Training and Certification of Field Personnel for Unbonded Post-tensioning Flashcards
(20 cards)
What is the first step in the construction sequence for post-tensioned concrete?
Erect forms and place unstressed post-tensioning tendons in proper location.
What is placed and secured before concrete is poured in post-tensioned concrete?
Bonded rebar and all steel.
What happens after the forms are filled with concrete?
Concrete is allowed to harden to the required strength.
What happens after the concrete hardens?
Pre-stressing steel is stressed by a hydraulic jack.
When are tendons stressed in post-tensioned concrete?
After concrete reaches about 75% of full strength.
What should be used to unload post-tensioning tendons?
Nylon straps.
What should never be used to unload tendons?
Chains or hooks.
How should tendon coils be handled?
Cradle in straps and hook each eye to hoisting equipment.
How much tendon tail should be left for stressing from both ends?
At least 12 inches at each end.
How far should sheathing be cut back from anchor?
Maximum of 1 inch.
What is the maximum number of tendons in a group?
5 tendons (½” diameter tendons) or 4 tendons (0.6” diameter tendons).
What is the minimum clearance around blockouts?
6 inches
Why are additional support bars used for tendons?
To avoid reverse curvature.
What is the minimum size support bar for tendons?
4 bar
What is the spacing between bundles of tendons?
Approximately 1 ½ inches.
When using two or more extensions of the stressing jack, how far should it be pulled?
Final pull should be about 60% of full stroke.
When must a watertight cap be installed for encapsulated systems?
Within 24 hours, not to exceed 96 hours after stressing.
What must grout for bonded tendons not contain?
Chlorides or other materials harmful to prestressing steel.
What is the most common strand used for barrier cables?
½ inch diameter, seven-wire strand.
What is the required back-stressing force for barrier cables?
Equal to 80% of the ultimate strength of the strand.
