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?
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