Formwork Tie Load and Spacing
Sizes the wall-form ties that take the lateral concrete pressure in tension.
Example
You enter
- Design lateral form pressure (psf) 600
- Tie horizontal spacing (ft) 2
- Tie vertical spacing (ft) 2
- Tie safe working load (lb) 3000
You get
- Load per tie 2,400 lb (OK)
- Utilization 0.8
- Max tributary per tie 5.00 sf
No published worked example is on file for this calculation. It is checked against a hand-worked derivation of its method and an independent reference test.
Details, formula, and sources
ScopeTie load = pressure x horizontal spacing x vertical spacing; max tributary = SWL / pressure. At 600 psf on a 24 x 24 in grid, each tie carries 2,400 lb - inside a 3,000 lb tie (5 sf max tributary). Pour faster (900 psf) and the tie hits 3,600 lb, over - tighten to 18 in and it drops to 2,025 lb. A tie failure is a form blowout; the tie manufacturer and ACI 347 govern.
Formula or tabletie_load_lb = lateral_pressure_psf x h_spacing_ft x v_spacing_ft; utilization = tie_load_lb / tie_swl_lb; max_trib_area_ft2 = tie_swl_lb / lateral_pressure_psf.
Source and editionFormwork tie-load identity by name (tie load = pressure x tributary area; max tributary = SWL / pressure); first-principles statics.
Free accessThe tributary-load statics are public first-principles; the lateral pressure (ACI 347) and the tie rating come from formwork-pressure and the tie manufacturer.
What governsEstimate. AHJ and licensed professional govern.
API field nameslateral_pressure_psf, h_spacing_ft, v_spacing_ft, tie_swl_lb, tie_load_lb, utilization, max_trib_area_ft2
- Lateral pressure the design form pressure from formwork-pressure (ACI 347 rate-of-rise)ACI 347 / formwork-pressure
- Tie SWL the manufacturer's rated safe working load, with its own safety factortie manufacturer