ws atkins bridge engineering research activities mike chubb

WS Atkins WS Atkins

Bridge Engineering Bridge Engineering

Research ActivitiesResearch Activities

Mike ChubbMike Chubb

WS Atkins Bridge Engineering ResearchWS Atkins Bridge Engineering Research

•Deteriorated reinforced concrete structuresDeteriorated reinforced concrete structures

– Lab testing of rc specimensLab testing of rc specimens

•Hidden strengths of structuresHidden strengths of structures

– Testing of rc slabs for shear distributionTesting of rc slabs for shear distribution

•Precast deck panels for composite bridgesPrecast deck panels for composite bridges

– ULS, SLS and fatigue testingULS, SLS and fatigue testing

Deteriorated Reinforced Deteriorated Reinforced Concrete StructuresConcrete Structures

Investigation by WS Atkins and Investigation by WS Atkins and Testing at Westminster University Testing at Westminster University • Desk StudyDesk Study

• TestingTesting

• Amendments to BD44 Assessment RulesAmendments to BD44 Assessment Rules

• Draft BA Advice NoteDraft BA Advice Note

Deteriorated Reinforced Concrete StructuresDeteriorated Reinforced Concrete Structures

• ScopeScope– Corrosion affected reinforced concreteCorrosion affected reinforced concrete

• loss of sectionloss of section• delamination of coverdelamination of cover

• CauseCause– Chlorides Chlorides – CarbonationCarbonation

Desk Study - EffectsDesk Study - Effects

• Low or reduced coverLow or reduced cover– DelaminationDelamination

• CorrosionCorrosion– Loss of section of reinforcementLoss of section of reinforcement

• Weakened concreteWeakened concrete– CrackingCracking

ConclusionConclusion

Assessment standards not adequate for Assessment standards not adequate for deteriorationdeterioration

Need data on:-Need data on:-• bond for reduced coverbond for reduced cover

• effect on corrosion of reinforcementeffect on corrosion of reinforcement

• effect of weak concreteeffect of weak concrete

• effect of cracking on strengtheffect of cracking on strength

TestingTesting

Bond TestsBond Tests 132 N132 Noo

Beam TestsBeam Tests 65 N65 Noo

Slab TestsSlab Tests 10 N10 Noo

Column TestsColumn Tests 3 N3 Noo

Punching TestsPunching Tests 3 N3 Noo

Cracked Model TestsCracked Model Tests 12 N12 Noo

Bond TestingBond Testing

Pull Out TestsPull Out Tests

Bond TestingBond Testing

VariablesVariables• Concrete strengthConcrete strength• Bar type and diameterBar type and diameter• Link type, spacing and diameterLink type, spacing and diameter• Clamping (from bearings)Clamping (from bearings)• Top or bottom castTop or bottom cast• Cover including effects of delaminationCover including effects of delamination• CorrosionCorrosion

Bond Testing ResultsBond Testing Results

Laboratory Induced CorrosionLaboratory Induced Corrosion

Unbonded Loss of Flexural StrengthUnbonded Loss of Flexural Strength

Ultimate Moment Ultimate Moment

of Resistanceof Resistance

for bonded andfor bonded and

unbonded unbonded

reinforcement reinforcement

in beamsin beams

Amendments to BD44Amendments to BD44

Accounts for:Accounts for:

• Loss of coverLoss of cover

• Corrosion of reinforcementCorrosion of reinforcement

• CrackingCracking

• Clamping of bearingsClamping of bearings

Rebar AnchorageRebar Anchorage

Build-up of Bar Capacity fromBuild-up of Bar Capacity fromCurtailment or Corrosion PointCurtailment or Corrosion Point

Amendment to BD44Amendment to BD44

Regan’s MethodRegan’s Method


CAUTIONCAUTION• Deterioration is on-goingDeterioration is on-going

• Record present conditionRecord present condition– Delamination not easy to accurately recordDelamination not easy to accurately record

– Corrosion very difficult to estimateCorrosion very difficult to estimate

• Allow for future trendAllow for future trend– Delamination is a sudden eventDelamination is a sudden event

– Corrosion is progressiveCorrosion is progressive

EndEnd

Deterioration ProcessDeterioration Process

Deterioration ProcessDeterioration Process

Bond Testing ResultsBond Testing Results

Corrosion and DelaminationCorrosion and Delamination• half barrel equivalenthalf barrel equivalent

Corroded Links Corroded Links

ResultsResults• Over-conservative to ignore strength of Over-conservative to ignore strength of

corroded linkscorroded links

Desk Study - Identified CausesDesk Study - Identified Causes

• Original construction defectsOriginal construction defects• ShrinkageShrinkage• OverstressingOverstressing• Chemical attackChemical attack• CorrosionCorrosion• ClimaticClimatic• Hazard eventsHazard events• Construction detailingConstruction detailing


Low or reduced coverLow or reduced cover• construction defectsconstruction defects

– stablestable

• delamination due to corrosiondelamination due to corrosion– progressive deteriorationprogressive deterioration


Loss of section reinforcement due to Loss of section reinforcement due to corrosioncorrosion• pittingpitting

• uniform rustinguniform rusting


Weak ConcreteWeak Concrete• honeycombinghoneycombing

• substandard mixsubstandard mix

• chemical attackchemical attack

• crackingcracking– shrinkageshrinkage

– overstressingoverstressing

– chemical eg, ASR, TSAchemical eg, ASR, TSA

Laboratory TestingLaboratory Testing

ObjectivesObjectives• Study bond strength variationsStudy bond strength variations

• Study failure modes with delaminated Study failure modes with delaminated covercover

• Shear in cracked beamsShear in cracked beams

Restrained Beam TestsRestrained Beam Tests

Bond notBond not

additiveadditive

betweenbetween

bars withbars with

differentdifferent

stirrupstirrup

restraintrestraint


Loss of Cover - StrengthLoss of Cover - Strength• slenderness of columns and wallsslenderness of columns and walls

• reduced cross-section for flexurereduced cross-section for flexure

• shear strength reduced in slabs and shear strength reduced in slabs and beamsbeams

Amendment to BD 44Amendment to BD 44

Where the longitudinal reinforcement Where the longitudinal reinforcement is insufficient or is insufficiently is insufficient or is insufficiently anchored, the shear link capacity shall anchored, the shear link capacity shall be proportionately reduced.be proportionately reduced.


Corrosion of Main ReinforcementCorrosion of Main Reinforcement• reduced sectionreduced section

• take account of bondtake account of bond


Analysis Analysis • Reinforcement strength from anchorage Reinforcement strength from anchorage

bondbond

• Regan’s methodRegan’s method


Regan’s MethodRegan’s MethodForce in bar at xForce in bar at x

MomentMoment

Lever ArmLever Arm

ShearShear

Angle of shear failure plane to horizontalAngle of shear failure plane to horizontal

Stirrup spacing along beamStirrup spacing along beam

Effective area of row of stirrups across beamEffective area of row of stirrups across beam

Stress in stirrups (0.87 x yield)Stress in stirrups (0.87 x yield)sv

sv1

x

fAS

VZMF


Corrosion of Link ReinforcementCorrosion of Link Reinforcement• compression bar effectiveness reducedcompression bar effectiveness reduced

• shear effectiveness partly reducedshear effectiveness partly reduced

• torsional capacity reducedtorsional capacity reduced

Shear with CorrosionShear with Corrosion

Corroded corners of linksCorroded corners of links

50% of actual loss50% of actual loss

If actual loss >67% beam is too If actual loss >67% beam is too corroded to assesscorroded to assess

Shear with Vertical CrackingShear with Vertical Cracking

2-3 mm cracks2-3 mm cracks

25% loss of concrete contribution25% loss of concrete contribution

7 mm cracks7 mm cracks

no concrete contributionno concrete contribution

ws atkins bridge engineering research activities mike chubb

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