Prestressing Operations and Strand Handling
What this domain tests
This domain tests tensioning, elongation control, anchorage, strand handling, and transfer. Questions often require comparing measured elongation with calculated elongation and deciding whether the operation may proceed.
Core rules
- Prestressing strand is commonly ASTM A416, seven-wire, low-relaxation. Verify grade, diameter, area, certification, and condition before use.
- Store strand off the ground, protected from mud, oil, and mechanical damage. Do not weld, arc, or heat strand.
- Tensioning equipment must be calibrated and the gauge or load cell must be in calibration. The tensioning procedure must identify sequence, initial force, and seating allowance.
- Elongation is a check on force. Compute elongation from force, length, area, and modulus; compare measured elongation with the calculated value and the project tolerance, commonly plus or minus 7% unless otherwise specified.
- Never stand behind a tensioned strand or jack. Use shielding and exclusion zones during tensioning and cutting.
Worked example
A 0.153 in2 strand is tensioned to 202.5 ksi over 100 ft, or 1,200 in. Force = 202.5 x 0.153 = 30.98 kip. Using E = 28,500 ksi, elongation = PL/AE = (30.98 x 1,200)/(0.153 x 28,500) = 8.53 in. Measured elongation is 8.05 in, a difference of 0.48 in, or 5.6%. With a plus or minus 7% criterion, the elongation is acceptable; the plant still checks gauge force, seating, and slip.
Traps
Using nominal area from the wrong strand size; ignoring seating or temperature corrections; accepting elongation alone without force; and cutting strand without shielding.