HCB Bridge Inspection · PDF fileThe Hillman-Composite Beam ... To date this has never been seen on an HCB laminate ... HCB®Bridge Inspection Guidelines 9

BUILDBETTERHCB,Inc. www.HCBridge.comChicago,IL|Raleigh,NC|Atlanta,GA v1.2–Apr.2016

HCB® BridgeInspectionGuidelines

HCB®BridgeInspectionGuidelines 2

TABLEOFCONTENTS1. Introduction...................................................................................................................................3

2. WhatisanHCB®?..........................................................................................................................42.1 Components...........................................................................................................................................42.2 HowitWorks.........................................................................................................................................5

3. InspectionAndRating.................................................................................................................63.1 InspectionMethods.............................................................................................................................63.2 DeterminationofRatingforaHCB..............................................................................................11

4. Summary.......................................................................................................................................14


1. IntroductionThe Hillman-Composite Beam (HCB®) was invented in the 1990’s by acclaimed bridgeengineer,Mr. JohnHillman, PE, SE. TheHCB canbe thought of as a reinforced concretebeam that is enhanced with a fiber reinforced polymer (FRP) shell. This documentprovidesageneralguideforengineersandinspectorstotheinspectionofastructurebuiltwithHCBs.Additionally,itcontainsasuggestedmethodforconditionratingbridgesona0–9scaleconsistentwiththeNationalBridgeInspectionStandards(NBIS)ratingscaleusedfor bridges made with concrete, steel or wood. Since state specifications, local siteconditionsandotheruniquecharacteristicscanaffecttheratingofastructure;theownerwill likely develop more specific guidelines for rating and inspection of their HCBstructures.If youdohave anyquestions about theHCBor inspecting a structurewithHCBs, pleasevisitourwebsiteatwww.hcbridge.comorcontactourstaff.


2. WhatisanHCB®?2.1 ComponentsThe HCB comprises concrete, steel and fiber reinforced polymer components actingtogetherasatiedarchtoformanefficientstructuralmemberthatbehaveslikeareinforcedconcretebeam.Themaincomponentsare:

Figure1-HCBAnnotatedFragmentaryPerspective

• Fiber-Reinforced Polymer Shell (FRP) – this holds the tension and

compression reinforcement, provides some shear and tensile capacity andprovidesabarriertocorrosiveelements.Theshellmayalsohaveflangesthatactasdeckforms.

• Tension Reinforcement – this usually consists of galvanized 270 ksi low-relaxationprestressingstrandthatisencapsulatedwithintheFRPshell.

• CompressionReinforcement– this is thearchprofile that is filledwith self-consolidatingconcrete.

• Shear Connectors – these are usually galvanized rebars that tie the archcomponent of the beam to the concrete deck in the same manner as aconventionalprestressedconcretebeamorsteelbeamstructure.

The fragmentary perspective in Figure 1 provides a schematic of these components.

What is the HCB? �Tied Arch in A Fiberglass Box� A structural member using several different building materials resulting in a cost effective composite beam designed to be stronger, lighter, and more corrosion resistant !  Compression Arch - SCC Concrete !  Tension Reinforcement - Galvanized P/S Strand - Fiberglass Cloth !  FRP Shell !  Galvanized Shear Connectors

Tension Reinforcement - Galvanized P/S Strand - Fiberglass Cloth

FRP Shell

Compression Arch

Shear Connectors


2.2 HowitWorksTheHCBworks as a tied arch system. When a beam is fabricated, the required tensionreinforcementis“infused”intothebottomflangeoftheFRPshell.Oncetheshellsarefilledwithconcrete,thebeamactssimilartoareinforcedconcretebeam.Whenaloadisplacedonthebeam,theloadisthentransferredtothecompressionreinforcement(concretearch)that tends to push the arch out at it ends. This force is equilibrated by the tensionreinforcement in the bottom flange resisting the thrust of the arch. If the beam ismadecompositewiththedeckthroughtheuseofshearconnectorsthenthedeckalsoactsasacompression flange to balance the tension in the bottom flange as in a conventionalstructure.CharacteristicsofHCBsandtheircomponents.

• FRPsareverystrong,resilientandflexible. Theycanbehandledwithslingsorcablesandwon’tspalllikeconcreteordeformlikeasteelbeamflange.

• While prestressing strands are used, they are not prestressed in thetraditionalmanner.Theonlyprestressinthestrandsisduetotheplacementof the compression reinforcement and concrete deck. The strands aregalvanized to provide an extra level of corrosion protection and arecompletelyencapsulatedinthesameresinusedtofabricatetheFRPshell.

• SinceFRP’sareflexible,itcanbedifficultfortheFRPshellalonetomeetthedeflectionrequirementsofthebridgecodes. Usuallyhalfoftheprestressingstrandsinthebottomflangeareprovidedtofacilitatetherequiredstiffnesstothestructuretosatisfyliveloaddeflectioncriteria.

• Self-ConsolidatingConcrete(SCC)isahigh-performanceconcretewidelyusedintheprecastindustryandsuppliedbyseveralready-mixsuppliers.Byusingappropriateadmixtures,aflowableconcretewithalowwater-cementratioiscreated.Insteadofthetraditionalslump,aspreadismeasuredtodeterminetheappropriateflowofabatch.TypicalspreadmeasurementsusedforHCBsare28”to32”.


3. InspectionAndRatingQuestionsoftenariseastomethodsforinspectionandratingoftheHCBduetotheuniqueembodiment that includes concrete, steel and FRP components. In addition to theguidelinescontainedherein,agoodreferenceisNCHRPReport564,FieldInspectionofIn-Service FRP Bridge Decks (Telang, et.al., 2006). Although the FRP decks and bridgeelementsaddressed in this reportaremoreconsistentwithhomogenousFRPstructures,many of the NDE techniques discussed and explanations of characteristics of FRPperformanceareapplicabletotheHCB.

3.1 InspectionMethodsIntermsofinspectionofhighwaybridges,federallawsmandatethatbiennialinspectionsbeperformedforallbridgesontheNationalBridgeInventory(NBI).Differentstatesmayhave different forms and processes that are incorporated as part of these inspections,howevermost followrecommendationscontained inTheManualforConditionEvaluationof Bridgespublished by the American Association of State Highway and TransportationOfficials(AASHTO).Duetothefactthatcompositebridgecomponentshaveonlyrecentlyfound their way into the NBI, limited information has been available in the past forpurposesofinspectingthesetypesofbridges.Although composite structuresmanufactured frompultrudedFRP’s havebeen in serviceforover thirtyyears, the firstall compositevehicularbridgeswerenot really introduceduntil around1994. Since that time, nearly one-hundredbridgesutilizingFRP compositedecksof various typeshavebeen constructed in theUnitedStates. Itwas the long-termmonitoring and evaluation of these bridges that prompted the National CooperativeHighway Research Program (NCHRP) to commission a study related to this subject,resultinginNCHRPReport564.This study was focused on composite bridge decks, however the characteristics of, andconstituent properties of someof thedecks investigated are very similar to those of theHCB.Subsequently,mostoftheinformationinthereportisequallyapplicabletotheHCB.Inadditiontoinspectionandmaintenanceissues,NCHRPReport564servesasanexcellentreferenceprovidinganoverviewofcompositemanufacturing forbridgerelatedproductsand somewhat of an anthology of composite bridge construction to the date it waspublished.The NCHRP report also contains useful information regarding suggested forms forsummarizinginspectiondatawhenevaluatingcompositebridgedecksaswellasabridgecondition rating table that categorizes the severity of the condition of the bridgecomponents on a scale from 0 to 9, consistent with condition ratings for conventionalbridge components as outlined in the Recording and Coding Guide for the StructuresInventoryandAppraisaloftheNation’sBridgesaspublishedbyFHWA.

1.1InspectionMethods(Continued)


In order to effectively utilize the information in NCHRP Report 564 it is worth notingparticulartypesofdamagesanddefectsforwhichtheHCBmaybeprone. Tothisextent,Report 564 is primarily useful only in evaluating the FRP components of the HCB. TheothercomponentsincludingtheinternalarchconcreteandtheembeddedsteelreinforcingarenotaddressedintheReport564.FRPLaminates:ThepotentialFRPdamagetypessuggestedinNCHRPReport564includethe following list. Comments specific to theHCBhavebeen interjected to provide someguidancetotheinspector.

• Blistering:TodatethishasneverbeenseenonanHCBlaminate,butmightbemoreevidentonanHCBhavingagelcoatorintumescentpaintapplication.

• Voids:TodatevoidsinthelaminatehavenotbeenevidentinHCBunits.Ingeneral,

thelaminatesontheHCBareverythin,providinglessopportunityforvoidsduringmanufacturing.Thevacuumassistedresintransfermolding,orVARTMprocessalsoresultsinhighfibervolumeratiosandconsequentlytheselaminatesarelesspronetovoidsthancompositesmanufacturedusingotherprocesses.

• Discoloration: When pigments are used in the resin, it is difficult to detect

discolorationoftheresinsinthenewHCB.Thistypeofdamagewilllikelybemoreevidentwithtime,suchaschalkiness,yellowingorlighteningofthecolorduetoUVexposure. This discoloration itself should not be an indication of a problemrequiring mitigation, but may warrant remediation if cracking of the laminatebecomesevident.Cosmeticrepairscanbemadeusingmarinefairingcompoundsorgelcoatstofillthecracks.

• Cracks: Aswithconcrete,crackinginanFRPlaminatecanbequalifiedindifferent

levelsofseverity.Ifthecracksaresmallanddonotseemtopropagateorincreaseinseverity,noremediationmaybenecessary.Forcosmeticrepairs,marinefairingcompoundsorgelcoatsmaybeapplied.Ifthecracksappeartobemoreanalogoustotearingordelamination,seethediscussionbelow.



• Delaminationofthelaminatefromthefoamcore: Delaminationshavebeenevidentin laboratory testing of HCBs, but typically at loads well in excess of factoreddemand.Thetypesofdelaminationobservedinlaboratorytestinggenerallyrelatesto thedebondingof theweb laminate from the interiorpolyiso foamcore. Thesetypes of delamination appeared to be the result of high shear loadings causingtension field action in the webs and have usually been obvious from visualobservationsand typically followa45-degreeangle fromthe top to thebottomofthebeam(seeFigure2). Asthewebsexhibitelasticbucklinginshear,portionsofthe web can delaminate from the foam. This does not necessarily indicate acompromise in the beam capacity. Furthermore, there may be other causes ofdelaminationresulting fromexterior traumato thebeam. Regardless, if it isclearthat the foamhasdelaminated fromthe laminate, restoring thebondbetween thecomponentsorfillingthevoidbetweenthelaminateandthefoammaybedesirable.

Figure2-DelaminationofWebsfromFoamCoreDuetoTensionFieldAction

If the delamination appears to be of greater severity, e.g. if there is a clearseparationof laminate layersorsufficientseparation to facilitatemoisture ingressintothelaminateitselfamoresubstantialrepairmaybewarranted.Thesetypesofrepairs may require the services of a specialty consultant/contractor. PleasecontactHCB,Inc.ifthesetypesofseveredelaminationarediscovered.

• PresenceofMoisture: FRP laminates are subject tomoisture absorption. For the

mostpart,theFRPlaminatesintheHCBoperateatverylowstrainlevels(typicallyon the order of 10% of ultimate strain). These low strain levels result in lessprobabilityofmicrocrackinginthematrixandreducedabsorptionrates.Ifthereisevidenceof increasedpropagationofcracking, itmaybenecessarytoevaluatetheneedforapplyingagelcoattotheexterioroftheHCBasamoisturebarrier.



• Abrasionortearing: This typeof damage is not anticipatedundernormal serviceoperations.Howeverthistypeofdamagemightoccurduetoisolatedincidentsthatcould result from stream flows at highwater levels or from impact fromvehiclesbelow thebridge. If there is any concernabout lossof sectionor capacity, repairmethodssuchasthosefoundinACI440orothersourcesshouldbeinvestigatedtostrengthentheHCBasneeded.

• CreepfloworCreeprupture:Asthestiffnessoftheconcreteandsteelcomponentsis

very high compared to the FRP laminates, the sustained loads and subsequentstresses on the FRP laminates are very low. Subsequently, creep flow or creeprupturearehighlyunlikely. Oneexceptiontothisiswherethetensionreinforcingmight be limited to glass reinforcing. In this case the sustaineddead loadon thetensionreinforcingshouldbelimitedto25%oftheultimatestrainofthelaminate.This is a generally accepted limit state to mitigate creep rupture in an FRPcomponent.Historically,incaseswhereglasshasbeenusedastheprimarytensionreinforcingoftheHCB,thiscriteriahasbeenevaluatedcarefullyinthedesign.

NCHRP Report 564 also includes a short list of Non-Destructive Evaluation (NDE)techniques for evaluation of the laminate and the HCB in general. These test methodsincludethefollowing:

• Visualinspectionandtesting• Taptesting• Thermaltesting• Acoustictesting• Ultrasonictesting• Radiography• Modal-parameteranalysis

As noted in the NCHRP report, the final five methods list above can be fairly costly orcomplicated. Formanyof the laminatedamage typesnotedabove, thevisual inspectionand the tap test techniquesmaybemore thanadequatemostof the time. However, theFRPlaminateisonlyonecomponentoftheHCB.Theothercriticalcomponentsincludethearchconcreteandthesteeltensionreinforcing.Likeaconcretebeam,thesteelreinforcingintheHCBisnotvisibletothenakedeye.Asaresult, there is always some concern about the condition evaluation of this component.Likewise,theconcretearchisnotvisibleeither.Neitherthetaptestnorvisualinspectionprovidesmuchguidance in conditionevaluationof these twocomponents. For themostpart, the simple visual and tap test techniques should be sufficient for routine biennialinspections.Itisrecommendedthatattheendoftenyearsofservicelife,oneofthemoresophisticatedNDE techniques be employed to determine if there is any deterioration ordamagetotheinternalcomponentsoftheHCB.



Another NDE technique that is becoming more common in the construction industry is“Ground Penetrating Radar” (GPR). This type of technology is used for a multitude ofpurposes, including location and condition evaluation of reinforcing steel and post-tensioningtendonsaswellaslocationofvoidsinpost-tensioninggrout.Itisalsobecomingmore popular as a technique for finding voids in concrete and condition evaluation ofconcrete. Although still more expensive than visual inspection and tap testing, thistechnologyisbecomingmorereadilyavailableandmaybewarrantedforamorethoroughinvestigationthanwouldbeconductedunderanormalbiennialinspection.Again,thetensionsteelisprotectedbyseveralbarriersincluding;nolessthan¼”ofhighqualityFRP laminate, completeencasement in thesamevinylester resinas the laminateandagalvanizedcoating.Further,asnotedbefore,thequantityofsteelistypicallyontheorderoftwicethatrequiredforultimatebendingcapacity. Likewise,theconcretearchisalmostalwaysincompressionandiscompletelyencapsulated. Withproperplacementoftheconcreteduringconstruction,itisnotlikelythattherewillbeanydegradationofthesecomponentsundernormalserviceoperations.


3.2 DeterminationofRatingforaHCBAs stated before, due to the relative newness of the HCB structures and the anticipateddurabilityof thematerials,astatisticaldatabaseofdamageordeteriorationforassessingthe condition ratingof thisportionof thebridge superstructure is slowlyemergingwithtime. Regardless, it is important to provide the inspectorwith some type of guidance inassessingtheconditionoftheHCBtodetermineaconsistentratingas isdonewithothertypesof bridge subcomponents.The following is to serve as a guideline to the inspectorwithrespecttodeterminationoftheconditionratingconsistentwithanNBISratingscalerangingfrom0to9.Itshouldbenotedthatthecurrentconditionratingispurelybasedonthe current understanding of the performance of the HCB and the FRP materialscomprising the beams. It is also based on speculation of what types of damage and ordegradationmightresultovertimeandhowthesemightrelatetosimilarratingsforothertypesofmaterialsusedinbridgesuperstructures.Theinspectorshouldexercisetheproperstandard of care in the assessment of the condition ratings and be cognizant of thelikelihoodthatovertimetheseconditionassessmentsmayneedtobecalibratedbasedonobserved and documented performance of theHCB through the years. Additionally, theratingsmaybechangedbytheownerbasedontheirownrequirements.Rating9: ExcellentCondition.

A. Nodeficienciesnoted.Rating8: VeryGoodCondition.Potentialexistsforminorpreventivemaintenance.

A. No noticeable or noteworthy deficiencies that affect the condition of thesuperstructure.

B. Insignificantcosmeticblemishes.Rating7: GoodCondition.Potentialexistsforminormaintenance.

A. Minor cracking in laminate matrix evident in the surface either from UVexposure,weatherrelateddamageorimpact.

B. Abrasionor scratcheson the surfaceof the laminate,butdonotpenetrate thefibers.

C. Smallholesinthelaminateduetoimpactorvandalism(e.g.bulletholes).D. Blisteringornoticeablebubblesonthesurfaceorgelcoatwhereapplied.E. Flakingorpeelingofthegelcoatorpaintcoating.F. Minor concrete cracking in the cast-in-place diaphragms at piers and/or

abutments.G. Normal undulations or mounds seen on the webs of the FRP shell consistent

withtensionfieldaction(TFA)anticipatedtoresistshearinthebeams.

1.2DeterminationofRating(Continued)


Rating6: SatisfactoryCondition:Potentialexistsformajormaintenance.

A. Cracking and/or damage to the laminate with no evidence of damage ordeteriorationofthesteelstrandsinthetensionreinforcement.

B. AbnormalundulationsormoundsseenontheotherwiseflatsurfaceoftheFRPsurfacesontheHCB.

C. Thepresenceofmoisturestainsontheunderside,awayfromthedeckinterfacewithnovisiblepathforwatercollection.Thiscouldbeasignofporosityinthelaminate.

D. Heavy leaching through concrete diaphragms at girder encasement of integralbents.

Rating5: FairCondition: Potentialexistsforminorrehabilitation.Noaffectonstructuralcapacity.

A. Significantdelamination(s)ofFRPfromfoamcore.B. Exposureofsteeltensionreinforcementorconcretecompressionreinforcement

throughthelaminate.C. AbrasionorscratchesintheFRPlaminateresultinginexposureoforseveringof

glassfibers.D. CollisionorimpactdamagetoFRPlaminates.E. Considerable open cracking of concrete diaphragms at girder encasement of

integralbents.F. EvidenceoftearingoftheFRPlaminatealongsurfacesoratcorners.

Rating4: Poor Condition: Potential exists formajor rehabilitation. Some affect on load

capacity.Blockingorshoringmayberequiredasprecautionarymeasure.

A. Evidenceofrustorsignificantexposureofthesteeltensionreinforcement.B. Evidence of significant deterioration or crushing of the concrete compression

reinforcement.C. Collision or impact damage resulting in large tears or penetrations of the FRP

laminate, severing of tension or compression reinforcement, or any visiblyevidentsignificantdistortionsinthegeometryoftheHCBshell.

D. Rust or spalling of concrete at the anchorage zones of the beam or in theconcretediaphragmsatgirderencasementofintegralbents.

E. Sectionlossofthelaminateduetoexposuretofire.

Rating3: SeriousCondition:Repairorrehabilitationrequiredimmediately.

A. AnyconditiondescribedinRating4,whichisofaseveremagnitudeorforwhichblocking,shoringorloadrestrictionsarenecessary.

B. Excessivedeflectionsevidentinthebeams.

1.2DeterminationofRating(Continued)


Rating2: Critical Condition: CRITICAL INSPECTION FINDING. The need for repair orrehabilitation is urgent. Facility should be closed until the indicated repair iscompleted.

A. Structureonvergeofcollapseorportionofsuperstructurehasfailed.Rating1: “Imminent” Failure Condition – facility is closed. CRITICAL INSPECTION

FINDING.Studyshoulddeterminefeasibilityforrepair.Correctiveactionmayputstructurebackintolightservice.

Rating0: FailedCondition–facilityisclosedandbeyondrepair.Replacementofstructureisnecessary.Again, the ratingdeterminations shownabovewill further evolveover timeashistoricaldatarelatedtotheserviceperformanceofHCBbridgesisdocumented.Theymayalsobemodifiedbytheowner’sspecificrequirements.ThesesuggestedratingdeterminationsareintendedtobefortheHCBcomponentofthesuperstructureonly.Othercomponentsofthebridgeshouldbeevaluatedbasedontheowner’scriteria.Pleasecheckwww.hcbridge.comforanyupdatestotheseguidelinesastheymaybeupdatedperiodically.


4. SummaryThe HCB is a structural member that derives its strength and stiffness primarily fromconventionalmaterials. Thesematerials are encapsulated in an FRP shell that providesadditional strength and provides a barrier to deleterious and corrosivematerials. As arelatively new component for bridge constructionwith a unique embodiment, questionsexistoninspectionandratingofbridgesbuiltwiththeHCB. Theguidelinespresentedinthis document are the current best practices for inspection and evaluation of the HCB.Combining thisdocumentwith theowner’s own requirements, provides the experiencedbridge inspector with tools to inspect and subsequently rate an HCB Bridge. Since therepairofanHCBisbeyondthescopeofthedocument,ifinspectionindicatestheneedforarepair, please consult HCB, Inc. or a firm specializing in the repair of FRP compositematerials.Sincethisdocumentissubjecttochangeatanytime,pleasecheckwww.hcbridge.comforanupdatedversionoftheseguidelines.Asalways,ifyouhaveanyquestions,pleaseconsultthestaffatHCB,Inc.

Documents

HCB Bridge Inspection · PDF fileThe Hillman-Composite Beam ... To date this has never been seen on an HCB laminate ... HCB®Bridge Inspection Guidelines 9