Lightweight Concrete for High Strength - Expanded Shale & Clay

Shrinkage of concrete. Prestress losses due to drying shrinkage are estimated by Equation D.16.
The denominator K SE represents the stiffening effect of the steel and the effect of concrete creep.
Without K SE the losses due to drying shrinkage are somewhat overestimated.
E
ps
SH = ( ε
sh
) ⋅
(D.16)
t
K
SE
where
SH: shrinkage of concrete loss (ksi)
(ε sh ) t : shrinkage strain as defined by ACI-209 (Equation B.3 of Appendix B)
E ps : Elastic modulus of prestressing steel
K
SE
= 1 + n ⋅ ρξ =1.25 (design simplification)
s
n: modular ratio at the time of prestressing
ρ: non-prestressing reinforcement ratio
ξ s : cross section shape coefficient
Steel relaxation. Steel relaxation losses depend on the steel of the strands (stress-relieved or low
relaxation), and time. For low relaxation strands, the relaxation losses are given by Equation
D.17.
[] t
RE = 0.005⋅
f
pj
⋅ log10
(D.17)
where
RE: steel relaxation loss (ksi)
f pj : initial prestress (ksi)
t: time under load in hours (for t>10 5 , RE = 0 . 025⋅
f
pj
)
D-10