Carbon Fiber Reinforced Polymer Strengthening Research Articles

Study on CFRP-Strengthened Welded Steel Plates with Inclined Welds Considering Welding Residual Stress.

Welded steel plates are widely used in various structural applications, and the presence of inclined welds is often encountered in practical scenarios. Carbon fiber reinforced polymer (CFRP) has been proven to be effective for strengthening steel structures. However, the behavior of CFRP-strengthened welded steel plates with inclined welds, particularly considering the influence of welding residual stress, is limited. This paper aims to investigate the tensile behavior of CFRP-strengthened welded Q355 steel plates with inclined welds considering welding residual stress (WRS). First, WRS data were obtained by the X-ray diffraction (XRD) method at different locations. The maximum tensile and compressive residual stresses are 0.39 and 0.14 times the yield strength of the steel, respectively. Then, finite element models were established to investigate the effects of weld angles, weld width, and height on the WRS distribution of welded steel plates. Finally, the tensile performance of CFRP-strengthened welded plates with WRS was studied by numerical simulation. The results showed that the weld angles have little effect on the distribution pattern of residual stress but significantly affect the peak tensile WRS. When the weld angle changes from 0° to 60°, the peak tensile WRS decreases significantly from 0.32 to 0.06 times the yield strength of steel; furthermore, the influence of weld width and height on WRS is relatively limited. Under tension loading, the maximum stress occurs near the weld. The ends of the weld enter the yielding state later than the middle part of the weld due to the distribution of the WRS. As the weld angle increases and the length of the weld increases, the stress in the weld zone decreases, while the stress in the base material zone correspondingly increases. In addition, CFRP strengthening can reduce the magnitude of stress. This study provides preliminary references for understanding the tensile behavior of CFRP-strengthened welded steel plates with inclined welds.

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.

Influence of deteriorated stirrups on the shear performance of RC beams incorporating fly ash and enhanced with carbon fiber-reinforced polymer strengthening

Influence of deteriorated stirrups on the shear performance of RC beams incorporating fly ash and enhanced with carbon fiber-reinforced polymer strengthening

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.

CFRP strengthening of web perforated CFS lipped channel short columns: An experimental study

Web perforations provided in the columns or studs of light-gauge steel buildings to meet the functional requirements, decrease the axial capacity and lead to localized failure. Hence, the aim of this study is to experimentally investigate the influence of carbon fiber reinforced polymer (CFRP) strengthening on the stability, axial strength, and stiffness of the CFS web-perforated lipped channel short columns (of 600 mm length) subjected to monotonic axial compression. A total of 20 specimens, provided with circular perforation at mid-height and at the centre of the web, were tested by adopting different CFRP skin-strengthening configurations, considering Uni-Directional CFRP (CF_UD) and Bi-Directional CFRP (CF_BD) laminas or laminates. From the tests conducted, it was observed that CF_UD and CF_UD / UD were found to result in an increase in axial capacity of 11.12% and 22.23% for the cases of single- and double-layered CFRP, respectively. Similarly, the axial stiffness increased by 9.23% and 26.07%, respectively. However, the only considered triple-layered laminate, CF_UD / UD / BD has outperformed among the entire adopted strengthening configurations, with an increase in axial strength and stiffness of 28.90% and 38.33%, respectively, in comparison to the bare steel specimens. Notably, a local-distortional interactive buckling mode of failure was noticed in the cases of both bare steel and CFRP-strengthened specimens.

Flexural behavior of RC beams externally reinforced with CFRP composites using various strategies

Abstract The external composite material bonding is an effective and practical method for flexural strengthening of reinforced concrete (RC) beams, providing a large opportunity to develop high-performance and cost-effective structures. Numerous uses exist for carbon fiber-reinforced polymer (CFRP) materials as RC-member strengthening methods. However, issues with bonding and de-bonding continue to be a barrier to this technique's accomplishment. In this research, the CFRP sheets were integrated as an external strengthening material to evaluate their contribution to the flexural performance and so determine how well the CFRP sheets are being used. The experimental work includes one control beam and ten RC beams with CFRP sheets as external strengthening. All beams have the same dimensions: a length of 1.7 m and a sectional area of 20 cm × 25 cm. Experimental tests were carried out with varying CFRP types, lengths, numbers, and arrangements. Each beam’s performance was evaluated in terms of failure mode, ultimate load capacity, ultimate deflection, and a load–deflection curve. The findings demonstrate the effectiveness of CFRP strengthening by demonstrating a considerable improvement in the majority of the study variables. Furthermore, the CFRP strengthening offered an exterior crack-arresting mechanism.

Improved Bond Stress-Slip Relationships for Carbon Fibre-Reinforced Polymer-Strengthened Masonry Triplets

Carbon fibre-reinforced polymer (CFRP) emerges as a viable solution for reinforcing unreinforced masonry (URM) walls subjected to shear loads. While masonry structures are straightforward to construct, the complexity of the construction materials, especially in terms of their mechanical properties, poses challenges for numerical studies of their structural behaviour. Walls, being fundamental components in masonry construction, play a crucial role in transferring both horizontal and vertical lateral forces. This study investigates the enhancement of masonry wall behaviour through the reinforcement of CFRP. CFRP reinforcement increases ductility and strength, reducing the risk of failure under shear conditions. Additionally, CFRP composites present a practical solution to strengthening masonry structures compared to traditional reinforcement. However, brick, mortar, and CFRP have not been thoroughly investigated. Experimental tests on the bond behaviour of different configurations of CFRP-retrofitted masonry triplets have not been performed before and are therefore presented in this paper. Triplet specimens, comprising three bricks and two mortar joints, both with and without CFRP strengthening, were subjected to bond testing. The study affirms that masonry triplets strengthened with CFRP under shear loads exhibit strength levels at least four to six times greater than those without CFRP. The experimental work was carried out with eight different CFRP configurations on triplet masonry, and each test was repeated four times. Further, the bond stress-slip relationship in the case of masonry triplets with and without CFRP was predicted with new mathematical equations based on the conducted test results. These equations were included in the commercial finite element software ANSYS and used to conduct simulations of CFRP-reinforced masonry triplets. The numerical results indicate good agreement between the finite element model and the test results. The outcome of this research improves the current knowledge on the use of CFRP to reinforce masonry walls with brick and mortar, which will contribute to the understanding of the effect of CFRP on masonry structures.

Experimental study and numerical analysis on axial compression of round-ended concrete filled CFRP-aluminum tube columns.

To enhance the concrete confinement ability of circular-ended aluminum alloy tubes, carbon fiber reinforced polymer (CFRP) was bonded onto the tube surface to form CFRP confined concrete columns with circular ends (RCFCAT). Eight specimens were designed with number of CFRP layers and section aspect ratio as variables. Axial loading test and finite element analysis were carried out. Results showed CFRP delayed buckling of the aluminum alloy tube flat surfaces, transforming inclined shear buckling failure into CFRP fracture failure. Specimens with aspect ratio above 4 experienced instability failures. Under same cross-section, CFRP increased axial compression bearing capacity and ductility by up to 30.8% and 43.4% respectively. As aspect ratio increased, enhancement coefficients of bearing capacity and ductility gradually decreased, the aspect ratio is restrictive when it is less than 2.5. CFRP strengthening increased initial axial compression stiffness of specimens by up to 117.9%. The stiffness decreased gradually with increasing aspect ratio, with most significant increase at aspect ratio of 4. Strain analysis showed CFRP bonding remarkably reduced circumferential and longitudinal strains. Confinement effect was optimal at aspect ratio around 2.0. The rationality of the refined FE model established has been verified in terms of load displacement curves, capturing circular aluminum tube oblique shear buckling, concrete "V" shaped crushing, and CFRP tearing during specimen failure. The parameter analysis showed that increasing the number of CFRP layers is one of the most effective methods for improving the ultimate bearing capacity of RCFCAT.

Analytical study of CFRP strengthening steel plates with a semi-elliptical surface crack

Flaws and defects are unavoidable in the manufacturing process of steel members. Surface cracks are a common type of defect in steel structures that can introduce fatigue failure under cyclic loading. In this study, stress analysis of carbon fiber reinforced polymer (CFRP) repaired specimens with a semi-elliptical surface crack was conducted by theoretical analysis. The analysis was used to calculate stress intensity factors at crack tips. Finite element analysis was carried out to verify the proposed equations considering CFRP strengthening. Both single-sided and double-sided strengthening methods were considered. Thereafter, a modified Paris Law model was adopted to predict fatigue crack propagation life. Several parameters, which are crack aspect ratio, crack depth ratio, layers of CFRP, CFRP width and stress range are considered to analyze their influence on fatigue life. It was found that the augmentation of crack aspect ratio, layers of CFRP and CFRP width can significantly increase fatigue crack propagation life of repaired specimens. Furthermore, single-sided repairing on cracked side is better than double-sided repairing.

Behavior of CFRP strengthened concrete-filled steel tubes with spherical-cap gap under axial compression

Carbon fiber-reinforced polymer (CFRP) strengthening can be considered as an effect approach to compensate the unfavorable influence caused by the spherical-cap gap on concrete-filled steel tube (CFST) structures. In the present study, the influence of CFRP wrapped on the mechanical behavior of CFST with spherical-cap gap (CFST-G) is examined. Sixteen CFST stub columns are experimentally tested under axial compression loads, considering the gap ratio and the number of CFRP layers (nCFRP) as the main parameters for analysis. The test results show that the bearing capacity decreases with increasing gap ratio, and the wrapped CFRP effectively improves the axial bearing capacity of CFST-G. Notably, the strengthening effect increases as nCFRP increases. Meanwhile, finite element (FE) models are established and verified against the test results. The proposed FE model is then used to conduct behavior analysis, and the working mechanism of CFST-G with CFRP strengthened is revealed. Parametric studies are also carried out by the FE model. The results show that, under the same gap ratio, the strength index decreases with increasing steel strength, steel ratio, and nCFRP, whereas it increases as the concrete strength increases. Based on the test and numerical analysis results, a simplified formula to calculate the bearing capacity of CFRP-strengthened CFST-G is proposed, providing a basis and reference for practical engineering and design codes.

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.

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.

Experimental investigation on the behaviour of FRP strengthened square hollow section steel members under monotonic and cyclic loading

Strengthening and rehabilitation of square hollow sections (SHS) are a major concern nowadays as SHS may fail due to higher service loads, fabrication and construction errors, degradation of material over time and adverse effects of the cyclic loading due to earthquakes. In this study, a detailed experimental investigation has been carried out for the implications of using carbon fibre reinforced polymer (CFRP) and glass fibre reinforced polymer (GFRP) as a strengthening measure to mitigate the failure of SHS members under monotonic and cyclic loadings. Strengthened members displayed lower moment degradation and higher moment and energy dissipation capacities and higher stiffness and ductility compared to the bare steel members. Although the amount of CFRP and GFRP fibres were almost equal, CFRP strengthening can result in higher capacity sections due to having higher strength material properties compared to GFRP strengthening. The cyclic responses of the GFRP-strengthened member were close to that of the CFRP-strengthened member and can be more effective for strengthening steel SHS under cyclic flexural loading. The established theoretical model in the current paper can predict reliably the ultimate moment capacities of the strengthened SHS members. This study confirmed that strengthening SHS members with fibre composites will be effective for structures in seismically active regions.

Practical Investigation on the Strengthening of the Built-Up Steel Main Girder of a Metro Station with Carbon-Fiber-Reinforced Polymer on the Inside Part of the Tensioned Flange

This study investigates the effectiveness of a carbon-fiber-reinforced polymer (CFRP) in enhancing the load-carrying capacity of a steel main girder in a metro station. The objective is to evaluate the applicability of CFRPs in sustaining increases in applied loads and assessing their effectiveness on curved surfaces. Finite element analysis (FEA) identified the most stressed areas of the girder under design loads. Based on the FEA results, a targeted strengthening procedure using CFRP sheets was proposed. Various arrangements of CFRP sheets were tested, including different orientations and thicknesses up to 60% of the girder’s flange thickness. To validate the FEA accuracy, two small-scale specimen beams were prepared and tested in the laboratory. One beam was strengthened with CFRP sheets on the tension part of the inner flange side, similar to the suggested strengthening method for the girder. The FEA results show that the CFRP increases stresses by an average of 8% to 10% for the steel main girder, with strengthening effects up to 19% at the center of the CFRP strengthening positions, differing from a regular straight flange shape. Significantly reducing stresses required a total CFRP layer thickness of at least 50% of the flange’s total thickness. Applying a CFRP on the inner face of the girder preserves its usability without the need for openings in finishes or the metal deck surface. The findings highlight CFRP’s potential to enhance load-carrying capacity on curved surfaces and sustain increased applied loads, offering a promising solution for strengthening infrastructure and similar applications.

Enhancement of collapse-resistant capacity of non-seismically designed RC frames using various CFRP strengthening schemes

The existing studies have demonstrated relatively weak robustness of non-seismically designed reinforced concrete (RC) frames against collapse than seismically designed RC frames, causing the demand of efficient strengthening schemes to enhance their collapse-resistant capacity. Therefore, this paper presents an experimental program aiming at strengthening the collapse-resistant capacity of non-seismically designed RC frames using carbon fiber reinforced polymer (CFRP). A total of seven sub-frames were tested, of which the penultimate column or edge column was notionally removed to replicate the initial damage caused by accidental loads. Two sub-frames without strengthening were tested first as reference tests. Similar to existing research outcomes, the referential sub-frames experienced premature rebar fracture at the beam ends near the removed column, resulting in a severe softening in load resistance. Whilst the load resistance could reascend, the fracture of the rebar at the beam ends near the side columns only allowed an insufficient mobilization of catenary action (CA). In addition, the side joint of the referential sub-frame representing a penultimate column removal scenario suffered significant damage. Subsequently, five strengthening schemes were applied to the referential sub-frame, they are designed to increase the compressive arch action (CAA) capacity or CA capacity, or both the CAA and CA capacities through CFRP strengthening. Test results demonstrated that the proposed strengthening schemes in this paper can efficiently increase the load resistance at the CAA and CA stages but failed to mitigate the severe load resistance softening. The strengthening scheme planned to increase the CAA capacity unexpectedly decreased the deformation capacity of the strengthened sub-frame due to premature fracture of beam rebar near the side columns. The strengthening schemes planned to increase the CA capacity or both the CAA and CA capacities could increase not only the CAA capacity but also the CA capacity. The enhanced load resistance at the CA stage was mainly attributed to the continuous CFRP strips attached to the soffits. Unfortunately, the energy method demonstrated that the dynamic load resistance of the tested sub-frames to prevent collapse was achieved at the CAA stage rather than the CA stage because of the severe load resistance softening. Thus, the efforts devoted to increasing the CA capacity by this paper were valid in a real collapse of building scenario. In addition, 113 available test results were collected to compare with the acceptance criteria in existing codes for collapse-resistant design. Based on the test results and comparison, design suggestions were given for the collapse-resistant design.

Durability performance of RC beams strengthened with CFRP laminates and galvanized steel mesh bonded with epoxy and mortar systems

The galvanized steel mesh (GSM) systems are novel strengthening materials for the concrete structural elements, but their mechanical and long-term durability properties are needed to be investigated to enhance understanding and reliability in their use. This study investigates the behavior of reinforced concrete (RC) beams strengthened with carbon fiber reinforced polymers (CFRP) and GSM sheets under harsh climatic conditions of saline water and direct sunlight. The main focus was to recommend two important reduction factors, the bond reduction factor and the overall flexural reduction actor, when concrete beams are subjected to two said environments for a long period. These factors were compared to the ones recommended by different codes. The CFRP sheets were attached to the beams’ soffit with epoxy adhesive, whereas the GSM sheets were bonded either with epoxy (SME) or epoxy-based mortar (SMM). The specimens were weathered under saline water and direct sunlight for a period of 6, 12, and 24 months. The load-carrying capacity of CFRP, SMM, and SME strengthened specimens increased by 47%, 55%, and 55%, respectively, when compared to the unstrengthened specimens at 28 days. The bond capacity reduction factors (Rb) for CFRP, SMM, and SME strengthening systems were 0.75, 0.85, and 0.95 for saline water exposure, and 0.95, 0.85, and 0.85 for sun exposure, respectively, over a period of two years. On the other hand, the recommended overall flexure strength reduction factors (Rn) for CFRP, SMM, and SME strengthening systems were 0.85, 0.85, and 0.90 for saline water exposure, and 0.95, 0.90, and 0.90 for sun exposure, respectively. The results suggest that epoxy-based strengthening systems are more durable compared to the mortar-based systems under harsh climatic conditions.

Behavior and Load Capacity of Concrete Slab Reinforced by CFRP Bar and Strengthening by CFRP Laminates

Abstract The most common FRP materials used are carbon fiber reinforced polymers (CFRPs), and glass fiber reinforced polymers (GFRPs). The use of CFRPs has grown rapidly in the construction industry, specifically in structural retrofitting, due to their strengthening property of CFRP. CFRPs are moreover high strength, lightweight, noncorrosive, and easy-to-install materials. In the present study, six reinforced concrete slab specimens included two control specimens reinforced by traditional steel reinforcements and the other reinforced by carbon fiber reinforced polymer CFRP bars without strengthening by laminated CFRP strips. The remaining four specimens are interiorly reinforced by CFRP bars and strengthened by CFRP laminates strips with different scheme layouts named Type 1 and Type 2. The specimens were tested under a uniformly distributed load applied at the top surface area of each specimen up to failure. The parameters considered in the present study are the amount of CFRP bars and CFRP laminates layout. Test results indicated that the strength carrying capacity and failure mode of tested specimens differ based on the steel reinforcement type and the presence of CFRP laminates layout.

Efficiency of CFRP torsional strengthening technique for L-shaped spandrel reinforced concrete beams

Abstract The present study aims to get experimentally a deeper understanding of the efficiency of carbon fiber-reinforced polymer (CFRP) sheets applied to improve the torsional behavior of L-shaped reinforced concrete spandrel beams in which their ledges were loaded in two stages under monotonic loading. An experimental program was conducted on spandrel beams considering different key parameters including the cross-sectional aspect ratio (i.e., web height/web thickness), and the availability of the CFRP strengthening system. The ledge of the spandrel beams was exposed during testing to a very high eccentric load, which was transferred to the web of the spandrel beam causing high shear, torsion, and bending moments. Consequently, the applied load resulted in in-plane and out-of-plane deformations of the web accompanied by flexural and shear cracks. This article demonstrates the advantage of using CFRP sheets to strengthen the mentioned members. The applied CFRP sheets increased the failure torsional load by about 37% compared to the identical L-spandrels without strengthening. The outcomes indicate that using CFRP sheets show improvement in restricting the deflections and rotation of L-spandrels due to increasing spandrel stiffness. The reduction in the degree of rotation attained more than 33% in comparison to the spandrel beams without strengthening. The experimental program confirmed the applicability of the proposed strengthening technique for compacted and slender L-shaped spandrel-reinforced concrete beams.

Numerical Analysis on Dynamic Response of CFRP-Wrapped RC Columns under Lateral Impact Loading

This paper presents a numerical study examining the dynamic response and resistance mechanism of reinforced concrete (RC) columns strengthened with or without carbon-fiber-reinforced polymer (CFRP) wraps under lateral impact loading by using the software LS-DYNA. First, the information of eight column models was briefly introduced as part of the laboratory experimental program from the literature. Secondly, finite element (FE) models were established in terms of the geometries of impact tests. Then, a detailed comparison between numerical results and experimental results was made, and FE models showed a relatively high simulation accuracy. Subsequently, a series of parametric analyses were carried out with a focus on the effects of axial compression ratio, the boundary condition at the column top, the layer number of CFRP wraps, and the impact velocity and impact height on the dynamic responses of plain and strengthened columns. The results demonstrated that the CFRP retrofit mechanism was not activated during the initial Stage-I when the impact force rapidly increased to the first peak and then decreased to zero. CFRP strengthening came into play in the second stage, Stage-II, and affected the response of the shear force and moment along the column height, as well as had a great influence on the control of shear damage. The dynamic response of RC columns was more sensitive to the impact velocity than to other parameters, regardless of whether CFRP wrapping was applied. The axial compression ratio would have a different influence on the column failure mode if the impact velocity was varied. The variation in impact height and boundary condition at the column top had little influence on the damage mode of strengthened columns.

CFRP contribution to load-carrying capacity of retrofitted geopolymer concrete beams

In this study, reference geopolymer concrete (GC) beams were loaded up to the failure state with a three-point bending test to obtain load–deflection behavior. These damaged reference GC beams were then repaired, strengthened with Carbon Fiber Reinforced Polymer (CFRP) in both shear and flexure. These retrofitted GC beams have been then tested in the same conditions as reference GC beams and the effect of the CFRP strengthening on the strength and behavior was investigated. The load-carrying capacities of the retrofitted GC beams were higher than the reference GC beams in all series. The increase in capacities due to CFRP strengthening was higher in retrofitted GC beams without stirrups than in retrofitted beams with stirrups. The initial stiffness of the retrofitted GC beams were lower than those of the reference GC beams. This decrease was more evident in GC beams without stirrups than in GC beams with stirrups. Strengthening with CFRP enhanced the deflection and ductility capacities of the repaired GC reference beams without stirrups compared to the reference GC beams. The experimental CFRP contribution to shear strength was tried to be estimated using the equations proposed for the CFRP contribution in reinforced concrete (RC) beams. The predicted contribution of CFRP to shear strength using all investigated equations was greater than the experimentally obtained CFRP contribution.