Structural Concrete - Hassoun

22.8 Loss of Prestress (AASHTO 5.9.5) 913
where
A v = area of transverse reinforcement within distance s (in 2 .)
b v = width of web adjusted for presence of ducts
s = spacing of transverse reinforcement (in.)
f y = yield strength of transverse reinforcement (ksi)
22.7.9 Maximum Spacing of Transverse Reinforcement (AASHTO 5.8.2.7)
The spacing of the transverse reinforcement shall not exceed the maximum permitted spacing, s max ,
determined as
If v u < 0.125f ′ c, then
s max = 0.8d v ≤ 24.0 in. (22.31)
If v u ≥ 0.125f ′ c, then
s max = 0.4d v ≤ 12.0 in. (22.32)
22.7.10 Minimum Longitudinal Reinforcement (AASHTO 5.8.3.5)
At each section the tensile capacity of the longitudinal reinforcement on the flexural tension side
of the member shall be proportioned to satisfy
A ps f ps + A s f y ≥ M u
+ 0.5 N ( )
u |||| V
+ u
|
− V
d v φ f φ c φ p ||| − 0.5V s cot θ (22.33)
v
where
V s = shear resistance provided by transverse reinforcement at section under investigation
except V s shall not be taken as greater than V u /φ (kip)
θ = angle of inclination of diagonal compressive stresses used in determining nominal shear
resistance of section under investigation
φ f φ v φ c = resistance factors as appropriate for moment, shear, and axial resistance
22.8 LOSS OF PRESTRESS (AASHTO 5.9.5)
22.8.1 Total Loss of Prestress (AASHTO 5.9.5.1)
Loss of prestress can be characterized as that due to instantaneous loss and time-dependent loss.
Losses due to anchorage set, friction, and elastic shortening are instantaneous. Losses due to creep,
shrinkage, and relaxation are time dependent.
In pretensioned members:
In posttensioned members:
Total losses = instantaneous losses + time − dependent losses
Δf pT = Δf pES + Δf pLT (22.34)
Δf pT = Δf pF + Δf pA + Δf pES + Δf pLT (22.35)