Structural Concrete - Hassoun

22.9 Deflections (AASHTO 5.7.3.6) 937
C L Span
63”
52.47”
6”
10 Strands
28 Strands
?
Harp point
y m = 4.53”
30’–0” 20’–0”
Figure 22.16
Prestressing strand profile.
h = D s = 72 in.
y cr = 11.25 in.
Depth of composite section
From Figure 22.16. e 0 is calculated to be 11.25 in at 36 ′′ from
the face of support.
d e = h − y cr = 72 − 11.25 = 60.75
d v = d e − a 2.159
= 60.75 − = 59.67 in.
2 2
and d v need not to be smaller than 0.9d e or 0.72h:
Therefore, use
d v ≥ max(0.9d e , 0.72h)
d v_ min = max(0.9d e , 0.72h) =max[0.9(60.75), 0.72(72)] = 54.675 in.
d v = 59.7 in.
3. Prestress contribution to shear resistance
Vertical component of prestressing force is calculated as:
where
V p = N ps_harped
F
N f sinφ
ps
N ps_harped = 10
N ps = 38
Number of harped strands
Total number of strands
F f = 942.174 K
ψ = tan −1 ( 52.47 − 6
360
)
= 7.36π
180