seismic retrofitting using precast elements

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SEISMIC RETROFITTING USING PRECAST ELEMENTS

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general description how precast elements are used in retrofitting.

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Page 1: seismic retrofitting using precast elements

SEISMIC RETROFITTING USING PRECAST ELEMENTS

Page 2: 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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Page 3: seismic retrofitting using precast elements

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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Page 4: seismic retrofitting using precast elements

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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Page 19: seismic retrofitting using precast elements

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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Page 20: seismic retrofitting using precast elements

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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Page 25: seismic retrofitting using precast elements

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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Page 26: seismic retrofitting using precast elements

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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