Formwork for Concrete Structures by R.L.Peurifoy and G.D- By EasyEngineering.net

32 Chapter Three
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FIGURE 3-5 Distribution of concrete pressure for Example 3-4.
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Checks on limitations on pressures calculated from Eq. (3-3):
Limited to greater than 600C w
= 600(1.0) = 600 lb per sq ft
Limited to less than P m
= wh = 150(14) = 2,100 lb per sq ft
The calculated value from Eq. (3-4) is 1,410, which is above the
minimum of 600 and below the maximum of wh = 2,100. Therefore,
use 1,410 lb per sq ft lateral pressure on the forms. The 1,410-lb per sq ft
maximum pressure will occur a depth of 1,410/150 = 9.4 ft below the
top of the form.
Example 3-5
A column form 12 ft high is filled with 150 lb per cu ft concrete at a
temperature of 60°F. The concrete is Type I with a retarder. Concrete
will be placed with normal internal vibration to a depth of less than
4 ft. The concrete will be in 1 hr.
Rate of placement = 12 ft/1 hr = 12 ft per hr
From Table 3-1, the value of C w
is 1.0 and from Table 3-2 the value
of C c
is 1.2. Using Eq. (3-4), the lateral pressure can be calculated.
P m
= C w
C c
[150 + 9,000R/T]
= (1.0)(1.2)[150 + 9,000(12/60)]
= 2,340 lb per sq ft
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