Civil Engineering Reference
In-Depth Information
(1) Design Data:
Service surcharge = 50 psf
Assume weight of soil and concrete above footing base = 130 pcf
Interior columns: 16 in.
16 in. (see Examples 5.7.1 and 5.7.2)
4-No.8 bars (non-sway frame)
8-No.10 bars (sway frame)
f
c
= 4000 psi (column)
f
c
= 4000 psi (footing)
(2) Load combinations
a) gravity loads (Alternate (2)):
P
DL
= 351 kips
P
LL
= 56.4 kips
M
service
= 6.6 ft-kips (10.6/1.6)
P
u
= 512 kips (ACI Eq. 9-2)
M
u
= 10.6 ft-kips
b) gravity loads + wind (Alternate (1)): P
DL
= 339.4 kips
P
LL
= 56.4 kips
M
service
= 75.4 ft-kips
P
u
= 498 kips (ACI Eq. 9-3)
M
u
= 66 ft-kips
Or
P
u
= 436 kips (ACI Eq. 9-4)
M
u
= 113 ft-kips
(3) Base area of footing
Determine footing base area for gravity loads only, then check footing size for gravity plus winds loads.
Total weight of surcharge = (0.130
5) + 0.05 = 0.70 ksf
Net permissible soil pressure = 6 - 0.70 = 5.3 ksf
351
56.4
5.3
+
A
f
=
=
76.9 sq ft
*
Try 9 ft-6 in.
9 ft-6 in. square footing (A
f
= 90.25 sq ft)
Check gravity plus wind loading for 9 ft-6 in.
9 ft-6 in. footing
A
f
= 90.25 sq ft
S
f
= bh
2
/6 = (9.5)
3
/6 = 142.9 ft
3
P
A
f
+
M
S
f
=
339.4
56.4
90.25
+
75.4
142.9
=
q
=
+
4.9
<
5.3 O.K.
*
Neglect small moment due to gravity loads.
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