Transcript OFR OCCUPANT FRIENDLY SEISMIC RETROFITTING

68th SOEAA, Florianapolis, Brazil
SEISMIC REHABILITATION
OF RC STRUCTURES-
AN OVERVIEW
A. T. Tankut
Middle East Technical University, Turkey
A NOTE ON THE CONTENTS
* Initial intention was to discuss the
philosophy behind seismic strengthening
under the title “Seismic Rehab Strategy”
* Considering the audience consisting of
various disciplines, policy was changed.
* Basic concepts and methods that may
interest the audience will be reviewed.
OUTLINE
* Introduction and Basic Concepts
* Common Structural Systems
* Rehabilitation Techniques Available
* An Innovative Rehabilitation Technique
INTRODUCTION &
BASIC CONCEPTS
INTRODUCTION
“Earthquake” is a natural phenomenon
* It is tolerable in countries where the
people and the built environment are
prepared for it;
* It leads to a disaster in countries
where the built environment and the
people are not prepared for it.
INTRODUCTION
“Earthquake Preparedness” consists of
* Disaster Management (post-quake) –
Search & rescue, sheltering, food,
medical care etc. (Easy but not effective)
* Risk Management (pre-quake) – Safe
towns, safe structures, well educated
public, well trained engineers, effective
financing etc.
(Hard but very effective)
INTRODUCTION
* Seismic rehab of the existing bldg stock
is the most critical item in risk mitigation.
* A huge unsafe building stock exists.
* A systematic assessment reveals that
- A small number is seismically safe,
- A certain portion is to be demolished,
- The majority is to be strengthened.
COMMON
STRUCTURAL
SYSTEM
COMMON TYPE OF STR
* Reinforced concrete framed building
structures are common in southeast
Europe including Turkey.
* Partitioning walls of hollow brick
masonry make the structure infilled
frame and changes its behaviour.
COMMON DEFICIENCIES
Of these RC framed building structures
with hollow brick masonry infill,
* Low-rise (12 floor) are not vulnerable;
* High-rise (> 1012 floor) buildings are
carefully designed and constructed;
.
* Mid-rise (38floor) bldgs of inferior
material, poor design and construction
quality present the major problem.
.
.
COMMON DEFICIENCIES
Mid-rise buildings of inferior quality
* Constitute the majority in small towns;
* Collapse in the pancake mode; thus
* Are responsible from the high number
of human losses and severe damage,
* Are generally too good for demolition;
* Are greatly in need of rehabilitation.
COMMON DEFICIENCIES
Common deficiencies of such buildings:
* Insufficient lateral stiffness
* Deficient reinforcement detailing
* Deficient design practice
* Poor concrete
* poor workmanship etc.
REHABILITATION
TECHNIQUES
AVAILABLE
Member
Strengthening
Techniques
COLUMN STRENGTHENING
Methods for column strengthening
* For axial load and bending
- Reinforced concrete jacketing
* For axial load only
- Steel jacketing
* For concrete strength/lap splice
- CFRP confinement
BEAM STRENGTHENING
Methods for beam strengthening
* For bending
- Additional layer with new steel
- CFRP applications to the same effect
* For shear
- External clamps
- CFRP applications to the same effect
JOINT STRENGTHENING
Methods for joint strengthening
* For shear
- Diagonal steel/CFRP dovels
- External clamps
- Confining devices
SLAB STRENGTHENING
Method for slab strengthening
* For diapragm action
- Additional layer with new steel
Sysyem Behaviour
Improvement
Techniques
SYSTEM IMPROVEMENT
Devices reducing seismic loads
* Base isolation
* Active / passive control
* Smart structures
* Dampers
* Energy absorbers etc.
SYSTEM IMPROVEMENT
Lateral stiffness increasing elements
* Cast-in-place reinf conc infilled frames
* Masonry infills, reinforced with
high strength precast concrete panels
* Steel cross bracing
* Post tensioning
* External rigid frame to support the str
AN INNOVATIVE
REHABILITATION
TECHNIQUE
INTRODUCTION
The basic question:
* Cast-in-place reif conc infilled frame
technique is suitable for post-quake
repair of the evacuated buildings; but
not for pre-quake rehabilitation of the
buildings still in use.
* Suitable techniques should be developed.
THE CHALLENGE
To develop a rehabilitation method,
* Suitable for the common building type
(Hollow brick infilled RC frame)
* Practical & economical, and above all
* Occupant friendly (no more disturbance
than an ordinary painting job)
THE ANSWER
The answer is OFR (occupant friendly rehab)
* To reinforce existing masonry infill wall
with epoxy bonded PC panels, which are,
- Light enough to be handled by two
- Small enough to go through doors
- Relatively thin, 40~50 mm (high str)
- Connected to infill wall by epoxy, and
to frame by epoxy bonded dowels
EXPERIMENTAL
WORK
TEST FRAMES
* 1/3 scale, one-bay, two-storey
inferior quality RC frames,
(representing the actual practice)
- Strong beam-weak column
- Insufficient confinement
- Low quality concrete (C13~C16)
REFERENCE
200
150
L ateral L oad (kN )
100
50
0
-50
-40
-30
-20
-10
0
-50
-100
-150
-200
a. T est P R
10
20
30
40
50
T op displacem ent (m m )
STRENGTHENED (SQUARE)
200
150
L ateral L oad (kN )
100
50
0
-50
-40
-30
-20
-10
0
-50
-100
-150
-200
b. T est P I1
10
20
30
40
50
T op displacem ent (m m )
REFERENCE
STRENGTHENED (SQUARE)
INTERPRETATION
Significantly improved performance:
* Increased load carrying capacity
* Increased initial & final stiffness
* Delayed strength degradation
* Decelerated stiffness degradation
* Better ductility
* Much higher energy dissipation
PERFORMANCE IMPROVEMENT
Relative to masonry
infilled frame
Relative to
bare frame
Lateral load capacity
2.5 times
 15 times
Lateral stiffness
 3 times
 20 times
Ductility
 2 times
 0.2 times
Energy dissipation
 3 times
 60 times
CONCLUSION
CONCLUSION
* PC panel technique is a very effective
and practical seismic rehabilitation
method for existing buildings.
* Leads to a significant improvement in
seismic performance
* Is easily applied to buildings in use with
minimal disturbance
* Is cost effective (Comparable to cast-
in-place RC infills)
THANKS
for your attention...
68th SOEAA, Florianapolis, Brazil
SEISMIC REHABILITATION
OF RC STRUCTURES-
AN OVERVIEW
A. T. Tankut
Middle East Technical University, Turkey