Seismic Retrofitting of Columns & Foundations

A Seminar on on

SEISMIC RETROFITTING OF COLUMNS & FOUNDA FOUNDAT TIONS

CONTENTS: 1.

Introduction

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!a"ic conce#t" o$ retro$ittin%

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Need $or retro$ittin% retro$ittin%

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!ui'din% de$iciencie" •

('an irre%u'aritie"

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)ertica' irre%u'aritie"

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Ste#" ta+en #rior to ret retro$ ro$ittin ittin% %

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C'a""i$ication o$ "ei"mic retro$ittin% retro$ittin% tec-niue" tec-niue"

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Sei"mic retro$ittin% $or Co'umn" & Foundation"

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Conc'u"ion"

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Re$erence"

INTRODUCTION:   DEFINITION: 

Methods of increasing resistant capacity of structure by various techniques called retrofitting.  Seismic

retrofitting is the modification of existing structures to make them more resistant to the seismic activity, ground motion, or soil failure due to earthquakes. The retrofit techniques are also applicable for other natural hazards such as tropical cyclones, tornadoes & severe inds from thunderstorms. Structure can be !arthquake damaged !arthquake vulnerable • •

!ASIC CONCE(T OF RETROFITTING "p

gradation of lateral strength of the structure.

#ncrease

the ductility of structure.

#ncrease

the strength & ductility.

NEED FOR RETROFITTING     

Makes building safer & less prone to damage. To ensure the safety & security of the building, employees, structural functionality, machinery & inventory. !ssential to reduce hazard & losses from non structural elements. $redominantly concerned ith structural improvements to reduce seismic hazard. %emands on existing structures are increasing.

!UILDING DEFICIENCIES: $lan irregularities . Torsional irregularity due to plan symmetry & eccentric mass from ater tank. '. (e)entrant corners in "),*), & T) shaped buildings. +. %iaphragm discontinuity due to openings . -ut)of)plane offset for floating columns along perimeter  ertical irregularities . Stiffness irregularity, extreme soft storey due to open ground storey. '. Mass irregularity. +. ertical geometric irregularity . #n)plane discontinuity for floating columns along  perimeter.

STE(S TA2EN (RIOR TO RETROFITTING: 

Screening

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!valuation

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retrofit

RETROFIT OF STRUCTURES USING INNO)ATI)E MATERIALS:   

/igh performance concrete /igh performance steel 0iber reinforced plastic

CLASSIFICATION OF RETROFITTING TEC3NI4UES: 1lobal

*ocal

. 2dding shear all '. 2dding infill all +. 2dding bracing . 2dding ing all 3. 4all thickening 5. Mass reduction 6. 7ase isolation 8. Mass dampers

. 9acketing of beams '. 9acketing of columns +. 9acketing of beam) columns :oints . Strengthening of individual footing

RETROFITTING OF RC STRUCTURES: a;

Strengthening of existing members

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(einforced concrete :acketing

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Steel plate bonding & steel plate caging< 0($

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$late bonding & :acketing

b; adding a ne member  

Shear alls

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0rames

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7racings

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7uttresses

RETROFITTING FOR T3E COLUMNS:

5AC2ETING: 

Most popular method of strengthening of columns.

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Types .Steel :acket '.(einforced concrete :acket +. 0($= :acket

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$urpose <

•

•

 To increase the concrete confinement  To increase the shear strength & flexural strength

0($ rapping 

#n this method fiber should be located horizontally  perpendicular to the axis of column.

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#t increases the strength of concrete by confinement & also improves ductility.

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Main draback is high cost & inadequate fire resistance

ADDING NE6 S3EAR 6ALLS: 

0requently used for

(etrofitting of non ductile  (einforced concrete frame  7uildings 

2dded members are may be cast)in)place or pre cast concrete elements.

ADDING OF STEEL !RACINGS: 

2n effective solutions hen large openings are required.

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$otential advantages for the folloing reasons )/igher strength & stiffness )-penings for the natural light )adds less eight to existing structure

RETROFITTING OF FOUNDATION: 

*oad from the superstructure get transmitted to the soil through foundation.

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Seismic retrofit includes the strengthening of inadequate foundations or supplementing ith ne foundation.

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7efore retrofitting to be carried out e need to study the location of foundation, dimension, geometry, quality &  bearing capacity & degree of damage to the foundation.

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%epending upon the evaluation of performance different methods are to be adopted.

EART34UA2E 3A7ARDS ON FOUNDATIONS: 

Ground "'idin%

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Di$$erentia' "ett'ement

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Ground ti'tin%

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Liue$action

 #mportant methods used for retrofitting of foundations of  buildings are< Groutin%: 

1rout is highly pressurized into loose ground & compresses the surrounding soil in the lateral direction.

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2fter the some time grout is solidified & increase the shear strength of underlying soil to mitigate liquefaction.

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=ement grout is commonly used because of its excellent durability.

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To restore the differential settlement impermeable grout is in:ected into ground on the depressed side hich increases volume causing the ground to rise.

DRILLING OF MICRI(ILES: 

Micro piles are of diameter +>>mm or less can be drilled through the existing foundations.

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2fter the hole is drilled, it is grouted ith the cement slurry & reinforcement bars are inserted.

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The piles extend much beyond the foundation level and transfer the loads to the deeper level over a ider idth. UNDER (INNING 6IT3 (ILES:

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#t is used hen strata belo the foundation is very eak & increasing area of footing is not sufficient.

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2dditional piles are symmetrically placed around the edge of existing foundation to ensure the effective load transfer.

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2fter the construction of piles the size of footing is increased & doel bars are provided beteen existing & ne concrete.

 MICROPILES (ILES

UNDER (INNING 6IT3

CONCLUSIONS:     

#t is an effective method of reducing the risks for existing seismically deficient structures. (etrofitting techniques are also applicable for the other natural hazards. 1ives the safety to the occupants. =ost effective. #t is important to obtain accurate as)built information & analytical data to perform the seismic evaluation of existing structure & to select the appropriate retrofitting strategy based on the performance, economy & constructability.

8(re9ention i" etter t-an cure;

REFERENCES: 

“Seismic retroftting o RC buildings” 9o'. 0 I""ue  < ma=>  ?une @1B ##B *>/

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ISET Journal o Eart!ua"e tecnolog#$ #a#er no.*,*B 9o'.* no >