Consequences of Strong Vertical Accelerations on...

Consequences of Strong Vertical Accelerations on Shear Behavior of Reinforced Concrete Bridge Columns

Khalid M. Mosalam, Professor, UC Berkeley

Hyerin Lee, Post-doctoral researcher, UC Berkeley

Selim Günay, Post-doctoral researcher, UC Berkeley

Pardeep Kumar, PhD student, UC Berkeley

Shakhzod Takhirov, Lab. Manager, UC Berkeley

Sashi Kunnath, Professor and Chair, UC Davis

Sponsors: Caltrans and PEER

5th Kwang-Hwa Forum, Tongji University, Shanghai, China, December 8-10, 2012

December 9, 2012

Outline

Motivation

Test Specimens and Test Sequence

Test Results: Evidence of Axial Force Effect on Shear Strength

Test Results vs. Code Estimations

Post-Test Simulation

Concluding Remarks

Further Developments: Laser Scanning & Repair



Motivation

Shear Failure

Various codes and guidelines

Consensus?

- Unexpected increase of shear force from P-M interaction

- Axial force or axial strain affects the shear strength of RC members

RC structures damaged by past earthquakes Papazoglou and Elnashai (1996)

Bridge Structures

- Do not have enough redundancy

- Columns are the most critical part

Shear Strength Shear Demand

i jV M M L

Test Specimens

¼ -scale Plumas-Arboga Overhead Bridge (prototype)

Two specimens (SP1 & SP2) with Aspect Ratio=3.5, D=20″, H=70″

Reinf. Ratio: Longitudinal=1.56%

Transverse=0.55% (SP1) > 0.47% by BDS

0.36% (SP2) < 0.47% by BDS

Weight of mass blocks = 85.6 kips (6.8% axial load ratio)

Periods: Lateral = 0.49 sec.

Rotational = 0.10 sec.

Vertical = 0.03 sec.


Test Specimens

16-#5

hoops

#2@2” (SP 1)

#2@3” (SP 2)

D=20”

cover=1”

AA

B

B A-A B-B

24”

70”

18”

60” 84.85”

42.4” 30”

109”CC

C-C

16-#5

hoops

#2@2” (SP 1)

#2@3” (SP 2)

D=20”

cover=1”

16-#5

hoops

#2@2” (SP 1)

#2@3” (SP 2)

D=20”

cover=1”

AA

B

B

AA

B

B A-A B-B

24”

70”

18”

60” 84.85”

42.4” 30”

109”CC

C-C


Test Sequence

Input: 1994 Northridge EQ at Pacoima Dam

2D (X and Z) and 1D (X) excitations

½ time-compressed

-2

-1

0

1

2

0 2 4 6 8

Time (sec)

(a) X direction

1.585g

-2

-1

0

1

2

0 2 4 6 8

Time (sec)

(b) Z direction

1.229g

Acc

ele

ration (

g)

Acc

ele

ration (

g)

-2

-1

0

1

2

0 2 4 6 8

Time (sec)

(a) X direction

1.585g

-2

-1

0

1

2

0 2 4 6 8

Time (sec)

(b) Z direction

1.229g

Acc

ele

ration (

g)

Acc

ele

ration (

g)



Drift Ratio = 1.92~2.04% Drift Ratio = 1.82~2.34%

Shear force-lateral displacement relationships in the 125% tests

Decrease in stiffness

Shear degradation due to significant axial tension

-1

-0.5

0

0.5

1

-1.5 0 1.5 3

1st X+Z

X only

2nd X+Z

-1

-0.5

0

0.5

1

-1.5 0 1.5 3

1st X+Z

X only

2nd X+Z

(a) SP1 (b) SP2

Forc

e (

100 k

ips)

Drift (%)

4

2

0

-4

-2Forc

e (

100

kN

)

Forc

e (

100 k

ips)

Drift (%)

4

2

0

-4

-2

Forc

e (

100

kN

)



Shear and axial force histories in the 125% tests

Shear degradation due to significant axial tension

-100

0

100

200

300

0.0 0.5 1.0 1.5 2.0

-100

0

100

200

300

0.0 0.5 1.0 1.5 2.0

-100

0

100

200

300

0.0 0.5 1.0 1.5 2.0

Axial Force(+ → Compression)

12

8

4

-4

0

0.0 0.5 1.0 1.5 2.0

3

2

1

0

-1

Forc

e (

100 k

ips)

Time (sec)

Forc

e (

100

kN

)

(a) SP2 1st X+Z (2-9)

-100

-50

0

50

100

0.0 0.5 1.0 1.5 2.0

77.4 kips

0.195 s

Shear Force4

2

0

-4

-2

0.5 1.0 1.5 2.0

1

0.5

0

-0.5

-1

Forc

e (

100 k

ips)

Time (sec)

Forc

e (

100

kN

)

0.0

-61.6 kips

56.7 kips

Axial Force (+ → Compression)

(b) SP2 X only (2-10)

-100

-50

0

50

100

0.0 0.5 1.0 1.5 2.0

80.9 kips

Shear Force

12

8

4

-4

0

0.0 0.5 1.0 1.5 2.0

3

2

1

0

-1

Forc

e (

100 k

ips)

Time (sec)

Forc

e (

100

kN

)

4

2

0

-4

-2

0.5 1.0 1.5 2.0

1

0.5

0

-0.5

-1

Forc

e (

100 k

ips)

Time (sec)

Forc

e (

100

kN

)0.0

Axial Force (+ → Compression)

(c) SP2 2nd X+Z (2-11)

-100

-50

0

50

100

0.0 0.5 1.0 1.5 2.0

67.0 kips

0.180 s

Shear Force

-63.3 kips

12

8

4

-4

0

0.0 0.5 1.0 1.5 2.0

3

2

1

0

-1

Forc

e (

100 k

ips)

Time (sec)

Forc

e (

100

kN

)

4

2

0

-4

-2

0.5 1.0 1.5 2.0

1

0.5

0

-0.5

-1

Forc

e (

100 k

ips)

Time (sec)

Forc

e (

100

kN

)

0.0



0”

10”

20”

30”

40”

50”

60”

70”

60° 90° 180° 270° 0°

W S E N

60°

After 70%-scale (1-7) test After 70%-scale (2-7) test

0”

10”

20”

30”

40”

50”

60”

70”

60° 90° 180° 270° 0°

W S E N

60°

16-#5

hoops

#2@2” (SP 1)

#2@3” (SP 2)

D=20”

cover=1”

AA

B

B A-A B-B

24”

70”

18”

60” 84.85”

42.4” 30”

109”CC

C-C

16-#5

hoops

#2@2” (SP 1)

#2@3” (SP 2)

D=20”

cover=1”

16-#5

hoops

#2@2” (SP 1)

#2@3” (SP 2)

D=20”

cover=1”

AA

B

B

AA

B

B A-A B-B

24”

70”

18”

60” 84.85”

42.4” 30”

109”CC

C-C

N S

W

E SP1 SP2


0”

10”

20”

30”

40”

50”

60”

70”

60° 90° 180° 270° 0°

W S E N

60°


After 125%-scale

“1st X+Z” test


Crack Pattern of SP2

0”

10”

20”

30”

40”

50”

60”

70”

60° 90° 180° 270° 0°

W S E N

60°


After 125%-scale

“X only” test



0”

10”

20”

30”

40”

50”

60”

70”

60° 90° 180° 270° 0°

W S E N

60°


After 125%-scale

“2nd X+Z” test

(a) First shear peak

N SN S N S

(b) Second shear peak (c) Third shear peak

lateraltranslation

rotation

Shear crack opening and closing at each shear peak during the 125%-scale tests



Micro-cracks produced by tensile axial forces contribute to further widening of diagonal cracks under combined effect of vertical & horizontal excitations.


Code Estimations: Different design approaches and code equations

Influences of axial load, flexural ductility, and size of members & aggregates are not well agreed upon within different codes.

Three main approaches:

I. Axial force: ACI, Eurocode

II. Axial force + Ductility: SDC, Priestley et al.

III. Axial strain: AASHTO, CSA (based on MCFT)


s

DfAV

yv

s

)8.0(

' 22 1 0.82000

c c

g

NV f D

A

' 22 1 0.8500

c c

g

NV f D

A

Circular member: Axial compression

Circular member: Axial tension

N: axial force (+ if compression, - if tension)

scn VVV

ACI (318-08) Eurocode (2004)

s

DfAV

yv

s

72.0

2

1.2 40 0.154

cc rd l cp

DV k

scn VVV

'0.25 0.7rd cf

1kcp

c

N

A

bwc dcDD 22

Approach I: Axial force affects the estimated shear strength



0c

scn VVV

Priestley et al. (1996) Caltrans SDC (2010)

Approach II: Axial force and ductility affect the estimated shear strength.

'

cot2

v y

s

A f DV

s

'c c eV k f A

1: 0.29

1 3: 0.10 0.19(3 ) 2

3 7 : 0.05 0.05(7 ) 4

7 : 0.05

k

k

k

k

tan2

p

D cV P P

a


'

v y

s

A f DV

s

c c eV A

' 'Factor1 Factor2 0.33c c cf f

' '0.25 Factor2 0.33c c cf f

0.025 Factor1 0.305 0.083 0.2512.5

s yh

d

f

Factor2 1 1.513.8

c

g

P

A

scn VVV

Inside PHZ

Outside PHZ

for axial tension shear strength increase by axial compression


s

dfAV

vyv

s

sincotcot

'0.083c c v vV f b d

scn VVV

Dbv ev dd 9.02

re

DDd

, : function of /f’c and

AASHTO (2010) CSA (2004)

s

dfAV

vyv

s

cot

'

c c v vV f b d

scn VVV

Dbv Ddv 72.0

'

,max 0.25n c v vV f b d

700029 o

zes1000

1300

15001

4.0

350.85

15

zze z

g

ss s

a

Approach III: Longitudinal strain at the centroid of the section affects the estimated shear strength.

300mmz vs or d


: angle of inclination of transverse rebars


0

20

40

60

80

100

120

140

160

180

200

6.5 7 7.5 8 8.5 9 9.5 10 10.5 11 11.5

Forc

e (

kip

s)

Time (sec)

Shear Force ACI

Eurocode AASHTO

CSA SDC

0

20

40

60

80

100

120

140

160

180

200

6.5 7 7.5 8 8.5 9 9.5 10 10.5 11 11.5

Fo

rce

(kip

s)

Time (sec)

Shear Force ACI

Eurocode AASHTO

CSA SDC

Comparison of 1-10 and 1-11, 125% Northridge EQ 1-10: X only, 1-11: 2nd X+Z

X only (1-10) at h=10” 2nd X+Z (1-11) at h=10”

h=10”

h=60” Test Results vs. Code Estimates


SP1

0

20

40

60

80

100

120

140

160

180

200

6.5 7 7.5 8 8.5 9 9.5 10 10.5 11 11.5

Fo

rce

(kip

s)

Time (sec)

Shear Force ACI

Eurocode AASHTO

CSA SDC

0

20

40

60

80

100

120

140

160

180

200

6.5 7 7.5 8 8.5 9 9.5 10 10.5 11 11.5

Forc

e (

kip

s)

Time (sec)

Shear Force ACI

Eurocode AASHTO

CSA SDC


h=10”



Significant difference between AASHTO/CSA estimations at h=10” & 60” ACI, Eurocode/SDC are similar, but there are transient differences due to axial

tension or large displacement ductility.


SP1

0

20

40

60

80

100

120

140

160

180

200

7 7.5 8 8.5 9 9.5 10 10.5 11 11.5 12

Forc

e (

kip

s)

Time (sec)

Shear Force ACI

Eurocode AASHTO

CSA SDC

0

20

40

60

80

100

120

140

160

180

200

7 7.5 8 8.5 9 9.5 10 10.5 11 11.5 12

Forc

e (

kip

s)

Time (sec)

Shear Force ACI

Eurocode AASHTO

CSA SDC


h=10”




SP2

0

20

40

60

80

100

120

140

160

180

200

7 7.5 8 8.5 9 9.5 10 10.5 11 11.5 12

Fo

rce

(kip

s)

Time (sec)

Shear Force ACI

Eurocode AASHTO

CSA SDC

0

20

40

60

80

100

120

140

160

180

200

7 7.5 8 8.5 9 9.5 10 10.5 11 11.5 12

Fo

rce

(kip

s)

Time (sec)

Shear Force ACI

Eurocode AASHTO

CSA SDC


h=10”



A similar trend is observed, but AASHTO/CSA estimations are lower due to larger strains, especially at h=10”


SP2


OpenSees ACI/SDC shear spring:

Based on the “Test Results vs. Code Estimations”, two methods chosen from Approaches I and II

Incorporates ACI & SDC code equations for shear capacity as a new material implemented into source code.

Within a zero-length element connected to a beam-column element, this material can be effectively used.

Displacement0

Forc

e

Vy

-Vy

Kelastic

rKelastic

0

Displacement0

Forc

e

Vy

-Vy

Kelastic

rKelastic

0Depends on axial load, … etc.



OpenSees ACI/SDC shear spring: 1. Before the shear demand reaches the capacity (i.e. before yielding):

The yield force is updated at each integration time step.

2. At the time step where the demand reaches the capacity:

Yielding takes place & force-displacement relationship follows a post-yield behavior.

3. After 2: Yield force is not updated & kept constant unless the column experiences any axial tension for Caltrans SDC spring & a predetermined tension for ACI spring. The yield force is kept constant after this final modification.


0

Forc

e

Displacement

0

Kelastic

0

Forc

e

Displacement

0

Kelastic

Vy

-Vy

0 Fo

rce

Displacement

0

Vy

-Vy rKelastic


Case A-1 Case A-2

Nodal Mass

Mx, My, Mz

Imx, Imy, Imz

Case B-1 Case B-2

BWH

Element70”

Shear Spring

Rigid

End Zone

Rigid

End Zone

Rotational Spring

(a) Beam With Hinges Element

Nodal Mass

NLBC

Elements

Shear Spring

Rigid

End Zone

Rigid

End Zone

Rotational Spring

(b) Nonlinear Beam Column Elements

Nodal Mass

15”

20”

20”

15”

Lp

Lp

Lp

Lp

Sectionat integration points

OpenSees model: BWH element (Model A) or NLBC elements (Model B)



247 248 249 250 251-100

-50

0

50

100

time (sec)

sh

ea

r fo

rce

(kip

)

test data

B-2-SDC

247 248 249 250 251-100

-50

0

50

100

time (sec)

sh

ea

r fo

rce

(kip

)

test data

B-2-ACI

247 248 249 250 251-100

-50

0

50

100

time (sec)

sh

ea

r fo

rce

(kip

)

test data

A-2-SDC

247 248 249 250 251-100

-50

0

50

100

time (sec)

sh

ea

r fo

rce

(kip

)

test data

A-2-SDC

247 248 249 250 251-100

-50

0

50

100

time (sec)

sh

ea

r fo

rce

(kip

)

test data

A-1

247 248 249 250 251-100

-50

0

50

100

time (sec)

sh

ea

r fo

rce

(kip

)

test data

B-1

A-2-SDC and Run 2-11

A-2-ACI and Run 2-11

A-1 and Run 2-11

B-2-SDC and Run 2-11

B-2-ACI and Run 2-11

B-1 and Run 2-11

(c) 125% 2nd X+Z

Beam

wit

h H

ing

es E

lem

en

t (M

od

el A

)

No

nlin

ear

Beam

-Co

lum

n E

lem

en

ts (

Mo

del B

)

No

Shear

Spring

SDC

Shear

Spring

ACI

Shear

Spring

SP2 125%-scale “2nd X+Z” test data and simulation results

ACI



247 248 249 250 251-100

-50

0

50

100

time (sec)

sh

ea

r fo

rce

(kip

)

test data

B-2-SDC

247 248 249 250 251-100

-50

0

50

100

time (sec)

sh

ea

r fo

rce

(kip

)

test data

B-2-ACI

247 248 249 250 251-100

-50

0

50

100

time (sec)

sh

ea

r fo

rce

(kip

)

test data

A-2-SDC

247 248 249 250 251-100

-50

0

50

100

time (sec)

sh

ea

r fo

rce

(kip

)

test data

A-2-SDC

247 248 249 250 251-100

-50

0

50

100

time (sec)

sh

ea

r fo

rce

(kip

)

test data

A-1

247 248 249 250 251-100

-50

0

50

100

time (sec)

sh

ea

r fo

rce

(kip

)

test data

B-1



A-1 and Run 2-11



B-1 and Run 2-11

(c) 125% 2nd X+Z

SP2 125%-scale “2nd X+Z” test data and simulation results from Model A


247 248 249 250 251-100

-50

0

50

100

time (sec)

sh

ea

r fo

rce

(kip

)

test data

B-2-SDC

247 248 249 250 251-100

-50

0

50

100

time (sec)

sh

ea

r fo

rce

(kip

)

test data

B-2-ACI

247 248 249 250 251-100

-50

0

50

100

time (sec)

sh

ea

r fo

rce

(kip

)

test data

A-2-SDC

247 248 249 250 251-100

-50

0

50

100

time (sec)

sh

ea

r fo

rce

(kip

)

test data

A-2-SDC

247 248 249 250 251-100

-50

0

50

100

time (sec)

sh

ea

r fo

rce

(kip

)

test data

A-1

247 248 249 250 251-100

-50

0

50

100

time (sec)

sh

ea

r fo

rce

(kip

)

test data

B-1



A-1 and Run 2-11



B-1 and Run 2-11

(c) 125% 2nd X+Z

247 248 249 250 251-100

-50

0

50

100

time (sec)

sh

ea

r fo

rce

(kip

)

test data

B-2-SDC

247 248 249 250 251-100

-50

0

50

100

time (sec)

sh

ea

r fo

rce

(kip

)

test data

B-2-ACI

247 248 249 250 251-100

-50

0

50

100

time (sec)

sh

ea

r fo

rce

(kip

)

test data

A-2-SDC

247 248 249 250 251-100

-50

0

50

100

time (sec)

sh

ea

r fo

rce

(kip

)

test data

A-2-SDC

247 248 249 250 251-100

-50

0

50

100

time (sec)

sh

ea

r fo

rce

(kip

)

test data

A-1

247 248 249 250 251-100

-50

0

50

100

time (sec)

sh

ea

r fo

rce

(kip

)

test data

B-1



A-1 and Run 2-11



B-1 and Run 2-11

(c) 125% 2nd X+Z

ACI

Effect of OpenSees ACI/SDC shear spring Close resemblance in shear force responses

Notable difference in the inelastic response of the shear spring for the peak values.

SDC shear spring provides more conservative estimates than ACI spring does due to the different yielding patterns of the springs observed in the hysteresis.



AC

I sh

ear

sp

rin

g h

yste

res

is

SD

C s

hear

sp

rin

g h

yste

res

is 125%

1st X+Z

2nd X+Z

X only

-1.5 -1 -0.5 0 0.5 1 1.5-100

-50

0

50

100

displacement (in)sh

ea

r fo

rce

(kip

)

A-2-ACI

-1.5 -1 -0.5 0 0.5 1 1.5-100

-50

0

50

100

displacement (in)

sh

ea

r fo

rce

(kip

)

A-2-ACI

-1.5 -1 -0.5 0 0.5 1 1.5-100

-50

0

50

100

displacement (in)

sh

ea

r fo

rce

(kip

)

A-2-ACI

-1.5 -1 -0.5 0 0.5 1 1.5-100

-50

0

50

100

displacement (in)

sh

ea

r fo

rce

(kip

)

A-2-SDC

-1.5 -1 -0.5 0 0.5 1 1.5-100

-50

0

50

100

displacement (in)

sh

ea

r fo

rce

(kip

)

A-2-SDC

-1.5 -1 -0.5 0 0.5 1 1.5-100

-50

0

50

100

displacement (in)

sh

ea

r fo

rce

(kip

)

A-2-SDC(a-1) 1st X+Z (a-2) 1st X+Z

(b-1) X only (b-2) X only

(c-1) 2nd X+Z (c-2) 2nd X+Z

ACI/SDC spring hysteresis obtained from Model A (SP2 125%-scale simulations)

Concluding Remarks

There exists an apparent evidence of shear strength reduction due to the presence of axial tension from:

The shear force measurements

The crack patterns

Shear strength reduction is mainly due to the degradation of concrete contribution to this strength.

ACI & SDC capture the shear strength degradation due to axial force.

Both approaches provide results on the conservative side with SDC predictions being more conservative. They can be enhanced by:

Modifying ACI to consider effect of ductility

Replacing the sharp tensile force effect in SDC to be more gradual


Further Developments: Laser Scanning


Leica ScanStation C10

Measured @10.8%

Measured @11.8%

Lab. (nees@berkeley)

Filed (Haiti)

Point Cloud: Specimen SP1, Undamaged Configuration


Point Clouds at the Center of Column in Loading Direction: Raw Data

Undamaged Damaged

Footing

Column

Top Block

N S

W

E


-15 -10 -5 0 5 10 15 20 25 30 35-40

-20

0

20

40

60

80

100

Longitudin

al coord

inate

, in

ch

Transversal coordinate, inch

Damaged configuration

Undamaged configuration

Footing

Column

Top Block

Steel Plate

-15 -10 -5 0 5 10 15 20 25 30 35-40

-20

0

20

40

60

80

100

Longitudin

al coord

inate

, in

ch




-6.5 -6 -5.5 -5 -4.5 -4

0

10

20

30

40

50

60

Longitudin

al coord

inate

, in

ch




Undam

aged

Dam

aged

Point Clouds at the Center of Column in Loading Direction: Processing


0 0.1 0.2 0.30

10

20

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Lo

ng

itu

din

al co

ord

ina

te, in

ch



0 0.1 0.2 0.30

10

20

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70

Lo

ng

itu

din

al co

ord

ina

te, in

ch

Residual Displacement, inch

0 0.1 0.2 0.30

10

20

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Lo

ng

itu

din

al co

ord

ina

te, in

ch



0 0.1 0.2 0.30

10

20

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50

60

70

Lo

ng

itu

din

al co

ord

ina

te, in

ch



0 0.1 0.2 0.30

10

20

30

40

50

60

70

Lo

ng

itu

din

al co

ord

ina

te, in

ch


0 0.1 0.2 0.30

10

20

30

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70

Lo

ng

itu

din

al co

ord

ina

te, in

ch



Deformed Shape from Point Clouds

Points with squares are from averaging points in the cloud within 2 inches

0 0.1 0.2 0.30

10

20

30

40

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Lo

ng

itu

din

al co

ord

ina

te, in

ch



0 0.1 0.2 0.30

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20

30

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60

70

Lo

ng

itu

din

al co

ord

ina

te, in

ch


0 0.1 0.2 0.30

10

20

30

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60

70

Lo

ng

itu

din

al co

ord

ina

te, in

ch



Point Clouds at the Center of Column in Loading Direction: Interpretation


0 0.1 0.2 0.30

10

20

30

40

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60

70

Lo

ng

itu

din

al co

ord

ina

te, in

ch



0 0.1 0.2 0.30

10

20

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70

Lo

ng

itu

din

al co

ord

ina

te, in

ch


0 0.1 0.2 0.30

10

20

30

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60

70

Lo

ng

itu

din

al co

ord

ina

te, in

ch



h=55”

0.10” (Laser Scanner) 0.11” (Wire Potentiometer)

h=35”

0.15” (Laser Scanner) 0.18” (Wire Potentiometer)

h=15” 0.05” (Laser Scanner) 0.04” (Wire Potentiometer)

16.7%

9.1%

-25.0%

(W-L)/W×100

Deformed Shape from Point Clouds

Point Clouds at the Center of Column in Loading Direction: Interpretation


SP1

After Before

SP2

After Before


Further Developments: Repair

Grind Surface Remove Loose Concrete Mortar and Epoxy Gel Epoxy Injection

1 2 3 4

Thank You!

Questions? Comments?


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