Seismic Design of Adjacent Rail Bridges in Deep Liquefiable Soils

Kelly Burnell, PE, Kleinfelder, San Diego, CAEbrahim Amirihormozaki, PhD, PE, Kleinfelder, San Diego, CA

Project Purposes

Carries Commuter, Amtrak and BNSF Freight rail linesConstruct 0.9-mile segment of second main track

-LOSSAN Project-

Project Purposes

11 mile Extension9 new stations

-Mid-Coast LightrailExtension Project-

San Diego River Bridge

200 ft

Proposed Mid-Coast LRT Bridge

Existing LOSSAN BR 263.8

Existing LRT Bridge

N

Proposed LOSSAN Bridge Double Track

Ocean Beach Bike Path

Typical SectionMid-Coast Lightrail BridgeNew LOSSAN Bridge

Design Criteria for Different Structures

AREMA– 3 Level Seismic Performance

Criteria– Site Specific RSA

PGA (g)

Return Period(years)

Performance

Serviceability 0.13 100 Minor Damage, Structure useable

Ultimate 0.27 500 Inspectable Damage

Survivability 0.53 2400 Collapse Prevention

Design Criteria for Different Structures

AREMA– 3 Level Seismic Performance

Criteria– Site Specific RSA

Mid-Coast Lightrail– Caltrans Seismic Design

Criteria• 1000-yr Return Period• PGA – 0.42g• Collapse PreventionPGA

(g)Return Period(years)

Performance

Serviceability 0.13 100 Minor Damage, Structure useable

Ultimate 0.27 500 Inspectable Damage

Survivability 0.53 2400 Collapse Prevention

Response Spectra

0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

0 1 2 3 4 5 6

PGA

(g)

Period (sec)

ARS Curves

Lightrail

AREMA - Level 1

AREMA - Level 2

AREMA- Level 3

River Soil Conditions During Earthquake

Ultimate and Survivability Events – Liquefaction up to 80’ deepScour is up to 20 feetSlope Stability and Lateral Spreading

50

0

-50

-100

Original Approach – Ground Improvement

Original Approach – Ground Improvement

Ground improvement 90 feet deepConflicts with existing foundationsStaging of ground improvement

Existing Trolley Bridge Approach– Ground Improvement

Ground Improvement around Shafts

Alternative Approach – Permanent Steel Casings

LiquifiableAlluviam

Dense Gravels

11’

9’

San Diego River

Approx. $4M Cost Savings

Alternative Approach

Why not just use larger diameter conventional shafts?

Seismic Design of Superstructure

EQ EQ

Column Column

Bent Cap

Bearing

Deck

Girder

Floor Beam

Seismic Design of Superstructure

Bent Elevation

Seismic Design of Superstructure

Local Seismic Design

Global Seismic Design

Bridge Plan

Seismic Force

Seismic Design of Superstructure

Resisting Cross Section

Seismic Force

Seismic Design of Superstructure

Resisting Cross Section

Seismic Force

Seismic Design of Superstructure

Resisting Cross Section

Seismic Force

Seismic Design of Superstructure

Finite Element Model (SAP 2000)

Seismic Design of Superstructure

Bridge Plan

Seismic Force

Shear Flow

Seismic Design of Superstructure

1. Simplified Resisting Cross Section

2. Pay Attention to Shear Flow actions at ends of floor beams

Seismic Design of Superstructure – Key Points