Chubb Presentation on concrete detailing
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Transcript of Chubb Presentation on concrete detailing
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7/29/2019 Chubb Presentation on concrete detailing
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WS Atkins
Bridge Engineering
Research Activities
Mike Chubb
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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
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Deteriorated ReinforcedConcrete Structures
Investigation by WS Atkins and
Testing at Westminster University
Desk Study Testing
Amendments to BD44 Assessment Rules
Draft BA Advice Note
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Deteriorated Reinforced Concrete Structures
Scope Corrosion affected reinforced concrete
loss of section delamination of cover
Cause Chlorides Carbonation
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Desk Study - Effects
Low or reduced cover
Delamination
Corrosion
Loss of section of reinforcement
Weakened concrete
Cracking
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Conclusion
Assessment standards not adequate fordeterioration
Need data on:-
bond for reduced cover
effect on corrosion of reinforcement
effect of weak concrete
effect of cracking on strength
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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
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Bond Testing
Pull Out Tests
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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
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Bond Testing Results
Laboratory Induced Corrosion
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Unbonded Loss of Flexural Strength
Ultimate Moment
of Resistance
for bonded and
unbonded
reinforcement
in beams
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Amendments to BD44
Accounts for:
Loss of cover
Corrosion of reinforcement
Cracking
Clamping of bearings
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Rebar Anchorage
Build-up of Bar Capacity fromCurtailment or Corrosion Point
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Amendment to BD44
Regans Method
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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
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End
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End
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Deterioration Process
Deterioration Process
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Bond Testing Results
Corrosion and Delamination
half barrel equivalent
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Corroded Links
Results
Over-conservative to ignore strength of
corroded links
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Desk Study - Identified Causes
Original construction defects Shrinkage
Overstressing
Chemical attack
Corrosion
Climatic Hazard events
Construction detailing
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Desk Study - Effects
Low or reduced cover
construction defects
stable delamination due to corrosion
progressive deterioration
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Desk Study - Effects
Loss of section reinforcement due tocorrosion
pitting uniform rusting
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Desk Study - Effects
Weak Concrete honeycombing
substandard mix
chemical attack
cracking
shrinkage overstressing
chemical eg, ASR, TSA
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Laboratory Testing
Objectives
Study bond strength variations
Study failure modes with delaminatedcover
Shear in cracked beams
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Restrained Beam Tests
Bond notadditive
between
bars withdifferent
stirrup
restraint
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Amendment to BD44
Loss of Cover - Strength
slenderness of columns and walls
reduced cross-section for flexure shear strength reduced in slabs and
beams
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Amendment to BD 44
Where the longitudinal reinforcementis insufficient or is insufficiently
anchored, the shear link capacity shall
be proportionately reduced.
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Amendment to BD44
Corrosion of Main Reinforcement
reduced section
take account of bond
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Amendment to BD44
Analysis
Reinforcement strength from anchorage
bond
Regans method
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Amendment to BD44
Regans MethodForce in bar at x
Moment
Lever ArmShear
Angle of shear failure plane to horizontal
Stirrup spacing along beamEffective area of row of stirrups across beam
Stress in stirrups (0.87 x yield)sv
sv1
x
f
AS
VZ
M
F
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Amendment to BD44
Corrosion of Link Reinforcement
compression bar effectiveness reduced
shear effectiveness partly reduced torsional capacity reduced
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Shear with Corrosion
Corroded corners of links
50% of actual loss
If actual loss >67% beam is toocorroded to assess
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Shear with Vertical Cracking
2-3 mm cracks25% loss of concrete contribution
7 mm cracks
no concrete contribution