PARAMETRIC STUDY OF BEHAVIOR OF AN ELEVATED CIRCULAR WATER TANK BY NON LINEAR STATIC ANALYSIS. Prakash Mahadeo Mohite and Saurabh Arun Jangam

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1 Research Paper: Prakash Mahadeo Mohite and Saurabh Arun Jangam, 2012: Pp PARAMETRIC STUDY OF BEHAVIOR OF AN ELEVATED CIRCULAR WATER TANK BY NON LINEAR STATIC ANALYSIS Prakash Mahadeo Mohite and Saurabh Arun Jangam Dept. of Civil Engineering, Rajarambapu Institute of Technology, Sakharale, Tal-Walwa, Sangli,(MS) Corresponding author: ABSTRACT In this paper the parametric study behavior of an elevated circular water tank by Non Linear Static Analysis is carried out considering various parameters like water storage capacity 400 m 3, staging height 16 m and 20 m, diameter of columns 500 mm and 650 mm, number of columns 8, 10 and 12 number of columns with single layered and double layered column By inter-combining each of these parameters we get 20 models of tank. All tank models have their locality in earthquake zone III. The behavior of each tank with respect to other will be checked for base reaction, top roof displacement and plastic hinge formation sequence and its pattern within the staging. We have made use of SAP2000 computer program. It describes structure s behavior with the help of graphs i.e. capacity curve or pushover curve. Due to cantilever action of the structures and increasing stiffness there is change in magnitude of displacement and base reaction. There is not much change in base reaction and roof displacement due to arrangement of columns in single layer and double layer. The structural behavior remains same with reference to plastic hinge formation sequence for different water storage capacities, staging heights and number of columns. Keywords: Elevated Circular Water Tank, water storage capacity, staging heights and columns. INTRODUCTION For any city the one of the most important requirement is water supply system and an elevated water storage tank is one of the important components. So optimum design of such elevated storage tank should satisfy all requirements for which it is constructed. Therefore for such high rise structures seismic analysis is essential. Up till now various studies are made on the elevated structures and their methods of analysis. In some papers effects of plastic hinge properties induced in RCC frame are studied (Nikos and Michalis, 2010). Thus in this paper, study will be carried out for the nonlinear static analysis of an elevated circular water tank for different parameters, by which we can predict the behavior of an elevated water tank for specific earthquake zones (Providakis, 2007). The purpose of non linear static analysis is to evaluate and bring the structure to the expected behavior by estimating its strength and deformation demands in design earthquakes by means of static inelastic analysis and comparing these demands to available capacities at the performance levels of interest. The analysis is based on important performance parameters, including earthquake zone, stiffness of structures, deformations between elements, and element connection forces. The inelastic static non linear analysis can be viewed as a method for predicting seismic force and deformation demands, which gives an approximate structural behavior. Although the non linear static analysis cannot be carried out manually, designers go for non linear static analysis for high rise structures. Thus now-adays the Non - Linear Static Analysis takes a new face in Civil Engineering Design fields (Gernnaro Magliulo et al., 2007). OBJECTIVES The objectives of this investigation are to study the behavior of an elevated circular water tank considering the various structural and geometrical parameters using computer program. Here we shall use SAP, Structural Analysis Program. The final conclusion will be drawn with help of graphs of Base Reaction Versus Displacement (Roof Displacement) for each tank; from which we can compare one tank structure with other tank structures and then can predict the behavior of the same. Also we can make a statement about the suitability of any tank for specific earthquake zone. The main objectives are as given below. To study the behavior of an elevated water tank by Pushover Analysis for 1. Base shear and displacement for ((a) Different Staging heights and water storage capacities and (b) Number of columns, column sizes and their arrangements) and 2. Plastic hinge pattern and formation sequence within the staging (for earthquake Zone III). Non linear static analysis: Non Linear Static Analysis is the practical method in which analysis is carried out under permanent vertical loads and gradually increasing lateral loads to estimate the deformation and damage pattern of a structure. The non linear static analysis of a structure is a analysis under permanent vertical loads and gradually increasing lateral loads. The equivalent static lateral loads approximately represent earthquake induced forces. A plot of the total base shear versus top displacement (roof displacement) in a structure is obtained by this analysis that would indicate any premature weakness. This plot is known as Capacity Curve. The sample capacity Global Journal Engineering and Applied Sciences - ISSN (online): (Print) - Rising Research Journal Publication 138

2 curve is as given below in figure no.1 consists various plastic hinge locations. There are labels from A to E at the F a S s F v S 1 point where graph line profile changes (Shuraim and Charif, 2007). Within B to C there are three sub-locations of plastic hinges namely IO, LS and CP stands for Immediate Occupancy, Life Safety and Collapse Prevention, respectively. The analysis is carried out upto complete collapse, thus it can be used for determination of collapse load and ductility capacity. This analysis enables weakness in the structure to be identified and thus the decision can be taken for the strengthening of the required members (Fig 1). The analysis procedure consists of the design process that involves demand/capacity evaluation at all important capacity parameters, as well as the prediction of demands imposed by ground motion. Suitable capacity parameters and their acceptable values, as well as suitable methods for demand prediction will depend on the performance level to be evaluated. Here in this study we shall carry out Non Linear Static Analysis using SAP2000. The basic of non linear static analysis can be explained by FEMA273. Referring the same we get target displacement for Non Linear Static Analysis as given below, Target Displacement = t t C 0C 1C 2C 3S a 2 T e g.. (1) 2 4 Where, C 0:- Modification factor to relate spectral displacement. C 0 Number of Stories C 1:- Modification factor to relate expected inelastic displacement = C2:- Modification factor to represent the effect of hysteresis shape on the maximum displacement response = C3:- Modification factor to represent increased displacement due to dynamic effect = S a :- Response spectrum acceleration, at the fundamental period and damping ratio of the building in the direction under consideration. The value of shall be obtained from the procedure in Section T e :- Effective Fundamental Period, T e = T i Ki Ke Where, T i = Elastic Fundamental Period, K i = Elastic lateral stiffness of the building in the direction under consideration, K e= Effective lateral stiffness of the building in the direction under consideration Now From FEMA 273, we get, S a = S X BT 1 1 (For T > T0)..(2) and S S a = XS 3T (For 0 < T <= 0.2T0) BS T0..(3) But, SX1 BS T 0 =..(4) SXS B1 Where, = F a S s..(5) S X 1 S XS = Fv S1..(6) B s = B 1 = (For 5% Damping). Thus for all 20 models we get target displacement. These target displacements are tabulated which can be used as check point with displacement shown by SAP2000 computer program (Table 2). METHODOLOGY For each assumed parametric combination we will get various elevated water tanks and for convenience this different examples of elevated water tank are designated as Model and will be known by a specific Model Number (Mehnet and Hayri Baytan, 2006). Now scope of work is tabulated as given below by defining various parameters, their specific values and total number of models of elevated water tank (Fig 3). 1) Capacity of Water Tank :- 400 m 3 2) Staging Height of Water Tank :- 16 m and 20 m 3) Column Size :- 500 mm diameter and 650 mm diameter 4) Number of Columns and Their Arrangement:- Now by considering above parameters, we will get various models and total number of such elevated circular water tanks used in SAP2000 (Table 3). Thus total numbers of models of elevated circular water tank are 20. Other structural parameters which are kept same for all models are as follows: 1) Type of Frame: Open Frame Elevated Water Tank 2) Number of Panels: 4 and 5 for 16 m and 20 m staging height, respectively. 3) Story Height : 4 m 4) Diameter of Container : m 5) Bracing Size :- 300 mm 500 mm 6) Top Ring Beam Size : 600 mm 1200 mm 7) Thickness of Wall of Container : 190 mm 8) Earthquake Zone : Zone III Global Journal Engineering and Applied Sciences - ISSN (online): (Print) - Rising Research Journal Publication 139

3 RESULT AND DISCUSSION After performing the Non Linear Static Analysis using SAP2000 for all 20 models of elevated circular water tank we get the final displacement and base reaction. We get different non linear steps for each of model. The number of these non linear steps varies with model to model. In each step the model is subjected a base reaction and relative displacement. This will continue until structure gets collapsed or the structure reaches to target displacement. Thus here we have target displacement for each model obtained by SAP2000. From the Table 1 we get approximate target displacement as per FEMA273 provisions. The displacement and the base reaction obtained by SAP2000 are given in Table No. 4. The variation in displacement and the base reaction can be easily studied by the graphical representation. From the graphs (Fig 4 and 5) the displacement goes on decreasing as the number of column increases while it increases for increasing staging heights (Table 5). From the graphs (Fig 6 and 7) the base reaction goes on increasing as the number of column increases but no much variation for increasing staging heights (Table 6). CONCLUSION By performing the Non Linear Static Analysis of 20 models of elevated circular water tank considering various parameters and their combination, the following conclusions can be drawn. 1) For staging height 16 m, with different column the model number 1 as reference model, the model number 1 to 5 is 0 to the model number 5 as reference model, the model number 5 to 10 is 0 to (c) Thus from model number 1 to 5 and 6 to 10, model number 5 (staging height 16 m, column diameter 500 mm, total 12 columns, out of which 8 arranged on radius m and 4 arranged on radius m) shows least displacement i.e m because of increased number of columns and provided at two different radii. 2) For staging height 20 m, with different column the model number 11 as reference model, the model number 11 to 15 is 0 to 6.533, expect model number 14. the model number 16 as reference model, the model number 16 to 20 is 0 to , expect model number 19. (c) Model number 20 (expect model number 14 and 19), shows least displacement i.e m because of increased number of column and provided columns at two different radii. (d) For model number 14 the displacement is increased by 0.67% (with reference to model no 11) and for model no 19 by 7.21% (with reference to model no 16). (e) Model number 14 and 19 gives more displacement than model number 11 and 16, respectively. 3) For staging height 16 m, with different column the model number 1 as reference model, the model number 1 to 5 is 0 to the model number 5 as reference model, the model number 5 to 10 is 0 to (c) Thus from model number 1 to 5 and 6 to 10, model number 10 (staging height is 16 m, column diameter is 650 mm, total 12 columns are arranged out of which 8 are on radius m and 4 are on radius m) shows highest base reaction i.e KN because of increased number of columns and provided at two different radii. 4) For staging height 20 m, with different column the model number 11 as reference model, the model number 11 to 15 is 0 to the model number 16 as reference model, the model number 16 to 20 is 0 to (c) Thus from model number 11 to 15 and 16 to 20, model number 20 (staging height is 16 m, column diameter is 650 mm, total 12 columns are arranged out of which 8 are on radius m and 4 are on radius m) shows highest base reaction i.e KN because of increased number of columns and provided columns at two different radii. (d) Model number 4, 9, 14 and 19 consisting of 10 column out of which 6 are at radius m and 4 at m show the inconsistent displacement and base reaction as compared to other models because the arrangement of column about X-X and Y-Y axis is not the same. (e) As the number of column increases the base reaction also increases because increase in stiffness of the structure. 5) For all models of 16m staging height hinge formation starts at 8m and for 20 m staging height starts at 4m from base. The sequence of hinge Global Journal Engineering and Applied Sciences - ISSN (online): (Print) - Rising Research Journal Publication 140

4 formation remains approximately the same in all models. REFERENCES Gernnaro Magliulo, Guiseppe, Maddoloni, Edoardo Cosenza Comparison between Non- Linear Dynamic Analysis Performed According to EC8 and Elastic and Non Linear Static Analysis, Engineering Structures Mehnet Inel and Hayri Baytan Ozmen Effect of Plastic Hinge Properties in Non-Linear Analysis of Reinforced Concrete Buildings, Engineering Structures, Figure 1. Various Type of Hinges on Capacity Curve Nikos.D.Laaros and Michalis Fragiadakis Evaluation of ASCE-41, ATC-40 and N2-Static Pushover Method Based on Optimally Designed Buildings, Soil Dynamics and Earthquake Engineering Journal, Providakis, C.P Pushover Analysis of Base Isolated Steel Concrete Composite Structure Near Under Fault Excitations, Soil Dynamics And Earthquake Engineering Journal, Shuraim, A and A. Charif, Performance of Pushover Procedure in Evaluating. The Seismic Adequacy of Reinforced Concrete Frame, 7 th Saudi Engineering Conference, King Saud University, Saudi Arabia. Figure 2. Capacity Curve Figure 3. Arrangement of Columns for different models (Note:- From above Figure No.(1) Ki = Ke) 8A 10A 10B(6+4) 12A 12B(8+4) Figure 4. Variation in Displacement for Model No. 1 to Model No. 10 Figure 5. Variation in Displacement for Model No. 11 to Model No. 20 Figure 6. Variation in Base Reaction for Model No. 1 to Model No. 10. Figure 7. Variation in Base Reaction for Model No. 11 to Model No. 20 Global Journal Engineering and Applied Sciences - ISSN (online): (Print) - Rising Research Journal Publication 141

5 Table 1. Fundamental Period of Time Model No. Model Designation Table 4. Displacement and Base Reaction Obtained by SAP2000 Number Diameter of of Column Columns Height of Tank Displacement by FEMA273 Displacement by SAP2000 Base Reaction by SAP2000 (KN) 1 8A 8C A 10C A 12C B 10C(6+4) B 12C(8+4) A 8C A 10C A 12C B 10C(6+4) B 12C(8+4) A 8C A 10C A 12C B 10C(6+4) B 12C(8+4) A 8C A 10C A 12C B 10C(6+4) B 12C(8+4) Global Journal Engineering and Applied Sciences - ISSN (online): (Print) - Rising Research Journal Publication 142

6 Number of Columns Global J. of Engg. & Appl. Sciences, 2012: 2 (1) Table 2. Number of Columns and Their Arrangement Arrangement of Columns in plan Designation 8 1) 8 columns arranged on a radius of 5.65 m 8A ) 10 Columns arranged on a radius of 5.65 m 2) (6 + 4), 6 columns arranged on a radius of 5.65 m and 4 columns arranged on a radius m. 1) 12 Columns arranged on a radius of 5.65 m 2) (8 + 4), 8 columns arranged on a radius of 5.65 m and 4 columns arranged on a radius of m.. Table 3. Models Number in SAP2000 Models Number Details of Elevated Water Circular Tank of 400 m 3 8A 10A 12A 10B 12B Column Diameter :- 500 mm Staging Height :- 16 m Column Diameter :- 500 mm Staging Height :- 20 m Column Diameter :- 650 mm Staging Height :- 16 m Column Diameter :- 650 mm Staging Height :- 20 m Table 6. Percentage Increment in Base Reaction for Model No. 1 to Model No. 20 Model No. Designation Displacement % Increments in Base Reaction 1(R) 8C 16 m 500d C 16 m 500d C 16 m 500d C(6+4) 16 m 500d C(8+4) 16 m 500d (R) 8C 20 m 500d C 20 m 500d C 20 m 500d C(6+4) 20 m 500d C(8+4) 20 m 500d (R) 8C 16 m 650d C 16 m 650d C 16 m 650d C(6+4) 16 m 650d C(8+4) 16 m 650d (R) 8C 20 m 650d C 20 m 650d C 20 m 650d C(6+4) 20 m 650d C(8+4) 20 m 650d (Hint:- R stands for Reference Model for other four model) **************** 10A 10B 12A 12B Global Journal Engineering and Applied Sciences - ISSN (online): (Print) - Rising Research Journal Publication 143