Column form pressure (ACI 347) = Cw·Cc·(150 + 9000R/T) psf, at least 600·Cw psf and never more than full liquid head w·h. Columns are often poured fast, so the cap usually governs: a 3.5 m column filled at 6 m/h is designed for full hydrostatic pressure, 82.4 kPa at the base.
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Facing sheets required
3sheets, 10% waste incl.
Contact area
7.0 m²
Clamp / yoke sets
9 sets
Concrete volume
0.84 m³
Peak lateral pressure on formwork
82.4 kPa
100% of full hydrostatic pressure at this height: full liquid head w·h governs.
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Cw = 1.000 (from density); Cc = 1.0; R = 19.69 ft/h; T = 68 °F
ACI 347: p = Cw·Cc·(150 + 9000R/T) = 131.9 kPa
Limits: minimum 600·Cw psf; maximum w·h = 82.4 kPa
Design pressure = 82.4 kPa, reached 3.50 m below the top of the pour
Contact area = 2 × (W + D) × H × n = 2 × (0.40 + 0.60) × 3.50 × 1 = 7.0 m²
Clamp sets = (⌈H ÷ 450⌉ + 1) × 1 = 9
Clamps at the base carry the highest pressure (82.4 kPa); many suppliers close up clamp spacing in the bottom third.
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Formulas
Pressure (ACI 347R-14): p = Cw · Cc · (150 + 9000 R / T) psfLimits: 600 · Cw ≤ p ≤ w · hContact area: 2 × (W + D) × H × n (circular: π × D × H × n)Clamp sets: (⌈H ÷ spacing⌉ + 1) × n
Worked example
A 400 × 600 mm column, 3.5 m high, filled at 6 m/h with normal concrete at 20 °C:
Full liquid head: 2,400 kg/m³ × 9.81 × 3.5 m = 82.4 kPa: lower, so it governs
Design pressure = 82.4 kPa at the base
Contact area = 2 × (0.4 + 0.6) × 3.5 = 7.0 m² → 3 sheets of 1220 × 2440 with 10% waste
Clamps at 450 mm = ⌈3.5 ÷ 0.45⌉ + 1 = 9 sets
When does the equation govern? (normal concrete, 20 °C)
Column height
Full liquid head
Rate where the equation drops below it
3 m
70.6 kPa
about 3.0 m/h
4 m
94.1 kPa
about 4.2 m/h
5 m
117.7 kPa
about 5.3 m/h
Pour faster than these rates and the form sees full liquid head at the base. The 600·Cw psf (28.7 kPa) minimum still applies to slow pours.
Assumptions and limits
Placement from the top with normal internal vibration.
Clamp count assumes even spacing with a clamp at the base and the top. Your supplier’s layout governs.
Circular forms (tubes or steel shutters) report the form length, not plywood sheets.
Not a formwork design: the capacity of the plywood, clamps and bracing must be checked separately.
Frequently Asked Questions
What is the pressure on column formwork?
ACI 347R-14 gives Cw·Cc·(150 + 9000R/T) psf for columns, with R the rate of rise in ft/h and T the concrete temperature in °F. It must be at least 600·Cw psf and is never more than the full liquid head, density × height.
Why is my column result 100% hydrostatic?
Columns hold a small volume, so they fill quickly. When the rate is high the equation gives more than density × height, and the full liquid head becomes the design pressure. That is normal for columns.
What counts as a column under ACI 347?
A vertical element with no plan dimension greater than 6.5 ft (2 m). Anything wider is treated as a wall.
How far apart should column clamps be?
That depends on the clamp or yoke capacity, the plywood and the pressure, so take it from the formwork supplier's tables or a formwork design. Spacing is usually closer near the base, where pressure is highest.
References
ACI 347R-14 Guide to Formwork for Concrete, §4.2.2 columns
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