Civil Engineering Reference
In-Depth Information
resist the overturning moment. The footing extension will be designed as a grade beam.
Try an 8 ft length of footing.
L
ftg
= 8
ft
wt conc
.
. = 150
pcfreinforced
w
DL
= 0 345
.
klfdeadloadoffdn includings
.
oilwtand turndown
.
P
DL
=
067133 0150178
.
(.
(. )
=
.
kdeadloadoff
oundationwall
∑
M
right
=
0
M
o
=+
64 1352
.
.
()
=
91
.
ft-k
2
133
2
.
+
0 345 8
2
.
()
M
R
=
(.
0 178
+
23305
.
).
−
=
1
3396
.
ft-k
13 96
91
.
.
FS
..
/
=
=
15415
.
>
.
∴
OK
ot
∑
M
left
=
0
(.
0 178
+
233683
.
(. )
+
1352
.
()
++
64 0 345 84)
.
.
()(
x
=
=
7 075
.
ft
5 268
.
8
2
L
e
=
7 075
.
− =
3 075
.
ft
> =
133
.
ft
6
Therefore the resultant is outside the kern.
m
=−
87075
.
=
0 925
.
ft
2
3
P
bm
25268
3133 0 925
(.
)
SBP
=
=
=
2 855
.
ksf
∴
OK
(. )( .
)
Check the ultimate moment in the footing at the inside face of the pier.
The length of the soil bearing pressures is almost directly under the pier section as
shown in the figure. Therefore, the maximum moment applied to the extended footing
at the inside face of the pier is caused by uplift. The loads applied to this section is from
the dead load of the soil above the footing plus the footing dead load.
14
.
wL
(
)
2
140 345 617
2
.(.
)(. )
2
extended ftg
M
u
=
=
= 9 194
.
ft-k
2
82
−
25
=
V
u
=
14
.
(
L
−
d
)
=
140 345
. (.
).
617
−
275
.
k
extended ftg
ftg
12
By inspection of Fig. 13.8, the designated footing or a 12″ turndown footing does not
have enough capacity to resist the applied moment and is subject to failure. A founda-
tion similar to Fig. 13.10 is required if a prescriptive portal frame is used. Foundations
of lesser strength and stiffness should be carefully reviewed.
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