FEM-based modelling of NSM-FRP bond behaviour

Bond between Fibre Reinforced Polymer (FRP) Near-Surface Mounted (NSM) reinforcement and concrete is one of the key factors affecting the behaviour of this strengthening methodology. Properties of FRP, adhesive and concrete greatly affect the effectiveness of the NSM technique. Due to the variety of factors involved in the behaviour of FRP NSM strengthening systems, mechanical models able to incorporate the influencing variables acquire major importance for the prediction of the load capacity and the contribution of the different parameters. By predicting the results obtained in experimental direct pullout tests, a finite element model is adopted to assess the influence of relevant parameters on bond behaviour, namely: bar type, bar size, bond length, epoxy properties and concrete strength. The finite element approach considers interface finite elements for modelling the bond between FRP reinforcement and concrete, and a smeared crack model to simulate the crack initiation and propagation in the surrounding concrete

End concrete cover separation in RC structures strengthened in flexure with NSM FRP: Analytical design approach

Fiber-reinforced-polymer (FRP) composite materials applied according to the near-surface-mounted (NSM) technique are very effective for the flexural strengthening of reinforced-concrete (RC) structures. However, the flexural strengthening effectiveness of this NSM technique is sometimes compromised by end concrete cover separation (CCS) failure, which is a premature failure before occurring the conventional flexural failure modes. Due to the complexity of this failure mode, no analytical approach, with a design framework for its accurate prediction, was published despite the available experimental results on this premature failure. In the present study, a novel simplified analytical approach is developed based on a closed form solution for an almost accurate prediction of CCS failure in RC structures strengthened in flexure with NSM FRP reinforcement. After demonstrating the good predictive performance of the proposed model, it was used for executing parametric studies in order to evaluate the influence of the material properties and FRP strengthening configuration on the susceptibility of occurring the CCS failure. At the end, regarding to the FRP strengthening configuration, some design recommendations were proposed to maximize the resistance of NSM FRP strengthened structures to the susceptibility of occurring the CCS failure.The authors acknowledge the financial support provided by QREN (through the Operational Program COMPETE) in the scope of the CutInov Project (n. 38780) involving the Clever Reinforcement Company and the Structural Composites Research group of ISISE-Minho University

Experimental study of the influence of adhesive properties and bond length on the bond behaviour of NSM FRP bars in concrete

The near-surface mounted (NSM) fibre reinforced polymer (FRP) technique is a relatively recent system for strengthening concrete structures. Bond is a key factor in its behaviour, and is affected by many factors whose influence can only be tested through experimental studies. In this study, the modified pull-out test was used to study the effect of epoxy properties and bond length on the behaviour of NSM FRP bars. Three epoxy types, two FRP materials (carbon and glass) and four bond lengths (6db, 12db, 24db and 30db) are used. The load capacity, slips at the loaded end and free end and average bond stress are all analysed. The test results indicate that the role of epoxy properties appear to be a key factor in bond performance in the NSM FRP strengthening technique, and that their effect varies depending on bond length and FRP properties

Mechanical properties and durability assessment of nylon fiber reinforced self-compacting concrete

[EN] The higher paste volume in Self Compacting Concrete (SCC) makes it susceptible to have a higher creep coefficient and cracking and has brittle nature. This brittle nature of concrete is unacceptable for any construction industry. The addition of fibers is one of the most prevalent methods to enhance the ductile and tensile behavior of concrete. Fibers reduce the cracking phenomena and improve the energy absorption capacity of the structure. Conversely, the addition of fibers has a negative impact on the workability of fresh concrete. In this research work, a detailed investigation of the influence of Nylon fibers (NFs) on fresh properties, durability, and mechanical properties of SCC was carried out. NFs were added into concrete mixes in a proportion of 0.5%, 1%, 1.5%, and 2% by weight of cement to achieve the research objectives. Durability assessment of modified SCC having Nylon fibers was performed using water absorption, permeability, carbonation resistance, and acid attack resistant. Mechanical tests (compressive and tensile) were conducted for modified as well as control mix. Test results indicate that the passing and filling ability decreased while segregation and bleeding resistance increased with NFs. Furthermore, test results showed a significant increase in strength up to 1.5% addition of nylon fibers and then strength decreases gradually. Durability parameters were significantly improved with the incorporation of NFs relative to the control mix. Overall, this study demonstrated the potential of using nylon fibers in self-compacting concrete with improved durability and mechanical properties.SIThe author(s) disclosed receipt of the following financial support for the research, authorship, and/or publication of this article: The authors extend their appreciation to the Deanship of Scientific Research at King Khalid University for funding this work through group research program under grant number RGP. 1/100/42 and Taif University Researchers Supporting Project (number TURSP- 2020/276), Taif University, Taif, Saudi Arabi

Flexural Response of RC beams cast with normal and steel fibre concrete internally reinforced with various types of FRP bars

Šipke od vlaknima armiranih polimera (FRP) mogu se koristiti kao zamjena za čelične šipke da bi se izbjegla korozija čelika. U ovom radu su pripremljeni i ispitani uzorci armiranobetonskih greda od običnog betona i betona s čeličnim vlaknima (SFC) armirani šipkama od staklenih vlakana, armiranih polimera (GFRP) ili čeličnim šipkama. Rezultati ispitivanja pokazali su da se tlačna čvrstoća betona povećala s povećanjem omjera čeličnih vlakana (SF) koji su korišteni u ovom istraživanju (od 0 % do 1,5 %). Jednako tako, grede armirane GFRP šipkama imale su nižu početnu krutost i veću duktilnost nego one armirane čeličnim šipkama.Fibre Reinforced Polymer (FRP) bars can be used as an alternate for reinforcing bars to avoid corrosion of steel. Samples of reinforced concrete beams cast with normal or steel fibre concrete (SFC), internally reinforced with Glass Fibre Reinforced Polymer (GFRP) or steel bars, are prepared and tested in this paper. Experimental results show that compressive strength of concrete increases with an increase in steel fibre (SF) ratio used in this study (from 0% to 1.5%). Also, the beams reinforced with GFRP bars have a lower initial stiffness and higher ductility than those reinforced with steel bars

Experimental Studies on Bond Performance of BFRP bars reinforced Coral Aggregate Concrete

As part of this study, has been developed a numerical method which allows to establish abacuses connecting the normal force with bending moment for a circular section and therefore to predict the rupture of this type of section. This may be for reinforced concrete (traditional steel) or concrete reinforced with steel fibers. The numerical simulation was performed in nonlinear elasticity up to exhaustion of the bearing capacity of the section. The rupture modes considered occur by plasticization of the steel or rupture of the concrete (under compressive stresses or tensile stresses). Regarding the fiber-reinforced concrete, the rupture occurs, usually, by tearing of the fibers. The behavior laws of the different materials (concrete and steel) correspond to the real behavior. The influence of several parameters was investigated, namely; diameter of the section, concrete strength, type of steel, percentage of reinforcement and contribution of concrete in tension between two successive cracks of bending. A comparison was made with the behavior of a section considering the conventional diagrams of materials; provided by the BAEL rules. A second comparative study was performed for fibers reinforced section

A study of the bond and flexural behaviour of reinforced concrete elements strengthened with near surface mounted (NSM) FRP reinforcement

The main objective of the thesis is to study the bond behaviour of NSM FRP reinforcement in concrete elements. With this aim an extensive program of experimental tests complemented with numerical analysis has been performed to study the effect of the variables affecting this technique. In the first part of this thesis the modified pull-out test is carried out. A Finite Element Analysis (using the program FEMIX V.4) was used to perform several trials to fit as much as possible (inverse analysis) the force versus loaded end slip responses obtained experimentally in direct pullout tests. In the second part of this thesis an experimental program of flexural tests on RC beams strengthened with NSM FRP has been carried out to study the effect on the flexural behaviour of some of the previous variables studied in the first partL’objectiu principal d’aquesta tesi és l’estudi del comportament adherent entre el reforç NSM FRP i l’element de formigó. D’aquesta manera s’ha realitzat un extens programa d’assajos experimentals complementat amb anàlisis numèriques per tal d’estudiar les variables que incideixen en aquesta tècnica. En la primera part de la tesi es fa un estudi de l’adherència emprant l’assaig de pull-out modificat. S’ha realitzat una anàlisi amb el MEF (emprant el programa FEMIX V.4) per tal de fer diverses proves per ajustar amb la màxima precisió possible (anàlisi inversa) la resposta força-lliscament de l’extrem carregat de la barra obtinguda experimentalment en els assajos de pull-out. A la segona part de la tesi s’ha portat a terme un programa d’assajos a flexió d’elements de formigó armat reforçats amb NSM FRP per tal d’estudiar l’efecte d’algunes de les variables analitzades en la primera par

Effect and long-term outcome of hemithyroidectomy for patients with low-risk papillary thyroid carcinoma

Background Although the incidence of papillary thyroid carcinoma (PTC) has increased during the recent years, most of the PTCs are slow growing and considered as low-risk tumors with an excellent prognosis. This observed increase in small tumors leads to many controversies regarding the optimal surgical approach, and the extent of surgery for low-risk PTC is still the subject of debate. Recently, there is a trend toward utilizing a less-aggressive surgical approach, including the option of hemithyroidectomy for small PTCs up to 4 cm. Patients and methods This study included 60 patients with a proven diagnosis of PTC. According to the guidelines of the British Thyroid Association, the American Thyroid Association, and the American Joint Committee on Cancer, these patients would have low-risk PTCs and considered eligible for hemithyroidectomy (total lobectomy with isthmusectomy) as an initial treatment and followed up for about 5 years to detect recurrence and survival rate. Results Hemithyroidectomy was performed as an initial treatment. Completion thyroidectomy (CTx) was performed in five (8.33%) patients in the postoperative period within 1 week after the initial operation owing to identifying high-risk features in the final histopathology. During the follow-up period of the 60 patients, there was no locoregional recurrence. Recurrence was observed in three (5%) patients in the contralateral thyroid lobe within 3–4 years and was treated with a second surgery in the form of CTx. The overall rate of CTx was eight (13.33%) of 60 patients. The prognosis and the 5-year survival rate were excellent (100%). Conclusion Hemithyroidectomy in appropriately selected patients is an optimal surgical approach for treating low-risk PTC, and if recurrence occurs in the contralateral lobe, it can be treated safely by CTx, which yielded excellent curative results

Flexural response of GFRP RC beams strengthened with side and bottom NSM GFRP bars

This study exhibits the bending performance of reinforced concrete (RC) beams with glass fiber-reinforced polymer (GFRP) rods. The beams were strengthened with the bottom or side near surface mounted (BNSM or SNSM) methods. Applying BNSM strengthening to the RC beam is difficult in some cases, so the SNSM became essential. Due to the limited research dealing with this type of beam, this study focuses on the effect of internal and NSM reinforcement areas and the NSM position on the response of the beams. Two un-strengthened and six strengthened RC beams were tested in bending. The GFRP RC beams upgraded with SNSM GFRP bars showed higher deflection, energy dissipation, ductility, and ductile failure than those upgraded with BNSM ones. On the contrary, the load-carrying capability and flexural stiffness of GFRP RC beams strengthened with BNSM GFRP rods were slightly higher than those strengthened with SNSM GFRP. Consequently, a parametric investigation relying on the verified finite element (FE) model was executed. This parametric work aimed to add additional data to the literature related to the influences of the internal and NSM reinforcement type and area on the performance of beams with ‎SNSM. According to the FE results, increasing the NSM reinforcement area improved the capacity and stiffness of the upgraded beams regardless of the combination of the internal and NSM reinforcement. The relative axial stiffness between internal and NSM materials significantly impacted the beam performance. Moreover, using GFRP with CFRP or steel with CFRP indicated higher performance than using steel with GFRP, regardless of which one was located as NSM