ws atkins bridge engineering research activities mike chubb
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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
Amendment to BD44Amendment to BD44
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
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
Desk Study - EffectsDesk Study - Effects
Low or reduced coverLow or reduced cover• construction defectsconstruction defects
– stablestable
• delamination due to corrosiondelamination due to corrosion– progressive deteriorationprogressive deterioration
Desk Study - EffectsDesk Study - Effects
Loss of section reinforcement due to Loss of section reinforcement due to corrosioncorrosion• pittingpitting
• uniform rustinguniform rusting
Desk Study - EffectsDesk Study - Effects
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
Amendment to BD44Amendment to BD44
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.
Amendment to BD44Amendment to BD44
Corrosion of Main ReinforcementCorrosion of Main Reinforcement• reduced sectionreduced section
• take account of bondtake account of bond
Amendment to BD44Amendment to BD44
Analysis Analysis • Reinforcement strength from anchorage Reinforcement strength from anchorage
bondbond
• Regan’s methodRegan’s method
Amendment to BD44Amendment to BD44
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
Amendment to BD44Amendment to BD44
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
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