Study on the Behaviour of High Strength Concrete Beam under Combined Bending and Torsion with and without Hybrid Fibres

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1 ISSN (ONLINE): -, ISSN (PRINT): 9-9 Volume-, Issue-, February- International Journal of Engineering and Management Research Page Number: -9 Study on the Behaviour of High Strength Concrete Beam under Combined Bending and Torsion with and without Hybrid Fibres T. Sakthi Subramanian, C. Arun Kumar Student, SRM University, Department of Civil Engineering, INDIA Assistant Professor, SRM University, Department of Civil Engineering, INDIA ABSTRACT The reinforced concrete structural elements such as the peripheral beams in each floor of multi storied buildings, ring beams at the bottom of circular tanks, edge beams of shell roofs, the beams supporting canopy slabs and the helical staircases are subjected to significant torsional loading in addition to flexure. So it becomes necessary to investigate the behaviour of beam under combined bending and torsion in an experimental way. In this project high strength beams will be subjected to combined bending and torsion. In addition to that hybrid fibres are added to the concrete and subjected to combined bending and torsion. The behaviour of reinforced beams under combined bending and torsion with and without hybrid fibre are investigated. Keywords Bending, Hybrid fibre, Reinforced Concrete, Torsion. I. INTRODUCTION High-strength concrete leads to more economical structures. It also leads to reduction in overall building height and dead load, because of the use of thinner slabs and shallower beams. The reinforced concrete (RC) structural elements such as the peripheral beams in each floor of multi storied buildings, ring beams at the bottom of circular tanks, edge beams of shell roofs, the beams supporting canopy slabs and the helical staircases are subjected to significant torsional loading in addition to flexure. Therefore, for understanding the behaviour of reinforced high strength beam, it is necessary to study the beam under combined bending and torsion. In this project the high strength concrete beam will be subjected to combined bending and torsion. In addition to that hybrid fibres are added to the concrete and it will be subjected to combined bending and torsion. The effect of concrete strength and behaviour of combined bending and torsion will be investigated in reinforced concrete beams. The significant effect of concrete strength on stiffness and torsional capacity of the beams have been investigated. Copyright -. Vandana Publications. All Rights Reserved. II. MATERIAL PROPERTIES AND MIX PROPORTIONS A. Concrete Mix Concrete is a composite product produced by mixing cement, aggregates and water. Each constituent has its own role in contributing strength to the composite element. The strength of concrete and steel and deformations of the beam define the limits of strength of reinforced concrete beams. The cracking of the specimens and that of a ductile material like steel define the strength of a brittle material like concrete by yielding. Concrete being a poly-phase material, its properties depend on the properties of the constituent materials. Raw materials listed below were used for preparation of the specimens i Ordinary Portland Cement (OPC) grade ii Coarse aggregate with. mm maximum size iii Fine aggregate iv Superplasticizer v Steel fibres vi Polypropylene fibres Mix proportions for the concrete made under the guidelines of IS -9 are indicated in Table.Ordinary Portland cement (OPC) with a Specific gravity of., fineness of % and cement consistency as % is used.water cement ratio (W/C) of. is used. Crushed gravel with maximum size of mm was used for coarse

2 ISSN (ONLINE): -, ISSN (PRINT): 9-9 aggregate (CA). They have crushing value as.%, Aggregate impact value as.% and specific gravity of..fineness modulus of CA is. River sand of zone II according to IS -9 was used for fine aggregate (FA) with specific gravity of. and fineness modulus of. C. Compressive strength results Compressive strengths were measured using a Compression Testing Machine (CTM) with a maximum capacity of kn. For all tests, each value was taken as the average of three samples. Test results for conventional concrete and Hybrid fibre reinforced concrete after days of curing period was tabulated in Table B. Fibre Properties Fibres used are of two types of fibres namely steel and polypropylene were used and details are given below. Table shows the details of steel fibres and polypropylene fibres. Table shows the properties of polypropylene fibres. Table shows the properties of steel fibres. Figure Hybrid fibres (Polypropylene and steel fibres )in concrete III. SPECIMEN DETAILS The project deals with the behaviour of high strength concrete beams subjected to combined bending and torsion. The effect on the torsional stiffness and ultimate torque carrying capacity of the conventional concrete beams and hybrid fibre reinforced beams are Copyright -. Vandana Publications. All Rights Reserved.

3 ISSN (ONLINE): -, ISSN (PRINT): 9-9 studied. The mode of failure of the beam is studied. The results are compared with the conventional and hybrid fibre reinforced concrete beams. Eight full size beams were tested under combined bending and torsion. These eight beams were divided into two sets A and A. Set A contains four beams A, B, C and D with strength of concrete M conventional concrete and the beams have cantilever projections at edge, L/, L/, L/ distance along the length of beam respectively. Set A contains four beams A, B, C and D with strength of concrete M Hybrid fibre reinforced concrete and the beams have cantilever projections at edge, L/, L/, L/ respectively. The investigated parameters under this study were each beam has cantilever projection varying from other and the results are compared with the hybrid fibre reinforced concrete. The cross sectional dimension of beam is taken as x mm and length of the beam is taken as mm for both conventional and hybrid fibre reinforced concrete beams. In both the cases the grade of concrete has been considered as M. The reinforcement percentage for both conventional and HFRC concrete has been presented in Table and Table Table Details of reinforcements for conventional high strength concrete and HFRC (Cantilever portion) for all specimens The plan of the beam specimen is shown in Figure.. Cross section of the specimens A, and A is shown in Figure.. Cross section of the specimen B, and B is shown in Fig..cross section of the specimen C, and C is shown in Figure. cross section of the specimen D, and D is shown in Figure.. The cross section of A, B, C, D and A, B, C and D and the cantilever beam are shown in Figure. respectively. Figure Plan of the beam specimen A&A (Cantilever at edge) Figure. Plan of the beam specimen B&B (Cantilever at L/ distance along the length of beam) Copyright -. Vandana Publications. All Rights Reserved.

4 ISSN (ONLINE): -, ISSN (PRINT): 9-9 Figure Plan of the beam specimen C& C (Cantilever at L/ distance along the length of beam) Figure : Cross section of cantilever beam IV. MAKING OF SPECIMEN Figure Plan of the beam specimen D& D (Cantilever at L/ distance along the length of beam) A. MAKING OF MOULD AND CASTING: The reinforcement bars were cut to the required lengths. Plywood moulds for the beams were made as shown in the Figure. The inner surfaces of the mould were coated with a thin film of oil to prevent adhesion of concrete to the mould. All the ingredients of the mix were weighed and machine mixed. The concrete was placed in the plywood moulds in three layers and internally compacted using a needle vibrator. Care was taken to give uniform compaction in the specimens. The reinforcement with moulds is shown in figure below. Figure. Cross section of beam section Figure. shows beam specimens with cantilever portion at different points along the length B. CURING OF SPECIMEN: After hours of casting, the beams were covered with gunny bag and left for curing and the specimens are allowed for days curing. The cured specimens after days are shown in Figure 9. Before testing a coat of white wash was applied to the beams to facilitate the observations of cracking patterns during the tests. Copyright -. Vandana Publications. All Rights Reserved.

5 ISSN (ONLINE): -, ISSN (PRINT): 9-9 Figure 9 Cured specimens after days V. CONDUCT OF EXPERIMENT The testing was done in a loading frame of capacity tones. Load was applied by means of a hydraulic jack of capacity tones. The load was measured using a proving ring of tones capacity. Twists of the beam were measured by using dial gauges which are fixed at both the sides of twist meter and near the midpoint of the beam with a least count of. mm The beam to be tested was lifted and kept in the loading platform as shown in Figure.. ISMB was placed diagonally and seated on the top surfaces of the cantilever beam. Cantilever beam was specially designed and cast monolithically with the two ends of the main beam. The steel saddles were made ready to be placed under the beams on both edges to allow the twist when torque is applied. mm MS rods have been used in the saddles. Hydraulic jack of T capacity was placed above the ISMB I for application of load. T capacity proving ring was placed above the hydraulic jack in the center. The beam was so adjusted that the centers of the proving ring and beams are in the same line by using plumb-bob. Two dial gauges were fixed at two opposite sides of the cantilever in vertical direction and at the midpoint to measure the angle of twist. Now the arrangement has been made ready for performing the experiment and the dial gauges were also set for zero reading. Torque was constantly applied through the hydraulic jack. ISMB transferred the load to its edges equally. The concrete beam was subjected to a constant torque till the ultimate torque was reached. Spiral cracks were visible all-round the beams as shown in Figures and. Figure Side view of the loading frame with testing specimen Figure Specimen A during testing (spiral crack) Figure Front view of specimen C during testing (spiral crack) VI. RESULTS AND DISCUSSION A. TORQUE AND TWIST MEASUREMENTS: During the test for each increment of applied load corresponding torque, dial gauge readings Copyright -. Vandana Publications. All Rights Reserved.

6 ISSN (ONLINE): -, ISSN (PRINT): 9-9 are noted and the angle of twist in radians are calculated and are tabulated in Table for the specimens A, B C and A, B, C respectively. Table Ultimate torque Vs Twists for specimens A, A,B, B, C,C. Speci men Ulti mate Load W, in T Le ver ar m in m Ulti mate Torq ue in knm Dial gua ge read ing in mid - poin t in mm Aver age dial gaug e readi ng in divis ion Aver age dial gaug e readi ngs in mm Twist (θ) x - radia ns/m A A.. B. B. C C Table 9 Load Vs Deflection measurements for specimens D & D. Specimen Applied Dial Average Average Load W, guage dial dial in T reading gauge gauge in midpoint reading reading in in division mm division in mm D... D B. GRAPHS FOR TORQUE Vs TWIST MEASUREMENTS: The corresponding individual graphs are drawn for torque Vs twist for specimens A, B, C, and A, B, C and load Vs Deflection for specimens D and D are shown in figures respectively. The specimens B, B, C, C will have both combined bending and torsion. Copyright -. Vandana Publications. All Rights Reserved.

7 ISSN (ONLINE): -, ISSN (PRINT): 9-9 C. GRAPHS FOR LOAD AND DEFLECTION MEASUREMENTS: During the test for each increment of applied load corresponding dial gauge readings are noted and the deflection in mm are calculated and the graphs are drawn for specimens B C D and B, C, D respectively y =.x +. Load Vs Deflection Figure Load Vs Deflection for beam specimen B Copyright -. Vandana Publications. All Rights Reserved.

8 ISSN (ONLINE): -, ISSN (PRINT): y =.x +. Load Vs Deflecti on 9 y =.x +. Load Vs Deflect ion Figure Load Vs Deflection for beam specimen B Figure Load Vs Deflection for beam specimen C y =.x +. Load Vs Defl Deflection in mm Figure 9 Load Vs Deflection for beam specimen C y =.x +. Load Vs Deflection Figure Load Vs Deflection for beam specimen D y =.x +. Load V s Deflectio n Figure Load Vs Deflection for beam specimen D Copyright -. Vandana Publications. All Rights Reserved.

9 ISSN (ONLINE): -, ISSN (PRINT): 9-9 D.FAILURE CURVE: The specimens A, A are subjected to pure torsion. The specimens B, B, C, C are subjected to combined bending and torsion. The specimens D, D are subjected to bending alone. The failure curve shows the mode of failure for specimens A, B, C, D in Figure and for specimens A, B, C, D in Figure It has been found that among the specimens without fibre the highest ultimate load was in specimen D. This is due to the fact that the specimen experiences bending alone. The specimens C and B experiences both combined bending and torsion and therefore specimen C takes more load compared to B. The specimen A takes less load because it experiences pure torsion. Similarly, the same pattern is found in specimens with fibres. Specimen D takes more load compared to C followed by B and A.The addition of hybrid fibres increases the ultimate load of specimen A by. %, specimen by. %, specimen C by.%, specimen A by.%. REFERENCES Figure Mode of failure for specimens A, B, C, D [] Pawlak.W, Kaminski M, Cracking of reinforced concrete beams under torsion-theory and Experimental research. Archives of Civil and Mechanical Engineering () [] Tan. E.L, Uy. B, Experimental study on straight composite beams subjected to combined flexure and torsion. Journal of Construction Steel Research (9) [] Hao-Jan Chiu, I-Kuang Fang, Behaviour of Reinforced concrete beams with minimum torsional reinforcement, Engineering Structures 9 () [] Faisal F. Wafa, Sabri Shihata. A, Pre-stressed High strength concrete beams under torsion, J. Struct. Eng. 99. [] Ming B. Leung, ASCE.A.M, (9) Reinforced concrete beams subjected to bending and torsion. J. Struct. Eng. 9 Figure Mode of failure for specimens A, B, C, D V. CONCLUSION In this study, behaviour of beam under combined bending and torsion have been studied for both conventional concrete and Hybrid fibre reinforced concrete. From the experiment it has been found that the beam specimens A, A experience pure torsional load whereas specimens B, B, C, C experiences both combined bending and torsion. The specimens D, D are subjected to bending alone. 9 Copyright -. Vandana Publications. All Rights Reserved.