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

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Pressure of Concrete on Formwork 27
FIGURE 3-3 Distribution of Concrete Pressure for Example 3-2.
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The rate of placement R in ft per hr can be calculated as follows:
R = [volume pumped per hour]/[volume pumped in 1 ft height
of wall]
Volume pumped per hour = 18 cu yd per hr
Volume of 1 ft height of wall = (1 ft)(60 ft)(15/12 ft)
= 75 cu ft
= 2.78 cu yd of concrete in 1 ft height
of wall
Therefore, the rate of placement R = [18 cu yd per hr]/[2.8 cu yd per ft]
= 6.5 ft/hr
The rate of placement is less than 7 ft per hr and wall height does
not exceed 14 ft; therefore, Eq. (3-2) can be used to calculate the concrete
pressure.
P m
= C w
C c
[150 + 9,000R/T]
= (1.0)(1.0)[150 + 9,000 (6.5/80)]
= 882 lb per sq ft
Checks on limitations on pressures calculated from Eq. (3-2):
Limited to greater than 600C w
= 600(1.0) = 600 lb per sq ft
Limited to less than P m
= wh = 150(9) = 1,350 lb per sq ft
The calculated value from Eq. (3-2) is 882, which is above the minimum
of 600 and below the maximum of wh = 1,350. Therefore, use an
882 lb per sq ft lateral pressure on the forms. The 882-lb per sq ft maximum
pressure will occur at a depth of 882/150 = 5.9 ft as shown in
Figure 3-4.
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