Behavior Of Concrete Beams Research Articles

Comparison of shear behaviour of concrete beams reinforced with GFRP bars and steel bars

This paper presents the results of an experimental program focused on a comparison of the shear behaviour of concrete beams reinforced by longitudinal GFRP bars and beams reinforced by ordinary steel reinforcement. Altogether, 24 tests were conducted on 12 beams reinforced with GFRP bars and 28 tests on 14 beams reinforced with steel reinforcement. The beams were subjected to three-point loading with shear slenderness of 3.0. An effect of axial stiffness of longitudinal reinforcement was examined. Six different reinforcement ratios, ranging from 1.34% to 7.44%, in the case of beams with GFRP bars and six reinforcement ratios ranging from 0.89 % to 2.38% in the case of beams with steel reinforcement were tested until its failure occurred. An effective depth of the beams of 100 mm was kept constant and beams were without any transverse reinforcement. The results show a favourable effect of the axial stiffness of the longitudinal reinforcement on the shear capacity in both cases. However, in the case of beams with GFRP bars, a better shear performance per unit increase of the axial stiffness was observed than in beams with steel bars. The experimental program revealed that the relation between the reinforcement ratio and the shear strength can be approximated by the cubic root of the ratio. A comparison of measured shear strengths with state-of-art design provisions for predicting shear capacity indicates good quality of all the considered models when the CoV of shear strength ratio Vtest/Vmodel ranged from 0.079 to 0.109 in the case of beams with GFRP bars and from 0.062 to 0.110 in the beams with steel bars.

Flexural Performance of Concrete Structures Reinforced with Fiber Reinforced Polymer (FRP)

ne of the most recent uses of FRP is to replace the use of steel in reinforced concrete structures. There are multiple reasons for deciding to choose FRP instead of steel such as their lightweight which can be quite beneficial to the design of buildings, high strength, and high flexibility. However, the initial use of this material was anticipated in the retrofitting of heritage buildings or any other damaged structures. There are several studies that concentrated on the use of FRP to enhance shear and flexural strength of concrete structures. However, limited studies concentrated on the effect of FRP on flexural behavior of concrete beams. Therefore, the aim of this research is to investigate the flexural performance of concrete beams that are reinforced using fiber reinforced polymers. The experimental program that was conducted in this study was divided into 4 different beams, 2 of them were reinforced using ordinary steel, while the other 2 were reinforced using carbon fiber reinforced polymer (CFRP). The highest potential deflection occurred in steel beam was 4.2 mm after applying a maximum of 42 MPa. The second beam was reinforced with FRP and accomplished 38.06 MPa, and the resulted deflection was around 12mm. The third beam was reinforced with steel and highest flexural strength measured was 75.56 MPa, while the deflection resulted from this load is 5.52 mm. Finally, the last beam was reinforced using FRP rebar and resulted deflection was 11.11 from 60.84 MPa. This study has showed the potential of using FRP in concrete structures especially in terms of flexural performance. Further studies are needed to investigate the influence of water and chemical substances on the performance of concrete beams reinforced with FRP.

Experimental investigation of the shear behaviour of concrete beams with CFRP strip stirrups under static and fatigue loading

Existing reinforced concrete (RC) structures often decrease in safety and service life owing to reinforcement corrosion or fatigue. Therefore, there are urgent requirements to propose new structures for engineering applications. This study investigates the static and fatigue shear behaviours of concrete beams using carbon fibre reinforced polymer (CFRP) strips instead of steel stirrups. The study mainly conducted the shear tests on nine statically loaded beams and six cyclically loaded beams with varied shear span ratios (a /d = 1.0, 2.5 and 3.5) and configurations of CFRP strip stirrups. The results reveal that concrete beams with CFRP strip stirrups have similar static shear behaviour to RC beams. Nevertheless, the CFRP strip stirrup beams exhibit superior fatigue life compared to that of RC beams, which significantly restrain the development of deflection, concrete cracks, and stirrup strain. Using CFRP strip stirrups instead of steel stirrups can effectively improve the shear resistance of the concrete beams under static and fatigue loading.

Flexural Tensile Behavior of Single and Novel Multiple Hooked-End Steel Fiber–Reinforced Notched Concrete Beams

Novel multiple hooked-end steel fibers possessing high anchorage with the concrete matrix have been invented and are desired to achieve significant improvement in the performance of steel fiber–reinforced concrete (SFRC). In this study, C50/C70/C80 notched concrete beams containing 4D steel fibers with 1.5 hooked ends at a dosage of 0–110 kg/m3, 5D fibers with double hook-ends at a dosage of 0–110 kg/m3, and 3D steel fibers with a single hooked end at a dosage of 0–70 kg/m3 were tested under three-point bending. The experimental results indicated that increasing fiber dosage and the number of hooked ends were generally effective in improving the flexural tensile behavior of concrete beams, especially high-strength concrete beams. The two linear relationships of the equivalent flexural tensile strength feq,2 and feq,3, evaluated by RILEM TC 162-TDF, as well as the residual flexural tensile strength fr,1 and fr,4, evaluated by BS EN 14651, were confirmed to be appropriate for concrete beams reinforced by 3D, 4D, and 5D steel fibers. Based on the experimental results from this study and more in the literature, the analytical equation, proposed by Naaman et al. and simplified by Pajak et al., was verified to be reliable for predicting the maximum flexural tensile strength for concrete beams reinforced by 3D, 4D, and 5D steel fibers. Furthermore, the analytical equation, proposed by Venkateshwaran et al., that can explicitly take into account the effects of concrete compressive strength, fiber volume fraction, fiber aspect ratio, fiber length, and number of fiber hook ends, was modified for predicting the residual flexural tensile strength (fr,i) of novel multiple hooked-end SFRC. It was found that the modified Venkateshwaran et al. equation was approved as valid for high-strength SFRCs in this study, whereas the original one only applies for low-strength and normal-strength SFRCs. All these represent a step forward in advancement on the knowledge and understanding of SFRC with novel multiple hooked-end steel fibers.

Structural Performance of Lightweight Aggregate Concrete Reinforced by Glass or Basalt Fiber Reinforced Polymer Bars.

Lightweight aggregate concrete (LWC) and fiber reinforced polymer (FRP) reinforcement are potentially more sustainable alternatives to traditional steel-reinforced concrete structures, offering several important benefits. To further the knowledge in this area, the physical–mechanical properties of LWC produced with 0%, 50%, and 100% expanded clay aggregate were assessed. Subsequently, the flexural behavior of LWC beams reinforced with steel reinforcement and glass and basalt FRP bars was tested. The results of the experimental program allowed quantifying of the effect of expanded clay aggregate incorporation on LWC properties. The use of FRP reinforcement was also compared to steel-reinforced concrete beam behavior. The results of this study can provide additional support for the use of innovative materials such as LWA and FRP reinforcement.

Shear behavior of concrete beams reinforced with closed-type winding glass fiber-reinforced polymer stirrups

Conventional pultruded fiber-reinforced polymer (FRP) rod stirrups are susceptible to premature bent corner rupture and bond slip failure of overlapping legs. This research proposed a new type FRP shear reinforcement, closed-type winding GFRP (CW-GFRP) stirrups, featuring a fully closed rectangular cross-section. CW-GFRP stirrups completely avoided slip and significantly improved the strength of bent portion of stirrups. To investigate the feasibility of using CW-GFRP stirrups as shear reinforcement, shear test of 8 concrete beams reinforced with conventional pultruded stirrups and CW-GFRP stirrups was conducted. The beams were 300 mm deep and 150 mm wide, and their shear span ratio were 2.07. The effect of the material of stirrups, the spacing of stirrups, and the width of CW-GFRP stirrups were investigated. The test results showed that pultruded stirrups exhibited bond slip failure, in contrast, CW-GFRP stirrups reinforced beams prevented this failure and showed enhanced stiffness, narrower shear crack width and 1.09–1.12 times higher shear capacity. The splitting failure typical of CW-GFRP stirrups was reported, and a smaller stirrups width is expected to avoid splitting and generate greater strain at ultimate. It can be concluded that the new type of CW-GFRP stirrups is an optimized form of FRP shear reinforcement to supersede conventional pultruded stirrups. Strut-and-tie models based on ACI 318-19 and CSA S806-14 were used to predict the shear strength and produced a safe but relatively accurate prediction.

Long-term mechanical behaviors of uncracked concrete beams prestressed with external basalt fiber-reinforced polymer tendons

In this study, an experiment was conducted on four uncracked concrete beams prestressed with external basalt fiber-reinforced polymer (BFRP) tendons or stress-relieved strands subjected to 300-day sustained loads. The experimental variables included tendon type, prestress level (40 kN and 50 kN), and concrete strength grade (C40 and C60). The effects of these variables on the long-term deformation and prestress loss of the beams were discussed and analyzed. Based on an existing approach using an age-adjusted effective modulus method (AEMM), a modified model was proposed for predicting the long-term deformation and prestress loss of concrete beams prestressed with external BFRP tendons. The results indicated that the prestress level had significant effects on the long-term deformation and prestress loss. The concrete strength grade significantly affected the long-term deformation, but had no effect on the prestress loss. The stress-relieved strands exhibited a prestress loss that was 16% greater than that of the BFRP tendons. The theoretical results based on the modified model were consistent with the experimental results. The results of this study contribute to the design and prediction of the long-term behaviors of concrete beams prestressed with external BFRP tendons.

Contribution of Glass Textile to the Shear Behavior of Concrete Beams Reinforced with GFRP Rebars

Contribution of Glass Textile to the Shear Behavior of Concrete Beams Reinforced with GFRP Rebars

The behavior of concrete beams strengthened with NSM CFRP strips: a numerical parametric study

A non-linear finite element (NLFE) model was developed to predict the flexural response of concrete beams, strengthened with near surface-mounted (NSM) carbon fiber-reinforced polymer (CFRP) strips. The model was employed for predicting the influence of a wider spectrum of key parameters, concrete compressive strength (25–55 MPa), NSM FRP strips number (2–4) or spacing (20–35 mm), bond length (100–450 mm), FRP type (carbon, glass, and basalt) and loading pattern (four-point, three-point, and distributed load), upon the performance of these beams. The results showed a clear improvement in the performance of the CFRP-strengthened concrete beams when made at a higher-strength class of concrete. Using a higher number of NSM FRP strips of the same cross-sectional area contributed to enhancing the mechanical performance noticeably. Moreover, the model developed was capable of capturing the negative impact of using a lower spacing for a constant number of NSM CFRP strips. The impact of the FRP strips' type varied upon the mechanical property predicted and the strength grade of concrete used in the casting of the beams. The load resistance of NSM FRP-strengthened specimens was the highest under three-point load configuration, followed, in sequence, by distributed and four-point loads, respectively.

Carbon fiber-reinforced polymer mesh fabric as shear reinforcement in reinforced concrete beams

Steel corrosion is a significant threat to the durability of traditional reinforced concrete (RC) members. An effective method of counteracting steel corrosion is replacing steel reinforcement bars in concrete with fiber-reinforced polymer (FRP) bars. However, the FRP bar resists being bent into a stirrup because of its in-situ manufacturing techniques. Moreover, the tensile strength of the bent portion of an FRP stirrup is significantly lower than that of the longer straight bar because of stress concentration. This paper presents an experimental and analytical study on the shear behavior of concrete beams reinforced with a carbon FRP mesh fabric (CFRP-MF) as shear reinforcement for RC members. A new CFRP-MF, which was woven in vertical and parallel directions, as an alternative to the traditional methods used for shear reinforcement, was investigated. Six concrete beams were cast with CFRP-MF as the shear reinforcements, and three concrete beams were cast as controls to investigate the shear behavior of the novel composite beams. The configuration of CFRP-MF and the overlapping condition of the intersection point were the research variables. The test results indicated that these novel composite beams have similar shear capacities and ductilities to traditional concrete beams with steel stirrups. The predictions of the shear strength of the specimens using shear design provisions in ACI 440.1R-15, CSA S6-19 and CSA S806-12 are examined and compared. The finite element method was used to compare the experimental results with numerical values, and the percentage error in all scenarios was lower than 8%.

Experimental study on flexural behavior of GFRP reinforced concrete beams

Glass fiber reinforced polymer (GFRP) has been investigated and popularly used as internal reinforcement in the construction field worldwide. Although GFRP is not easy to be corroded, employing it requires an avoidance of the brittle failure mode in order to replace traditional reinforced concrete in designing flexural elements. Therefore, this study brings an incisive view to flexural behavior of concrete beams with GFRP as reinforcements in contribution to apply GFRP to coastal and island construction in Vietnam. This study is based on the tested beams under 3-point bending test and theoretical analysis. The moment resistance of GFRP reinforced concrete beams was designed according to ACI 440-1R code. Materials including GFRP bars and concrete to fabricate tested beams were produced in Vietnam. The investigation reached a conclusion that GFRP is eligible for manufacturing flexural components, which is a potential alternative for traditional concrete in the construction industry.

Flexural Behavior of RC Beams Using Fe-Based Shape Memory Alloy Rebars as Tensile Reinforcement

Recently, various studies for the use of Fe-based shape memory alloy (Fe-SMA) in the construction field have been widely conducted. However, most of the studies for using Fe-SMA are carried out for applying Fe-SMA for strengthening deteriorated structures. However, if Fe-SMA is used as a reinforcement for new structures, the disadvantages of conventional prestressed concrete can be effectively solved. Therefore, in this work, an experimental study was conducted to evaluate the flexural behavior of concrete beams in which Fe-SMA rebars were used as tensile reinforcement. For the study, ten specimens were constructed with the consideration of the cross-sectional area and activation of Fe-SMA rebars as experimental variable. Activation of the Fe-SMA rebars by electrical resistance heating applied an eccentric compressive force to the specimen to induce camber. The camber increased by an average of 0.093 mm as the cross-sectional area of the Fe-SMA rebar increased by 100 mm2. It was also confirmed through the four-point bending tests that the initial crack loads of the activated specimens were 47.6~112.8% greater than those of the nonactivated specimens. However, the ultimate strength of the activated specimens showed a slight difference of 3% to those of the nonactivated specimens. Therefore, it was confirmed that the effect of Fe-SMA activation on the ultimate strength of specimens was negligible.

Flexural and Bond Behavior of Concrete Beams Strengthened with CFRP and Galvanized Steel Mesh Laminates

AbstractCarbon fiber–reinforced polymer (CFRP) composites are effectively and predominantly used for flexure strengthening of RC beams. Recently, new emerging composite materials known as galvanize...

Studies on the Flexural Behavior of Concrete Beams with Lathe Waste in RC

Abstract: This paper emphasis on the study of using lathe scrap as fiber reinforced concrete in the innovative construction industry. Every day about 3 to 4kgs of lathe waste are generated by each lathe industries in the Pondicherry region and dumped in the barren soil there by contaminating the soil and ground water, which creates an environmental issue. Hence by adopting proper management by recycling the lathe scrap with concrete is considered to be one of the best solutions. The test were conducted as per the Indian standard procedure for its flexural, split tensile and compressive strength and compared with FRC and conventional PCC. Also the workability of fresh concrete that containing different ratios of lathe scrap was carried out by using slump test. The result showed that addition of lathe scrap in to PCC mixture enhanced its compressive strength while it decreased the workability of the fresh concrete containing the lathe scrap. Keywords: Fiber Reinforced Concrete (FRC), Plain Cement Concrete (PCC), lathe scrap reinforced concrete, lathes scrap.

Evaluation of fracture behavior of high-strength hydraulic concrete damaged by freeze-thaw cycle test

Hydraulic concrete structures in cold regions are vulnerable to freeze–thaw (FT) damage, which will affect the fracture performance of concrete structures. Hence, the fracture characteristics of high-strength hydraulic concrete subjected to different FT damage (0, 100, 200, 300, 400 FT cycles) are studied by experimental analysis and discrete element method (DEM) simulation. The results show that the FT damage has a significant weakening effect on the fracture characteristics of concrete beams. The elastic modulus E, critical crack length ac, fracture toughness KIc, fracture energy GF and critical crack tip opening displacement CTODc of concrete beams all show a linearly decreasing trend with the increase of the number of FT cycles. In addition, digital image correlation (DIC) and acoustic emission (AE) techniques are used to reveal the evolution law of internal cracks of FT damaged concrete beams under three-point flexural loads. On the basis of experimental research, the influence indexes of FT damage are introduced into DEM parameters, and a fracture model considering real aggregates is established, which can well predict the fracture behavior of concrete beams subjected to different FT cycles.

Bending Behaviour of Concrete Beams with Composite Reinforcement

Massive quantities of finite resources have been depleted due to the construction and building sectors. Using bio-products to reduce raw materials use is seen as a major step toward a sustainable building sector. In this regard, the current research developed a novel composite beam reinforced and double-confined using a flexural and shears continuous FRP-Jacket. The suggested method involves swapping out conventional Portland cement-based concrete with a greener variant made with a different mix percentage that includes dry clay and hydraulic lime. Experimental testing and theoretical modeling based on shear stress and deformation composite beams are used to assess the bends & shear performance of the suggested design with four-point flexural load. The double-confinement approach used resulted in a noticeable improvement in strength and deformability compared to conventional concrete beams, as shown by strong agreement between experimental and modeling results in terms of effective stress, pressure concentration, and cement reduction.

Integrated High-Performance Concrete Beams Reinforced with Hybrid BFRP and Steel Bars

AbstractThe flexural behavior of concrete beams reinforced with a combination of basalt fiber–reinforced polymer (BFRP) bars and steel bars is investigated herein. Five hybrid BFRP and steel bar RC...

Flexural Behaviors of Concrete Beams Under Monotonic and Cyclic Loadings

Flexural Behaviors of Concrete Beams Under Monotonic and Cyclic Loadings

Enhancement the Shear behavior of concrete beams reinforced with hybrid-wires bars by using steel fibers.

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Flexural behavior of concrete beams reinforced with glass fiber reinforced polymer and steel bars

In this study, a comparative experimental analysis is performed between steel-reinforced concrete beams, which are dimensioned based on NBR 6118 (2014), and beams reinforced with glass fiber-reinforced polymer (GFRP) rebar, which are dimensioned based on ACI 440.1R (2015) after being subjected to a four-point bending test. The beams are dimensioned to resist the same force and to satisfy the service limit state (SLS). Results show that the two groups of beams exhibit similar vertical displacement behaviors until the SLS-DEF, whereas the GFRP beams exhibit larger deflections. At the ultimate load, the beams with fiberglass bars indicate a higher resistance by approximately 64% compared with those with metal bars.