Investigation on flexural FRP strengthening of corrosion affected reinforced concrete beams using the finite element method

Investigation on flexural FRP strengthening of corrosion affected reinforced concrete beams using the finite element method

Table of Contents:

Table of Contents: 2

Introduction 3

Background 3

Significance 3

Gaps 4

Research Questions 4

Objectives 4

Keywords 4

Benefits 5

Literature Review 5

Brief Review 5

Simply Supported Beam as per AUS standards 5

Flexural strength on concrete SSB beam 6

Flexural strength on corroded SSB beam 7

Flexural strength on FRP used corroded beam 7

FRP failures 8

Finite element method 9

Conclusion 9

References 10

Introduction

Background

Reinforced concrete structures frequently need to confront change and improvement of their performance amid their lifetime. The fundamental contributing elements are, change in their utilization, new design guidelines, corrosion causing decay in the beam structure as they are exposed to extreme environments as well as several accidents including earthquakes. In such conditions, there are two conceivable arrangements: substitution (replacement) or retrofitting. Full structure substitution may have determinate negative factors such as costly material as well as manpower, impacts of extreme conditions and burden due to the intrusion of the capacity of the structure (1). In earlier times, the production of epoxy glue with strength has prompted a procedure which has extraordinary potential in the field of updating structures (3). Essentially the technique includes fibre reinforced polymer (also known as FRP) on the concrete surface. The FRP at that point works compositely along with the concrete and help in carrying the loads. FRP can be helpful for various reasons. These materials have higher extreme quality, strength as well as low density. The present review of literature investigates the flexural FRP strengthening of corrosion affected reinforced concrete beams using FEM (i.e., Finite element modelling) (2).

Significance

On the basis of the present search of the literature of this study, other than a careful profound chasing, to the best of the distributed researches and studies which are practiced by the authors, actually are deprived of the studies simulating the flexural FRP strengthening of corrosion on the demeanor of reinforced concrete beams using FEM approach. Hence, it has turned out to be important to fill this gap observed in many types of research through FEM to settle this issue. Consequently, the finite element method is simulated in the present study (4).

Gaps

Numerous studies have been led to research the impact of various fibre orientation, type, and FRP geometry as a fixing material among beams which are damaged due to corrosion. However, until now, exceptionally constrained data is present on the viability of utilizing the FRP to fix RC beams which are corroded with a distinctive ratio of reinforcements. Also, the flexural strength of the FRP beams having corrosion has not been broadly secured yet. To utilize this framework in practice, the examination of the adequacy of the FRP system is unquestionable and requesting (5).

Research Questions

The following research questions are recognised in the present study:

How the flexural FRP strengthening of corrosion affected reinforced concrete beams using finite element method?

What is the flexure strength on corroded simply supported beam and on FRP used corroded beam?

What are the FRP failure modes that are being identified in the present study?

Objectives

The major objective of the present study is assessment and identification on the use of flexural FRP for strengthening the corrosion affected reinforced concrete beams with the help of the finite element method. Another objective state is the investigation of the long-term response of FRP strengthening the reinforced concrete beam under sustained load. The study will also aim to analyze the effect of the concrete strength through setting strength variables (6).

Keywords

Fibre reinforced polymer (FRP), FRP failure mode, finite element method, Reinforced concrete beam, strengthening

Benefits

FRP helps to build quality as well as ductility without much increment in stiffness. Furthermore, such material could be intended to meet explicit needs through adjustment of fibre placement. Therefore, strengthening of different types of concrete would be easily carried out with the help of FRP composites which are bonded externally. The use of FRP in strengthening corrosion affected reinforced concrete beam provides high quality with strength, lightweight, resistant to corrosion, simple and quick establishment and insignificant change in basic geometry of the structures. FRP systems can also be utilized in zones with constrained access where conventional strategies would be illogical (7).

Literature Review

Brief Review

The following chapter helps in providing a review of literature on flexural FRP strengthening of corrosion affected reinforced concrete beams using finite element method.

Simply Supported Beam as per AUS standards

Grace et al. (9) examined the RC beam strengthened behaviour with CFRP and GFRP sheets and overlays (9). They contemplated the impact of the number of layers, different types of epoxy, and reinforcing design on the reaction of the beams. They recognized that all beams experienced fragile disappointment, with a considerable upgrade in quality, in this manner requiring a higher factor of safety in the plan. Experimental examinations, hypothetical estimations as well as numerical simulations demonstrated that strengthening the RC beams with externally reinforced CFRP sheets in the strain zone significantly expanded strengthening at bends, diminished deflections and the width of the cracks (8). The impact of the surface readiness of the concrete, glue type, and strength of the concrete on the strength of the bond is considered just as attributes of force exchange from the plate towards the concrete (10). Several authors have utilized remotely strengthened FRP composites to improve the flexural quality of strengthened members of concrete. To assess the flexural execution of the strengthened members, it is important to contemplate flexural firmness of FRP reinforced members at various stages, for example, pre and post-cracking, as well as post-yielding. However, just a few studies have been identified which are centred around the strengthening RC reinforced under pre-loading and cracking (11).

Flexural strength on concrete SSB beam

The study by Obaidat et al. (12) contemplated the retrofitting of strengthened concrete beams utilizing composite covers and the primary factors considered are the inner reinforcement proportion, retrofitting position as well as the FRP length. The experimental assessment was performed to research the behaviour of beams structured so that either flexural or sheer disappointment will be normal. The beams were stacked in four-point bending until a crack is created. The beams were then emptied and retrofitted with FRP, and then the beams were stacked until failure mode. Another study reported the use of ABAQUS program for creating finite element models for simulating the behaviour of the beams (13). The concrete was demonstrated utilizing a plastic harm model and two models, a perfect bond model as well as a strong model, were assessed for the concrete FRP interface. From the investigations the load redirection connections until disappointment, failure modes and crack designs were acquired and contrasted with the trial results. The FEM results concurred well with the trials when utilizing the strong model in regards to failure mode and burden limit while the ideal bond model was not ready to speak to the debonding failure mode. The outcomes demonstrated that when the length of FRP expands the load limit of the beam increments both for shear and flexural retrofitting (14).

In another examination, Radfar et al. (15) carried on test investigations of 14 strengthened concrete (RC) beams retrofitted with new half and half fibre fortified polymer (FRP) framework comprising carbon FRP (CFRP) and glass FRP (GFRP). The target of this examination was to analyze the impact of cross breed FRPs on basic conduct of retrofitted RC beams and to explore if distinctive successions of CFRP and GFRP sheets of the crossover FRPs have effects on the progress of strengthening RC beams. The beams are stacked with various sizes preceding retrofitting so as to research the impact of introductory stacking on the flexural conduct and strength of the retrofitted beam. Test outcomes infer that reinforcing impacts of half and half FRPs on pliability and stiffness of RC beams rely upon requests of FRP layers (16).

Flexural strength on corroded SSB beam

Triantafyllou et al. (17) proposed a model for registering the stiffness of corroded beams utilizing flexural strength calculation. This model predominantly involves the impacts both of corrosion instigated splitting and weariness. However, another author Elghazy et al. (18) performed 3D FE demonstrating of corrosion damaged RC beams reinforced in flexure with remotely strengthened composites. They utilized three parameters in the examination which are consumption levels, kind of composite, and the number of composite layers. A great understanding was accomplished between the systematic and exploratory results; accordingly, they affirmed that the FE models had the capacity to copy the nonlinear disposition of the strengthened beams. A similar study was carried out by Ye et al. (19) contemplating the sheer execution of corroded reinforced concrete beams in which the numerical outcomes demonstrated that FRP reinforcing as the wrapping or U-molded holding of FRP sheets was successful to improve the shear quality of RC beams (20).

The conclusion of the results of the study carried out by Roy et al. (21) called attention to the impact of strengthening RC by FRP is immaterial on precracks of concrete. The FRP that is utilized in the RC beams as restricted materials can limit the measure of splits and furthermore increment the flexural limit of beams (22). However, Fiore et al. (23) brought up that the load limit of the auxiliary part expanded dependent on the mechanical properties of BFRP. As per the exploratory work achieved by Duic et al. (24) and Chen et al. (25), the successful strategy to expand the flexural strength of RC beams is through bounding of the RC beams with outer BFRP sheets. Furthermore, the study of Dias et al. (26) suggested the adequacy of patch repair and FRP-fortified overlays to retrofit strengthened concrete beams with corrosion harm and also concluded that the shear strength improved the bond performance (27).

Flexural strength on FRP used corroded beam

Martinola et al. (28) assessed the post-fix execution of corrosion harmed fortified concrete beams fixed with FRP frameworks. The test variable was three fix plans, for example, I) the example reinforced with independent FRP covers for flexure and shear, II) equivalent to the plot I aside from that the shear covers were utilized as grapples for the flexural strength and III) a solitary FRP cover utilized as a full wrap. Test outcomes demonstrated that because of corrosion, strengthened beams lost somewhere in the range of 8 per cent and 15 per cent of their load conveying limit contrasted with the control beam. In the wake of fixing corrosion breaks, beams reinforced with FRP expanded the load conveying limit on 22 normal by 30 per cent over the control beam (47).

However, Gadve et al. (29) examined the movement of steel corrosion in a solid barrel after it has been treated with FRP. The distance across and tallness of the barrel was 102 and 229 mm. The test variable was the planning of FRP application (pre-corroded and corroding stage) and the sort of FRP overlays (carbon and glass). The test demonstrated that FRP wrappings significantly hindered the rate of corrosion. Likewise, because of high electric obstruction and thickness, glass FRP covers had blocked the rate of corrosion more than the carbon overlays. A similar examination was proposed by, Al-Hammoud et al. (30) which will lead to an exploratory examination on the flexural strength of corroded RC beams fixed with FRP covers under weakness stacking. The four test factors i.e., 1) the seriousness of corrosion, 2) the range of the load, 3) the season of the FRP fix and 4) the quantity of the FRP covers. FRP expanded the flexural exhaustion limit of the corrosion beams at a high corrosion level (31).

FRP failures

Different examinations uncovered that two kinds of failure happen which might be extensively arranged under debonding failure in flexural RC beams strengthened by FRP, plate end debonding and centre split. In the primary kind, failure starts from one of the plates closes in view of the nearby pressure fixation as stated by Chakrabartty et al (32), while the second sort, debonding starts from a flexural shear break or a flexural split. Nguyen et al. (33) detailed that six unique classes could be spoken to the failure modes. Different parameters in the structure of an RC strengthened FRP beams are influenced by the criteria for every one of these failures. It is suggested that the failure modes ought to happen with steel burst and extreme yielding preceding solid pulverizing failure Figure 1.

Figure 1 Different failure modes (33)

Different methods of failure, shear, and debonding failure rely upon further parameters, for example, break design before fortifying, existing shear fortification and cover length Likewise, Lee (34) perceived six primary sorts of failure modes as appeared in Figure. 2 are not by any stretch of the imagination modified from those of standard RC beams, despite the fact that there are some noteworthy fluctuations while failure modes appeared in Figs. 2 was not perceived in ordinary RC beams as per Esfahani et al. (35) but rather are used as substitute modes selective to beams strength with a lower part plate.

Figure 2 Different failure modes (34)

Sakr (36) inferred that when the failure extreme mode is of concern, a contact component between the CFRP sheet and concrete ought to be utilized. Ombres (37) Carried out a critical survey about the sort of mode failure in which he announced tentatively dependent on that three fundamental gatherings of failure modes in RC beam strengthening with FRP as appeared in Figure 10. Fig. 3 speaks to break of FRP pursued by the steel fortification yielding. Carpinteri et al (38) state that Fig. 3 speaks to the failure mode that happens because of solid smashing earlier or a short time later elastic steel yielding without FRP harm and failure because of a shear split tendency toward the finish of the plate as individually, while Figure 3 speaks to failure including loss of composite activity (38).

Figure 3 Different failure modes (38)

Finite element method

A study by Pathak (39) reported the use of FEM for the numerical investigations which are directly dependent on the FE approach by utilizing business ANSYS programming (42) to recreate all course of action examples of BFRP in the RC beam models. Another study reported the use of diverse components which are precisely chosen from a program to imitate the conduct of reinforcing and restoration of consumed RC beams by BFRP layers (41). However, the study of Monaco et al. (40) selected some fundamental components such as SOLID65, LINK180. Similarly, a study by Yang et al. (43) reported the relationship association between the reinforcements (fundamental and stirrups) with concrete and hence stating it is the ideal collaboration, other than the concrete nodes at the cooperation with similar nodes of fortifications (43). The concrete could be displayed as a homogeneous and isotropic material. The pressure strain for reinforcements is flexible full plastic, and for BFRP, it is of direct relationship. Full associations were found among primary and auxiliary strengths with encompassing concrete and no collaborations among fortifications and BFRP (44).

A study by Karayannis et al. (45) stated that the convergence of the arrangement was 5 per cent, while it was viewed as endless with dislodging control. The connected burden was isolated into substeps, and the model work was chosen to diminish arrangement time and get a precise arrangement, in which the most extreme substeps is 150, substeps 100, and least substeps 1 (45). Loadings, limit condition, RC beams arrangement, dispersion of BFRP layers, and mechanical properties of the segments of the composite framework were altogether embraced from the investigation of Duic et al. to confirm the legitimacy of the results (46).

Conclusion

A detailed review of literature is carried out in the present study using relevant literature and studies based on flexural FRP strengthening corrosion affected RC beams using finite element method. The review covered the simulation of finite element, covering of adhesive, failure modes of finite element simulations well as the performance of retrofitted RC beams with FRP. Commendable affirmation of the FEM along with connected tests ensures the advantages of the retrofitting components. Additionally, the attributes of strengthened beams under failure mode, shear load as well as flexural load are still the areas that need to be researched. Such type of concern FEA in a dependable manner. Failure beam modes give confinements about the rest of the service life of the RC beams. Consequently, it is noteworthy to analyze the structure on a regular basis in order to examine the corrosion past failure mode type. Further study is required for failure modes in the future. Utilizing FRP to strengthen RC beams improves the performance of the beams by expanding their strength and lifetime.

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