Carbon Fiber Reinforced Polymer Strips Research Articles

Numerical Modeling and Performance Evaluation of Carbon Fiber-Reinforced Polymer-Strengthened Concrete Culverts against Water-Induced Corrosion

Culverts fulfill the vital function of safely channeling water beneath railway tracks, highways, and overpasses. They serve various purposes, including facilitating drainage in areas such as watercourses, drainage zones, and regions with restricted ground-bearing capacity. Precast reinforced concrete (RC) box culverts are a popular choice because they are strong, durable, rigid, and economical. However, culverts are prone to corrosion due to exposure to a range of environmental factors and aggressive chemicals. Therefore, enhancing the design and construction of this crucial infrastructure is imperative to effectively combat corrosion and to adhere to modern standards of reliability and affordability. In this study, carbon fiber-reinforced polymer (CFRP) was used to strengthen corroded culverts, with promising potential to improve safety and longevity in these structures. This study compared the behavior of corroded RC box culverts to CFRP-strengthened ones using the finite element method (FEM). It explored the impact of varying the damage thicknesses owing to corrosion, ranging from 0 mm to 20 mm, on the structural performance of the box culverts. The results showed that the CFRP model exhibited a substantial 25% increase in the capacity and reduced the damage compared to the reference model. Moreover, a parametric study was conducted for establishing a cost-effective design, in which numerous CFRP strip configurations were examined for a damaged-culvert model. The results indicated that a complete CFRP sheet was most effective for the maximum design capacity and repair effectiveness. The study’s outcomes provide valuable insights for professionals engaged in enhancing the strength of box culverts, aiming to increase the capacity, enhance the stability, and strengthen corroded culverts.

Numerical investigation of bond-slip behaviour between CFRP strips and concrete in shear tests under static and blast loads

The paper is structured into two main sections. In the first part, the focus is on the finite element (FE) analysis of bond slip in a single bond shear test between concrete and carbon fiber reinforced polymer (CFRP) strips under static loads. To model the test set-up, a plastic damage material model and an elastic material model are used for the concrete prism and the unidirectional CFRP strip respectively. Three approaches, including a perfect bond model, a cohesive bond model, and contact algorithms based on recent bond slip models, are employed to simulate the bond interface. The numerical model's validity is confirmed through comparison with experimental results from the literature. The paper predicts the debonding failure mode, the strain evolution along the bond length, and the delamination loads of the CFRP strip. The cohesive bond model exhibits good agreement between numerical and experimental data. In the second part of the paper, the developed FE model is tested under blast loading and compared to the experimental results of the blast tests conducted by the authors. The experimental and numerical findings highlight a significant dynamic enhancement effect on bond-slip properties due to the propagation of the blast wave within the concrete and the high loading rate.

Flexural behavior of reinforced concrete beams strengthened with gradually prestressed near surface mounted carbon fiber-reinforced polymer strips under static and fatigue loading

The near surface mounted (NSM) carbon fiber-reinforced polymer (CFRP) strengthening technique, combined with gradually anchored prestressed technique, is utilized to delay the occurrence of concrete cover separation (CCS) and enhance the ductility of reinforced concrete beams. The load-carrying capacity of fully prestressed beams and gradually prestressed beams are investigated under both static and fatigue loading conditions. The study focused on the effect of gradient prestress on flexural behavior of strengthened beams, analyzed the failure mode, characteristic load, ductility, and stress distribution at CFRP-concrete interface under both prestress and load conditions. Results indicate that gradually prestressed beams outperform fully prestressed ones in restraining crack development, delaying yield of tensile reinforcement, improving bearing capacity and avoiding CCS failure. Bearing capacity was significantly increased by up to 35.48%, while ductility was greatly improved by 100.33% with ultimate deflection for gradually prestressed beams compared to fully prestressed ones. The fatigue life of gradually prestressed beams, which experienced a transition from CCS failure mode to fatigue fracture of tensile reinforcement, was significantly extended. Additionally, their ductility at failure was also greatly enhanced, thus confirming the effectiveness of gradually prestressed NSM CFRP strengthening technique.

Factors affecting flexural properties of RC beams strengthened with gradually prestressed NSM CFRP strips

In this study, the gradually anchored technique is combined with the prestressed near-surface-mounted (NSM) carbon fiber-reinforced polymer (CFRP) strengthening technique to reduce the stress concentration caused by prestress transfer at the CFRP end section and improve the failure mode and bearing capacity of strengthened beams. Flexural performance tests are conducted on one fully prestressed and six gradually prestressed NSM CFRP-strengthened reinforced concrete beams under static loads. The influencing factors include the gradient prestress, CFRP bond length, concrete cover thickness, and steel reinforcement type. The failure mode, characteristic load, shear stress distribution at the CFRP end section, as well as the crack development under prestress and load are analyzed. The test results indicate that the gradually prestressed beam is superior to the fully prestressed beam in reducing the stress concentration at the CFRP end, thereby inhibiting the development of cracks at the CFRP end, improving the bearing capacity, and delaying the separation of concrete cover. The bearing capacity and ductility of the strengthened beams are significantly improved, with a maximum increase of 35% and 100.33% for them respectively, confirming the effectiveness of the gradually prestressed NSM CFRP strengthening technique. Finite element analysis is conducted to further investigate the effect of gradient prestress on flexural performance of strengthened beams and propose design suggestions.

Experimental and numerical investigation of the flexural behavior of one–way RC slabs strengthened with near–surface mounted and externally bonded systems

This study investigated the flexural performance of one-way reinforced concrete (RC) slabs strengthened with two distinct strengthening systems: near–surface mounted (NSM) bars and externally bonded (EB) carbon fiber-reinforced polymer (FRP) strips. The NSM bars comprised four types: carbon FRP (CFRP), basalt FRP (BFRP), glass FRP (GFRP), and stainless–steel (SS) bars. The NSM–strengthened slabs showcased substantial enhancements in yield and ultimate load capacity, ranging from 20 % to 55 % and 59–123 %, respectively. In comparison, those strengthened with EB–CFRP strips displayed increases from 46 % to 107 % and 45–177 %, respectively, depending on the axial stiffness ratio of the strengthening system provided. Furthermore, the slabs reinforced with NSM–BFRP bars showed an 11–25 % improvement in their ductility indices. In contrast, the slabs reinforced with EB experienced a decrease in ductility ranging from 38 % to 50 %. This reduction was attributed to the differences in the modes of failure observed in both strengthening systems. The rupture of the NSM–FRP bars and the strain readings associated at the end of testing confirmed that the tensile strength of the NSM–FRP bars was fully exploited whereas the EB–CFRP strips utilized only 29–36 % of their ultimate tensile strain due to debonding. A finite element (FE) model was formulated to anticipate the behavior of the strengthened slabs. A strong correlation between the numerical predictions and the experimental outcomes was observed. The experimental–to–numerical ratios of the ultimate load ranged between 1.0 and 1.08 for the NSM–strengthened slabs and between 0.98 and 1.38 for the EB–strengthened slabs. This validated the FE models’ ability to capture the nonlinear performance of the strengthened slabs.

Behavior of Reinforced Concrete Corbels Strengthened with CFRP Strips Subjected to Monotonic and Repeated Loading

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.

Experimental Investigation on the Rehabilitation of RC Flat Slabs Using CFRP Sheets to Enhance Punching Shear Capacity

In this paper, the feasibility of strengthening a flat column–slab connection within the carbon fiber reinforced polymer (CFRP) has been investigated through experimental study. The experimental program includes a set of nine reinforced concrete flat slab specimens. Three unaltered specimens served as control slabs, while an additional six samples were strengthened with various CFRP configurations to enhance their shear capacity. The strain distribution, ductility, punching shear resistance, stiffness, and crack formation were studied. The result of experimental studies showed that in the direct method of strengthening in which two layers of unidirectional CFRP sheets were employed in two opposite directions, the ultimate punching shear resistance improved by 64%, 44.7%, and 15.3%, with respect to the location of the column connection, as compared with the control specimens. In the case of using one layer of unidirectional CFRP strips, the punching shear resistance was enhanced by approximately 16% and 39%, considering the configuration of CFRP sheets and the amount of strengthened and adhesive layers used. Following the outcomes of this research, the application of CFRPs in improving the resistance capacity of flat slabs against the punching shear is considerable. The reported outcomes were compared with the latest provisions of ACI to show the efficiency of the presented strengthening. Finally, a parametric study was performed assuming different loading locations to assess the effect of the loading region on the response of RC slabs. Results indicate that approaching the loading location toward the RC slab supports results of an increase in the load-bearing capacity and a reduction in the ductility of the RC slab.

Strengthening of GFRP Reinforced Concrete Slabs with Openings

Using fiber-reinforced polymer (FRP) could effectively improve the strength and endurance of reinforced concrete (RC) constructions. This study evaluated the flexural behavior of one-way concrete slabs with openings reinforced with glass fiber-reinforced polymers (GFRP) bars. It strengthened using carbon fiber-reinforced polymer (CFRP) sheets around the openings. The experimental program of this study is adopted by casting and testing four one-way concrete slabs with dimensions of (150*750*2650) mm. These slabs are divided into two groups based on whether they were strengthened or un-strengthened. For each group, two different openings (either one rectangular or two square) measured 250*500 mm and 250*250 mm, respectively, were fabricated within the pure flexural zone of the specimens. The experimental results indicate that using CFRP strips increases the maximum load capacity by around 29% for the slab with one rectangular opening and 21% for the slab with two square openings compared to the un-strengthened slabs. On the other hand, the deflection at a service load is decreased by about 35% and 37% for the slabs mentioned above, respectively.  

Strengthening of Reinforced Concrete Beams via CFRP Orientation

The utilization of externally bonded carbon fiber-reinforced polymers (CFRPs) and glass fiber-reinforced polymers (GFRPs) for reinforcing and retrofitting components has garnered considerable interest recently, as such composites provide beneficial properties, including a high modulus of elasticity, high strength, and low weight. This work conducts a finite element analysis, verified through laboratory experiments on 14 reinforced concrete (RC) beams. The primary focus is the final load of these components, considering varying CFRP orientations relative to the loading direction. In this research, the performances of control beams and RC beams are compared to assess the effectiveness and efficiency of different strengthening methods. The results demonstrated that bonding CFRP sheets with V-shaped end anchorages on the tension side was highly effective in improving the flexural capacity of RC beams in the weaker concrete strength group. This strengthening method resulted in a substantial increase in strength (of around 29.8%) in the higher concrete strength group. In addition, utilizing V-shaped end anchorages to bond CFRP sheets on the tension side proved to be a highly efficient technique for improving flexural strength. Conversely, bonding inclined CFRP strips to the sides of RC beams was highly effective at enhancing the shear capacity of the beams. These outcomes convincingly demonstrate the effectiveness of FRP for the reinforcement of structural components. The specimens strengthened with inclined strips exhibited enhanced shear and deformation capacity compared to those strengthened with vertical strips.

Flexural-shear strengthening of reinforced concrete T-beams subjected to asymmetric loading using CFRP system combined by NSM strips and U-wraps

This paper presents a developed three-dimensional (3D) finite element model (FEM) of flexural and shearstrengthening of reinforced concrete (RC) T-beams using a CFRP (Carbon Fiber-Reinforced Polymer) system combined by near-surface mounted (NSM) strips and U-wraps subjected by asymmetric loading. The 3D FEM was verified by experimental results. Concrete was simulated by a total-strain-based rotating smeared crack model. NSM CFRP strips and CFRP U-wrap sheets were modeled as shell elements. Steel reinforcement and NSM CFRP strips were embedded in concrete, corresponding to a perfect bond. U-wrap sheets were modeled as a shell element and bonded to the concrete surface using an interface element, considering appropriate bond properties. Four RC T-beams from an experimental work were analyzed, and predictions of the applied load-displacement curve and failure mode were presented to demonstrate the accuracy of the developed finiteelement analysis. It is shown that the finite element results of T-beams agree well with the experimental behavior in terms of applied load versus displacement and failure mode. Moreover, a parametric study was conducted to examine the influence of some design-oriented parameters such as concrete compressive strength, amount of longitudinal tension reinforcement, amount of stirrups, multiple layers of externally bonded (EXB) CFRP sheets, and flange width.

Axially-compressed behavior of carbon-FRP strengthening CFT short columns having circumferential void defects

To clarify the viability of externally bonding carbon-fiber-reinforced polymer (FRP) for strengthening the structural integrity of concrete-filled steel tube (CFT) short columns having circumferential void defects, this study comprehensively explores the strengthening effectiveness of various wrapping parameters (i.e., carbon-FRP strength, wrapping layers, and wrapping ratio) on the axially-compressed CFT short columns with various void ratios, material strengths, and geometric parameters by numerical method. Detailed mechanical responses, encompassing failure patterns, load-shortening (N-Δ) curves and stress distribution, are delved to reveal the strengthening mechanisms. Finally, strength prediction formulas for these composite columns are proposed rooted in the ring extension and local force transmission theories. Results show that the presence of initial voids delays the occurrence of steel-concrete contact stress (p) and weakens the p-value at peak load, thus reducing the axial resistance of column. Particularly when the void ratio exceeds 0.2%, the longitudinal strain when the concrete contacts with outer tube is beyond the concrete's peak compressive strain, thus the shape of the N-Δ curve is obviously changed, exhibiting two peaks. Externally bonding carbon-FRP strips can obviously improve the peak load of the column with a void ratio ≤ 0.2%. If the void ratio exceeds 0.2%, externally bonding carbon-FRP strips can also improve the column's second peak load, even exceeding the strength of pure CFT column, while it has no effect on the first load. The formulas proposed herein have a satisfactory accuracy based on the tested validation, which are expected to guide the design of strengthening scheme in engineering.

Shear capacity of PVC-CFRP confined concrete column-RC beam interior joint strengthened with core steel tube

This paper presents an experimental investigation on polyvinyl chloride (PVC)-carbon fiber reinforced polymer (CFRP) confined concrete (PCCC) column-RC beam interior joint strengthened with core steel tube (CST). Thirteen interior joints are designed and tested under low cyclic loading considering the impacts of six variables, such as diameter-thickness ratio of CST, stirrup ratio of joint, axial compression ratio, CFRP strips spacing, reinforcement ratio of beam and reinforcement ratio of column. Distinct shear deformation in joint region finally dominates the failure of specimens. The load-displacement hysteretic curves are relatively full and eventually show inverse S shape, indicating the specimens have considerable seismic behavior and energy dissipation capacity. The yield and peak shear capacities increase as diameter-thickness ratio, stirrup ratio of joint, reinforcement ratio of column or reinforcement ratio of beam increases. Comparatively, the axial compression ratio and CFRP strips spacing exert less influence on shear capacity. Considering the impact of diameter-thickness ratio, stirrup ratio of joint and reinforcement ratio of column, a formula for estimating shear capacity of PCCC column-RC beam interior joints strengthened with CST is proposed and its accuracy is verified by test data.

Rehabilitation of post‐heated rectangular reinforced concrete columns using different strengthening configuration

AbstractIt is common knowledge that increased temperatures have a negative impact on the axial load‐capacity and stiffness of reinforced concrete (RC) rectangular columns. This is something that is commonly acknowledged. For the purpose of restoring the axial capacity and stiffness of heat‐damaged RC columns, it is absolutely essential to carefully pick a suitable method for strengthening and repairing the columns. This research paper investigates the performance of various strengthening methods, such as the use of carbon fiber‐reinforced polymer (CFRP) jackets with near‐surface mounted (NSM) steel bars and a combination of welded wire mesh (WWM) and CFRP strengthening techniques, for the rehabilitation of RC rectangular columns that have been damaged due to exposure to high temperatures. Specifically, the paper focuses on the performance of these methods in relation to the rehabilitation of RC rectangular columns. There were three groups of tested RC rectangular columns: pre‐heated and unstrengthened, post‐heated and unstrengthened, and post‐heated and strengthened. Over a period of 3 h, 600°C was applied to the heated columns. Both a scheme utilizing a combination of unidirectional CFRP strips and NSM steel bars and another utilizing a combination of unidirectional CFRP strips and WWM were evaluated. Axial compression tests were performed on each column until failure occurred. The experimental test outcomes revealed that exposure to high elevated temperatures led to a decrease in the axial load‐carrying capacity of 38.6% and a decrease of 75.9% in initial stiffness, compared to unheated RC columns. Both strengthening schemes proved effective in restoring and surpassing the initial load‐carrying capacity of undamaged RC rectangular columns by an average of 35%. Notably, the combination of CFRP strips and WWM exhibited superior performance in restoring the initial stiffness of post‐heated RC rectangular columns, representing a novel finding. The strengthening scheme employing WWM and CFRP recovered 61.3% of the lost axial strength caused by high temperature, while the NSM/CFRP scheme restored 34.5% of the lost axial strength. In addition, the utilization of NSM in combination with CFRP strips as well as utilization of the WWM and CFRP systems leads to stiffness enhancement of 52.1% and 123.7%, respectively, when compared to post‐heated and unstrengthened RC columns. However, the study's findings have clearly shown that combination of WWM and CFRP strips is efficient in enhancing the strength of heated and unheated damage RC beams.

Full-Range fatigue behavior of NSM CFRP-to-Concrete bonded joints

The interfacial bond characteristics and failure mechanism of near-surface mounted (NSM) fiber reinforced polymer (FRP) composites in concrete under fatigue loading are less understood compared to their bond behavior under static loading. In this paper, degradation of the local bond strength of FRP-to-concrete bonded joints subjected to direct pull-out fatigue loading is presented for both carbon FRP (CFRP) rods and strips under different fatigue load ranges, i.e., 10–50%, 10–60%, and 10–70%, of the corresponding static load-carrying capacity. The interfacial debonding between FRP and adhesive was observed during fatigue cycles for CFRP rod specimens to different extents. Specimens using CFRP rods with sand-coated and spirally wound surface treatment presented a higher local bond strength and a slower degradation rate, as compared to the ones using CFRP rods with roughened or sand-coated treatment. Using epoxy adhesives with higher strengths benefitted the fatigue bond performance of the tested specimens in terms of local bond strength and stable behavior. Higher fatigue load ranges substantially accelerated the local bond degradation resulting in a much shorter fatigue life of the bonded joints.

Experimental and finite element analysis of reinforced concrete multi-cell box girders retrofitted with carbon fiber reinforced polymer strips under torsion

This study expands the state of the art in studies that assess torsional retrofit of reinforced concrete (RC) multi-cell box girders with carbon fiber reinforced polymer (CFRP) strips. The torsional behavior of non-damaged and pre-damaged RC multi-cell box girder specimens externally retrofitted by CFRP strips was investigated through a series of laboratory experiments. It was found that retrofitting the pre-damaged specimens with CFRP strips increased the ultimate torsional capacity by more than 50% as compared to the un-damaged specimens subjected to equivalent retrofitting. This indicated that the retrofit has been less effective for the girder specimen that did not develop distortion beforehand as a result of pre-loading. From experimental observations, when the girder specimen was cracked and the transverse steel reinforcement bars started straining, the CFRP strips started to work more effectively and contributed together with the transverse steel reinforcement to resist torsion load. Additionally, Finite Element (FE) simulations were developed using Abaqus to model the torsional behavior of the retrofitted girders, the results of which were validated with the experimental data. With the numerical model, the effect of concrete compressive strength, transverse reinforcement spacing, and CFRP strip spacing were examined. The effectiveness of the CFRP strips in enhancing the torsional strength of the girder was found to increase with increasing the spacing between the transverse reinforcement.

Fatigue performance improvement of U-rib butt-welded connections of steel bridge decks using externally bonded CFRP strips

U-rib butt-welded connections in steel bridge decks are known to be highly susceptible to fatigue cracking, which can pose a direct threat to the safety and durability of bridge structures. Carbon fiber-reinforced polymer (CFRP) materials have shown promising potential for fatigue strengthening. This study investigated the effectiveness of CFRP application on the fatigue performance of U-rib butt-welded connections by employing full-scale fatigue tests and finite element analysis. Two single U-rib specimens with welded splice joints were initially tested to initiate real fatigue cracks under cyclic loading. Different techniques of CFRP installation were then proposed to promote the fatigue performance of cracked butt-welded connections. The failure modes and fatigue strength of the tested specimens were evaluated before and after strengthening. Research results showed that fatigue cracks were observed at the arc transition of butt welds, where remarkable incomplete penetration was also discovered. The fatigue strength grade of the tested U-rib butt-welded details was less than 71 MPa stipulated by Eurocode 3. However, after being repaired by CFRP sheet bonding, the equivalent fatigue life of U-rib butt welds with different damage degrees can be extended by 0.5–16.6 times that of the original ones. These findings suggest that CFRP strengthening should be applied instantly on U-rib butt-welded connections once fatigue cracks are found.

CONFINED REINFORCED CONCRETE VERTICAL ELEMENT DUCTILITY UNDER LATERAL LOAD: INFERENCE FROM TEST RESULTS

Vertical elements fail during earthquakes due to lateral load. Carbon-fiber-reinforced polymer (CFRP) can play a significant role in preventing sudden collapse due to lateral load. Confinement provided by transverse shear reinforcement and polymer sheets increases both the compressive and lateral strength of concrete. To test the effect of CFRP confinement on concrete columns, seven square and four circular vertical specimens were tested and results were compared with theoretical predictions at Bangladesh University of Engineering and Technology. The specimens were wrapped at the vertical portion on an intermittent basis so that CFRP strips fell at the gap of horizontal reinforcements of the specimens’ vertical portion. Cyclic shear test was performed while maintaining axial compression. The test results were close to the theoretical predictions. The results thus suggest that CFRP wraps can contribute increased shear strength and ductility of vertical elements. High-strength concrete specimens did not reach their maximum strength due to the testing facility’s limitations, but they provided the expected results in the lower bound.

Experimental and Numerical Study on RC Beams Strengthened by NSM Using CFRP Reinforcements

Near Surface Mounted (NSM) Carbon Fiber-Reinforced Polymer (CFRP) reinforcement technique to improve the flexural strength of reinforced concrete members has become increasingly attractive in recent years. In this study, the practical problem of concrete cover depth cutting limitation was investigated. Twelve specimens were tested by four-point bending until failure. Experimental parameters include concrete cover depth, CFRP reinforcement type, CFRP positioning, and stirrups status. Furthermore, a nonlinear FEA model was developed to simulate the tested beams and was able to predict the experimental behavior satisfactorily. A series of parametric studies were then performed using this model to understand the effect of various reinforcement parameters on the flexural performance of the beam. The results showed that Strengthening with CFRP resulted in a significant increase in yield and ultimate strengths, but a significant ductility loss was recorded due to CFRP strip debonding in the strengthened beams, this problem was addressed by using more efficient strengthening techniques utilizing the effective bond length and a proper groove depth and positioning for the NSM bars.

Experimental Study of Pre-Cast Reinforced Concrete Deep Beams (Hallow Core section) Retrofitting with Carbon Fiber Reinforced Polymer (CFRP)

Experimental programs based test results has been used as a means to find out the response of individual elements of structure. In the present study involves investigated behavior of five reinforced concrete deep beams of dimension (length 1200 x height 300 x width150mm) under two points concentrated load with shear span to depth ratio of (1.52), four of these beams with hallow core andretrofit with carbon fiber reinforced polymer CFRP (with single or double or sides Strips). Two shapes of hallow are investigated (circle and square section) to evaluated the response of beams in case experimental behavior. Test on simply supported beam was performed in the laboratory & loaddeflection, strain of concrete data and crack pattern of those five reinforced concrete beams was recorded. Parametric studies are also conducted in this study includes the effect of hallow opening (shapes and materials), and CFRP ratio (single, double strips and side horizontal stirrups). Comparisons of test results from experimental data are based on load capacity, deflection, crack pattern and strain of concrete for all beams. From this comparison it was found that hallow effect on strength capacity i.e. decrease by about (13%) and increased in deflection and strain by about (18%, 24%) respectively compared with solid section. Also find that CFRP give more enhancements in loading capacity by about(33 to 66%) and decreased deflection for same applied load by about (26%). Test results that show when sides of beams retrofit with CFRP strip against horizontal shear increased strength by about by (20%). Finally the using double CFRP strips for hallow section gives equivalent or more than strength capacity of solid section. 

Prediction of fatigue crack propagation in center cracked steel plate strengthened with partially covered CFRP strip

Evaluating the fatigue performance of steel members strengthened with carbon fiber reinforced polymer (CFRP) is of great significance for formulating maintenance strategies and making full use of materials. Current analytical models are mainly developed for fully covered CFRP strengthening method without considering different mechanisms at each stage. In this paper, an analytical model considering different stages of crack propagation was proposed to predict the fatigue performance of center cracked steel plates strengthened with partially covered CFRP strips. The strengthening effects of CFRP strips were numerically analyzed based on the extended finite element model (XFEM) calibrated by test data. The validity of the analytical model was checked by several sets of test data and numerical simulations. The results show that the proposed analysis model can reasonably predict the fatigue life of center cracked steel plates strengthened with partially covered CFRP strips. This study may provide a reference for the application of the partially covered CFRP fatigue strengthening method in engineering structures.