How it calcs prestress losses.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
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Total Loss
Assumptions:
ΔfpR = 2.4 ksi for low relaxation strand
ΔfpR2 = ΔfpR1
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Low Relaxation Strand
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Stress Relieved
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where:
RH = relative humidity
P = applied sustained load