Prestress Losses

Owned by Tim Kostka
Last updated: Nov 09, 2022
2 min read

Prestress losses are based on AASHTO LRFD 9th Edition. There are two methods of loss included, specified loss and computed loss. Specified loss uses the supplied percentage from the input and multiplies the initial strand stress by the specified percentage loss for both the initial and final losses. Compute loss first identifies the initial strand stress and then computes the initial prestress loss after transfer and the total loss.

Initial Loss

Assumptions:

  • ΔfpR1 = 1.2 ksi if strand is low relaxation

  • Stress in strands immediately after transfer are assumed to be 0.70fpu

LRFD Eq. 5.9.3.4.2c-1

Total Loss

Assumptions:

  • ΔfpR = 2.4 ksi for low relaxation strand

  • ΔfpR2 = ΔfpR1

Low Relaxation Strand

Stress Relieved

where:

RH = relative humidity

P = applied sustained load