by Dr. Mark A. Ketchum, OPAC Consulting Engineers for the EERI 100 th Anniversary Earthquake Conference, April 17, 2006

Transcription

1 Principles of Earthquake Engineering of Bridges Part 1: Principles & Approach by Dr. Mark A. Ketchum, OPAC Consulting Engineers for the EERI 100 th Anniversary Earthquake Conference, April 17, 2006

2 Presentation Outline Introduction Performance Criteria Fundamental Principles Ground Motions Structural Design Demand Analysis Capacity Analysis Detailing Advanced Topics

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4 Introduction Part 1: Principles & Approach Part 2: Structural Analysis Types of Structures AASHTO Methodology California Methodology

5 Types of Structures Ordinary Bridges Special Bridges

6 Special Bridges

7 Ordinary Bridges

8 Typical California Bridge

9 AASHTO Methodology Force-based Conformance Checking Response Modification Factors Importance Classification I: Essential Bridges II: Other Bridges Seismic Performance Category (SPC) Importance Classification Peak Ground Acceleration Categories A, B, C, D

10 AASHTO Design Requirements Ground Motion Minimum 0.2g Static Lateral Load Seismic Response Coefficient Hazard, Soil, and Frequency dependent Site-specific spectra & motions allowed Analysis Static Lateral Load Single & Multi Mode Spectral Analysis Time History Analysis Force D/C with Response Modification Factors

11 California Methodology Displacement Ductility Approach Pre-determined Damage Locations Hazard & Soil Dependent Motions Category (influences performance requirements) Ordinary Important (Post-EQ Service Required) Classification (influences analysis / design requirements) Geometry (multilevel / curved / skew) Framing (stiffness / strength distribution) Geotechnical (near fault / soft soil / liquefaction)

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13 California Performance Criteria Ground Motions Ordinary Bridge Safety Event year Return Period Maximum Credible Limited Service Significant Damage Functional Event Higher Probability year Return Period Immediate Service Repairable Damage Important Bridge Immediate Service Repairable Damage Immediate Service Minimal Damage

14 Fundamental Principles Strength Analysis under Design Ground Motions Capacity Controlled Components Redundancy Stiffness Balance with a Frame Frequency Balance between Frames Ductility Capacity > Demand Minimum Ductility regardless of Demand

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16 Design Ground Motion Site Specific Assessment for Important Bridges Probabilistic Seismic Hazard Assessment Deterministic Seismic Hazard Assessment Rock Motion Spectra Rock Motion Histories Site Response Analysis Soil / Foundation / Structure Interaction Analysis Simplified Procedures for Ordinary Bridges

17 Design Ground Motion Simplified Procedures for Ordinary Bridges EQ Magnitude from Seismic Map PGA from Seismic Map Select Representative Standard Soil Profile Response Spectra for EQ / PGA / Soil Profile

18 California Seismic Map

19 California Seismic Map

20 Soil Profile Classifications

21 Response Spectra

22 Response Spectra

23 Response Spectra

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25 Structural Design Proportioning Minimum Column Dimensions & Lateral Loads Balanced Stiffnesses and Frequencies Redundancy Demand Controlled Elements Columns / Bents Foundations Capacity Protected Elements Bent Caps / Girders Pile Caps / Footings

26 Structural Design

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28 Seismic Demand Analysis

29 Seismic Demand Analysis 3D Model of Bridge Dynamic Elastic, Cracked (usually) Inelastic (special cases) Response Spectra Analysis Time History Analysis in special cases Directional Combination of Ground Motions Horizontal Motions Vertical Motions Displacement & Force Demands

30 Prototype Design

31 3D Elastic Dynamic Model

32 Displacement Demands

33 Displacement Demands

34 Force Demands Demand Controlled Elements Columns / Bents Plastic Capacities Capacity Protected Elements Column Shear / Bent Caps / Girders / Footings Overstrength Capacity of Controlling Elements

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36 Seismic Capacity Analysis Inelastic (Nonlinear) Analysis Displacement Capacities of Components (e.g. columns) Subsystems (e.g. frames / bents) Curvature Capacities of Sections By Moment vs. Curvature Analysis Strain Capacities of Materials Steel Concrete

37 Strain Capacities of Materials Mild Steel Prestressing Steel Concrete Confined Unconfined

38 Mild Steel

39 Prestressing Steel

40 Concrete

41 Curvature Capacities of Sections Inelastic Analysis of a R/C Cross Section

42 Displacement Capacity Pushover Analysis single-column system

43 Displacement Capacity Pushover Analysis multi-column system

44 Displacement Capacity Pushover Analysis complex system

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46 Unified Demand & Capacity Global Inelastic Time History Analysis

47 Unified Demand & Capacity Global Inelastic Time History Analysis

48 Capacity Protected Elements Superstructures Bent Caps Footings Designed to direct inelastic damage into the columns, pier walls, and abutments Strength > connecting elements

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50 Detailing Column confinement Ductile column connections Joint shear Hinge restrainers Abutments

51 Influence on Cost Model Structure Type Geometry Deck Width* Deck Depth Span Arrangement Bent Columns Column Type (Estimated Size) Column Height 1 CIP/PS box Straight x8.25 oblong 22 2 CIP/PS box Straight circular 22 3 CIP/PS box Straight x6 oblong 22 4 CIP/PS box Straight circular 22 5 PC/PS girder Straight x6 oblong 22 6 PC/PS girder Straight circular 22 7 PC/PS girder Straight x6 oblong 22 8 PC/PS girder Straight circular 22 9 CIP/PS box 1000 radius x8.25 oblong CIP/PS box 30 skew circular CIP/PS box Straight circular 50

52 Cost Trends Cost/SF vs. PGA for Magnitude 7.25 Earthquake $ $ $ $ $ $ $ Type 1 Type 3 Type 4 Type 6 Type 9 Type 10 Type 11 $ Cost/SF ($/SF) $ $90.00 $80.00 $70.00 $60.00 $50.00 $40.00 $30.00 $20.00 $10.00 $ PGA (%g)

53 Summary Documented Approach Supported by Theory & Testing Directly applicable to standard bridges Approach applicable to special bridges Performance basis Details

54 Part 2: Structural Analysis Robert Dameron