Formwork - Design of Reinforced Concrete - page 641

plied to each tie is then dependent on the pressure from the liquid concrete and on the hor-
izontal and vertical spacing of the ties. If the spacing of ties for a certain wall is 2 ft verti-
cally and 3 ft horizontally, and the calculated wall pressure is 800 psf, the total tensile
force on each tie equals 2

3 800 4800 lb, assuming a uniform pressure.

F at a rate of 4 ft/hr in a 12-ft high wall, the lateral
pressure for the semiliquid concrete could be calculated from the ACI expression as follows:

Should concrete be placed at 50

(9000)(4)
50

9000 R
T

p 150 150 870 psf

The resulting pressure diagram for the wall would be as shown in Figure 20.8.
Assuming a uniform pressure of 870 psf, the spacing of the studs could be selected as
was the spacing for the joists in the floor slab formwork. Example 20.5 shows the design
procedure for the sheathing, studs, wales, and ties for a wall form.

EXAMPLE 20.5

Design the forms for a 12-ft-high concrete wall for which the concrete is to be placed at a rate of 4
ft/hr at a temperature of 50 F. (Refer to Figure 20.8.) Use the following data:
1. Sheathing is to be Class I plyform, f 1930 psi, and E 1,650,000 psi.
2. Studs and wales are to consist of Douglas fir, coastal construction, f 1875 psi, H 180
psi, and E 1,760,000 psi. Allowable compression perpendicular to the grain is 490 psi.
3. Ties can carry 5000 lb each, and the tie washers are the same size as the one shown in Fig-
ure 20.7.
4. Double wales are used to avoid drilling for ties.
5. Maximum deflection in any form component is

3
4 -in.

1
360

of the span.

SOLUTION Design of Sheathing

Properties of 12-in.-wide piece of

3
4

plyform from Table 20.2:

S 0.455 in. 3 , I 0.199 in. 4

Load 870 lb/ft

Figure 20.8