A. T. Tankut Middle East Technical University, Turkey 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

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

STRENGTHENED (SQUARE)

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...

A. T. Tankut Middle East Technical University, Turkey 68th SOEAA, Florianapolis, Brazil SEISMIC REHABILITATION OF RC STRUCTURES- AN OVERVIEW A. T. Tankut Middle East Technical University, Turkey