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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
KLEINFELDER CONFIDENTIAL North Torrey Pines Bridge Seismic Retrofit 2
Presentation Outline
The Bridge
Site Conditions
Earthquake Ground Motion Development
Soil-Structure Interaction Evaluations
Retrofit Strategy
KLEINFELDER CONFIDENTIAL North Torrey Pines Bridge Seismic Retrofit 5
South AbutmentNorth Abutment
Old River Channel
Pre-Construction Circa 1930
KLEINFELDER CONFIDENTIAL North Torrey Pines Bridge Seismic Retrofit 6
Early Days of the Bridge - Late 1930’s
KLEINFELDER CONFIDENTIAL North Torrey Pines Bridge Seismic Retrofit 9
Earthquake Ground Motions and Soil-Structure Interaction
KLEINFELDER CONFIDENTIAL North Torrey Pines Bridge Seismic Retrofit 10
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)
KLEINFELDER CONFIDENTIAL North Torrey Pines Bridge Seismic Retrofit 11
Directivity Effects on Ground Motions
KLEINFELDER CONFIDENTIAL North Torrey Pines Bridge Seismic Retrofit 12
Directivity of Seed Time Histories
KLEINFELDER CONFIDENTIAL North Torrey Pines Bridge Seismic Retrofit 13
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
KLEINFELDER CONFIDENTIAL North Torrey Pines Bridge Seismic Retrofit 16
Earthquake Ground Motions
(2 directions) X (3 EQ’s) X (5 profiles) = 30 site response analyses and time histories!1
2
3
4
5
KLEINFELDER CONFIDENTIAL North Torrey Pines Bridge Seismic Retrofit 17
Soil-Structure Interaction
K
KZ
KX
FZ = KZ*Z
KLEINFELDER CONFIDENTIAL North Torrey Pines Bridge Seismic Retrofit 18
Soil-Structure Interaction
K
KZ
KX
6X6 Foundation Stiffness Matrix
KLEINFELDER CONFIDENTIAL North Torrey Pines Bridge Seismic Retrofit 19
6X6 Stiffness Matrix for Piled Footings
Individual pile
Pile cap
Pile group
Cross Coupling
Linearization & displacement compatibility
KLEINFELDER CONFIDENTIAL North Torrey Pines Bridge Seismic Retrofit 20
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
KLEINFELDER CONFIDENTIAL North Torrey Pines Bridge Seismic Retrofit 21
Liquefaction Hazard at the Site
KLEINFELDER CONFIDENTIAL North Torrey Pines Bridge Seismic Retrofit 25
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)