Strengthening Of Concrete Beams Research Articles

Shear strengthening of self-compacting lightweight concrete beams with steel fibers and unbonded prestressing bars

This study aims to investigate the shear behavior of self-compacting lightweight concrete (SCLC) beams strengthened with steel fibers and unbonded prestressing bars. For this, the experimental program included the use of hooked-end steel fibers with volume fractions of 0.5 %−0.75 %, and high-strength prestressing bars with varying prestressing forces and transverse reinforcement ratios. The addition of steel fibers in SCLC significantly increased the normalized shear capacity of beams, reaching up to 2.50 times higher values, whereas the substitution of normal coarse aggregates with lightweight aggregate resulted in a decrease of up to 10.1 %. The shear strengthening of SCLC beams with unbonded prestressing bars provided a substantial increase in the ultimate shear capacity up to 2.06 times higher than that of beam without reinforcement. Increasing the prestressing force of bars effectively restrained the occurrence of critical shear cracking, consequently enhancing the shear capacity. Utilizing hybrid reinforcement with fibers and prestressing bars resulted in a transition of failure mode from shear to flexural, attributed to the improved shear capacity. For the SCLC beams reinforced with steel fibers, the shear strengths were predicted by previous prediction models. When modifier for lightweight concrete was considered, the Imam’s model most precisely predicted the shear strengths with an average vu/vn ratio of 1.00 and SD of 0.07. The fib model Code, based on the modified compression field theory, provided accurate predictions for the shear capacities of SCLC beams with unbonded prestressing bars, exhibiting an average Vu/Vn ratio of 1.00 and SD of 0.09. The fiber-resisting component was reasonably considered in the model with an average Vu/Vn ratio of 1.02 and SD of 0.07.

Shear strengthening of concrete deep beams using pre-fabricated strain-hardening cementitious composite plates

This study investigates the efficiency of near surface embedded (NSE) pre-fabricated strain-hardening cementitious composite (P-SHCC) plates for shear strengthening of reinforced concrete deep beams (RC-DBs) through testing 12 identical specimens. For this purpose, P-SHCC plates of 20 mm thickness have been prepared according to the test variables, cured for about 30 days, and then dipped into the concrete cover of the strengthened DBs at the critical shear span. The use of pre-fabricated plates is intended to alleviate any volumetric change issues associated with SHCC material. The studied parameters were the net spacing between the P-SHCC plates (0, 75, 112, and 150 mm), the width of the strengthening plates (60, 75, and 90 mm), and the ratio of steel reinforcement embedded inside the P-SHCC plates (0 %, 0.67 %, 1.50 %, and 3.00 %). Furthermore, the prestressing level relative to the yielding strain of the steel reinforcement embedded inside the P-SHCC plates was of interest. Experimental results exhibited a successful employment of the P-SHCC plates in enhancing the ultimate load capacity of RC deep beams, especially when prestressing was introduced. The gain in the ultimate capacity reached up to 68.5 %, relative to the un-strengthened control beam (BC), depending on the test parameters. Besides, incorporating steel reinforcement inside the P-SHCC plates had a pronounced effect on both the serviceability and ductility characteristics of the strengthened DBs. Specimens strengthened by reinforced P-SHCC plates demonstrated around 1.57-times improvement in energy absorption capacity when compared to their counterparts strengthened by plain P-SHCC plates. Finally, a strut-and-tie model (STM) in addition to a simpler equation based on regression analysis were used to assess the shear capacity of the strengthened DBs, considering the contribution of P-SHCC plates. The proposed two equations were in good accord with the experimental results.

Flexural behavior of reinforced concrete beams strengthened with hybrid Steel-FRP reinforcements by using near surface mounted technique

This paper investigated the behavior of reinforced concrete (RC) beams of near surface mounted (NSM) strengthening technique with using steel bar and hybrid steel bar. The effects of NSM reinforcement and load patterns on the flexural behavior and ductility of the RC beams have been studied. A four-point bending test was carried out on five reinforced concrete beams divided into two groups. The first group was tested under the effect of static load, whereas the second group was tested under repeated load. The experimental results are reported regarding the failure mode, flexural strength, load-deflection response, cracking behavior, and ductility. These results showed that strengthening of concrete beams with NSM steel bar increased the yielding and ultimate loads by about 28.6% and 28.5% respectively as compared to control beam, whereas the yielding and ultimate load increased to 33% and 35.7% over the control beam when strengthened with hybrid NSM steel bar. The ductility index of the control beam was equal to 2.6, this value increased to about 24.6% and 52.3% of the NSM steel bar and NSM hybrid steel bar strengthened beams respectively. The repeated load decreased the load capacity of the strengthened hybrid beams by about 65%, whereas the mid-span deflection is nearly the same.

Strengthening of beam against shear failure by means of vertical prestressed shear reinforcement

Strengthening of concrete beams, limited by shear resistance, is one possibility how to extend life span of a structure. Application of a vertical prestressed shear reinforcement is an efficient way how to increase the shear resistance of concrete beam. Unfortunately, current codes lack the information how to design optimal amount of the vertical prestressed shear reinforcement and how to assess retrofitted structure. In this paper, applicability of various codes of practise is assessed as option for design of vertical prestresses shear reinforcement. The presented models are compared with test data available in literature. The results of this paper show that presented models provide un-conservative approach for assessment of reinforced concrete structure strengthened by vertical prestressed shear reinforcement with the space for improvement.

Experimental and numerical analysis of RC beams strengthened with ECC and stainless steel strips

Strengthening of reinforced concrete (RC) structures may be required for several reasons and flexural strengthening of normal concrete (NC) beams is widely carried out using laminated fibres. However, the incompatibility of the concrete cover can lead to fibre debonding or concrete cover dislocation. These are some of the critical setbacks in common practice and the cost of fibre can be high. A novel flexural strengthening technique for NC beams is thus proposed: durable strips of stainless steel plate (SSP) bonded over a engineered cementitious composite (ECC), which is in complete contact with the flexural reinforcement of a slave beam through shear connectors. The flexural behaviour of NC beams strengthened with ECC and SSP strips was investigated experimentally and numerically. Three variables were investigated: the thickness of the SSP, the ECC layer with or without deformed steel bars and three different strengthening techniques. The experimental results showed that hybrid ECC–SSP strengthening improved the ultimate capacity of the NC beams by as much as 156%. A three-dimensional finite-element model (FEM) was developed and validated using the experimental results. The FEM accurately predicted the experimentally observed flexural behaviour of the NC beams with hybrid ECC–SSP strengthening. An analytical model to predict the ultimate load of NC beams with hybrid ECC–SSP strengthening was also developed.

Experimental Study on the Flexural Behavior of Large-Scale Reinforced Concrete Beams Strengthened with Prestressed CFRP Plates

Carbon fiber–reinforced polymer (CFRP) systems have been widely used to strengthen concrete structures. To further study the flexural strengthening of concrete beams with prestressed CFRP plates, flexural tests of large-scale reinforced concrete beams were performed, and a tensioning and anchorage system suitable for engineering applications was used in this study. The effects of the prestressing level, strengthening amount, type, and bonding position of the prestressed CFRP plate on the flexural behavior were investigated. The test results showed that the cracking load, yielding load, and ultimate load of all prestressed strengthened beams could reach 2.25–3.38 times, 1.27–1.53 times, and 1.24–1.61 times those of the unstrengthened beam, respectively. The postcracking stiffness, cracking load, and yielding load could be increased by increasing the prestressing level and strengthening the amount of the prestressed CFRP plate. However, a high prestressing level of 50% could lead to a premature intermediate debonding of the CFRP plate before yielding of the steel reinforcements and a reduction in the ultimate load. The use of a low-strength prestressed CFRP plate could achieve a strengthening efficacy similar to that of a high-strength CFRP plate before yielding of the steel reinforcements, whereas the low-strength CFRP plate reduced the ultimate load by 25 kN compared with the high-strength one. The prestressed CFRP plate bonded on the two sides provided a lower flexural strengthening efficacy than that bonded on the bottom of the beam owing to the shorter force arm and the nonuniform stress of the side-bonded CFRP plate.

Modelling of strengthening of concrete beams with FRP in Ansys software

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Experimental Investigation on the Strengthening of Reinforced Concrete Beams Using Externally Bonded and Near-Surface Mounted Natural Fibre Reinforced Polymer Composites-A Review.

Developing more resilient and sustainable physical infrastructure increases the demand for sustainable materials and strengthening approaches. Many investigations into strengthening RC beam structures have used either externally bonded (EB) or near-surface mounted (NSM) systems with synthetic fibre reinforced polymer composites. These synthetic fibres are unsustainable since they involve the use of nonrenewable resources and a large amount of energy. Research shows that natural fibre reinforced polymer (NFRP) composites may be an alternative to synthetic FRP composites in the strengthening of concrete beams. However, there is limited literature that validates their performance in various structural applications. Hence, the purpose of this paper is to explore the advances, prospects, and gaps of using EB/NSM NFRP techniques in strengthening concrete beams to provide areas for future research directions. The NSM FRP technique provides improved strengthening effects and mitigates the concerns associated with the EB system, based on a wider range of applications using synthetic FRPs. However, the NSM NFRP strengthening technique has been underutilized, though the EB NFRP system has been more commonly explored in reviewed studies. The knowledge gaps and areas for proposed future research directions are essential in developing work in emerging NFRPs and strengthening techniques for sustainable infrastructure.

Flexural Strengthening of Normal Strength Plain Concrete Beams using Ultra-High Performance Fiber Reinforced Concrete Strips

In recent years, the strengthening of reinforced concrete elements in existing structures has become a very important interest topic because of the demand for development structures and extending their service life. Since the ultra-high-performance fiber-reinforced concrete properties in terms of durability and strength are fully exploited, it became early in the rehabilitation and strengthening field. This paper highlights the flexural behavior of small-scale plain normal strength concrete beam strengthened in flexure by ultra-high performance fiber reinforced concrete strips at the tensile surface by adhesive epoxy material to evaluate and quantify the effect on strength in flexure. Experimental results indicated that the ultra-high performance fiber reinforced concrete strengthening strips enhanced the flexural capacity and stiffness of the normal strength concrete substrate by 369%, 364%, and 168% at crack load and 364%, 232%, and 127% at ultimate load for concrete grades 20.8, 32.6 and 43.3 MPa respectively, delayed the crack development corresponding to apply load more than 0.37, 0.97 and 1.25 kN for strips thickness 10, 15 and 20 mm respectively in all grades of concrete beam and improved beams' ductility behavior. The main important point that affects the performance of flexural strengthening concrete beams using adhesive material is the quality of the interfacial transition bonded zone of the composite system produced between the strengthening material and the existing concrete substrate.

Assessment of the Integrity of Reinforced Concrete Beams Strengthened With Carbon Fibre Reinforced Polymer Using the Acoustic Emission Technique

Today, the use of a non-destructive technique to assess the integrity of reinforced concrete structures strengthened with carbon fibre-reinforced polymer (CFRP) is becoming increasingly important. It is highly important to assess the behaviour of the structure under load. This paper presents the evaluation of a reinforced concrete beam laminated with CFRP at the soffit using the acoustic emission technique. Two types of beams were made, a normal reinforced concrete beam and a reinforced concrete beam laminated with CFRP. CFRP was used to reinforce the bottom part of the beam. The beams were subjected to three-point loading and loaded to failure. During the loading tests, the integrity of the beams was monitored using the acoustic emission technique, and the crack patterns were observed visually. The intensity analysis was carried out on two sensors, designated as CH6 and CH7. CH6 and CH7 were located on top of the beam. Based on the intensity analysis of the acoustic emissions, five intensity crack zones were identified, namely zone A-no crack, zone B-minor, zone C-intermediate, zone D-follow up and zone E-major. With increasing load, which tended to progress the crack modes in the beam, the plots in the intensity zones developed for each crack mode from zone A to zone E. The crack progression matched well with the plots in the intensity zones. Using the intensity zones enables the early detection and prediction of damage.

Critical Investigations on Shear and Flexural Behaviour of RCC Beam Retrofitted with Various Fibre Reinforced Polymer (FRP) Composites

Experimental investigations on retrofitting of RC beams over the past thirty-five years using FRP techniques have been clearly developed the potential use of different fibre reinforced polymer fabric for improving the flexural strength, toughness index and shear strength of reinforced cement concrete beams. In recent years among the different techniques of rehabilitation of existing structures, Basalt Fibre Reinforced Polymer (BFRP) as an external bonding has been considered as a popular one. This review paper is mainly to used on several features of RC retrofitted concrete beams such as strengthening of concrete beams by suitable retrofitting techniques, to extend the fatigue life of the structural element and eliminates the crack growth rate.

Flexural strengthening of fire-damaged GFRP-reinforced concrete beams using CFRP sheet: Experimental and analytical study

Since the strengthening of fiber-reinforced polymer (FRP) bar-reinforced structures after a fire incident has rarely been considered in research works, in this work, the flexural response of plain and fiber-reinforced concrete beam specimens with embedded glass FRP (GFRP) bars strengthened with carbon FRP (CFRP) sheets was examined after a fire. Variables understudy in 10 GFRP bar-reinforced concrete beams included the exposure temperature (20, 400, and 600 °C), percentage of steel fiber in volume (0 and 1%), ratio of rebars (0.00314 and 0.00872), and CFRP sheet layers (0, 1, and 2), together with the presence or absence of the U-shaped anchorage. After conducting the four-point quasi-static bending experiment on the non-heated and heated beams, several parameters including the ductility, cracking pattern, and failure mode of the beams, together with their load–deflection diagrams, were assessed. The results showed that the flexural strengthening using CFRP sheets improved the flexural capacity of the specimens and this performance improvement became more notable with an increase in the exposure temperature. In the end, the sectional analysis method was utilized to propose an analytical model capable of estimating the load–deflection response of beams strengthened with CFRP sheets; this model properly estimated the test results.

Shear strengthening of continuous prestressed concrete beams with precast SIFCON laminates subjected to monotonic and repeated loads

Slurry Infiltrated Fibre Concrete (SIFCON) is one of the recently developed construction material that can be considered as a special type of high performance fibre reinforced concrete (HPFRC) with higher fibre content. This study describes the findings of an experimental research to determine the contribution of Precast SIFCON Laminates to the enhancement of the shear strength of continuous prestressed concrete beams. Precast SIFCON Laminates were used in the investigation. It was decided to test six two-span prestressed high strength concrete continuous beams with rectangular cross-sections, each of which had a rectangular cross section. In this case, two beams were left un-enhanced as a control, and the other four beams were strengthened with varied arrangements of Precast SIFCON Laminates. The variables chosen were several wrapping strategies for the Precast SIFCON Laminates, which were then tested. The aim was to develop a better understanding of the shear contribution of Precast SIFCON Laminates and to investigate the effect of repeated loading. The results indicate that the strengthening the maximum shear regions with precast SIFCON laminates glued by epoxy resin led to improve the shear behavior the delay in first crack appearance time reached (26.4%−105.7%), Increased the ultimate shear capacity of the tested beams (19.2%–46.5%), The improvement in stiffness about (94.5%–144.9%) and the Experimental results explained that the ultimate shear strength for beams that are tested under repeated loads is a little reduced (2.2%–3.8%), comparing with the strength of the same beams under monotonic static loading.

Shear Strengthening of High Strength Concrete Beams That Contain Hooked-End Steel Fiber

Steel fiber has been used successfully in concrete mixtures to control volumetric changes, including shrinkage. However, the feasibility of the use of steel fiber has been restricted to nonstructural construction, such as ‘slab on ground’. Recently, researchers have attempted to expand the applications of steel fiber to replace structural reinforcement (rebar) and have shown promising results in its substitution for shear reinforcement. Few studies have been conducted to ensure the feasibility of using steel fiber in structural components, however. This experimental study was designed to investigate the shear performance of steel fiber-reinforced concrete beams using the tensile strength of steel fiber and the shear span-to-depth ratio as variables. The experimental results indicate that the tensile strength of steel fiber significantly affects the shear strength of steel fiber-reinforced concrete beams, regardless of the shear span-to-depth ratio, and that steel fiber can play a role in shear reinforcement of concrete beams.

Shear Strengthening of Reinforced Concrete Beams Using Fibre Reinforced Polymer: A Critical Review

The primary purpose of reinforcing bar stirrups in a reinforced concrete beam is to improve shear strength. The FRP system may significantly improve a concrete beam’s ultimate shear strength, serviceability, and ductility. The application of FRP for the repair and reinforcement of the structures has become very popular due to its low weight, high tensile strength, and simplicity of installation on uneven surfaces. FRP material outperforms other traditional materials in strengthening applications due to its high strength-to-weight and stiffness-to-weight ratios, resistance to corrosion, and ease of handling. The overall objective of this research is to investigate and improve the understanding of the recent research in the area of shear FRP strengthening of reinforced concrete beams. In this paper, recent publications were reviewed to see how different anchoring procedures, different factors that affect FRP performance and different failure scenarios affect the shear strengthening of concrete beams. The benefits and limits of FRP systems, as well as some current research trends are discussed in this project. From the research, it can be stated that type of anchorage technique and different parameter give a different impact to failure mode of the beam.

Hybrid and External strengthening of T-Reinforced Concrete Beams under Negative Bending Moment Using Steel Plates and CFRP

This study compares external bonded techniques and hybrid strengthening when used. The percentage of material for strengthening is different. This study suggests using a steel plate and a CFRP sheet to strengthen the reinforced concrete beam applied with two methods. Nine reinforced concrete T-beams divided into four groups were casted and tested under a negative bending moment. Two groups strengthened by external bonded and two groups strengthened by hybrid strengthening. All beams had the same amount of reinforcement and dimensions of 2300 mm length, an overall depth of 265 mm (200 mm web depth and flange thickness of 65 mm), an effective flange width of 390 mm, and a 130 mm web width. The strengthening by steel plate or CFRP sheet and steel plate and CFRP together, increasing the first cracking load of 40% of the span length is higher than 80%. Also, the decrease of deflection is higher than 80%. At the same time, the ultimate load of 80% is higher than 40%. CFRP sheet in strengthening with 40% lead increase in the first cracking load and ultimate load is better than steel plate when the percentage 40%, while strengthening by steel plate with 80% lead increase in the first crack load and ultimate load is better than CFRP sheet when the ratio 80%.

Cement-Based Mortar Panels Reinforced with Recycled Steel Fibers in Flexural Strengthening of Concrete Beams

The effectiveness of a strengthening technique devised for the concrete beams subjected to bending is presented in this study, where recycled-steel fiber-reinforced mortar (RSFRM) panels are used as an eco-friendly replacement for ordinary steel fibers. Different mix designs for RSFRM are first investigated experimentally by testing 160 × 400 × 400 mm3 notched beam-like specimens in 3-point bending, while 100 × 100 × 100 mm3 cubes are tested in compression, to optimize the mix design. Finite element (FE) analyses are carried out on strengthened and non-strengthened beams to investigate the effectiveness of the proposed strengthening technique based on RSFRM panels. Starting from the tests on notched beams, an inverse FE analysis is used to optimize the RSFRM’s parameters to be implemented into the numerical model. The results show that applying RSFRM panels not only markedly increases the load-bearing capacity of the beams (up to 3.19 times with 3% of fibers by volume), but also changes their fracture mechanism from brittle to ductile fracture.

Reinforcement of concrete structures with external reinforcement system with composite materials

In the article propose two methods of strengthening of concrete beams with carbon fiber. The mechanism of destruction of samples and the maximum breaking stress depending on the method of reinforcement and the density of the carbon fiber are studied. The obtained results indicate the efficiency of the system of external reinforcement of concrete beams with composite materials.

Experimental Study of the Effect of High Service Temperature on the Flexural Performance of Near-Surface Mounted (NSM) Carbon Fiber-Reinforced Polymer (CFRP)-Strengthened Concrete Beams.

This paper presents a study of the effect of high service temperature (near or beyond glass transition temperature (Tg) of structural epoxy adhesive) on the behavior of near-surface mounted (NSM) carbon fiber-reinforced polymer (CFRP)-strengthened reinforced concrete (RC) beams. The study includes experimental work as well as analytical and numerical analysis. To this end, fourteen beams have been tested up to failure in two different series. In series 1, specimens with three different CFRP areas have been tested at two different temperatures (i.e., 20 and 40 °C). In series 2, and with the aim of evaluating the effect of higher temperatures, only one CFRP area was tested under four different temperatures (i.e., 20, 60, 70, and 85 °C). Experimental results are evaluated in terms of load–deflections, failure modes, and bond performance. Furthermore, the experimental load–deflection curves are satisfactorily compared to both analytical predictions and finite element (FE) numerical simulations. In both cases, shrinkage and temperature effects on the short-term response of flexural elements have been accounted for. No significant reduction in stiffness and ultimate load was observed for specimens being tested up to 60 °C (in the range of epoxy Tg), showing FRP rupture failure in all of them. For specimens under 70 and 85 °C, the failure mode changed from FRP rupture to FRP end debonding and concrete crushing, respectively.

Shear Behavior of RC Beams Strengthened by External Vertical Prestressing Rebar

Shear design is an important part of structural design. External vertical prestressing rebars (EVPRs) have proven to be an effective way to enhance structural shear resistance. The objectives of this study are to simulate EVPR strengthening of concrete beams using a nonlinear three-dimensional finite element model and to explore its shear enhancement features under different EVPR stirrup ratios, vertical compressive stress degrees, and optimal arrangements of EVPRs. Concrete, common reinforced bars, and EVPRs use solid, steel, and truss elements, respectively. In addition, the total strain crack model is used to characterise the concrete. The results indicate that the EVPR stirrup ratio can reduce the diagonal crack width and improve the shear capacity, and the vertical compressive stress degree can effectively control crack development in the initial loading. A “small-area EVPR dense arrangement” is the recommended EVPR configuration method. Both experiments and numerical analyses show that EVPRs can effectively improve the shear performance of concrete.