Abstract
JOURNAL OF ASIAN ARCHITECTURE AND BUILDING ENGINEERING 2021, VOL. 20, NO. 5, 520–532 https://doi.org/10.1080/13467581.2020.1870983 BUILDING STRUCTURES AND MATERIALS Experimental and numerical studies on the flexural behavior of fibre reinforced concrete beams with innovative hybrid FRP-wrapped steel bars a b Sivaramakrishnan Subbaram and Chinnaraju Komarasamy a b Civil Engineering Department, Sri Sairam Institute of Technology, Chennai, Tamilnadu, India; Civil Engineering Department, College of Engineering, Anna University, Chennai, Tamilnadu, India ABSTRACT ARTICLE HISTORY Received 12 June 2020 The durability and lifespan of concrete structures are significantly affected by the corrosion of Accepted 22 December 2020 steel reinforcement. Though epoxy-coated steel reinforcement is being used for practical applications, slight damage in the coating during the construction process is enough to initiate KEYWORDS the corrosion process. The shortcomings in the current practices to prevent corrosion of steel Corrosion; hybrid rebars; reinforcement have led the researchers to look for alternatives. Innovative hybrid reinforcing reinforcement; FRP; flexure; elements with solid steel core and fibre-reinforced polymer (FRP) wrapping (called steel–FRP fem composite bars (SFCB)) can be considered as a suitable alternative to conventional steel reinforcement. In this research paper, experimental and numerical studies that investigated the flexural behaviour of concrete beam specimens reinforced with SFCB produced using glass fibres or carbon fibres are presented and discussed. Experimental study consisted of flexural testing of six concrete beam specimens with conventional steel reinforcement or SFCB with glass fibres or SFCB with carbon fibres. Two different spacings of shear stirrups were consid- ered. Failure mode, first crack load, ultimate flexural load and load-deflection behaviour were recorded during the experiment. The test results showed that beam specimens with SFCB reinforced achieved less ultimate flexural load as compared to beam specimens with conven- tional steel reinforcement. The failure mode was found to be influenced by the spacing of the shear stirrups. The results of the numerical analysis were close to the experimental results. . 1. Introduction members (Xu et al. (2019), Sun et al. (2019)). This type of reinforcement would reduce the cost of construction Reinforced concrete (RC) is inevitable in the construction as compared to that incurred by using only FRP bars. of civil infrastructure facilities such as bridges and build- While using hybrid reinforcement, FRP bars are placed ings. The durability of RC structures is significantly near the outer surface of the concrete members (with affected due to corrosion of steel reinforcement, and lesser cover thickness) and steel bars are placed at inner this reduces their life span. It has been reported that the areas (with higher cover thickness) thereby prolonging United States spends around 276 USD billion (3.1% of the time of initiation of corrosion and enhancing the GDP) annually as a direct cost to corrosion (URL-1). In lifespan of the structures. It is to be noted that, even order to curb the cost incurred due to corrosion in the though adopting hybrid reinforcement would increase future, new innovative reinforcing elements such as fibre- the concrete cover for tension steel, steel stirrups that reinforced polymer (FRP), plasma rebars, corrosion- would have lesser cover would be used. Steel stirrups resistant rebars (steel rebars with higher content of chro- would therefore provide an electrical contact of the mium) and epoxy-coated rebars are being adopted for inner steel bars, and there are possibilities that the practical applications. envisaged lifespan of the RC members might not be research studies (Toutanji and Saafi (2000), Toutanji achieved. Towards improving the possibilities of com- and Young (2003), Masmoudi, Theriault, and bined use of steel bars and FRP bars for reinforcing Benmokrane (2001)) have been conducted that investi- concrete members, attempts have been made as early gated the influence of using FRP bars as reinforcement as the 1980s for developing rebars consisting of steel on the flexural behaviour of concrete beams. However, core and FRP wrapping around the core (herein called as the use of FRP rebars for practical applications is limited steel-FRP composite bars (SFCB)). A typical photograph primarily due to lower elastic modulus, brittle nature of SFCB is shown in Figure 1. The FRP shielding would and high cost. In order to reduce the cost and achieve prevent or significantly reduce corrosion of steel core, durable and ductile RC structures, researchers have pro- thereby improving the lifespan of RC structures rein- posed using combined steel and FRP bars as reinforce- forced with SFCB and subjected to corrosive environ- ment (called hybrid reinforcement) in concrete ment, especially in coastal regions. CONTACT Sivaramakrishnan Subbaram sivag1984@gmail.com Sri Sairam Institute of Technology, Chennai, Tamilnadu 600044, India © 2021 The Author(s). Published by Informa UK Limited, trading as Taylor & Francis Group on behalf of the Architectural Institute of Japan, Architectural Institute of Korea and Architectural Society of China. This is an Open Access article distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/4.0/), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. JOURNAL OF ASIAN ARCHITECTURE AND BUILDING ENGINEERING 521 compared well with the experimental results. Hawileh (2014) conducted finite element studies to predict the load vs deflection behaviour of concrete beams reinforced with hybrid steel and FRP bars produced with aramid fibers. The authors observed that the load vs deflection behaviour could be predicted well using the model devel- oped. The author also remarked that only limited numer- ical studies that investigated the behaviour of FRP- reinforced concrete elements are available in the literature. Bencardino, Condello, and Ombres (2016) have carried out numerical studies on the behaviour of concrete beams with steel, FRP and hybrid FRP–steel reinforcements. The authors have observed that the tension stiffening model Figure 1. Typical SFCB. they have considered predicted the behaviour well for beams with low and normal reinforcement ratio; however, for beams with higher reinforcement ratio, the numerical Zhou et al. (2019) have conducted experiments for predictions were not comparable to the test results. Similar studying the corrosion behaviour of SFCB using X-ray numerical studies can be found elsewhere in the literature microcomputed tomography. Test results have showed (Al-Rahmani and Abed (2013), D D, Pisano, and Fuschi that the type of fibre, micropore structure of the fibre (2014), Ferreira et al. (2001), Rafi, Nadjai, and Ali (2008), coating layer and manufacturing process arethe factors Nour et al. (2007)). To the authors' knowledge, numerical that influenced the corrosion resistance of the rebars. The simulation studies that predicted the flexural behaviour of corrosion rate of SFCB was found to be significantly less concrete beams consisting of SFCB as reinforcing elements than that of bare steel rebars. The authors have also found are not available in the literature. through tensile tests that the elastic modulus of the SFCB The combined use of SFCB and steel fibres as reinfor- was more than that of GFRP and the tensile strength was cement can be considered to be a novel technique for more than that of steel rebars. Zhao et al. (2020) have achieving higher durability and improved cracking resis- conducted experimental studies to determine the tensile tance in concrete structural members. For developing properties of SFCB and their bonding performance in design guidelines for practical applications, flexural beha- concrete. Test results have showed that SFCB with vior of concrete beams reinforced with SFCB and fibres round steel core and FRP wrapping showed better tensile has to be investigated experimentally and numerically, behaviour as compared to those with ribbed steel core and that motivated the research presented in this paper. and FRP wrapping. The authors have observed that the In order to fill these gaps in the literature, in this paper, rule of mixtures can be used to describe the tensile experimental studies are conducted to investigate the behaviour of SFCB. The stress–strain curve of SFCB flexural behaviour of fibre-reinforced concrete beam speci- showed a bilinear trend. Bond strength of SFCB was mens consisting of SFCB as tensile reinforcement. Two influenced by the diameter and the surface treatment. types of SFCB produced with glass fibers and carbon fibres Fibre-reinforced concrete consisting of steel or syn- are considered. The flexural behaviour of concrete beam thetic fibres is reported to enhance the ductility of con- specimens with SFCB is compared with control concrete crete, and it has also been shown that the addition of beam specimens reinforced with conventional steel bars. fibres improves the resistance of concrete to formation The beam specimens are tested under 4-point bending and propagation of cracks (Zhao et al. (2016), Yehia et al. with simply supported boundary conditions. Numerical (2016), Aldabagh, Abed, and Yehia (2016), Farrag and analyses consisted of developing models of the tested Yehia (2015), Yehia et al. (2015), Yehia (2012)). beam specimens in general-purpose finite-element soft- In the literature, experimental research studies that ware ABAQUS and validating with test results. determined the behaviour of concrete structural elements with SFCB are reported. However, experimental and numerical studies that investigated the flexural behaviour 2. Accelerated corrosion test of fibre-reinforced concrete beams consisting of SFCB are not found to be reported. Numerical studies reported in A pilot experimental study (Accelerated corrosion test) the literature consisted of simulating the flexural behaviour was conducted to determine the corrosion behaviour of concrete beams with FRP bars as reinforcing elements or (gravimetric weight loss) of the proposed SFCB and hybrid steel and FRP bars as reinforcing elements. Abed compare it with that of conventional steel bars. It is et al. (2020) have carried out numerical simulations on the known that corrosion of steel is an electrochemical behaviour of concrete elements reinforced with FRP bars process, and it involves anode, cathode and an elec- under different loading conditions. The authors have trolytic solution. The process of corrosion is shown in observed that the predicted behaviour of the elements Figure 2. (URL-2). 522 S. SUBBARAM AND C. KOMARASAMY Figure 2. Corrosion process (URL-2). Figure 4. Rebars for accelerated corrosion test. The corroding portion of steel is the anode and the un-corroded portion is the cathode. Electrolyte solution It was observed from the test results that the conven- provides electrical contact between the anode and the tional bare steel rebar lost most of its material due to cathode. Under favourable conditions, ferrous ions from corrosion. However, SFCB rebars with glass fibers or car- anode (steel) enter into the electrolyte. The electrons that bon fibers were found to be less affected. It was observed are released from the corroding part of the steel (anode) that the percentage loss of conventional steel rebar was move towards the cathode and form hydroxyl ions by very high as compared to the percentage loss of steel in combining them with water and oxygen. These hydroxyl SFCB with glass or carbon fibers. The corrosion test results ions react with the ferrous ions that are released from the showed that the durability of concrete structures could be anodic portion of steel and form hydrated ferrous oxide. improved enormously by using SFCB as reinforcing ele- The ferrous oxide further gets oxidized to form ferric ments. It was noted that the accelerated corrosion tests oxide which is known as the “red dust”. were conducted on bare steel bars and SFCB. However, in Three bare specimens such as (i) steel, (ii) SFCB with practical applications, the steel reinforcement would be glass fibers and (iii) SFCB with carbon fibers were con- embedded in concrete. Further research studies on the sidered for accelerated corrosion test. The SFCB were corrosion behaviour of SFCB embedded in concrete are manufactured manually. Details of the manufacturing required to determine their actual corrosion behaviour. procedure of SFCB are available in the literature (Sivaraman and Chinnaraju 2019). The acceleration of the corrosion process was 3. Details of beam specimens and flexure test achieved by impressing an anodic potential between setup the rebar anode and steel plate (Saraswathy and Song The experimental program consisted of testing six con- (2008), Güneyisi, Özturan, and Gesolu (2006), Song et al. crete beam specimens of dimension 130x230x1400mm (2009)). The rebars were immersed in a 3.5% sodium (bxdxl) and reinforced with conventional steel rebars or chloride (NaCl) solution during the test. An impressed voltage of 10 V was applied to accelerate the corrosion process. The accelerated corrosion process was carried Table 1. Corrosion test results. out for 24 h. The schematic diagram of the accelerated Weight before Loss of Sl. Type of corrosion in Weight after corro- weight in corrosion test setup is shown in Figure 3. No. Rebar grams sion test in grams % The SFCB specimens for the corrosion tests are 1 Steel rebar 115.58 63.14 45 shown in Figure 4. 2 SFCB with 102.34 97.12 2 glass The weight of steel and SFCB specimens was deter- fibers mined before the corrosion test and after the corrosion 3 SFCB with 100.47 99.95 3 carbon test and listed in Table 1. Figure 5 shows the steel and fibers SFCB specimens after the accelerated corrosion test. Figure 3. Schematic diagram of accelerated corrosion test setup. Figure 5. Rebars after accelerated corrosion test. JOURNAL OF ASIAN ARCHITECTURE AND BUILDING ENGINEERING 523 SFCB with glass fibers (GFRP wrapping) or SFCB with The beams were subjected to 4-point bending. The carbon fibers (CFRP wrapping) in the tensile zone. In beams were simply supported at both edges with SFCB, GFRP or CFRP wrapping was provided over the a clear span of 1200 mm. The loading was applied entire length of the steel core. The diameter of the con- using a 300 kN hydraulic jack and the load was trans- ventional steel rebars was 10 mm, and the diameter of ferred using a rigid transfer beam to form two point SFCB produced by wrapping GFRP or CFRP for a thickness loads on the beam specimens. The distance between of 1 mm over the steel core of 10 mm diameter was one of the loading points and the nearest support was 12 mm. Fe500 grade steel rebars were used. The hanger 400 mm, and the shear span-to-depth ratio was kept as bars consisted of 2#10 mm diameter steel rebars, and 1.95. A schematic diagram of the beam specimen with stirrups were made of 8 mm steel rebars spaced at reinforcement details is shown in Figure 6(a) and 150 mm c/c or 300 mm c/c. The effective cover for the a typical photograph of the test setup used is shown tensile reinforcement was kept as 30 mm. Fibre- in Figure 6(b). reinforced concrete with an average 28-day compressive strength of 26.3 was used for casting the specimens. The mix proportion of the concrete mix used was 4. Details of numerical model 1:1.51:2.77:0.45 in the order of cement (Portland The FE model was validated first with beam speci- Pozzolana Cement), fine aggregates (river sand) and mens with conventional steel reinforcement (Figure coarse aggregates (20 mm gravel). Water–cement ratio 12a) and only then used for modelling beam speci- of 0.5 was considered. Hooked type steel fibres with an mens with SFCB. Numerical models were developed aspect ratio of 60 were used in the concrete mix. The for all the tested beams consisting of shear stirrups amount of fibres considered was 2% of cement content. at a spacing of 150 mm in the finite element soft- The details of the beam specimens tested are given in ware ABAQUS. Concrete and reinforcement (steel Table 2. and SFCB) were modelled as 3D parts using In Table 2, the effective reinforcement ratios are C3D8Relements. SFCB was modelled with a steel determined using the equation given below, core of diameter 10 mm and GFRP/CFRP wrapping over the steel core for a thickness of 1 mm. The ρ ¼ ρ þ ρ (1) bond between the steel core and the GFRP/CFRP eff s f σ orσ cg cc wrapping was assumed to be perfect, and it was achieved by using Tie constraint. Test results indi- where ρ = A /bh , ρ = A /bh , A is area of steel bars, s s o f f o s cated that the tested beam specimens with SFCB as A is the area of FRP bars, b is section width, h is f o tensile reinforcement achieved lesser ultimate flex - section effective depth, f is yield strength of steel, ural load as compared to the beams specimens with σ or σ is tensile strength of FRP using glass or cg cc conventional steel reinforcement. The reason for carbon fiber. The corresponding balanced reinforce- this observation was attributed due to the lesser ment ratio can be calculated as the ratio where con- bonding action between the SFCB and the sur- crete crushing and steel yield occur simultaneously rounding concrete due to the smoother surface of given by ACI 440–1 R-06. the SFCB reinforcement (see Section 4.3). This beha- viour was simulated in the model by specifying f E ε f cu ρ ¼ 0:85β1 (2) fb interaction property at the SFCB–concrete interface. f E ε þ f fu f cu fu Guo et al. (2020) have observed that the friction where f is tensile strength of FRP, ε is ultimate strain coefficient at the steel–concrete interface could fu cu in concrete, ε is rupture strain of FRP bars, E is vary in the range 0.377–0.458. In this numerical fu f modulus of elasticity of FRP bars, β1 is the strength model developed, the steel–concrete friction coeffi - reduction factor taken as 0.85 for concrete strength up cient at the interface was kept as 0.3 for conven- to 27.6 Mpa. This factor can be reduced if the strength tional steel reinforcement. For the beam specimens is in excess of 27.6 Mpa, but it should not be taken less with SFCB, the friction coefficient of the SFCB–con- than 0.65. crete interface was adjusted so as to get load– Table 2. Beam specimen details. Sl. No. Beam ID Tensile Reinforcement Type of FRP Stirrups Spacing Balanced Reinforcement Ratio Effective Reinforcement Ratio (mm) (ρ ) (ρ ) fb eff 1 BS150 2#10 mm dia steel rebars -NA- 150 0.0197 0.0059 2 BS300 300 3 HBG150 2#12 mm dia of SFCB rebar GFRP 150 0.0014 0.0070 4 HBG300 300 5 HBC150 CFRP 150 0.0025 0.0074 6 HBC300 300 524 S. SUBBARAM AND C. KOMARASAMY Figure 6. (a) Schematic diagram of specimen details. (b) Typical beam specimen in test setup. deflection curves comparable to that of test results. 640 Mpa; tensile strength of GFRP and CFRP wrap- Iterations were made to get numerical load–deflec - ping was obtained based on the rule of mixtures, tion curves close to experimental load–deflection and it was 1157MPa and 882MPa, respectively curves. Based on iteration, a friction coefficient of (Sivaraman and Chinnaraju 2019). The elastic mod- 0.1 was finalized as it resulted in numerical load– ulus of GFRP and CFRP wrapping was also obtained deflection curves close to experimental load–deflec - based on the rule of mixtures and were found to be tion curves. 37,920 MPa and 41,400 MPa, respectively Unidirectional tensile test specimen was prepared (Sivaraman and Chinnaraju 2019). according to ASTM D3916. UTM was used for the ten- The constitutive relationship for concrete was mod- sile test. The loading rate was 5 mm/min. After the rods elled using Concrete Damaged Plasticity option avail- are cured, additional epoxy resin impregnated glass able in ABAQUS. The uni-axial stress–strain curve of fabrics were wrapped around the ends to increase their end diameter at least 1 mm to serve as tabs for gripping in a tensile testing machine. The rods are approximately 10 mm in diameter and 600 mm in length. The hybrid rebars using glass fibers consist of 30 numbers of glass fiber strands and hybrid rebars using carbon fibers consist of 14 numbers of carbon fiber strands. Figure 7 shows the tensile specimen and unidirectional test set up. Figure 8 shows the stress– strain graph of the hybrid rebars. The material property of steel was assumed to be bi- linear. An earlier study by Zhao et al. (2020) indicated that the tensile strength of FRP based on the rule of mixtures was compared well with the experimental results. In the present study, the yield strength of steel is 510 Mpa and the ultimate tensile strength of steel is Figure 8. Stress–strain behaviour of hybrid rebars. JOURNAL OF ASIAN ARCHITECTURE AND BUILDING ENGINEERING 525 Figure 7. Tensile specimen and Unidirectional test setup. Elastic modulus, pffiffiffiffiffi 0:5 E ¼ 5000 f ¼ 5000 x ð25Þ ¼ 25000 MPa (5) ck where f is the characteristic compressive strength ck and f is the mean compressive strength of concrete. cm 5. Test results and discussion 5.1. Failure mode The photograph of the tested beam specimens is shown in Figure 10. It is observed from Figure 8 that the cracking pattern of the tested beam specimens was influ - Figure 9. Stress–strain curve for concrete under Uni-axial enced by the type of reinforcement used and the compression. spacing of shear stirrups. More number of flexural cracks occurred in the beam specimens BS150 and concrete in compression was modelled using the BS300 (as compared to other beam specimens equation proposed by Saenz (1964) and is shown in tested), and the final failure was due to the opening Figure 9. of one flexural crack formed near the mid-span. The The behaviour of concrete under tension was mod- number of cracks in the beam specimen BS150 was elled using the fracture energy criterion. The fracture more than that formed in the beam specimen energy of the concrete was calculated using Fib Model BS300. It was also observed that, at failure, in Code (2010) equation as given below. beam specimen BS150, crushing of concrete in the Fracture lab energy compression zone occurred in the mid-span. The 0:18 0:18 2 beam specimens BS150 and BS300 failed in flexural G ¼ 73 ðf Þ ¼ 73 x ð25Þ ¼ 130 J=m (3) f cm mode. The tensile strength of concrete was determined using In the beam specimens HBG150 and HBG300, the the formula suggested by Graham and Scanlon (1986) number of cracks formed at failure was significantly as given below. influenced by the spacing of the shear stirrups. The Tensile strength, number of cracks in the beam specimen HBG150 was pffiffiffiffiffi more than that in the beam specimen HBG300. The 0:5 f ¼ 0:33 f ¼ 0:33 x ð25Þ ¼ 1:65 MPa (4) t ck beam specimen HBG150 failed by the widening of the The elastic modulus of concrete was arrived based on crack formed in the shear span region. The crack was IS 456:2000. initially oriented vertically such that it occurred 526 S. SUBBARAM AND C. KOMARASAMY Figure 10. Tested beam specimens. primarily due to flexural stress; however, it became concrete in the compression zone of the beam speci- inclined with an increased magnitude of applied flex - men HBG300 also failed due to crushing. It is worth to ural loading. The crack tended to join one of the load- note the difference in the observed failure modes of ing points and the bottom edge of a cross-section that the beam specimens HBG150 and HBG300. The differ - was located slightly away from the nearest support. ence was that the inclined shear crack tended to join The beam specimen HBG300 failed due to an one of the loading points and bottom edge of the inclined shear crack that tended to join one of the cross-section that was located slightly away from the loading points and the nearest support. At failure, the support in the beam specimen HBG150 (called flexure– JOURNAL OF ASIAN ARCHITECTURE AND BUILDING ENGINEERING 527 Table 3. Test results. Sl. No. Beam ID First Crack Load Ultimate Flexural Load Flexural Toughness Failure Mode (kN) (kN) (kNmm) 1 BS150 46.0 116.9 1870 Flexure 2 BS300 39.0 111.5 977 Flexure 3 HBG150 11.0 56.4 325 Flexure-Shear interaction 4 HBG300 22.0 54.5 610 Shear 5 HBC150 14.8 60.1 651 Flexure-Shear interaction 6 HBC300 20.0 56.2 564 Shear shear interaction failure mode); however, the inclined HBG300 and HBC300 were 100% and 35%, respec- shear crack tended to join one of the loading points tively, more than that of the beam specimens and the support in the beam specimen HBG300 (called HBG150 and HBC150. This observation indicated as shear failure mode). The failure mode of the beam that the first crack load was significantly influenced specimen HBG300 was exactly similar to the failure of by the spacing of the shear stirrups in the beam deep beams. These observations clearly indicated that specimens reinforced with SFCB produced using the spacing of shear stirrups influenced the failure glass fibres as compared to those produced using mode of the beams reinforced using SFCB produced carbon fibres. using glass fibre wrapping. Except for the crushing failure of concrete in the compression zone in HBG300, the failure modes of the 5.3. Ultimate flexural load beam specimens HBC150 and HBC300 were similar to The ultimate flexural load of the tested beam speci- that of the beam specimens HBG150 and HBG300, mens are given in Table 3. It is observed from Table 3 respectively. that the ultimate flexural load of the tested beam specimens (BS150, HBG150 and HBC150) with 150 mm shear stirrups spacing was 5%, 3% and 7%, 5.2. First crack load respectively, more than that of the corresponding The first crack load of the tested beam specimens is beam specimens (BS300, HBG300 and HBC300) with given in Table 3. 300 mm shear stirrups spacing. This observation indi- It is observed from Table 3 that the first crack load of cated that the ultimate flexural load of the tested all the tested beam specimens was influenced by the beams specimens was not significantly influenced by spacing of the shear connectors. For the beam speci- the spacing of the shear stirrups considered in this mens reinforced with conventional steel reinforce- study. ment, the first crack load increased with a decrease in The beam specimens with conventional steel the spacing of the shear connectors. However, for the reinforcement achieved higher ultimate flexural beam specimens reinforced with SFCB, test results load as compared to the beam specimens with showed that the first crack load increased with an SFCB are tensile reinforcement. The ultimate flexural increased spacing of the shear connectors. load of the beam specimens HBG150 and HBC150 The first crack load of the beam specimen BS150 was nearly 50% of the ultimate flexural load of the was 18% more than that of the beam specimen beam specimen BS150. Similarly, the ultimate flex - BS300. The first crack load of the beam specimens ural load of the beam specimens HBG300 and Figure 12. Variation in flexural toughness of tested beam Figure 11. Load–deflection curves of tested beam specimens. specimens. 528 S. SUBBARAM AND C. KOMARASAMY HBC300 was nearly 50% of the ultimate flexural load have been less as compared to that of conventional of the beam specimen BS300. The reason for less steel reinforcement, and this could have resulted in ultimate flexural load of the tested beams speci- lesser ultimate flexural load. mens with SFCB as tensile reinforcement could be attributed to the following. Visual observations indi- cated that the surface of SFCB reinforcement was 5.4. Load–deflection behavior relatively smooth as compared to conventional steel The load–deflection curves of the tested beam speci- reinforcement. Due to the smoother surface of the mens are shown in Figure 11. SFCB reinforcement, its bond with concrete could Figure 13. Comparison of failure modes. JOURNAL OF ASIAN ARCHITECTURE AND BUILDING ENGINEERING 529 Figure 13. (Continued). It is observed from Figure 11 that the load–deflec - HBG300 and HBC300 was similar to that of deep tion curves of all the tested beam specimens showed beams, their behaviour was slightly stiffer (due to rela- tri-linear behaviour. The stiffness of the tested beam tively less ductile behaviour) than the beam specimens specimens was found to be influenced by the type of HBG150 and HBC150, respectively. reinforcement and spacing of the shear stirrups. It is observed from Figure 11 that the initial stiffness 5.5. Flexural toughness of the tested beams BS150&, BS300, and HBC150 & HBC300 can be assumed to be nearly the same irre- The flexural toughness of the tested beam specimens spective of the spacing of the shear stirrups. However, was obtained as the area under the load–deflection Figure 11 shows that the initial stiffness of the tested curves and is given in Table 3. The variation in the beams HBG150 and HBG300 was found to be influ - flexural toughness of the tested beams is also shown enced by the spacing of the shear stirrups. The initial in Figure 12. stiffness of the beam specimen HBG300 was more than It is observed from Table 3 and Figure 12 that, irre- that of the beam specimen HBG150. spective of spacing of shear stirrups, the flexural tough- With the increase in the applied flexural loading ness of the beam specimens BS150 and BS300 with beyond the first crack load of the tested beam speci- conventional steel reinforcement was more than that mens, the flexural stiffness of the tested beams of other beam specimens consisting of SFCB as reinfor- decreased linearly due to the formation and widening cement. Among the beam specimens with SFCB as rein- of cracks. Critical observation of Figure 11 indicated forcement, HBC150 achieved higher flexural toughness. that even with increased loading magnitude (beyond first crack load), the stiffness of the beam specimen 6. Numerical analysis results HBG150 was more than that of the beam specimen HBG300 till ultimate load. However, test results Comparison of failure modes of beam specimens (Figure 11) showed that, in general, the stiffness of BS150, HBG150 and HBC150 obtained from the numer- the beam specimens HBG300 and HBC300 was more ical simulation and experiment is shown in Figure 13. than the beam specimens HBG150 and HBC150, It is observed from Figure 13 that the numerical respectively. The reason for this observation could be models developed are able to predict the flexural fail- attributed due to the difference in the failure modes of ure of beam specimen BS150 and failure due to com- the beam specimens HBG300 and HBC300 as com- bined shear-flexural stresses of the beam specimens pared to that of the beam specimens HBG150 and HBG150 and HBC150. Comparison of load–deflection HBC150. Since the failure mode of the beam specimens curves of the beam specimens BS150, HBG150 and 530 S. SUBBARAM AND C. KOMARASAMY Figure 14. Comparison of load–deflection curves. HBC150 obtained from numerical simulation and comparable. However, it is observed from Figure 14(b experiment is shown in Figure 14. and c) that the initial stiffness of the beam specimens It is observed from Figure 14(a) that the load– HBG150 and HBC150 as obtained from the numerical deflection curves of beam specimen BS150 obtained analyses was more than that obtained experimentally. from numerical analysis and experiment are The deviation was more for beam specimen HBG150 JOURNAL OF ASIAN ARCHITECTURE AND BUILDING ENGINEERING 531 Table 4. Comparison of ultimate flexural loads. Ultimate Flexural Load Sl. No. Beam Specimen Experimental (P ) Numerical (P ) P /P e n n e 1 BS150 116.9 109.2 0.93 2 HBG150 56.4 61.8 1.10 3 HBC150 60.1 62.5 1.04 towards improving the lifespan of reinforced con- crete structures located in a corrosive environment. The flexural behaviour of concrete beams speci- mens was influenced by the type of reinforce- ment used in the tension zone. The beam specimens with hybrid reinforcement failed either due to shear-flexural stresses interac- tion or due to shear depending upon the spacing of the shear stirrups. ● The numerical models developed were able to predict the ultimate flexural load comparable to the concrete beam specimens BS150, HBG150 and HBC150 with reasonable accuracy. ● Further research is required in this area towards developing design guidelines. Figure 14. (Continued). Disclosure statement No potential conflict of interest was reported by the authors. than that for the beam specimen HBC150. Comparison Notes on contributors of experimental ultimate flexural load and as obtained from the numerical analyses of the tested beams Sivaramakrishnan Subbaram, corresponding author, is work- BS150, HBG150 and HBC150 is shown in Table 4. ing as a assistant professor in Sri Sairam Institute of Technology Chennai. It was observed from Table 4 the predicted ultimate flexural load of beam specimen BS150 was 7% less than Chinnaraju Komarasamy, is working as Professor in College of the experimental results. The predicted ultimate flexural Engineering Guindy. The first author is doing Ph.D under the guidance of second author. load of the beam specimens HBG150 and HBC150 was 10% and 4%, respectively, more than the experimental results. In general, the results indicated that the predicted References ultimate flexural load of the beam specimens was Abed, F., C. Oucif, Y. Awera, H. H. Mhanna, and H. Alkhraisha. within ±10%. 2020. “FE Modeling SFCB Reinforced Beams Can Be Very Useful in Marine Environment Where Chloride Induced Corrosion of Reinforcing Bars Form a Severe Threat to 7. Summary and conclusions Durability of RCC Structures. 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Journal
Journal of Asian Architecture and Building Engineering
– Taylor & Francis
Published: Sep 3, 2021
Keywords: Corrosion; hybrid rebars; reinforcement; FRP; flexure; fem
