Finite Element Analysis of Different Types of Composite Column

Transcription

1 Finite Element Analysis of Different Types of Composite Column Richa Pateriya 1, Dr. Saleem Akhtar 2, Prof. Nita Rajvaidya 3 1,2 Department of Civil Engineering, UIT RGPV, Bhopal, India 3 Department of Civil Engineering, TIEIT, Bhopal, India Abstract - The use of composite materials has been increased in strengthening of concrete columns in recent years. One of the applications is to use FRP (fiber reinforced polymer) reinforcement instead of steel reinforcement in concrete columns. In this paper, the results of an analytical investigation on the behavior of RC column reinforced with Steel rebar and Glass fiber reinforced polymer (GFRP) bars are comprised and discussed. Linear and Nonlinear finite element analysis (FEA) on 12-column specimens were accomplished by using ANSYS software. In this research, we investigated the benefits of superseding steel rebar with FRP bars in concrete columns. An extensive set of parameters was scrutinized, including different main reinforcement ratios, main reinforcement types (GFRP, Steel), ultimate load carrying capacity of columns and deformations. A comparison between the theoretical results and those obtained by analytical modeling using ANSYS are presented. The analysis done will be useful for predicting the ultimate load bearing capacity and deformations of concrete columns reinforced with GFRP bars. Keywords: ANSYS, Fiber reinforced polymer (FRP), Finite Element Analysis (FEA), GFRP Reinforced Concrete columns (GFRP). I. INTRODUCTION The traditional reinforcement methods in reinforced concrete column have been accepted for several years as a common practice amongst designers and contractors. There has been a large amount of research completed and designers are capable of predicting the future functioning of the columns. Fiber reinforced polymer (FRP) is continuously used for reinforcing new structures, and also for rehabilitation of existing structures. FRP composites, in form of sheets, cables, rods, and plates, have proven to be a future alternative to steel reinforcements because of their light weight, no corrosiveness, high specific strength, specific stiffness and are easily constructed. The most common types of FRP are aramid, glass, and carbon; AFRP, GFRP and CFRP respectively [1]. Fiberglass is a cheaper composite material made from glass fibers in a polymeric matrix (GFRP). The fibers provide the main load carrying capability of the material and the polymer serves to protect the fibers and permit load transfer for them. FRP composite materials have been used as internal and external reinforcement in the field of civil engineering constructions. It has been used as internal reinforcement for beams, slabs and pavements [2,3] and also as external reinforcement for rehabilitation and strengthening different structures [4,5]. Fibers reinforced polymer composites, developed primarily for the aerospace and defence industries, are a class of materials with great potential to be used in civil infrastructures. Since the construction of the first all-composite bridge superstructure in Miyun, China, in 1982, they have been gradually gaining acceptance from civil engineers as a new construction material. During these 30 years, they proved to be useful in a few areas of application: mostly in the form of sheets and strips for strengthening existing bridge structures and to some extent, as reinforcing bars substituting steel as concrete reinforcement. So, the purpose of this research is to study the behavior of reinforced concrete columns with GFRP. The results and observations presented in this paper are useful for engineers to predict the compressive strength of concrete column while using GFRP. II. OBJECTIVES The chief objectives of this study are: To study the compressive behavior of reinforced concrete columns reinforced longitudinally as well as transversely with steel rebar under pure axial load. To study the compressive behavior of reinforced concrete columns reinforced longitudinally as well as transversely with Glass fiber reinforced polymer under pure axial load. To compare the Structural behavior of RCC and GFRP Column. To perform linear and non-linear analysis of column with steel and GFRP reinforcement. III. SCOPE Analysis of the results will create a conclusion on the effectiveness of analytical analysis and effectiveness of GFRP as reinforcement. 173

2 IV. DETAILS OF COLUMN SPECIMENS Length of all Column Specimens =3200mm Cross Section of all column specimen=300mm 300mm The used element is capable of plastic deformation, cracking in three orthogonal directions, and crushing [9], [10]. TABLE I DETAILS OF COLUMN SPECIMENS Figure 2: Solid-65 Element for concrete A link8 element was used to model the reinforcement Polymer bar; two nodes are required for this element. Each node has three degrees of freedom, translation in the nodal x, y, and z directions. The element is also capable of plastic deformation [9], [10]. V. FINITE ELEMENT MODELING 5.1 Geometry The details of testing columns were shown in Fig.1. Analysis was carried out in 12-column specimens, where all columns had a square cross-section with a 300mm side and length of 3200mm. Analyzed columns had main reinforcement(steel, GFRP) 6#12mm, 6#16mm,6#20mm 8#12mm,8#16mm and 8#20mm. The transverse reinforcement (Steel, GFRP) was ф8 mm stirrups spaced 200mm, characteristic compressive strength of concrete columns 30 N/mm 2. Figure 3: A link 8 Element for Reinforcement 5.3 Material Properties The input data for the concrete, GFRP, and steel properties are shown in Table II, which is taken from Indian Standard code 2000 [14], Table III is taken from ACI Code 2008 [7, 11], Table IV is taken from EGYPTIAN Code 2001 [12], and Table V is taken from British Standards Institution 1997 [13]. IS code does not provide any recommendations for FRP. TABLE II INPUT DATA AS PER IS 456: Element types Figure 1: Details of reinforcement of columns An eight-node solid element, solid65, was used to model the concrete. Solid element has eight nodes with three degrees of freedom at each node, translation in the nodal x, y, and z directions. 174

3 TABLE III INPUT DATA AS PER ACI CODE 4.1: IS 456:2000 TABLE IV INPUT DATA AS PER EGYPTIAN CODE 4.2: ACI CODE TABLE V INPUT DATA AS PER BS 8110 CODE 4.3: BS CODE Figure 4: Stress-Strain Curves for Concrete as per various codes VI. LINEAR & NON-LINEAR ANALYSIS For Linear & nonlinear analysis of column, first, we define stress strain curve for concrete, steel, and FRP using different codes [11], [12], [13], [14] : IS 456:2000

4 5.2: ACI CODE 6.3: EGYPTIAN CODE Figure 6: Stress-Strain Curve for FRP as per various codes 5.3: BS CODE Figure 5: Stress-Strain Curve for Steel as per various codes VII. LOADINGS The parametric studies included in this investigation are the reinforcement ratios and reinforcement types, and the characteristic compressive strength of concrete, ultimate load bearing capacity etc. Table VI shows the ultimate loads on columns using ultimate load carrying capacity formula on the basis of different codes [11], [12], [13], [14]. TABLE VI ULTIMATE LOAD ON COLUMN (KN) 6.1: ACI CODE VIII. ANALYSIS OF COLUMN USING ANSYS & COMPARISON OF RESULTS 8.1 Linear Analysis: Table VII shows analytical results of deformations using ANSYS and also shows the comparison of deformations in columns using Steel and GFRP as a reinforcement as per various codes. The analysis results are shown graphically in figure 7 to figure : BS CODE 176

5 TABLE VII ANSYS RESULTS FOR DEFORMATION (LINEAR ANALYSIS) 8.3 Non Linear Analysis: Table X shows analytical results of deformations using ANSYS and also shows the comparison of deformations using Steel and GFRP as a reinforcement as per various codes. The analysis results are shown graphically in figure 11 to figure 14. TABLE X ANSYS RESULTS FOR DEFORMATION (NON LINEAR ANALYSIS) 8.2 Validation for deformations: The values of deformations obtained from ANSYS (In Linear Analysis) are validated with the help of Equation of Elasticity for composite material. [6]. Table VIII and Table IX show the validation of deformation when steel and GFRP is used as reinforcement in concrete columns. Table VIII VALIDATION FOR DEFORMATION (mm) [WHEN STEEL IS USED AS REINFORCEMENT 8.4 Reinforcement ratio Vs Deformation Graph: Figure 7: Reinforcement ratio Vs Deformation Graph as per IS code TABLE IX VALIDATION FOR DEFORMATION (mm) [WHEN GFRP IS USED AS REINFORCEMENT] IS code does not give recommendations for FRP & hence this graph represents reinforcement ratio Vs deformation only for Steel. Figure 8: Reinforcement ratio Vs Deformation Graph as per ACI code 177

6 Figure 9: Reinforcement ratio Vs Deformation Graph as per BS Code Figure 13: Reinforcement ratio Vs Deformation Graph as per BS Code Figure 10: Reinforcement ratio Vs Deformation Graph as per Egyptian Code Figure 14: Reinforcement ratio Vs Deformation Graph as per EGYPTIAN Code IX. COST COMPARISON OF STEEL AND GFRP FOR DEIFFERENT REINFORCEMENT RATIO TABLE XI: COST ANALYSIS & COMPARISON Figure 11: Reinforcement ratio Vs Deformation as per IS Code IS code does not give recommendations for FRP & hence this graph represents reinforcement ratio Vs deformation only for Steel. Figure 12: Reinforcement ratio Vs Deformation Graph as per ACI code 178

7 Although the initial cost of GFRP columns is more, the use of GFRP is beneficial instead of steel as it is corrosion resistant, weighs 1/4 th of steel, has greater tensile strength and also it reduces the maintenance cost to a greater extent. Figure 15: Reinforcement ratio Vs total cost of reinforcement Initial cost of installation of GFRP reinforcement as compare to steel reinforcement is more however in the future; it becomes cost effective in the long run as: GFRP is corrosion free. Use of GFRP reduces concrete cover and eliminates corrosion protection measures. Using GFRP may minimize expensive repair work required in case of steel reinforcement. X. CONCLUSION The Linear and Non-linear behavior of 12 column specimens are investigated in this study. The conclusions made from this investigation are as follows: Increasing reinforcement ratio from 0.8 to % has a significant effect on ultimate loads. As per ACI and BS-8110 code, for the same reinforcement ratio GFRP does not affect the ultimate load capacity of the column. While as per Egyptian code, for the same reinforcement ratio GFRP significantly increases the ultimate load capacity of the column. As per ACI and BS-8110 code, for linear and nonlinear analysis and for the same reinforcement ratio deformation does not change when using GFRP, but as per Egyptian Code, for the same reinforcement ratio deformation significantly increases in case of GFRP. The cost of reinforcement increases in case of GFRP from 37% to 74% for different reinforcement ratio. REFERENCES [1] Ehab M. Lofty, (2010) Ehab M. Lofty, (2010) Behavior of reinforced concrete short columns with Fiber Reinforced polymer bars International Journal of Civil and Structural Engineering Volume 1, No 4 pp [2] Rizkalla, S., Hassan, T., and Hassan, N., [2003]. Design Recommendations for the use of FRP for Reinforcement and Strengthening of Concrete Structures. Journal of Progress in Structural Engineering and Materials, 5 (1), [3] Benmokrane, B., El-Salakawy, E., El-Ragaby, A., and Lackey, T. [2006]. Designing and Testing of Concrete Bridge Decks Reinforced with Glass FRP Bars. Journal of Bridge Engineering, 11 (2): [4] Demers, M., and Neale, K.W. [1999]. Confinement of Reinforced Concrete Columns with Fiber Reinforced Composite Sheets- an Experimental Study. Canadian Journal of Civil Engineering, 26, [5] Teng, J.G., Chen, J.F., Smith, S.T., and Lam, L., [2002]. FRP Strengthened RC Structures. John Wiley & Sons, New York, NY. [6] S S Bhavikatti strength of materials Vikas Publishing House Pvt Ltd, 2009, third edition. [7] ACI Committee 440, (2006) Guide for the design and construction of structural concrete reinforced with FRP bars, ACI 440.1R-06, American Concrete Institute, Farmington Hills, MI [8] Ching Chiaw Choo, Issam E. Harik, and Hans Gesund (2006) Minimum Reinforcement Ratio for Fiber-Reinforced Polymer Reinforced Concrete Rectangular Columns ACI Structural Journal/May-June, pp [9] ANSYS User's Manual, Swanson Systems, Inc [10] Ehab M. Lotfy, (2010) Behavior of reinforced concrete short columns with Fiber Reinforced polymers bars International Journal of Civil and Structural Engineering Volume 1, No 3, pp [11] American Concrete Institute, (2008) Building code requirements for structural concrete, ACI , ACI, Farmington Hills, MI [12] Egyptian Code for design and construction of concrete structures, code no 203, 2001 [13] British Standards Institution (BSI), (2002) Structural use of concrete Part 1: Code of practice for design and construction.bs8110-1:1997, London. [14] Indian Standards Code (IS),(2000) Plain and Reinforced Concrete Code of Practice Forth Revision, IS 456:2000, India. 179