Abstract The nonstructural protein NSm of tomato spotted wilt virus (TSWV) has been identified as the avirulence determinant of the tomato single dominant Sw‐5 resistance gene. Although Sw‐5 ...effectiveness has been shown for most TSWV isolates, the emergence of resistance‐breaking (RB) isolates has been observed. It is strongly associated with two point mutations (C118Y or T120N) in the NSm viral protein. TSWV‐like symptoms were observed in tomato crop cultivars (+ Sw‐5 ) in the Baja California peninsula, Mexico, and molecular methods confirmed the presence of TSWV. Sequence analysis of the NSm 118–120 motif and three‐dimensional protein modelling exhibited a noncanonical C118F substitution in seven isolates, suggesting that this substitution could emulate the C118Y‐related RB phenotype. Furthermore, phylogenetic and molecular analysis of the full‐length genome (TSWV‐MX) revealed its reassortment‐related evolution and confirmed that putative RB‐related features are restricted to the NSm protein. Biological and mutational NSm 118 residue assays in tomato (+ Sw‐5 ) confirmed the RB nature of TSWV‐MX isolate, and the F118 residue plays a critical role in the RB phenotype. The discovery of a novel TSWV‐RB Mexican isolate with the presence of C118F substitution highlights a not previously described viral adaptation in the genus Orthotospovirus , and hence, the necessity of further crop monitoring to alert the establishment of novel RB isolates in cultivated tomatoes.
Confinement of reinforced concrete (RC) columns through external bonding (EB) of fibre-reinforced polymer (FRP) composite becomes less effective in non-circular sections. The effectiveness of FRP ...confinement reduces with an increase in the size of the cross-section. Hence, it is essential to develop an effective FRP strengthening technique for large-sized square columns. Hybrid FRP strengthening combines the advantage of both near-surface mounting (NSM) and EB strengthening procedures for enhancing the overall performance of RC members under different load combinations. Sixteen square RC columns of various size ratios 1.0 and 1.5 were cast, strengthened and tested to understand the efficacy of the hybrid FRP technique. In addition to the tests, detailed nonlinear finite element (FE) models were developed and validated with the test results and data from the literature. Results show that the efficiency of EB and Hybrid FRP strengthening decreased with the increase in sectional ratio of square columns. Hybrid FRP strengthening improved strength and ductility for all size ratios compared to EB or NSM FRP strengthening alone. Using validated FE models, a parametric study was also conducted to understand the effect of EB and NSM reinforcement ratio and column size on the efficiency of Hybrid FRP strengthening.
•End anchoring with strengthening rebars aims to limit unexpected de-bonding of NSM bars at higher loads.•Strengthening with mild steel-GFRP rebars enhances ductility and beam stiffness.•The use of ...deformed steel-FRP rebars took the first place in improving the RC beams efficiency.
NSM bars enhance flexural strength of RC components but degrade ductility and transform the failure mechanism from ductile flexure to brittle shear. Failure due to debonding and other causes still has an impact on the strengthening system's efficiency. The focus of this research will be on how successful hybrid steel-CFRP/GFRP rebar strengthening is in enhancing the overall behaviour of reinforced concrete (RC) beams under flexure. Six rectangular RC beams were cast and strengthened using various semi-NSM procedures (120 mm width by 300 mm depth by 3000 mm length), then tested to failure in four-point bending tests. The beams were classified into four categories: (I) control beam, (II) strengthening with mild steel bar, (III) strengthening with mild steel-CFRP/GFRP hybrid rebars, and (IV) strengthening with high tensile steel-CFRP/GFRP hybrid rebars. To enhance the overall behaviour of RC beams, particularly beam ductility, and to avoid corrosion, FRP confinement was utilized in association with steel bars. End anchoring with strengthening rebars aims to limit unexpected de-bonding of NSM bars at higher loads, resulting in superior flexural performance of the RC members. In compared to the others, strengthening with mild steel-GFRP rebars enhances ductility and beam stiffness. This study also suggests and validates a 3D numerical model to simulate the performance and failure of NSM Strengthening mechanism with hybrid rebars for RC beams using the finite element (FE) software “ANSYS”. Regarding the behaviour of load-deflection, moment-curvature, load-crack width, and mode of failure, the FE results were accurate representations of the experimental results. An additional FEM specimen was examined to corroborate the effect of the experimental parameters.
This investigation aims to study the flexural behaviour of reinforced concrete (RC) beams strengthened with near-surface mounted (NSM) carbon fibre reinforced polymer prestressed concreteprisms ...(CFRP-PCPs). Eight RC beams were tested under monotonic loading until the failure load was reached. One beam was un-strengthened to act as a control beam. The other seven beams were strengthened with non-prestressed or prestressed NSM CFRP-PCPs. The effects of bond length, prestress level, and concrete type of the CFRP-PCPs on the flexural capacity, flexural crack and deflection are discussed in this paper. The results indicate that the flexural capacity of RC beams strengthened with NSM CFRP-PCPs was greater than the control beam. An obvious improvement was discovered in the crackresistance when the RC beams were strengthened with prestressed NSM CFRP-PCPs. The strengthened beams showed a higher first-cracking, yielding, and ultimate load as the bond length and prestress level of CFRP-PCPs increased up to a critical level. The beams strengthened with CFRP-PCPs, which were cast with ultra-high performance concrete (UHPC), exhibited greater load capacity than the corresponding beams with epoxyresin mortar. The analytical model of flexural response for the NSM CFRP-PCPs strengthening beams is presented. The analytical results are in good agreement with the experimental results, which revealed the NSM CFRP-PCPs is an effective technique for flexural strengthening of the RC beams.
Analytical and finite element studies on the behavior of Reinforced Concrete (RC) column elements strengthened using a hybrid Carbon Fiber Reinforced Polymer (CFRP) laminates and externally bonded ...fabric is explored in this study. The main objective of this study is to evaluate the effect of hybrid strengthening on the initial and post-cracking stiffness, peak and post-peak behavior, and change in failure modes of RC column elements. Both axial and eccentric loads are considered in this study. Experimental program is carried out by testing the column elements with and without different FRP strengthening. Analytical predictions are obtained using the strain compatibility approach based on the existing constitutive models for unconfined and confined concrete, steel and FRP composites. A numerical model of column elements is developed using a commercial software ABAQUS. The predictions obtained from the analytical and FE analysis were validated with the experimental results. Analytical and FE predictions exhibited a fair correlation with discrepancy of less than 5% when compared to test results. A parametric study is carried out using the validated FE analysis by varying the CFRP fabric ratio, CFRP laminate ratio and their hybrid combinations. Hybrid strengthening technique is found to be more efficient in improving the initial and post-cracking stiffness, strength and ultimate displacement ductility of RC column elements under compression.
In this article, an experimental program was carried out to investigate the flexural behaviour of RC beams strengthened using side and bottom near-surface mounted (NSM) CFRP strip and rope. Thirteen ...reinforced concrete beams (150x250x1600mm) with flexural deficiency were cast. Different configurations have been used for strengthening RC beams, including side NSM, bottom NSM and both of them. Test results have shown that specimens strengthened with NSM CFRP strips have higher load carrying capacity and higher ultimate deflection than that strengthened with NSM CFRP ropes for the same configuration. FRP debonding, concrete cracks and concrete cover separations are more depicted in specimens strengthened with NSM CFRP ropes than that strengthened with NSM CFRP strips. Using NSM CFRP ropes or strips has increased the elastic stiffness of the strengthened specimens. Flexural strengthening of RC beams using CFRP ropes and strips has increased the load-carrying capacity NSM in a range of (18%-51%) and (30%-80%), respectively, compared to the control specimen. It is also found that beams with bottom strengthening increased the flexural capacity by (25%-32%) compared to RC beams with side strengthening
This paper aims to present and analyze the results of an ongoing research project on the use of NSM and side-NSM-FRP composites for the purpose of increasing the load-carrying capacity of two-pan ...continuous RC beams. This research study comprises two parts; an experimental part and a finite element (FE) part. First, three large-scale two-span beams were statically investigated; one control beam and two other beams initially strengthened in bending with two 6 mm diameter CFRP bars. Second, a three dimensional (3D) FE model was developed, using the computer software ABAQUS, in order to predict the flexural performance of the tested beams and to investigate the influence of the models applied to the CFRP-resin-concrete interfaces. The results obtained indicated that the side-NSM-CFRP bars system is a convenient alternative to the conventional one for strengthening continuous beams. For some strengthening configurations, the side-NSM technique proved to be more efficient than the NSM technique, particularly when the CFRP bars were applied solely in the hogging region or the sagging regions. The moment redistribution of strengthened beams was negatively affected when the steel reinforcement ratio in the hogging region was increased. Nevertheless, the moment redistribution degree was significantly affected by the position and arrangement of the CFRP bars. The 3D-FE analysis developed with the cohesive zone model can capture the main aspects observed from the experiments.
•The NSM and side-NSM techniques could be used to improve the load-carrying capacity of the continuous RC beams.•The side-NSM-CFRP system is a convenient alternative to the NSM system for strengthening continuous beams.•The moment redistribution degree of NSM/side-NSM CFRP beams is affected by the position and arrangement of the CFRP bars.•The 3D FE analysis developed with the CZM can capture the main aspects observed from the experiments.
The near-surface mounted (NSM) fibre-reinforced polymer (FRP) strengthening technique has become a viable strengthening method for reinforced concrete (RC) beams. Premature debonding failure of the ...NSM FRP strips is a common failure mode though that severely limits the effectiveness of the FRP intervention that results in reduced beam strength and deformability. The application of FRP U-jackets near the ends of the NSM strips offers a potential solution to the debonding problem. This paper presents the first systematic experimental investigation on the use of FRP U-jackets for delaying or preventing debonding failure in RC beams strengthened in flexure with tension face NSM FRP strips. A total of 11 large-scale RC beams were tested, with the investigated parameters being (i) arrangement of NSM carbon FRP (CFRP) strips, (ii) U-jacket material type, (iii) layout, width and inclination angle of FRP U-jackets. Failure modes, load-deflection and strain distribution responses of all tested beams were recorded. The test results bring clarity and understanding to the tested parameters and they also demonstrate the effectiveness of the U-jacket intervention.
Debonding failures of FRP have been frequently observed in laboratory tests of reinforced concrete (RC) beams flexurally-strengthened with near-surface mounted (NSM) fibre-reinforced polymer (FRP). A ...number of numerical and theoretical studies have been carried out to predict debonding failures in NSM FRP-strengthened beams, and several strength models have also been proposed. The existing studies, however, were all based on the scenario of a simply supported beam tested under one or two-point loading, while the influence of load distribution has not yet been investigated. This paper presents the first ever study into the effect of load distribution on the behaviour of NSM FRP-strengthened RC beams. A series of large-scale RC beams flexurally-strengthened with NSM FRP strips were first tested under different load uniformities; then a finite element (FE) model, which can give close predictions to the behaviour of such strengthened beams, was developed; finally, the proposed FE model was utilized to investigate the influence of bond length of NSM FRP on the load uniformity effect. It was found that the load uniformity has a significant effect on the beam behaviour, and the degree of this effect varies with the bond length of NSM FRP.
This paper presents an experimental study on the strengthening of seismically deficient RC beam-column joints using carbon fiber reinforced polymer (CFRP). Six exterior RC beam-column joint specimens ...were tested to identify an effective method for improving the seismic performance of such joints in terms of their lateral strength and ductility. These six specimens included one non-seismically designed specimen, one seismically designed specimen, and four specimens retrofitted using different schemes. In these schemes, both externally bonded CFRP sheets and near-surface mounted (NSM) CFRP strips were explored as strengthening options. The test results showed that by adding CFRP reinforcement, the seismic performance of a seismically deficient beam-column joint can be significantly improved. In particular, the use of NSM CFRP strips in beams and joints was found to effectively relocate the plastic hinge away from the joint region, thereby leading to a ductile failure mode (beam flexural failure), which demonstrates the effectiveness of this seismic retrofit method. A good understanding of the hinge relocation mechanisms has been achieved through extensive and detailed strain measurement during the tests.
PDF
