Department of Civil Engineering

University of Ottawa

Ottawa, CANADA

Department of Civil EngineeringDepartment of Civil Engineering

University of OttawaUniversity of Ottawa

Ottawa, CANADAOttawa, CANADA

Seismic Risk Mitigation Through Seismic Risk Mitigation Through Retrofitting NonRetrofitting Non--ductile Concrete ductile Concrete

Frame Systems Frame Systems

By Murat Saatcioglu

Professor and University Research Chair

By Murat SaatciogluBy Murat Saatcioglu

Professor and University Research ChairProfessor and University Research Chair

The ProblemThe ProblemThe Problem

A large proportion of current building

infrastructure consists of non-ductile

reinforced concrete frame systems,

especially those;

• built prior to the enactment of

modern seismic code provisions,

• built in areas where code enforcement

can not be ensured.

The ProblemThe ProblemThe Problem

The ProblemThe ProblemThe Problem

The ProblemThe ProblemThe Problem

Seismic Retrofit Strategy?Seismic Retrofit Strategy?Seismic Retrofit Strategy?

• Retrofitting individual non-ductile

members (jacketing, FRP etc.)

• Bracing the structure so that lateral

drift is minimized and non-ductile

members are not forced beyond their

elastic limits.

Bracing by infill R/C WallsBracing by infill R/C WallsBracing by infill R/C WallsResearch at METU

Retrofitting Masonry Infills with FRPRetrofitting Masonry Infills with FRPRetrofitting Masonry Infills with FRPResearch at the University of Ottawa

FRP AnchorsFRP AnchorsFRP Anchors

Anchors

Predrilled holes

Wooden guides

FRP anchors in place

FRP AnchorsFRP AnchorsFRP Anchors

1825

18

25

250

62.5750400

350

400

2-#15

2- #15

1- #15

#2 (U.S.)@ 125 mm

500

8 - #15

Lap Splice:

24 db

= 390 mm

(ACI 318-63)

10 @ 150mm#25#10

#15 HooksConcrete cover :

25 mm (typ.)12 d

b +

(6d

b)/2 + d

b = 256 mm

(ACI 318-65 Manual of Standard for

Detailing R/C Structures, pg. 10)

TEST SPECIMENSTEST SPECIMENS

Preparation of Specimens

Strong

Floor

#15 Prestressing

wire strands

running externally*

Stiff Bars

running externally

Loading plate

#9 Prestressingwire running

externally on both

sides **

400 kN

(20% P0)(40 kN)

400 kN

(20% P0)

* Seven Wire Strand, Size Designation: #15, Grade 1720 MPa

** Seven Wire Strand, Size Designation: #9, Grade 1720 MPa

Three hollow structural sections(3"x3"x0.375") welded togetherAnchors

Reaction Frame

TEST SETUPTEST SETUP

Observed Behavior Wide Flexural Cracks at Beam Ends (1.5% Drift)

Crushing of Blocks at 2% Drift End of Test

Observed Behavior

ForceForce--Displacement Hysteretic Relationship Displacement Hysteretic Relationship

Displacement, mm (Drift)

(1%) (2%)

(-1%)(-2%)

(3%)

(-3%)

Force, kN

∆∆∆∆F

BL-1

Observed Behavior at 1% Lateral Drift

-800

-600

-400

-200

0

200

400

600

800

-60 -40 -20 0 20 40 60

Force-Displacement Hysteretic Relationship

Retrofitted Specimen

(1%) (2%)

(-1%)(-2%)(-3%)

Force, kN

(3%)

Displacement, mm

(Drift)

Retrofitted

Unretrofitted

BL-2

Rupturing of FRP anchors

at 1.75% driftLocal delamination of FRP sheet under

tension compression reversals (0.75% drift)

Observed Behavior

Force-Displacement Hysteretic Relationship

Retrofitted Specimen

(1%) (2%)

(-1%)(-2%)(-3%)

Force, kN

(3%)Displacement, mm

(Drift)

Retrofitted

Unretrofitted

BL-3

Dynamic Analysis of a 5-Story BuildingDynamic Analysis of a 5Dynamic Analysis of a 5--Story BuildingStory Building

q Four interior and two

exterior frames with

capacities equal to 1/3 the

level required by NBCC-2005

q Exterior frames were

retrofitted with FRP strips

q Single layer of FRP was used

either on one side or both

sides of walls in the middle

bay

q The structure was subjected

to design earthquake

compatible with uniform

hazard spectra

0

1

2

3

4

5

6

0 0.5 1 1.5 2 2.5 3Max. Interstorey Drift Ratio (%)

Sto

rey Unretrofitted

FRP on one sideFRP on both sides

Dynamic Analysis of the 5-Story BuildingDynamic Analysis of the 5Dynamic Analysis of the 5--Story BuildingStory Building

Retrofitting through Diagonal PrestressingRetrofitting through Diagonal PrestressingRetrofitting through Diagonal Prestressing

Research at the University of Ottawa

Reference specimen, reflecting as

built conditions

Retrofitted specimen, diagonally

prestressed to 30% of ultimate

on both sides

(1%)

(-4%) (-2%)

(2%)

(3%) (Drift)

ForceForce--Displacement Hysteretic RelationshipDisplacement Hysteretic Relationship

BR-1∆∆∆∆

F

ForceForce--Displacement Hysteretic RelationshipDisplacement Hysteretic Relationship

BR-2

(-4%) (-2%) (-1%)

(1%) (2%) (3%) (4%)

(-3%)

Displacement, mm

(Drift)

Retrofitted

Unretrofitted

q Four interior and two exterior frames with capacities equal to 1/3 the level required by NBCC-2005

q Exterior frames were retrofitted with 15.2 mm diameter 7-wire strands in the middle bay

q Pushover analysis was conducted

q Dynamic inelastic analysis was also conducted under design earthquakes compatible with uniform hazard spectra

Analysis of a 5-Story BuildingAnalysis of a 5Analysis of a 5--Story BuildingStory Building

Push-over Analysis of the 5-Story BuildingPushPush--over Analysis of the 5over Analysis of the 5--Story Story BuildingBuilding

0

500

1000

1500

2000

2500

0.0 1.0 2.0 3.0 4.0 5.0

Max. Interstory Drift Ratio (%)

Late

ral F

orc

e (k

N)

Unretrofitted

Retrofitted without

prestressing

Retrofitted with 100 kN

of prestressing

Dynamic Analysis of the 5-Story BuildingDynamic Analysis of the 5Dynamic Analysis of the 5--Story BuildingStory Building

0

1

2

3

4

5

6

0.0 0.5 1.0 1.5 2.0 2.5 3.0Max. Interstorey Drift Ratio (%)

Sto

rey

Unretrofitted

2 Strands

6 Strands10 Strands

No. of strands Max. strand stress

2 1728 MPa

6 1702 MPa

10 1660 MPa

Active seismic controlActive seismic controlActive seismic controlResearch at the University of Ottawa

Structural response and ground motion are recorded

by sensors, control forces are computed and applied

to minimize deformations.

)()( tDutxExKxCxM g +=++ ɺɺɺɺɺ

=

4

3

2

1

)(

F

F

F

F

tu

Control Force)(tu

F3

F1

F4

F2

F3

F4

Equation of motion with controlEquation of motion with controlEquation of motion with control

Controlled

Roof Displacement

1940 El Centro RecordUncontrolled

Roof Displacement

Controlled

Roof Displacement

Uncontrolled

Roof Displacement

Inelasticity in members are incorporated

Uncontrolled

element #6

Ductility=6.55

-200

-150

-100

-50

0

50

100

150

200

-0.006 -0.0045 -0.003 -0.0015 0 0.0015 0.003 0.0045 0.006

Deformation

M (

kN

-m)

Controlled - c/r =1E 7

Element #6

Ductility=3.85

-200

-150

-100

-50

0

50

100

150

200

-0.006 -0.0045 -0.003 -0.0015 0 0.0015 0.003 0.0045 0.006

Deformation

M (

kN

-m)

Uncontrolled Controlled

First story column of a 5-story building

Plastic Hinges in Uncontrolled Frame Plastic Hinges in Controlled Frame

Roof Displ. in Controlled FrameRoof Displ. in Uncontrolled Frame

Conclusions…ConclusionsConclusions……

Thank you for your attention…Thank you for your attentionThank you for your attention……

Questions and comments?Questions and comments?Questions and comments?