This document discusses methods for seismic retrofitting of existing buildings using precast concrete elements. There are three main methods - increasing lateral load capacity through the installation of precast concrete frames, braces, or armature cross walls. Precast concrete frames can be installed as an outer frame or parallel unit frames attached to new or existing foundations. Precast concrete braces are assembled off-site from precast leg and central units connected by pre-stressing cables. Armature cross walls involve replacing timber walls with precast wall panels connected by pins and light grouting.

1. SEISMIC RETROFITTING USING
PRECAST ELEMENTS

2. RETROFITTING
• Modification of existing building
• 3 methods
• Increasing lateral load carrying capacity
• Increasing ductility of beams and columns
• Reducing seismic response
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3. Improvement of
seismic
performance
Increase strength
Installation of
wall
Installation of
frame
Installation of
brace
Increase ductility
Confining
columns or
beams
Reduce response
Installation of
dampers
Installation of
isolators
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4. 1.PRECAST CONCRETE FRAMES
• External PCaPC frame
• On existing or new foundation
• 2 methods
• PCaPC outer-frame method
• PCaPC parallel unit-frame method
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5. 5

6. CONSTRUCTION
1. Evaluation of seismic capacity
2. Selecting desired retrofit method
3. Excavation of the ground for extending or
construction of foundation
4. Erection of PCaC columns
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7. 5. Setting of PCaC beams
6. Filling joints
7. Post-tensioning beam - column joints
8. Providing shear transfer
9. Integration of external frame with building
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8. Excavation of ground Assembling columns
and beams
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9. Post-tensioning beam
column joint
Tensioning diagonal
ties
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10. Shear transfer by pre-
stressing bar View after retrofit
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11. CONNECTIONS
• Column - foundation: splice sleeve connectors
• Column - column: splice sleeve connectors
• Column - beam: post-tensioning
• Vertical joints: high strength non-shrink grout
• Horizontal joints: non-shrink mortar
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12. JOINTS
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13. SHEAR TRANSFER
By pre-stressing bar By floor slab
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14. OUTER-FRAME METHOD
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15. PARALLEL UNIT-FRAME METHOD
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16. ADVANTAGES
• Faster construction
• Less or no interior work
• Ventilation and lighting unaffected
• Room layout unchanged
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17. LIMITATIONS
• Building concrete strength - 13.5MPa
• Cost - $20,000 to $25,000
• Outer-frame method – 14 storeys
• Parallel unit-frame method – 12 storeys
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18. NOTE
• Outer-frame method: 1999 to 2012: 493 projects
• Parallel unit-frame method: 2005 to 2012: 220
projects
• Tohoku earthquake (March 2011) of intensity 9
on moment magnitude scale - 59 buildings
survived
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19. 2.PRECAST CONCRETE BRACE
• 5 unit assemblage
• 4 legs and a central unit
• Pre-stress through external cables
• Brace fits the frame by itself
• Frictional control joints
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20. BRACE
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21. FSSP DEVICE
• When subjected to
seismic load only one
diagonal works
effectively
• Tension diagonal held in
place by FSSP
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22. DESIGN ISSUES
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23. 23

24. NOTE
• Suggested by Susumu Kono & Fumio
Watanabe
• Lateral load carrying capacity increased by 3
times
• Remedies to brittle failure: CFT & FRC
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25. 3.PRECAST ARMATURE CROSS WALL
• Replacement of timber members
• PCaP elements pinned at joints
• Light grouting
• Cotter pin
• Truss arrangement: tensional strength
• Pre-stress: bending strength
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26. Cross wall Joint
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27. NOTE
• Proposed by Wani Ahmad & Javed Ahmad
Bhat
• 18kN: 36mm x 36mm: 8-5mmφ: 8.1kg
• Revives traditional construction methodology
• Standardization required
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28. REFERENCE
• Kiyoji Takeda, Kyoya Tanaka, Toshiaki Someya, Asao Sakuda and Yoshiteru Ohno;
“Seismic retrofit of reinforced concrete buildings in Japan using external precast,
pre-stressed concrete frames”; PCI Journal Summer 2013, Volume 58, Pages 41-61.
• Mamoru Oda, Susumu Kono and Fumio Watanabe; “Seismic retrofit of RC buildings
with pre-stressed precast CFT and FRC braces”; The 14th World Conference on
Earthquake Engineering, October 2008, Beijing, China.
• Susumu Kono and Fumio Watanabe; “Retrofitting RC structures with precast pre-
stressed concrete braces”; Proceedings of the 8th U.S. National Conference on
Earthquake Engineering, April 2006, California, USA.
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29. REFERENCE
• Toshimi Kabeyasawa (Editor); “Recent development of seismic retrofit
methods in Japan”; Japan Building Disaster Prevention Association; January
2005.
• Wani Ahmad and Javed Ahmad Bhat; “Pre-tensioned precast elements as a
replacement to wooden bracings in the armature cross-wall system: An
approach to revive forgotten heritage”; IJCIET 2012, Volume 3, Issue 2, Pages
181-187.
• http://en.wikipedia.org/wiki/Seismic_retrofit
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30. THANK YOU
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