seismic retrofitting using precast elements

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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