Experimental Study on Hybrid Fiber Reinforced Concrete Deep Beams under Shear

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1 International Journal o Innovative Researh in Siene, (An ISO 3297: 2007 Certiied Organization) Experimental Study on Hybrid Fiber Reinored Conrete Deep Beams under Shear A. S. Shelke 1, Y. M. Ghugal 2, Manoj. M. More 3, Mayur. M. More 4 Assistant Proessor, Bhivarabai Sawant College o Engineering and Researh, Narhe, Pune, Maharashtra, India 1 Proessor, Department o Applied Mehanis, Government College o Engineering, Karad, Satara, Maharashtra, India 2 Assistant Proessor, Department o Civil Engineering, KIT s College o Engineering, Kolhapur, Maharashtra, India 3 Assistant Proessor, Department o Civil Engineering, Bharati Vidyapeeth s College o Engineering, Kolhapur, Maharashtra, India 4 ABSTRACT: The main objetive o this paper is to study the eet o addition o hybrid (Crimped steel- Polypropylene) ibers on shear strength o reinored onrete deep beams without shear reinorement. The eet o hybrid ibers on shear strength o reinored onrete deep beams with dierent steel iber volume rations (0 %, 1.0 % and 2.0 %), and shear span-to-depth (a/d) ratios 0.60 and 0.66 by keeping tensile reinorement onstant is studied. All the beam speimens are tested under our-point bending test set-up up to ailure, and ailure load, irst rak load, and entral deletion are reorded preisely. The tests results are ompared with the equations proposed by dierent odes and authors available in the literature. The test results indiate that the hybrid (Crimped steel-polypropylene) iber have signiiant inluene on the shear strength o longitudinally reinored onrete deep beams. Shear strength inreases with inrease in iber volume ration and derease in a/d ratio. KEYWORDS: shear strength, deep beam, onrete, a/d ratio, hybrid (Crimped steel-polypropylene) iber. I. INTRODUCTION Many a strutural elements like walls o bunkers, load-bearing walls in buildings, plate element in olded plates and pile aps behave as deep beams [1]. A beam is onsidered deep, aording to the Indian Standard Code IS: , when the ratio o eetive span to overall depth (L/D) is less than 2.0 or simply supported members and 2.5 or ontinuous members [2]. Deep beams transer heavy gravity loads predominantly through shearing ation by orming a diagonal rak. The onventional plane setion remaining plane approah is not appliable to analyses o deep beams [3]. Besides, or beams without web reinorement, it has been shown that shear strength dereases as member size inreases. This is assoiated with a phenomenon alled size eet [4]. Conrete being a non-homogeneous, heterogeneous material and has non-linearity in its material response [5]. As a result o this, it does not easible to apply a shearing ation (diret shearing ore) in a plane. Thus, Shear strength in reinored onrete beams has been the subjet o many ontroversies and debates sine the beginning o 20th entury. Transversely loaded reinored onrete beams may ail in shear beore attaining their ull lexural strengths i they are not adequately designed or shear. Unlike lexural ailures, shear ailures are very sudden and unexpeted, and sometimes violent and atastrophi. A thorough knowledge o the dierent modes o shear ailures and the mehanisms involved is neessary to prevent them [6]. To redue the brittleness and inrease the resistane to raking, reinorement with short randomly distributed ibers has been suessully used and the resulting omposite is known as FiberReinored Conrete (FRC). The perormane o FRC depends on many ators suh as iber material properties, iber geometry, iber volume ontent, matrix properties and interae properties. Most types o FRC used in pratie ontain only one type o iber. However, Copyright to IJIRSET DOI: /IJIRSET

2 International Journal o Innovative Researh in Siene, (An ISO 3297: 2007 Certiied Organization) it is known that ailure in onrete is a gradual, multi-sale proess. The pre-existing raks in onrete are o the order o mirons. Under an applied load, these raks grow and eventually join together to orm maro-raks. A marorak propagates at a stable rate until it attains onditions o unstable propagation and a rapid rature is preipitated. For optimal result thereore dierent types o ibers may be ombined and the resulting omposite is known as hybridiber-reinored onrete (HFRC). Steel ibers an be used either to boost the shear apaity or to replae the web reinorement in onventional RCC deep beams. Syntheti ibers an be used to ontrol the miro-rak. Thus, it transorms an inherently brittle material into a strong omposite with a superior rak resistane and improved dutility. II. EXPERIMENTAL WORK A. Material Properties The test speimens were ast using ement, ine aggregate, oarse aggregate, water, admixture and rimped steel ibers. The materials, in general, onirmed to the speiiations laid down in the relevant Indian Standard odes. For grading o ine and oarse aggregate, sieve analysis was arried out. Ordinary Portland ement o 53-grade onirming to IS 12269:1987 was used throughout the experimental work. The maximum size o oarse aggregate used was 20 mm along with 12.5 mm o same parent rok in % ration. Loally available Krishna river sand was used as ine aggregate. The speii gravity o sand was 2.85 and ineness modulus was 2.7. Crimped steel ibers o length 50 mm and diameter 1.0 mm were used throughout the experimental work. Polypropylene ibers o ut length 12mm were used. Reinoring steel o grade Fe 500 was used as tensile reinorement. B. Conrete Mix Design The onrete mixes were designed in aordane with the D.O.E method o onrete mix design. The onrete mix was prepared or M-50 grade o onrete. The water-ement ratio is kept at Super Plastiizers (3.5 ml/kg o ement) was used to enhane the workability o mix throughout experimental work. The mix proportion is given in Table I. Table I :Mix Proportion Material Cement Sand Aggregate Water Quantity (Kg/m 3 ) C. Test Speimens Total 18 deep beams were asted. The span o the deep beam has been kept onstant at 600 mm with 50 mm overhangs on either side o the supports. The shear span (a) has been kept at 200 mm. The depths o beam seleted were 360 mm and 330 mm to ahieve desire a/d ratio. Beam speimens were divided into two groups, namely, series-i and series-ii. All the beams o series-i were reinored with A st = mm 2. All the beams o series-ii were reinored A st = mm 2. All beams were retangular in ross setion with 90 mm width. Standard ubes o size 150 mm x 150 mm x 150 mm were ast with eah mix to know the ompressive strength o onrete. The details o test beams are given in Table II. Copyright to IJIRSET DOI: /IJIRSET

3 International Journal o Innovative Researh in Siene, Beam Designation Beam Size LxD (mm) (An ISO 3297: 2007 Certiied Organization) Table II :Test Beam Details Steel (Crimped) Fibers Fiber Content (%), V Polypropylene Fibers a/d ratio Eetive Depth d (mm) I-0% 700x I-1% 700x I-2% 700x II-0% 700x II-1% 700x II-2% 700x D. Test Proedure Ater 28-days uring period, the beam speimens were removed rom the uring tank and both sides o the beams were white-washed to aid observations o the rak development during testing. Figure I :Two point bending test set-up All the beams were tested to ailure under two-point loading test set-up as shown in Fig I. The ube speimens were tested or ompressive strength. E. Shear Design Models Various shear strength models have been used to veriy the strength o FRC deep beams in the present investigations. I. ACI Design Model[7] The shear strength o beam without stirrups an be omputed as ollows, In S.I. system (N, mm system) Copyright to IJIRSET DOI: /IJIRSET

4 International Journal o Innovative Researh in Siene, (An ISO 3297: 2007 Certiied Organization) M u Vud V bd Vu M ' 17 u where, M u and V u are the ultimate moment and shear at the setion under onsideration. is the onrete ompressive strength in MPa, is the longitudinal reinorement ratio (A s /bd) and A s is the area o longitudinal reinorement. II. CIRIA Guide-2 Design Model [8] CIRIA Guide-2 applies to simply supported beams o span-to-depth ratio (L/D) less than 2 and to ontinuous beams o span-to-depth ratio (L/D) less than 2.5. The shear strength o beam without shear reinorement is given as ollows. V a ' bd. d where, b is the width, d is the eetive depth o beam, is the harateristi ompressive strength o onrete and (=0.44) is empirial oeiient or normal weight onrete. III.Khuntia s Proposed Equation [9] The shear strength o FRC beams is governed by the onrete ontribution in the shear without stirrups and ontribution o ibers. The shear strength FRC beam is given as ollows, V ( F) ' bd r where, F V V r l d = Shear strength o FRC, α = 2.5(d/a), and = iber ator. in whih V = iber volume ration, l =length o iber and d =diameter o iber. IV. Mansur s Proposed Equation [10] The equation proposed by Mansur et al [10] or shear strength o FRC is ollows d V r ( 0.16 ' F) bd a where, = Charateristi ompressive strength o onrete, ρ = Longitudinal reinorement ratio, b and d = width and eetive depth o beam, F V l d = iber ator a = shear span, and in whih V = iber volume ration, l =length o iber and d =diameter o iber. Using equation (I) through (IV) shear strength are omputed and ompared with those o present investigation. Copyright to IJIRSET DOI: /IJIRSET

5 International Journal o Innovative Researh in Siene, (An ISO 3297: 2007 Certiied Organization) III. RESULT AND DISCUSSION The results obtained rom experimental investigation are tabulated in Table III. From the results obtained, the eet o various parameters on shear strength o onrete deep beam are analyzed and disussed below. A. Eet o Depth o Beam in Terms o Shear Span-to-Depth Ratio and Fiber Volume Fration: The ompressive strength, ultimate and raking shear stress o onrete or dierent iber volume rations and shear span-to-depth ratios at 28 days o uring age are given in Table III. The variation o ultimate shear strength o deep beam with respet to iber volume ration or beam series I and II are given Table III. It is evident that the ultimate shear strength o deep beam inreases with inrease in iber ontent. Ultimate shear stress at diagonal raking, whih is obtained by dividing measured ailure load to the nominal ross setional area (b x d). In deep beams, the signiiant portion o the shear is transmitted diretly to the support by inlined strut. This mehanism is requently reerred to as arh ation and the magnitude o the direst load transer inreases with dereasing a/d ratio. B. Inluene on Craking Shear : Results o raking shear stress are presented in Table III. It is onluded rom Table III that raking shear strength o deep beam inreases with inrease in iber ontent and dereases with inrease in a/d ratio. C. Central Deletion o Deep Beam: Typial load-deletion relationships or beam series I and II are shown in Fig III and Fig IV. From the graph it is evident that the entral deletion o beam inreases with inrease in iber ontent. Due addition o ibers, beam arries onsiderable load even ater irst raking. D. Inluene on Cube Compressive Strength: Cube ompressive strength o onrete or dierent iber ontent is given in Table III. Test Beam Designation Eetive Depth (d) mm a/d ratio Table III :Details o Test Results Longitudin al Steel (A st ) mm 2 Compressive Strength (MPa) Craking Shear (MPa) Ultimate Shear (MPa) % inrease in Crakin g Shear % inrease in Ultimate Shear I-0% I-1% I-2% II-0% II-1% II-2% Cube ompressive strength o onrete inreases with inrease in iber ontent. From table it is lear that there is onsiderable inrease in Craking Shear and Ultimate Shear with inrease in iber ontent. Copyright to IJIRSET DOI: /IJIRSET

6 International Journal o Innovative Researh in Siene, (An ISO 3297: 2007 Certiied Organization) Ultimate Shear Strength, MPa % Fiber 1 % Fiber 2 % Fiber a/d=0.60 a/d=0.66 Figure II : Ultimate shear strength o beam with respet to a/d ratio and iber ontent. Fig. II shows the eet o a/d ratio on ultimate shear strength o onrete. It is evident rom the igure that the higher shear strength is developed at lower value o shear span-to-depth ratio Load (KN) Load (KN) S e ri e s I (a /d = ) 2 % F i b e r C o n te n t 1 % F i b e r C o n te n t 0 % F i b e r C o n te n t S e ri e s II (a /d = ) 2 % F ib e r C o n te n t 1 % F ib e r C o n te n t 0 % F ib e r C o n te n t D e l e t io n (m m ) D e l e t io n (m m ) Figure III: The graph o entral deletion with respet to load, series-i Figure IV: The graph o entral deletion with respet to load, series-ii Typial load-deletion relationships or beam series I and II are shown in Fig III and Fig IV. From the graph it is evident that the entral deletion o beam inreases with inrease in iber ontent. Due addition o ibers, beam arries onsiderable load even ater irst raking. E. Comparison o Test Results with Shear Design Equation: Four design equations, namely, the ACI ode, CIRIA Guide ode, Khuntia and Mansur are used to estimate ultimate shear apaity. Comparison o test results with shear design is provided in Table IV. Copyright to IJIRSET DOI: /IJIRSET

7 International Journal o Innovative Researh in Siene, Beam Designation (An ISO 3297: 2007 Certiied Organization) Table IV Comparison o Test Results with Shear Design Equations Shear Strength (KN) V ACI V CIRIA V KHUNTIA V MANSUR V TEST V ACI Shear Strength Ratio V CIRIA V KHUNTIA V MANSUR I-0% I-1% I-2% II-0% II-1% II-2% Shear strength obtained rom ACI Design Model and CIRIA Guide-2 Design Model is lower ompared with test results, sine ontribution o ibers toward shear strength is not onsidered in above two equations. Thus, ACI Design Model and CIRIA Guide-2 Design Model are not appliable to ompute shear strength o iber reinored onrete deep beams. Results obtained rom Khuntia s equation are approximately similar to test results, sine ontribution o ibers toward shear strength is onsidered. Mansur s equation gives approximate shear strength as obtained in test or higher volume rations. From Table IV, it is evident that, Khuntia s equation holds good to alulate shear strength o iber reinored onrete deep beams. IV. CONCLUSION Based on the test results ollowing onlusions an be drawn, 1. Hybrid (Crimped steel-polypropylene) ibers in onrete deep beams provides better rak ontrol and deormation harateristi o beams. 2. Both the irst rak strength and ultimate strength in shear inreased with inrease in iber ontent beause o their inreased resistane to propagation o raks. 3. Maximum inrease o 52.71% in ultimate shear stress or beam (Series-I) ontaining 2 % ibers was observed when ompared it with beam without ibers. 4. Maximum inrease o 22.08% in raking shear stress or beam (Series-I) ontaining 2 % ibers was observed when ompared it with beam without ibers. REFERENCES [1] Murthy N. R. and Krishna Rao M. V., Behavior o polypropylene iber reinored ly ash onrete deep beams in lexure and shear, Asian Journal o Civil Engineering (Building And Housing), vol. 12(2): , [2] IS 456:2000, Indian standard ode o pratie or plain and reinored onrete or general building onstrution: Bureau o Indian Standards, New Delhi, India, [3] Kong, F.K., Reinored Conrete Deep Beams: Van Nostrand Reinhold, New York, [4] Ashor A.and Yang K.H., Appliation o plastiity theory to reinored onrete deep beams: a review, Conrete Res., vol. 60: , [5] Londhe R. S., Shear strength analysis and predition o reinored onrete transer beams in high-rise buildings, Strutural Engineering and Mehanis, vol. 37(1):39-59, [6] Londhe R.S., Experimental investigation on shear strength o SFRC beams reinored with longitudinal tension steel rebars, Asian Journal o Civil Engineering and Housing,vol. 11(3): , [7] Amerian Conrete Institute Committee, Building ode requirements or strutural onrete (ACI ) and ommentary (ACI 318R-05): Amerian Conrete Institute, Detroit, Mihigan, USA, [8] Leong C.L. and Tan K.H., Proposed revision on CIRIA design equation or normal and high strength onrete deep beams, Conrete Res., vol. 55(3): , [9] Dinh H. and Wight J. K., Shear strength model or steel iber reinored onrete beams without stirrup reinorement,journal o Strutural Engineering, ASCE, vol. 137(10): , [10] Mansur M. A. and Paramasivam P., Shear strength o ibrous onrete beams without stirrups, Journal o Strutural Engineering, ASCE,vol. 112(9): , Copyright to IJIRSET DOI: /IJIRSET