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Concrete Formwork Pressure Calculator
ACI 347R-14 • Maximum lateral pressure on vertical formwork
🏗️ Based on ACI 347R-14 • Calculates max fresh concrete pressure on walls & columns • US units (ft, lb/ft³, °F)
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Maximum Lateral Pressure (psf)
0 kPa
Metric Equivalent
0 psf
Hydrostatic Pressure (full liquid head)
0%
Reduction from Hydrostatic
0 ft
Max Safe Pour Height (based on pressure)
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📊 Pressure distribution
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⚠️ Engineering Disclaimer
This calculator provides estimates based on ACI 347R-14 guidelines. Actual formwork design must consider site conditions, vibration methods, and should be reviewed by a qualified structural engineer. Always consult the full ACI 347 standard for complete design requirements.
This calculator provides estimates based on ACI 347R-14 guidelines. Actual formwork design must consider site conditions, vibration methods, and should be reviewed by a qualified structural engineer. Always consult the full ACI 347 standard for complete design requirements.
Calculate formwork pressure — based on ACI 347R-14 • US units
What is Formwork Pressure?
Fresh concrete exerts lateral pressure on vertical formwork. This pressure depends on concrete density, slump, temperature, rate of placement, and vibration methods. ACI 347R-14 provides formulas to calculate maximum safe design pressure for formwork.
ACI 347R-14 Formula (for placement rate ≤ 7 ft/hr):
P = 150 + 9000 × R / T
Where: P = pressure (psf) | R = rate of pour (ft/hr) | T = temperature (°F)
Maximum pressure: P_max = 150 × H (hydrostatic) or as calculated, whichever is smaller
How to Use This Calculator
- Structure Type: Select Wall/Base or Column (affects maximum height limits)
- Concrete Type: Normal weight or lightweight (affects unit weight)
- Unit Weight: Typical values: 150 lb/ft³ for normal, 110 lb/ft³ for lightweight
- Slump: Standard slumps range from 2-6 inches; higher slumps increase pressure
- Placement Height: Total height of concrete pour (wall or column height)
- Temperature: Fresh concrete temperature at placement (lower temperature = higher pressure)
- Rate of Pour: How fast concrete is placed (ft/hr). Higher rates = higher pressure
- Internal Vibration: Check if vibration depth ≤ 4 ft (affects pressure coefficient)
Understanding Your Results
- Maximum Lateral Pressure: Design pressure for formwork (psf)
- Hydrostatic Pressure: Full liquid head pressure (w × H)
- Reduction Percentage: How much lower than hydrostatic due to setting
- Max Safe Pour Height: Maximum pour height without exceeding pressure limits
Factors Affecting Formwork Pressure
- Rate of Placement (R): Higher placement rates increase pressure
- Temperature (T): Lower temperatures increase pressure (slower setting)
- Concrete Density (w): Heavier concrete = higher pressure
- Slump: Higher slump concrete flows more easily, increasing pressure
- Vibration: Internal vibration liquefies concrete, increasing pressure at vibration depth
- Retarders: Delay setting time, increasing pressure duration
Typical Design Pressures
- Walls (normal conditions): 600-900 psf
- Columns (high pour rates): 1,000-1,500 psf
- Hydrostatic maximum: 150 × H (e.g., 10 ft wall = 1,500 psf)
- Minimum design pressure: 600 psf per ACI 347
Formwork Design Recommendations
- Use minimum 600 psf for all formwork regardless of calculation
- Design for pressure distribution: triangular from zero at top to maximum at bottom
- Consider impact loads from concrete placement (additional 25-50% for pump placement)
- Allow for wind loads and construction live loads
- Follow manufacturer recommendations for formwork systems
Frequently Asked Questions
- What is the minimum formwork pressure per ACI? — 600 psf (42.7 kN/m²) regardless of calculation.
- How does temperature affect pressure? — Cold concrete sets slower, requiring higher formwork pressure capacity.
- What is the typical formwork pressure for walls? — Usually 600-900 psf depending on pour rate and height.
- When does hydrostatic pressure govern? — When pour rate is very high or concrete is very fluid (self-consolidating).
- Can I use this for self-consolidating concrete (SCC)? — SCC requires full hydrostatic pressure unless test data shows otherwise.