Civil Engineering Reference
In-Depth Information
Q
ult
q
ult
B
L
(208 kN/m
2
) (1.4 m) (1.4 m)
408 kN
Q
ult
408 kN
___
_______
FS
Q
500 kN
0.82
8.14
Solution using Eq. (8.7):
Q
P
15,000 kips
for mat foundation
e
5 ft
(for middle third of mat,
e
cannot exceed 16.7 ft, so
e
is
within middle third of mat)
Converting
Q
to a load per unit length of the mat gives
Q
15,000 kips
__________
100 ft
150 kips/ft
150,000 lb/ft
q
Q
(
B
6
e
)
150,000 [100
6 (5)]
__________
___________________
B
2
100
2
1950 lb/ft
2
Since 1950
2500 lb/ft
2
, design is acceptable.
Solution using Fig. 8.9:
Q
P
15,000 kips
15,000,000 lb
for mat foundation
e
5 ft
B
B
2
e
100
2 (5)
90 ft
L
L
100 ft
(moment only in
B
direction of mat)
B
L
15,000,000
Q
____
__________
q
100 (90)
1670 lb/ft
2
Since 1670
2500 lb/ft
2
, design is acceptable.
8.15
Strip footing:
q
all
24 kPa
24 kN/m
2
Using
B
1.5 m yields
(24 kN/m
2
) (1.5 m)
Q
all
36 kN/m
Spread footing:
q
all
32 kPa
32 kN/m
2
Using
B
L
2.5 m gives
Q
all
q
all
BL
(32 kN/m
2
) (2.5 m) (2.5 m)
200 kN
