DISPELLING THE MYTH ABOUT UNBONDED PT...
Transcript of DISPELLING THE MYTH ABOUT UNBONDED PT...
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DISPELLING THE MYTH ABOUT UNBONDED PT BUILDINGS
Christopher Fulton, B.Sc.(Eng.) Lindsey Tourand, P.Eng.
Parsons Brinkerhoff Halsall Inc.
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Reference: Seinfeld, Keith 2011, Demolition of a Nearly‐New Seattle Tower, photograph, viewed 28 April 2014 <http://www.kplu.org/post/demolition‐nearly‐new‐seattle‐tower>
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Deterioration of Unbonded PT
Moisture during constructionMoisture during serviceMechanical damage
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The Evolution of Unbonded PT
Reference: Schupack, M., “Corrosion Protection for Unbonded Tendons,” Concrete International, February 1991
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The Study
Goal of the study was to answer:
What is Tendon Failure Rate?
What is the Cause of Failure?
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The Study
Data Collected:
Acoustic Monitoring Records for 26 Structures
Visual Review of 246 Tendon Failures from 7 Structures
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Background on Acoustic Monitoring
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Background on Acoustic Monitoring
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Study Part 1 –Review of Acoustic Monitoring Records
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Breakage Rates
0
1
2
3
4
5
0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29
Num
ber o
f Structures
Average Annual Wire Breakage Rate
Average Annual Wire Breakage Rate by Structure Type
Hi‐Rise Structure Parking Structure
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Breakage Rates
1.0
6.5
3.6
0.0
1.0
2.0
3.0
4.0
5.0
6.0
7.0
Hi‐Rise Parking Parking (Adjusted)
Average An
nual W
ire Breakage Ra
te
per 1
00,000ft²
Structure Type
Average Annual Wire Breakage Rate per 100,000ft² by Structure Type
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Study Part 2 –Review of Tendon Failure Causes
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Causes of Tendon Failure
Corrosion from Moisture
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Causes of Tendon Failure
Mechanical Damage
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Causes of Tendon Failure
Anchor Slippage
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Causes of Tendon Failure
Moisture During Service28%
Mechanical Damage22%Moisture Prior
to Service17%
Anchor Slippage8%
Understressed from
Construction10%
Unknown15%
Causes of Post‐Tensioned Tendon Failures in Interior Spaces (72 Tendon Sample Size)
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Causes of Tendon Failure
Moisture During Service95%
Moisture Prior to Service
5%
Causes of Post‐Tensioned Tendon Failure in Exterior Slabs(174 Tendon Sample Size)
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What Does It All Mean?
Large percentage of PT tendon failures are the result of moisture entry or mechanical damage during service. These failures can be mitigated through regular preventative maintenance
The stigma that unbonded PT structures are unpredictable and costly to maintain may not be
deserved
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Special Thanks
Study Co‐Authored by Stephan Trepanier, Partner at Edison Engineering
Acoustic Monitoring data provided by Pure Technologies Limited
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DISPELLING THE MYTH ABOUT UNBONDED PT BUILDINGS
Questions?
Christopher Fulton, B.Sc.(Eng.) Lindsey Tourand, P.Eng.
Parsons Brinkerhoff Halsall Inc.