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Chapter 6 Seismic Design of BridgesKazuhiko Kawashima Tokyo Institute of TechnologySeismic Designz Loading environment (dead, live, wind, earthquake etc)z Performance criteria for gravity (deflection, stresses) and environmental loads (damage, displacement, collapse)z Geometric (space) requirementsz Time available for constructionz Soil conditionz Costz..Seismic Design Process with Emphasis on Japanese Seismic DesignJapanese Codes for Design of Highway BridgesJapan Road Associationz Design Specifications of Highway Bridges9Part I Common Part9Part II Steel Bridges9Part III Concrete Bridges9Part IV Foundations9Part V Seismic Designz The code applies to highway bridges with acenter span no longer than 200m919809199091996920021971Code and the Latest Code (2002)20021971Part V Seismic Design, Design Specifications of Highway Bridges, Japan Road Association1. General2. Principles of seismic design3. Loads considered in seismic design4. Design ground motions5. Evaluation of seismic performance6. Performance evaluation by static analysis7. Performance evaluation by dynamic analysis8. Effect of unstable soils9. Menshin design (Seismic Isolation)Part V Seismic Design, Design Specifications of Highway Bridges, Japan Road Association (continued)10. Strength & Ductility of RC piers11. Demand & capacity of steel piers12. Demand & capacity of foundations13. Demand & capacity of abutment foundations on liquefiable ground14. Demand & capacity of superstructures15. Seismic design of bearings16. Unseating prevention devicesSeismic Performance GoalsSeismic Performance CriteriaJames Roberts (1999), Previous Caltran’s Chief Engineer z How do you want the structure to perform in an earthquake?z How much danger can you accept?z What are the reasonable alternate routes?Seismic Design ForceSeismic Design Forcez Seismic design force should be determined based on the seismic environment (seismicity, fault length and rupture, etc) around the construction sitesz Seismic hazard map in terms of PGA is frequently used to scale the seismic design force.z Response accelerations are widely used to provide the seismic design force of bridges. Multiplying it to mass, lateral force can be directly evaluated.z Standard response spectra are generally modified to take account of regional seismicity asz Importance of structures are sometimes reflected to evaluate the design seismic force. There are two groups in this treatment as9Larger design seismic force is considered for a structure with higher importance9Since seismic force which applies to a structure does not change depending on the importance of the structure, the importance is considered in the evaluation of the capacitySeismic Design Force (continued)dards A z design A T S c T S tan ),(),(ξξ⋅=JapanCaltransType IType IIM=7.25 0.25M=8.0 0.25++New ZealandEC8AASHTOComparison of Design Response Accelerations (continued)00.511.522.50123Period (sec)Soft Soil Sites00.511.522.50123S e i s m i c C o e f f i c i e n tPeriod (sec)Stiff Soil SitesDeterministic or Probabilistic?z Deterministic ground motions which occurred in Tokyo during the 1923 Kanto EQ and in Kobe during the 1995 Kobe EQ is used with modification of regionalM7.2, 2008. 6.14 M7.3, 2000.10.6Max. magnitude which could happen due to hidden faults inside Japanzzzz ECzz9M J7.29 M J8Seismic Zoning Map widely accepted in Japan since 1983z 12 100z53 3This minimum value was very important tomitigate damage 0.7 0.8Evaluation of DemandWhere do we consider the damping characteristics of the bridge in the static design?Safety Evaluation Ground MotionType II GM⎪⎩⎪⎨⎧≤≤≤≤<⋅=TT T S T T T S T T T S c S s s s Z esSII 63/4965853/27 / 0 ⎪⎩⎪⎨⎧<≤<≤<⋅⋅⋅=)( /)( )0( 63/5965853/27T T T S T T T S T T T S c c S D Z SII Japanese practice to take the damping ratio of bridge into account in the static design forceDynamic response analysis )05.0,(T S A Static analysis )/02.0,(T T S AJapanese practice to take the damping ratio of bridge into account in the static design force0.511.522.501234R e s p o n s e A c c l e r a t i o n (g )Natural Period (s)Ground IGround II Ground III Ground IGround II Ground IIIType I Type II SDynamic response analysis)05.0,(T S A 00.511.522.501234Natural Period (s)R e s p o n s e A c c l e r a t i o n (g )S SGround IGround II Ground III Ground IGround II Ground IIIType I Type II (b)RA l i f E i lStatic analysis)/02.0,(T T S A。
