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

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Presentation on theme: "68th SOEAA, Florianapolis, Brazil SEISMIC REHABILITATION OF RC STRUCTURES- AN OVERVIEW A. T. Tankut Middle East Technical University, Turkey."— Presentation transcript:

1 68th SOEAA, Florianapolis, Brazil SEISMIC 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 (> 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 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

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 masonryRelative 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


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