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UNBONDED POST-TENSIONING: SEISMIC APPLICATIONS IN CONCRETE

STRUCTURAL WALLS

Yahya C. Kurama

University of Notre Dame

Notre Dame, Indiana, U.S.A

Tokyo Institute of TechnologyYokohama, JapanAugust 16, 2000

wall panel

horizontaljoint

unbondedPT steel

spiralreinforcement

foundation

anchorage

ELEVATION

LATERAL DISPLACEMENT

precast wall gap opening shear slip

BEHAVIOR UNDER LATERAL LOAD

base shear, kips (kN)

roof drift, %

gap opening(decompression)

PT bar yielding(flexural capacity)

concretecrushing (failure)

effective linear limit(softening)

0 1 2

800(3558)

BONDED VERSUS UNBONDED BEHAVIOR

bonded wall

unbonded wall

HN

HYSTERETIC BEHAVIOR


roof drift, %

0 1 2

800(3558)

-800(-3558)

-1-2

OUTLINE

• Unbonded post-tensioned precast walls

–without supplemental damping

–with supplemental damping

• Unbonded post-tensioned hybrid coupled walls

UNBONDED POST-TENSIONED WALLSWITHOUT SUPPLEMENTAL

ENERGY DISSIPATION

Analytical Modeling

ANALYTICAL MODEL

node trusselement

fiberelement

wall model

cross-section

constraint

BEAM-COLUMN SUBASSEMBLAGE TESTS

uppercrosshead

lowercrosshead

4.3 ft(1.3 m)

7.5 ft (2.3 m)

NIST (1993)H

N

MEASURED VERSUS PREDICTED RESPONSE

lateral load, kips (kN)

drift, %

-50 (222)

0

50

-6

measured (NIST)predicted

6

El-Sheikh et al. 1997

FINITE ELEMENT (ABAQUS) MODEL

truss elements

contact elements

nonlinearplane stress elements

GAP OPENING

FINITE ELEMENT VERSUS FIBER ELEMENT


0 0.5 1 1.5 2 2.5

500

1000(4448)

roof drift, %

fiber element

yielding state

gap openingstate finite element

Seismic Design andResponse Evaluation

DESIGN OBJECTIVES

baseshear

roof drift

immediateoccupancy

collapseprevention

designlevel gr. mt.

survivallevel gr. mt.

BUILDING LAYOUT FOR HIGH SEISMICITY

8 x 24 ft = 192 ft (60 m)

110 ft(35 m)

N

hollow-corepanels

gravity loadframe

lateral loadframe

wall

column L-beam invertedT-beam

S

WALL WH1CROSS SECTION

12 in(31 cm)

10 ft (3 m)

half wall length

#3 spiralssp=7%

PT barsap=1.5 in2 (9.6 cm2)fpi=0.60fpu

CL

ROOF-DRIFT TIME-HISTORY

-4

-2

0

2

4

0 10 20 30

roof drift, %

time, seconds

Hollister(survival)

unbonded PT precast wallcast-in-place RC wall

WALLS WITH SUPPLEMENTAL ENERGY DISSIPATION

U.S. National Science Foundation

CMS 98-74872

CAREER Program

VISCOUS DAMPED WALLS

viscous damper

bracingcolumn

diagonal brace

wall floorslab

DAMPER DEFORMATION

viscousdamper

bracingcolumn

diagonalbrace

wallpanel

gap

DAMPER DEFORMATION

floor

damper deformation, in (cm)

1

2

3

4

5

6

-2 (-5) -1 0 1 2 (5)

compression tension

at yielding state llp=0.84%

DESIGN OBJECTIVEbaseshear

roof drift

SURVIVAL LEVEL GROUND MOTION

damped system undamped system

DAMPER DESIGN - WALL WH1

spectral displacement Sd , in (cm)

Sa, g

1

2

3

0 4 8 12 16 (41)

Teff=0.80 sec.

MIV=67 in/sec (171 cm/sec)

X

ev=3%

10%

15%23%

30%40%

llp=0.84%Te = 0.64 sec.

r=22%

ROOF DRIFT TIME HISTORY - WALL WH1

dampedundamped

Newhall, 0.66g

-3

0

3

0 20time, seconds

llp=0.84%

llp=0.84%

, %

MAXIMUM ROOF DRIFT - WALL WH1max, %

peak ground acceleration PGA, g

undamped walldamped wall

llp= 0.84%

7

0 0.4 0.8 1.2

MAXIMUM ROOF DRIFT - WALL WP1

7

0 0.4 0.8 1.2

max, %



llp= 1.14%

MAXIMUM ROOF DRIFT - WALL WP2

7

0 0.4 0.8 1.2

max, %



llp= 1.47%

MAXIMUM ROOF ACCELERATION - WALL WH1amax, g

0

0.5

1

1.5

2

0.4 0.8 1.2peak ground acceleration PGA, g


UNBONDED POST-TENSIONED HYBRID COUPLED WALL SYSTEMS

U.S. National Science Foundation

CMS 98-10067

U.S.-Japan Cooperative Program onComposite and Hybrid Structures

EMBEDDED STEEL COUPLING BEAM

steel beamembedment region

TEST RESULTS FOR EMBEDDED BEAMS

Harries et al.1997

POST-TENSIONED COUPLING BEAM

beam

PT steel

connectionregion

PTanchor

embeddedplate

angle

PT steel

wall region

DEFORMED SHAPE

contactregion

gapopening

COUPLING FORCES

Vcoupling =P z

lb

P

P

Vcoupling

Vcoupling

dbz

lb

RESEARCH ISSUES

• Force/deformation capacity of beam-wall connection region

–beam–angle

• Yielding of the PT steel• Energy dissipation• Self-centering• Overall/local stability

ANALYTICAL WALL MODEL

fiberelement

kinematicconstraint

trusselement

fiberelement

wall beam wall

BEAM-WALL SUBASSEMBLAGE

W18x234PT strand

L8x8x3/4

ap = 1.28 in2 (840 mm2)

lw = 10 ft lb = 10 ft (3.0 m) lw = 10 ft

F

fpi = 0.5-0.7 fpu

MOMENT-ROTATION BEHAVIOR

0 4 8

1250

2500(3390)

moment Mb, kip.ft (kN.m)

rotationb, percent

Mp

My

ultimatePT-yieldsofteningdecompression

2 6 10

CYCLIC LOAD BEHAVIORmoment Mb, kip.ft (kN.m)

-10 -5 0 5 10 -2500

0

2500(3390)

rotationb, percent

monotoniccyclic

ap and fpi (Pi = constant)

0 4 8 10

2500(3390)


rotationb, percent2 6

1250

PT STEEL AREA

0 4 8 10

2500(3390)


rotationb, percent

1250

2 6

TRILINEAR ESTIMATION

0 4 8 10

1250

2500(3390)

ultimatePT-yieldsoftening

smooth relationshiptrilinear estimate


rotationb, percent2 6

PROTOTYPE WALL

W18x234

ap = 0.868 in2

(560 mm2)

12 ft 8 ft 12 ft

82 ft(24.9 m)

fpi = 0.7 fpu

(3.7m 2.4m 3.7 m)

COUPLING EFFECT

0 1 2 3 4roof drift, percent

40000

80000

120000 (162720)

base moment, kip.ft (kN.m)

coupled wall

two uncoupled walls

EXPERIMENTAL PROGRAM

Objectives• Investigate beam M- behavior• Verify analytical model• Verify design tools and procedures

• Beam-wall connection subassemblages

• Ten half-scale tests

ELEVATION VIEW (HALF-SCALE)

W10X100PT strand

L4x7x3/8

ap = 0.217 in2 (140 mm2)

lw = 5 ft lb = 5 ft (1.5 m) lw = 5 ft

strong floor

fpi = 0.7 fpu

CONCLUSIONS

• Unbonded post-tensioning is a feasible construction method for reinforced concrete walls in seismic regions

• Large self-centering capability• Softening, thus, period elongation• Small inelastic energy dissipation• Need supplemental energy dissipation in high seismic regions

http://www.nd.edu/~concrete