Carbon Fiber Reinforced Polymer Sheets Research Articles

Bond Slip Behavior for CFRP-to-Concrete Joints at Room Temperature

Fiber-reinforced polymer (FRP) composites have increasingly been used in the past 40 years. They are ideal option for external strengthening of reinforced concrete (RC) structures due to their superior properties, including the high strength-to-weight ratio and ease of installment. The structural behavior of strengthened RC beams and the efficiency of the external FRP applied are both highly dependent on the bond performance between FRP and concrete. This paper presents an experimental study on the bond slip behavior of carbon fiber reinforced polymer (CFRP) sheets, applied to concrete structures under room temperature conditions. The experimental investigation involved the strengthening of three concrete prism specimens with CFRP sheets. The prism specimens were tested under a three-point bending setup. The bond slip phenomenon was analyzed using strain gauge readings attached to the CFRP laminate before testing. The calculated model aimed to accurately capture the bond slip behavior and its associated parameters, including the maximum shear stress, and maximum slip. These parameters were compared with theoretically derived formulas available in the literature. The theoretical equations overestimated the FRP stresses when compared to experimental measurements. The comparative analysis assesses the accuracy and reliability of the theoretical derivations by benchmarking it against the experimentally derived bond-slip model for CFRP-to-concrete joints.

Durability of FRP-strengthened RC beams subjected to 110 months accelerated laboratory and field exposure

This paper presents an experimental investigation of the long-term performance of fiber reinforced polymer (FRP) composites strengthened reinforced concrete (RC) beams. The beam specimens had identical dimensions. Different FRP composites and adhesives were used, including carbon FRP (CFRP) plate bonded with Sika 30; CFRP plate bonded with Araldite 106; CFRP sheet bonded with SW-3C; and glass FRP (GFRP) bonded with Sika 330. Their performance was tested after 8, 18, 31, and 110 months of exposure to the wet-dry cyclic environment, and 48 and 110 months of exposure to the outdoor environment. Test results show that the FRP-strengthened RC beams subjected to the wet-dry cyclic environment exhibited more significant degradation compared to those subjected to the outdoor environment. In the wet-dry cyclic environment, CFRP plate/Sika 30 strengthened beams and CFRP sheet/SW-3C strengthened beams exhibited better durability performance with only 6 % and 4 % reductions in the flexural capacity after 110 months, respectively. In contrast, CFRP plate/Araldite 106 strengthened beams and GFRP sheet/Sika 330 strengthened beams exhibited larger reductions of 30 % and 31 %, respectively. Furthermore, the FRP debonding strain was reduced over time. A reduction factor is proposed for the design of FRP debonding strain based on test results to ensure long-term safety.

Performance of Steel Beams reinforced by CFRP Sheets with Fire-Retardant Coating

The objective of this study was to determine the physical, mechanical, and chemical aspects of bonding and priming Fire-Retardant Coatings (FRCs) to steel surfaces before and after fire testing. Carbon Fiber Reinforced Polymers (CFRP) have been used to strengthen steel components. Certain types of polymer systems have demonstrated high fire retardancy without additives, while others require additives to achieve optimum fire resistance. A wide range of compounds are available to enhance the fire retardant properties of these materials, characterized by their chemical nature and behavior (such as halogenated, metal complex, silicon-based, and phosphorus additives) and mode of action (either condensed or gas-phase active systems).This article provides a comprehensive overview of fire retardant additives for CFRP used in various large-scale applications, including the aerospace, automotive, railway, electronics, and civil engineering industries, as well as their fire retardant mechanisms at the microscopic, macroscopic, and nanoscale levels. In addition to fire retardant properties, this study also discusses the effects of additives on other material parameters and coatings, such as glass transition temperature, mechanical performance, and FRP processability. The primary focus is on thermoset systems, with a brief mention of thermoplastics according to the matrix compounds relevant to the FRP market size. Test results show that the direct velocity ultrasonic value varied between 3.016 and 3.618 km/s, giving an estimated compressive strength of 15.974 MPa. The standard deviation was 0.533 km/s with a relative standard deviation of 16.407%.

Reinforcement of RC Two-Way Slabs with CFRP Laminates: Plastic Limit Method for Carbon Emissions and Deformation Control

Carbon-fiber-reinforced polymer (CFRP) laminates have gained attention for their potential to reduce carbon emissions in construction. The impact of carbon-fiber-reinforced polymer (CFRP Laminate) on carbon emissions and the influence of elasto-plastic analysis on this technique were studied in this research. This study focuses on how CFRP can affect the environmental footprint of reinforced concrete structures and how elasto-plastic analysis contributes to optimizing this strengthening method. Four flat RC slabs were created to evaluate this technique in strengthening. One slab was used as a reference without strengthening, while the other three were externally strengthened with CFRP. The slabs, which were identical in terms of their overall (length, width, and thickness) as well as their flexural steel reinforcement, were subjected to concentrated patch load until they failed. The strength of two-way RC slabs was analyzed using a concrete plastic damage constitutive model (CDP). Additionally, CFRP strips were applied to the tension surface of existing RC slabs to improve their strength. The load–deflection curves obtained from the simulations closely match the experimental data, demonstrating the validity and accuracy of the model. Strengthening concrete slabs with CFRP sheets reduced central deflection by 17.68% and crack width by 40%, while increasing the cracking load by 97.73% and the ultimate load capacity by 134.02%. However, it also led to a 15.47% increase in CO2 emissions. Also, the numerical results show that increasing the strengthening ratio significantly impacts shear strength and damage percentage.

Carbon fiber reinforced polymer (CFRP) laminates: flexural strengthening method for prestressed concrete beams with anchorage loss

Abstract Post-tensioning (PT), a method of pre-stressing, involves the use of high-strength steel strands/ tendons to reinforce concrete or other materials. On the contrary, Carbon Fiber-Reinforced Polymers (CFRP) are lightweight, high-strength materials with used to strengthen concrete structures by adhering the polymer to the concrete element. Challenges with post-tensioned elements include reverse curvature of the post-tensioning strands, tendon misplacement, and frequent damage in the anchorage and dead-end zones. These difficulties frequently cause bulging of the surrounding concrete, even at lower stress levels, and can lead to concrete bursting when tension exceeds certain threshold. This study investigates into the potential of CFRP strengthening technique to improve the flexural capacity of post-tensioned concrete beams with anchorage loss. Through an experimental program, the study compares the performance of control beams to those reinforced with different layers of CFRP. The results of this study demonstrated that there was a significant increase in flexural capacity, ranging from 45.31% to 78.62% for single layers and 87.17% to 153% for double layers of CFRP sheet. Additionally, the research examines how different levels of prestressing and CFRP wraps influence crack formation and delamination patterns of carbon fiber, with promising results. It was also noted that optimal usage of CFRP fibers and tendons is found to be critical. The study suggests exploring alternative fiber types and orientations for future study.

Research on fatigue life of carbon fiber reinforced polymer strengthened single-sided butt welded joints utilizing resin pre-coating for strong adhesive bonding

Single-sided butt welding is a common connection method used in box beam structures such as excavator booms. Single-sided butt weld joints are prone to fatigue failure since the structures are subjected to cyclic loads over extended periods. The purpose of this study is to improve the fatigue performance of single-sided butt welded joints. Carbon fiber reinforced polymer (CFRP) strengthened single-sided butt welded joint specimens with permanent backing plates were prepared by pre-coating method, and constant-amplitude tension–tension fatigue tests were carried out on the specimens. The effects of welding groove parameters and CFRP reinforcement on fatigue life were studied. The test results show that the CFRP-strengthened specimens without blunt edges and with a groove angle of 40° show the highest average fatigue life. The single-sided bonding of 10 layers of CFRP sheets effectively inhibits the propagation of fatigue cracks and significantly improves the fatigue life of welded joints. In the CFRP/welded joint composite structure, the strain monitoring results show that the peak strain of the interface is the largest in the middle position, and the peak strain rises sharply in the rapid crack propagation stage, which indicates that the real-time interface strain peak can reflect the fatigue crack propagation. It provides an early warning method for real-time monitoring of fatigue life failure of welded structures in practical engineering.

Use of bore-epoxy anchorage system with CFRP laminates for shear strengthening of RC beams: An experimental and analytical investigation

Shear strengthening of reinforced concrete (RC) beams with externally bonded reinforcement (EBR) using carbon fiber reinforced polymer (CFRP) plates and sheets have become a widely accepted practice. To avoid the associated premature debonding failure, this study presents an experimental and analytical investigation on the use of bore-epoxy as an anchorage system for CFRP plates and sheets bonded on both sides of shear deficient RC beams of rectangular cross-sections. Nine (9) RC beams were prepared and strengthened with CFRP plates and sheets as EBR with bore-epoxy anchorage system considering different bore diameters and tested under four point bending. The results indicate that RC beams strengthened with bore-epoxy anchorage system have high shear strength as compared with the unstrengthened control beam and those strenghtended with the conventional EBR approach (without boring). The increase in the shear strength over the control beam was found to be up to 67 % and 121 % for cases of CFRP plates and sheets, respectively. Moreover, the increase of shear strength in comparison with the conventional EBR method ranged from 9.33 % to 20.36 % for CFRP plates and from 12.97 % to 36.10 % for CFRP sheets. Consistently, the contribution of bore-epoxy on the shear strength increased with the increase of bore diameter. Consequently, the existing formulas in the ACI440.2 R for predicting the shear strength of FRP strengthened RC beams were modified to incorporate the improvement made by the proposed bore-epoxy approach. The revised models predicted the experimental shear strength of RC beams, strengthened with bore-epoxy, with a good level of accuracy with average mean absolute percentage error (MAPE) = 6.07 %, 14.71 %, normalized mean square error (NMSE) = 0.097, 0.16, and coefficient of determination R2 = 0.912, 0.974 for plates and sheets, respectively.

A model for predicting flexural capacity of PVC‐CFRP tube confined reinforced concrete beams

AbstractThis paper presents an experimental study on 18 specimens, including 15 polyvinyl chloride (PVC)‐carbon fiber‐reinforced polymer (CFRP) tube confined reinforced concrete beams with longitudinal CFRP sheets (PCT‐RCBs‐LCS) and 3 PVC‐CFRP tube confined reinforced concrete beams (PCT‐RCBs). The effects of five studied parameters, such as longitudinal reinforcement rate (), concrete strength grade (), width () and number () of longitudinal CFRP sheet, and specimen dimensions (), on the failure mode and flexural capacity are investigated. The PCT‐RCBs‐LCS with lower and fail by the breakage of the PVC tube and the fracture of longitudinal CFRP sheets. Conversely, the cracking of PVC tube dominates the damage of the PCT‐RCBs‐LCS with higher and , while the longitudinal CFRP sheets are not broken. The introduction of longitudinal CFRP sheets can significantly improve the flexural capacity. The ultimate flexural capacity of the PCT‐RCBs‐LCS increases as the , , , or increases. In addition. considering the influence of RC beam section shape, a model for predicting the ultimate flexural capacity of the PCT‐RCBs‐LCS is proposed based on the limit equilibrium theory and cross‐sectional strain relationship. The predicted results of the proposed model agree well with test data.

Study of FRP on Preloaded Beam as A Method of Retrofitting - A Review

Over the past two decades, fiber-reinforced polymers have gained prominence in structural engineering due to their unique properties, offering an alternative to traditional materials like steel and concrete. FRPs consist of high-strength fibers embedded in a polymer matrix, resulting in superior strength-to-weight ratios, excellent corrosion resistance, and fatigue durability. These materials are widely used in aerospace, automotive, and infrastructure applications. Key types of FRPs include carbon fiber reinforced polymer, glass fiber reinforced polymer, aramid fiber reinforced polymer, and basalt fiber reinforced polymer, each offering specific advantages. CFRP is recognized for its high tensile strength, while GFRP is widely chosen for its affordability and adequate performance in less demanding structural applications. This review paper focuses on retrofitting predamaged reinforced concrete beams using carbon fiber-reinforced polymer and glass fiber-reinforced polymer sheets. It examines how preloading, fiber material, and fiber arrangement affect the structural performance of these beams, particularly in terms of flexural strength, ductility, stiffness, and failure mechanisms. Going through several papers the studies showed that CFRP and GFRP significantly enhance load-bearing capacity, energy absorption, and delay failure due to deboning. Key factors such as preload levels and fiber configuration were compared by go thronging several paper. The paper highlights real-world applications, where CFRP is commonly used in bridge rehabilitation and GFRP is favored for less demanding tasks, such as retrofitting low-rise building beams, both playing a critical role in extending the service life of structures while reducing costs.

Impact of Carbon Fiber‐Reinforced Polymer Sheets and Bolt Diameter on the Seismic Performance Enhancement of Steel Beam‐Column Joints

ABSTRACTBeam‐column joints are pivotal for ensuring the resilience of prefabricated steel structures under various loading conditions. Following the major earthquakes of the 1990s, semi‐rigid bolted connections emerged as a promising alternative to traditional welded connections. This study investigates a fully prefabricated Intermediate Beam‐Column Joint (IBCJ) with extended endplates, renowned for its excellent seismic resistance. While significant progress has been made in existing research, there is still a need to thoroughly examine the tension capacity of IBCJs concerning bolt size and explore the potential of Carbon Fiber‐Reinforced Polymer (CFRP) sheets to enhance joint performance under seismic loading. Using the finite element method, this research evaluates the performance of IBCJ under both monotonic and cyclic loading conditions. After validation with experimental data, the study examines various bolt diameters to assess their tension capacity, ductility ratio, secant stiffness, and energy dissipation capacity. The findings indicate that larger bolts exhibit higher ultimate capacities and reduced deformation at failure. Additionally, the study investigates the optimal placement and configuration of CFRP sheets, identifying the backside of the endplates as the most effective location. The application of CFRP significantly enhances bolt tension capacity by up to 1.2 to 1.3 times, demonstrating its potential in reducing bolt failure risk and improving structural reliability under seismic conditions. The superior performance of CFRP‐strengthened bolts can play a crucial role in the design and retrofitting of prefabricated steel structures, potentially contributing to the improvement of existing standards and practices of seismic enhancement of IBCJ.

Numerical analysis of load-bearing capacity of shear-strengthened reinforced concrete beams without shear reinforcement using side-bonded CFRP sheets

As CFRP (carbon fiber-reinforced polymer) offers high retrofit efficiency for structural members in bending and shear due to its superior mechanical properties compared to steel, sheets made from this material have become ubiquitous in strengthening existing reinforced concrete (RC) structures. However, there needs to be more research on RC beams with no stirrups that have been shear-strengthened with side-bonded CFRP sheets. As such, this study aims to investigate this specific topic and assess design-related parameters that impact the load-bearing capacity of these shear-strengthened beams. To achieve this, nonlinear finite element models of four RC beams, including one control beam and three beams strengthened with side-bonded CFRP sheets, were built and verified regarding shear capacity, crack patterns, and failure mechanisms. The simulated beams demonstrated a high level of accuracy in all mentioned aspects. Numerical models were then developed to evaluate the design-oriented parameters that affect the response of shear-strengthened beams, including the concrete compressive strength, the amount of steel reinforcement, the number of CFRP layers, the CFRP bonding configuration, and the shear span-to-effective depth ratio. The results showed that not only the compressive strength of the concrete but also the amount of steel longitudinal reinforcement had a significant relationship with the load-bearing capacity of shear-strengthened beams. Meanwhile, the bonding configuration and the layer number of side-bonded CFRP sheets considerably influenced the ductility, the crack pattern, and the failure mode of shear-strengthened beams.

An Experimental Study and Result Analysis on the Dynamic Effective Bond Length of a Carbon Fiber-Reinforced Polymer Sheet Attached to a Concrete Surface

A carbon fiber-reinforced polymer (CFRP) is a common material utilized for the enhancement in reinforced concrete (RC) constructions. Previous research indicates that the bonding performance between a CFRP sheet and concrete determines whether the bonding of CFRP material is effective. However, the majority of existing research on the bonding performance of the CFRP–concrete interface is concentrated on static loading conditions. In order to clarify the effect of dynamic load on the bonding performance of the CFRP sheet–concrete interface, this study adopts the double-sided shear test method to carry out dynamic experimental research. The test findings reveal that the damage pattern of the CFRP sheet–concrete interface remains consistent across different loading rates. The ultimate bearing capacity increases as the strain rate increases. As the strain rate increases from 10−5 s−1 to 10−2 s−1, the effect of bond length on ultimate bearing capacity increases by about 7%. As the strain rate increases, both the maximum strain of CFRP and the maximum interfacial shear stress demonstrate a corresponding increase, with respective increase rates of 60% and 20%. The effective bond length decreases by about 20% when the strain rate rises from 10−5 s−1 to 10−2 s−1. Finally, a formula for calculating the dynamic effective bond length of a CFRP sheet, grounded in the Chen and Teng formula, has been proposed and verified.

Mechanical Properties of Full-Scale Wooden Beams Strengthened with Carbon-Fibre-Reinforced Polymer Sheets

The strengthening, rehabilitation and repair of wooden beams and beams made of wood-based materials are still important scientific and technical issues. This is reflected, among other things, in the number of scientific articles appearing and the involvement of research centres around the world. This is also related to society’s growing belief in the importance of ecological and sustainable development. This article presents an overview of the latest work in this field and the results of our own research on strengthening solid wooden beams with carbon-fibre-reinforced polymer (CFRP) sheets. The tests were carried out on full-size solid beams with nominal dimensions of 70 × 170 × 3300 mm. A 0.333 mm thick CFRP sheet was used for reinforcement. The research analysed various reinforcement configurations and different reinforcement ratios. For the most effective solution, a 46% increase in load capacity, 35% stiffness and 249% ductility were achieved with a reinforcement ratio of 1.7%. Generally, the higher the reinforcement ratio and coverage of the surface of the wood, the higher the strengthening effectiveness. The brittle fracture of wood in the tensile zone for unreinforced beams and the ductile crushing of wood in the compressive zone for reinforced beams were obtained. The most important achievement of this work is the description of the static work of beams in previously unanalysed configurations of strengthening and the confirmation of their effectiveness. The described solutions should extend the life of existing wooden buildings and structures and increase the competitiveness of wooden-based structures. The results indicate that, from the point of view of optimizing the cost of reinforcement, it is crucial to develop cheaper ways of combining wood and composite than to verify different types of fibres.

Experimental study to unraveling the seismic behavior of CFRP retrofitting composite coupled shear walls for enhanced resilience

This study focuses on the empirical examination of the nonlinear seismic performance of carbon fiber-reinforced polymer (CFRP)-strengthened composite coupled reinforced concrete (RC) shear walls. The experimental setup involves testing the structure in two distinct states, wherein CFRP sheets are utilized for retrofitting and reinforcement. In the initial phase, three samples undergo reinforcement utilizing distinct patterns of CFRP sheets. In the subsequent stage, an additional trio of specimens is fabricated and tested without the application of CFRP sheets. Subsequently, all structures are exposed to a load equivalent to 60 % of their flexural capacity. Following this, the tested specimens undergo retrofitting with CFRP sheets, utilizing the same patterns as in the initial phase. The retrofitted composite coupled shear walls are then subjected to retesting. The principal aim of CFRP retrofitting is to amplify the flexural and shear capacities of the specimens, empowering them to endure heightened seismic loads in comparison to their original configurations. This research contributes by evaluating ductility, ultimate strength, energy dissipation, and construction costs associated with composite coupled steel plate-concrete shear walls. All specimens underwent cyclic loading in accordance with the ATC-24 guidelines [1], which provide standard protocols for testing the cyclic performance of structural components. These guidelines, outline procedures for simulating seismic loading conditions in laboratory settings to evaluate the performance of structural systems under cyclic loading. Finally, a parametric study explores the impact of CFRP sheets and their adhesion patterns on the seismic behavior of composite coupled shear walls. The selection of the optimal retrofitting scheme considers the construction cost of each specimen based on the total area of CFRP sheets utilized.

Interface mechanical properties of CFRP-seawater sea sand concrete under simulated seawater immersion

In this study, the interfacial mechanical properties of carbon fiber-reinforced polymer (CFRP) sheet reinforced seawater sea sand concrete (SSSC) in simulated seawater immersion environment were studied. The results present that the interface bearing capacity of CFRP-SSSC decreases significantly after seawater immersion. The decreasing rate increases greatly with the extending of immersion periods. Seawater immersion also affects the failure mode of interface between CFRP and SSSC, which leads to the damaged surface expanding from the base layer of concrete to the junction section of resin and aggregate. The distribution of strain and stress along the bonding direction presents the load transfer from the loading end to the free end. The shear stress peak locates near the loading end and decreased about 15–20 % due to seawater immersion as a result of the deterioration of the interfacial property. The analysis on the microstructure of CFRP-SSSC interface proves that the chemical ions in seawater causes the hydrolyzation of epoxy resin adhesive layer. The CFRP-SSSC interface presents a lower interfacial bonding properties than CFRP reinforced normal concrete (NC). The improvement of strength grade of concrete from C30 to C50 increases the bonding properties of the CFRP about 9–12 % and mitigates the influence of seawater immersion. The obtained bond-slip curve indicates that the seawater immersion decreases the interface ductility. A modified Popovics model is applied to predict the bond-slip curve and presents a high fitting degree.

Experimental study on bond-slip behaviors of CFRP sheet-Q690 high strength steel plate considering the effect of CFRP sheet thickness and bonding length

With the increasing application of carbon fiber reinforced polymer (CFRP) in steel structure engineering, the bond-slip behavior between the two has attracted much attention. Firstly, 18 sets of CFRP sheet-Q690qD high-strength steel double strap shear specimens were fabricated considering the effects of CFRP sheet thicknesses and bond length. Then, static and fatigue tests were conducted on them. Subsequently, based on the 3D-DIC acquisition technology, the bond-slip curves were obtained using the smoothing method and the fitting method respectively Finally, the three key parameters of τmax, s1and sf in the bifurcated model at each working condition were obtained. The experimental results indicated that the bond length was positively correlated with the static load ultimate strength, while the thickness of the CFRP sheet had less effect on the ultimate strength. The fatigue life of the specimen with a bond length of 40 mm under equal stress ratio fatigue loading was much higher than that of the specimens with bond lengths of 60 mm and 80 mm. It was found that the fitting method had better stability and accuracy in fitting the bond-slip curves of CFRP sheet-Q690qD high-strength steel specimens. The accuracy of the fitting maximum bond load was above 80 %, which can provide a relevant basis for the subsequent numerical simulation calculation.

Pre-and post-heating bar-concrete bond behavior of CFRP-wrapped concrete containing polymeric aggregates and steel fibers: Experimental and theoretical study

The present research attempted to explore the impact of steel fibers and carbon fiber-reinforced polymer (CFRP) sheets on the pre-and post-heating bond behavior of steel bars in high-strength concrete incorporating waste polyethylene terephthalate (WPET) by conducting the pullout and beam tests and in both pullout and splitting failure modes. To achieve this aim, one hundred and forty-four cubes and forty-eight prisms were cast for the pullout and beam tests, respectively. The variable parameters included the replacement ratio of the fine aggregates with waste polyethylene terephthalate (WPET) particles (0 % and 10 % by volume), steel-fiber content (0 % and 1 % by volume), bar diameter (12-and 16-mm), target temperature (25, 200, and 600 °C), and confinement level (no confinement or CFRP wrapping applied after the thermal regime). Bond strength, bond stress-slip behavior between rebar and concrete, failure mode, and rebar debonding energy were among the parameters investigated after cooling. The results showed that in contrast with the positive effect of CFRP sheets on debonding energy, steel fibers have a positive effect on debonding energy only at 600 °C. Steel fibers did not offset the negative effect of polymeric aggregate, negatively changed the pullout mode to a mixed pullout/splitting failure at 200 °C, and tended to favor splitting failure mode to mixed mode at 600 °C. Moreover, steel fibers negatively affected the bond strength of pullout specimens in both confined and unconfined conditions, especially at 25 and 200 °C, and were less effective than CFRP sheets in avoiding splitting. Small-diameter bars reduced the negative effect of steel fibers on the bond, while polymeric aggregate tended to enhance the bond strength differences between large- and small-diameter bars. The effect of increasing the bar diameter on the effectiveness of CFRP sheets on the bond strength was not clear, but as a general trend, the effectiveness increased with the increase of the bar diameter. A predictive model based on the experimental results of this study and other studies was proposed as well to introduce the positive effect of the CFRP confinement and the dubious effect of steel fibers and polymeric aggregate on bond strength.

Experimental study on strengthening steel-truss bridge diagonal members using carbon-fibre-reinforced polymer bonding methods

This study investigated the effectiveness of carbon fibre-reinforced polymer (CFRP) materials in strengthening the diagonal tension members of steel-truss bridges. Monotonic tensile and cyclic loading tests were performed on CFRP-strengthened specimens with variations in the CFRP-bonding range on the flanges. This study focused on the strengthening methods A and B, which were proposed to address insufficient CFRP anchoring near gusset plates by bonding CFRP sheets to both sides of the flanges of the diagonal tension members. The results of the monotonic tensile loading tests indicated a significant increase in tensile stiffness and substantial improvements in yield strength (27%) and ultimate load-bearing capacity (51%) when the strengthening methods A and B were employed. Delamination of the bonded CFRP sheets was effectively delayed, occurring only after the steel yielded, owing to the use of a ductile adhesive (polyurea putty). On the other hand, the cyclic loading tests demonstrated a significant enhancement in the load-bearing capacities (33% for tensile, 32% for compressive) of the strengthened specimens. Moreover, the energy dissipation capacities of the specimens strengthened by methods A and B exhibited linear increases, with 12% and 14% higher values respectively than those of the non-strengthened specimen. Although the stiffnesses (tensile and compressive) of the strengthened specimens decreased in each loading loop, the strengthening methods A and B maintained the stiffness values at approximately 35% higher than those of the non-strengthened specimen.

Shear strengthening and damage control effects of CFRP and self-prestressing iron-based SMA for concrete columns

Although prestressed shape memory alloy (SMA) has shown a great performance in flexural retrofitting of slender RC columns, its shear strengthening effect for squat RC columns has been barely studied. This study explores the shear strengthening and damage control effects of iron-based SMA (Fe SMA) for squat RC columns. The heat-activated prestressing of Fe SMA was evaluated first at material level, then applied to component level structural testing of RC columns. The four circular RC columns with different retrofitting schemes were tested under quasi-static lateral cyclic loading. The specimens strengthened with carbon fiber-reinforced polymer (CFRP) sheet and Fe SMA strip exhibited satisfactory global responses without showing significant shear failure. From the visual inspection and non-destructive damage assessment, the prestressed Fe SMA was found to be superior in delaying damage accumulation in concrete compared to CFRP.

Shear Strengthening of RC Corbels with Carbon Fiber Reinforced Polymer Sheets: A Critical Review

Shear Strengthening of RC Corbels with Carbon Fiber Reinforced Polymer Sheets: A Critical Review