68th SOEAA, Florianapolis, Brazil68th SOEAA, Florianapolis, Brazil

SEISMIC REHABILITATION SEISMIC REHABILITATION OF RC STRUCTURES-OF RC STRUCTURES-

AN OVERVIEWAN OVERVIEW

A. T. TankutA. T. TankutMiddle East Technical University, TurkeyMiddle East Technical University, Turkey

A NOTE ON THE CONTENTSA NOTE ON THE CONTENTS

* Initial intention was to discussInitial intention was to discuss the the philosophy behind seismic philosophy behind seismic strengtheningstrengthening under the title under the title “Seismic Rehab Strategy”“Seismic Rehab Strategy”

* Considering the audience consisting of Considering the audience consisting of various disciplines, various disciplines, policypolicy was changed. was changed.

* Basic concepts and methods that may Basic concepts and methods that may interest the audience will be reviewed.interest the audience will be reviewed.

OUTLINEOUTLINE

* Introduction and Basic ConceptsIntroduction and Basic Concepts

* Common Structural SystemsCommon Structural Systems

* Rehabilitation Techniques AvailableRehabilitation Techniques Available

* An Innovative Rehabilitation An Innovative Rehabilitation TechniqueTechnique

INTRODUCTION & INTRODUCTION & BASIC CONCEPTSBASIC CONCEPTS

INTRODUCTIONINTRODUCTION

““Earthquake”Earthquake” is a natural is a natural phenomenonphenomenon

* It is It is tolerabletolerable in countries where in countries where the people and the built the people and the built environment are prepared for it;environment are prepared for it;

* It leads to a It leads to a disasterdisaster in countries in countries wherewhere the built environment the built environment and and the peoplethe people are are not prepared for it. not prepared for it.

INTRODUCTIONINTRODUCTION

““Earthquake Preparedness”Earthquake Preparedness” consists of consists of

* Disaster ManagementDisaster Management (post-quake) – (post-quake) – Search & rescue, sheltering, food, Search & rescue, sheltering, food, medical care etc.medical care etc. ((EasyEasy but but not not effective)effective)

* Risk ManagementRisk Management (pre-quake) – Safe (pre-quake) – Safe towns, safe structures, well educated towns, safe structures, well educated public, well trained engineers, effective public, well trained engineers, effective financing etc. financing etc. ((HardHard but but very very effective)effective)

INTRODUCTIONINTRODUCTION

* Seismic rehab of the existing bldg Seismic rehab of the existing bldg stock is the most critical item in risk stock is the most critical item in risk mitigation.mitigation.

* A huge unsafe building stockA huge unsafe building stock exists. exists.

* A systematic assessment reveals thatA systematic assessment reveals that

-- A small number is seismically safe,A small number is seismically safe,

- A certain portion is to be demolished,- A certain portion is to be demolished,

- - The majority is to be The majority is to be strengthenedstrengthened..

COMMON COMMON STRUCTURAL STRUCTURAL

SYSTEMSYSTEM

COMMON TYPE OF STRCOMMON TYPE OF STR

* Reinforced concrete Reinforced concrete framed framed building structuresbuilding structures are common in are common in southeast Europe including southeast Europe including Turkey.Turkey.

* Partitioning walls ofPartitioning walls of hollow brick hollow brick masonrymasonry make the structure make the structure infilled frame and changes its infilled frame and changes its behaviour.behaviour.

COMMON DEFICIENCIESCOMMON DEFICIENCIES

Of these RC framed building structures Of these RC framed building structures with hollow brick masonry infill,with hollow brick masonry infill,

* * Low-rise (1Low-rise (12 floor)2 floor) are not vulnerable; are not vulnerable;

* * High-rise (> 10High-rise (> 1012 floor)12 floor) buildings are buildings are .. carefully designed and constructed; carefully designed and constructed;

* * Mid-rise (3Mid-rise (38floor)8floor) bldgs of inferior bldgs of inferior .. material, poor design and construction material, poor design and construction .. quality present the major problem. quality present the major problem.

COMMON DEFICIENCIESCOMMON DEFICIENCIES

Mid-rise buildings of inferior qualityMid-rise buildings of inferior quality

* Constitute the Constitute the majoritymajority in small in small towns;towns;

* Collapse in the Collapse in the pancake modepancake mode; thus; thus

* Are responsible from the high number Are responsible from the high number of of human losses and severe damagehuman losses and severe damage,,

* Are generally too good for demolition;Are generally too good for demolition;

* Are greatly in Are greatly in need of rehabilitationneed of rehabilitation..

COMMON DEFICIENCIESCOMMON DEFICIENCIES

Common deficiencies of such Common deficiencies of such buildings:buildings:

* Insufficient lateral stiffnessInsufficient lateral stiffness

* Deficient reinforcement detailingDeficient reinforcement detailing

* Deficient design practiceDeficient design practice

* Poor concretePoor concrete

* poor workmanship etc.poor workmanship etc.

REHABILITATION REHABILITATION TECHNIQUES TECHNIQUES AVAILABLEAVAILABLE

Member Member Strengthening Strengthening

TechniquesTechniques

COLUMN STRENGTHENINGCOLUMN STRENGTHENING

Methods for column strengtheningMethods for column strengthening

* For axial load and bendingFor axial load and bending - - Reinforced concrete jacketingReinforced concrete jacketing

* For axial load onlyFor axial load only - - SteelSteel jacketing jacketing

* For concrete strength/lap spliceFor concrete strength/lap splice - CFRP confinement- CFRP confinement

BEAM STRENGTHENINGBEAM STRENGTHENING

Methods for beam strengtheningMethods for beam strengthening

* For bendingFor bending - - Additional layer with new steelAdditional layer with new steel- CFRP applications to the same - CFRP applications to the same effecteffect

* For shearFor shear- - External clampsExternal clamps- CFRP applications to the same - CFRP applications to the same effecteffect

JOINT STRENGTHENINGJOINT STRENGTHENING

Methods for joint Methods for joint strengtheningstrengthening

* For shearFor shear - Diagonal steel/CFRP - Diagonal steel/CFRP dovels - External clampsdovels - External clamps

- Confining devices - Confining devices

SLAB STRENGTHENINGSLAB STRENGTHENING

Method for slab strengtheningMethod for slab strengthening

* For diapragm actionFor diapragm action - - Additional layer with Additional layer with

new steelnew steel

Sysyem Behaviour Sysyem Behaviour Improvement Improvement TechniquesTechniques

SYSTEM IMPROVEMENTSYSTEM IMPROVEMENT

Devices reducing seismic Devices reducing seismic loadsloads

* Base isolationBase isolation

* Active / passive controlActive / passive control

* Smart structuresSmart structures

* DampersDampers

* Energy absorbers etc.Energy absorbers etc.

SYSTEM IMPROVEMENTSYSTEM IMPROVEMENT

Lateral stiffness increasing elementsLateral stiffness increasing elements

* Cast-in-place reinf conc infilled framesCast-in-place reinf conc infilled frames

* Masonry infillsMasonry infills,, reinforced with reinforced with highhigh strength precast concrete panelsstrength precast concrete panels

* Steel cross bracingSteel cross bracing

* Post tensioningPost tensioning

* External rigid frame to support the strExternal rigid frame to support the str

AN INNOVATIVE AN INNOVATIVE REHABILITATION REHABILITATION

TECHNIQUETECHNIQUE

INTRODUCTIONINTRODUCTION

The basic question:The basic question:

* Cast-in-place reif conc infilled frame Cast-in-place reif conc infilled frame technique is technique is suitable for post-quake suitable for post-quake repairrepair of the evacuated buildings; but of the evacuated buildings; but not for pre-quake rehabilitationnot for pre-quake rehabilitation of the of the buildings still in use.buildings still in use.

* Suitable techniques should be Suitable techniques should be developed.developed.

THE CHALLENGETHE CHALLENGE

To develop a rehabilitation method,To develop a rehabilitation method,

* Suitable for the common building Suitable for the common building type (Hollow brick infilled RC frame)type (Hollow brick infilled RC frame)

* Practical & economical, and above allPractical & economical, and above all

* Occupant friendly Occupant friendly ((no more disturbance no more disturbance than an ordinary painting job)than an ordinary painting job)

THE ANSWERTHE ANSWER

The answer is The answer is OFROFR (occupant friendly rehab)(occupant friendly rehab)

* To reinforce existing masonry infill wall To reinforce existing masonry infill wall with epoxy bonded PC panels, which with epoxy bonded PC panels, which are,are,

- Light enough to be handled by two- Light enough to be handled by two

- Small enough to go through doors- Small enough to go through doors

- Relatively thin, 40~50 mm (high str)- Relatively thin, 40~50 mm (high str)

- Connected to infill wall by epoxy, and - Connected to infill wall by epoxy, and to frame by epoxy bonded dowelsto frame by epoxy bonded dowels

EXPERIMENTAL EXPERIMENTAL WORKWORK

TEST FRAMESTEST FRAMES

* 1/3 scale, one-bay, two-storey 1/3 scale, one-bay, two-storey inferior quality RC frames,inferior quality RC frames,

(representing the actual practice)(representing the actual practice)

- Strong beam-weak column- Strong beam-weak column

- Insufficient confinement- Insufficient confinement

- Low quality concrete (C13~C16)- Low quality concrete (C13~C16)

RREFERENCEEFERENCE

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a. Test PR

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Top displacement (mm)

STRENGTHENED STRENGTHENED (SQUARE)(SQUARE)

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b. Test PI1

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Top displacement (mm)

REFERENCEREFERENCE

STRENGTHENED STRENGTHENED (SQUARE)(SQUARE)

INTERPRETATIONINTERPRETATIONSignificantly improved performance:Significantly improved performance:

* Increased load carrying capacityIncreased load carrying capacity

* Increased initial & final stiffnessIncreased initial & final stiffness

* Delayed strength degradationDelayed strength degradation

* Decelerated stiffness degradationDecelerated stiffness degradation

* Better ductilityBetter ductility

* Much higher energy dissipationMuch higher energy dissipation

PERFORMANCE PERFORMANCE IMPROVEMENTIMPROVEMENT

Relative to masonryRelative to masonry Relative toRelative toinfilled frame infilled frame bare framebare frame

Lateral load capacityLateral load capacity 2.5 times2.5 times 15 times 15 times

Lateral stiffnessLateral stiffness 3 times 3 times 20 times 20 times

DuctilityDuctility 2 times 2 times 0.2 times 0.2 times

Energy dissipationEnergy dissipation 3 times 3 times 60 times 60 times

CONCLUSIONCONCLUSION

CONCLUSIONCONCLUSION* PC panel technique is a very effective PC panel technique is a very effective

and practical seismic rehabilitation and practical seismic rehabilitation method for existing buildings.method for existing buildings.

* Leads to a significant improvement in Leads to a significant improvement in seismic performanceseismic performance

* Is easily applied to buildings in use Is easily applied to buildings in use with minimal disturbancewith minimal disturbance

* Is cost effective Is cost effective (Comparable to cast-(Comparable to cast-in-place RC infills)in-place RC infills)

THANKSTHANKS

for your for your attention...attention...

68th SOEAA, Florianapolis, Brazil 68th SOEAA, Florianapolis, Brazil

SEISMIC REHABILITATION SEISMIC REHABILITATION OF RC STRUCTURES-OF RC STRUCTURES-

AN OVERVIEWAN OVERVIEW

A. T. TankutA. T. TankutMiddle East Technical University, TurkeyMiddle East Technical University, Turkey