Seismic Design of Bridges ICE IStructE Part1
Transcript of Seismic Design of Bridges ICE IStructE Part1
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Eur Ing Athanasios Bistolas, Member of Technical Chamber of Greece
Principal Engineer
Seismic Design of Bridges-An Overview
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The devastation
Christchurch2010
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The devastation
Sandiago,Chile 2010
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Risk to Structures
Risk=Seismic Hazard x Vulnerability
DSHA or PSHA bySeismologistsMajority depends on
nature. Human Beings areobservers.
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Risk to Structures
Seismicity and Seismic Hazard Evaluation
Deterministic ApproachIts objective is to DETERMINE theMAXIMUM earthquake shaking.
Advantage- Easy to apply
Disadvantages
-Conservative
-Does not treat uncertainty well
-No info on the likelihood of the controlearthquake
-No info on the level of shaking duringthe lifespan of the structure
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Risk to Structures
Seismicity and Seismic Hazard Evaluation
Probabilistic ApproachRectifies a number of problemsinherent in DSHA by quantifyinguncertainty and the probability ofearthquake occurrence. Its objective is
to DETERMINE the MOST probablelevel of earthquake shaking during thelifetime o a structure on the particularsite.
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Risk to Structures
Risk=Seismic Hazard x Vulnerability
DSHA or PSHA bySeismologistsMajority depends on
nature. Human Beings areobservers.
Depends on engineers.Set of rules to address theseismic hazard. The main
purpose of the Antiseismicrules in Codes of Practice
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The Past-1920s-70s
• Seismic Loads 2-10% of dead loads
• Loads applied as static• Elastic Design-Stiffness based on gross section properties
• No account of the dynamic behaviour of structures
• No differentiation of response due to various soil conditions
• No account of inelastic behaviour and ductility
RESULT?
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The Past-1920s-70sThe wrong approach which lead to poor performance
• Seismic Loads 2-10% of dead loads
• Loads applied as static• Elastic Design-Stiffness based on gross section properties
• No account of the dynamic behaviour of structures
• No differentiation of response due to various soil conditions
• No account of inelastic behaviour and ductility
RESULT?
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Elastic ApproachWhere have we got it wrong?
Vertical Loads Transverse Response Combined Response
Specified Rebar
ActualStrength
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Displacement damages
Unseating
San Fernando,1971 Kobe, 1995
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Displacement damages
Unseating-Skewed spans
Chile, 2010
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Displacement damages
Unseating - Use of Restrainers and shock absorbers
Cable restrainers and buffer stops
Shock absorbers
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Displacement/Foundation damages
Dynamic Amplification-Soft soils
Costa Rica,1990
Liquefaction
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Displacement/Foundation damages
Lateral Spread
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Displacement/Foundation damages
Liquefaction and Lateral Spread-Soil Improvements
Stone Columns Compaction Grouting
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Displacement damages
Pounding
Northridge, 1994 Loma Prieta,1989
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Displacement/Foundation damages
Abutment Slumping
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Displacement/Foundation damages
Abutment Slumping
Costa Rica earthquake,1990
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Column failures
Very common type of failure with
dramatic consequences for the
majority of the cases. Mainly due to:
•Inadequate Flexural Strength•Undependable Flexural Strength
•Premature Termination of Laps
•Shear Brittle Failures
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Column Failures
Undependable flexural strength
Loma Prieta, 1989 Kobe, 1995