68th SOEAA, Florianapolis, Brazil SEISMIC REHABILITATION OF RC STRUCTURES- AN OVERVIEW

1. 68th SOEAA, Florianapolis, BrazilSEISMIC REHABILITATION OF RC STRUCTURES-AN OVERVIEW A. T. Tankut Middle East Technical University, Turkey

2. 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.

3. OUTLINE • Introduction and Basic Concepts • Common Structural Systems • Rehabilitation Techniques Available • An Innovative Rehabilitation Technique

4. INTRODUCTION & BASIC CONCEPTS

5. 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.

6. 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)

7. 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.

8. COMMON STRUCTURAL SYSTEM

9. 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.

10. 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.

11. 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.

12. COMMON DEFICIENCIES Common deficiencies of such buildings: • Insufficient lateral stiffness • Deficient reinforcement detailing • Deficient design practice • Poor concrete • poor workmanship etc.

13. REHABILITATION TECHNIQUES AVAILABLE

14. Member Strengthening Techniques

15. 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

16. 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

17. JOINT STRENGTHENING Methods for joint strengthening • For shear - Diagonal steel/CFRP dovels - External clamps - Confining devices

18. SLAB STRENGTHENING Method for slab strengthening • For diapragm action - Additional layer with new steel

19. Sysyem Behaviour Improvement Techniques

20. SYSTEM IMPROVEMENT Devices reducing seismic loads • Base isolation • Active / passive control • Smart structures • Dampers • Energy absorbers etc.

21. 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

22. AN INNOVATIVE REHABILITATION TECHNIQUE

23. 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.

24. 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)

25. 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

26. EXPERIMENTAL WORK

27. 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)

28. REFERENCE

29. STRENGTHENED (SQUARE)

30. REFERENCE

31. STRENGTHENED (SQUARE)

32. INTERPRETATION Significantly improved performance: • Increased load carrying capacity • Increased initial & final stiffness • Delayed strength degradation • Decelerated stiffness degradation • Better ductility • Much higher energy dissipation

33. 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

34. CONCLUSION

35. 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)

36. THANKS for your attention...

37. 68th SOEAA, Florianapolis, Brazil SEISMIC REHABILITATION OF RC STRUCTURES-AN OVERVIEW A. T. Tankut Middle East Technical University, Turkey