COMPARITIVE STUDY OF BASE ISOLATORS AND VISCOUS FLUID DAMPERS ON SEISMIC RESPONSE OF RC STRUCTURES

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1 International Journal of Civil Engineering and Technology (IJCIET) Volume 9, Issue 8, August 2018, pp , Article ID: IJCIET_09_08_081 Available online at ISSN Print: and ISSN Online: IAEME Publication Scopus Indexed COMPARITIVE STUDY OF BASE ISOLATORS AND VISCOUS FLUID DAMPERS ON SEISMIC RESPONSE OF RC STRUCTURES Y. Rajesh Kumar Assistant Professor, Geethanjali College of Engineering and Technology, India ABSTRACT An earthquake is a sudden violent shaking of earth which results in great destruction to life as well as property by virtue of movements that were caused in earth s crust. Due to the sudden violent shaking, a large amount of energy will be released and imparted to the. Due to this imparted energy, the s experiences large displacements, drifts which leads to the failure of the. Hence for the safety of there is a need to dissipate the energy imparted to the which can be made through earthquake protection systems. The can be made resistant to seismic activity by vibration control systems. The can be made earthquake resistant by techniques such as base isolation and provision of dampers in the s. Base isolation is a technique of isolating the from the ground such that earthquake effects are reduced to a larger extent. Base isolators also increase the flexibility of the and reduce the forces transferred to the. Seismic dampers on the other hand absorb the energy provided by earthquake ground motions to the. The present study aims in understanding the seismic response of R C s of varying floor levels when subjected to an earthquake ground motion such as Elcentro by using base isolation and fluid viscous dampers as vibration control system and a comparative study is made between the two vibration control systems. Models of varying floor levels of 5,8,12 and 15 which are fixed base s were considered in the study and modal time history analysis is performed using ETABS software. All the s were modelled with the base isolators and fluid viscous dampers and observed the variation in seismic response. The parameters considered in the study were base shear, lateral roof displacement and fundamental time period. It has been observed that base shear decreased largely to an extent of 96%, lateral roof displacement increases to an extent of 45% in base isolated where as base shear decreased to an extent 38%, roof displacements decreased to an extent of 71% in s with viscous dampers when compared to bare frame s. Key words: Base isolation, Viscous dampers, vibration control, seismic response, ETABS, Elcentro, Time history analysis editor@iaeme.com

2 Comparitive Study of Base Isolators and Viscous Fluid Dampers on Seismic Response of RC Structures Cite this Article: Y. Rajesh Kumar, Comparitive Study of Base Isolators and Viscous Fluid Dampers on Seismic Response of RC Structures. International Journal of Civil Engineering and Technology, 9(8), 2018, pp INTRODUCTION The earthquake zoning map of India divides India into four seismic zones ranging from zone II to zone V where zone V experiences larger seismic action and zone II experiences lesser seismic action. When s located in Zone V are subjected to earthquake, the experiences larger forces and also a larger amount of energy will be imparted to. Hence for the safety of there is a need to dissipate the energy imparted to the which can be made through earthquake protection systems. Two vibration control systems base isolation and fluid viscous dampers were considered and a comparative study is made between the two systems. Base isolation is a technique of isolating the from the ground such that earthquake effects are reduced to a larger extent. Isolation systems, such as high-damping rubber bearings, have enough energy dissipating capacity which do not require any additional damping devices. In base isolation technique, flexible elements added to the elongate its fundamental natural period to a value far enough from dominant periods of the expected Earth quakes. The flexible elements are usually located at the base of the, taking much of the deformation produced by the earthquake while the tends to move as a rigid body. Another vibration control system, fluid viscous damper dissipates energy by pushing fluid through an orifice, producing a damping pressure which creates a force. This means that the damping force does not significantly increase the seismic loads for a comparable degree of structural deformation. Fluid viscous dampers provides high damping to the s which may be greater than 30% of the critical damping which causes a proportionate reduction in seismic excitation. Models of varying floor levels of 5,8,12 and 15 were considered for the present study. The s which were assumed to be fixed at the base were subjected to El centro ground motion and parameters such as lateral roof displacements, base shear and fundamental time period were observed by performing modal time history analysis in ETABS. All the s were then modeled with base isolators and fluid viscous dampers and observed the variation in seismic response. 2. LITERATURE REVIEW N. Torunbalci describes the effectiveness of various structural isolation techniques of a six story to reduce base shear forces, story shear forces, maximum absolute accelerations and relative story drifts. A numerical example analysis is taken with five different seismic protection alternatives as fixed base, rubber bearing, friction pendulum bearing, additional isolated story and viscous damper. Three dimensional non linear time history analysis is performed on RC building model for fixed base with respect to earthquake protection alternatives. The natural period of the being 0.58 seconds in the fixed base situation is increased to 2 seconds in the systems containing base isolators. When the storey shear, relative drift and acceleration values are examined, it is seen that this value is adequate for the being completely removed from the resonance range of the earthquake. Shirule. P.A studied the effect of lead rubber bearing and friction bearing on the seismic performance of 18-story symmetrical R.C.C. building. Nonlinear Time history analysis is used on both fixed base and base isolated buildings by subjecting the models with three different ground motions such as Bhuj, Koyana and Lacc T.H. From the study, it has been observed that the displacement increased with period of the isolated building. The base shears editor@iaeme.com

3 Y. Rajesh Kumar in each direction are decreased by 46 % and 35%with lead rubber bearing and friction bearing in base-isolated building compared to the fixed base building. Doo-Hoon KIM conducted a numerical study on viscous damper from an experimental investigation. The performing test parameters were the area of the resistant plate, relative velocity between resistant plate and base plate, oil film thickness of the viscous fluid, but the temperature effect was neglected. The numerical model was established by assuming non- Newtonian fluid behavior. The ground motion for El Centro 1940 NS was used as the input signal, and time history analysis with a linear model was performed along with the damping ratio ranges of 0% ~ 50%. To reduce the displacement of base isolated building viscous fluid dampers were designed and tested. M. K. Dethariya performed seismic response of building frame with & without viscous damper using SAP A nine storied building frame was analyzed with and without braced type viscous damper placed at different storey level by using non-linear time history analysis. The dampers are placed from the bottom storey and gradually placed at upper stories till the criteria for drift (maximum 1.2%) is satisfied as per IS: The value of damping coefficient C is taken as 40000kN.s/m.By the provision of viscous dampers up to five stories, maximum drift is reduced from 3.187% to 1.19%.The maximum acceleration decreases from 2.2% to 0.4% and base shear increase from 0.8% to 1.67% by providing dampers up to five stories. 3. MODELS CONSIDERED FOR STUDY The following models were considered for the analysis. Model 1 : 5 storey fixed base Model 2 : 8 storey fixed base Model 3 : 12 storey fixed base Model 4 : 15 storey fixed base Model 5 : 5 storey base isolated Model 6 : 8 storey base isolated Model 7 : 12 storey base isolated Model 8 : 15 storey base isolated Model 9 : 5 storey with fluid viscous dampers Model 10 : 8 storey with fluid viscous dampers Model 11 : 12 storey with fluid viscous dampers Model 12: 15 storey with fluid viscous dampers 4. PRELIMINARY DATA 5,8,12 and 15 storied s with and without base isolators and viscous dampers were analysed using time history analysis in ETABS. The plan size of the building is m 2 (19.80m x 6.78m). All the s considered in the study are assumed to be located in zone V and seismic parameters are taken as follows Zone factor: 0.36; Response reduction factor: 5; Importance factor: 1. The grades of concrete and steel were taken as M-25 and Fe-415 for beams, columns and slabs. The slabs were assumed to be 125mm thick and exterior and interior walls were assumed to be 230mm and 100mm thick. The following properties of beams and columns were considered in the work Beams : a) 230mm x425mm b) 230mm x 500mm editor@iaeme.com

4 Comparitive Study of Base Isolators and Viscous Fluid Dampers on Seismic Response of RC Structures Columns : a) 360mm x 610mm b) 360mm x460mm c) 310mm x 610mm d) 360mm x 760mm. The following figures shows the plan view, 3 dimensional view of bare frame, base isolated s and s with fluid viscous dampers Figure 1 Plan View of the building Figure 2 3D View of the building Figure 33D View of with dampers in the exterior frames editor@iaeme.com

5 Y. Rajesh Kumar 5. LOADING Figure 4 3D view of the with base isolators Gravity Loading: Dead load of the will be calculated by the software based on the sizes and properties assigned. The live load of 2kN/m 2 is considered for entire floor and floor finishes of 1.5kN/m 2 is applied as super imposed dead load. Time history Loading: The time history loading is applied from earthquake data functions. The El Centro 1940 North South Component data file loading is used in global-x direction with 8 points per line at a time interval 0.02 seconds. Figure 5 Acceleration Vs Time graph for an El Centro ground motion data 6. MODELLING OF BASE ISOLATORS AND VISCOUS DAMPERS The isolators in ETABS are modelled using link properties. The parameters selected to define isolators in ETABS program are as follows : Nonlinear Link Type: Rubber U1 Linear Effective Stiffness: kn/m U2 and U3 Linear Effective Stiffness: kN/m U2 and U3 Nonlinear Stiffness: 9000 kn/m Yield Strength: 72.22kN, Post Yield Stiffness Ratio: editor@iaeme.com

6 Comparitive Study of Base Isolators and Viscous Fluid Dampers on Seismic Response of RC Structures The viscous dampers in the system are defined as link property applied to the bracings used. The parameters selected to define utilized dampers in the ETABS program are as follows: Nonlinear Link Type: Rubber U1 Linear Effective Damping: kn.sec/m U1 Nonlinear stiffness: kN/m U1 Nonlinear Damping 2000kN.sec/m U1 Nonlinear Damping Exponent: RESULTS Time history analysis is performed on s with varying floor levels of 5,8,12 and 15 with and without base isolators and the following parameters were studied. Fundamental Time Period Table 1 Fundamental time period (Seconds) for different models Model Bare frame Base isolated Structure with Viscous damper 5 storey storey storey storey Fundamental time period (Seconds) storey 8 storey 12 storey 15 storey Models Bare frame Base isolated Structure with Viscous damper Figure 5 Comparison graph for fundamental time period between fixed base and base isolated The maximum fundamental time period of 1.56seconds has observed in 15 storey building in a bare frame which increased to 7.02 seconds in a base isolated and decreased to seconds in with dampers. An increase in fundamental time period in a base isolated is observed since the is more flexible when compared to fixed base and a decrease in fundamental time period in a with viscous dampers is observed since the dampers impart extra stiffness to the. Also an increase in the number of floor levels resulted in an increase in fundamental time period in bare frame, base isolated s and s with dampers respectively editor@iaeme.com

7 Y. Rajesh Kumar Lateral roof displacements Table 2 Lateral roof displacements (mm) for different models Model Bare frame Base isolated Structure with dampers 5 storey storey storey storey The maximum lateral roof displacement of 24.26mm has observed in 15 storey building in a bare frame which increased to 28.65mm in a base isolated and drastic reduction of 8.895mm is observed in with viscous dampers. In a base isolated, due to its flexibility the building deforms more in the lateral direction when compared to bare frame which is fixed at the base. On the other hand, in s with fluid viscous dampers due to its stiffness the building deforms only by a small amount when compared to bare frame and base isolated s. An increase in the number of floor levels also resulted in an increase in lateral roof displacement in bare frame, base isolated s and s with fluid viscous dampers respectively Lateral roof displacements (mm) Bare frame Base isolated Structure with dampers storey 8 storey 12 storey 15 storey Models Figure 6 Comparison graph for lateral roof displacement between fixed base and base isolated Base Shear Table 3 Base shear in kn for different models Model Bare frame Base isolated Structure with dampers 5 storey storey storey storey editor@iaeme.com

8 Comparitive Study of Base Isolators and Viscous Fluid Dampers on Seismic Response of RC Structures Base Shear (kn) storey 8 storey 12 storey Models 15 storey Bare frame Base isolated Structure with dampers Figure 7 Comparison graph for base shear between fixed base and base isolated A maximum base shear of 9214 kn has observed in a 15 storied building in a bare frame which reduced to 336.1kN in a base isolated and a sudden increase of 5787kN has been observed in a with dampers. An increase in number of floor levels resulted in an increase in base shear in bare frame, base isolated and s with viscous dampers respectively. Base isolators are very effective in reducing base shear when compared to fluid viscous dampers. 8. CONCLUSIONS The fundamental time period in a base isolated is more due to its flexibility when compared to bare frame. The fundamental time period in a with fluid viscous damper is less since the with dampers offer greater stiffness when compared to bare frame. Due to the flexibility, the lateral roof displacement increased to a large extent in a base isolated when compared to a bare frame in all the models. Because of inherent stiffness of the damper, the lateral roof displacements have shown a drastic reduction in s with viscous dampers when compared with bare frame s. The maximum percentage reduction in lateral roof displacement s found to be 71% in 5 and 8 storey buildings respectively and 58% and 63% in 12 and 15 storey buildings respectively. Base shear decreased largely to an extent of 96% by using base isolators since the forces transferred to the in base isolation will be less. The decrement in base shear in a with viscous dampers are less when compared with base isolated and percentage reduction in base shear was found to be 38% with dampers. REFERENCES [1] N. Torunbalci and G. Ozpalanlar(2008)., Earthquake Response Analysis Of Mid-Story Buildings Isolated With Various Seismic Isolation Techniques, The 14 th World Conference on Earthquake Engineering October 12-17, 2008, Beijing, China editor@iaeme.com

9 Y. Rajesh Kumar [2] Shirule. P.A, Jagtap. L. P, Sonawane. K. R, Patil. T. D, Jadwanir. N, Sonar. S. K(2011)., Time History Analysis of Base Isolated Multi-Storied Building, International Journal of Earth Sciences and Engineering, ISSN , Volume 05, No. 04. [3] M. K. Dethariya, B. J. Shah(2011)., Seismic response of building frame with & without viscous damper with using SAP 2000, International Journal of Earth Sciences and Engineering, Volume 04, Issue No 06, October [4] Beytollah.Taromi, Kiarash.Nasserasadi, Asghar.VataniOskouei(2011)., Parametric study of concrete base isolated building in the near field earthquakes, 6th National Congress on Civil Engineering, April 26-27, 2011, Semnan University, Semnan, Iran. [5] Shirule Pravin Ashok, Niraj Mehta, Rahulwagh, Mayur Padhiyar,Ankesh Samare, Yogesh Patil(2012)., Response Spectrum Analysis Of Multi Storied Base-Isolated Building, International Journal Of Civil, Structural, Environmental And Infra Engineering Research And Development (IJCSEIERD), Vol.2, Issue 3, Sep