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

24 Chapter Three
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T = temperature of concrete in form, degrees Fahrenheit
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
For all wall forms with concrete placement rate from 7 to 15 ft per
hr, and for walls where the placement rate is less than 7 ft per hr and
the placement height exceeds 14 ft.
P m
= C w
C c
[150 + 43,400/T + 2,800 R/T] (3-3)
ww.EasyEngineering.n
where P m
= maximum 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 Eqs. (3-2) and (3-3) are
shown in Table 3-1 and the values for the chemistry coefficient C c
are
shown in Table 3-2. For concrete placed in wall forms at rates of pour
greater than 15 ft per hr, the lateral pressure should be wh, where h is
the full height of the form. ACI Committee 347 recommends that the
form be designed for a full hydrostatic head of concrete wh plus a
minimum allowance of 25% for pump surge pressure if concrete is
pumped from the base of the form.
Example 3-1
A wall form 12 ft high is filled with 150 lb per cu ft concrete at a temperature
of 70°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 5 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. The rate of placement is less than 7 ft per hr and the placement
height does not exceed 14 ft, therefore Eq. (3-2) can be used to
calculate the lateral pressure as follows.
P m
= C w
C c
[150 + 9,000R/T]
P m
= C w
C c
[150 + 9,000R/T]
= (1.0)(1.0)[150 + 9,000(5/70)]
= 793 lb per sq ft
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