Seismic Retrofit of the Historic North Torrey Pines Bridge

Jim Gingery, PE, GE

Principal Engineer, Kleinfelder, San Diego

PhD Student, University of California San Diego

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Presentation Outline

The Bridge

Site Conditions

Earthquake Ground Motion Development

Soil-Structure Interaction Evaluations

Retrofit Strategy

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The Bridge

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The Bridge

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South AbutmentNorth Abutment

Old River Channel

Pre-Construction Circa 1930

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Early Days of the Bridge - Late 1930’s

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Difficult Field Conditions!

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Site Conditions

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Earthquake Ground Motions and Soil-Structure Interaction

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Earthquake Ground Motion Development

1. PSHA and DSHA at bedrock

2. Seed time history selection

3. Rotation of seeds to principal axes

4. Spectral matching to FN and FP bedrock targets

5. Baseline correction

6. Site response analysis (5 soil profiles)

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Directivity Effects on Ground Motions

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Directivity of Seed Time Histories

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Spectral Matching Process

Acce

lera

tion

Disp

lace

men

tV

eloc

ity

Seed time histories

Target (design)

0

0.5

1

1.5

2

2.5

0 0.5 1 1.5 2 2.5 3 3.5 4

Period (sec)

Sp

ec

tra

l Ac

ce

lera

tio

n (

g) Fault-Parallel Target

Duzce, Bolu

Landers, Joshua Tree

Loma Prieta, LGPC

Seeds matched to target

RSPMatch

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1 2 3 4 5

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Earthquake Ground Motions

(2 directions) X (3 EQ’s) X (5 profiles) = 30 site response analyses and time histories!1

2

3

4

5

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Soil-Structure Interaction

K

KZ

KX

FZ = KZ*Z

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Soil-Structure Interaction

K

KZ

KX

6X6 Foundation Stiffness Matrix

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6X6 Stiffness Matrix for Piled Footings

Individual pile

Pile cap

Pile group

Cross Coupling

Linearization & displacement compatibility

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Liquefaction Hazard at the Site

Typical (N1)60 of liquefiable layers 12+/-

Layers typically <=5 ft thick north of Bent 4

Layers typically 5 to 12 ft thick s. of Bent 4

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Liquefaction Hazard at the Site

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Seismic Slope Stability

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Seismic Slope Stability

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Retrofit Strategy

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Project PartnersCity of Del Mar (owner)

Simon Wong Enrg. (prime, structural)

David Evans & Assc. (nonlinear FE modeling)

Caltrans (review)

Earth Mechanics, Inc. (peer review)

Frieder Seible (peer review)

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THANK YOU!