Page 70 - Handbook of Civil Engineering Calculations, Second Edition

STATICS, STRESS AND STRAIN, AND FLEXURAL ANALYSIS 1.53

(40.03 kN); W 18,000 9000 27,000 lb (120.10 kN). Then x 1 ( /3)(12) 8.0 ft
2
2
(2.44 m); x 12 1.5 13.5 ft (4.11 m).
2. Find the magnitude and location of the resultant of the
hydrostatic pressure
2
2
Calling the resultant H /2wh /2(62.4)(20) 12,480 lb (55.51 kN), where w weight
1
1
3
3
of water, lb/ft (N/m ), and h water height, ft (m), then y ( /3)(20) 6.67 ft (2.03 m).
1
3. Compute the moment of the loads with respect to the
base centerline
Thus, M 18,000(8 7.5) 9000(13.5 7.5) 12,480(6.67) 20,200 lb·ft (27,391
N·m) counterclockwise.
4. Compute the section modulus of the base
3
3
2
2
Use the relation S ( /6)bd ( /6)(1)(15) 37.5 ft (1.06 m ).
1
1
5. Determine the soil pressure at the dam toe and heel
Compute the soil pressure caused by the combined axial load and bending. Thus f 1 W/A
M/S 27,000/15 20,200/37.5 2339 lb/sq.ft. (111.99 kPa); f 2 1800 539 1261
lb/sq.ft. (60.37 kPa).
6. Verify the computed results
Locate the resultant R of the trapezoidal pressure prism, and take its moment with respect to the
centerline of the base. Thus R 27,000 lb (120.10 kN); m (15/3)[(2 1261 2339)/(1261
2339)] 6.75 ft (2.05 m); M R 27,000(7.50 6.75) 20,200 lb·ft (27,391 N·m). Since
the applied and resisting moments are numerically equal, the computed results are correct.
LOAD DISTRIBUTION IN PILE GROUP
A continuous wall is founded on three rows of piles spaced 3 ft (0.91 m) apart. The longi-
tudinal pile spacing is 4 ft (1.21 m) in the front and center rows and 6 ft (1.82 m) in the
rear row. The resultant of vertical loads on the wall is 20,000 lb/lin ft (291.87 kN/m) and
lies 3 ft 3 in. (99.06 cm) from the front row. Determine the pile load in each row.

FIGURE 35