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Tendons FAQ


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Commonly asked questions about unbonded tendons and their installation.

What are the properties of the prestressing strand that you specify for tendon fabrication?

Prestressing strand is generally made up of 6 wires wrapped around a center wire.  It's properties are defined in the Specification ASTM A-416 and for slab foundations we normally specify 0.5" diameter, grade 270 (270 ksi).

What are unbonded tendons?

Unbonded tendons are fabricated to easily elongate within the cured concrete by being isolated along their length with a lubricated sheath (typically plastic) similar to that of an insulated electrical wire.  As such they do not bond to the concrete.

What force is present in a tendon after it has been stressed and locked off?

Typically and with a 0.5" dia. tendon, the force should be no less than 31,000 lbs.

How can you tell if the tendons have been stressed properly?

By measuring their elongation as related to the face of the jacking-end anchor and comparing that value with the calculated value (Δ) listed on the engineered plan.

What is the recommended procedure for field inspection?

This is most easily accomplished by placing a mark on the exposed tendon tail at a fixed length from the face of the concrete prior to jacking and then measuring and noting the difference after the stressing has been completed.





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