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

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Pressure of Concrete on Formwork 31
Lateral Pressure of Concrete on Column Forms
For determining pressure of concrete on formwork ACI 347 defines a
column as a vertical structural member with no plan dimensions
greater than 6.5 ft. As previously presented, the American Concrete
Institute recommends that formwork be designed for it full hydrostatic
lateral pressure as given by Eq. (3-1), P m
= wh, where P m
is the lateral
pressure (lb per sq ft), w is the unit weight (lb per cu ft) of the newly
placed concrete, and h is the depth (ft) of the plastic concrete. Concrete
is often placed rapidly in columns with intensive vibration or with selfconsolidating
concrete. Therefore, h should be taken as the full height
of the column form. There are no maximum or minimum values given
for the pressure calculated from Eq. (3-1).
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For concrete with a slump 7 in. or less and placement by normal
internal vibration to a depth of 4 ft or less, formwork for columns can
be designed for the following lateral pressure.
P m
= C w
C c
[150 + 9,000R/T] (3-4)
where P m
= calculated lateral pressure, lb per sq ft
C w
= unit weight coefficient
C c
= chemistry coefficient
R = rate of fill of concrete in form, ft per hr
T = temperature of concrete in form, °F
Minimum value of P m
is 600C w
, but in no case greater
than wh.
Applies to concrete with a slump of 7 in. or less
Applies to normal internal vibration to a depth of 4 ft or
less
Values for the unit weight coefficient C w
in Eq. (3-4) are shown in
Table 3-1 and the values for the chemistry coefficient C c
are shown in
Table 3-2. The minimum pressure in Eq. (3-4) is 600C w
lb per sq ft, but
in no case greater than wh.
Example 3-4
A column form 14 ft high is filled with 150 lb per cu ft concrete at a
temperature of 50°F. The concrete is Type I without a retarder. Concrete
will be placed with normal internal vibration to a depth of less
than 4 ft. The rate of placement is 7 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 1.0. Using Eq. (3-4), the lateral pressure can be calculated.
P m
= C w
C c
[150 + 9,000R/T]
= (1.0)(1.0)[150 + 9,000(7/50)]
= 1,410 lb per sq ft
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