Civil Engineering Reference
In-Depth Information
Determine preliminary h based on two-way shear at an corner column (see Fig. 1-10).
Live load reduction: AI (one panels) = 24.5
20.5 = 502 sq ft
L = 50(0.25 + 15/
502
)
= 46.0 psf
q
u
= 1.2(142) + 1.6(46.0)
= 244 psf
A = (20/2 + 0.5) (24/2 + 0.5)
= 131.25 ft
2
c
1
2
= 12
12
= 144 in.
2
= 1.0 ft
2
A/c
1
2
= 131.25/1.0
= 131.25
From Fig. 1-10, required d/c
1
= 0.47
Required d = 0.47
12
= 5.6 in.
h = 5.6 + 1.25
= 6.85 in.
To account for moment transfer at the edge columns, increase h by 20%
Try preliminary h = 9 in.
2. Check the preliminary slab thickness for deflection control and shear strength.
(a)
Deflection control:
From Table 4-1 (flat plate): h = ˜
n
/30 = (22.67
12)/30 = 9.07 in.
where ˜
n
= 24 - (16/12) = 22.67 ft
(b)
Shear Strength:
From Fig. 4-13: Check two-way shear strength at interior slab column support for h = 9 in.
From Table 4-7: A
c
= 736.3 in.
2
for 9 in. slab with 16
16 in column.
b
1
= b
2
= 2(11.88) = 23.76 in. = 1.98 ft
V
u
= 0.218(24
20 - 1.98*) = 103.8 kips
From Fig. 4-13, with
β
= 1 and b
o
/d = 4(23.76) /(9 - 1.25) = 12.3:
φ
V
c
= 0.19 A
c
= 0.19(736.3) = 139.9 kips > 118.5 kips O.K.
Check for fire resistance: From Table 10 -1, for fire resistance rating of 2 hours, required slab thickness =
4.6 in. < 9.0 in. O.K.
Use 9 in. slab.
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