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SEISMIC TIPS 21 TO 24

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					SEISMIC TIPS (21 TO 24)




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                 CONTENTS
1.INTRODUCTION.

2.WHY ARE OPEN GROUND BUILDINGS
  ARE VULNERABLE IN EARTHQUKE?

3. WHY ARE SHORT COLUMS DAMAGED DURING EARTHQUAKE?

4. WHY ARE BUILDINGS WITH SHEAR WALLS PREFERRED IN
   SEISMIC ZONES?

5. HOW TO REDUCE EARTHQUAKE EFFECTS ON BUILDINGS?

6. CONCLUSION.

7. REFERENCES.
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INTRODUCTION
 • EFFECTS OF EARTHQUAKE DEVELOPED ON

 OPEN GROUND STOREY BUILDING.

 •EFFECT OF EARTHQUAKE ON SHORT COLUMN.

 •REMEDIES.




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WHY ARE OPEN GROUND BUILDINGS
ARE VULNERABLE IN EARTHQUAKES?

  BASIC FEATURE

  •GROUND STOREY KEPT OPEN

  •NO PARTITION WALL

  • 2   DISTINCT CHARACTER

  1. SOFT STOREY

  2. WEAK STOREY



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2.2 EARTHQUAKE BEHAVIOUR

BHUJ EARTHQUAKE.

UPPER STOREY ACT AS A SINGLE BLOCK.

INVERTED PENDULUMS

COLOUMNS IN GROUND STOREY SEVERELY STRESSED.




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2.3 THE PROBLEM

•GROUND STOREY BUILDINGS ARE INHERENTLY POOR SYSTEM.

•SUDDEN DROP IN STIFFNESS AND STRENGTH.

•BARE FRAME ARE CONSIDERED IN DESIGN CALCULATIONS.

•INVERTED PENDULUM EFFECT NOT CAPTURED IN DESIGN.




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2.4 IMPROVED DESIGN STRATEGIES

•INDIAN SEISMIC CODE INCLUDE SPECIAL DESIGN FOR SOFT STOREY.

•BUILDING SHOULD BE CONSIDERED AS SOFT STOREY.

•SPECIFY HIGHER DESIGN FORCES FOR SOFT STOREY.

•BEAMS AND COLUMNS DESIGNED FOR 2.5 TIMES THE FORCES

OBTAINED FROM THIS BARE FRAME ANALYSIS.




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•BEST OPTION TO AVOID SUCH SUDEN DECREASE IN STRENGTH.
•IDEAL TO BUILD WALLS IN GROUND STOREY.




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3 WHY ARE SHORT COLOUMNS
MORE DAMAGED DURING
EARTHQUAKE?
3.1 WHICH COLUMNS ARE SHORT?

•SHORT COLUMNS SUFFER MORE DAMAGE THAN TALL COLUMNS.

•EG:BUILDING ON SLOPING GROUND AND BUILDING WITH
A MEZZANINE FLOOR.

•SHORT COLUMN IS STIFFER THAN TALL COLUMNS.




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•SHORT COLUMN EFFECT.

•SHEAR FAILURE.

3.2 THE SHORT COLUMN BEHAVIOUR.

•RIGID FLOOR DIAPHRAM ACTION.

•ANOTHER IS WALLS WITH PARTIAL HEIGHT.

•MORE DAMAGE-X CRACKING.




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3.3 THE SOLUTION

•BETTER IS TO AVOID SHORT COLUMNS.

•IF IT IS NOT POSSIBLE THIS EFFECT MUST BE ADDRESSED
 IN STRUCURAL DESIGN.

•SPECIAL CONFINING REINFORCEMENT SHOULD PROVIDE.

•IN EXISTING BUILDING RETROFIT SOLUTION CAN BE EMPLOYED.

•WALLS OF PARTIAL HEIGHT CLOSED BY WALLS OF FULL HEIGHT.




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4. WHY ARE BUILDINGS WITH
 SHEAR WALLS PREFERRED
IN SEISMIC REGIONS?
4.1 WHAT IS A SHEAR WALL BUILDING?

•VERTICAL PLATE LIKE RC WALLS CALLED SHEAR WALLS.

•START FROM FOUNDATION LEVEL CONTINOUS
 THROUGHT OUT BUILDING HEIGHT.



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     •LIKE VERTICALLY-ORIENTED WIDE BEAMS THAT CARRY
      EARTHQUAKE LOADS DOWNWARDS TO THE FOUNDATION.

•RANGE OF THICKNESS 150MM-400MM.

4.2 ADVANTAGES OF SHEAR WALLS IN RC BUILDINGS

“We cannot afford to build concrete buildings meant
To resist severe earthquakes without shear walls.”
                                                   Mark Fintel.

•MORE POPULAR CHOICE IN EARTHQUAKE PRONE COUNTRIES.

•EASY TO CONSTRUCT.




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•REINFORCEMENT DETAILING IS RELATIVELY STRAIGHT FORWARD.

•EFFICIENT BOTH IN TERMS OF CONSTRUCTION COST

AND MINIMIZING EARTHQUAKE DAMAGE IN STRUCTURAL

AND NON SRTUCTURAL ELEMENTS.




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4.3 ARCHITECTURAL ASPECTS OF SHEAR WALLS

•PROVIDE LARGE STRENGTH AND STIFFNESS TO BUILDING
 IN THE DIREECTION OF ORIENTATION.

•REDUCE LATERAL SWAY.

•OVERTURING EFFECT IS LARGE.

•DESIGN OF FOUNDATION REQUIRE SPECIAL ATTENTION.

•MOMENT RESISTANT FRAME.

•SIZE OF OPENINGS ARE SMALL.

•REDUCE ILL EFFEECTS OF TWISTING.
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4.8 OVERALL GEOMETRY OF
WALLS

•SHEAR WALLS ARE
 OBLONG IN CROSS-SECTION.

•THIN WALLED HOLLOW
 RC SHAFTS AROUND THE
 ELEVATOR CORE OF BUILDIG
 ACT AS A SHEAR WALL.




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4.9 REINFORCED BARS IN RC WALLS

•CURTAILS

•MINIMUM AREA OF REINFORCING STEEL IS
 0.0025 TIMES THE C/S AREA.

4.9 BOUNDARY ELEMENTS

•OVERTURING EFFECT CAUSE HIGH COMPRESSIVE
AND TENSILE STRESS ON WALLS.

•BOUNDARY ELEMENTS.HIGHER BENDING STRENGTH AND
 HORIZONTAL SHEAR FORCE CARRYING CAPACITY.




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5. HOW TO REDUCE EARTHQUAKE
EFFCTS ON BUILDINGS?
5.1 WHY EARTHQUAKE EFFECTS ARE TO BE REDUCED


 •TO MAKE THE BUILDING FUNCTIONAL AFTER THE EARTHQUAKE.
 •TWO TECHNOLOGIES ARE USED.

 5.2 BASE ISOLATION

 •EXPLAINED THROUGHT AN EXAMPLE BUILDING RESTING ON
 FRICTIONLESS ROLLERS.

 •BUILDING IS RESTED ON FLEXIBLE PADS.

 •FLEXIBLE PADS ARE CALLED BASE ISOLATORS.

 •MAIN FEATURE IS TO INTRODUCE FLEXIBILITY IN THE STRUCTURE.
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•BASE ISOLATORS ARE USED TO ABSORB ENERGY AND

ADD DAMPING TO THE SYSTEM.

•BASE ISOLATION IS NOT SUITABLE FOR ALL BULDING.

•SUITABLE FOR LOW TO MEDIUM RISEE BUILDING.

•NOT SUITABLE FOR HIGH RISEE BUILDING.




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5.3 BASE ISOLATION IN REAL BUILDINGS

•SEISMIC ISOLATION IS A RELATIVELY RECENT AND
EVOLVING TECHNOLOGY.

•IT HAS BEEN AN INCREASED USE IN 1980s.

•NOW USED IN COUNTRIES ITALY,NEW ZEALAND,USA.

•USEFUL FOR RETROFITTING IMP BUILDING.




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5.4 SEISMIC DAMPERS

•INSTALLING SEISMIC DAMPERS IN PLACE OF STRUCTURAL ELEMENTS.

•SUCH AS DIAGONAL BRACES.

•DAMPERS ABSORB PART OF ENERGY PASSING THROUGH IT.

•DAMPERS USED SINCE 1960s.

•TYPES-VISCOUS DAMPERS,FRICTIONAL DAMPERS

AND YIELDING DAMPERS.


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6. CONCLUSION
TO BUILD A COMPLETE EARTHQUAKE RESISTANT BUILDING IS NOT

POSSIBLE.BUT WE CAN IMPROVE THE STRENGTH OF BUILDING

BY AVOIDING OPEN GROUND STOREYS AND SHORT COLUMS.

OR WE CAN US BASE ISOLATIN OR DAMPING TO REDUCE

THE EARTHQUAKE EFFECT ON BUILDINGS.




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 REFERENCE
•IS 1893(Part 1) (2002), Indian Standard Code of Practice for Criteria for
Design of Earthquake Resistant Structures, Bureau of Indian
Standards, New Delhi.


•IS 13920, (1993), Indian Standard Code of Practice for Ductile Detailing of
Reinforced Concrete Structures Subjected to Seismic Forces, Bureau of
Indian Standards, New Delhi.
•Paulay,T., and Priestley,M.J.N., (1992), Seismic Design of Reinforced
Concrete and Masonry Buildings, John Wiley & Sons, USA




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EERI, (1999), Lessons Learnt Over Time – Learning from Earthquakes
Series: Volume II Innovative Recovery in India, Earthquake
Engineering Research Institute, Oakland (CA), USA; also
available at http://www.nicee.org/readings/EERI_Report.htm.
Hanson,R.D., and Soong,T.T., (2001), Seismic Design with
Supplemental Energy Dissipation Devices, Earthquake Engineering
Research Institute, Oakland (CA), USA.
Skinner,R.I., Robinson,W.H., and McVerry,G.H., (1999), An
Introduction to Seismic Isolation, John Wiley & Sons, New York.




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