shotcrete or frp jacketing of concrete columns … · 15 columns retrofitted w/ full -height...

SfP PROJECT 977231:SfP PROJECT 977231:

SEISMIC ASSESSMENT AND REHABILITATION OF EXISTING BUILDINGSSEISMIC ASSESSMENT AND REHABILITATION OF EXISTING BUILDINGS

INTERNATIONAL CLOSING WORKSHOP INTERNATIONAL CLOSING WORKSHOP

ISTANBUL, 30 MAYISTANBUL, 30 MAY--JUNE 1, 2005JUNE 1, 2005

SHOTCRETE OR FRP JACKETING OF CONCRETE SHOTCRETE OR FRP JACKETING OF CONCRETE

COLUMNS FOR SEISMIC RETROFITTINGCOLUMNS FOR SEISMIC RETROFITTING

S.N. BOUSIAS, M.N. FARDIS, A.S.N. BOUSIAS, M.N. FARDIS, A.--L. SPATHIS, D. BISKINISL. SPATHIS, D. BISKINIS

Structures Laboratory, Department of Civil Engineering, Structures Laboratory, Department of Civil Engineering,

University of Patras, GreeceUniversity of Patras, Greece

•• RC Jacketing is widely used & costRC Jacketing is widely used & cost--effective for RC effective for RC

buildings:buildings:

–– familiar to engineers & construction industry;familiar to engineers & construction industry;

–– suitable for repair of damage;suitable for repair of damage;

–– jacket can encapsulate members & joints providing structural jacket can encapsulate members & joints providing structural

continuity;continuity;

–– multiple effects on stiffness, flexural/shear resistance, multiple effects on stiffness, flexural/shear resistance,

deformation capacity, anchorage & continuity of deformation capacity, anchorage & continuity of

reinforcement.reinforcement.

•• FRP wrapping of FRP wrapping of member ends is becoming the method member ends is becoming the method

of choice:of choice:

–– vvery effective for confinement ery effective for confinement & shear strengthening;& shear strengthening;

–– less disruption of building use by retrofitting.less disruption of building use by retrofitting.

Part I:Part I:Tests on individual columns w/ or w/o Tests on individual columns w/ or w/o shotcreteshotcrete or or

FRP jackets;FRP jackets;

Design expression or rules for:Design expression or rules for:

ØØ strengthstrength, ,

ØØ stiffness & stiffness &

ØØ deformation capacitydeformation capacity

of of columns columns w/ w/ shotcreteshotcrete or FRP jacket, including or FRP jacket, including

effeffect of lap splicing in original column.ect of lap splicing in original column.

EXPERIMENTAL CAMPAIGN ON RETROFITTING OF RC COLUMNSEXPERIMENTAL CAMPAIGN ON RETROFITTING OF RC COLUMNS

Total of 39 tests on RC columns, w/ ribbed (deformed) or Total of 39 tests on RC columns, w/ ribbed (deformed) or smooth/hooked bars, smooth/hooked bars, w/ or w/o bar lapw/ or w/o bar lap--splicing in the plastic hingesplicing in the plastic hinge, , cyclically tested to ultimate deformation under const. axial loacyclically tested to ultimate deformation under const. axial load:d:9 9 unretrofittedunretrofitted controls;controls;

15 columns retrofitted w/ 2 or 4 layers of 15 columns retrofitted w/ 2 or 4 layers of CFRPCFRP at 2 different heights from base;at 2 different heights from base;

15 columns retrofitted w/ full15 columns retrofitted w/ full--height height concrete jacketconcrete jacket, including investigation of , including investigation of different connection at the interface of jacket & old column.different connection at the interface of jacket & old column.

Results supplemented w/ data from the literature (mainly on retrResults supplemented w/ data from the literature (mainly on retrofitted ofitted columns w/o bar lapcolumns w/o bar lap--splicing) to derive/calibrate expressions for:splicing) to derive/calibrate expressions for:

•• The The flexural & shear force resistanceflexural & shear force resistance of retrofitted columns, Mof retrofitted columns, Myy, V, VRR;;

•• The The effective stiffnesseffective stiffness of retrofitted columns at incipient yielding, of retrofitted columns at incipient yielding, EIEIeffeff=M=MyyLLss/3/3

θθyy, ,

as determined from the yield moment Mas determined from the yield moment Myy and the chord rotation at yielding, and the chord rotation at yielding,

θθyy;;

•• The The ultimate chord rotationultimate chord rotation of flexureof flexure--controlled retrofitted columns, controlled retrofitted columns,

θθuu

as affected by any lapas affected by any lap--splices of bars in original column.splices of bars in original column.

Shotcrete RetrofittingShotcrete Retrofitting

Φ14

75 mm

Φ20

Φ14

CFRP RetrofittingCFRP Retrofitting

Φ8/200Φ

18 Φ18

250

500Φ8/200

Φ18

~440

~185 Φ

14

Φ14

~190

250

250

Example of possible use of results: Example of possible use of results:

RC member verifications in terms of chord RC member verifications in terms of chord

rotation at yielding or ultimate rotation at yielding or ultimate –– EN1998EN1998--3 Annex3 Annex

Member:

VE ≤ VRm,EC2, VE ≤VRm,EC8

VE ≤ VRd,EC2, VE ≤VRd,EC8/1.15

θE ≤ θum

θE ≤ θu,m-

σNear CollapseSignificant Damage

θE ≤ 0.75θum

θE ≤ 0.75θu,m-

σCheck only if Near Collapse (NC) Limit State not checked, using NC

criteria with VE from analysis

θE ≤ θy

Damage LimitationLimit State:

brittle secondary

brittle primary

ductile secondary

ductile primary

θE, VE chord rotation & shear force demand from analysis (if linear, VE from capacity design);

θy chord rotation at yielding;

θum: expected value of ultimate chord rotation;

θu,m-

σ mean-minus-sigma ultimate chord rotation;

VRd, VRm shear resistance, w/ or w/o material safety factors, respectively;

VR,EC2 shear resistance in monotonic loading;

VR,EC8 shear resistance in cyclic loading after flexural yielding.

EN1998-3 Annex A: Chord-rotation at member yielding

c

yby

ssyy

f

fd

h

LzLφφθ 13.0]

8,1max[1002.0

3+

−+

+=

c

yb

y

s

syy

f

fd

L

hzLφφθ 13.05.110013.0

3+

++

+=

• φy: yield curvature (via 1st principles, adapted to median My);• Ls = M/V: shear span at member end (~L/2); • z~0.9d: tension shift (= 0 if member not diagonally cracked by

shear at flexural yielding: My/Ls);

• h : section depth;• fy, fc: MPa;

• db: bar diameter;• Last term: Due to bar slip from anchorage zone beyond member end

(omitted if such slippage not possible)

Beams, rect. columns:

Walls:

EN1998-3 Annex A: Seismically-detailed members w/ rect. web

Expected value of ultimate chord rotation (20% drop in resistance)

αst,pl: 0.0145 for hot-rolled ductile steel or heat-treated (tempcore);0.0075 for brittle cold-worked steel;

αwall: 1 for shear walls;

ω, ω': mechanical ratio of tension (including web) & compression steel;

ν: N/bhfc (b: width of compression zone; N>0 for compression);

Ls/h : M/Vh: shear span ratio;α: confinement effectiveness factor :

ρsx: Ash/bwsh: transverse steel ratio // direction (x) of loading;ρd: ratio of diagonal reinforcement.

Non-seismically detailed members w/o lap splices - cyclic loading• Plastic part, θpl

um=

θum-θy, of ultimate chord rotation is multiplied by 0.825.

−

−

−=α

∑

cc

2i

c

h

c

h

hb6

b1

h2

s1

b2

s1

( )( )

( )dc

ywsx

f

f

sc

h

Lf

ραρ

ω

ω 10035.0

2.0

3.0

275.125,01.0max

',01.0max

( )( )ναθθ 25.04.01, wallplstyum a−+=

Members w/ or w/o seismic detailing, w/ ribbed

bars lap-spliced over lo in plastic hinge region

0

1

2

3

4

5

6

7

8

9

10

0 1 2 3 4 5 6 7 8 9 10θu,pred (%)

θu,e

xp (

%)

UoP test

b&c other sources

walls

0

1

2

3

4

5

6

7

8

9

10

0 1 2 3 4 5 6 7 8 9 10θu,pred (%)

θu,e

xp (

%)

UoP test

b&c other sources

walls

0

200

400

600

800

1000

1200

1400

0 200 400 600 800 1000 1200 1400

My,pred (kNm)

M y,

exp

(kN

m) .

UoP test

b&c other sources

walls

• Compression reinforcement counts as double.

• For yield properties My, φy ,

θy: fy of tension steel multiplied x lo/loy,min if lo<loy,min=(0.3fy/

√fc)db

• For ultimate chord rotation

θum=θy+θpl

um: θplum x lo/lou,min if lo<lou,min=dbfy/[(1.05+14.5

αrs

ωsx)

√fc],

– fy, fc in MPa,

ωsx=

ρsxfyw/fc: mech. transverse steel ratio // loading,

–

αrs=(1-sh/2bo)(1-sh/2bo)nrestr/ntot (nrestr/ntotrestrained-to-total lap-spliced bars).

Test-My model comparison

(# 81, median=1.005, C.o.V=11.9%)

Test-

θy model comparison

(# 61, median=1.025, C.o.V=18.9%)

Test-

θum model comparison

(# 40, median=1.00, C.o.V=31.3%)

Test-EIeff model comparison

(# 61, median=0.975, C.o.V=23.3%)

My

θy

θu

Concrete JacketsConcrete Jackets

Concrete Jackets (continued/anchored in joint; w/ or w/o lap splices in old member)

Calculation assumptions:• Full composite action of jacket & old concrete assumed (jacketed member:

monolithic”), even for minimal shear connection at interface (roughened interface,steel dowels epoxied into old concrete: useful but not essential);

• fc of “monolithic member”= that of the jacket (avoid large differences in old & new fc)• Axial load considered to act on full, composite section;• Longitudinal reinforcement of jacketed column: mainly that of the jacket. Vertical

bars of old column considered at actual location between tension & compression bars of composite member (~ “web” longitudinal reinforcement), with its own fy;

• Only the transverse reinforcement of the jacket considered for confinement;• For shear resistance, the old transverse reinforcement taken into account only in

walls, if anchored in the (new) boundary elements.

Then:ü MR & My of jacketed member: ~100% of

ü

θy of jacketed member for pre-yield (elastic) stiffness:

if roughening of interface ~105%, if no roughening ~120% of

ü Shear resistance of jacketed member: ~90% ofü Flexure-controlled ultimate deformation

θu: ~100% of

those of “monolithic member” calculated w/ assumptions above.

Concrete Jackets w/ bars not continued/anchored in joint:

Jacket considered only to confine the full old section.

# 54 members w/ or w/o lap splices: test-to-calculation after RC-jacketing

0

0.2

0.4

0.6

0.8

1

1.2

1.4

1.6

- 1 . 5 - 0 . 5 0 . 5 1 . 5 2 . 5 3 . 5 4 . 5 5 . 5 6 . 5 7 . 5 8 . 5

θ u,exp / (θ upl +

θ *y )a b c d e f g h i j k

0

0.2

0.4

0.6

0.8

1

1.2

M y,

exp /

M y

,th

no laps 15db deformed

15db plain 25db plain

30db plain 45db deformed

continuous jacket bars discontinuous jacket bars

group average

Present tests:

a b c d e f g h i j

Other tests:

standard deviation of

group mean

± stand. deviation bounds, pure scatter

± stand. deviation bounds, monolithic members

0

0.2

0.4

0.6

0.8

1

1.2

1.4

1.6θ y,e

xp /

θ y,th

My

θyθu

a: no treatment, b: no treatment, predamaged, c: welded U-bars, d: dowels, e: roughened,f: roughened, predamaged, g: U-bars & roughened, h: U-bars & roughened, predamaged,

i: roughened & dowels, j: roughened & dowels, predamaged, k: monolithic

0

0.2

0.4

0.6

0.8

1

1.2

1.4

1.6

1.8

2

2.2

- 1 . 5 - 0 . 5 0 . 5 1 . 5 2 . 5 3 . 5 4 . 5 5 . 5 6 . 5 7 . 5 8 . 5

EI e

xp / E

I th

a b c d e f g h i j k

EIeff

FRP JacketsFRP Jackets

FRP Jackets (not continued/anchored in joint; w/o lap splices in old member)

Rectangular X-section w/ continuous longitudinal bars (no lap splices):• MR & My, pre-yield (elastic) stiffness EIeff of RC member:

not significantly enhanced by FRP jacket (increase neglected);

• Flexure-controlled ultimate deformation,

θu: confinement factor due to stirrups

enhanced due to FRP confinement by

α ρfff,e/fc

–

ρf=2tf/bw : FRP ratio;

– ff,e: FRP effective strength:

where:

fu,f, Ef : FRP tensile strength & Modulus; εu,f: FRP limit strain; CFRP, AFRP:

εu,f=0.015; GFRP:

εu,f=0.02; polyacetal FRP:

εu,f= 0.032;

– confinement effectiveness: b, h: sides of X-section;

R: radius at corner

( ) ( )

−+−−=

bh

RbRh

3

221

22

α

( ) ( )

−=

c

fffu,fu,ffu,fu,ef,

fEfEff

ρεε ,min7.01,min

# 112 FRP-wrapped members w/o lap splices: test-to-calculated ratio

0

50

100

150

200

250

300

350

0 50 100 150 200 250 300 350

EIpred

EI e

xp

0

500

1000

1500

2000

2500

0 500 1000 1500 2000 2500

My,pred (kNm)

M y

,exp

(kN

m)_

0

2

4

6

8

10

12

0 2 4 6 8 10 12θu

pl+

θy (%)

θ u,exp (%) _ 0

0.5

1

1.5

2

2.5

3

0 0.5 1 1.5 2 2.5 3θy,pred (%)

θ y,exp (%) _My

θy

EIeff

θu

# 112

median=1.04

C.o.V=18.8%

# 105

median=1.00

C.o.V=35.8%

# 105

median=1.02

C.o.V=29%

# 90

median=1.00

C.o.V=31.2%

Rectangular X-section w/ longit. bars lap-spliced over lo in plastic hinge:• Compression reinforcement counts as double.

• For yield properties My, φy ,

θy: fy of tension steel multiplied x lo/loy,min if lo<loy,min=(0.2fy/

√fc)db

• For ultimate chord rotation

θum=θy+θpl

um: θplum calculated on the basis of confinement by te

stirrups alone, multiplied x lo/lou,min if lo<lou,min=dbfy/[(1.05+14.5

αrs

ρf ff,e/fc)

√fc],

– fc in MPa,

ρf=2tf/bw: FRP ratio, ff,e: effective FRP strength in MPa,

–

αrs=4/ntot (ntot : total lap-spliced bars, only the 4 corner ones restrained).

Test-My model comparison

(# 20, median=1.065, C.o.V=9.2%)

Test-

θy model comparison

(# 20, median=1.085, C.o.V=18.9%)

Test-

θum model comparison

(# 16, median=1.00, C.o.V=21.7%)

FRP Jackets (not continued/anchored in joint; w/ lap splices in old member)

Test-EIeff model comparison

(# 20, median=1.01, C.o.V=22%)

0

0.2

0.4

0.6

0.8

1

1.2

1.4

1.6

0.000 0.200 0.400 0.600 0.800 1.000 1.200 1.400 1.600θy,pred (%)

θ y

,exp

(%

) .

UoP test

other sources

0

200

400

600

800

1000

1200

1400

0 200 400 600 800 1000 1200 1400

My,pred (kNm)

M y,

exp

(kN

m) .

UoP test

other sources

0

1

2

3

4

5

6

0 1 2 3 4 5 6θu,pred (%)

θu,e

xp (

%)

UoP test

other sources

θyMy

θu

FRP Jackets – Shear resistance in cyclic loading past flexural yielding

• Shear resistance of FRP-jacketed member:

Vf= min(

εu,fEu,f, fu,f)

ρf bwz/2

contributes to member shear resistance as controlled by diagonal tension

–

ρf :FRP ratio,

ρf = 2tf/bw;

– fu,f:FRP tensile strength;

– z : internal lever arm.

Test-to-prediction ratio vs.

�# 10, median=1.04, C.o.V=12.9%:

• Total shear resistance of retrofitted member as controlled by diagonal tension, should not exceed shear resistance of old RC member as controlled by web crushing.

( ) ( )( ) fwccs

tot

pl

cc

s

R VVAfh

LfAN

L

xhV +

+

−−+

−= ,5min16.01)100,5.0max(16.0,5min05.0155.0,min

2ρµθ

0

0.25

0.5

0.75

1

1.25

1.5

0 0.5 1 1.5 2 2.5 3 3.5 4 4.5

ductility

Vu,e

xp / V u,

pre

d .

Part II:

•• PPseudodynamic testseudodynamic test of 0.7:1 scale of 0.7:1 scale 22--story story

unsymmetric structureunsymmetric structure, w/ or w/o FRP, w/ or w/o FRP--retrofittingretrofitting

x

y

CoG

dx

dθ

dy

rθ ry

rx

ACTUATOR REFERENCE FRAME

REA

x

y

• Pseudodynamic tests of structure:

– Unretrofitted

– After repair of damage & FRP-wraps at all column ends

(top & bottom, both stories).

– With 2nd story infilled & FRP-wraps at all column ends.

• 15sec Herceg-Novi (Montenegro 1979) record,

modified to fit EC8 spectrum on firm soil w/ PGA: 0.3g

0.0

1.02.0

3.0

0.0 0.5 1.0 1.5 2.0 2.5

Period (s)S

a (

m/s

2)

EC8Record

Story drifts Story drifts -- UnretrofittedUnretrofitted structure at 0.30gstructure at 0.30g

• Test was stopped before end of record, due to heavy damage

at base of ground-story soft-side columns (lap splices):

– Peak drifts of soft-side columns:

• Ground story: 2.9% and 1.5% in orthogonal direction (simultaneous);

• 2nd story: 2.6% and 1.1% in orthogonal direction (simultaneous).

0 1 2 3 4 5 6 7 8-0.02

-0.015

-0.01

-0.005

0

0.005

0.01

0.015

Time (sec)

Dri

ft D

isp

lacem

en

t (r

ad

)

p18Theta-Level 1-

p18Theta-Level 2-

0 1 2 3 4 5 6 7 8-0.04

-0.03

-0.02

-0.01

0

0.01

0.02

0.03

Time (sec)

Dri

ft D

isp

lacem

en

t (m

)

p18X (E->W)-Level 1-


Column drifts Column drifts -- UnretrofittedUnretrofitted structure at 0.30gstructure at 0.30g

0 2 4 6 8 10 12 14 16-4

-3

-2

-1

0

1

2

3

4

Time (sec)

Drift rat

io (%

)

p18

Soft column - Lev. 1

Stiff column - Lev. 1

-3 -2 -1 0 1 2 3-2

-1.5

-1

-0.5

0

0.5

1

1.5

2

i-s Drift Ratio X (%)

i-s

Drift R

atio

Y (%

)

Col. 1, Lev. 1

0 2 4 6 8 10 12 14 16-4

-3

-2

-1

0

1

2

3

4

Time (sec)

Drift rat

io (%

)

p18



-3 -2 -1 0 1 2 3-2

-1.5

-1

-0.5

0

0.5

1

1.5

2

i-s Drift Ratio X (%)

i-s

Drift R

atio

Y (%

)

Col. 1, Lev. 2

FRP-wraps at all

column ends (top &

bottom, both stories)

Story drifts and story forceStory drifts and story force--displacement loops displacement loops -- FRPFRP--wraps 0.3gwraps 0.3g

0 2 4 6 8 10 12 14 16-0.05

-0.04

-0.03

-0.02

-0.01

0

0.01

0.02

0.03

0.04

Time (sec)

Dri

ft D

ispla

cem

ent (m

)

p11



0 2 4 6 8 10 12 14 16-0.02

-0.015

-0.01

-0.005

0

0.005

0.01

0.015

0.02

Time (sec)

Dri

ft D

ispla

cem

ent (r

ad)

p11

p11Theta-Level 1-

p11Theta-Level 2-

-0.05 -0.04 -0.03 -0.02 -0.01 0 0.01 0.02 0.03 0.04-80

-60

-40

-20

0

20

40

60

Displacement (m)

Forc

e (kN

)


-0.05 -0.04 -0.03 -0.02 -0.01 0 0.01 0.02 0.03 0.04-60

-40

-20

0

20

40

60

Displacement (m)

Forc

e (kN

)


Interstory drifts Interstory drifts -- FRPFRP--wraps 0.3g (top & bottom, both stories)wraps 0.3g (top & bottom, both stories)

0 2 4 6 8 10 12 14 16-4

-3

-2

-1

0

1

2

3

4

Time (sec)

Dri

ft r

atio

(%

)

p11



0 2 4 6 8 10 12 14 16-4

-3

-2

-1

0

1

2

3

4

Time (sec)

Dri

ft r

atio

(%

)

p11



2nd story infilled; FRP-

wraps at all column ends

Story drifts - 2nd story infilled;

FRP-wraps at all column ends

0 2 4 6 8 10 12 14 16-0.03

-0.02

-0.01

0

0.01

0.02

0.03

Time (sec)

Drift D

ispla

cem

ent (rad)

p12

p12Theta-Level 1-

p12Theta-Level 2-

0 2 4 6 8 10 12 14 16-0.06

-0.04

-0.02

0

0.02

0.04

0.06

Time (sec)

Drift D

ispla

cem

ent (m

)

p12



22ndnd story infilled; FRPstory infilled; FRP--wraps at all column endswraps at all column ends

-0.06 -0.04 -0.02 0 0.02 0.04 0.06-100

-80

-60

-40

-20

0

20

40

60

80

Displacement (m)

Forc

e (

kN

)


0 2 4 6 8 10 12 14 16-8

-6

-4

-2

0

2

4

6

8

Time (sec)

Dri

ft r

atio

(%

)

p12



THANK YOU!THANK YOU!

shotcrete or frp jacketing of concrete columns … · 15 columns retrofitted w/ full -height...

Documents