Model Design and Dynamic Similitude (1g/Large Scale...

NHERI @ UCSD Workshop, 13-14 December, 2018

Model Design and Dynamic Similitude (1g/Large Scale Testing)

Seismic Response of MSE Bridge Abutments

John S. McCartney, Professor and ChairUniversity of California San Diego

Yewei Zheng, Assistant ProfessorOld Dominion UniversityDecember 13-14, 2018

Acknowledgements

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• Project sponsors: – Caltrans– Pooled fund members

(WA, UT, ID & MS DOT)• Project team:

– Prof. Yewei Zheng, Old Dominion University

– Prof. Benson Shing, UCSD– Prof. Patrick Fox, Head of CEE

at Penn State University

Seismic Response of MSE Bridge Abutments

Roadways

SlopesEmbankments

Retaining wallsBridge abutments

MSE abutments have many advantages over pile-supported bridge abutments, including cost savings, easier and faster construction, and smoother transition

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Geosynthetics in transportation applications:

MSE Bridge Abutment vs. GRS-IBS

• MSE: inextensible metallic reinforcements or extensible geosynthetic reinforcements embedded in compacted granular soil, and the reinforcement spacing and length is designed assuming that they are tie-backs

• GRS: closely-spaced geosynthetic reinforcements (≤ 12 in) embedded in compacted granular soil in order to form a GRS composite material

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MSE Bridge Abutment GRS-IBS AbutmentReinforced soil foundation

Bridge seat

Pavement Integrated approach

GRS abutment

Bearing bed reinforcement

Primary reinforcement

Bridge

RiprapCut slope

Bridge seat set back from facing with jointJointless integrated approach

Research MotivationMSE bridge abutments have been widely used in US, but there are concerns regarding the seismic performance, like in California:• Geotechnical: backfill settlements and facing displacements• Structural: bridge deck and seat movements, impact force between bridge

deck and seat, and interaction between bridge superstructure and abutment

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5

MSE wall performance

in Maule Earthquake,

Chile

Research MotivationMSE bridge abutments have been widely used in US, but there are concerns regarding the seismic performance, like in California:• Geotechnical: backfill settlements and facing displacements• Structural: bridge deck and seat movements, impact force between bridge

deck and seat, and interaction between bridge superstructure and abutment

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6

MSE bridge abutment

performance in Maule

Earthquake, Chile

Project Objectives

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• Bridge seat movement and rocking – bridge seat may rock or translate in different directions during shaking, leading to interactions with the bridge deck and upper wall backfill;

• Volumetric compression of the backfill soils – seismic shaking can induce compression of reinforced soil backfill under the bridge surcharge or approach slab loads, and this compression may result in differential settlement between the bridge and approach slab;

• Bridge beam impact forces on the bridge seat and impacts on retained fill – seismic shaking can cause relative movement between the bridge deck and bridge seat, result in impact forces that may damage the bridge seat or cause the formation of a passive wedge in the retained backfill behind the bridge seat;

• Transverse vs. longitudinal seismic behavior – to investigate the 3D behavior of the wall during one-dimensional shaking in different directions, in particular the movement of the bridge seat;

• Design details (reinforcement spacing, reinforcement stiffness, reinforcement type) – the different tests performed in this study having different configurations and reinforcement types will help understand the impact of these details on the seismic performance of the MSE bridge abutment, and the effect of these design variables need to be investigated;

• Wall face displacements during static and seismic loading – it is important to understand the facing displacements after shaking as they may lead to serviceability or maintenance problems;

• Reinforcement strains during static and seismic loading – to investigate the tensile forces developed during shaking and check the design assumptions for internal stability design

Literature Review – MSE Wall Seismic Performance• El-Emam and Bathurst (2004, 2005, 2007) performed a series of

shake table tests on reduced-scale MSE walls with a full-height rigid facing panel

• Ling et al. (2005, 2012) conducted full-scale shake table tests on MSE walls with battered modular block facing using fine sand and silty sand as backfill soils

• Yen et al. (2011) found that a MSE abutment performed well from post-earthquake reconnaissance for 2010 Maule Earthquake

• Helwany et al. (2012) conducted large-scale shaking table tests on a GRS abutment and found that it could sustain sinusoidal motions with an acceleration amplitude up to 1g without significant distress

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Motivation for Using 1g Shake Table Testing • Shake table testing has been successfully to investigate the

seismic performance of MSE walls:• MSE walls/slopes with no surcharge (El-Emam and Bathurst 2004, 2005,

2007; Ling et al. 2005, 2012; Tatsuoka et al. 2009, 2012)• Shake table testing has been used to evaluate MSE walls with a

surcharge load to simulate a bridge abutment (Helwany et al. 2012)• Can use actual (or similar) materials used in the field (backfill soil,

geosynthetic reinforcements, facing blocks, reinforced concrete)• Can use similar construction techniques• Can evaluate actual construction details• Can evaluate interaction between abutment and bridge deck• Can incorporate instrumentation on reinforcements

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UCSD Shake TableUCSD South Powell Structural Lab Shake Table:• Dimensions: 10 ft. x 16 ft.• Shaking DOF: 1D in N-S direction• Maximum gravity load: 80 kips• Dynamic stroke: ± 6 in.• Dynamic capacity: 90 kips

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Need for Scaling in Reduced Scale 1g Tests

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• When testing a model at 1g with a geometry that is N times smaller than a prototype, the self-weight is still proportional to the height of the soil layer

• The effective stresses in a model will be reduced proportional to the geometric scaling

Prototype earthen

structureγ=20kN/m3

σv'

z σv'=γz

4m σv,mid'=40 kPaModel

earthen structure

γ=20kN/m3

σv'

z σv'=γz

2m σv,mid'=20 kPa

Need for Scaling in Reduced Scale 1g Tests

Monotonic and cyclic stress-strain relationships for model and prototype (Rocha 1957; Roscoe 1968)

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• Shear strength and stiffness of soils depend on the effective stress• Shear strength is typically linearly related to the effective stress• Stiffness is nonlinearly related to the effective stress

• The stress-strain curve may change as a function of effective stress (peak values may not occur at the same strain)

• Scaling relationships are thus required to design a reduced scale model so that results can be extrapolated from model to prototype

1g Similitude Relationships

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Appropriate similitude relationships are needed for the design of reduced-scale model so that experimental results from reduced scale 1g shaking table tests can be extrapolated to full-scale conditions

Most widely used set of 1g similitude relationships - Iai (1989)

o Basis: equilibrium and mass balance of soil, structures, and pore watero Assumption: scaled stress-strain relationships for soil are independent of

confining stress if appropriate scaling factors are selectedo Three independent scaling factors:

• Geometry scaling factor λ – most important for reduce scale model design• Density scaling factor λρ – typically assumed to be 1 for the same soil• Strain scaling factor λε – can be determined using shear wave velocity

measurements, typically assumed to be 1o Applicability: applicable to deformation analysis prior to failure, not applicable to

the ultimate state of stability due to large deformations or loss of soil contact

1g Similitude Relationships

Original stress-strain relationships for soil in the model and prototype (Rocha 1957)

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Goal: Choose soil conditions to have a similar normalized stress-strain response

in model and prototype for λε = 1Variable Scaling factor

λρ = 1λε = 1 λ = 2

Length λ λ 2Density λρ 1 1Strain λε 1 1Mass λ3λρ λ3 8

Acceleration 1 1 1Velocity (λλε)1/2 λ1/2 1.414Stress λλρ λ 2

Modulus λλρ/λε λ 2Stiffness λ2λρ/λε λ2 4

Force λ3λρ λ3 8Time (λλε)1/2 λ1/2 1.414

Frequency (λλε)-1/2 λ-1/2 0.707

Similitude relationships (Iai 1989)

Normalized stress-strain relationships for soil in the model and prototype for λε=1

τ12/σ3'

γ12

0

2

4

6

8

10

12

0 5 10 15

Dr = 85%, σ3' = 5 psiDr = 85%, σ3' = 10 psi

Stre

ss R

atio

, σ1'/

σ 3'

Axial Strain (%)

Selection of Compaction Conditions

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15

• Typical relative density (Dr) for prototype structures = 85% (RC = 96%)

Stress ratio

0

100

200

300

400

500

600

0 5 10 15

Dr = 85%, σ3' = 5 psiDr = 85%, σ3' = 10 psi

Dev

iato

ric

Stre

ss, σ

1'-σ 3'

(kPa

)

Axial Strain (%)

Deviator stress

Model

Prototype

Peak stresses occur at approximately same axial strain (5%), which indicates

that the assumption of λε = 1 is valid

However, due to the nonlinear effects of confining stress on shear strength and stiffness, the normalized curves are not

similar for model and prototype for same Dr

Model

Prototype

Half-scale Modelλ = 2

Half-scale Modelλ = 2


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16

0

2

4

6

8

10

12

0 5 10 15

e0 = 0.636, Dr = 45%, σ3' = 5 psie0 = 0.564, Dr = 60%, σ3' = 5 psie0 = 0.515, Dr = 70%, σ3' = 5 psie0 = 0.443, Dr = 85%, σ3' = 5 psie0 = 0.443, Dr = 85%, σ3' = 10 psi

Stre

ss R

atio

, σ1'/

σ 3'

Axial Strain (%)

• Typical relative density (Dr) for prototype structures = 85% (RC = 96%)• Target relative density (Dr) for model specimens = 70% (RC = 92%)

Model

Prototype

Stress ratio

0

100

200

300

400

500

600

0 5 10 15

Dr = 45%, σ3' = 5 psiDr = 60%, σ3' = 5 psiDr = 70%, σ3' = 5 psiDr = 85%, σ3' = 5 psiDr = 85%, σ3' = 10 psi

Dev

iato

ric

Stre

ss, σ

1'-σ 3'

(kPa

)

Axial Strain (%)

Deviatoric stress

Model

Prototype

Dr = 70% for model yields a similar norm. response

with Dr = 85% for prototype


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• Typical relative density (Dr) for prototype structures = 85% (RC = 96%)• Target relative density (Dr) for model specimens = 70 % (RC = 92%)

0

50

100

150

200

250

300

350

400

0 1 2 3 4 5

Dr = 45%, σ3' = 5 psiDr = 60%, σ3' = 5 psiDr = 70%, σ3' = 5 psiDr = 85%, σ3' = 5 psiDr = 85%, σ3' = 10 psiTheoretical for λ = 2, σ3' = 10 psi

Seca

nt M

odul

us (k

Pa)

Axial Strain (%)

Secant modulus

Model

PrototypeTheoretically-scaled secant modulus as a function of strain is consistent with the target relative density

Total unit weights for wc = 5% are close for both prototype and model relative densities for this soil:γ = 113 pcf for Dr = 70%γ = 119 pcf for Dr = 85%So assumption of λρ = 1 is reasonable

Backfill Soil• Sieve analysis – Gradation curve• Standard Proctor compaction curve (not sensitive

0

20

40

60

80

100

0.01 0.1 1 10

Perc

ent F

iner

(%)

Particle Size (mm)

Cu = 6.1, Cz = 1.2Well-graded sand SW

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18

80

90

100

110

120

130

140

150

160

0 2 4 6 8 10 12 14 16

Dry

Uni

t Wei

ght (

pcf)

Gravimetric Water Content (%)

Backfill Soil• Shear strength and volumetric

behavior for Dr = 70%

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19

0

20

40

60

80

100

0 5 10 15

Dev

iato

r St

ress

(psi)

Axial Strain (%)

σ3' = 10 psi

σ3' = 5 psi

σ3' = 2 psi

γd = 108 pcfe0 = 0.515Dr = 70%

-2

0

2

4

6

8

0 5 10 15

Vol

umet

ric

Stra

in (%

) σ3' = 2 psi

Axial Strain (%)

σ3' = 10 psi

σ3' = 5 psi

φ’= 51.3°c = 0 kPa

0

1

2

3

4

0 5 10 15 20

Tens

ile F

orce

(kip

s/ft)

Axial Strain (%)

1%/min

5%/min10%/min

50%/min100%/min

Geogrid Reinforcement

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Prototype: Tensar UX 1700Model: Tensar LH 800 • Index stiffness = 26 kips/ft• Stiffness scaling factor = 4

Typical strain range in tests0

0.5

1.0

1.5

2.0

2.5

3.0

0 5 10 15 20

Tens

ile F

orce

(kip

s/ft)

Axial Strain (%)

Machine directionJ

5% = 26.0 kips/ft

Cross-machine directionJ

5% = 5.5 kips/ft

Target Prototype and Model Design

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Prototype Model

Product - Keystone

Dimensions (L x W x H)

24 in x 12 in x12 in 12 in x 10 in x 6 in

Prototype Model

Product UX1700 LH800

Stiffness (kips/ft) 100 26

Prototype Model

Wall height (ft) 14 7

Bridge seat thickness (in) 12 6

Clearanceheight (ft) 15 7.5

Wall length (ft) 15.6 7.8

Wall width (ft) 14 7

Bridge width (ft) 6 3

Block scaling Reinforcement scaling

Model geometry scaling for λ =2

Testing Plan

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Test No. Variable

BridgeSurcharge

Stress(psf)

Reinforcement Spacing

(in)

Reinforcement Stiffness(kips/ft)

Shaking Direction

1 Baseline 1380 6 26 Longitudinal

2 Bridge Surcharge Stress 900 6 26 Longitudinal

3 Geogrid Reinforcement Spacing 1380 12 26 Longitudinal

4 Geogrid Reinforcement Stiffness 1380 6 13 Longitudinal

5 Steel mesh Reinforcement 1380 6 330 Longitudinal

6 Shaking Direction 1380 6 26 Transverse

Longitudinal Test Configuration

23

23

24

24

Transverse Test Configuration

25

25

26

26

0

2

4

6

8

0 2 4 6 8 10 12 14 16

Test 1Test 2Test 3Test 4Test 5Test 6

Elev

atio

n, z

(ft)

Gravmetric Water Content (%)

Construction Data

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Test No. 1 2 3 4 5 6 Target

Average dry unit weight (pcf) 105.4 108.7 108.6 106.5 105.3 107.8 16.9

Average relativedensity (%) 64 73 73 67 64 65 70

Average water content (%) 4.7 6.7 5.5 4.3 5.5 5.0 5.0

0

2

4

6

8

0 20 40 60 80 100

Test 1Test 2Test 3Test 4Test 5Test 6

Elev

atio

n, z

(ft)

Apparent Cohesion (psf)

Gravimetric water content

Apparent cohesion

Instrumentation - Longitudinal Test

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Instrumented sections

Longitudinal section L1


Transverse section T1

Scaling of Earthquake Motions

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For a ½ scale model:• Frequency of motion is

increased by √2, which shortens the duration

• Acceleration amplitude stays the same as the original motion

• Displacement amplitude is scaled by 1/2

Imperial Valley Motion

-0.4

-0.3

-0.2

-0.1

0

0.1

0.2

0.3

0.4

0 5 10 15 20 25 30 35 40

OriginalScaled

Acc

eler

atio

n (g

)Time (s)

-6

-4

-2

0

2

4

6

0 5 10 15 20 25 30 35 40

OriginalScaled

Disp

lace

men

t (in

)

Time (s)

Input Motions

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30

Shaking event Motion PGA (g) PGD (in)1 White Noise 0.10 0.112 1940 Imperial Valley 0.31 2.573 White Noise 0.10 0.114 2010 Maule 0.40 4.255 White Noise 0.10 0.116 1994 Northridge* 0.58 3.497 White Noise 0.10 0.118 Sin @ 0.5 Hz 0.05 1.979 Sin @ 1 Hz 0.10 0.98

10 Sin @ 2 Hz 0.20 0.4911 Sin @ 5 Hz 0.25 0.1012 White Noise 0.10 0.11

Longitudinal Testing System• Measured displacement time

histories for the shaking table, reaction wall, and support wall are identical with the target input displacement time history

• Actual shaking table acceleration time history in general matches well with the target input accelerations

• Actual pseudo-spectral accelerations for the shaking table agree reasonably well with the target values

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31

Imperial Valley Earthquake Acceleration Time History

Response Spectra

-0.4

-0.2

0

0.2

0.4

0 4 8 12 16 20 24 28

Target inputShaking table

Acc

eler

atio

n (g

)

Time (s)

Peak = 0.42 g

0

0.2

0.4

0.6

0.8

1.0

1.2

0.1 1 10

Target inputShaking tableSupport wall

Pseu

do S

pect

ral A

ccel

erat

ion

(g)

Frequency (Hz)

0

1

2

3

4

5

6

7

0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8

L1 - ResidualL1 - MaximumL2 - ResidualL2 - MaximumT1 - ResidualT1 - Maximum

Elev

atio

n, z

(ft)

Facing Displacement (in)

0

1

2

3

4

5

6

7

0 0.05 0.10 0.15 0.20 0.25

L1 - ResidualL1 - MaximumL2 - ResidualL2 - MaximumT1 - ResidualT1 - Maximum

Elev

atio

n, z

(ft)


Facing Displacements

• Seismic displacements at the top are larger than the bottom• Residual displacements are generally small (max 0.14 in for the Northridge motion)• Longitudinal shaking resulted in displacements in transverse direction

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32

Imperial Valley motion

Northridge motion


• Reinforcement spacing and stiffness have the most significant effects• Greater bridge load resulted in larger displacements under static loading, but

smaller residual displacements from seismic loading

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Test No. 1 2 3 4 5

Description BaselineReduced Bridge Load

Increased Reinforcement

Spacing

Reduced Reinforcement

Stiffness

Steel Reinforcement

0

1

2

3

4

5

6

7

0 0.05 0.10 0.15 0.20

Test 1Test 2Test 3Test 4Test 5

Elev

atio

n, z

(ft)


L1 - Imperial Valley

0

1

2

3

4

5

6

7

0 0.05 0.10 0.15 0.20


Elev

atio

n, z

(ft)


L1 – Placement of bridge beam

Bridge Seat Settlements

SE SW

NE NW

Bridge Seat Instrumentation

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• Maximum dynamic settlement is 0.28 in, and residual settlement is 0.06 in, corresponding to a vertical strain of 0.07%

• This residual settlement would not be expected to cause significant damage

Average Bridge Seat Settlement

Bridge Seat Settlement Measurements at Corners

-0.2

-0.1

0

0.1

0.2

0.3

0.4

0 20 40 60 80 100

NWNE

SWSE

Settl

emen

t (in

)

Time (s)

-0.1

0

0.1

0.2

0.3

0 20 40 60 80 100

Ave

rage

Set

tlem

ent (

in)

Time (s)


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35

• Reinforcement spacing and stiffness have the most significant effects• Greater bridge load resulted in larger settlements for static loading, but smaller

settlements for seismic loading

-0.1

0

0.1

0.2

0.3

0.4

0.5

0 20 40 60 80 100


Ave

rage

Set

tlem

ent (

in)

Time (s)0

0.1

0.2

0.3

Bridge load Imperial Valley Maule Northridge


Settl

emen

t (in

)

Testing Stage

Test No. 1 2 3 4 5

Description BaselineReduced Bridge Load

Increased Reinforcement

Spacing

Reduced Reinforcement

Stiffness

Steel Reinforcement

-0.8

-0.6

-0.4

-0.2

0

0.2

0.4

0.6

0.8Bridge seatBridge beam

0 4 8 12 16 20 24 28Time (s)

Hor

izon

tal A

ccel

erat

ion

(g)

Peak = 0.53g

Peak = 0.63g

Acceleration Responses

36

36

0

1

2

3

4

5

6

7

1.0 1.1 1.2 1.3 1.4 1.5 1.6

Wall facingReinforced zoneRetained zone

Elev

atio

n, z

(ft)

RMS Acceleration Ratio

• Acceleration amplification increases with elevation in the MSE bridge abutment• Amplification ratios increase from retained zone to reinforced zone to wall facing• Amplification ratio for bridge beam is larger than bridge seat

Amplification ratio = 1.60 for bridge seat Amplification ratio = 1.80 for bridge beam

Accelerations for the Imperial Valley motion in Test 1

Reinforcement Strains

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• Max strains are small and far from the ultimate capacity of the geogrids

• Location of max strains under the bridge seat in upper layers and near connections in lower layers

• Longitudinal shaking resulted in strains in the transverse direction

bridge load

Rei

nfor

cem

ent S

trai

n (%

)

Distance from West Side Wall Facing, yw (ft)

0

0.1

0.2

0.3

InitialMaximum

MinimumResidual

z = 6.5 ftlayer 13

0

0.1

0.2

0.3z = 3.5 ftlayer 7

0

0.1

0.2

0.3

0 0.5 1.0 1.5 2.0 2.5

z = 0.5 ftlayer 1

Test 1 - Imperial Valley Motion

0

0.1

0.2

0.3

InitialMaximum

MinimumResidual

Rei

nfor

cem

ent S

trai

n (%

)

Distance from Front Wall Facing, x (ft)

bridge load

z = 6.5 ftlayer 13

0

0.1

0.2

0.3z = 5.0 ftlayer 10

0

0.1

0.2


0

0.1

0.2


0

0.1

0.2

0.3

0 1 2 3 4 5

z = 0.5 ftlayer 1

L1 T1


38

38R

einf

orce

men

t Str

ain

(%)

Distance from Front Wall Facing, x (ft)

bridge loadL1

0

0.1

0.2

0.3

Test 1 Test 2 Test 3 Test 4

z = 6.5 ftlayer 13

0

0.1

0.2


0

0.1

0.2

0.3

0 1 2 3 4 5

z = 0.5 ftlayer 1

bridge load

Distance from West Side Wall Facing, yw (ft)

0

0.1

0.2

0.3

Test 1 Test 2 Test 3 Test 4

z = 6.5 ftlayer 13

0

0.1

0.2


0

0.1

0.2

0.3

0 0.5 1.0 1.5 2.0 2.5

z = 0.5 ftlayer 1

T1

Imperial Valley Motion

• Reinforcement spacing and stiffness have the most significant effects• Greater bridge load results in larger reinforcement strains

Incremental residual reinforcement strains

-20

-15

-10

-5

0

0 4 8 12 16 20 24 28

EastWest

Hor

izon

tal C

onta

ct F

orce

(kip

s)

Time (s)

0

0.5

1.0

1.5

2.0

0 4 8 12 16 20 24 28

Join

t Wid

th (i

n)

Time (s)

Contact Forces

39

39

closed

open

Seismic joint size for the Northridge motion

Impact force = 20 kips

Instrumentation - Transverse Test

40

40

Instrumented sections




0

1

2

3

4

5

6

7

-0.2 0 0.2 0.4 0.6 0.8 1.0 1.2 1.4 1.6

L1 - ResidualL1 - MaximumT1-South - ResidualT1-South - MaximumT1-North - ResidualT1-North - Maximum

Elev

atio

n, z

(ft)


0

1

2

3

4

5

6

7

0 0.5 1.0 1.5

Imperial Valley - ResidualImperial Valley - MaxMaule - ResidualMaule - MaxNorthridge - ResidualNorthridge - Max

Elev

atio

n (ft

)

Lateral Facing Displacement (in)


• Seismic-induced maximum facing displacements are much larger for the Northridge motion than the other two motions, but most of the displacements were recovered after shaking

• T1-South had outward displacements, whereas T1-North had inward displacements• Transverse shaking resulted in displacements in longitudinal direction

41

41

T1-South

Northridge Motion


42

42

Transverse > Longitudinal

ShakingDirection

Imperial Valley (in)

Maule(in)

Northridge(in)

Longitudinal 0.06 0.06 0.09Transverse 0.10 0.19 0.19

Average incremental residual bridge seat settlement (model scale)

-0.1

0

0.1

0.2

0.3

0.4

0 4 8 12 16 20 24 28

Test 1Test 6

Settl

emen

t (in

)

Time (s)

Northridge Motion


43

43

00.10.20.30.40.50.6

00.51.01.52.02.5

bridge load

T1 - South

Rei

nfor

cem

ent S

trai

n (%

)

Distance from South Side Wall Facing, ys (ft)

00.10.20.30.40.50.6

InitialMaximumMinimumResidual

z = 6.5 ftlayer 13

00.10.20.30.40.50.6

z = 5.0 ftlayer 10

00.10.20.30.40.50.6

z = 3.5 ftlayer 7

00.10.20.30.40.50.6

z = 2.0 ftlayer 4

00.10.20.30.40.50.6

0 0.5 1.0 1.5 2.0 2.5

z = 0.5 ftlayer 1

bridge load

T1 - North

Reinforcem

ent Strain (%)

Distance from North Side Wall Facing, yn (ft)

00.10.20.30.40.50.6

InitialMaximumMinimumResidual

z = 6.5 ftlayer 13

00.10.20.30.40.50.6

z = 5.0 ftlayer 10

00.10.20.30.40.50.6

z = 3.5 ftlayer 7

00.10.20.30.40.50.6

z = 2.0 ftlayer 4

z = 0.5 ftlayer 1

Connection strength is important

Northridge motion

0

0.2

0.4

0.6

0.8

1.0

0 4 8 12 16 20 24 28

Join

t Wid

th (i

n)

Time (s)

Contact Forces

44

44

closed

open

-5

-4

-3

-2

-1

0

0 4 8 12 16 20 24 28

SouthNorthH

oriz

onta

l Con

tact

For

ce (k

ips)

Time (s)

Impact force = 4 kips

Future Testing on LHPOST

• Compare the response of actual bridge abutment designs using full-scale models– Caltrans-approved MSE bridge abutment (footing embedded in GRS mass with setback)– FHWA GRS-IBS abutment (bridge beam resting on GRS mass)

• No similitude required, can use actual construction materials, can use representative geometry of field-scale system

45

45

MSE Bridge Abutment GRS-IBS AbutmentReinforced soil foundation

Bridge seat

Pavement Integrated approach

GRS abutment

Bearing bed reinforcement

Primary reinforcement

Bridge

RiprapCut slope

Bridge seat with jointJointless integrated approach

Future Testing on LHPOST: Plane-Strain Container

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Conclusions• MSE bridge abutment seismic/residual displacements are small and are not

expected to cause significant damage to bridge superstructures– Seismic longitudinal residual bridge seat settlements range from 0.06 to 0.28 in. – Seismic longitudinal residual lateral facing displacements range from 0.05 to 0.17 in.

• Main take-aways:– Reducing reinforcement spacing and increasing reinforcement stiffness are the

most effective means to reduce static and seismic abutment deformations– Greater bridge load results in larger deformations for static loading, but smaller

deformations for seismic loading, which is attributed to the larger soil stiffness under greater bridge load

• Seismic residual bridge seat settlements due to transverse shaking are larger than for the longitudinal shaking

• Overall, the MSE bridge abutments show good seismic performance in terms of facing displacements and bridge seat movements

• The limitation of available shaking table size/capacity in the Powell lab had some effects which can be alleviated with numerical simulations and full-scale testing

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References• Zheng, Y., McCartney, J.S., Shing, P.B., and Fox, P.J. (2018). “Half-scale transverse

shaking table test of a geosynthetic reinforced soil bridge abutment.” Geosynthetics International. 10.1680/jgein.18.00019.

• Zheng, Y., Sander, A.C., Rong, W., Fox, P.J., Shing, P.B., and McCartney, J.S. (2017). “Shaking table test of a half-scale geosynthetic-reinforced soil bridge abutment.” ASTM Geotechnical Testing Journal. 41(1), 171-192. DOI: 10.1520/GTJ20160268.

• Trautner, C., Zheng, Y., McCartney, J.S., and Hutchinson, T. (2017). “An approach for the evaluation of shake table performance evaluation during repair and retrofit actions.” Earthquake Engineering & Structural Dynamics. 47, 131–146. DOI: 10.1002/eqe.2942.

• Zheng, Y., Fox, P.J., Shing, P.B., and McCartney, J.S. “Physical model tests on half-scale geosynthetic reinforced soil bridge abutments. I: Static loading.” Journal of Geotechnical and Geoenvironmental Engineering. In review.

• Zheng, Y., Fox, P.J., Shing, P.B., and McCartney, J.S. “Physical model tests on half-scale geosynthetic reinforced soil bridge abutments. II: Dynamic loading.” Journal of Geotechnical and Geoenvironmental Engineering. In review.

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