DESIGN OF SLABS-ON-GROUND 360R-41
9.7—Residential slabs with post-tensioned
reinforcement for structural action
9.7.1 Soil properties—The designer should have the
following information about soil properties:
• Allowable soil bearing pressure q
allow
, lb/ft
2
(N/m
2
);
• Edge moisture variation distance e
m
(ft [m]), center lift,
and edge lift;
• Differential soil movement y
m
(in. [mm]), center lift,
and edge lift; and
• Slab-subgrade friction coefficient
μ.
9.7.2 Structural data and materials properties—The
necessary data for design is: slab length L, ft (m); beam
spacing S, ft (m); overall depth h, in. (mm); width b (in.
[mm]) of the stiffening beams; and the perimeter loading P,
lb/ft (N/m).
Required material properties:
• Specified 28-day compressive strength of concrete f
c
′ ,
psi (MPa);
• Type, grade, and strength of the prestressing steel; and
• Type and grade of nonprestressed reinforcement.
9.7.3 Design stresses for the concrete—The following
stresses are used when designing by the PTI method:
Allowable tensile stress
f
t
= 6
(in.-lb) (9-3)
f
t
= 0.5
(SI)
Allowable compressive stress
f
c
= 0.45f
c
′ (9-4)
Estimated tensile cracking stress
f
cr
= 7.5
(in.-lb) (9-5)
f
cr
= 0.62
(SI)
Allowable shear stress
v
c
= 1.7
+ 0.2f
p
(in.-lb) (9-6)
v
c
= 0.14
+ 0.2f
p
(SI)
Allowable concrete bearing stress at anchorages:
At service load
(9-7)
At transfer
(9-8)
Allowable stresses in prestressing steel:
Allowable stress due to tendon jacking force
f
pj
= 0.8f
pu
≤ 0.94f
py
(9-9)
Allowable stress immediately after prestress transfer
f
pi
= 0.7f
pu
(9-10)
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