Effective Stress After Prestress Losses
Easylossesprestress
Initial prestressing-steel stress is 1,400 MPa before any of four listed losses occurs. The losses are mutually exclusive and additive stresses: elastic shortening 40 MPa, creep 60 MPa, shrinkage 30 MPa, relaxation 20 MPa. What is the effective prestressing-steel stress after all four losses?
- A1,250 MPa
- B1,210 MPa
- C1,201 MPa
- D1,310 MPa
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Answer: A. 1,250 MPa
fpe = fpi − Σ losses. Total loss = 40 + 60 + 30 + 20 = 150 MPa, so fpe = 1,400 − 150 = 1,250 MPa. The losses are absolute stresses, subtracted once. 1,210 MPa double-counts elastic shortening (subtracting 40 MPa a second time). 1,201 MPa wrongly treats 40, 60, 30, 20 as percentages and compounds them. 1,310 MPa leaves out the elastic-shortening (transfer) loss.
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