Vol. 4(6), pp. 174-183, June, 2013 DOI: 10.5897/JCECT2013.0283
ISSN 1991-637X 2013 Academic Journals
http://www.academicjournals.org/JECET Journal of Civil Engineering
ConstructionTechnology Full length Research Paper Simplified method
of strengthening RC continuous T beam in the hogging zone using
carbon fiber reinforced polymer laminate A numerical investigation
Muhammad Mukhlesur Rahman* and Md. Waliur Rahman Eastern Bangladesh
Bridge Improvement Project, Room No-601, Shetu Bhaban, Chairman
Bari, Dhaka-1212. Accepted 20 June 2013
ThoughReinforcedConcrete(RC)continuousbeamsarevastlyusedincivilengineering,little
experimentalworkonrepairingandstrengtheningofcontinuousTbeamshasbeencarriedout;
especially, experiments on strengthening the hogging zone of
continuous T beams are very rare. This paper attempts to address an
important practical issue which is not considered in existing
conventional strengthening technique that is, the installation
constrains due to the presence of column. This paper
alsopresentsastraightforwardtechniqueofapplyingCFRPlaminateforstrengtheningthehogging
zone of continuous T beam considering the constrains caused by the
column. The beams are modelled using FEM (LUSAS). Existing two
well-known research works on strengthening continuous beams are
alsomodelledusingthisFEMascasestudy,whereagoodagreementbetweenthetestresultsand
resultsfromFEMisobserved.Finally,itisconcludedthattheproposedmethodisveryeasyand
effective,andforobtainingcompletedesignguidelineforstrengtheningTbeam;future
recommendations are also visualized through this paper. Key words:
Carbon fiber, strengthening, hogging zone, continuous beam,
numerical investigation. INTRODUCTION
Concretestructurescanbecomedeficientduringtheir
servicelifeandmayrequirestrengtheningandrepair.
Thisneedmayariseduetodesign,constructionerrors,
functionalchanges,designcodesupdates,damage
accumulatedovertimeorcausedbyaccidental
overloading,fires,orearthquakes.Sincereplacementof
deficientstructuresrequireshugeinvestments, strengthening has
become the suitable way for improving
theirloadcarryingcapacityandprolongingtheirservice
life.Whilecompletereplacementofadeficient/
deterioratedstructureisadesirableoption,
strengthening/repairisoftenthemoreeconomicalone.
Whilemanymethodsofstrengtheningstructuresare
available,strengtheningstructuresviaexternalbonding of
advancedfiber-reinforcedpolymercomposite(FRP) has become very
popular worldwide. In the past decade,
theirapplicationinthisfieldhasbeenrisingduetothe
well-knownadvantagesofFRPcompositesoverother
materials.Consequently,agreatquantityofresearch,
bothexperimentalandtheoretical,hasbeenconducted
onthebehaviourofFRPstrengthenedreinforced
concrete(RC)structures,includingbeams,slabs,and
columns(Tengetal.,2002).Inthisregard,theevolving
technologyofusingcarbon-bondedfibrereinforced polymers (CFRP), for
strengthening simply supported RC
beams,hasattractedmuchattentioninrecentyears.
Fibrereinforcedpolymermaterials(FRP)suchas pultrudedplates,
fabrics,andsheetshavebeenusedas
strengtheningmaterialsforRCbeams.Inparticular,their practical
implementationsforflexuralstrengtheningare *Corresponding author.
E-mail: [email protected], [email protected].
numerous(Lietal.,2008;Camataetal.,2007;Toutanji et al., 2006;
Bencardino et al., 2002; Arduini et al., 1997;
Nanni,1995;Chajesetal.,1994;Saadatmaneshetal., 1991).
Failuremechanismsinexperimentaltestswere
reportedbyTengetal.(2002).DelaminationandFRP
laminateseparationcansignificantlylimitthe
enhancementpropertyandtheultimateflexuralcapacity of the
retrofitted beams. Several studies were conducted
toidentifymethodsofpreventingprematurefailurewith the aim of
improving the load capacity and ductility of RC
beams.Researchersstudiedtheuseofendanchorage
techniques,suchasU-straps,L-shapejacketsandsteel
clampsforpreventingprematurefailureofRCbeams strengthened with FRP
sheets ( Jumaat and Alam, 2008;
Xiongetal.,2007;PhamandAl-Mahaidi,2006).Itis seenthatmostofthe
conductedexperimentsto validate
thedesignmethodologyforFRPflexuralstrengthening,
consistofrectangularorT-beamsonwhichthe
strengtheningwasappliedtothesaggingregionofthe
member.Generally,theresearcheswereconductedon
RCrectangularsectionswhicharenotrepresentative because most RC
beams would have a T- Section due to the presence of a top slab.
PREVIOUS RESEARCHES ON CONTINUOUS BEAMS
Althoughseveralresearchstudieshavebeenconducted
onthestrengtheningandrepairofsimplysupported
reinforcedconcretebeamsusingexternalplates,there are few reported
works on the behaviour of strengthened
continuousbeams.Inaddition,mostdesignguidelines
havebeendevelopedforsimplesupportedbeamswith
externalFRPlaminates(JSCE,2001,ConcreteSociety
2000,TR55,ACI440R-1996).Anexhaustiveliterature review revealed that
a minimum amount of research work
hadbeendoneforaddressingthepossibilityof
strengtheningthehoggingzoneofcontinuousbeam using FRP materials. On
the field of strengthened continuous beam, Grace et
al.(1999)testedfivecontinuousbeams.Later,Graceet al. (2001) also
investigated the experimental performance
ofCFRPstripsusedforflexuralstrengtheninginthe
hoggingregionofafull-scalereinforcedconcretebeam.
Graceetal.(2005)alsoworkedonanotherresearch where three continuous
beams were tested. On the other
hand,El-Refaieetal.(2003a)examinedeleven
reinforcedconcrete(RC)two-spanbeamsstrengthened in flexure with
external bonded CFRP sheets. In another
research,El-Refaieetal.(2003b)testedfivereinforced
concretecontinuousbeamsstrengthenedinflexurewith external CFRP
laminates. Ashour et al. (2004) tested16 reinforced concrete (RC)
continuous beams with different
arrangementsofinternalsteelbarsandexternalCFRP
laminates.Aielloetal.(2007)comparedthebehaviour between continuous
RC beams strengthenedwith CFRP sheets
athoggingorsaggingregionsandRCbeams Rahman and Rahman175
strengthened at both sagging and hogging regions.
Recently,Maghsoudietal.(2008)examinedthe
flexuralbehaviourandmomentredistributionof
reinforcedhighstrengthconcrete(RHSC)continuous beams strengthened
with CFRP. Finally, Akbarzadeh and Maghsoudi (2010) conducted an
experimental program to study the flexural behaviour and moment
redistribution of reinforcedhighstrengthconcrete(RHSC)continuous
beams strengthened with CFRP and GFRP sheets. In all the above
cases it is seen that all the researches
wereconductedonRCrectangularsectionswhichare not representative of
the fact that most RC beams would have a T- Section due to the
presence of a top slab. In all
theabovecases,theconstraintsduetothecolumnsin
theapplicationofthestrengtheningsystemwerenot considered.
PROBLEMSOFSTRENGTHENINGTHEHOGGING ZONE OF CONTINUOUS T BEAM
Thehoggingzone,namelythesupportregion,of
continuousreinforcedconcrete(RC)beamsisacritical
zoneduetothesimultaneousoccurrenceofmaximum moment and shear. In
addition, the presence of columns
andothercomponentssuchaselectricandplumbing
linesorHVACductsmakedifficulttostrengthenthis
regionusingconventionaltechniques,likesteelplate bonding, section
enlargement, external stirrups etc. In the hogging zone, the
strengthening is not as simple as in the
caseofsaggingzonebecausethecolumnspreventthe
applicationofFRPsystemoverthewebportionofthe
beam.Anotherimportantpointisthat,theuseofthick steel plates bonded
to the floor surface will raise the floor level, which might be
undesirable. PROPOSEDMETHODOFSTRENGTHENINGTHEHOGGING ZONE OF T BEAM
Toovercometheproblemsofstrengtheningthehoggingzoneof
continuousTbeam,anewmethodisproposedinFigure1.Inthis
proposedmethod,CFRPisappliedonbothsidesofthecolumn
accordingtoFigure1.ThismethodofapplyingCFRPwillbeeasy
toimplementinexistingconcretestructures.Inthiscontext,dueto its
high strength ratio and ease of installation, CFRP can be used to
provideaneconomicalandversatilesolutionforextendingthe service life
of concrete structures. FEM MODELLING FOR THE PROPOSED METHOD
Discretization Afiniteelementprogram(LUSAS)isusedtoinvestigatethe
structural behavior of continuous T beam. Two beams are modeled.
Thefirstoneiscontrol,thatis,devoidofstrengtheningwhilethe
secondoneisstrengthenedwithCFRPlaminate.Thesteminthe
strengthenedbeamisrepresentingthecolumnandtheloading arrangement is
madein sucha way that the flangeportionof theT
beamisintensiontorepresentthepracticalsituation.The
superpositionofnodaldegreesoffreedomassumesthatthe concrete and
reinforcement are perfectly bonded. It is assumed that 176J. Civ.
Eng. Constr. Technol. CFRP CFRP stum
Figure1.MethodofapplyingCFRPinthehoggingzoneof continuous T beam.
150 mm 225 mm 1002 #16 mm 380 mm 2 #12 mm Figure 2. Crosssection of
the beam. XYZ Figure 3. Meshing for control beam. XYZ Figure 4.
Loading pattern for control beam. XYZ Figure 5. Deformed mesh of
control beam. the self-weightof thebeamis negligible comparedwith
theapplied load and that the effects of any shear reinforcement can
be ignored. CFRP surface elements are attached to the surface of
the concrete
directlyandperfectbondingbetweenstrengtheningplateandthe concrete
surfaceisassumed toavoid prematuredebonding failure.
TheconcreteaswellasCFRPsectionisrepresentedbyplane
stress(QPM8)elements,andthereinforcementbarsare represented by bar
(BAR3) elements. A nonlinear concrete cracking
materialmodel(crackingmodel94)isappliedtotheplanestress
elementsandavonMiscesplasticmaterialisappliedtothe reinforcement
bars. Units of N, mm, t, s, C are used throughout. Control beam,
strengthened beam and material properties Detailsof the
controlbeamare shownin Figures 2 to 6; thatofthe
strengthenedbeamareshowninFigures7to9;andmaterial
propertiesofconcretebeamfornumericalmodelingareshownin Table 1.
RESULTS OF FEM AND CASE STUDY The results obtained from the FEM are
shown in Table 2. Tovalidatetheproposedmodel(casestudy),eight
continuous beams based on previous research works are
modeledandtheresultsobtained from the modeling are
comparedwiththeirexperimentalresults.Thefollowing are the
description of FEM of previously tested beams by other researchers:
Continuous beams testing
DetailsofcontinuousbeamstestedbyAkbarzadehand
Maghsoudi(2010)areshowninFigures10to15and Table 3; and that tested
by El-Refaie et al. (2003a, b) are shown in Figures 16 to 18 and
Table 4. DISCUSSION Comparison and comments on results
TestresultsandFEMresultsarecomparedinTable5.
FromTable2,itisseenthat58%loadincrementis
possiblebythisproposedmethodofapplyingCFRPfor
strengtheningthehoggingzoneofcontinuousTbeam. From
thecasestudyweobserveagoodrelationshipRahman and Rahman177 Figure
6. Load versus Deflection graph of control beam. XYZ Figure 7.
Meshing for strengthened beam. XYZ Figure 8. Deformed mesh of
strengthened beam. between the experimental results and the FEM
results. It canbeconcludedthattheproposedmethodofapplying
CFRPforstrengtheningthecontinuousTbeamsinthe hogging zone is very
effective, efficient and easy. FUTURE NEEDS AND CONCLUSION
AreviewonexistingresearchworksshowsthatstrengtheningRCcontinuousbeams,especially
continuous T beam is still in itsinfancy.Theparameters such as
effective length, width, thickness and appropriate
anchoragesystemofCFRPforstrengtheningRC
continuousTbeamsareintheneedofextensive
research.Inotherwords,toprepareacompletedesign
guidelineforstrengtheningRCcontinuousTbeamwith CFRP, further
research is necessary.
Thispapermodelledtwoexistingwell-knownresearch
worksoncontinuousRCbeamsstrengthenedbyCFRP.
Itaddressedanimportantpracticalissueon strengthening the hogging
ofRCcontinuous Tbeam.A178J. Civ. Eng. Constr. Technol. Figure 9.
Load versus Deflection graph of strengthened beam. Table 1.
Material properties of concrete beam used for numerical modeling.
ConcreteSteel barStrengthening plate Span of the beam (m) f/c
(MPa)Ec(MPa)Poisson ratiofy (MPa)Es(MPa)Poisson ratioEp(MPa)Poisson
ratio 40300000.25602000000.31650000.43.3 Figure 10. Details of
beams tested by Akbarzadeh and Maghsoudi (2010). Rahman and
Rahman179 Table 2. Results from FEM. SpecimenUltimate load
(KN)Increase over control beam (%) Control beam75 58 Strengthened
beam119 XYZ Figure 11. Meshing and loading pattern of beams. Figure
12. Load versus Deflection graph of beam CB. Figure 13. Load versus
Deflection graph of beam SC1. 180J. Civ. Eng. Constr. Technol.
Figure 14. Load versus Deflection graph of beam SC3. Figure 15.
Load versus Deflection graph of beam E1. Table 3. Material
properties of the beam tested by Akbarzadeh and Maghsoudi (2010).
Beam no. f/c (MPa) fy (MPa) Type of FRP Positive moment
strengthening Negative moment strengthening Thickness of each layer
(mm) Width of CFRP (mm) Youngs Modulus of FRP Ef(MPa) No. of layers
Strengthened length(m) No. of layers Strengthened length(m) CB74.2
412.5 -0 2.20 0 1.80.11145242000 SC174.6CFRP11 SC274.1CFRP22
SC374.4CFRP33 Rahman and Rahman181 Figure 16. Load versus
Deflection graph of beam E2. Figure 17. Load versus Deflection
graph of beam E3. Table 4. Material properties of the beam tested
by S.A. Ei-Refaie, A.F. Ashour and S.W. Garrity, 2003. Beam no f/c
(MPa) fy (MPa) Type of FRP Positive moment strengthening Negative
moment strengthening Thickness of each layer (mm) Width of CFRP
(mm) Youngs Modulus of FRP Ef(MPa) No. of layers Strengthened
length (m) No. of layers Strengthened length (m) E124.0 520 -0-0-
1.2100150000 E243.6CFRP0-12500 E347.8CFRP135000-
E446.1CFRP1350012500 182J. Civ. Eng. Constr. Technol. Figure 18.
Load versus Deflection graph of beam E4. Table 5. Comparison
between experimental results and FEM results. Beam no. Ultimate
load FEM (KN)Experimental (KN) CB163162 SC1185190.6 SC2220219.3
SC3250259.3 E1132129.67 E2162178.67 E3183207.06 E4205231.42
simplemethodofapplyingCFRPforstrengtheningthe
hoggingzoneofRCcontinuousTbeamisproposedin
thispaperanditsappropriatenessisvisualizedthrough
FEMandcasestudies.TheFEMthusverifiedthe
proposedmethodofapplyingCFRPtostrengthenthe
hoggingzoneofconcreteTbeam.Itfurtherprovesthat
thismethodofstrengtheningissuitableforpractical application.
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