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

Downloaded From : www.EasyEngineering.net
Forms for Columns 293
vertical wood battens to provide increased spacing of column clamps.
The strength and deflection equations presented at the beginning of
this chapter may be used to determine the maximum permissible
spacing of column clamps, which is equivalent to the allowable span
length of the composite plywood with the wood battens.
Example 10-2
Forms for a 20-in.-square column consist of ¾-in.-thick Plyform,
backed with vertical 2 × 4 No. 2 grade Southern Pine wood battens
laid flat, similar to the forming system shown in Figure 10-2. A
plan view of one side of the 20-in. square column form is shown in
Figure 10-3. Concrete, having a unit weight of 150 lb per cu ft, will
be placed in the 10-ft-high column form. Class I Plyform, which is
ww.EasyEngineering.n
¾-in. thick, will be placed in the horizontal direction (face grain
across supports) as sheathing.
The maximum pressure of the concrete on the forms will occur at
the bottom of the column form. This maximum pressure can be calculated
as follows:
From Eq. (10-1), P m
= wh
= (150 lb per cu ft)(10 ft)
= 1,500 lb per sq ft
This pressure acts against the Plyform, which must transfer it in a
horizontal direction to the adjacent vertical wood battens. For a 20-in.
column formed with ¾-in. Plyform backed with 2 × 4 vertical wood
battens laid flat, the clear span distance between the 2 × 4 s will be
5.875 in., as shown in Figure 10-3. Thus, the Plyform must have adequate
strength and rigidity to transfer the 1,500 lb per sq ft concrete
pressure over the 5.875-in. span length.
For this example, the Plyform will be placed with the face grain in
the horizontal direction. A review of Table 10-3 indicates that ¾-in.
Class I Plyform can sustain a pressure of 1,500 lb per sq ft with support
spacing up to 7 in. when the panels are placed in the horizontal
0.75''
20.75''
0.75''
9.375''
3.5'' 5.875'' 3.5'' 5.875''
3.5''
FIGURE 10-3 Plan view of one side of 20-in.-square column form constructed
of ¾-in. Plyform with 2 × 4 vertical battens.
Downloaded From : www.EasyEngineering.net