Liquid-Head Form Pressure

p = γ h (p_{m a x} may be capped by ACI rate/temperature formulas)

Full-liquid hydrostatic pressure p = γh if the concrete behaves as a fluid to depth h (slow rate, vibration, retarding admixtures). ACI caps pmax using pour rate and temperature for walls/columns. γc ≈ 150 pcf (23.6 kN/m³).

$p$ (psf): Lateral pressure
$γ$ (pcf): Unit weight of concrete
$h$ (ft): Fluid head

Step-by-step solved example

γ = 150 pcf, fluid head h = 8 ft (uncapped). p?

Fresh concrete as a fluid: p = γh until ACI pmax caps it.

1. Hydrostatic
p = 150×8 = 1,200 psf.
$p = 1200 psf$
2. Note
Compare with ACI pmax; use the smaller for design of wall ties.

Answer: 1,200 psf

10 practice questions

0/10 correct

1.If ACI pmax = 2000 psf and γh = 1200 psf, design p =

2.Faster pour rate tends to

3.Higher concrete temperature tends to

4.γ = 23.5 kN/m³, h = 2.0 m. p =

5.Vibration of the lift

6.Slab formwork (bottom) is designed for

7.150 pcf × 1 ft =

8.Retarding admixture

9.Tie load ≈ p × tributary area of the tie.

10.Lightweight concrete (smaller γ) gives