bridge abutment passive soil pressures in earthquakes
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Bridge Abutment Passive
Soil Pressures
in
Earthquakes2009 NZSEE
CONFERENCE
John Wood
John Wood Consulting, Lower Hutt
SH 1 Ohau River BridgeConstructed 1953: 10-Spans: 136 m total length
Under longitudinal EQ plastic hinges in piers which have low ductility
Horsethief Canyon Bridge: Interstate 15: California, 1984
31 m long: 4 m high monolithic abutment walls on footings
Field Testing Objective:
Stiffness of Abutments
MWD Central Laboratories, 1986
Wall Model Tests: 1.0 m high wall:
Translated & rotated against sand backfills
Caltech Centrifuge Tests, 1984: 1:100 Scale Model Horsethief Canyon Bridge: Nevada Sand
Backfill
Static and dynamic tests
to determine abutment
stiffness
Force/Distplacement Hysteresis CurvesThurston (1986) Tests on Dense and Loose Sand
P = Pd x ( 0.5 g H2
W )
Wall Tests: Force/Displacement Curves:8 independent test projects: 1985 to 2009
P = Pd x ( 0.5 g H2
W )
Mainly cyclic
tests to give
backbone
curves.
Test
variations
eliminate
possibility of
detailed
comparisons.
Comparison of Test Ultimate Loads with Log-Spiral
Theoretical Solutions
In terms of
dimensionless
force.
Theoretical
solutions not
available for all
tests.
Loose Sand
EQ Performance Assessment Example:Waiwhetu Stream Bridge, Lower Hutt
Constructed 1962: 3-Span, total length 20.9 m
Piers:
Nine, 460 mm square
prestressed concrete
piles
Abutments:
Spread footings,
0.91 m high
Waiwhetu Stream Bridge Example
Response and demand curves:
With and without abutment stiffness
Response
curves from
nonlinear
FEA
pushover
analyses
Demand
curve from
NZS 1170.5
1000 yr RPPier piles yield
Conclusions
1.Abutment passive resistance on bridges
with monolithic abutments can be
substantial reducing ductility demands on
other substructure components.
2.Further research on the dynamic
response of abutment structures is
required to provide design rules for
estimating the damping from soil-
structure interaction.
Wall Design Acceleration Coefficient on Soil
Design
Parameter
Typical Values
Wellington
Typical Values
Westport
Ch(T=0) 1.33 1.1
Sp 0.80 0.67
Z 0.40 0.30
Ru 1.8 1.8
Co 0.77 0.40
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