Lightweight Concrete for High Strength - Expanded Shale & Clay

P i : initial prestressing force after anchorage seating loss (kip)
e: eccentricity of the cgs. with respect to the center of gravity of the section at the cross section
considered. Eccentricity is negative if below concrete section neutral axis (in)
A g : gross area of the section (in 2 )
I g : gross moment of inertia (in 4 )
M g : the dead load gravity moment applied to the section at time of prestressing (kip-in)
Creep of concrete. Equation D.15 shows the expression used for creep losses estimate.
⎛ Ft
⎞
CR = ES ⋅φ ⋅
⎜1−
⎟
t
(D.15)
⎝ 2 ⋅ F0
⎠
where
CR: creep of concrete loss (ksi)
ES: elastic shortening loss (ksi)
φ t : creep coefficient as defined by ACI-209 (Equation B.1 of Appendix B)
F t : Loss of prestress ratio given in Table D.1
F 0
Table D.1. Loss of prestress ratios for different concretes and time under loading conditions
Type of concrete
Normal
weight
concrete
Sandlightweight
concrete
Alllightweight
concrete
For three weeks to one month between
0.10 0.12 0.14
prestressing and sustained load application
For two to three months between prestressing 0.14 0.16 0.18
and sustained load application
Ultimate 0.18 0.21 0.23
D-9