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WS Atkins Bridge Engineering Research Activities Mike Chubb

WS Atkins Bridge Engineering Research Activities Mike Chubb. WS Atkins Bridge Engineering Research. Deteriorated reinforced concrete structures Lab testing of rc specimens Hidden strengths of structures Testing of rc slabs for shear distribution Precast deck panels for composite bridges

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WS Atkins Bridge Engineering Research Activities Mike Chubb

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  1. WS Atkins • Bridge Engineering • Research Activities • Mike Chubb

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

  3. Deteriorated Reinforced Concrete Structures • Investigation by WS Atkins and Testing at Westminster University • Desk Study • Testing • Amendments to BD44 Assessment Rules • Draft BA Advice Note

  4. Deteriorated Reinforced Concrete Structures • Scope • Corrosion affected reinforced concrete • loss of section • delamination of cover • Cause • Chlorides • Carbonation

  5. Desk Study - Effects • Low or reduced cover • Delamination • Corrosion • Loss of section of reinforcement • Weakened concrete • Cracking

  6. Conclusion • Assessment standards not adequate for deterioration • Need data on:- • bond for reduced cover • effect on corrosion of reinforcement • effect of weak concrete • effect of cracking on strength

  7. Testing • Bond Tests 132 No • Beam Tests 65 No • Slab Tests 10 No • Column Tests 3 No • Punching Tests 3 No • Cracked Model Tests 12 No

  8. Bond Testing • Pull Out Tests

  9. Bond Testing • Variables • Concrete strength • Bar type and diameter • Link type, spacing and diameter • Clamping (from bearings) • Top or bottom cast • Cover including effects of delamination • Corrosion

  10. Bond Testing Results • Laboratory Induced Corrosion

  11. Unbonded Loss of Flexural Strength • Ultimate Moment • of Resistance • for bonded and • unbonded • reinforcement • in beams

  12. Amendments to BD44 • Accounts for: • Loss of cover • Corrosion of reinforcement • Cracking • Clamping of bearings

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

  14. Amendment to BD44 • Regan’s Method

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

  16. End

  17. End

  18. Deterioration Process • Deterioration Process

  19. Bond Testing Results • Corrosion and Delamination • half barrel equivalent

  20. Corroded Links • Results • Over-conservative to ignore strength of corroded links

  21. Desk Study - Identified Causes • Original construction defects • Shrinkage • Overstressing • Chemical attack • Corrosion • Climatic • Hazard events • Construction detailing

  22. Desk Study - Effects • Low or reduced cover • construction defects • stable • delamination due to corrosion • progressive deterioration

  23. Desk Study - Effects • Loss of section reinforcement due to corrosion • pitting • uniform rusting

  24. Desk Study - Effects • Weak Concrete • honeycombing • substandard mix • chemical attack • cracking • shrinkage • overstressing • chemical eg, ASR, TSA

  25. Laboratory Testing • Objectives • Study bond strength variations • Study failure modes with delaminated cover • Shear in cracked beams

  26. Restrained Beam Tests • Bond not • additive • between • bars with • different • stirrup • restraint

  27. Amendment to BD44 • Loss of Cover - Strength • slenderness of columns and walls • reduced cross-section for flexure • shear strength reduced in slabs and beams

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

  29. Amendment to BD44 • Corrosion of Main Reinforcement • reduced section • take account of bond

  30. Amendment to BD44 • Analysis • Reinforcement strength from anchorage bond • Regan’s method

  31. 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)

  32. Amendment to BD44 • Corrosion of Link Reinforcement • compression bar effectiveness reduced • shear effectiveness partly reduced • torsional capacity reduced

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

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

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