SEISMIC EXCITATION OF LOW TO HIGH RISE RCC STRUCTURE WITH LEAD RUBBER BEARING BASE ISOLATION

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1 International Journal of Civil Engineering and Technology (IJCIET) Volume 7, Issue 6, November-December 2016, pp , Article ID: IJCIET_07_06_052 Available online at ISSN Print: and ISSN Online: IAEME Publication SEISMIC EXCITATION OF LOW TO HIGH RISE RCC STRUCTURE WITH LEAD RUBBER BEARING BASE ISOLATION Iswarya G Department of Civil Engineering, JNTUA College of Engineering (Autonomous), Ananthapuramu, Andhra Pradesh, India. Vaishali G Ghorpade Professor, Department of Civil Engineering, JNTUA College of Engineering (Autonomous), Ananthapuramu, Andhra Pradesh, India. Sudarsana Rao H Professor, Department of Civil Engineering, JNTUA College of Engineering (Autonomous), Ananthapuramu, Andhra Pradesh, India. ABSTRACT Earthquakes cause severe damage to property, especially to man-made structures and necessitate architects and engineers with a number of important design criteria foreign to the normal design process. As many researchers studied and reviewed that seismic isolation is the better solution for the earth quake resistant design of the structures and its application is the most constructive technique to protect structures against vandalization from the earth quake strike and has gained growing majority during past decades.this is because base isolation confines the effects of the earthquake strike, a workable base largely separating the structure from the ground motion, and the structural counter accelerations are usually less as compared to the ground acceleration. The present work is intended to provide a systematic procedure to assess the behavior of a structure during the seismic excitation. In this work, a lead rubber bearing isolator is used from low to high rise RC buildings [1] by doing Time History Analysis. The fundamental goal of base isolation is to reduce substantially the absorption of the earthquake induced force and energy by the structure. This is accomplished by placing a structure on a support mechanism with low lateral stiffness so that in an event of earthquake, when the ground undergoes strong motion, only moderate motion is induced in the structure itself. Base isolation system significantly reduces the super structure lateral stiffness and ductility compared to un-isolated structure which is demonstrated by the results of this work. This allow cost saving from less material being spend on lateral system and implication of structural detailing. Key words: Time History Analysis, Lead Rubber Base Isolator, ETABS. Cite this Article: Iswarya G, Vaishali G Ghorpade and Sudarsana Rao H, Seismic Excitation of Low to High Rise RCC Structure with Lead Rubber Bearing Base Isolation. International Journal of Civil Engineering and Technology, 7(6), 2016, pp editor@iaeme.com

2 Seismic Excitation of Low to High Rise RCC Structure with Lead Rubber Bearing Base Isolation 1. INTRODUCTION To perform non-linear analyses, it involves significantly more effort and should be approached with specific objectives in mind. Typical instances where nonlinear analysis is applied in structural earthquake engineering: Assess and design seismic retrofit solutions for already existing buildings; Design new buildings that employ structural materials, systems, or other properties that do not conform to current building code requirements; The performance of buildings for specific owner/stakeholder should be assessed. The use of lead rubber base isolator [2] for symmetric buildings for low rise and high rise structures in the present work aims to demonstrate the effect of base isolation techniques. The buildings studied in this section are 5, 10, 15 & 20-storey Reinforced concrete Moment Resisting Space Frames Designed for Gravity and Seismic Loads Using Linear Analysis. Using Non-linear time history analysis in accordance with seismic code IS-1893:2002, the structure is evaluated with the help of the ETABS2015 software ( CSI Ltd) analysis engine. A real time Earthquake Ground acceleration data was selected from the seismic Zone-V for performing Non-linear time history analysis according to the IS part-1 classification, which has a zone factor of 0.36 from a place called Bhuj in the state of Gujarat which had devastating effects when the earthquake caused havoc in the year 2001.The earthquake record was scaled to the peak acceleration to increase the intensity of the earthquake. The response history of the structure was displayed at every time step was displayed in the output by the software package ETABS which included displacement responses, Force responses and various other responses. 2. RESEARCH SIGNIFICANCE Ground vibrations during earthquakes cause forces and deformations in structures. Designed structures should have the ability to withstand such forces and deformations. Seismic codes help to improve the behavior of structures so that they may withstand the earthquake effects without significant loss of property and life. The first Indian earthquake design code was published in the year 1962 as IS 1893:1962. In view of this, the present work aims at the following objectives: To Study the Seismic demands of regular R.C buildings using the Non-linear time history analysis. To illustrate the effects of base isolators, on the response of the low rise to High-rise Symmetric Buildings. To develop displacement curves for the considered buildings. To conduct time history analysis for the evaluation of dynamic structural response under loading which may vary according to specified time function 3. MATERIALS & METHODS Seismic Analysis methods can be carried out in different methods as outlined below Non Linear Time History Analysis To elaborate this, two earth-quake ground acceleration records namely N-E Bhuj and N-W Bhuj components of the Bhuj Earthquake record have been selected. Bhuj is a place in the state of Gujarat which is a high intensity earthquake zone that has zone factor 0.36 which comes under the Zone-V according to the classification of seismic zones by IS part-1. From the records the acceleration points with respect to a time-interval of second. It is to be considered that the acceleration record has units of m/ and has a total number of 26,706 acceleration data coordinates out of which the most critical data points which are of the highest intensity are the first 10,000 acceleration editor@iaeme.com

3 Iswarya G, Vaishali G Ghorpade and Sudarsana Rao H Figure 1 Bhuj-N-E component earthquake ground acceleration record Non-Linear Direct-Integration Time History Load Cases The Non-Linear time history analysis is carried out through the Direct-Integration methods by defining the Non-Linear time history by direct integration load cases. The data points of acceleration are converted to loading by multiplying the acceleration data points with the mass matrix of the structure. Non-linear static load case is defined as the time history load case is continued from state end of a non-linear load case. The appropriate additional parameters such as P- effects, damping matrix, selection of time step, number of time steps, time-integration method etc. Figure 2 Illustrates the non-linear direct integration time history (th-x) load case using Bhuj-N-E time history function Base Isolation Base isolation is the concept of protecting a building from the damaging effects [4] of an earthquake by introducing some type of support that isolates it from the shaking ground is an attractive one, and there are many mechanisms to achieve this result have been proposed. For earthquake resistant design, although the earlier proposals go back hundred years, it is only in recent years that base isolation has become a practical strategy. Base isolation is a passive control device that is installed between the foundation and the base of the building editor@iaeme.com

4 Seismic Excitation of Low to High Rise RCC Structure with Lead Rubber Bearing Base Isolation Figure 3 Function of Base Isolation system. Figure 4 Illustrates the lengthening of time period due to Base-Isolation system Parametric Design of Lead Rubber Bearing Base Isolators (New Zealand Rubber Bearing) 1. The maximum vertical reaction R of the footing is estimated for the fixed base structure. 2. The fundamental time period of the structure should also be calculated 3. The effective stiffness of the isolator is calculated by, = 4. From the response spectrum curves of the fixed base isolation system, the design (maximum) displacement of the base isolator is, = 4 5. The energy dissipation per cycle, can be approximately calculated by assuming for a very small post yield stiffness as =2 6. The short term yield force is = 4 = 7. The post yield horizontal stiffness can be obtained as editor@iaeme.com

5 Iswarya G, Vaishali G Ghorpade and Sudarsana Rao H = 8. Using the expression for and the approximate value of as given above, can be calculated as = 9 9. The yield force is given by = Properties of Base Isolators Figure 5 Construction of New Zealand Rubber Bearing System. Figure 6 Illustrates rubber bearing Base Isolator properties in the functional local axes editor@iaeme.com

6 Seismic Excitation of Low to High Rise RCC Structure with Lead Rubber Bearing Base Isolation Figure 7 Illustrates the rubber bearing base isolator material properties like effective stiffness, stiffness, yield strength and post-yield stiffness ratio for five storey building. Figure 8 Illustrates the Base Isolation provided to the structure to control the seismic response of the structure Step by Step Process To Perform the Non-Linear Modal Time History Analysis 1. Define the ground accelerationu % & numerically at every time step 2. For defining the structural properties. a. The mass matrix m is to be determined and lateral stiffness matrix k b. Estimate the modal dumping ratiosζ " 3. Determine the natural frequencies ω " and natural modes of vibration 4. The modal components s " of the effective earthquake force distribution is to be determined. 5. Compute the response contribution of the nth mode by the following steps, which are repeated for all modes. 6. Perform static analysis of the building subjected to lateral forces * to determine r,- ", the modal static response for each desired response quantity r editor@iaeme.com

7 Iswarya G, Vaishali G Ghorpade and Sudarsana Rao H 7. Determine the pseudo acceleration response A " 0t2of the nth mode SDOF system using numerical step methods. 8. Determine. * (t) using summation rule given in equation to get the final response Non Linear Modal Time History Analysis in ETABS Following are the general sequence of steps involved in performing NLTHA using ETABS in the present study: A two or three dimensional model that represents the overall structural behavior created. For reinforced concrete elements the appropriate reinforcement is provided for the cross sections. Frame hinge properties are defined and assigned to the frame elements. Gravity loads composed of dead loads and a specified proportion of live load is assigned as seismic weight to the structure. Free vibration un-damped modal analysis is performed to make note of the frequencies and time periods of the structure. The time history function from a file is selected and the time history function is defined [16]. Non-linear link elements are included in the structure like isolators and dampers. The non-linear modal time history load cases are defined by assigning the ground acceleration time history function as loading in X and Y directions. and by assigning proportional damping NLTHA is set to run. After the completion of the analysis the displacement pattern of the structure is studied and inter story drifts are calculated. The other responses such as base shear, member forces, and response spectrum curves are noted. 4. RESULTS & DISCUSSION The Results obtained for different parameters such as Storey drifts, Base shear, Modal Periods, Torsion etc. are presented in this section. Firstly the results obtained by carrying out Non-Linear Time History Analysis using Base Isolation techniques for Symmetric building for 5, 10, 15& 20 storey are presented. Subsequent discussions are made about the Results Obtained for Base isolation based on the storey drifts, Base shear, Torsion etc. for Symmetric buildings individually are presented Base Isolation of Five Storey Symmetric Building DRIFT IN Ux DIRECTION DISPLACEMENT VALUE WITHOUT ISOLATOR WITH ISOLATOR STORY Figure 9 Comparison of storey drifts of the FIVE storey symmetrical building with and without base isolation editor@iaeme.com

8 Seismic Excitation of Low to High Rise RCC Structure with Lead Rubber Bearing Base Isolation 5000 BASE SHEAR WITHOUT ISOLATOR WITH ISOLATOR Figure 10 Comparison of Base-shear of the five storey building with and without base isolation BASE MOMENT WITHOUT ISOLATOR WITH ISOLATOR Figure 11 Comparison of base moment of the five storey building with and without base isolation 6 TIME PERIOD WITHOUT ISOLATOR WITH ISOLATOR Figure 12 Comparison of time period of the five storey building with and without base isolation Following observations can be made from the above results presented. The storey drifts were decreased by 98% for five storey symmetric building. Due to the Base Isolators there is a reduction of Base shear by 66.8% for symmetric Buildings and reduction of base torsion moment by 94%. The time periods were increased for the structure with base isolator compared to fixed base by75.4%. The storey drifts were decreased by 31% for ten storey symmetric building. The base shear and base moment were reduced by 83%and 79.7% compared to fixed base building. The time period were increased for the structure with base isolator compared to fixed base by 53.8% editor@iaeme.com

9 Iswarya G, Vaishali G Ghorpade and Sudarsana Rao H The story drift for fifteen stories were reduced by 71.3% compared to fixed base. The base shear and base moment were reduced by 24%and 31.7% compared to fixed base building. The time period were increased for the structure with base isolator compared to fixed base by 38%. The story drift for twenty stories were reduced by 33.3% compared to fixed base. The base shear and base moment were reduced by 11%and 19.4% compared to fixed base building. The time period were increased for the structure with base isolator compared to fixed base by 28.9%. 5. CONCLUSION This study presents both theoretical investigation and modeling for building subjected to earthquakeinduced load with fixed base and with base-isolation method using rubber bearing. The aim of this work is to contribute to the efficient design of base-isolated structure subjected to seismic ground motion. The following sections summarize the conclusions resulting from this research work. The storey drifts were decreased by 98% for five storey symmetric building suggesting the effectiveness of Base Isolators for Low-Rise Buildings. The Base Isolators were found to be excellent seismic control devices for five storey buildings in controlling forced Responses such as base shear for symmetric buildings because of the reduction in Base shear by 66.8% for symmetric Buildings and by reducing the base torsion moment by 94%. The results of this work demonstrated that base isolators are excellent seismic control devices for both lowrise and high raise symmetric Buildings. Base isolation method has proved to be a reliable method of earthquake resistant design As the base isolators [10] are extensively used worldwide in high seismic areas, in near future, we will expect the same in India also. At least in seismic zone 4 and 5 the use of base isolators has to be encouraged, as they are technically very effective and economically feasible. The use of base isolators reduces interstorey drift and structural damages during earthquake. The building will be ready to occupy with minor repair. The base-isolated structure exhibit less lateral deflection, since the lateral displacement at the base never equals to zero, and less moment values than the fixed base structure REFERENCE [1] Abdul Raheem Faghaly"Optimum Design of Systems for Tall Buildings."International Journal of optimization in civil engineering, August 2012 [2] Allen J. Clark "Multiple Passive base isolator For Reducing the Earthquake Induced Ground Motion." proceedings of ninth world conference on Earthquake engineering, august 2-9,1988 [3] Amr.W.Sadek "Non-Linear Response of Torsionally Coupled structures". World Earthquake Engineering conference 1980 [4] FahimSadek, BijanMohraj, Andrew W.taylor and Riley M.Chung"A method of estimating the parameters of tuned mass dampers for seismic applications ". Earthquake Engineering and Structural Dynamics, Vol 26, (1997). [5] J.Ormondroyd and J.P. Den hartog," the theory of dynamic vibration absorber",trans. ASME APM-50-7, 1928, pp [6] Jonathan Chambers and Trevor Kelly "Non-Linear Dynamic Analysis-the only option for irregular structures." 13 th World Conference on Earthquake Engineering Vancouver, Canada. August 1-6, Paper No.1389 [7] K.S.Jagadish, B.K.R.Prasad and P.V.Rao,"The Inelastic Vibration Absorber Subjected To Earthquake Ground Motions."Earthquake engineering and Structural Dynamics. 7, (1979). [8] Kim Sd, Hong Wk, JuYk"A modified dynamic inelastic analysis of tall buildings considering changes of dynamic characteristics" the structural design of tall Buildings 02/ editor@iaeme.com

10 Seismic Excitation of Low to High Rise RCC Structure with Lead Rubber Bearing Base Isolation [9] P.C.Tsopelas, S. Nagarajaiah, M. C. Constantinou and A. M. Reinhorn"Nonlinear Dynamic Analysis Of Multiple Building base isolated structures". Computers and Structures Vol.50, No.1,pp ,1994. Rahul Rana "Response control of structures by tuned mass dampers and their generalizations." paper no. 498 Eleventh world conference on Earthquake engineering.1996 [10] Randall,S.E.Halsted, D.M. and Taylor,D.L.(1981)"Optimum vibration absorbers for linear damped systems".j.mech. Design, ASME,103, [11] RomyMohan and C Prabha, "Dynamic analysis of RCC Buildings with shear wall."international Journal of Earth Sciences and Engineering ISSN , volume 04, October 2011,pp [12] R.Villavard,"Reduction in Seismic Response with Heavily Damped Vibration Absorber."Earthquakeeng. structural dynamics 13,pp [13] R.Villaverde,"Seismic Control Of Structures With Damped Resonant Appendages. " First world conference on structural control,3-5 August, Los angeles, California USA,1994,pp [14] S.M. Kalantari, H.Naderpour and S.R.HoseiniVaez"Nonlinear Dynamic Analysis of Multiple Building Base Isolated Structures by Investigation Of Base-Isolator Type Selection On Seismic Behavior Of Structures Including Storey Drifts And Plastic Hinge Formation."The 14th World Conference on Earthquake Engineering October 12-17, 2008, Beijing, China. [15] G. Arya and Dr. Alice Mathai, Nonlinear Finite Element Analysis of High Damping Rubber Bearings for Base Isolation. International Journal of Civil Engineering and Technology (IJCIET), 5(9), 2014, pp [16] S.M.Wilkinson,R.A.Hiley"A Non-Linear Response History Model For The Seismic Analysis Of High- Rise Framed Buildings"september 2005,Computers and Structures. [17] S.N.Khante,B.P.Nirwan"Mitigation of response of Asymmetric Building Using Passive Tuned Mass Damper."International Journal of scientific & engineering research, volume-4,issue 7,July [18] Thakur V.M.,Pachpor P.D. "Seismic Analysis Of Multi-storey building with Tuned Mass Damper." International Journal of Engineering Research and Earthquake Applications (IJERA). Vol.2, Issue 1,Jan- Feb.2012, pp [19] T.Miyama, "Seismic response of Multi-storey frames equipped with energy absorbing storey at the top". Tenth World conference on Earthquake Engineering, July, Madrid, Spain, Vol 7,1992, pp editor@iaeme.com