+ + Caltrans Guidelines

Report
Caltrans Guidelines on Foundation Loading Due
to Liquefaction Induced Lateral Spreading
Tom Shantz, Caltrans
2010 PEER Annual Meeting
PEER TEAM
Scott Ashford (OSU)
Ross Boulanger (UCD)
Scott Brandenberg (UCLA)
Project
Participants
and
Organization
PEER
Guidelines
CALTRANS TEAM
Tom Shantz
Internal Review Team
Caltrans
Guidelines
Lessons from history….
Source: ce.washington.edu
Showa Bridge, Niigata (1964)
Nishinomiya-ko bridge,
Kobe (1995)
Photo by Yashinsky
Puente Tubul, Chile (2010)
Better performance…
Shukugawa Bridge, Kobe (1995)
Better performance…
Photos by Yashinsky
Heisei Bridge, Sabaichi River, Niigata (2007)
Better performance…
Photos by Yashinsky
Kaiun Bridge, Sabaichi River, Niigata (2007)
Better performance…
Photos by Yashinsky
Rinko Yasaka Bridge, Ugawa River, Niigata (2007)
Caltrans’ current practice per Memo to Designer 20-15.
Crust
0.67 PULT
Liquefied
Dense
• liquefied soil modeled as factored p-y curves (0.10 p-multiplier)
• 67% of the ultimate passive crust load is applied to the cap
• no inertial loads are considered
• performance criteria: piles remain elastic
Issues the Guidelines Team sought to address…
Fill
Liquefiable Soil
Dense Soil
• Crust load–deformation behavior. How much deformation to reach
ultimate passive pressure? Adjustments for non-plane strain behavior.
• Prediction of crust displacement.
• Potential restraining effect of the foundation.
• Potential restraining effect of the superstructure.
• Contribution of inertial loads to the foundation displacement demand.
• More specific performance criteria
The team must confront challenging issues…
Pile pinning effect
Crust – pile cap
interaction
Estimation of crust
displacement
Residual strength
Static vs. dynamic loading
Kinematic and inertial
load combination
Strategy: Where possible, rely on test results.
NIED Shake Table: Elgamal (2003)
UC Davis centrifuge: Boulanger, Chang, Brandenberg, Armstrong,
and Kutter (2006)
Field testing…
Port of Takachi Tests by Ashford (2002)
Extend test results with numerical modeling…
Fill in gaps with judgment…
+
+
Caltrans Guidelines
Limitations
“Since every project has unique aspects, these guidelines should not be used
to constrain or replace engineering judgment.”
Software Options
Nonlinear moment-stiffness behavior: xSECTION, XTRACT, LPILE 5, others…
Soil-foundation interaction: LPILE 5, wFRAME, SAP2000
Slope stability: most commercial codes – no special requirements
Caltrans Guidelines
Two design cases considered…
Fill
Liquefiable Soil
Dense Soil
Unrestrained ground displacement
Foundation restrained
ground displacement
Caltrans Guidelines
Unrestrained ground displacement case:
Equivalent Nonlinear Static Analysis Approach
Crust loads applied through
imposed soil displacement profile
mp = 0.0031N +
0.00034N2
pgroup =(psingle
)(Npiles
p) or solution
Fult based
on)(m
log-spiral
pgroup =(psoft clay)(Npiles)
pgroup =(psingle)(N
1 piles)(GRF)
1
Adjustment for wedge effect
Matlock (74) soft clay p-y
model with
Su = SKres
and
by Ovensen
(1964).
1.3e50 = 0.05
Matlock
w~
0
0
(Zc –D)/T
3
0
0
WT/T
LPILE 5 is limited to a single pile analysis
14
Caltrans Guidelines
Unrestrained ground displacement case:
Equivalent Nonlinear Static Analysis Approach
Crust loads applied through
imposed soil displacement profile
Pile stiffness
Linear case:
EIgroup =(EIsingle)(Npiles)
Nonlinear case:
Mmax
Moment
(fa,Ma)
fa= 12 fy
Stiffness (EI)
(See plot…)
Ma = 1.1 Mmax
fy
Curvature
fa
Moment
LPILE 5 is limited
to a single pile analysis
Caltrans Guidelines
Unrestrained ground displacement case:
Equivalent Nonlinear Static Analysis Approach
Crust loads applied through
imposed soil displacement profile
xi
Kax, ni
K
M
144 Kax
ni xi 2
Class 100 pile: Kax = 0.75 (400 kips) / 0.25 in = 1200 kips/in
LPILE 5 is limited to a single pile analysis
Caltrans Guidelines
Unrestrained ground displacement case:
Equivalent Nonlinear Static Analysis Approach
Crust loads applied through
imposed soil displacement profile
Inertial Loads
Vi =
H
M
V
Mo
H
Mi =Mo (LPILE 5: Mi
0)
Fcapi=0.65 PGA mcap
o
Abutment Case: assume inertial loads are zero
LPILE 5 is limited to a single pile analysis
Caltrans Guidelines
Unrestrained ground displacement case:
Equivalent Nonlinear Static Analysis Approach
Combination of kinematic and inertial loading
Crust loads applied through
imposed soil displacement profile
LPILE 5 is limited to a single pile analysis
Caltrans Guidelines
Performance Criteria
Cap Displacement
Pile Moment
Pile Shear
Well confined
pilings
H/20
Ma
SDC 3.6
Well confined
abutment pilings
12 inches
Ma
SDC 3.6
Poorly confined
pilings
2 inches
-
-
*H = column
height
Caltrans Guidelines
Guideline availability and adoption:
The new guidelines will be available on the Geotechnical
Services and Office of Earthquake Engineering websites
Guidelines official adoption date has not yet been determined.
Any questions or concerns, or you can’t find the guidelines,
contact me at [email protected]

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