26647449 retrofitting of earthquake affected buildings ppt

7/30/2019 26647449 Retrofitting of Earthquake Affected Buildings Ppt

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RETROFITTING OFEARTHQUAKE AFFECTED

BUILDINGS


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WHATIS

RETROFITTING

IS 13935To upgrade the earthquake resistence up to the levelof the level of the present day codes by approriatetechniques.

CEB 1995Concepts including strengthening, repairing andremoulding

Newman , 2001It is an upgrading of certain building system, such asmechanical, electrical, or structural, to improveperformance, function or appearance


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Seismic retrofitting is the modification ofexisting structures to make them more resistant

to seismic activity, ground motion, or soil failuredue to earthquakes.

The retrofit techniques are also applicable forother natural hazards such as tropical cyclones,tornadoes, and severe winds fromthunderstorms.


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CIRCUMSTANCES

(i ) earthquake damaged buildings ( ii) earthquake vulnerable buildings.

WHEN & FOR WHAT?


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WHYRETROFITTING

Thisprovestobeabetteroptioncateringtotheeconomicconsiderationsand

immediateshelter

problems

rather

than

replacementofbuildings


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RETROFITPERFORMANCEOBJECTIVES STRUCTUREFUNCTIONALITY.Primarystructure

undamagedand

the

structure

is

undiminished

in

utilityforitsprimaryapplication.Ahighlevelofretrofit,thisensuresthatanyrequiredrepairsare

only

"cosmetic"

for

example,

minor

cracks

in

plaster,drywallandstucco.Thisistheminimumacceptablelevelofretrofitforhospitals.

STRUCTUREUNAFFECTED.Thislevelofretrofitispreferredforhistoricstructuresofhighculturalsignificance.


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NEEDIN

EARTHQUAKE

VULNERABLE

BUILDINGS

(a)thebuildingshavebeendesignedaccordingtoaseismiccode,butthecodehasbeenupgradedinlateryears;

(b)buildings

designed

to

meet

the

modern

seismic

codes,

butdeficienciesexistinthedesignorconstruction;

(c)essentialbuildingsmustbestrengthenedlikehospitalshistorical

monuments

and

architectural

buildings;

(d)importantbuildingswhoseserviceisassumedtobeessentialevenjustafteranearthquake;

(e)buildingstheuseofwhichhaschangedthroughtheyears;

(f)buildings

that

are

expanded,

renovated

or

rebuilt.


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SEISMICEVALUATION

OF

BUILDINGS

toassesstheseismiccapacityofearthquake

vulnerablebuildings

or

earthquake

damaged

buildingsforthefutureuse.

helpfulfordegreeofinterventionrequiredin

seismicallydeficientstructure


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Methodologies

(i)qualitative

methods

(ii)analyticalmethods


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QUALITATIVEMETHODS

basedonthebackgroundinformation

availableof

the

building

and

its

constructionsite

architecturalandstructuraldrawings

pastperformance

of

similar

buildings

under

severeearthquakes,

visualinspectionreport,

somenon

destructive

test

results.


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methods FieldEvaluationMethod,

RapidVisual

Screening

Method,

ATC14methodologyetc.


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AN

ANALYTICALMETHOD

Basedontheconsiderationofthecapacityandductilityofbuildingsonthebasisofavailabledrawings.

METHODS

Capacity/Demand(C/D)method, Screeningmethod,

Pushoveranalysis,

Nonlinearinelasticanalysisetc.

Evaluationprocedureshouldbeverysimpleandimmediate

based

on

synthetic

information

that

can

prove

suitable

for

riskevaluation

on

large

populations.

Therefore,qualitativeevaluationofthebuildingsisgenerallybeingcarriedout.


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COMPONENTSOFSEISMICEVALUATION

METHODOLOGY

1.CONDITIONASSESSMENTbasedon (i)

data

collection

or

information

gathering

of

structuresfromarchitecturalandstructuraldrawings

(ii)performance

characteristics

of

similar

typeof

buildingsinpastearthquakes

(iii)rapidevaluationofstrength,drift,materials,

structural

components

and

structural

details.

usedbasicallyforundamagedexistingstructures'


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2.VISUALINSPECTION/FIELDEVALUATION

basedon

observed

distress

and

damage

in

structures.

Visualinspectionismoreusefulfordamaged

structureshowever

it

may

also

be

conducted

for

undamagedstructures.


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SOURCEOFWEAKNESSINRCFRAME

BUILDING

(i)discontinuousloadpath/interruptedload

path/irregularload

path

(ii)lackofdeformationcompatibilityofstructuralmembers

(iii)qualityofworkmanshipandpoorqualityofmaterials


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CONCRETE

RETROFITTING


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BASICCONCEPTS

at

(CEB,

1997):

(a)upgradationofthelateralstrengthofthe

structure;

(b)increaseintheductilityofstructure;

(c)

increase

in

strength

and

ductility.

It is suggested that the cost of retrofitting of a

structure should remain below 25% of thereplacement as major justification of retrofitting


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CONSIDERATIONINRETROFITTINGOF

STRUCTURES

METHODUSEDdependson

thehorizontal

and

vertical

load

resisting

systemofthestructure

the

type

of

materials

used

for

parent

construction.

Onthetechnologythatisfeasibleand

economical.


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CONSIDERATIONINRETROFITTINGOF

STRUCTURES

SELECTIONOFRETROFITTINGMETHODSOF

BUILDINGSALSO

DEPENDS

ON:

asderivedfromtheearthquakedamagesurveysby

understandingof

mode

of

failure,

structuralbehavior

weakandstrongdesignaspects


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STRUCTURALDAMAGEDUETO

DISCONTINUOUSLOAD

PATH

seismicforcesshouldbeproperlycollectedby

thehorizontal

framing

system

and

properly

transferredintoverticallateralresisting

system

discontinuity/irregularityinthisloadpathorloadtransfermaycause structuraldamage

during

strong

earthquakes.


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SOURCEOFWEAKNESSINRCFRAME

BUILDING

(i)discontinuousloadpath/interruptedload

path/irregularload

path

(ii)lackofdeformationcompatibilityofstructuralmembers

(iii)qualityofworkmanshipandpoorqualityofmaterials


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STRUCTURALDAMAGEDUETO

DISCONTINUOUSLOAD

PATH

seismicforcesshouldbeproperlycollectedby

thehorizontal

framing

system

and

properly

transferredintoverticallateralresisting

system

discontinuity/irregularityinthisloadpathorloadtransfermaycause structuraldamage

during

strong

earthquakes.


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STRUCTURALDAMAGEDUETOLACK

OFDEFORMATION

MAINPROBLEMS

limitedamount

of

ductility and

theinabilitytoredistributeloadinordertosafelywithstandthedeformationsimposedupon

inresponsetoseismicloads.


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STRUCTURALDAMAGEDUETOLACK

OFDEFORMATION

The most common regions of failurein an existing reinforced concrete frame


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ColoumnsIn reinforced concrete columns several interaction mechanisminfluences its lateral load behaviour. The main actions areassociated with axial, flexure, shear, and bond


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Beams

Inreinforcedconcretebeams,themajor

problemsexist

at

the

right

end,

considering

seismicforceslefttoright

Abrittleshearfailurecouldoccurduetosuperposing

of

shear

forces caused

by

verticalloadingandseismicloading.


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Beamcolumnjoints

incaseofstrongcolumnweakbeam

behaviour, thejoint maybeheavilystressedafterbeam

yieldinganddiagonalcrackingmaybeformedin

the

connection. Wideflexuralcracksmaydevelopatthebeamend

partiallyattributabletotheslipofbeamreinforcement withintheconnection.

Suchshearcrackingmayreducethestiffnessofabuilding.


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Behaviorofbeamsforverticaland

seismicloading


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QUALITY

OF

WORKMANSHIP

AND

MATERIAL

faultyconstructionpractices

lack

of

amount

and

detailing

of

reinforcement

as

per

requirementofcode

theendoflateralreinforcementisnotbentby135degree

lackofqualitycontrol of

design

material

strength

as

specified,

spallingofconcretebythecorrosionofembeddedreinforcingbars,

porousconcrete,

ageof

concrete,

Propermaintenanceetc


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CLASSIFICATION


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RETROFITTINGSTRATEGIESFORRC

BUITDINGS StructuralLevel(orGlobal)RetrofitMethods

Twoapproaches

(i)conventionalmethodsbasedonincreasingtheseismicresistanceofexisting

structure

(ii)nonconventionalmethods.basedon

reduction

of

seismic

demands.


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CONVENTIONALMETHODS

ADDINGNEWSHEARWALLS

Frequentlyused

for

retrofitting

of

non

ductile

reinforcedconcreteframebuildings.

Theaddedelementscanbeeithercastinplaceor

precast

concrete

elements.

Newelementspreferablybeplacedattheexteriorofthebuilding.

Notpreferred

in

the

interior

of

the

structure

to

avoidinteriormouldings.


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TECHNICALCONSIDERATIONS:

(a)determining

the

adequacy

of

existing

floor

and

roofslabstocarrytheseismicforces;

(b)transferofdiaphragmshearintothenewshearwallswithdowels;

(c)addingnewcollectoranddragmemberstothediaphragm;

(d)increaseintheweightandconcentrationof

shearby

the

addition

of

wall

which

may

affect

the

foundations


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CONSTRUCTIONALCONSIDERATION

tofindlocationswherewallscanbeaddedandwelllocatedwhichmayaligntothefullheightofthebuildingtominimize

torsion

desirabletolocatewallsadjacenttothebeambetweencolumnssothatonlyminimumslabdemolitionisrequired

withconnectionsmadetobeamatthesidesofcolumns


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Thelongitudinalreinforcementmustbeplacedattheendsofthewallrunningcontinuouslythroughtheentireheight.

thereinforcementhastopassthroughholesinslabsandaroundthebeamstoavoidinterference.

Wallthicknessalsovariesfrom15to25cm(6to10inch)andisnormallyplacedexternally


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ADDING

STEEL

BRACINGS aneffectivesolutionwhenlargeopeningsarerequired. Potentialadvantageoverotherschemesforthe

followingreasons:

higherstrengthandstiffness,canbeproved, openingfornaturallightcanbemadeeasily,

amount

of

work

is

less

since

foundation

cost

may

be

minimized,

thebracingsystemaddsmuchlessweighttotheexistingstructure,

mostoftheretrofittingworkcanbeperformedwithprefabricated

elements

and

disturbance

to

the

occupants

maybeminimized.


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TECHNICALCONSIDERATIONS

can

be

used

for

steel

structures

as

well

as

concretestructure.

Theeffectiveslendernessratioofbracekeptrelativelylowsothatbracesareeffectivein

compressionas

well

as

tension,

suggestedratioare80to60orevenlower Collector'smembersarerecommendedfor

transferringforces

between

the

frame

and

bracingsystem.


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JACKETING

Mostpopularmethodforstrengtheningofbuildingcolumns

Steeljacket,reinforcedconcretejacket,fibrereinforcedpolymercompositejacketetc

Purposeforjacketing:1.Toincreaseconcreteconfinement

2.Toincreaseshearstrength

3.

To

increase

flexural

strength

RECTANGULARANDCIRCULARCROSSSECTIONS

Transversefibreiswrappedalongentirecircumferenceofthememberstoincreaseconcreteconfinementandshearstrengthmember

Forsquareorrectangularcrosssections,circular/oval/ellipticaljacketsareusedandthespacebetweenthejacketandcolumnisfilledwithconcrete.


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Multishapedjacketsprovideahighdegreeofconfinement moreeffective.

Rectangularjacketstypicallylacktheflexuralstiffnessneeded tofullyconfinetheconcrete.

Circularandovaljacketsislessdesirabledueto

1.Need

of

large

space

in

the

building

2.Ovalorellipticaljacketabilitytoconfinetheconcretealongthelong

dimensionisopentoquestion.


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TECHNICALCONSIDERATIONSJacketing

ObjectiveToincreasetheseismiccapacityofframedstructures.

Jacketingofreinforcedconcretecolumnsyieldsbetterconfinementthanthatofconcretebeamswithslabs slabcauseshindrance

Waffleslab increasedstiffnessisobtained,jacketingcolumnsandribs.

Foundationgridsarestrengthenedandstiffenedbyjacketingtheirbeams.

Improvethelateralstrengthandductilitybyconfinementofcompressionconcrete

Retrofittingofafewmembersmightnotbeeffectiveenoughtoimprovetheoverallbehaviourofthestructure,iftheremainingmembers arenotductile.


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Reinforcedconcretejacketing

Damagedregionsoftheexistingmembersshouldberepairedpriortotheirjacketing

Therearetwomainpurposeofjacketingofcolumns:(i)

increase

in

shear

capacity

of

columns

strong

column

weak

beam

design)

(ii)toimprovethecolumnsflexuralstrength

Itis

done

by

passing

the

longitudinal

reinforcement

through

holes

drilledintheslabandplacingnewconcreteinthebeamcolumnjoints.

Rehabilitatedsectionsaredesignedinthiswaysothattheflexuralstrengthofcolumnsshouldbegreaterthanthatofthebeams.


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Detailsforreinforcedconcretejacketing

Propertiesofjacket hMatchwiththe existingstructure

hCompressivestrength > existingstructuresby5N/mm

(50kg/cm),oratleastequaltothatoftheexisting

structure.

Minimumwidthofjacket h10cm concretecastinplace

4cm shotcrete.

hMonolithic

behaviour

hNarrowgap topreventincreasesinflexuralcapacity.

Minimumareaoflongitudinalh3A/fy

hSpacing

should

not

exceed

6times

the

width

of

the

jacket

h% ofsteelinthejacketw.r.tthejacketareashouldbe

limitedbetween0.015and0.04.


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Minimumareaoftransverse hDesignedandspaced

hMinimum

bar

dia

used

for

ties

is

not

less

that

10mm

hThetiesshouldhave135degreehooks

hDuetothedifficultyofmanufacturing135degreehooks

onthefield,tiesmadeuptomultiplepieces,canbeused

Shearstressintheinterface hProvideadequatesheartransfermechanismtoassured

monolithicbehaviour.

hrelativemovementbetweenthejacketandtheexisting

elementshouldbeprevented.

hChipping

the

concrete

cover

of

the

original

member

and

rougheningitssurfacemayimprovethebondbetweenthe

oldandthenewconcrete.

hFoursidedjackettiesshouldbeusedtoconfine

andforshearreinforcementinthecompositeelement.

h1,

2,

3side

jackets

special

reinforcement

should

be

providedtoenhanceamonolithicbehaviour.


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SteelJacketing

Local

strengthening

of

columns

has

been

frequently

accomplished

by

jacketing

withsteelplates.

Detailsofsteeljacketing

Steelplate

thickness hAt

least

6mm

Heightofjacket hFlexuralcolumns 1.2to1.5timessplicelength

hshearcolumnsfullheightofcolumn

Shapeofjackets h Rectangularjacketing,prefabricatedtwoL

shapedpanels

hTheuseofrectangularjacketshasbeensuccessfulin

caseofsmallsizecolumnsupto36inchwidthbut

hasbeen

less

successful

on

larger

rectangular

columns.Onlargercolumns,rectangularjackets

appeartobeincapabletoprovideadequate

confinement.

Bottom clearance h38 mm (1 5 inch)


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Bottomclearance 38mm(1.5inch)

Gapbetweensteeljacket h25mm(1inch)fillwithcementationsgrout.

Andconcretecolumn

Sizeofanchorbolt h25mm(1inch)indiameter

hBoltswereinstalledthroughpredrilledholes

onthesteeljacket

Numberofanchorbolts hTwoanchorboltsareintendedtostiffenthesteel

jacketandimproveconfinementofthesplice.


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Slab column connection


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Slabcolumnconnection

The most critical structural damage is the slab column connection whichresultsinthepunchingshearfailureduetothetransferofunbalancemoments.

Retrofitting PreventionofpunchingshearfailuresAdding concrete capitals or steelplates on both sides of slab canprevent

punchingshear

failure

Foundations

The repair and retrofitting offoundations isprincipally required due to twotypesofproblems:

(i) the change of loads on the foundation by strengthening the

structure

(ii)thefailureoffoundationitself.

In

thefirst

case,

reinforced

concrete

jacketing

of

basement

beams

and

the

additionofnewpilesaredone.


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CASESTUDIES

CASESTUDY1:SEISMICRETROFITTINGOFRCBUILDINGWITH


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C S S U S S C O G O C U G

JACKETINGANDSHEARWALLS

TypicalFeaturesoftheBuilding

NumberofStories eightstorieswithbasement

Lateralload

resisting

system

reinforced

concrete

frames

Floorsystem two wayslabwithbeam

Foundation gridfoundationwithretainingwallsaroundthe

perimeter

FeaturesofDamagesinMexicoEarthquake,1979

Minorcracksinbeamsandcolumns

RetrofittingTechniques

Employed

after

Mexico

Earthquake,

1979

Additionofconcreteshearwall inaxis2andA

Additionofmasonrywallinaxis5


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RetrofittingTechniquesEmployed


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Crackedbeams

and

columns Repaired

with

epoxy

injection

ThecolumnsofFrames1and5 Encasedinsteelthroughtheforthstorey

level

Frame1and5Bracedsteelframeswereattachedontheoutsideofthe

buildinginEWdirection.

ExpectedPerformance

Resultsindicatethatthesteelbraced

framesattachedtothebuildingstrengthened

andtheystiffenedthestructure,movingits

naturalperiod

away

from

the

predominant

groundperiodof2.0sec


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Thebuildingalsoexperiencedlargeinterstoreydeformationsofitsframe:

resulting in damage to the exterior walls (both longitudinal and transverse).


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resultingindamagetotheexteriorwalls(bothlongitudinaland transverse).

Thelongitudinal

and

transverse

partition

walls

were

badly

cracked

at

several

levels

Noindicationsofthefoundationfailurewereobserved.

RetrofittingTechniques

Employed

Diagonalsteel

bracing wasaddedto

thecentralbayof

frames1,

2and

3in

the

transversedirection

Insertionofnew

reinforcedconcrete

infillwalls of4cm

thicknessto

all

bays

of

theexteriorlongitudinal

frames


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CASESTUDY5:SEISMICRETROFITTING OFRCBUILDINGWITHSHEAR WALLS

ANDJACKETING


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TypicalFeaturesoftheBuilding

Numberofstories Eightstoreyreinforcedconcreteapartmentbuilding

Buildingdimension floorarea245m andstoreyheightis3.0mabovethe

foundationlevel,includingpenthouse

Designand

construction

1984

Lateralloadresistingsystems momentresistingRCframes.Astructuralwall

aroundtheelevator

Floorsystem concreteslabsinthefirststoriesandjustslabsinthetoptwo

stories

Foundationsystem stripfoundationinboththedirection.

FeaturesofDamagesinAdana Ceyhan(Turkey)Earthquake,1998

Buildingundermoderatedamagecategory

Extensivedamage

was

observed

in

beams

especially

between

the

first

and

fifth

floors


Infillingof

appropriate

frame

bays

by

in

situ

reinforced

concrete

shear

walls with


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CASESTUDY6:SEISMICRETROFITTINGOFRC BUILDINGBYADDING

FRAMES


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FRAMES

TypicalFeaturesofthebuilding

Numberofstories eightstoriesconsistingofgroundfloorwithseven

upperfloors

Typicalfeatures

soft

storey,

mixed

construction

masonry

with

reinforced

concrete

Yearofconstruction 1979

Lateralloadresistingsystems masonrybearingwallsexceptattheground

floor.Columnsareonlyatthegroundfloor

Floorsystem

waffle

slab

at

the

first

level

and

beam

block

slab

at

the

otherlevels

Foundationsystem gridandslabwithfrictionpileslocatedundereach

column

Typicalfloor

plan

and

elevation

FeaturesofDamagesinMexicoEarthquake,1985

Severedamageoccurredinmasonrywalls

Foundationofthecolumnsatthefirstlevelsufferednodamage


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Principal

failure

direction

was

east

west

due

to

irregularities

in

plan

andinsufficientareaofwallsineast westdirection.


Addingofreinforcedconcreteframesovertheexistingcolumnin the

groundfloor

along

axis

1,3,

4and

6

Addingtwoconcreteshearwallsfromfirstleveltotheupperstoreywere

placedinaxis3and4

Theexistingmasonrywallswereretrofittedusingwiremeshand30mm

of

mortarThecoveroftheexistingcolumnswasremovedtopermitthecontinuity

ofthenewlongitudinalreinforcement. Thedimensionsoftheexisting

columnswereincreased

Themonolithicbehaviourbetweenthenewframesandthefloorsystem

wasprovided

by

eliminating

part

of

the

floor

system

so

that

the new

reinforcementoftheframewascasttogetherwithslab

Foundation Thefoundationgridwasencasedtopermittheanchorage

tothenewlongitudinalreinforcement


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NECESSITY OF RETROFITTING OF EXISTING MASONRY

BUILDINGS


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Majority of seismically deficient buildings.

Economic considerations & immediate shelter requirements

Earthquake damaged buildings cant be replaced or rebuilt in a shorttime.

Retrofitting schemes depend upon :-

1)Material of parent construction

2) type of masonry

3) location and amount of damage

4) Failure mode


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1) OUT OF PLANE FAILURE:


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Structural walls perpendicular to seismic motion subjected toout-of-plane bending.

vertical cracks at corners andmiddle of walls

CAUSE

Inadequate anchorage of thewall into the roof diaphragm.

Limited tensile strength ofmasonry & mortar

Resulting flexural stress exceedstensile strength of masonry


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3) DIAPHRAGM FAILURE

R h i th t f i i ti


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Rare phenomenon in the event of seismic motion.

Damage to the diaphragm never impairs its gravity load carrying capacity.

CAUSE - Lack of tension anchoring produces a non-bending cantilever

action at the base of the wall resulting from the push of diaphragm against

the wall.

The in-plane rotation of the diaphragm ends and the absence of a

good shear transfer between diaphragms and reacting walls

RESULT - damage at the corners of the wall.

In strengthened buildings, separation remains worse at or near the centerlineof the diaphragm.


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4) FAILURE OF CONNECTION

Seismic inertial forces that originate in all elements of the building are


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Seismic inertial forces that originate in all elements of the building aredelivered to horizontal diaphragms through structural connections.

FORCE DISTRIBUTIONdiaphragms vertical elements foundation.

* transfer in-plane shear stress from the diaphragms to the verticalelements

to provide support to out-of-plan forces on these elements

diagonal cracks disposed on both the walls edges causingseparation and collapse of corner zones.

inadequately strengthened openings near the walls edges and byfloors insufficiently connected to the external walls.


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5) NON-STRUCTURAL COMPONENTS


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These non-structural elements behave like cantilevers if they remainunrestrained and are subjected to greater amplification as compared to groundmotion becoming prone to failures.


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2. Local/Member Retrofitting

It enhances the shear resistance of un-reinforced masonry componentsespecially against in-plane forces


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especially against in plane forces.

Feasible retrofitting techniques are:

(1)surface coatings

(2) Shotcrete overlays or adhered fabric with wire mesh or FRP materials

(3) use of RC and steel frames in openings.


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THROUGH STONES/BOND STONES

"Through" stones of full-length equal to wall thickness may be inserted at an

interval of 0.6 m in vertical direction atI.2m in horizontal direction.


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In the non-availability of full-length stones, stones in pairs each of about3/4 of thewall thickness may be used providing an overlap between them.

use of "S" shape elements of bars 8 to 10 or a hooked link with a cover of 25 mmfrom each face of the wall or wooden bars of size 38 mm x 38 mm cross section orequivalent.


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STRUCTURAL OVERLAY / ADHERED

FABRIC

FRP used for repair and retrofitting

high strength to weight ratio


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high strength to weight ratioStiffness to weight ratiocorrosion resistant

fatigue resistant

Adhered fabric materials - Carbon Fibre Reinforced Plastic (CFRP) sheets

Glass Fibre Reinforced Polymer (GFRP) sheets

latest developments as medium of retrofitting of RC structures.


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CONNECTION BETWEEN INTERSECTING WALLSSTITCHING OF WALL CORNERS


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2) Creation of a composite structure formed by the wood structure and by areinforced concrete thin slab.

Requires complicated operations and the use of resins or special screws, toensure the cooperation between the reinforced concrete slab and the woodgirders.


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PRE-STRESSING

To increase the lateral strength, stability and integrated behavior of load bearing

walls, prestressing is very effective and viable method of retrofitting.


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In prestressing of wall, two steel rods are placed on the two sides of the wall and

tightened by turnbuckles.


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SPLINT AND BANDAGE TECHNIQUE

to strengthen the walls as well as bind them together economically.

The horizontal bands are called bandage while vertical steel are called splints.


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g p

The welded mesh type of steel is to be provided on both outdoor and inner surfaces at

critical sections.

The welded mesh should be nailed to the masonry and then be covered with micro-

concrete.

As a minimum provision these must be provided on all-external walls along with cross-tiebars across the building in both directions and embedded in external bands.

The cross-tie bars are necessary to ensure integral action of bearing walls like a crate.

INSERTING NEW WALLS

To increase strength and to correct deficiency caused due to asymmetry.

The main problem in such modification is the connection of new wall with


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old wall.

The link to the old walls is maintained by means of a number of keysmade in old walls.

EXTERIOR SUPPLEMENTAL ELEMENTS

Provision of shear walls at the perimeter of the building or external buttresses

To increase in-plane strength of the existing masonry walls


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Must have sufficient capacity against overturning forces and uplift forces

Requires an additional foundation

It should have proper connection with the existing walls through dowel so that the

forces are transferred from the existing building to the new external vertical resisting

elements

This technique has limitations in case of buildings constructed at the property lines or

not having much space.

STRENGTHENING OF PARAPETS

* bracing parapets, roofs and connecting floor diaphragms towalls through anchor.


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* parapets with height to thickness ration of less than 2.5 to bestable and in no need of strengthening.

26647449 retrofitting of earthquake affected buildings ppt

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