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Testing of Post-Tensioning Tendons
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| Figure
1: |
Deflected
shape of the deck under the load from the wheel of the loaded
forklift |
The investigation plan included the physical
examination of a representative number of post-tensioning anchors,
the load testing of the tendons where anchors had been exposed,
and structural analysis of the safe service loads which could be
expected on the deck.
The exposure of the tendon anchors showed the
anchors to be in remarkably good condition. Corrosion is most likely
to occur at the tendon anchors in post-tensioned structures because
the configuration of the anchors, the mechanics of the button-head
assembly, and the manner in which the anchors are encased after
being stressed. In this investigation, there was no significant
corrosion present at the exposed anchor locations, and no broken
wires were observed at the anchors.
Load testing of the anchors revealed that the majority of tendons
were maintaining a load equal to or above what could be reasonably
expected for a system of this type. Thirteen percent of the wires
were estimated to be broken. Two of the tendons tested were completely
broken, and could support no load. One of the tendons had four of
the seven wires broken. In the judgment of the engineer, the total
number of tendons that could not support a reasonable load would
be three tendons; or 11% of the tendons tested. During the repair
process, however, additional delaminated areas of concrete were
removed, indicating that the delaminations were caused by corrosion
and/or breakage of the tendons that had originally tested good.
Accordingly, confidence in the results of the load test was reduced,
and exposure of other "adequate" tendon locations was
undertaken to prove or disprove the acceptability of the tendons.
The repair plan was altered based upon these findings.
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| Figure 2: |
Relationship between curvature
and bending showing the maximum curvature the strengthened
slab can withstand and the maximum measured curvature. |
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