Principles of Earthquake Engineering of Bridges Part 1: Principles & Approach
by Dr. Mark A. Ketchum, OPAC Consulting Engineers for the EERI 100th Anniversary Earthquake Conference, April 17, 2006
Principles of Earthquake Engineering of Bridges Part 1
Presentation Outline
Introduction Performance Criteria Fundamental Principles Ground Motions Structural Design Demand Analysis Capacity Analysis Detailing Advanced Topics
Principles of Earthquake Engineering of Bridges Part 1
Principles of Earthquake Engineering of Bridges Part 1
Introduction
Part 1: Principles & Approach Part 2: Structural Analysis Types of Structures AASHTO Methodology California Methodology
Principles of Earthquake Engineering of Bridges Part 1
Types of Structures
Ordinary Bridges Special Bridges
Principles of Earthquake Engineering of Bridges Part 1
Special Bridges
Principles of Earthquake Engineering of Bridges Part 1
Ordinary Bridges
Principles of Earthquake Engineering of Bridges Part 1
Typical California Bridge
Principles of Earthquake Engineering of Bridges Part 1
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
Principles of Earthquake Engineering of Bridges Part 1
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
Principles of Earthquake Engineering of Bridges Part 1
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)
Principles of Earthquake Engineering of Bridges Part 1
Principles of Earthquake Engineering of Bridges Part 1
California Performance Criteria
Safety Event Ground Motions 1000 - 2000 year Return Period “Maximum Credible” Limited Service Significant Damage Immediate Service Repairable Damage Functional Event Higher Probability 150 - 500 year Return Period Immediate Service Repairable Damage Immediate Service Minimal Damage
Ordinary Bridge
Important Bridge
Principles of Earthquake Engineering of Bridges Part 1
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
Principles of Earthquake Engineering of Bridges Part 1
Principles of Earthquake Engineering of Bridges Part 1
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
Principles of Earthquake Engineering of Bridges Part 1
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
Principles of Earthquake Engineering of Bridges Part 1
California Seismic Map
Principles of Earthquake Engineering of Bridges Part 1
California Seismic Map
Principles of Earthquake Engineering of Bridges Part 1
Soil Profile Classifications
Principles of Earthquake Engineering of Bridges Part 1
Response Spectra
Principles of Earthquake Engineering of Bridges Part 1
Response Spectra
Principles of Earthquake Engineering of Bridges Part 1
Response Spectra
Principles of Earthquake Engineering of Bridges Part 1
Principles of Earthquake Engineering of Bridges Part 1
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
Principles of Earthquake Engineering of Bridges Part 1
Structural Design
Principles of Earthquake Engineering of Bridges Part 1
Principles of Earthquake Engineering of Bridges Part 1
Seismic Demand Analysis
Principles of Earthquake Engineering of Bridges Part 1
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
Principles of Earthquake Engineering of Bridges Part 1
Prototype Design
Principles of Earthquake Engineering of Bridges Part 1
3D Elastic Dynamic Model
Principles of Earthquake Engineering of Bridges Part 1
Displacement Demands
Principles of Earthquake Engineering of Bridges Part 1
Displacement Demands
Principles of Earthquake Engineering of Bridges Part 1
Force Demands
Demand Controlled Elements
– Columns / Bents – Plastic Capacities
Capacity Protected Elements
– Column Shear / Bent Caps / Girders / Footings – Overstrength Capacity of Controlling Elements
Principles of Earthquake Engineering of Bridges Part 1
Principles of Earthquake Engineering of Bridges Part 1
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
Principles of Earthquake Engineering of Bridges Part 1
Strain Capacities of Materials
Mild Steel Prestressing Steel Concrete
– Confined – Unconfined
Principles of Earthquake Engineering of Bridges Part 1
Mild Steel
Principles of Earthquake Engineering of Bridges Part 1
Prestressing Steel
Principles of Earthquake Engineering of Bridges Part 1
Concrete
Principles of Earthquake Engineering of Bridges Part 1
Curvature Capacities of Sections
Inelastic Analysis of a R/C Cross Section
Principles of Earthquake Engineering of Bridges Part 1
Displacement Capacity
Pushover Analysis – single-column system
Principles of Earthquake Engineering of Bridges Part 1
Displacement Capacity
Pushover Analysis – multi-column system
Principles of Earthquake Engineering of Bridges Part 1
Displacement Capacity
Pushover Analysis – complex system
Principles of Earthquake Engineering of Bridges Part 1
Principles of Earthquake Engineering of Bridges Part 1
Unified Demand & Capacity
Global Inelastic Time History Analysis
Principles of Earthquake Engineering of Bridges Part 1
Unified Demand & Capacity
Global Inelastic Time History Analysis
Principles of Earthquake Engineering of Bridges Part 1
Capacity Protected Elements
Superstructures Bent Caps Footings Designed to direct inelastic damage into the columns, pier walls, and abutments Strength > connecting elements
Principles of Earthquake Engineering of Bridges Part 1
Principles of Earthquake Engineering of Bridges Part 1
Detailing
Column confinement Ductile column connections Joint shear Hinge restrainers Abutments
Principles of Earthquake Engineering of Bridges Part 1
Influence on Cost
Model 1 2 3 4 5 6 7 8 9 10 11 Structure Type Geometry CIP/PS box CIP/PS box CIP/PS box CIP/PS box PC/PS girder PC/PS girder PC/PS girder PC/PS girder CIP/PS box CIP/PS box CIP/PS box Straight Straight Straight Straight Straight Straight Straight Straight 1000’ radius 30° skew Straight Deck Width* 39’ 68’ 39’ 68’ 39’ 68’ 39’ 68’ 27’ 68’ 39’ Deck Depth 6’ 6’ 4’ 4’ 5’-2” 5’-2” 6’-2” 6’-2” 6’ 6’ 6’ Span Arrangement 120’+150’+150’+150’+120’ 120’+150’+150’+150’+120’ 80’+100’+100’+100’+80’ 80’+100’+100’+100’+80’ 80’+100’+100’+100’+80’ 80’+100’+100’+100’+80’ 120’+120’ 120’+120’ 120’+150’+150’+150’+120’ 120’+150’+150’+150’+120’ 120’+150’+150’+150’+120’ Bent Columns 1 3 1 3 1 3 1 3 1 3 1 Column Type (Estimated Size) 5.5’x8.25’ oblong 5.5’ circular 4’x6’ oblong 4’ circular 4’x6’ oblong 4’ circular 4’x6’ oblong 4’ circular 5.5’x8.25’ oblong 5.5’ circular 5.5’ circular Column Height 22’ 22’ 22’ 22’ 22’ 22’ 22’ 22’ 22’ 22’ 50’
Principles of Earthquake Engineering of Bridges Part 1
Cost Trends
Cost/SF vs. PGA for Magnitude 7.25 Earthquake
$180.00 $170.00
Type 1
$160.00 $150.00 $140.00 $130.00 $120.00 $110.00
Type 3 Type 4 Type 6 Type 9 Type 10 Type 11
Cost/SF ($/SF)
$100.00 $90.00 $80.00 $70.00 $60.00 $50.00 $40.00 $30.00 $20.00 $10.00 $0.00 0.50
0.55
0.60
0.65
0.70
0.75
0.80
0.85
0.90
0.95
1.00
PGA (%g)
Principles of Earthquake Engineering of Bridges Part 1
Summary
Documented Approach Supported by Theory & Testing Directly applicable to standard bridges Approach applicable to special bridges Performance basis Details
Principles of Earthquake Engineering of Bridges Part 1
Part 2: Structural Analysis
Robert Dameron
Principles of Earthquake Engineering of Bridges Part 1