INTRODUCTION - Confea

siennatearfulUrban and Civil

Nov 25, 2013 (3 years and 6 months ago)

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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)

R
EFERENCE

-200
-150
-100
-50
0
50
100
150
200
-50
-40
-30
-20
-10
0
10
20
30
40
50
a. Test PR
Lateral Load (kN)
Top displacement (mm)
STRENGTHENED (SQUARE)

-200
-150
-100
-50
0
50
100
150
200
-50
-40
-30
-20
-10
0
10
20
30
40
50
b. Test PI1
Lateral Load (kN)
Top displacement (mm)
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

Relative to





infilled frame

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