Buckle Presentation Dimensionare Izolator

8/12/2019 Buckle Presentation Dimensionare Izolator

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Highway BridgesIan Buckle

Foundation ProfessorDepartment of Civil and Environmental Engineering

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University of Nevada Reno Reno NV 89557


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Topics

Background

Principles of Seismic Isolation

Some Applications System Design

Testing Requirements

Sources: FHWA/MCEER 2006, Seismic

so a on o g way r ges, pec aPublication MCEER-06-SP07

2

,

Seismic Isolation Design, Third Edition


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System Design Testing Requirements

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Conventional Seismic Design

Superstructure

Bearin su men

Footing

& piles

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gravity and earthquake loads,dissipate energy, and not collapse

EQ ground motion


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Unacceptable Performance

Collapsed

Superstructure

Bearin s

Fractured

u menu men

Footing

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EQ ground motion


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Seismic Design Objective

column strength

ac or o sa e y =

earthquake force

> .

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Seismic Design Objective

capacity

ac or o sa e y = > .

demand

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Conventional Design Approach

INCREASE CAPACITY

capacity


demand

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Conventional Design

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Conventional Design

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Seismic Isolation an Alternative

capacity


demand

REDUCE DEMAND

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suspension

system

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EQ ground motion


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Basic Idea of Seismic Isolation

Isolate the bridge from ground motion by:

Inserting a flexible support system between the

super- and sub-structure (isolation bearings).This will lengthen the natural period of the

are significantly reduced.

columns elastic.

Control the liveliness of the bridge (due to theflexible bearings) using energy dissipators

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.


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Seismic Isolation: Key Point

Seismic isolation reduces the earthquakedemand on a bridge, rather than increases

its capacity.

In many cases the reduction in demand is

such that it may be feasible to have

substructures perform elastically.

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In addition to flexibility and energy dissipation

most isolation s stems also com rise:

Adequate rigidity for non-seismic loads. .

accommodating thermal, creep, and other

,

Self-centering capability

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Most seismic isolation systems

comprise:1.Flexibility

2.Energy dissipation

3.Ri idit for non-seismic loads4.Self-centering

Above criteria means all isolation systemshave nonlinear properties. exceptions exist

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but are rare.


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Principles of Seismic Isolation Isolator Force, F

Kd

Kisol

Qd

Fy Fisol

Ku

dyKu

disol Isolator

Displacement, dKu

=

Kd

Q = Characteristic stren th

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u

Kisol = Effective stiffness

disol = Isolator lateral displacement

Fy = Yield strength

Fisol = Isolator lateral forceKd = Post-elastic stiffness


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POLISHED STAINLESS STEEL SURFACEPOLISHED STAINLESS STEEL SURFACE

SEALSEAL

Lead-Rubber Isolator

STAINLESS STEELARTICULATED SLIDER(ROTATIONAL PART)

COMPOSITE LINER MATERIALSTAINLESS STEELARTICULATED SLIDER(ROTATIONAL PART)

COMPOSITE LINER MATERIAL

-

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Isolator


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Eradiquake Isolator

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Bridges Not Suitable for Isolation

Bridges on soft sites, because lengthening

the eriod ma increase rather than

decrease, spectral accelerations

spectrumRock

spectrum

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Bridges Not Suitable for Isolation

Brid es in hi h seismic zones on soft sites

where displacements may be large andcostly expansion joints may be required toaccommodate movements

Bridges with tall flexible piers, which alreadyhave long periods and little advantage is

ga ne w so a on

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Bridges that are most suitable forisolation are

(a) located on stiff and medium-stiff soil

sites,(b) have relatively stiff substructures

(e.g. short-to-medium height columns)

(c) continuous superstructures, and(d) seat-type abutments.

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Applications: So. Rangitikei River, NZ

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Applications: US 101 Sierra Point, CA

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A li ti I 680 B i


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Applications: I-680 Benecia-

,

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Applications: JFK Airport Light Rail, NY

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Applications: Bolu Viaduct, Turkey

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Applications in U.S, Canada, Mexico

Applications

Isolator Type

number ofisolated bridges

n or

America)

-

Eradiquake isolator 20%

Other: Friction pendulum, Highdamping rubber, Natural 5%

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Design of a Bridge Isolation System

Three step process:

1. Determine re uired erformance criteria

2. Determine properties of the isolation systeme. . Q and K to achieve re uired

performance using one or more methods of

analysis V K3. Select isolator type and

design hardware to achieve

Qd

required system properties(i.e.,Qd and Kd values) using

D

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a rational design procedure


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Performance Criteria

Usually set by owner

o Not-to-exceed total base shear for Design

o Elastic columns during DE

- -superstructure during DE.

Considered Earthquake (MCE)

o Re arable dama e in MCE but not colla se

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Analysis Methods for Isolated


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Analysis Methods for Isolated

analyzed using linear methods provided,

effective stiffness and

equ va en v scous amp ng ase on

the hysteretic energy dissipated by the

so a ors.

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A l i M th d


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Analysis Methods

Single Mode Spectral Method

u mo e pec ra e o

Time History Method

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Si lifi d M th d A ti


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Simplified Method Assumptions

1. Superstructure acts a rigid-diaphragm comparedto flexibility of isolators

.

superstructure, i.e. single degree-of-freedoms stem

3. Nonlinear properties of isolators may be

represented by bilinear loops4. Bilinear loops can be

represented by Kisol,

e ect ve st ness, anenergy dissipated per cycle

K isol D

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= area o oop

Note Kisol & loop area are dependent on displacement, D.



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5. Energy dissipated per cycle may berepresented by viscous damping, i.e., workdone during plastic deformation can berepresented by work done moving viscous

.damping ratio given by

)1(2

isol

y

isol

d

d

d

F

Qh

6. Acceleration spectrum is inversely

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proportional to period ( A = a / T)



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7. Acceleration spectra for 5% viscousdamping may be scaled for actualdamping (h%) by dividing by a dampingcoefficient, BL

3.0

hB

L .

L - .A second factor (BS) is used in short-period

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. -

range.

AASHTO D i R S t


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AASHTO Design Response Spectra

AASHTO Spectra (SA) are for 5%damping on a rock site (Site Class

SA (A) Spectral Acceleration (g)

5 % damping

For sites other than rock, thes ectra are modified b SiteSD1

h % damping

Factors, Fa and Fv

For damping other than 5%, the1.0s

SD1 / BL

spectra are modified by a

Damping Factor, BLSSF

,

SD (D)Spectral

Displacement

TBTB LL

v

A 10SD1

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L

D

L

vD

BBDS 11

2 79.9

4

Period, T1.0s

h % damping10SD1 / BL

Simplified Method


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Simplified Method

This method is alsoFisolQd

Kd

known as the-

K isol D

Methodd isol

an s app ca e o

a wide range of

D

Displacement5 % damping

structural types - not D1

h % dam in

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.

Period, T1.0s

Simplified Method


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Simplified Method

Basic steps:

1. Assume value for

VFisolQd

disol

2. Calculate effective K isol

d

stiffness, Kisol

3. Calculate max. force,

d isol

Fisol

4. Calculate effective

per o , eff

dQ W

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d

isol

isold isolisol isol

egK

Simplified Method Continued


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Simplified Method Continued

5. Calculate viscous

damping ratio, h

VFisolQd

6. Calculate damping

coefficient, BL K isol

d

7. Calculate disol

8. Compare with value

d isoldy

for disol in Step (1).

Repeat if necessary effL

visol T

B

SFgd 1

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.

)1(2 yd dQh 3.0

hB )(79.9 1 inchesT

SFd e

visol

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isolisol . L

Example: Simplified Method


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Example: Simplified Method

The superstructure of a 2-span bridge weighs

. D1

0.55. The bridge is seismically isolated with

abutments.

Isolation

system

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Example


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Example

d .

Kd = 13.0 K/in (summed over all the

isolators), calculate the maximum

displacement of the superstructure and thetotal base shear.

Neglect pier flexibility.

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Example 1


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Example 1

Solution:

1. Initialize

1.1 Qd =0.075 W = 0.075 (533) = 40 K. so

Take Teff= 1.5 sec,

L .

D = 9.79 SD1 Teff/ BL

= . . .= 8.08 in

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Take initial value for disol = D

Example 1 Continued


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Example 1 Continued

Solution:

1. Initialize

Qd = 40 K= .

.

2.1 Set disol = D and proceed with Steps 1-7

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Example 1 Continued


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Example 1 Continued

Step Trial 1 Trial 2 Trial n

0. Characteristic strength, Qd 40.0

0. Post-elastic stiffness, Kd 13.0

1. Isolator Displacement, disol

2. Effective stiffness, Kisol

3. Max. isolator force, Fm

4. Effective period, Teff

5. Viscous damping ratio, h%

. amp ng coe c en ,L

7. Isolator displacement, disol

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Example 1 Continued


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Example 1 Continued




1. Isolator Displacement, disol 8.08

2. Effective stiffness, Kisol






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Example 1 Continued


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Example 1 Continued





2. Effective stiffness, Kisol 17.95






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Example 1 Continued


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Example 1 Continued






3. Max. isolator force, Fm 144.9



. amp ng coe c en , L


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Example 1 Continued


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Example 1 Continued







4. Effective period, Teff 1.46




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Example 1 Continued


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Example 1 Continued








5. Viscous damping ratio, h% 17.6



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Example 1 Continued


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Example 1 Continued









. amp ng coe c en , L .


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Example 1 Continued


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p









. amp ng coe c en , L .

7. Isolator displacement, disol 6.43

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Example 1 Continued


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p


0. Characteristic strength, Qd 40.0 40.0 40.0

0. Post-elastic stiffness, Kd 13.0 13.0 13.0

1. Isolator Displacement, disol 8.08 6.43 5.66

2. Effective stiffness, Kisol 17.95 20.06

3. Max. isolator force, Fm 144.9 113.6

4. Effective period, Teff 1.46 1.65

5. Viscous damping ratio, h% 17.6 22.4

. amp ng coe c en , L . .

7. Isolator displacement, disol 6.43 5.66

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Example 1 Continued


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p


0. Characteristic strength, Qd 40.0 40.0 40.0

0. Post-elastic stiffness, Kd 13.0 13.0 13.0

1. Isolator Displacement, disol 8.08 6.43 5.66

2. Effective stiffness, Kisol 17.95 20.06

3. Max. isolator force, Fm 144.9 113.6

4. Effective period, Teff 1.46 1.65

5. Viscous damping ratio, h% 17.6 22.4

. amp ng coe c en , L . .

7. Isolator displacement, disol 6.43 5.66

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Simplified Method


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p

Basic method

assumes ver

Kd

Qd Kisol

stiff piers butmethod can

dy disol

F

SuperstructureIsolator Effective Stiffness, Kisol

be modified

to includedsub

Ksub

Substructure, Ksub

Isolator(s), Kisol

pier flexibility.Fdisoldsub

Substructure Stiffness, Ksub

Keffd

63MCEER,2006.

d = disol + dsub

Combined Effective Stiffness, Keff

Multimodal Spectral Method


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Elastic Multimodal Method, developed forconventional bridges, may be used for isolatedbridges even though they are nonlinear systems.

Modeling the nonlinear properties of the isolatorsis usually done with equivalent linearized springs

additional damping .

Recall earlier discussionof the com osite s ectrum

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Multimodal Spectral Method


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use the results from the Simplified Method of

iteration.

In this case convergence in 1 or 2 cycles is

poss e usua y

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Isolator Design


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Analysis gives required system properties

Q and K to meet desired erformance

Next step is to design an isolation system to

Isolators used in bridge design include:

-Rubber Bearing)

Flat plate slider with elastomeric spring

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Elastomeric Isolator Design (LRB)


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Elastomeric Isolator Design (LRB)


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Qd = 0.9 d2 (K)where

d = diameter of lead core (in)

d r rwhere

. . .Ar= bonded area of elastomer

=r

Period ost- ield = TWT rc 22

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d

Curved Sliding Isolators (FPS)


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R

W

Restoring force

Friction

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D

Curved Sliding Isolator Design (FPS)


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POLISHED STAINLESS STEEL SURFACEPOLISHED STAINLESS STEEL SURFACE

Qd = Wwhere

= coefficient of friction=STAINLESS STEEL

ARTICULATED SLIDERROTATIONAL PART


RSTAINLESS STEEL

ARTICULATED SLIDERROTATIONAL PART


R

Wd where

R

=ra us o curva ure o s er

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Period when sliding = gTd 2

Summary of LRB and FPS Designs


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as omer c

(LRB)

urve er

(FPS)

Number of isolators 12 12

9.4 in diam. 18 in diam. x 7.75 in height x 5 in (est.) height

Internal dimensions 11 x in layers radius = 41 in

Other 1.92 in diam. leadcore

coefficient offriction = 0.075

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Eradiquake Isolator


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Other Design Issues (All)


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Restoring force capability

Clearances (expansion joints, utility crossings )

Vertical load capacity and stability at high shear

strain

Uplift restrainers, tensile capacity

Non-seismic requirements (wind, braking, thermalmovements )

System Property Modification Factors (-factors) for

aging, temperature, wear and tear, andcontamination

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Topics


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Background

Principles of Seismic Isolation,

Some A lications

System Design

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Basic Testing Requirements


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Because isolators are subject to extremedeformations and loads durin lar e

earthquakes, most design codes require they

be tested to demonstrate conformance with

design expectations

extensive testing), design provisions for

conventional bearings e.g., Section 14,

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Basic Testing Requirements


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Usually three categories of tests are required:

1. Characterization Tests to confirm basic

properties such as effect of velocity, pressure,

and temperature to develop models for analysis

2. Prototype Tests for each project prior to

production to confirm mechanical properties

used in design

3. Production Tests performed on each isolator

a ong w ma er a es s or qua y

control/quality assurance.

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During this lecture we have learned:

Basic purpose of seismic isolation

Bridge types / configurations suitable for

How to calculate displacement and base

Simplified Method

About three kinds of isolators in use today


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Five questions

1. What is basic purpose of seismic isolation?. .

3. Describe bridge types and configurations that

4. Name three common types of isolators on the

market toda in the U.S.

5. Name three types of tests used to assure the

Buckle Presentation Dimensionare Izolator

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