BASE ISOLATION USING PERIODIC FOUNDATIONS

BASE ISOLATION USING PERIODIC FOUNDATIONSPresented bySANJITH R.M140136CE

Guided by

1INTRODUCTIONEarthquakes are one of the worst natural calamities

Causes instantaneous destruction of property and loss of life

2Source: www.omegaearthscience.pbworks.comDamages due to earthquakesINTRODUCTION3Generates P and S waves at the earthquake focus

Source: www. academic.brooklyn.cuny.edu.com3INTRODUCTIONStructures are usually designed to resist the transient horizontal forces

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Behaviour of buildings during earthquake Source: www. mceer.buffalo.comBASE ISOLATION SYSTEMSOne of the most effective means of protecting structure from earthquakesDecouples the structure from horizontal ground motion induced by earthquakesIncreases the natural time period of vibration

5Source:Dhawade, 2014Behaviour of fixed and base isolated buildingsCommon Methods Of Base IsolationBy introducing a layer with low horizontal stiffness between structure and foundation Eg. Elastomeric bearings

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Source: Ribakov and Ishakov,20087

Common Methods Of Base IsolationBy keeping the coefficient of friction as low as possible thereby limiting the transfer of shear Eg. Spherical sliding system

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Source: www.oiles.co.jp.com89

AdvantagesReduces structural damageBuilding remains functional even after a major earthquakeSlender structural elements can be used since earthquake forces acting on super structure is lessSecondary damage and injury is restrictedReduces maintenance and repair costs

10DisadvantagesBuilding will have large residual horizontal displacement relative to foundation after an earthquake

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Source: Monfared et al., 2013Elastic design SpectrumDisadvantagesChances of overturn of structure as vertical bearing capacity of rubber base is relatively poorThe effect of soil foundation interaction is ignoredIsolation systems subjected to seismic waves from an oblique direction not considered 12PERIODIC STRUCTURESCharacteristics:Made up of an infinite or finite repetition of unit cells in one, two or three direction

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Source: Shi et al., 2014PERIODIC STRUCTURES. . .Possess bands of frequency gaps known as attenuation zones (AZ)Does not allow the propagation of wave whose frequency falls within the frequency gap of the material in any direction

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Source: Xiang et al., 2012PERIODIC FOUNDATIONSRequirements:Made of common construction materials such as concrete, steel and rubber

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Source: Xiang et al., 201215PERIODIC FOUNDATIONS. . .Attenuation zone -within the strong frequency range of the earthquake (usually 0.1 Hz to 20 Hz)Width of Attenuation Zone(WAZ)= Upper Bound Frequency(UBF) Lower Bound Frequency(LBF) Height of each unit cell (periodic constant) should not be too largeThickness of concrete matrix should not be too small

16STUDIES USING PERIODIC FOUNDATION Parameters governing the influence of periodic foundation:

a-periodic constant r- core radius

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Source: Shi and Huang, 2013Material Parameters Some of the properties of the material used for the analysis are:

18Material (kg/m3)E (GPa) Soil19003x10-10.35Concrete2500300.2Rubber13001.37x10-40.463Steel 78902100.275Lead1160040.80.37Aluminium2716700.3Copper89001080.34 Source: Shi and Huang, 201318Influence of Periodic Constant (A)and Core Radius(R) on Attenuation Zones19

Source: Cheng and Shi, 2013For periodic structures with 2 components:Influence of Periodic Constant and Core Radius on Attenuation ZonesFor periodic structures with 3 components:

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Source: Cheng and Shi, 2013Type- CRSA=2md- coating thicknessInfluence of Periodic Constant and Core Radius on Attenuation Zones21

Source: Cheng and Shi, 2013Type- CRSd= 0.1mInterpretation from the graphs:For periodic structures with 3 components:LBF depends only on coating thickness and core radius

Wider AZs are obtained withDecrease in periodic constant for a given coating thicknessDecrease in coating thickness for a given periodic constant

22Influence of Periodic Constant and Core Radius on Attenuation ZonesInfluence of Core Density on Attenuation Zones23

Source: Shi and Huang, 2013Influence of Filling Fraction on Attenuation ZonesFilling fraction ff - ratio of volume of core to the volume of coating material in a typical cell

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Source: Shi and Huang, 2013Effect of Periodic Foundation on Base IsolationCase Study 1:

Vibration Attenuation and Frequency Band Gaps in Layered Periodic Foundation: Theory and Experiment (Xiang et al., 2012)

25Case Study 1Periodic structure consisting of reinforced concrete and rubber was consideredThickness of concrete and rubber was taken as 0.2mRange of frequency gaps of the periodic foundation was analyzed26Dispersion Curves27

Source: Xiang et al, 2012Analysis using ANSYS28

Source: Xiang et al., 2012Analysis using ANSYS. . .Frequency Response Function FRF =20 log(0/1)0- amplitude of displacement of point A1- amplitude of applied horizontal harmonic motion at bottom Negative no. in FRF represents very effective base isolationObtained similar results when vertical harmonic motion was applied at bottom

29Experimental StudyScaled model of the periodic foundation were tested using shake table tests

Tests were conducted at the National Centre for Research on Earthquake Engineering, Taiwan

Results were compared with specimen having no periodic foundation30Shake Table Test Setup31

Source: Xiang et al., 2012Shake Table Test Setup. . .Contact area of rubber and RC slab was 1m2Total mass of test specimen with periodic foundation=1.5 tBiaxial shaking table test was performed1975 Oroville seismogram obtained from PEER Ground Database, 2011 was used as input motionA background vibration frequency of 50Hz was recorded32Dynamic responses induced by background vibration33

Source: Xiang et al., 2012Horizontal Acceleration Responses of the top of the frames34

Source: Xiang et al., 2012Vertical time history of the top of the frames35

Source: Xiang et al., 2012Case Study 2Seismic isolation foundations with effective attenuation zones (Shi et al., 2014)36Case Study 2Compared the performance of periodic foundation with structure having rubber bearings and those without any base isolationA 6 storey frame was considered for the analysisStructures were modeled in ANSYS 10.0Acceleration records corresponding to 3 different seismic ground motions were taken as input

37ANSYS model38

Source: Shi et al., 2014Acceleration in x-direction of node A and their Fourier spectra39

Source: Shi et al., 2014Applied Peak acceleration-65 gal39Acceleration in x-direction of node A and their Fourier spectra40Source: Shi et al., 2014Applied Peak acceleration-109 gal

Acceleration in x-direction of node A and their Fourier spectra41Source: Shi et al., 2014Applied Peak acceleration-262 gal

Maximum relative displacement of super structure under different seismic inputs42

Source:Shi et al., 2014CONCLUSIONPeriodic foundation made of RC and rubber can serve as a multi dimensional seismically isolated foundationPerformance depends on LBF, UBF and WAZ High density of core & increase in filling fraction decreases LBFHigh density of core & increase in filling fraction and size of core increases WAZ

43Interpretation by AuthorProperty of periodic structures to reflect/block certain frequencies is utilized for base isolation

Similar to traditional rubber bearings, yet more effective in base isolation

Material and geometrical parameters can be adjusted so that AZs of the material match with the possible seismic wave input

Can also be used as a filter to isolate environmental vibrations

44REFERENCESH.J Xiang, Z.F Shi, S.J Wang, Y.L Mo (2012). Vibration Attenuation and Frequency Band Gaps in Layered Periodic Foundation: Theory and Experiment. Proc. Of the 15th World Conference on Earthquake Engineering.Hossein Monfared, Ayoub Shirvani, Sunny Nwaubani (2013). An investigation into the seismic base isolation from practical perspective. International Journal of Civil and Structural Engineering, 33(3), pp. 451-463S.M. Dhawade (2014). Comparative Study for Seismic Performance of Base Isolated & Fixed Based RC Frame Structure. International Journal of Civil Engineering Research, Research India publications, 5(2), pp. 183-190Y. Ribakov and I. Iskhakov (2008). Experimental Methods for Selecting Base Isolation Parameters for Public Buildings. The Open Construction and Building Technology Journal, Bentham Science Publishers Ltd., Vol. 2, pp. 1-6

45REFERENCESZhibao Cheng and Zhifei Shi (2013). Novel composite periodic structures with attenuation zones. Engineering Structures, Elsevier, 56, pp.1271-1282Zhifei Shi and Jiankun Huang (2013). Feasibility of reducing three-dimensional wave energy by introducing periodic foundations. Soil Dynamics and Earthquake Engineering, Elsevier, 50, pp. 204-212 Zhifei Shi, Zhibao Cheng, Hongjun Xiang (2014). Seismic isolation foundations with effective attenuation zones. Soil Dynamics and Earthquake Engineering, Elsevier, 57, pp.143-151www.academic.brooklyn.cuny.edu/geology/grocha/plates/platetec18.htm accessed on 1/10/2014www.oiles.co.jp/en/menshin/buildig/menshin/products/fps accessed on 1/10/2014

46 THANK YOU47