EXTERNAL CONFINEMENT OF PLAIN AND REINFORCED CONCRETE COLUMNS USING PVC PIPES

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1 19 th - 2 th November 216, in Dubai, U.A.E ISBN: EXTERNAL CONFINEMENT OF PLAIN AND REINFORCED CONCRETE COLUMNS USING PVC PIPES Dr.R.Kumutha Department of Civil Engineering, Sethu Institute of Technology, Virudhunagar District, Tamilnadu, India Dr.K.Vijai Department of Civil Engineering, Sethu Institute of Technology, Virudhunagar District, Tamilnadu, India Abstract - An experimental investigation has been carried out to evaluate the effectiveness of PVC confinements in concrete columns. The strength characteristics of the plain and reinforced concrete columns under axial compression with and without external confinement using PVC pipes were studied. The parameters investigated were diameter of the specimens (12 and 178 ) and thickness of PVC pipes (3 and 4 ). Test results show that the external confinement of concrete columns by PVC pipes results in enhancing compressive strength, ultimate load and energy absorption capacity. Test results also indicated that as the thickness of PVC pipes increases, the confining pressure also increases which in turn increases the compressive strength of concrete. This increased compressive strength leads to an enhancement in ultimate load carrying capacity of reinforced concrete columns. Keywords - Columns, confinement, PVC pipes, compressive strength, energy absorption capacity. I.INTRODUCTION Deterioration of reinforced concrete structures in marine environment has become a serious problem in the last decade. This phenomenon is mainly due to environmental effects. Cracking and spalling of concrete columns are often accompanied with corrosion of internal steel reinforcements. Different methods have been proposed for rehabilitation and strengthening of such corroded concrete columns. Recently PVC has become one of the viable methods of strengthening columns as the lateral pressure exerted by PVC will increase the compressive strength of concrete resulting in higher load carrying capacity. In the case of PVC confined columns, as the PVC tube itself acts as the permanent formwork, it protects the concrete as well as the internal reinforcement from environmental effects such as chloride and corrosion. The present study will focus on the use of PVC pipes as a jacketing material to strengthen concrete compression members. The mechanical properties of PVC tubed short concrete columns were investigated by Jun Dong et al. The principal influencing factors such as concrete strength, loading condition and ratio of height to diameter were studied. Test results indicated that the strength and deformation performance of core concrete increased as a result of confinement using PVC tube.pvc confinement effect on concrete decreases with the increase in strength of concrete. As the ratio of height to diameter increases, the load carrying of short concrete columns decreased gradually [1]. 72

2 19 th - 2 th November 216, in Dubai, U.A.E ISBN: A new type of concrete columns has been developed at the University of Alabama in Huntsville for new construction to achieve more durable and economical structures by Toutanji and Saafi. The columns are made of concrete cores encased in a PVC tube reinforced with fiber reinforced polymer (FRP). The PVC tubes are externally reinforced with continuous impregnated fibers in the form of hoops at different spacing s. The PVC acts as formwork and a protective jacket, while the FRP hoops provide confinement to the concrete so that the ultimate compressive strength and ductility of concrete columns can be significantly increased. The stress-strain behavior of these new composite concrete cylinders under axial compression loading was also discussed. Test variables include the type of fiber, volume of fiber, and the spacing between the FRP hoops. A theoretical analysis was performed to predict the ultimate strength, failure strain and the entire stressstrain curve of concrete confined with PVC-FRP tubes. Test results show that the external confinement of concrete columns by PVC-FRP tubes results in enhancing compressive strength, ductility and energy absorption capacity. A comparison between experimental and analytical results indicates that the models provide satisfactory predictions of ultimate compressive strength, failure strain and stress-strain response [2]. The load-carrying capacity and strains of circular concrete columns, strengthened with external glass fibre composite have been investigated by Saravanan et al. Test results revealed that the high strength concrete columns with GFRP wrapping exhibited better performance in terms of strength, deformation and ductility capacity [3]. Carl. E.Kurt conducted a theoretical analysis and experimental tests on coercially available plastic pipe (PVC and ABS) filled with a concrete core. The theoretical analysis implied an interaction between the concrete core and plastic pipe and a corresponding increase in strength of the concrete core. Under a column loading, the structural behavior of the plastic pipe was similar to the behavior of spiral reinforcement. The plastic pipe increased the strength of the concrete core approximately 3.2 times the pipe burst pressure. Slenderness ratio effects reduced the column capacity once they reached a value of 2. Test results show that concrete filled plastic pipe columns show considerable promise for structural applications [4]. Jingsi Huo et al. carried out an experimental investigation on axially loaded normal strength concrete columns confined by 1 different types of materials, including steel tube, glass fiber confined steel tube (GFRP), PVC tube, carbon fiber confined PVC tube (CFRP), glass fiber confined PVC tube (GFRP), CFRP, GFRP, polyethylene (PE), PE hybrid CFRP and PE hybrid GFRP. The deformation, macroscopical deformation characters, failure mechanism and failure modes are studied in this paper. The ultimate bearing capacity of these 1 types of confined concrete columns and the influences of the confining materials on the ultimate bearing capacity are obtained. The advantages and disadvantages of these 1 types of confining methods are compared []. Lee et al. introduced a new type of composite grid tubes for the reinforcement of concrete columns. The fibers were wound in the pre-cut grooves on the surface of a PVC tube to form a grid structure. The pattern could be either orthogonal or helical. Once the composite grid tube was fabricated, cement concrete was poured into the tube to form a hybrid column structure. The effect of confinement provided by the reinforcing composite grid tube on the compressive 73

3 19 th - 2 th November 216, in Dubai, U.A.E ISBN: strength of concrete columns was also investigated. The hybrid columns were subjected to uni-axial compression. The same test was performed on a pure concrete column as well for benchmarking. It was identified that the composite grid tube could substantially increase the compressive strength and toughness of concrete columns. With further investigation on durability, the present hybrid structure may have good potential to compete with the conventional steel rebar reinforced concrete columns [6]. A model for calculating the load-carrying capacity of PVC-FRP confined concrete column was presented by Feng Yu and Ditao Niu. The influences of the hoop spacing of FRP strips and equivalent confinement effect coefficient on load-carrying capacity were well considered. According to the ingression of experimental data, a calculating formula of the ultimate axial strain is also put forward. For this last case, a bilinear stress-strain model of PVC-FRP confined concrete column in axial and lateral directions is established. The comparison between experimental and numerical results indicates that the model provides satisfactory predictions of the stress-strain response of the columns [7]. II. EXPERIMENTAL INVESTIGATION A. Materials Ordinary locally available Portland cement having a specific gravity of 3.8, consistency of 3%, initial setting time of 11 minutes was made use of, in the casting of the specimens. Locally available river sand having a bulk density of 192kg/m 3, fineness modulus of 2.69, and a specific gravity of 2.68 was used. Crushed granite coarse aggregates of 2 maximum size having a fineness modulus of 7.94 and specific gravity of 2.86 were used. Water conforming to the requirements of water for concreting and curing as per IS: 46 2 was used throughout. The mix ratio adopted was 1:2:4 with a water-cement ratio of.. The slump value for this mix ratio was 1.Concrete columns were confined by PVC pipes of two different diameters namely 12 and 178. Two different thicknesses were considered in the study such as 3 and 4.The PVC pipe used in this investigation was having a young s modulus of N/ 2, tensile strength of 1.37 N/ 2 and a flexural strength of 99.63N/ 2.PVC pipes used for confinements are shown in Fig.1. Fig. 1 PVC Pipes used for Confinement B. Details of Test Specimens Totally eighteen plain concrete cylinders were cast out of which nine cylinders were having a size of 12 x 3 and the remaining nine cylinders were having a size of 178 x 3. For each size, three specimens were used as control specimens without any confinement, another three specimens were provided with 3 thick PVC confinement and the remaining three specimens were provided with 4 thick PVC confinement. Then six reinforced concrete columns, three each of 12 diameter and another three of 178 diameter were cast. For each diameter, one specimen is kept as a control column, and the remaining two columns were provided with PVC 74

4 Percentage increase in compressive strength Proceedings of 2nd International Conference on Structural Architectural and Civil Engineering, Held on 19 th - 2 th November 216, in Dubai, U.A.E ISBN: confinements of thickness 3 and 4 respectively. The height of all the columns was fixed as 7.All columns had longitudinal reinforcement consisting of 6 deformed bars, 12 in diameter with yield strength f y =477.N/ 2 and ultimate strength f u =63.N/ 2.In addition,8 diameter lateral spacing were used as ties.all the specimens were moist cured for 28 days at room temperature. B. Experimental Setup and Test Procedure All specimens were loaded in axial compression until failure, using a Universal Testing Machine (UTM) of capacity 1kN.The load was applied gradually at a constant rate till failure. For plain concrete cylinders, load at failure was noted. The axial deformations were measured for reinforced concrete columns, at every 2kN increment of load by using a dial gauge. III. RESULTS AND DISCUSSION A. Compressive Strength The test results of the plain concrete cylinders are given in Table 1. From the test results, it can be seen that, confinement of concrete specimens using PVC resulted in an increase in compressive strength. As the thickness of the confinement increases, the compressive strength also increases as shown in Fig.2. This is applicable for both the diameters of the specimens. For specimens of 12 diameter, the unconfined concrete compressive strength is 18.6 N/ 2. The compressive strength enhances by 18.16% and 42.86% for 3 and 4 thick confinements respectively, as compared with that of unconfined specimens. Similarly for specimens of 178 diameter, the unconfined compressive strength is N/ 2. When confined with PVC pipes, the compressive strength improves by 22.78% and 43.94% for 3 and 4 thick confinements respectively, as compared with that of control specimens. Diameter of the Specime n TABLE I COMPRESSIVE STRENGTH OF PLAIN CONCRETE CYLINDERS Thicknes s of PVC pipe D=12 Spec Ultimate load kn Spec Spec Fig.2. Effect of PVC confinement on compressive strength Diameter of the specimen D= Average Compres sive Strength N/

5 Gain in ultimate load (%) Proceedings of 2nd International Conference on Structural Architectural and Civil Engineering, Held on 19 th - 2 th November 216, in Dubai, U.A.E ISBN: B. Ultimate load of reinforced concrete columns The load carrying capacity of the reinforced concrete columns obtained from all the tests are suarized in Table 2. From the results, it can be seen that the confinement of columns with PVC pipes increases the load carrying capacity of reinforced concrete columns D= D= Diameter of the column Diameter of the Specimen TABLE II ULTIMATE LOAD Thickness of PVC Ultimate load pipe kn In addition, the greater the thickness of PVC pipe, the greater is the gain in axial load carrying capacity with respect to unconfined columns. For 12 diameter columns, the confinement using 3 thick PVC pipe increases the load carrying capacity by 6.28% and the confinement using 4 thick PVC pipe increases the ultimate load by 68.9% when compared with unconfined control columns. In case of 178 diameter columns, when the thickness of PVC pipe is 3, the ultimate load increases by 19.92% and when the thickness of PVC pipe is increased to 4, the load carrying capacity increases by 4.27% in comparison with unconfined columns as shown in Fig.3. Fig. 3. Gain in ultimate load Vs Thickness of PVC C. Energy Absorption Capacity Energy Absorption was calculated by finding out the area under the load deflection curve upto the ultimate load. The load - deflection curves for all the tested columns are shown in Figs 4 and.energy absorption capacity of the reinforced concrete columns increases with the increase in the thickness of the PVC confinements. For 12 diameter Columns, confinement using 3 thick PVC pipe increases the energy absorption capacity by 164.7% and confinement using 4 thick PVC pipe increases the energy absorption capacity by % when compared with unconfined control columns. For 178 diameter Columns, confinement with 3 thick PVC pipe increases the energy absorption capacity by 26.22% and confinement using 4 thick PVC pipe increases the energy absorption capacity by 386.9% when compared with unconfined columns as shown in Fig.6. Fig. 4. Load Vs Deflection for 12 diameter columns 76

6 Energy absorption capacity in kn. Proceedings of 2nd International Conference on Structural Architectural and Civil Engineering, Held on 19 th - 2 th November 216, in Dubai, U.A.E ISBN: specimens as compared to control specimens, thereby showing an increased ductility. Externally confined columns using PVC can be used in structures located in corrosion prone areas as it prevents the internal reinforcements from corrosion and chloride action. Fig.. Load Vs Deflection for 178 diameter columns 6 6 D=12 42 D= Thickness of PVC Confinement Fig. 6. Energy absorption capacity IV. CONCLUSION External confinement of concrete columns using PVC pipes increases the compressive strength, load carrying capacity and energy absorption capacity. When the thickness of PVC pipes increased, the compressive strength of the plain concrete specimens also increased. In the case of reinforced concrete columns, when the thickness of PVC pipes is increased, the load carrying capacity of the columns gets increased. For reinforced concrete columns, as the diameter of the columns increases, the gain in ultimate load is less. Energy absorption capacity increased by a considerable amount, for PVC strengthened cylinders and column IV. REFERENCES [1] Jun Dong, DePing Chen, Ju Mei Zhao, De Shan Shan, Xin Yue Liu, Gang Liu. (211) Experimental study on mechanical properties of axially loaded PVC tubed short concrete columns, Applied Mechanics and Materials, 99-1, [2] Toutanji H, Saafi M. (22) Stress-strain behaviour of concrete columns confined with hybrid composite materials, Materials and Structures, 3, [3] Saravanan J, Suguna K, Raghunath PNR. (212) Strength and ductility of high strength concrete columns with glass fibre reinforced polymer wraps, Asian Journal of Civil Engineering (Building and Housing), No., 13,8-9. [4] Carl.E.Kurt. (1978) Concrete filled structural plastic columns, Journal of Structural Division, 14,-63. [] Jingsi Huo, Yan Xiao, Zongjin Li, Shuaib Ahmad. (28). Experimental studies on axially loaded concrete columns confined by different materials, Key Engineering Materials, [6] Lee SWR, Li Z, Tang JM, Lee S, Tong P. (28) Development of composite grid tubes for the reinforcement of concrete columns, Proceedings of the International Conference ICCM-12, Europe, 4-42,49. [7] Feng Yu, Ditao Niu. (21). Stress-strain model of PVC-FRP confined concrete column 77

7 19 th - 2 th November 216, in Dubai, U.A.E ISBN: subjected to axial compression, International Journal of Physical Sciences, (1), Institution of Engineers (India), Life member of Indian Concrete Institute (ICI) and Indian Society for Technical Education (ISTE). Dr.R.Kumutha graduated in Civil Engineering from Thiagarajar College of Engineering, Madurai, Tamil Nadu, India in the year 1997 and obtained her Masters Degree in Structural Engineering in 1998, from the same college. She obtained her Doctorate Degree in the year 27 from Anna University, Chennai. She has authored about 42 papers in various International / National Journals and presented 2 papers in International / National Conferences. She is the recipient of AICTE Career Award and DST Young Scientist Award in the year 212.She has also received a National Award for Innovative research from ISTE, New Delhi in the year 214. She is a member of Dr.K.Vijai graduated in Civil Engineering from Madurai Kamaraj University, Tamil Nadu, India in the year 1997 and obtained his Masters Degree in Structural Engineering in 1998, REC, Trichy. He obtained his Doctorate Degree in the year 213 from Anna University, Chennai. He has authored about 3 papers in various International / National Journals and presented 2 papers in International / National Conferences. He is a member of Institution of Engineers (India), Life member of Indian Concrete Institute (ICI) and Indian Society for Technical Education (ISTE). 78