seismic retrofitting using precast elements
DESCRIPTION
general description how precast elements are used in retrofitting.TRANSCRIPT
SEISMIC RETROFITTING USING PRECAST ELEMENTS
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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Improvement of seismic
performance
Increase strength
Installation of wall
Installation of frame
Installation of brace
Increase ductilityConfining
columns or beams
Reduce response
Installation of dampers
Installation of isolators
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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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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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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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Excavation of ground Assembling columns and beams
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Post-tensioning beam column joint
Tensioning diagonal ties
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Shear transfer by pre-stressing bar View after retrofit
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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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JOINTS
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SHEAR TRANSFER
By pre-stressing bar By floor slab
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OUTER-FRAME METHOD
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PARALLEL UNIT-FRAME METHOD
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ADVANTAGES
• Faster construction
• Less or no interior work
• Ventilation and lighting unaffected
• Room layout unchanged
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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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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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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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BRACE
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FSSP DEVICE
• When subjected to
seismic load only one
diagonal works
effectively
• Tension diagonal held in
place by FSSP
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DESIGN ISSUES
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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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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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Cross wall Joint
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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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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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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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THANK YOU
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