Bridge Abutment Passive Soil Pressures in Earthquakes

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

Monolithic Abutment Isolated Abutment

SH 2 Mangaroa River Bridge

Constructed 1977

2-Span: 51 m total length

Isolated Abutments

Pomare-Wingate Overbridge

Hutt City

Constructed 1954

4-Span: 64 m total length

Monolithic Abutments

Horsethief Canyon Bridge: Interstate 15: California, 1984

31 m long: 4 m high monolithic abutment walls on footings

Field Testing Objective:

Stiffness of Abutments

Rotating Mass Shaker:

Peak load 445 kN at 14 Hz: Anchored to Deck

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

Finite Element ModelsNonlinear Analyses: Wood (1985), Martin and Yan (1995)

Y

Design

Method for

Force/

Displacement

Hyperbolic

curve

fit to test

results

ultP

u

K

uP

9.01

max

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:

EQ Load Model

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.

Thank-you for your interest

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