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seismic retrofitting using precast elements
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- 2. RETROFITTING • Modification ofexisting building • 3 methods • Increasing lateral load carrying capacity • Increasing ductility of beams and columns • Reducing seismic response 2
- 3. Improvement of seismic performance Increase strength Installationof wall Installation of frame Installation of brace Increase ductility Confining columns or beams Reduce response Installation of dampers Installation of isolators 3
- 4. 1.PRECAST CONCRETE FRAMES •External PCaPC frame • On existing or new foundation • 2 methods • PCaPC outer-frame method • PCaPC parallel unit-frame method 4
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- 6. CONSTRUCTION 1. Evaluation ofseismic capacity 2. Selecting desired retrofit method 3. Excavation of the ground for extending or construction of foundation 4. Erection of PCaC columns 6
- 7. 5. Setting ofPCaC beams 6. Filling joints 7. Post-tensioning beam - column joints 8. Providing shear transfer 9. Integration of external frame with building 7
- 8. Excavation of groundAssembling columns and beams 8
- 9. Post-tensioning beam column joint Tensioningdiagonal ties 9
- 10. Shear transfer bypre- stressing bar View after retrofit 10
- 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 11
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- 13. SHEAR TRANSFER By pre-stressingbar By floor slab 13
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- 16. ADVANTAGES • Faster construction •Less or no interior work • Ventilation and lighting unaffected • Room layout unchanged 16
- 17. LIMITATIONS • Building concretestrength - 13.5MPa • Cost - $20,000 to $25,000 • Outer-frame method – 14 storeys • Parallel unit-frame method – 12 storeys 17
- 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 18
- 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 19
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- 21. FSSP DEVICE • Whensubjected to seismic load only one diagonal works effectively • Tension diagonal held in place by FSSP 21
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- 24. NOTE • Suggested bySusumu Kono & Fumio Watanabe • Lateral load carrying capacity increased by 3 times • Remedies to brittle failure: CFT & FRC 24
- 25. 3.PRECAST ARMATURE CROSSWALL • Replacement of timber members • PCaP elements pinned at joints • Light grouting • Cotter pin • Truss arrangement: tensional strength • Pre-stress: bending strength 25
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- 27. NOTE • Proposed byWani Ahmad & Javed Ahmad Bhat • 18kN: 36mm x 36mm: 8-5mmφ: 8.1kg • Revives traditional construction methodology • Standardization required 27
- 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. 28
- 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 29
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