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Retrofitting of BridgesRetrofitting of Bridges
Technical paper on
a Case Study
By
Saket P Borgaonkar
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Need of RetrofittingN
eed of Retrofitting Upgrading of seismic coefficients as a result
of revised seismic zone
Updating design criteria due to revision ofcode
Bridges not designed to seismic force
Bridges that damaged in earthquakes
Deterioration and aging
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WhyN
ot Demolition and ReconstructionW
hyN
ot Demolition and Reconstruction New structure needs large cost.
New alignment necessitates acquisition of land,
property.
Large quantity of material required for reconstructionthat has to be obtained from nature by destroying itand thus a loss of ecological balance.
New routs add to inconvenience of public and otherliving beings.
The residual utility of old structure goes to waste.
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Methods of Retrofitting
Methods of Retrofitting
SuperStructure
Most common retrofit for superstructures is
installation of unseating prevention devices
Sub Structure
steel jacketing, reinforced concrete
jacketing, FRP jacketing.
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Methods of Retrofitting
Methods of Retrofitting
Bearings. Replacing steel bearings by base isolation bearings.
Bearing seat extension. Provision of stoppers and devices to prevent jumpingof girders.
Abutment.A unique retrofit for tilt of abutments in the frontdirection is to replace some part of the back-fills withexpanded polystyrene (EPS).
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Case StudyCase StudyRetrofitting of the Bridge
across Vishwaganga River
between Malkapur & Nandura
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Salient Features of the BridgeSalient Features of the BridgeYear of construction 1964
Carriageway 7.5 m
Superstructure RCC girder deck system
Substructure CR masonry
Foundation open
No. Of spans 10 spans of 13.72 m,Thickness of deck slab 215 mm
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Salient Features of the BridgeSalient Features of the BridgeNumber of girders
3 main girders at 2.25m c/c with size 300mm
and 1400mm deep and 450 x 300 mm bottomflange and
2 cross girders at 4.40 m c /c
Wearing courseRCC wearing course followed by bituminouswearing course
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History
History
Repairs were carried out twice in 1994
and 2001.
In 1994 mostly cement grouting was
done which could not have served the
purpose.
In 2001, 3 spans were tackled by epoxygrouting, but pot holes to slabs were
not treated.
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Field ObservationsField Observations Considerable holes in deck slab with spalling
of concrete and virtually no bond between
concrete and steel. Reinforcement broken atmany places.
At number of places in bottom bulb of girders,
concrete had not reached due to congestion ofreinforcement & heavy cracks observed ingirders with porous & spalled concrete. Heavyvibrations observed with vehicle movement.
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Field ObservationsField Observations In the bottom surface of cantilever portion,
steel was corroded thereby cracking & spalling
of concrete was observed.
The wearing course was totally damaged withheavy leakages in rainy season thereby further
damaging deck slab.
Weep holes provided for draining of rain waterover the bridge had been blocked.
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Span wise visual observationsSpan wise visual observationsSPAN MAIN GIRDERS DECK SLAB CANTILEVERS
Span 1(N) Crack Honey
Combing
Mapping Cracks Corroded Reinforcement
Span 2 MinorHoney
Combing
Mapping Cracks Corroded Reinforcement
Span 3 Cracked Holes Corroded Reinforcement
Span 4 Cracked Concrete Spalling Corroded Reinforcement
Span 5 Cracked MinorHoles Repaired but No Bond with Old
Concrete
Span 6 Steel Exposed
Cracked
Holes Developed Repaired but No Bond with Old
ConcreteSpan 7 Minor Cracks Severally Damaged Corroded Reinforcement
Span 8 Slightly Damaged Holes Developed Corroded Reinforcement
Span 9 Ok Concrete Spalling Corroded Reinforcement
Span 10 Cracked Concrete Spalling Corroded and Spall
ing
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Non Destructive TestsNon Destructive Tests
To decide exact strength of existingconcrete ultrasonic testing and
rebound hammer testing of girders wascarried out.
Concrete found to be porous with
pulse velocity from 2.5 to 3.0 km/sec.
Rebound hammer test indicated
average strength of about 14.0 N/mm2
.
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Restoration MeasuresRestoration Measures
The quality of concrete was insufficientin strength to withstand dynamic loads
resulting from movement of very heavyvehicles. As a matter of fact due to holesin deck slab, cracks in girders a totalretrofitting was necessary to enhancethe life of structure.
the retrofitting work was divided inseveral activities member wise.
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Restoration MeasuresRestoration Measures
Main and cross Girders
Girders were strengthenedby injecting low viscous
epoxy grout (SLV grout).Holes were drilled at 150 mmc/c along the cracks byelectric drill and nipples,then cracks were sealedwith epoxy patchingcompound. After grouting,welded mesh was fixed togirders & entire girders were
shotcreted.
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Restoration MeasuresRestoration Measures
Deck Slab
For portion where Reinforcedsteel was broken, loose
concrete of wearing courseand deck slab was removed.Additional reinforcement waswelded to girder reinforcement.Anticorrosive coating was
applied to rebar. super fluidmicro concrete was pouredwith 3 days compressivestrength of 250 kg/cm2
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Restoration MeasuresRestoration Measures
Cantilever
The loose cover concrete wasremoved by chisel. Near
corroded reinforcement EPCOKP 100 was applied along theexposed concrete surface. Theexposed and corroded steelwas cleaned with wire brush
and the bars were coated withIPN BR as anticorrosivecoating. The welded meshwas fixed. EPI bond epoxy was
applied and the surface wasshotcreted 50 mm thick.
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Restoration MeasuresRestoration Measures
Wearing Coat
The Wearing Coat was removed from half
portion i.e. one lane up to deck slab. Holeswere drilled @ 1000 c/c and grouted with
polymer grout. The removed wearing course
was redone with M 35 with superplisizers,
micro silica and polypropelene fibers.
The entire lane was relaid with bituminous
concrete.
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ConclusionConclusion
The girders, which were cracked severely haveshown improvement through out section ofgirder. Integrity of girder and strain carrying
capacity has shown significant improvementwith vibrations reduced to great extent.
The effectiveness of restoration process wasascertained by same NDT techniques.
The average velocity was 3.75 km/s withimprovement of 25 to 30% and concrete qualitywas good.
The average compressive strength was 25.0
N/mm2
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