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Concrete formwork pressure calculator (ACI 347)
Fresh concrete behaves like a heavy fluid as it is placed, pushing outward on the forms, and that lateral pressure is what the ties, sheathing, walers, and shores have to resist. The ACI 347 formula for columns is P equals Cw times Cc times the quantity 150 plus 9000 times R divided by T, where R is the rate of placement in feet per hour and T is the concrete temperature in degrees Fahrenheit. This calculator takes the unit-weight coefficient Cw and the chemistry coefficient Cc as 1.0, which fits normal-weight concrete with no set retarders or special admixtures; for lightweight mixes, retarded concrete, or blended cements those coefficients change, so adjust them per ACI 347. The design pressure is bounded by a minimum of 600 psf and a maximum of 3000 psf, or the full hydrostatic head of the concrete, whichever is less. The takeaway for the field is that a fast pour in cold concrete builds the highest pressure, which is exactly when forms blow out, so the pour rate is a safety control, not just a schedule choice. Walls use a different formula and rate ranges. Treat this as a planning figure and confirm the design pressure and the formwork design with ACI 347 and the engineer.
Result
Formwork lateral pressure (ACI 347 column form): P = Cw × Cc × (150 + 9000 × R / T), where R is the rate of placement in feet per hour and T is the concrete temperature in degrees Fahrenheit. This calculator takes the weight coefficient Cw and the chemistry coefficient Cc as 1.0, which fits normal-weight concrete with no retarders or special admixtures; adjust them for lightweight mixes, set retarders, or blends per ACI 347. The result is bounded by a minimum of 600 psf and a maximum of 3000 psf (or the full hydrostatic head, whichever is less). Fresh concrete acts like a fluid as it is placed, so a fast pour in cold concrete builds the most pressure, which is what the ties, sheathing, walers, and shores have to resist. Walls use a different formula and rate ranges. Treat this as a planning figure and confirm the design pressure and the formwork design with ACI 347 and the engineer.
anvilfield.com/calculators/concrete-formwork-pressure-calculator · Free field calculators and FieldOS. A planning estimate, verify against the code, the manufacturer, and the engineer of record.
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Formwork pressure FAQ
What is concrete formwork?
Concrete formwork is the temporary mold that shapes fresh concrete plus the framing and hardware that hold it in place until the concrete sets. It has to hold the shape, resist the lateral pressure the wet concrete pushes back with, and leave the right finish, then strip clean. ACI 347 governs the design, and a failure is a collapse.
What is a gang form?
A gang form is many form panels joined into one rigid unit, sized so the whole assembly is set, stripped, and flown by crane as a single piece. It suits large, repeating walls and cores because fewer cycles mean fewer picks and faster pours. Gangs usually run reusable taper ties so they strip and fly clean every cycle.
What are form ties?
Form ties are the tension members holding the two faces of a wall form together against the outward pressure of fresh concrete, and they set the wall thickness. Snap ties are light duty, she-bolts and coil ties heavier, and taper ties pull fully out for gang forms. Space them to the pressure, tightest at the bottom of the form.
Why does formwork fail?
Formwork fails when it is loaded harder than it was designed for or stripped too early. A wall blows out from under-spaced ties or a pour rate that ran past the design, a tower buckles from poor bracing or bad bearing, and a slab drops when stripped before strength. Pour rate is the field cause that hides in plain sight.
Which formwork system should I use for a repetitive wall?
For a wall that repeats many times, a modular panel or gang system beats job-built lumber, because the cost spreads across the cycles and each set-and-strip is faster. Job-built wins on low-quantity, odd shapes. The break-even is repetition, so count the cycles honestly before you choose, and match the face material to the finish.