Guide to Concrete Pressures
APA Plyform has to be stronger than conventional plywood to withstand the additional pressures. The normal concrete weight of 150pcf (pounds per square foot) will place a load on the forms of 12.5psf for each inch of thickness.
Check out APA’s complete Concrete Forming Design/Construction Guide for the recommended maximum pressures for Plyform Class I and Structural 1 Plyform. APA follows best practice guidance from American Concrete Institute (ACI).
They are based on a deflection limitation of 1/360th or 1/270th of the span, shear or bending strength, whichever is the lowest load value.
Recommended pressures take into account the number of continuous spans in the formwork design and whether the panel’s main strength axis is parallel or perpendicular to the supports. So it is also important to know the panel’s span rating and official Performance Category. See examples on APA trademarked panels.
For instance, a panel with a Performance Category of 15/32 in. will require a span rating of 32/16; for one measuring 19/32 it will be 40/20 and for a panel marked with a performance category of 23/32 the span rating will be 48/24. For more about span ratings for unsanded plyform panels used for concrete formwork, click here.
The pressures given in APA’s guide are based on a density of 150pcf and appropriate for the standard range of concrete poured. Lateral pressures for newly placed concrete deals with rate of pour, column/wall height and temperature. Where exterior vibration is involved or a pumped placement system is used, the pressures need to be increased.