Repair, Restoration & Retrofitting of Masonry Buildings in Kachchh Earthquake Affected Areas
26647449 Retrofitting of Earthquake Affected Buildings Ppt
Transcript of 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
RetrofittingTechniquesEmployed
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.
RetrofittingTechniquesEmployed
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.