chubb presentation on concrete detailing

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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Low or reduced cover

construction defects

stable delamination due to corrosion

progressive deterioration


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Loss of section reinforcement due tocorrosion

pitting uniform rusting


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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

chubb presentation on concrete detailing

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