model design and dynamic similitude (1g/large scale...
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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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2
• 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
15
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
Selection of Compaction Conditions
16
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
Selection of Compaction Conditions
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17
• 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
20
20
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
21
21
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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22
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
27
27
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
28
28
Instrumented sections
Longitudinal section L1
Longitudinal section L2
Transverse section T1
Scaling of Earthquake Motions
29
29
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
30
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
31
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 Displacement (in)
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
32
32
Imperial Valley motion
Northridge motion
Facing Displacements
• 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
33
33
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)
Facing Displacement (in)
L1 - Imperial Valley
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)
Facing Displacement (in)
L1 – Placement of bridge beam
Bridge Seat Settlements
SE SW
NE NW
Bridge Seat Instrumentation
34
34
• 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)
Bridge Seat Settlements
35
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
Test 1Test 2Test 3Test 4Test 5
Ave
rage
Set
tlem
ent (
in)
Time (s)0
0.1
0.2
0.3
Bridge load Imperial Valley Maule Northridge
Test 1Test 2Test 3Test 4Test 5
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
37
37
• 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
0.3z = 3.5 ftlayer 7
0
0.1
0.2
0.3z = 2.0 ftlayer 4
0
0.1
0.2
0.3
0 1 2 3 4 5
z = 0.5 ftlayer 1
L1 T1
Reinforcement Strains
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
0.3z = 3.5 ftlayer 7
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
0.3z = 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
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
Transverse section T1
Longitudinal section L1
Transverse section T2
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)
Facing Displacement (in)
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)
Facing Displacements
• 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
Bridge Seat Settlements
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
Reinforcement Strains
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
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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 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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