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

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Pressure of Concrete on Formwork 25
Weight of Concrete
Less than 140 lb per cu ft
Value of C w
0.5 [1 + (w/145 lb per cu ft)],
but not less than 0.8
140 to 150 lb per cu ft 1.0
More than 150 lb per cu ft w/145 lb per cu ft
TABLE 3-1 Values of Unit Weight Coefficient, C w
ww.EasyEngineering.n
Cement Type or Blend
Types I, II, and III without retarders ∗ 1.0
Types I, II, and III with a retarder 1.2
Other types or blends containing less than 70% 1.2
slag or 40% fly ash without retarders ∗
Other types or blends containing less than 70% 1.4
slag or 40% fly ash with a retarder ∗
Blends containing more than 70% slag or 40% fly
ash
Value of C c
1.4
∗
Retarders include any admixture, such as a retarder, retarding water reducer,
retarding mid-range water-reducing admixtures, or high-range water-reducing
admixture (superplasticizers), that delay setting of concrete.
TABLE 3-2 Values of Chemistry Coefficient, C c
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(12) = 1,800 lb per sq ft
The calculated value from Eq. (3-2) is 793, which is above the minimum
of 600 and below the maximum 1,800. Therefore, use 793 lb per
sq ft lateral pressure on the forms. The 793 lb per sq ft maximum pressure
will occur at a depth of 793/150 = 5.3 ft below the top of the form
as shown in Figure 3-2.
Example 3-2
A wall form 8 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 rate of placement will be 10 ft per hr.
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