BEHAVIOUR OF GLASS FIBER WRAPPED CONCRETE COLUMNS UNDER UNIAXIAL COMPRESSION

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1 Research Paper BEHAVIOUR OF GLASS FIBER WRAPPED CONCRETE COLUMNS UNDER UNIAXIAL COMPRESSION P.Sangeetha 1, R.Sumathi 2 Address for Correspondence 1 Lecturer, Department of Civil Engineering,Sri Venkateswara College of Engineering, Pennalur, Sriperumbudur-6 Tamilnadu. id: p_sangeetha77@yahoo.co.in 2 Assistant Professor, Department of Civil Engineering, Arulmugu Meenakshi Amman College of Engineering, Thiruvanamalai District. Tamilnadu =============================================================== ABSTRACT Fiber Wrapping using Fibre Reinforced Plastic (FRP) shells is one of effective methods, significantly enhances the strength and ductility of concrete columns. The paper reports the behaviour of the GFRP wrapped concrete columns under uniaxial compression. The cross section of the concrete columns considered in the work is circular with diameter of 1mm and height mm. The Parameters that are varied in the investigation are wrapping shell materials, (which includes GFRP Materials Surface Mat(SM), Chopped Strand Mat (CSM) and Woven Roving Mat (WRM)), Number of Plies (1Ply and 3plies) and Period of Curing (7 & 28 Days). Results from a series of the experimental study were reported and discussed. The study on small scale specimens showed that confinement increased the strength of the concrete columns loaded axially. KEY WORDS Fiber Reinforcement, Compressive Strength, Curing, Concrete, Glass Fiber. ============================================================== INTRODUCTION In recent years, retrofitting of concrete columns by wrapping and bonding of fiber reinforced plastic (FRP) sheets, straps, belts, or precured shells around the columns has become increasingly popular. Studies of concrete columns confined with glass, aramid, or carbon fibers have been used successfully to retrofit building columns, bridge or expressway piers, and chimneys. An incremental finite element approach [4], are used to evaluate the response of fiber-wrapped square columns confined with carbon and aramid fibers. Many researchers [1-3 & ], have proposed models for concrete cylinders and square

2 columns strengthened with FRP sheets. The axial load behavior of concretefilled tubular (CFT) columns with the width-to-thickness ratios are studied [6] and stiffening scheme to enhance the ultimate strength and ductility of square CFT columns was proposed. The proper material constitutive models for concrete filled tube (CFT) columns are proposed [7] and verified by the nonlinear finite element program ABAQUS against experimental data. This paper, investigates the characteristics behaviour of reinforced concrete columns. FRP is used to wrap the columns circumferentially. All columns were tested to failure by applying axial concentric loads. Results of testing the columns showed that FRP is effective in producing columns with high compressive strength. Experimental Study Specimen preparation and Testing A total of forty-two cylindrical columns of size 1 X mm were prepared and twenty one specimens were cured for 7 days and remaining specimens were cured for 28 days. Out of 21 specimens of 7 days cured and 28 days cured, eighteen columns were wrapped circumferentially with glass fiber reinforced polymer of Surface Mat type, Chopped Strand Mat and Woven Roving Mat after 7 and 28days curing of single and triple plies and three columns without wrapping respectively. All the specimens were tested in the Compression testing machine of capacity kn. Ultimate load readings were taken to study the compression behavior of the specimens. Table 1 shows the description of various specimens prepared for testing. Fig.1 shows the column specimens without wrapping. Fig.1: Column Specimens before wrapping Fig.2-4 shows 28 days cured column specimens wrapped with SM, CSM and WRM of single ply. Fig. shows the compression test carried out on Triple plies chopped Strand Mat wrapped on columns cured for 28 days

3 Fig.2:Columns with Single ply Surface Mat Fig.3: Columns with Single ply of Chopped Strand Mat Fig.4: Columns with single ply of Woven Roving Mat Fig.:Compression testing carried out on 28 days cured Triple Plies Chopped Strand Mat column.

4 1 7 days cured Columns Wrapped with Single Ply 28 days cured Columns Wrapped with Single Ply UC SM CSM WRM Types of GFRP Material Fig. 6:Variation in Compressive Strength after 7 and 28 days cured specimens wrapped with single ply of GFRP UC SM CSM WRM Types of GFRP Material 7 days cured Columns Wrapped with Triple Plies 28 days cured Columns Wrapped with Triple Plies Fig.7:Variation in Compressive Strength after 7 and 28 days cured specimens wrapped with Triple plies of GFRP.

5 days Cured columns Wrapped with Single Ply 7 days cured columns Wrapped with Triple plies UC SM CSM WRM Types of GFRP Material days cured Columns Wrapped with Single Ply 28 days cured Columns Wrapped with Triple Plies UC SM CSM WRM Types of GFRP Material Fig. 8:(a) and (b)variation in Compressive Strength of specimens wrapped with Single and Triple plies of GFRP after 7 and 28 days of curing.

6 Un Confined Columns Columns Wrapped with SM Columns Wrapped with CSM Columns Wrapped with WRM Single Ply Triple Plies No. of Plies Un Confined Column Columns Wrapped with SM Columns Wrapped with CSM Column Wrapped with WRM Single Ply Triple Plies No. of Plies Fig. 9:Shows the comparison between the compressive strength of 7 & 28 days cured specimens.

7 EXPERIMENTAL RESULTS AND DISCUSSION Table 2 shows the results of tested column specimens. The columns wrapped with Woven Roving Mat of Glass fiber exhibited better results than other type of Glass fiber columns. The compressive strength of the GFRP wrapped concrete columns shows better results when columns are wrapped with 3 plies than single ply. Effect of FRP Wrapping Materials The Percentage increase in the Compressive Strength for change in Ply from to 1 for specimens wrapped with Surface Mat, Chopped Strand Mat and Woven Roving Mat after 7 days curing were 3.6, and 28.97% respectively and after 28 days curing were, and %. Fig.6. Show the variation in compressive strength after 7 and 28 days cured specimens wrapped with single ply of GFRP. The Percentage increases in the Compressive Strength for change in Ply from to 3 for specimen wrapped with Surface Mat, Chopped Strand Mat and Woven Roving Mat after 7 days curing were, and % respectively and after 28 days curing were, and 31.46%. Fig.7. Show the variation in compressive strength after 7 and 28 days cured specimens wrapped with Triple plies of GFRP. Effect of Plies The percentage increase in the Compressive Strength for 7 days & 28 days cured column wrapped with Surface Mat for Single Ply and Triple Plies is 3.6 and % respectively. The percentage increase in the Compressive Strength for column wrapped with Chopped Strand Mat for Single Ply and Triple Plies is and 136% respectively. The percentage increase in the Compressive Strength for column wrapped with Woven Roving Mat for Single Ply and Triple Plies is 29 and 168% respectively.fig. 8 (a) and (b) show the variation in compressive strength of specimens wrapped with Single and Triple plies of GFRP after 7 and 28 days of curing. Effect of Curing The percentage increases in the Compressive Strength for column wrapped with Single ply of Surface Mat, Chopped Strand Mat and Woven Roving Mat from 7 to 28 days cured are 32.72,.87 and 27.4% respectively and with Triple Plies are 21.46, 6. and 6.66% respectively.

8 Table.1:.Descripition of various specimens prepared for testing S. No. Specimen Descriptions No. of 1 Unconfined Column (UC) 2 Surface Mat Column (SMC) 3 Chopped Strand Mat Column (CSMC) 4 Woven Roving Mat Column (WRMC) Casted columns taken Period of curing (days) Number of plies Table.2.Results of tested column specimens under Compressive loading condition S. No. Specimen Descriptions 1 Unconfined Column (UC) 2 Surface Mat Column (SMC) 3 Chopped Strand Mat Column (CSMC) 4 Woven Roving Mat Column (WRMC) Period of curing (days) Number of plies Compressive Strength (N/mm 2 )

9 The over all Percentage increase in Compressive Strength for different materials is % for single ply from 7 days to 28days of curing and % for Triple Plies.. Fig..Tested Columns CONCLUSIONS The present study used forty-two columns, wrapped with GFRP of types Surface Mat(SM), Chopped Strand Mat (CSM) and Woven Roving Mat (WRM). Based on the results from a series of the experimental work the following Conclusions are made. The confinement of columns with GFRP wrap increased the strength and ductility of the concrete Column. Different types of glass fiber are Surface Mat, Chopped Stand Mat and Woven Roving Mat also increasing the compressive strength of the columns. Compressive Strength of the Concrete Columns increases with increase in the number of plies of GFRP. Period of Curing also increases the load carrying capacity of columns. REFERENCES 1. Amir Mirmiran and Mohsen Shahawy, Behavior of concrete columns confined by fiber composites, J of Struct Engg 123 (1997) (), pp M.Samaan, A.Mirmiran and M. Shahawy, Model of concrete confined by fiber composites, J of Struct Engg 124 (1998) (9), pp R. Marijn, Spoelstra and Giorgio Monti, FRP-confined concrete model, J of Compos for Construction 3 (1999) (3), pp P.Rochettee and P. Labossiere, Axial testing of rectangular column model confined with composites, J of compos for construction 4 () (3), pp A.Parvin and W. Wang, Behavior of FRP jacketed concrete columns under eccentric loading, J of compos

10 for construction 4 () (3), pp C.S.Huang, Y.K.Yeh, G.Y.Liu, H.T. Hu, K.C.Tsai, Y.T.Weng, S.H.Wang and M.H.Wu, Axial load behaviour of stiffened concrete- filled steel columns, J of Struct Engg. 128 (2) (9), pp A.Ghobarah,M.N. Ghorbel,S.E. Chidiac, Upgrading torsional resistance of reinforced concrete beams using fiber reinforced polymer, J of compos for construction, (2),pp Hsuan-Teh Hu, Chiung Shiann Huang, Ming- Hsien Wu & Yih-Min Wu, Nonlinear analysis of axially loaded concrete- filled tube columns with confinement effect, J of struct Engg. 129 (3) (), pp