Formwork Pressure
Lateral form pressure per ACI 347R-14...
Example
You enter
- Pour rate (ft/hr) 5
- Concrete temperature (°F) 70
- Weight factor normal
- Unit weight (pcf, blank = from the weight factor) 150
- Wall height (ft) 12
You get
- Pressure 793 psf
- ACI value 793 psf
- Wet-head cap 1,800 psf
- Weight factor 1
Checked against published worked examples from: ACI 347 Guide to Formwork for Concrete.
Details, formula, and sources
ScopeLateral form pressure per ACI 347R-14 (short form for R < 7 ft/hr in walls up to 14 ft, else the tall-wall / 7-15 ft/hr form; full head above 15 ft/hr; at least 600 Cw), capped at the wet head.
Formula or tableACI 347R wall pressure: P = C_c × C_w × (150 + 9000 × R / T) for R < 7 ft/hr and walls up to 14 ft; C_c × C_w × (150 + 43,400 / T + 2,800 × R / T) for taller walls at R < 7 or any wall at 7-15 ft/hr; full wet head above 15 ft/hr; never below 600 × C_w psf; capped at the wet-head pressure ρgh. R is pour rate (ft/hr), T is concrete temperature (°F), C_w is unit-weight coefficient.
Source and editionACI 347R-14 (Guide to Formwork for Concrete) by name.
Free accessACI 347 licensed; engineering-practice formulas free in published concrete texts.
What governsEstimate. AHJ and licensed structural engineer govern.
API field namespour_rate_ft_per_hr, concrete_temp_F, weight_factor, unit_weight_pcf, wall_height_ft, pressure_psf, aci_pressure_psf, wet_head_psf
- Concrete unit weight 150 pcf normal-weight (115 / 135 for the lightweight options) unless user suppliesACI 347
- Unit weight coefficient C_w 0.5 (1 + w/145) but not less than 0.80 below 140 pcf; 1.0 at 140-150 pcf; w/145 above 150ACI 347R-14 Table 4.2.2.1a(c)
- Chemistry coefficient C_c 1.0 Type I/II/III without retarder up to 1.5 for >= 70% slag or >= 40% fly ash with retarder; an HRWR counts as a retarderACI 347R-14 Table 4.2.2.1a(b)