WS Atkins Bridge Engineering Research Activities Mike Chubb

WS Atkins Bridge Engineering Research Deteriorated reinforced concrete structuresDeteriorated reinforced concrete structures –Lab testing of rc specimens Hidden strengths of structuresHidden strengths of structures –Testing of rc slabs for shear distribution Precast deck panels for composite bridgesPrecast deck panels for composite bridges –ULS, SLS and fatigue testing

Deteriorated Reinforced Concrete Structures Investigation by WS Atkins and 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 Structures ScopeScope –Corrosion affected reinforced concrete loss of sectionloss of section delamination of coverdelamination of cover CauseCause –Chlorides –Carbonation

Desk Study - Effects Low or reduced coverLow or reduced cover –Delamination CorrosionCorrosion –Loss of section of reinforcement Weakened concreteWeakened concrete –Cracking

Conclusion Assessment standards not adequate for deterioration 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

Testing Bond Tests132 N o Beam Tests65 N o Slab Tests10 N o Column Tests3 N o Punching Tests3 N o Cracked Model Tests12 N o

Bond Testing Pull Out Tests

Bond Testing Variables 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 Results Laboratory Induced Corrosion

Unbonded Loss of Flexural Strength Ultimate Moment of Resistance for bonded and unbondedreinforcement in beams

Amendments to BD44 Accounts for: Loss of coverLoss of cover Corrosion of reinforcementCorrosion of reinforcement CrackingCracking Clamping of bearingsClamping of bearings

Rebar Anchorage Build-up of Bar Capacity from Curtailment or Corrosion Point

Amendment to BD44 Regan’s Method

Amendment to BD44 CAUTION Deterioration is on-goingDeterioration is on-going Record present conditionRecord present condition –Delamination not easy to accurately record –Corrosion very difficult to estimate Allow for future trendAllow for future trend –Delamination is a sudden event –Corrosion is progressive

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Deterioration Process

Bond Testing Results Corrosion and Delamination half barrel equivalenthalf barrel equivalent

Corroded Links Results Over-conservative to ignore strength of corroded linksOver-conservative to ignore strength of corroded links

Desk Study - Identified Causes Original construction defectsOriginal construction defects ShrinkageShrinkage OverstressingOverstressing Chemical attackChemical attack CorrosionCorrosion ClimaticClimatic Hazard eventsHazard events Construction detailingConstruction detailing

Desk Study - Effects Low or reduced cover construction defectsconstruction defects –stable delamination due to corrosiondelamination due to corrosion –progressive deterioration

Desk Study - Effects Loss of section reinforcement due to corrosion pittingpitting uniform rustinguniform rusting

Desk Study - Effects Weak Concrete honeycombinghoneycombing substandard mixsubstandard mix chemical attackchemical attack crackingcracking –shrinkage –overstressing –chemical eg, ASR, TSA

Laboratory Testing Objectives Study bond strength variationsStudy bond strength variations Study failure modes with delaminated coverStudy failure modes with delaminated cover Shear in cracked beamsShear in cracked beams

Restrained Beam Tests Bond not additivebetween bars with differentstirruprestraint

Amendment to BD44 Loss 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 beamsshear strength reduced in slabs and beams

Amendment to BD 44 Where the longitudinal reinforcement is insufficient or is insufficiently anchored, the shear link capacity shall be proportionately reduced.

Amendment to BD44 Corrosion of Main Reinforcement reduced sectionreduced section take account of bondtake account of bond

Amendment to BD44 Analysis Reinforcement strength from anchorage bondReinforcement strength from anchorage bond Regan’s methodRegan’s method

Amendment to BD44 Regan’s Method Force in bar at x Moment Lever Arm Shear Angle of shear failure plane to horizontal Stirrup spacing along beam Effective area of row of stirrups across beam Stress in stirrups (0.87 x yield)

Amendment to BD44 Corrosion of Link Reinforcement compression bar effectiveness reducedcompression bar effectiveness reduced shear effectiveness partly reducedshear effectiveness partly reduced torsional capacity reducedtorsional capacity reduced

Shear with Corrosion Corroded corners of links 50% of actual loss If actual loss >67% beam is too corroded to assess

Shear with Vertical Cracking 2-3 mm cracks 25% loss of concrete contribution 7 mm cracks no concrete contribution