Civil Engineering Tools
BeamTrussMohr's CircleUnit ConversionsCentroidDeflectionBucklingConcreteRebarFE Prep

Prestressed Beam Stress at Transfer

Hardprestressload stagesstress
The same uncracked noncomposite section applies at both stages: A = 0.25 m², Sb = 0.04 m³, tendon eccentricity e = 0.10 m below the centroid. At transfer, Pt = 1,000 kN with total sagging moment 60 kN·m. At service, effective Pe = 800 kN with total sagging moment 180 kN·m (including every load then present). Compression is positive. Which stage gives the larger bottom-fiber compression, and what is its value?
  1. A3.70 MPa at transfer
  2. B0.70 MPa at service
  3. C5.00 MPa at transfer
  4. D3.50 MPa at transfer
Show solution

Answer: C. 5.00 MPa at transfer

Apply σb = P/A + P·e/Sb − M/Sb at each stage. Transfer: 1,000/0.25 = 4,000 kPa; 1,000(0.10)/0.04 = 2,500 kPa; 60/0.04 = 1,500 kPa tension; σ = 4,000 + 2,500 − 1,500 = 5,000 kPa = 5.00 MPa. Service: 3,200 + 2,000 − 4,500 = 700 kPa = 0.70 MPa. Transfer is larger. 3.70 MPa at transfer mixes the effective force (800 kN) into the transfer stage. 0.70 MPa at service is the smaller stage value. 3.50 MPa at transfer counts the self-weight moment twice (M = 120 kN·m).
MPa MPa
Practice this deckUntimed, one problem at a time, with your progress saved.

Related problems

Keep studying