Formwork Designer

How the Formwork Designer checks a form

The designer works out the largest lateral pressure of the fresh concrete to ACI 347R-14 section 4.2.2, the same way as the formwork pressure calculator, and follows it through the form. Each part is a beam continuous over its supports, under the largest pressure along its whole length:

• Sheathing: a 12 in strip of plywood spanning across the studs, checked for bending, rolling shear and deflection with APA's section properties for Plyform Class I.
• Studs: each carries a strip as wide as the stud spacing, spanning between the walers.
• Walers: each carries a strip as tall as the waler spacing, spanning between the ties, with the studs' loads taken as spread along it.
• Bearing: each stud's reaction pressing on the waler plies, perpendicular to the grain of both.
• Ties: each takes the waler's reaction over it, against the tie's safe working load.

The lumber is checked to NDS 2024 by allowable stress design, with the load duration factor (1.25 for seven days), the wet service factors, the size factor, and the repetitive member factor for studs 24 in or closer. Shear leaves out the load within d of each support. For each part, the designer also gives the longest span that works, so you can space the studs, walers and ties out as far as they'll go.

Not checked: the bracing against wind and construction loads, the form's bottom plate and anchorage, uplift on sloping forms, and steel or aluminum form systems, which come with their makers' load tables.