Flexural Strengthening Research Articles

An experimental and numerical investigation on the flexural strengthening of full-scale corrosion-damaged RC columns using UHPC layers

When exposed to chloride-rich environments, reinforced concrete (RC) structures have serious concerns about rebar corrosion. In this study, a strengthening method was developed for RC columns with corrosion damage. Five full-scale RC columns with the same dimensions and rebar arrangements were experimented under reversed cyclic loading, where an axial stress equal to 1 MPa was applied to the specimens. Out of the five test specimens, two specimens underwent an average of 10 % rebar corrosion (Group 1), another two specimens underwent an average of 15 % rebar corrosion (Group 2), and one specimen acted as the sound specimen. One specimen from each group was retrofitted with 50 mm thick ultra-high-performance concrete (UHPC) layers. The experimental outcomes showed that reinforcement corrosion reduced ductility and maximum load-carrying capacity (MLC) significantly. The ductility and MLC of the specimen with 15 % rebar corrosion was decreased by 17 % and 9.2 %, respectively, compared to the sound specimen. However, the 15 % corroded specimen strengthened with UHPC layers displayed superior structural performance, for example, the MLC was increased by 24 % compared to the sound specimen. The performance of the strengthening scheme was evaluated using important performance indices, i.e., MLC, ductility, stiffness degradation, energy absorption, curvature distribution, etc. A simplified numerical model was developed and verified with experimental results. Experimental and numerical results revealed that the proposed approach can be very effective in strengthening corrosion-damaged RC columns.

Flexural strengthening of reinforced concrete cantilever beams having insufficient splice length

Structural systems often undergo changes due to variations in the usage, the loading conditions, or the presence of defects in their elements. The problem can be exacerbated when there is insufficient overlap between reinforcing bars in critical moment zones. This article investigates the behavior of reinforced concrete cantilever beams exhibiting insufficient overlap between bars that used as main reinforcing steel bars in the negative moment zone. Various strengthening techniques were employed in order to improve these defected cantilever beams. Eleven beams underwent flexural testing until reaching failure. The experimental parameters encompassed the strengthening scenarios and the bonded length. Three strategies were used: the application of stainless-steel plates (SSPs) as externally bonded reinforcement, near surface mounted (NSM) reinforcement in which additional deformed steel bars were bonded utilizing engineering cementitious composites, and externally pre-stressing technique. The anchorage length was examined at 40, 50, and 60 times the internal bar diameter. It was noted that the most substantial improvement achieved with the NSM method, followed by the externally pre-stressing method. It is worth mentioning that most of the beams failed in a flexural manner, with partial debonding occurring in beams strengthened using external strengthening. Moreover, this article includes the development of a numerical model employing the finite element method to replicate the response observed from the experimentally tested beams. The accuracy of the model was confirmed through the comparison of its outcomes with the experimental data, demonstrating an acceptable level of accuracy with deviations of less than 4.4 %. This successful numerical investigation was also used to conduct a parametric study. From this study it is evident that the effect of debonding on SSPs can be reduced by adding steel anchors at the ends of these plates. Finally, an analytical method was proposed to calculate the ultimate load capacity of strengthened reinforced concrete beams.

Finite Element Analysis of Reinforced Concrete Beams Strengthened with Hybrid Fiber Reinforced Polymer Systems using ANSYS

Background: Existing reinforced concrete (RC) structures can deteriorate over time due to aging, poor construction design, natural disasters, etc. In recent years, fiber-reinforced polymer (FRP) composite materials are becoming a preferred choice for concrete construction repair due to their durability, high strength, and corrosion resistance. This study aimed to study and analyze the properties of the constituent materials to identify any weaknesses and potential improvements. Methods: The present study investigated the effectiveness of flexural strengthening of RC beams using a hybrid grouping of glass-FRP (GFRP) and carbon-FRP (CFRP) unidirectional laminates. ANSYS finite element analysis (FE) software was used to investigate the failure modes of the beams and the stress-strain parameters. The impact of adopting two different grades of reinforcing bars in RC beam modeling was also contrasted in the study. Results: Comparisons between the finite element analysis and experimental literature results were made. Based on the test findings, it could be concluded that retrofitted beams perform better than non-retrofitted beams. According to experimental results, the HY14 sheet enhanced beam had a 188.46% higher ultimate load than the unenhanced beams. Conclusion: Comparing experimental findings to the conclusions of the numerical analysis, a maximum difference of ultimate load and deflection at mid-span of 3.40% and 4.91%, respectively, were used to assess the accuracy of the results.

Flexural strengthening of RC beams using external unbonded rebar: an experimental investigation

ABSTRACT Flexural strengthening of reinforced concrete (RC) beams is an important research topic due to its huge practical demand. In the present study, a new flexural strengthening method for RC beams, called the Shear-key Mounted Unbonded Rebar (SMUR) technique, is proposed and its effectiveness is examined through an experimental investigation. A total of 12 RC beams were cast and tested under four-point loading. Ten were strengthened and the remaining two the original or control beams. Before casting the RC beams, their constituent materials, such as cement, aggregate and rebar, were tested to ensure the quality of casting. The beams were strengthened with unbonded rebars attached to their tension faces through shear keys. One of the main advantages of the proposed technique was its speed and ease of application. As well as its effectiveness, the effects of other important aspects, such as the size and location of the rebar, were also examined. It was found that the proposed method noticeably enhanced the flexural capacity of a control beam. The ultimate load capacity of a strengthened beam was 60% higher than that of a control one. The flexural performances of the beams could be further improved by increasing the bar size and its location. The welding and conventional flexure were the dominant modes of failure in the strengthened beams.

Effectiveness of Fiber Anchors in CFRP Flexural Strengthening of RC Girders

Effectiveness of Fiber Anchors in CFRP Flexural Strengthening of RC Girders

Flexural performance of the negative moment region in bonded steel-wire-rope-strengthened reinforced concrete T-beams at different prestressing levels

This work examines the performance of reinforced concrete (RC) beams strengthened using bonded steel wire rope (SWR) at various prestressing levels. The strengthening approach has, however, been applied to the flexural strengthening of RC T-beams in the negative moment region, in order to determine its advantages. For this purpose, four RC T-beams were fabricated and tested under monotonic four-point bending: one control beam (S00), one beam strengthened with non-prestressed SWR (S20), and two beams strengthened with SWR (prestressed at 10% and 20% of their ultimate tensile strength: S21 and S22). The results indicate that the strengthened beams exhibit higher load-carrying capacities. Specifically, the cracking load, yield load, and ultimate load of S20, S21, and S22 increase by 10%–30%, 30%–50%, and 50%–90%, respectively, compared to S00. Additionally, there is an improvement in stiffness and energy absorption capacity. However, these strategies may have a dual effect on the specimens, resulting in a reduction in their ductility index. Finally, the tested beams were replicated using a three-dimensional finite element model, which has proved effective in predicting the behavior of such structures and, therefore, was found to be appropriate for use in future studies.

Flexural behavior of RC beams externally strengthened with side-bonded CFRP laminates with variable internal reinforcement

This study investigates the flexural behavior of reinforced concrete (RC) beams externally strengthened with bottom- and side-bonded carbon fiber-reinforced polymer (CFRP) sheets with variable steel ratio. The choice of applying the CFRP sheets in a bottom- or side-bonded configuration depends on the accessibility of the beam. This experimental investigation is aimed at studying and comparing the efficacy of bottom- and side-bonded CFRP sheets for flexural strengthening of RC beams with variable internal steel ratios. The effect of steel reinforcement ratio, and the number of CFRP plies are examined by testing 10 RC beams under a four-point bending configuration. The results in terms of load-deflection response, ultimate load-carrying capacity, failure modes, and ductility are studied and compared with control unstrengthened beams. The study revealed that side-bonded beams provided flexural capacity comparable to the bottom-bonded beams for both ratios of internal reinforcement used in the study. The study also showed that both strengthening configurations were more effective when the internal steel ratio was low. In terms of ductility, the side-bonded scheme provided ductility indices comparable to the bottom-bonded beams. The findings of this study confirm the feasibility of using side-bonded fiber-reinforced polymer (FRP) sheets as a strengthening technique for RC beams when the soffit of the beam is inaccessible.

Flexural behavior of RC beams strengthened with CFRP grid-reinforced engineering cementitious composite

Flexural strengthening of RC beams by replacing the tension part with carbon fiber reinforced polymer (CFRP) grid‐reinforced engineering cementitious composite (ECC) matrix has been proved to be a reliable way in the marine environments. However, few studies have been conducted on the arrangement of CFRP grids so far, which is supposed to be a possible way to deal with the premature fracture of CFRP grid and debonding of strengthening layer. In this paper, the flexural behavior of RC beams strengthened with CFRP grid‐reinforced ECC matrix is experimentally studied. The location of CFRP grid and the number of CFRP grid layers were specially discussed. Results from experiments indicated an improvement range of 66.67 %∼100 % in the peak load of strengthened RC beams, with a higher initial cracking load from 4.72 %∼20.47 % when compared to the reference beam. The generating of initial cracks was delayed with the CFRP grid close to the bottom, whereas the development of cracks was accelerated. The bearing capacity showed a nonlinear relationship with the distance from CFRP grid to the beam bottom, and a linear relationship with the number of CFRP grid layers. Finally, the formulas for the flexural capacity of strengthened beams were developed, considering the plasticity and cracking of concrete.

Flexural strengthening of RC beams using PGFRP bars embedded in strain-hardening cementitious composites (SHCC)

The application of the near surface mounted (NSM) fiber reinforced polymer (FRP) as an additional reinforcement at tension side of flexural members is efficient to upgrade the flexural strength. However, this technique must be applied to concrete beams having hard concrete cover to avoid premature failure induced by concrete cover deterioration. The current research aims to improve and evaluate the flexural behavior of reinforced concrete (RC) beams strengthened with embedded prestressed glass fiber reinforced polymer (PGFRP) bars, based on replacement of weak concrete cover with a layer of strain hardening cementitious composites (SHCC). For this investigation, one reference beam (without strengthening) and nine flexural strengthened beams were tested under a four-point bending scheme. All beams had the same reinforcement and geometry, 150 mm width, 300 mm total depth, a total length of 3000 mm and the effective span was 2700 mm. The test parameters were: (1) the strengthening technique (conventional NSM-PGFRP bars, NSM-PGFRP bars covered with external SHCC layer and PGFRP bars embedded in SHCC replaced cover), (2) the prestressing levels in the GFRP bars (0, 10 % and 20 % of the ultimate bar strength) and (3) the thickness of the SHCC layer (30, 40 and 50 mm). Compared to the conventional NSM strengthened beams, the conjunction of SHCC with PGFRP bars not only prevented the spalling of the concrete cover but also increased the load carrying capacity up to 26.5 % and the ductility up to 16 %. A model for the prediction of flexural capacity of the strengthened beams having SHCC replaced cover was conducted, the predicted ultimate loads have a good consistency with the test results.

Flexural strength of surrounding columns in URM-Infilled RC frames retrofitted by thick hybrid wall technique

This study investigated the flexural strengthening effect of the Thick Hybrid Wall (THW) technique as a seismic retrofit approach for Unreinforced Masonry Wall (URM)-infilled Reinforced Concrete (RC) frames. THW is a strength–ductility-type seismic retrofit technique, which was developed for pilotis-type RC buildings. In this study, the flexural strength and failure mechanisms of URM-infilled RC frames retrofitted using the THW technique were investigated. Consequently, a comprehensive theoretical model was developed to measure the flexural strength, and a previously proposed equation was modified. Additionally, an equation was developed to determine the minimum additional-wall length, and another equation was developed to determine the demand length of the additional wall to obtain the demand flexural strength. These equations enhance the cost-efficiency and reduce the irregularities risks. The interaction between the URM infill and surrounding RC columns was modeled, and a cyclic loading test was performed under the influence of a constant axial force on the four specimens. The results indicate that THW technique changes the failure mechanism of URM-infilled RC frames from shear to flexure and that the retrofitted URM acts as part of the lateral resisting system owing to the active lateral confinement pressure. The accuracy of the analytical models was confirmed via experimental results, and the developed models facilitate the practical implementation of the THW technique on intended frames.

Closed-form solutions for FPR-to-concrete bonded joints with loaded-end anchorage: Insight into the interfacial shear transferring mechanism

Incorporation of end anchorage has not only proven to be an effective method for enhancing the low utilization rate of the expensive fiber-reinforced polymer (FRP) material in the application of flexural strengthening of reinforced concrete (RC) beams but also improving the poor ductility and low load-bearing capacity of the FRP-to-concrete interface. The shear transfer mechanism at the interface with free-end anchorage has been understood, but for the interface with loaded-end anchorage, the shear transfer mechanism remains unclear. In this paper, a new analytical model is present to elucidate the shear transfer mechanism of the FRP-to-concrete bonded joint with loaded-end anchorage, including the U-jacket, FRP anchor, and mechanical fastener. The analytical solutions are presented and compared with the finite element analysis (FEA) results, and the good agreement between them verifies the accuracy of the proposed model. A comparison of the load-slip curves is conducted for the FRP-to-concrete bonded joint under various conditions, including scenarios without any anchorage, with free-end anchorage, and with loaded-end anchorage. Finally, design strategies are put forth for multiple anchorages to improve the load-bearing capacity and ductility of the FRP-to-concrete interface.

Flexural strengthening of LWRC beams using RSHCC reinforced with glass fiber textile mesh

This study aims to explore the flexural behavior of crushed clay brick (CCB) lightweight concrete (LWC) beams strengthened with rubberized strain-hardening cementitious composite reinforced with glass fiber textile mesh layers (GFTM-RSHCC) at the tension side. For this purpose, an experimental investigation consisting of seven simply supported beams, including one un-strengthened specimen, was produced and tested using a monotonic 4-point loading scheme. All specimens had a 120 × 250 mm cross-section, a total length of 2400 mm, and a loaded span of 2200 mm. The studied parameters were the number of GFTM inside the RSHCC (1, 2, or 3) and the thickness of GFTM-RSHCC layer (30 or 40 mm). All the following aspects were tracked: crack pattern, ultimate load, mid-span defection, and ductility. The results show that increasing the number of layers of GFTM and the thickness of RSHCC generally leads to an increase in the ultimate loads and ductility, up to 68% and 83%, respectively, compared to the control beam. Finally, a proposed equation considering the contribution of the GFTM-RSHCC layer was developed to predict the flexural capacity of the strengthened beams. The proposed equation showed good agreement with the experimental results.

Review of Behavior Flexural Strengthened RC Beams Using Ultra-High Performance Concrete

The use of ultra-high performance concrete (UHPC) to reinforce existing reinforced concrete (RC) structures in flexure has made great strides in research recently. In addition to creating an experimental archive, the research provided a thorough technical literature review. The effectiveness of UHPC strengthening schemes for RC beams was assessed by examining the effect of size on the flexural strengthening performance of RC members with UHPC. Various dimensions of RC elements were considered in order to understand any possible size-related effects. Factors like material strength and stiffness of the current RC members were considered because they could affect the strengthening's overall effectiveness. To comprehend how the strengthening of the UHPC would impact the overall. In order to find the most successful strategy, various UHPC strengthening configurations were examined. prior to applying the UHPC, the concrete substrate must be prepared. The experimental results from the studies under review indicate that UHPC is a promising reinforcement that can successfully provide RC beams flexural strength. The plain overlay's bending capacity increased by 20% to 60% when the thickness of the UHPC overlay was increased within the range of 30 to 50 mm. In contrast to plain overlays, the reinforced overlay resulted in a notable 40%–85% increase in flexural capacity. To assist stakeholders in making decisions, a cost comparison of UHPC with other strengthening techniques, such as carbon fiber reinforced polymers (CFRP), was provided. The study concludes by highlighting the potential of UHPC as a workable option for flexural strengthening of existing RC structures and offers insightful information for furthering the advancement and application of this technology in the building sector.

Flexural behaviour and strengthening of reinforced concrete beams using concrete canvas

Flexural behaviour and strengthening of reinforced concrete beams using concrete canvas

Investigating the efficiency and reliability of different lap-splice configurations in NSM BFRP rods for strengthening RC beams

The use of near-surface mounted (NSM) fiber-reinforced polymer (FRP) reinforcement has shown great promise for flexural and shear strengthening of reinforced concrete (RC) members. However, the continuity of NSM FRP rods is often interrupted due to length constraints, necessitating lap splices to transfer forces between spliced rods. The performance of lap splices depends on design configuration factors, including anchorage shape, splice length, and connection method. This research describes an experimental investigation into the bond behaviour and failure mechanisms of various lap splice designs for NSM basalt FRP (BFRP) rods in RC beams. The parameters investigated were end anchorage shape (straight or Embedded Through-Section (ETS) anchors), and connection type (overlay rods or face-to-face with FRP sheet wrap). A total of 8 simply supported RC beams strengthened with different NSM BFRP lap splice configurations were tested under four-point bending. The load-deflection response, strain distribution, and failure modes were evaluated. Test results showed that beams with NSM FRP rods with ETS anchors exhibited higher bond strength and ductility than face-to-face connections. The outcomes of this study can help optimize lap splice design and detail provisions for NSM FRP systems in future strengthening applications.

Ponašanje tijekom sloma izvana pojačanih armiranobetonskih greda s primjesom krutih vlakana

In recent decades experimental investigations on fibre reinforced polymer (FRP) laminate-strengthened reinforced concrete (RC) beams have been extensively conducted. It has been found effective in flexural and shear strengthening perspectives. On the other hand, a primary problem frequently encountered in such technique is the separation of FRP laminate with the concrete bonded surface. Such failures are due to the formation of localized flexural and otherwise shear cracks in the fragile region of the FRP-concrete interface. The debonding occurrence also significantly affects the strength enhancement of the laminated beams. The emphasis of the study is to enhance the potential performance of externally FRP strengthened RC beams by incorporating an effective crack controlling agent, that is ‘rigid hooked-end steel fibres’ in the matrix. Nine RC beams were cast and tested in this study with variables including different quantities of hooked-ends steel and glass fibre reinforced polymer (GFRP) thickness. The pre-cracking and post-cracking behaviour of the externally FRP strengthened RC beams mixed with the short fibres were systematically evaluated and improved performance at various stages of cracking was found. Another finding is the transformation of failure pattern from brittle to ductile due to exceptional strain-hardening phenomenon caused by steel fibres in the strengthened RC beams, in comparison to that of other beams without steel fibres. The formations and propagations of the cracks at different stages were numerically modelled for all the beams using the ANSYS and compared the numerical design validation with the experiment.

Amelioration of Flexural Performance for Reinforced Concrete Beams by Soffit Bonded High Performance Self Compacting Concrete Prisms

Abstract This paper presents a strengthening technique using a high-performance fibre-reinforced cement-based composite (HPFRCC) mixture. To evaluate the performance of this approach, two types of concrete mixtures were used one high performance and other high strength in strengthening process and compared to strengthening using CFRP laminate. The results showed that the strengthening was in the proportions (42 %, 58.03 %, 74.32 %) for (Mhs, Mcfrp, Mhp), respectively, Where the strengthening improved the bending capacity for beam (Mhp) to a greater extent of the other types and it reduced the appearance of cracks in the beam when loading until occur failure. As appeared failure modes in all elements were due to rupture in the flexure region and crush in the compression region. In addition, ductility index of the strengthened beams was acceptable and energy absorption of the strengthened samples high if compared to the reference beam Therefore, it can be said that this technology may provide a safer alternative for flexural strengthening of RC beams.

Flexural and Shear Strengthening of Reinforced-Concrete Beams with Ultra-High-Performance Concrete (UHPC)

Ultra-high-performance concrete (UHPC) is considered to be a promising material for the strengthening of damaged reinforced concrete (RC) members due to its high mechanical strength and low permeability. However, its high material cost, limited code provisions, and scattered material properties limit its wide application. There is a great need to review existing articles and create a database to assist different technical committees for future code provisions on UHPC. This study presents a comprehensive overview focusing on the effect of the UHPC layer on the flexural and shear strengthening of RC beams. From this review, it was evident that (1) different retrofitting configurations have a remarkable effect on the cracking moment compared to the maximum moment in the case of flexural strengthening; (2) the ratios of the shear span and UHPC layer thickness have a notable effect on shear strengthening and the failure mode; and (3) different bonding techniques have insignificant effects on shear strengthening but a positive impact on flexural strengthening. Overall, it can be concluded that three-side strengthening has a higher increment range for flexural (maximum, 81%–120%; cracking, 300%–500%) and shear (maximum, 51%–80%; cracking, 121%–180%) strengthening. From this literature review, an experimental database was established, and different failure modes were identified. Finally, this research highlights current issues with UHPC and recommends some future works.

Performance Assessment of Concrete Utilizing Recycled Aggregate and Artificial Sand

In this paper the experimental program is done for overall investigation of compressive strengthening and flexural strengthening of total seventy-two reinforced concrete cubes and beam for partial replacement of recycled aggregate for 0,30,60&100 percent respectively. The casting of cubes having size 150 x 150 x 150 mm and beam having size 500 x 100 x 100 mm has done with use of M 20 grade of concrete as per IS 456:2000 and IS 10262:2019. Compressive strength and flexural strength is improved at 60 percent replacement of recycled aggregate with use of 100% artificial sand.

Development of a novel anchorage and tensioning system for strengthening steel beams with unbonded prestressed CFRP plates

Carbon fiber reinforced polymer (CFRP) plates have been widely used in the strengthening and retrofitting of engineering structures due to their excellent mechanical properties. Applying a prestress to a CFRP plate is an effective solution for increasing its strengthening effectiveness, whereas the high-efficient anchorage and convenient tensioning of the CFRP plate are critical issues in practical applications. A novel anchorage and tensioning system for the prestressed CFRP plate was developed in this study. The space requirement at the end of structural elements can be significantly reduced by using this novel system. A finite element analysis was first conducted on the CFRP plate-anchor assembly to investigate the main factors affecting the anchorage performance. Based on the FE results, the final geometric sizes of the anchors were determined. Tensioning tests of the CFRP plate-anchor assemblies were carried out to verify the anchorage efficiency. The test results indicated that the CFRP plate could be loaded to fracture completely, and the anchorage system exhibited excellent anchorage efficiency. Finally, this system was used in the flexural strengthening of steel beams with unbonded prestressed CFRP plates. The flexural test results demonstrated that this system was effective for enhancing the flexural behavior of steel beams. The unbonded prestressed CFRP plate could obviously increase the load-carrying capacity and reduce the deflection of steel beams. The developed novel anchorage and tensioning system was proven to be feasible and applicable for flexural strengthening of steel beams with unbonded prestressed CFRP plates.