Flexural Capacity Of RC Beams Research Articles

Research on the design method of flexural capacity of RC beams strengthen by ultra-high-performance concrete

Due to the increase in traffic volume, load level, and service life of existing bridges, the bending bearing capacity of reinforced concrete beams (hereinafter referred to as RC beams) has decreased, leading to safety issues. In order to solve the problem of insufficient flexural bearing capacity of RC beams, this article adopts the method of ultra-high performance concrete (UHPC) flexural strengthening RC beams, establishes a finite element model of UHPC-RC reinforcement system, and conducts stress analysis with reinforcement thickness, reinforcement range, reinforcement form, and reinforcement height as parameters to determine the optimal scheme of the reinforcement system. Based on the calculation results, a theoretical formula for the maximum principal stress and maximum deflection of the reinforcement system is proposed. To verify the feasibility of the plan, a reinforcement design was carried out on an existing beam, and it was found that the bending bearing capacity of the RC beam increased by 21%; the high tensile strength of UHPC and the addition of steel fibers have a good limiting effect on cracks; The steel plate of the reinforcement system can be used as a template, reducing construction costs and having good economy.

Failure Mode Analysis of Reinforced Concrete Beams Using GFRP Sheet as Shear Strengthening

Corrosion is an electrochemical reaction that can cause deterioration to the reinforcing steel which has implications for the decrease in the flexural capacity of the beam. The use of corrosion resistant GFRP bar as a substitute for conventional reinforcement and GFRP sheets as a substitute for shear reinforcement without a concrete cover can increase the flexural capacity of RC beams. This study aims to analyze the flexural capacity and failure mode of reinforced concrete beams with GFRP bar and GFRP sheet, with variations in width of 50 mm (BFGS50) and 100 mm (BFGS100). Conventional RC beams (BK) and beams with GFRP bars as tensile reinforcement and conventional shear reinforcement (BFSB) were made as control beams. The beam is given a static-monotonic load until failure. The results showed that the flexural capacity of the BFGS50 and BFGS100 beams was higher than the control beam (BK and BFSB). From the failure mode analysis, the control beam experienced compression failure, while BFGS50 and BFGS100 experienced shear failure.

Evaluation of mechanical properties and flexural behavior of FRCM system composed of different types of textile grid and AL powder

This experimental work aims to evaluate the flexural strengthening effectiveness of, as well as to mechanical characterize, the different types of textile grid and AL (Aluminum) powder surface coating. The experiment variables were weaving method (Pillar stitch, Leno weave) type of impregnation (SBR, EPOXY), and AL powder surface coating. The mechanical properties of FRCM systems were evaluated by direct tensile and bending tests of FRCM and flexural tests of RC beams. Direct tensile tests of FRCM were performed with clevis grips (AC434.13). Bending tests of FRCM were performed with ASTM C 1609 M. Flexural behavior and performance were analyzed in flexural tests using reinforced concrete beams strengthened with FRCM systems. For flexural tests, nine reinforced concrete beams 2,500 mm long, 150 mm wide, and 250 mm deep were fabricated. The RC beams were classified into two groups according to the rebar ratio (1.5ρmin, 0.75ρmax), and consisted of two reference specimens and seven specimens externally strengthened with the FRCM system. Test results showed that the mechanical property of FRCM systems and the flexural capacity of RC beams highly depend on the weaving methods and the impregnation types of textile grids.

Flexural Capacity of RC Beams with Opening Strengthened using CFRP Sheet

The use of Carbon Fibre Reinforced Polymer (CFRP) in strengthening has found to be an effective material which comprises of characteristic that comply to the requirement of structural component. CFRP was selected as strengthening material because of the capability to resist the corrosion and could regain the loss capacity due to presence of opening. The opening in structural member was essential in order to provide the route for the utility pipe, air conditioning, water supply and electrical conduit. However, the presence of opening has contributed to the reduction of stiffness, increase of deflection and extension of cracking of the beams. Therefore, this research was conducted to overcome the problem where the flexural capacity and the load deflection behavior of RC beam with opening strengthened by using CFRP sheet was analyzed. A total of five beam have been casted and tested. The specimens consist of beams with different type of opening which are rectangular and circular. The size of all specimen was 200 mm width, 250 mm height and 2000 mm for total length. The size of circular opening was 150 mm in diameter while rectangular opening was 150 x 200 mm. Bi-directional CFRP sheet were applied at the opening area as strengthening material and all beams were tested until failure. All of specimen were produced with the designed using 30 mm concrete cover, 6 mm link size and 10mm main bar size. The testing of specimens comprises of cube compressive test and four-point load for beam testing in order the determine the flexural strength of RC beam. The result from this research indicated that strengthened beam with circular opening which is SBOC-BI exhibit the highest ultimate load of 71.5 kN with flexural failure as the mode of failure.

Strengthening of RC Beams Using SCC Jacket Consisting of Glass Fiber and Fiber-Silica Fume Composite Gel

In this paper, strengthening of RC beams with self-consolodating concrete (SCC) jacket containing glass fiber (GF) and fiber-silica fume composite gel (FSCG) were investigated. FSCG can use as a substitute for a part of the cement that contains silica fume powder, polypropylene fibers, superplasticizer, concrete waterproof, and some other admixtures. In order to evaluate the performance of the proposed jacket, twelve beams were strengthened and a control beam was made. The variables included the amount of glass fibers consumed in the jacket (0, 0.25, 0.5, 0.75, 1 and 1.25% by volume) and the amount of FSCG gel (0 and 7.5%), respectively. Fresh and hardened concrete properties and flexural capacity of RC beams were investigated. The use of FSCG in RC jackets can compensate well for the deficiency in strength due to the GF entry into the concrete matrix. High affinity of these materials improve the cohesion between cement and GFs. RC jackets containing GF and FSCG increased the beams' energy absorption capacity by about 89 to 463%, depending on the percentages of GFs. RC jacket containing GF and FSCG delays the growth of the primary crack and it can significantly increase the maximum load. Also, GFRP sheets have poorer performance compared to the proposed method due to separation from the surface of the strengthened beams, and their load-bearing capacity and energy absorption are lower.

Finite element parametric study of RC beams strengthened with carbon nanotubes modified composites

This paper aims at investigating the capability of different FRP/concrete interface models to predict the effect of carbon nanotubes on the flexural behavior of RC beams strengthened with CFRP. Three different interfacial bond models are proposed to simulate the adhesion between CFRP composites and concrete, namely: full bond, nonlinear spring element, and cohesive zone model. 3D Nonlinear finite element model is developed then validated using experimental work conducted by the authors in a previous investigation. Cohesive zone model (CZM) has the best agreement with the experimental results in terms of load-deflection response. CZM is the only bond model that accurately predicted the cracks patterns and failure mode of the strengthened RC beams. The FE model is then expanded to predict the effect of bond strength on the flexural capacity of RC beams strengthened with externally bonded CNTs modified CFRP composites using CZM bond model. The results reveal that the flexural capacity of the strengthened beams increases with increasing the bond strength value. However, only 23% and 22% of the CFRP stress and strain capacity; in the case of full bond; can be utilized before failure.

Flexural capacity of RC beams strengthened with near-surface mounted steel bars

An experimental study carried out to observe the flexural capacity of reinforced concrete beams strengthened with Near Surface Mounted (NSM) steel bars is presented. The test was carried out on nine concrete beams. All tested beams were subjected to two-point monotonic loads. The ratio of longitudinal reinforcement (1%, 1.4%, and 2.4%) and NSM bars (1D16 and 2D16) were used as test variables. It was found from the test result that NSM steel bars significantly increase the flexural capacity of reinforced concrete beams. However, the strengthened beams failed in brittle mode, as indicated by a sudden drop of beams capacity. An analytical study was also conducted to obtain the flexural response of the specimens through all ranges of elastic and post-peak load. The prediction of the flexural capacity of the beams compares well with the test result.

Prediction of the Postfire Flexural Capacity of RC Beam Using GA-BPNN Machine Learning

AbstractTo accurately predict the flexural capacity of postfire RC beams is imperative for fire safety design. In this paper, the residual flexural capacity of postfire RC beams is predicted based ...

Análisis de elementos finitos de Vigas de Hormigón Armado CFRP

This study concerns with flexural behavior of RC beams strengthened by carbon fiber reinforced polymer (CFRP) using finite element method (FEM). ABAQUS program has been used in this research. The load-deflection relationship, crack pattern, strain in the concrete at mid-span section of the beam and failure modes of all tested beams are studied. After validation of FEM model, parametric studies are presented to assess the effect of the compressive strength of concrete, thickness, and length of CFRP, and the presence of CFRP on stress in steel bars. From the current results, it can be obtained that the flexural capacity of RC beams strengthened with CFRP increased by 6.6% for beam strengthed by EBR and to 108.8% for beam strengthed by near surface mounted (NSM) compared to the reference beams. According to parametric studies, it is found that by increasing the compressive strength of concrete from 30 MPa to 70 MPa, the beam capacity increase by 25.6%, while increasing the length of CFRP from 600 mm to 900 mm leads to increase the beam capacity by 12.7%. Increasing thickness of CFRP sheet from 0.11 mm to 0.5 mm leads to an increase in the stiffness and the flexural capacity of the beam by 47.9%. Also, the results of this study approved that the strengthening of RC beams by CFRP laminates using the NSM technique is more efficient than externally bonded reinforcement (EBR) techniques and this is agreed with the experimental results. Finally, it can be concluded that the finite element model provides good accuracy compared to the experimental results and ACI-440 results .

Effect steel reinforcement ratio on the behavior of RC beam without concrete at tension zone using truss-system reinforcement

Massive exploration of the natural materials for producing concretes affect to the environment condition and global warming that may cause natural disasters. Therefore the using of the concrete materials should be as efficient as possible. According to its natural behavior of the concrete material, it is strong in compression and weak in tension. Therefore the contribution of the tensile stresses of the concrete to the flexural capacity of the beams is neglected. However, removing concrete on the tension zone affects to the decreasing of flexural capacity. Based on the previous studies, beam without concrete at the tension zone using truss-system reinforcement causes the tension crack near the supports. This crack might because decreasing the flexural capacity of the beam. One of the solutions to solve this problem is by strengthening the beams using steel reinforcements. Therefore, this study aims to investigate the effect of steel reinforcement near the supports on the behavior of beam without concrete at the tension zone using truss-system reinforcement. The parameter of this study was the length of the additional reinforcement near the support. It was varied into 40D, 60D and 80D, where D is the diameter of longitudinal reinforcement. The results indicated that the tensile cracks near the support could be avoided by adding the longitudinal reinforcement. Finally, the flexural capacity of RC beams without concrete at the tension zone can be increased.

Experimental Study and Reliability Analysis of Flexural Capacity of RC Beams Reinforced with 600 MPa Grade Steel

Flexural capacity of beams reinforced with 400 or 500 MPa grade steel can be accurately estimated by using equations provided in design codes. Recently, 600 MPa grade steel has evolved in the construction industry, and the applicability of existing equations for this grade of steel should be verified by performing experimental investigation. By conducting tests on concrete beams reinforced with 600 MPa grade high‐strength steel, this study investigates the flexural performance for different concrete strength grades and different reinforcement ratios. Flexural capacities of concrete beams reinforced with 400 MPa, 500 MPa, and 600 MPa grade steel are analyzed based on equations in various codes and based on experimental studies in the literature. Furthermore, this study performs reliability analysis and verifies the three design values of 600 MPa grade steel yield strength in relation to the experimental performance and recommends the appropriate design values of 600 MPa grade steel yield strength. Research results show that when the measured values of yield strength of the steel bars and concrete strength are used, the ratio of the measured failure moment value to the calculated value for various beams based on different codes is nearly 1.0, demonstrating the high degree of fitting. Finally, the reliability analysis shows that the design yield strength of the 600 MPa grade high‐strength steel bars should be taken as 520 MPa.

Flexural experimental study on reinforced concrete beams strengthened with carbon fiber-reinforced polymer laminates using anchorage systems

Flexural capacity of RC beams gets significant improvement with externally bonded Carbon Fiber-reinforced Polymer (CFRP) sheet. The anchorage system is a valid means to restrain or delay debonding failure caused by stress concentration at the ends of CFRP sheets. In this paper, four RC beams, measuring 150 × 200 × 1900 mm, were examined under four-point bending test. One beam was applied for contrast. And other three were CFRP strengthened with no anchorage, CF anchors (carbon fiber anchors) and U-wraps (U-shaped CFRP wraps). The primary purpose of the experiment was to validate the effectiveness of CF anchors and U-wraps in improving the flexure character of beams strengthened with CFRP sheets. The experimental results revealed that the strengthened beams using anchorage systems performed remarkably in beam ductility, flexural capacity, load-deflection response and failure mode compared with the contrast beam. The anchorage systems were more effective and necessary to enhance the flexural behavior of beams as using CFRP laminates for flexural strengthening.

A novel and effective anchorage system for enhancing the flexural capacity of RC beams strengthened with FRCM composites

Previous experimental studies revealed that anchorage systems were able to increase the efficiency of fiber reinforced polymers (FRP) in terms of the flexure or shear enhancements and ductility performance of the structural members. This study was conducted to investigate the suitability and effectiveness of two anchorage systems for enhancing the bond performance of fiber reinforced cementitious matrix composite (FRCM), a more recent strengthening technique using a cementitious-based binding system. In the interest of improving its flexural performance, two anchorage systems were examined here: a glass spike anchor and a novel U-wrapped anchor. The novel U-wrapped anchor is a PBO strip where its’ ends had only the fabrics in the longitudinal direction that gathered and anchored into the concrete using epoxy adhesive agent. The idea behind anchoring the ends of the U-wrapped PBO strip into RC beams was to rely on the high tensile strength of the PBO strip to control the premature debonding of the FRCM composite. Real-scale simply supported RC beams were examined under the effect of strengthening with different reinforcement ratios and with and without anchorage systems engagement. Test results revealed the contribution of anchorage systems in preventing or delaying the FRCM debonding failure mechanism and enhancing the flexural performance of strengthened beams.

Research on Calculation Methods for Ductility of RC Beams with Near-Surface Mounted CFRP Plate Reinforcement

Fiber-reinforced polymer (FRP) strengthening systems are widely accepted in engineering practice as means to enhance the flexural strength of RC members, but resulting in decreased ductility. To improve the flexural capacity of RC beams strengthened with CFRP plate, but also to ensure the enough ductility, a study was carried out. Putting forward the design method of CFRP embedded reinforcement beams based on ductility ability. The result of the study revealed that the method was reliable by the analysis of an example, and the method can be used in the design of reinforcement project.

Increasing the flexural capacity of RC beams using steel angles and pre‐tensioned stainless steel ribbons

AbstractThis article presents an experimental programme on reinforced concrete beams retrofitted with steel angles and pre‐stressed stainless steel ribbons to increase their flexural strength and ductility. Two different configurations of the steel ribbon were designed, and two companion specimens for each type considered were subjected to a four‐point bending test to facilitate a direct comparison in the analysis of the effectiveness of the retrofitting technique. The influence of longitudinal steel angles and transverse stainless steel ribbons is analysed, and the concrete confinement due to stainless steel ribbons examined. The strengthened beams show remarkable increments in flexural strength and ductility with respect to the as‐built beam. Moreover, a simple cross‐sectional model was adopted to calculate the flexural strength; then sophisticated numerical tools were used to reproduce both the experimental load‐displacement curve and crack pattern for each specimen.

複数の腐食鉄筋を有するRC梁部材の非破壊検査による鉄筋断面積減少率と曲げ耐力の推定手法

腐食程度の異なる２本の鉄筋を有する鉄筋コンクリート梁供試体を対象として，非破壊検査（ひび割れ幅と超音波伝搬速度）による，鉄筋の断面積減少率の推定方法を検討した。非破壊検査は，２本の鉄筋の腐食による影響を区別できない状態を想定して実施し，その場合であっても充分安全側に断面積減少率を推定可能であることを示した。更に，得られた鉄筋の断面積減少率推定結果をインプットとして用いて，土木学会コンクリート示方書の曲げ耐力算定法に則って安全側に梁供試体の曲げ耐力を推定できることを確かめた。

Increasing the flexural capacity of RC beams using partially HPFRCC layers

High Performance Fiber Reinforced Cementitious Composites which are called HPFRCC, include cement matrices with strain hardening response under tension loading. In these composites, the cement mortar with fine aggregates, is reinforced by continuous or random distributed fibers and could be used for various applications including structural fuses and retrofitting of reinforced concrete members etc. In this paper, mechanical properties of HPFRCC materials are reviewed briefly. Moreover, a reinforced concrete beam (experimentally tested by Maalej et al.) is chosen and in different specimens, lower or upper or both parts of that beam are replaced with HPFRCC layers. After modeling of specimens in ABAQUS and calibration of those, mechanical properties of these specimens are investigated with different thicknesses, tensile strengths, tensile strains and compressive bars. Analytical results which are obtained by nonlinear finite analyses show that using HPFRCC layers with different parameters, increase loading capacity and ultimate displacement of these beams compare to RC specimens.

Experimental and numerical investigation for the flexural strengthening of RC beams using near-surface mounted steel or GFRP bars

In this paper, the effectiveness of NSM bars as a means of restoring or upgrading the flexural capacity of RC beams is experimentally and numerically investigated. The studied parameters included type of NSM bars: steel versus GFRP, and NSM reinforcement ratio (number and diameter of inserted NSM bars). A total of eight groups of 16 beams were tested under four-point bending. The two beams of the first group were reinforced with three main steel bars and were used as control specimens. The two beams of the second group were reinforced with three main GFRP bars and were utilized for comparison with control specimens. Assuming that one of the three main steel bars in the control specimen had corroded, three groups of six beams were designed in which one NSM steel or GFRP bar was inserted in the tension side. Yet, with the assumption of the corrosion of two main steel bars in the control beam, the last three groups of six beams were planned in which two NSM steel or GFRP bars were planted in the tension side. For NSM-upgraded beams, special type of epoxy paste was used as bonding agent. Test results showed that by using NSM steel or GFRP bars to compensate the difference in the main reinforcement, the original load capacity of the control beam was successfully restored. The ultimate capacity of the beams was predicted using the ACI 318-11 code and ACI 440.1R-06 guidelines. A numerical investigation utilizing nonlinear finite element (FE) analysis was also carried out using LS-DYNA software. A comparison was made between the experimental and numerical results and good agreement was obtained. Based on the validation of FE results, the numerical analysis was extended to include additional cases to study the effect of FRP reinforcement ratio on the flexural performance of NSM-upgraded beams.

Variation of steel loss and its effect on the ultimate flexural capacity of RC beams corroded and repaired under load

Abstract This paper presents results of an investigation on the variation of mass loss of deformed tensile steel bars in RC beams (153 × 254 × 3000 mm) that were corroded whilst under a sustained load using an impressed current, constant wetting cycles with 5% NaCl solution and two different drying cycles. Following the corrosion test, selected beams were patch repaired whilst under a sustained load, but eventually all beams were tested to failure. The results indicated that the highest level of corrosion occurred where there were longer drying cycles, and that the level of sustained load had little effect on the rate of corrosion. Maximum mass loss of steel was found to occur at the centre of the corrosion region. The ultimate flexural capacity of beams was found to be best related to the maximum gravimetric mass loss compared to the average mass loss of steel. A maximum mass loss of steel of 1% was found to reduce the flexural capacity of beams by 0.7%.

Experimental Study on Flexural Capacity of RC Beams with Cross-Section Patching Repair and Strengthening by CFRP Sheet

In recent years, deteriorated RC bridges due to chloride-induced corrosion have been generally rehabilitated using Fiber Reinforced Polymers (FRP) sheet. Especially for the bridge, in which the spalling and peeling of covering concrete were occurred, the delaminated covering concrete should be removed and repaired by cross-section patching before bonding FRP sheet. In this paper, the flexural capacity of RC beams with cross-section patching repair and strengthening by CFRP sheet has been studied. The RC beams repaired by four kinds of polymer cement mortar (PCM) and three kinds of polymer cement concrete (PCC) were evaluated for the different rehabilitation. And also the following two points were discussed. In the field, before the cross-section patching repair work, the adhesive was applied at the interface of placing joint (also tensile reinforcement). And the putty was applied before bonding CFRP sheet for enhancing the effect of strengthening. The effects of applying adhesive and applying putty were described in this study.As the results, if the beams were repaired by patch repair material with less 18kN/mm2 of the elastic modulus, the load bearing capability degrades a little compared with the beam without repair. But when CFRP sheet was bonded to, the effect of strengthening degrades greatly compared with the beam without repair. For applying putty, the increase of the effect of strengthening enhanced a little. And for adhesive coating, the initial bond strength between the rebar and PCM increased, but the bond strength decreased after the slip of rebar.