thermally damaged concrete beams using carbon fiber reinforced polymer (CFRP) strips with groove technique was experimentally investigated. Twenty reinforced concrete beams (150 × 200 × 1100 mm) were cast then cured for 28 days in moist burlap. A set of thirty-nine beams were heated at 250 °C, 500 °C, and 750 °C for two hours using an electrical furnace, whereas those of the second set of thirteen beams were left in laboratory air (23 °C). Nevertheless, debonding and anchoring problems remain a challenge for the success of this technique. In this study, an innovative application was implemented in which CFRP strip length with different lengths was integrated as external flexural reinforcement for reinforced concrete beams by using the groove technique. The intent was to assess the contribution of the CFRP strips to the flexural strength and thus evaluate the effectiveness of using them as primary or supplemental flexural reinforcement before and after exposing to elevated temperature. The investigated parameters include the number of transverse grooves and different elevated temperatures. The mechanical performance of other beams was evaluated under a four-point loading test setup, including measurement of strain in CFRP strips and mid-span deflection. Moreover, cracking and failure modes were monitored and characterized. Intact/strengthened and heat-damaged/strengthened beams showed improved ultimate strength, ultimate deflection, stiffness, and toughness compared to control ones. Different performance indicators revealed the good potential of strengthened heat-damaged beams using CFRP strips with grooves. Furthermore, the results showed that the grooving method performs better than surface preparation without grooves. So that the strengthening with grooves prevents premature delaminating and some of the concrete shatters in the tension side, and the weakness of beams in debonding phenomena disappeared, and flexural failure became dominant failure mode with full attachment of CFRP strips with concrete.

In the last few decades, several contributions have used the Fiber Reinforced Polymer (FRP) for reinforcing slabs. However, previous studies disregarded the effect of spacing between the bands of the Carbon Fiber Reinforced Polymer (CFRP), which appears scientifically to be of great importance for enriching the literature. The principal objective of this paper is to ascertain the experimental data and results on the strengthened concrete slabs' behavior when changing the spacing between the CFRP bands. To meet this objective, six slabs with 600 mm length, 500 mm width, and 50 mm thickness have been utilized. To begin with, we have put to test one reference slab without strengthening while the other slabs were strengthened with CFRP strips. Secondly, the strengthened slabs have been reinforced with three CFRP bands of 50 mm wide by varying either the spacing between them among 50 mm, 100 mm, and 150 mm, or the number of the CFRP layers. This research paper casts light on several points describing the strengthened concrete slabs' behavior. It is worth mentioning that the slab breaking load increased when the spacing between the CFRP strips was small; and the bands were distributed close to the center. [ABSTRACT FROM AUTHOR]

This paper presents the results of experimental testing on fifteen reinforced concrete (RC) columns repaired or strengthened using Near Surface Mounted-Carbon Fiber Reinforced Polymer (NSM-CFRP) under concentric load, eccentric load with 125 mm eccentricity (balanced state), and pure bending moment load, while considering the effect of several configurations on the interaction diagram. Furthermore, this paper investigates the efficiency of these new configurations in the capacity of the RC columns by varying the direction of CFRP strips to be used as reinforcement. The specimens of RC columns, having cross-sectional dimensions 1200 mm × 200 mm × 200 mm (length × width × height) with 150 mm corbel at both ends (in the plane of bending moment) and 1.13 % steel reinforcement ratio, were used. The specimens were divided into five groups: control group, preloaded until 80 % transversely strengthened group, preloaded until 80 % longitudinally strengthened group, preloaded until 80 % transversely and longitudinally strengthened group, and un-loaded transversely and longitudinally strengthened group. Each group included three specimens with a different type of loading as described above. The overall response of the specimens was investigated in terms of axial load carrying capacity, axial displacement, toughness, and failure modes. Furthermore, the interaction diagram for each group was developed and investigated. The strengthened and retrofitted specimens showed a significant increase in axial capacity and significant enhancement in the interaction diagram for all groups. The study showed that the most improvement in the interaction diagram, for both tension and compression control region, occurred when specimens were strengthened in both directions (transversely and longitudinally). In addition, the interaction diagrams were modified to provide a direct solution for the NSM-CFRP ratio. The modified design model was found to be capable of predicting the axial load capacity of NSM-CFRP strips columns.

The prestressed unidirectional carbon fibre reinforced polymer (CFRP) strips are currently often used for flexural strengthening of concrete structures. To ensure reliable strengthening, strips have to be anchored at their ends to the surface. However, anchoring of unidirectional CFRP strips is difficult because of their weak transversal mechanical properties. Although several CFRP strip anchorage approaches have been developed to date, only very few were applied on-site. The paper presents the development of hybrid bonded/bolted anchorages of CFRP strips used in a novel prestressing system. The anchorages are made of thin steel plates, clamped with the high-strength friction grip (HSFG) bolts and epoxy adhesive, to fix the CFRP strips. The paper describes the results of full-scale tests carried out on a series of axial tensile specimens. The developed anchorage has an ultimate tensile strength of about 200 kN, i.e. 70% of the ultra-high CFRP strips' strength, which is sufficient for strengthening purposes. After a series of tests in the laboratory, the anchorages have been implemented on-site and an example is presented in the paper. [ABSTRACT FROM AUTHOR]

The practical difficulties in upgrading the structural performance of existing reinforced concrete (RC) structures is discussed, when retrofitting structural members by conventional RC jacketing. The use of retrofitting schemes employing externally applied fiber reinforcing polymer (FRP) strips attracted considerable research attention as a preferable alternative. Such retrofitting FRP schemes aiming to upgrade the shear capacity of existing RC beams have been examined in many published works employing such externally applied FRP shear reinforcing schemes without confronting the practical difficulties arising from the presence of the RC slab. Anchoring external CFRP strips aiming to shear upgrade, which is the focus here, overrides this difficulty. It is shown that effective anchoring, using either mechanical anchors such as the ones devised by the authors or CFRP anchor ropes produced by the industry, can effectively upgrade the shear capacity of an RC T-beam under-designed in shear to the desired level. A novel laboratory test set-up, devised by the authors, can be utilized to quantify the tensile capacity of CFRP stirrups with or without anchors, that can be of practical use. The predicted, according to design guidelines, upgraded shear capacity of the tested prototype RC T-beam, employing the used shear retrofitting schemes, under-estimates the measured shear capacity by 58%. This conservatism can counter-balance uncertainties arising from in situ conditions in constructing the various parts of such a shear retrofitting scheme. [ABSTRACT FROM AUTHOR]

Copyright of Advanced Engineering Science / Gongcheng Kexue Yu Jishu is the property of Advanced Engineering Science Editorial Office and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

This work presented some selected results of laboratory tests and FEM analysis study of simple supported RC beams strengthened using carbon strips. The beams were examined to establish the effectiveness of this method of strengthening in terms of increasing their load-carrying capacity as well as flexural stiffness at different preloading states. A set of beams was divided into five groups, which differ in the level of the load applied before application of the composite strips on their bottom surfaces. Laboratory tests were supplemented with numerical analyses based on the finite-element method (FEM) using Abaqus software. The created numerical models were validated, and good agreement of the experimental results with the results obtained in the numerical analyses was observed. The deformation state existing in the main reinforcing bars, in concrete as well as in the strengthening composite strip, and its influence on the failure mechanism of the beams were analyzed. In the stiffness analysis, it was assumed that the stiffness of a beam strengthened with composite material after the elastic range (concrete and reinforcement steel) can be represented by the relation between the stiffness of the noncracked section B and beam curvature κ. The curvature–bending moment diagram as well as bending moment–stiffness diagram were prepared on the basis of laboratory and numerical results. Based on the results, it can be stated that the preload on the beam before strengthening affects the levels of deformation and the utilization rates of the composite material as well as reinforcing bars. The curvature and stiffness of the beams depend on the load level at which the CFRP strip strengthening is realized. The results of the analysis of preloaded beams before strengthening indicate that totally relieving them prior to strip application turns out to be the most beneficial solution.

This paper presents an experimental and numerical study into the shear response of brick masonry triplet prisms under different levels of precompression, as well as samples reinforced with carbon fiber-reinforced polymer (CFRP) strips. Masonry triplets were constructed with two different mortar mix ratios (1:1:3 and 1:1:5). In this study, finite element models for the analysis of shear triplets are developed using detailed micro-modelling (DMM) approach and validated with the experimental data. The failure mechanisms observed in the masonry triplets were simulated using a coupled XFEM-cohesive behaviour approach in ABAQUS finite element software. The nonlinear behaviour of mortar and brick was simulated using the concrete damaged plasticity (CDP) constitutive laws. The cohesive element with zero thicknesses was employed to simulate the behaviour of the unit–mortar interfaces. The extended finite element method (XFEM) was employed to simulate the crack propagation in the mortar layer without an initial definition of crack location. CFRP strips were simulated by 3D shell elements and connected to masonry elements by an interface model. The changes in failure mechanism and shear strength are calculated for varying types of mortar and fiber orientation of CFRP composite. Based on this study, it was concluded that the ultimate shear strength of masonry triplets is increased due to the external bonding of CFRP strips. The performance of masonry specimens strengthened with CFRP strips is assessed in terms of gain in shear strength and post-peak behaviour for all configurations and types of mortar considered. The comparison of FE and experimental results proved that the models have the potential to be used in practice to accurately predict the shear strength and reflect damage progression in unreinforced and CFRP-reinforced masonry triplets under in-plane loading, including the debonding of the CFRP reinforcement. Additionally, XFEM was found to be a powerful technique to be used for the location of crack initiation and crack propagation in the mortar layer.

Exposure of concrete structures to elevated temperatures causes a severe deterioration because of decomposition of cement hydration products, generation of vapor pressure, and the inhomogeneous volume changes of concrete's ingredients and beyond a temperature of 500 °C. The most Retrieval the structural performance of severely heat-damaged structural concrete members would be most significantly achieved using carbon fiber-reinforced polymer (CFRP) composite materials. Nevertheless, debonding and anchoring problems remain a challenge for the success of this technique. In this study, an innovative application was implemented in which CFRP strips were integrated as external shear reinforcement for reinforced concrete (RC) beams by using the groove technique. The intent was to assess the CFRP strips' contribution to the shear strength and thus evaluate the effectiveness of using them as main or supplemental shear reinforcement before and after exposure to elevated temperature. The investigated parameters include the area and number of layers of CFRP strips and different elevated temperatures. By demonstrating an outstanding structural performance with significant enhancement in the ultimate strength, ultimate deflection, stiffness, and toughness, this paper's findings strongly attest that CFRP strips can be effectively utilized as external shear reinforcement in reinforced concrete beams exposed to elevated temperatures. New guideline and proposed empirical model are developed to predict the damage level and shear strength of heated damaged RC beams externally reinforced with CFRP composites considering the influence of the number of CFRP strips and elevated temperature as groove technique.

In this study, an innovative application was implemented in which CFRP strips were integrated as internal shear reinforcement for reinforced concrete beams. The intent was to assess the CFRP strips' contribution to the shear strength and thus evaluate the effectiveness of using them as main or supplemental shear reinforcement before and after exposure to elevated temperature. Internal application of CFRP strips does not require an epoxy for attaching them, as they can be cut without difficulty to any width/length and then attaching them to the main steel bars. Similar to the steel shear stirrups, the CFRP strips work integrally with the beam concrete and steel reinforcement as the concrete confines them. The proposed technique applies only to new reinforced concrete (RC) elements and not as retrofitting existing members' strategy. Instead, externally bonded CFRP strips represent a popular strategy for structural retrofitting purposes. The investigated parameters include the area and number of layers of CFRP strips and different elevated temperatures. By demonstrating an outstanding structural performance with significant enhancement in the ultimate strength, ultimate deflection, stiffness, and toughness, this paper's findings strongly attest that CFRP strips can be effectively utilized as internal shear reinforcement in reinforced concrete beams exposed to elevated temperatures. A new guideline is proposed for predicting the damage level and shear strength of heated damaged RC beams internally reinforced with CFRP composites taking into consideration the influence of the number of CFRP strips and elevated temperature

This paper presents an experimental study of structural behavior of self compacting reinforced concrete beams strengthened in shear by vertical CFRP strips. The experimental work consists of casting and testing of eleven simply supported reinforced concrete beams. One of the tested beam was un-strengthened to be considered as beams, while the remaining beams were tested after being strengthened using vertical CFRP strips. In this study, three parameters were considered, the configuration of CFRP sheets wrapping system, i.e. two sides, U-shape and full wrapped, effect of horizontal strap of CFRP strips to enhance the vertical CFRP strips and CFRP amount. The results showed that the presence of horizontal strap of CFRP strips on the vertical strips increases the shear capacity of the beams ranged between (3-27)% for beams with the same properties, while the increase in the ultimate loads ranged between (20-26)% and (39.5-46)% by comparison of wrapping system (two side with U-shape) and (two side with full wrapped) of CFRP strips, respectively.

Considering that the use of thin-walled shells is expanding every day, it is important to examine the problem of instability in this form of structure. Many steel structures such as high-water tanks, water and oil reservoirs, marine structures, and pressure vessels, including shell elements, are under stress tension. In addition, shell elements are subject to instability owing to the loads applied. Ten thin-walled cylindrical shell specimens in two groups with different dent depths of tc and 2tc, and the different dent number subject to uniform external pressure were tested in the present research (tc is the thickness of cylindrical shell). The samples were modified to include either one or two dent line with amplitudes of h/3 in height (h the height of cylinder shell). Moreover, CFRP Strips on the dent depth was used in one of the groups. The results of testing under different theories and codes are compared. [ABSTRACT FROM AUTHOR]

This work is the result of experimental research conducted to determine the contribution of a composite material to improving the mechanical behavior of old, full-size reinforced T-beams in operation conditions under the action of short-term loads. The tension side of their ribs were strengthened by carbon strips of different lengths. Then, they were tested in loading by concentrated and uniformly distributed short-term loads. It was concluded that, for strengthening simply supported beams, there was no need for using CFRP strips longer than half of their length, and a lateral anchorage was not required. This refers to bending tests where no load increment exceeding 60% of the flexural strength is expected. The results obtained from this experiment may be of use in modern engineering practices, especially because tests conducted on old, full-size samples are very rare. [ABSTRACT FROM AUTHOR]

The practical difficulties in upgrading the structural performance of existing reinforced concrete (RC) structures is discussed, when retrofitting structural members by conventional RC jacketing. The use of retrofitting schemes employing externally applied fiber reinforcing polymer (FRP) strips attracted considerable research attention as a preferable alternative. Such retrofitting FRP schemes aiming to upgrade the shear capacity of existing RC beams have been examined in many published works employing such externally applied FRP shear reinforcing schemes without confronting the practical difficulties arising from the presence of the RC slab. Anchoring external CFRP strips aiming to shear upgrade, which is the focus here, overrides this difficulty. It is shown that effective anchoring, using either mechanical anchors such as the ones devised by the authors or CFRP anchor ropes produced by the industry, can effectively upgrade the shear capacity of an RC T-beam under-designed in shear to the desired level. A novel laboratory test set-up, devised by the authors, can be utilized to quantify the tensile capacity of CFRP stirrups with or without anchors, that can be of practical use. The predicted, according to design guidelines, upgraded shear capacity of the tested prototype RC T-beam, employing the used shear retrofitting schemes, under-estimates the measured shear capacity by 58%. This conservatism can counter-balance uncertainties arising from in situ conditions in constructing the various parts of such a shear retrofitting scheme.

To accommodate utilities in buildings, different sizes of openings are provided in the web of reinforced concrete deep beams, which cause reductions in the beam strength and stiffness. This paper aims to investigate experimentally and numerically the effectiveness of using carbon fiber reinforced polymer (CFRP) strips, as a strengthening technique, to externally strengthen reinforced concrete continuous deep beams (RCCDBs) with large openings. The experimental work included testing three RCCDBs under five-point bending. A reference specimen was prepared without openings to explore the reductions in strength and stiffness after providing large openings. Openings were created symmetrically at the center of spans of the other specimens to represent 40% of the overall beam depth. Moreover, finite elements (FE) analysis was validated using the experimental results to conduct a parametric study on RCCDBs strengthened with CFRP strips. The results confirmed reductions in the ultimate load by 21% and 7% for the un-strengthened and strengthened specimens, respectively, due to the large openings. Although the large openings caused reductions in capacities, the CFRP strips limited the deterioration by enhancing the specimen capacity by 17% relative to the un-strengthened one.

This paper presents an experimental study of structural behavior of self compacting reinforced concrete beams strengthened in shear by vertical CFRP strips. The experimental work consists of casting and testing of eleven simply supported reinforced concrete beams. One of the tested beam was un-strengthened to be considered as beams, while the remaining beams were tested after being strengthened using vertical CFRP strips. In this study, three parameters were considered, the configuration of CFRP sheets wrapping system, i.e. two sides, U-shape and full wrapped, effect of horizontal strap of CFRP strips to enhance the vertical CFRP strips and CFRP amount. The results showed that the presence of horizontal strap of CFRP strips on the vertical strips increases the shear capacity of the beams ranged between (3-27)% for beams with the same properties, while the increase in the ultimate loads ranged between (20-26)% and (39.5-46)% by comparison of wrapping system (two side with U-shape) and (two side with full wrapped) of CFRP strips, respectively. [ABSTRACT FROM AUTHOR]

CFRP (carbon fiber reinforced polymer) strips are currently often used to strengthen reinforced concrete structures in flexure. In order to ensure effective strengthening, proper connection between FRP material and concrete structure is needed. CFRP strips can be applied passively (only by bonding to the concrete surface) or actively (by prestressing before bonding). In the case of passive strengthening, CFRP strips connecting by bonding to the surface along the strengthened element are usually sufficient. However, active (prestressing) CFRP strips should be additionally anchored at their ends. Anchoring of unidirectional CFRP strips to the reinforced concrete is difficult because of their weak properties in transverse directions. The paper presents a development of mechanical steel anchorages used in an active CFRP flexural strengthening system for reinforced concrete structures. The anchorages were made of steel plates connected to CFRP strips with steel rivets and epoxy adhesive. They were developed within series of tests on specimens from small-scale to full-scale tested in an axial tensile scheme. The paper describes successive modifications of the anchorages as well as the results of full-scale tests. The final version of the anchorage developed during the research had a tensile failure force of 185 kN, which is sufficient value for CFRP strengthening purposes.

Externally Bonded Reinforcement (EBR) technique has been widely used for flexural strengthening of concrete structures by using carbon fiber-reinforced polymers (CFRP). EBR technique offers several structural advantages when the CFRP material is prestressed. This paper presents an experimental and numerical study on reinforced (RC) slabs strengthened in flexure with prestressed CFRP strips as a structural strengthening system. The strips are applied as an externally bonded reinforcement (EBR) and anchored with either a mechanical or a gradient anchorage. The former foresees metallic anchorage plates fixed to the concrete substrate, while the latter is based on an accelerated epoxy resin curing followed by a segment-wise prestress force decrease at the strip ends. Both anchorage systems, in combination with different CFRP strip geometries, were subjected to static loading tests. It could be demonstrated that the composite strip’s performance is better exploited when prestressing is used, with slightly higher overall load carrying capacities for mechanical anchorages than for the gradient anchorage. The performed investigations by means of a cross-section analysis supported the experimental observation that in case a mechanical anchorage is used, progressive strip debonding changes the fully bonded configuration to an unbonded end-anchored system. The inclusion of defined debonding criteria for both the anchorage zones and free length between the anchorage regions allowed to precisely capture the ultimate loading forces.

The behavior and shear strength characteristics of eight SFRHSC beams strengthened with CFRP strips subjected to combined bending and shear are studied in the present research (in addition to a 9th control beam without CFRP strengthening). The studied variables were shear span to effective depth ratio (a/d) and the deep beam effect, the effect of end anchorage of the CFRP strips with the beams, and effect of the amount of wrapping (width and spacing of the CFRP strips).Tests show that the presence of end anchorage for the strips increases the shear capacity of the beams by 12%for beams with the same properties regardless to the compressive strength.

Highlights • PRC beams strengthened with NSM CFRP strips were tested under overloading. • Influence of cycle number, overload amplitude, and strengthening under loading was investigated. • The above three variables had limited influence on the ultimate bearing capacity. • The above three variables affected stiffness and ductility of the strengthened beams. Abstract This paper investigates the flexural behaviors of the damaged prestressed reinforced concrete (PRC) beams strengthened with near surface mounted (NSM) carbon fiber-reinforced polymers (CFRP) strips under overloading. A bending test was carried out to evaluate the effects of three variables: the cycle number, overload amplitude and strengthening under loading or unloading. Different damage degrees were mainly controlled by cycle number and overload amplitude. The test results showed that strengthening with NSM CFRP strips could effectively inhibit crack development. Compared with the un-strengthened beam, the flexural load-carrying and stiffness of the strengthened beams were enhanced evidently. With the increase of cycle number and overload amplitude, the yield loads increased. The yield load of strengthened beam under unloading was higher than that of strengthened beams under loading. These three variables had limited influence on the ultimate bearing capacity. The deformations of the strengthened beams were smaller than that of the control beam, and decreased with the increase of cycle number, but increased with the increase of overload amplitude. The deformations of the strengthened beams under loading were slightly greater than that of the strengthened beam under unloading in the early phase but smaller in the later phase. The ductility of strengthened beams was evidently reduced compared with that of the control beam. The displacement ductility factors of the strengthened beams under loading decreased with the increase of cycle number and overload amplitude, and were smaller than that of strengthened beam under unloading. [ABSTRACT FROM AUTHOR]

In order to investigate the performance of damaged reinforced concrete beams strengthened with near surface mounted (NSM) carbon fiber reinforced polymer (CFRP) strips under overloading， the bending test of five reinforced concrete beams was carried out. The overloading state was simulated， and the failure mode， capacity and stiffness were studied. The influences of the overload cycle number and overload amplitude on the performance of reinforced concrete beams were also evaluated. The results show that embedding CFRP strips can enhance the capacity of overloaded damaged reinforced concrete beams to about 16% to 27%. The cycle number and overload amplitude affect the yield and ultimate load and stiffness in different ways. The yield and ultimate load decrease with the increase of cycle number and overload amplitude. The stiffness decreases with the increase of cycle number. The formula of ultimate bearing capacity is established， and the calculated results agree well with the experimental results. [ABSTRACT FROM AUTHOR]

Near Surface Mounted (NSM) reinforcement has been increasingly recognized as an efficient technique for strengthening Reinforced Concrete (RC) structures using Fiber Reinforced Polymer (FRP) reinforcement. Although a number of studies have investigated the short-term bond behavior between NSM FRP and concrete, little work has been done on its long-term behavior under sustained loading. This paper aims to experimentally investigate the bond response of NSM Carbon FRP (CFRP) strips in concrete under sustained loading and different temperature and humidity conditions. Thirty-three single shear pull-out specimens were subjected to monotonic and sustained loading. The long-term pull-out specimens were subjected to different environmental regimes including four combinations of temperature, humidity and sustained loading. For each environmental combination, three bonded lengths were tested and two levels of sustained loading were applied. Specimens were kept loaded and conditioned in a climatic chamber for 1000 h, while the slip evolution with time was monitored throughout the testing period. Results revealed that the changes in the parameters being studied did have a relevant effect on the bond response. [ABSTRACT FROM AUTHOR]

Side Near Surface Mounted (SNSM) strengthening technique is among the latest technique introduced recently. In this paper, SNSM carbon fiber reinforced polymer (CFRP) strips strengthening technique is proposed for enhancing the flexural performance of reinforced concrete (RC) beams. A total of seven RC beam specimens were tested: one un-strengthened control specimen, and six specimens strengthened by SNSM-CFRP strips. All beam specimens were tested under four-point bending. Analytical prediction methods were used to verify the experimental results. The load, mid-span, deflection, and strains data were recorded until failure of the specimens. The ductility, stiffness, and energy absorption capacity of the strengthened specimens by CFRP strips were enhanced due to SNSM technique. The results also showed that the SNSM-CFRP strips strengthening technique significantly enhanced the first cracking, yield, and ultimate load capacities up to 153%, 108%, and 147% respectively, compared with that of the control beam. Further, the comparison between the experimental and predicted values shows good agreement. [ABSTRACT FROM AUTHOR]

Using CFRP anchors to prevent the premature debonding failure of CFRP strips from concrete substrate is gaining acceptance. Although adequate CFRP anchors can fully develop the strength of CFRP strips, few recommendations for designing CFRP anchors are available. Based on experimental results obtained from 38 tests, a testing methodology using design strip strength is presented to evaluate the quality of CFRP anchors and to identify the design parameters including the strength ratio of CFRP anchor to CFRP strip, the strip width, the concrete strength, the fan angle, the embedment length, the bend radius, the hole diameter, the CFRP patch, the bond length and the bond condition. Design recommendations and installation procedures are also presented to ensure the desired performance of the anchorage system. [ABSTRACT FROM AUTHOR]

Efficient transfer of load between concrete substrate and fibre reinforced polymer (FRP) by the bonding agent is the key factor in any FRP strengthening system. An innovative high-strength self-compacting non-polymer cementitious adhesive (IHSSC-CA) was recently developed by the authors and has been used in a number of studies. Graphene oxide and cementitious materials are used to synthesise the new adhesive. The successful implementation of IHSSC-CA significantly increases carbon FRP (CFRP) strip utilization and the load-bearing capacity of the near-surface mounted (NSM) CFRP strengthening system. A number of tests were used to inspect the interfacial zone in the bonding area of NSM CFRP strips, including physical examination, pore structure analysis, and three-dimensional laser profilometery analysis. It was deduced from the physical inspection of NSM CFRP specimens made with IHSSC-CA that a smooth surface for load transfer was found in the CFRP strip without stress concentrations in some local regions. A smooth surface of the adhesive layer is very important for preventing localized brittle failure in the concrete. The pore structure analysis also confirmed that IHSSC-CA has better composite action between NSM CFRP strips and concrete substrate than other adhesives, resulting in the NSM CFRP specimens made with IHSSC-CA sustaining a greater load. Finally, the results of three-dimensional laser profilometery revealed a greater degree of roughness and less deformation on the surface of the CFRP strip when IHSSC-CA was used compared to other adhesives. [ABSTRACT FROM AUTHOR]

Torsion is resisted well by closed form reinforcement, due to the circulatory nature of the torsion inducing shear flow stresses in a beam. Therefore, it will be more efficient to have strengthening schemes, which are wrapped in closed form around the cross section. An experimental work was carried out and used superplasticizer with mix 1:1.5 to improve the mechanical properties of mortar. 12 rectangular beams (50x120)mm and 1m length are cast, strengthened and tested under pure torsion. The Variables considered in the test program include: effect number of wire mesh layers ( unit ), this unit consists of two layers of wire mesh with skeletal steel, (2, 3, 4) units and effect spacing of CFRP strips, (100,160,200) mm c/c. Test results are discussed based on torque – rotation behavior and influence of parameters on ultimate torque and failure modes. Generally, using optimum dosage of super plasticizer (1.4 % of weight of cement) gave compressive strength 65.65 MPa. Increasing the number of units from 2 to 4(reinforcement near the surface of beam section) led to increased ultimate torque by (13.44 %) and from 2 to 3(uniformly distributed reinforcement) led to increases the ultimate torque by only (3.24 %). When the beams are strengthened with CFRP strips, the lowest and highest increase in torque is at 112 % (4-units,@200 spacing) and 312 % (4-units,@100 spacing), respectively. The ultimate torque of beams with CFRP strips @ 100 mm and 160 mm spacing is greater than beams with CFRP strips @ 200 mm spacing by ( 94.34,45.28) %, respectively for the group having 4-units.

The purpose of this study is to improve the performance of walls under out-of-plane loads especially when subjected to the hammering action of the floors. The idea behind the paper is to provide the masonry walls with a device that behaves like a buttress, without having to build a traditional buttress. The solution presented in this paper consists of a mechanical coupling between the three-dimensional net of steel ribbons of the CAM (Active Confinement of Masonry) system and the CFRP (Carbon Fiber Reinforced Polymer) strips. Since the steel ribbons of the CAM system have a pre-tension, the mechanical coupling allows the steel ribbons to establish a semi-rigid transverse link between the CFRP strips bonded on the two opposite sides of a wall. Therefore, two vertical CFRP strips tied by the steel ribbons behave like the flanges of an I-beam and the flexural strength of the ideal I-beam counteracts the out-of-plane displacements of the wall. The experimental results showed that the combined technique inherits the strong points of both constituent techniques. In fact, the delamination load is comparable to that of the specimens reinforced with the CFRP strips and the overall behavior is as ductile as for the specimens reinforced with the CAM system. They also inspired a more performing combined technique.

In this study, a comprehensive 3D non-linear finite element modelling procedure is presented for the simulation of reinforced concrete flat plates, retrofitted with externally bonded carbon fibre-reinforced polymer (CFRP) strips and subjected to punching shear loads. The presented modelling procedure may be used to conduct parametric numerical analyses on the response of reinforced concrete elements similar to considered in this study. The modelling procedure is applied on: (i) a solid, un-retrofitted flat plate and (ii) eight flat plates with openings and retrofitted with externally bonded CFRP strips. In the procedure, debonding of CFRP strips from concrete surfaces is accounted for by defining appropriate bilinear shear stress–slip and normal stress–gap relationships. In the model, the corner lift-offs observed at the corners of the flat plates are also considered by defining appropriate restrains and frictional support conditions. Results obtained from the proposed modelling procedure are verified using experimental data available in the literature. From the verification, accuracy of the proposed modelling procedure is confirmed in terms of structural responses such as load displacement relationships and crack propagations of the test specimens. [ABSTRACT FROM PUBLISHER]