Deteriorated Reinforced Concrete Structures Sibdas Chakrabarti ...

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26 Νοε 2013 (πριν από 3 χρόνια και 6 μήνες)

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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


ULS, SLS and fatigue testing





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

Deteriorated Reinforced Concrete Structures


Scope


Corrosion affected reinforced concrete


loss of section


delamination of cover


Cause



Chlorides


Carbonation

Desk Study
-

Effects


Low or reduced cover


Delamination


Corrosion


Loss of section of reinforcement


Weakened concrete


Cracking

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

Testing

Bond Tests

132 N
o

Beam Tests

65 N
o

Slab Tests

10 N
o

Column Tests

3 N
o

Punching Tests

3 N
o

Cracked Model Tests

12 N
o

Bond Testing







Pull Out Tests

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

Bond Testing Results







Laboratory Induced Corrosion

Unbonded Loss of Flexural Strength



Ultimate Moment

of Resistance

for bonded and

unbonded

reinforcement

in beams

Amendments to BD44

Accounts for:


Loss of cover


Corrosion of reinforcement


Cracking


Clamping 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
-
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

End

End

Deterioration Process









Deterioration Process

Bond Testing Results

Corrosion and Delamination


half barrel equivalent

Corroded Links

Results


Over
-
conservative to ignore strength of
corroded links

Desk Study
-

Identified Causes


Original construction defects


Shrinkage


Overstressing


Chemical attack


Corrosion


Climatic


Hazard events


Construction detailing

Desk Study
-

Effects

Low or reduced cover


construction defects


stable


delamination due to corrosion


progressive deterioration

Desk Study
-

Effects

Loss of section reinforcement due to
corrosion


pitting


uniform rusting

Desk Study
-

Effects

Weak Concrete


honeycombing


substandard mix


chemical attack


cracking


shrinkage


overstressing


chemical eg, ASR, TSA


Laboratory Testing

Objectives


Study bond strength variations


Study failure modes with delaminated
cover


Shear in cracked beams

Restrained Beam Tests

Bond not

additive

between

bars with

different

stirrup

restraint

Amendment to BD44

Loss of Cover
-

Strength


slenderness of columns and walls


reduced cross
-
section for flexure


shear 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 section


take account of bond

Amendment to BD44

Analysis


Reinforcement strength from anchorage
bond


Regan’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)


sv
sv
1
x
f
A
S
V
Z
M
F

Amendment to BD44

Corrosion of Link Reinforcement


compression bar effectiveness reduced


shear effectiveness partly reduced


torsional 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