Document Type: FAQ Product(s): LEAP CONSPAN Version(s): All Original Author: Bentley Technical Support Group -VM
Document Type: FAQ
Product(s): LEAP CONSPAN
Version(s): All
Original Author: Bentley Technical Support Group -VM
ANSWER:
The Prestress loss due to relaxation of prestressing strands between time of transfer and deck placement ∆fpR1 is calculated as per AASHTO LRFD (7th edition,2014) Article 5.9.5.4.2c-1.
This example shows calculation for Low Relaxation Strands.
KL = 30 for Low Relaxation Strands and 7 for other prestressing Steel.
fpu = Tensile Strength of Prestressing Strand = 270 ksi for Low relaxation strands.
fpy = Yield Strength of Prestressing Strand = 0.9 x fpu = 0.9 x 270 = 243 ksi.
fpt = Stress in Prestressing strands immediately after transfer.= 0.75 x 270 = 202.5 ksi.
∆fpR1 = (fpt / KL ) x ( (fpt / fpy) - 0.55 )
∆fpR1 = (202.5 / 30 ) x ( ( 202.5 / 243) - 0.55) = 1.91 ksi
Reference : AASHTO LRFD BRIDGE DESIGN SPECIFICATIONS, SEVENTH EDITION ,2014.