Scaffold Mudsill Bearing Pressure and Sill Length
The soil pressure a scaffold leg presses through its mudsill (leg load / plank area).
Example
You enter
- Load on one scaffold leg (lb) 4000
- Mudsill board width (in, e.g. 9.25 for a 2x10) 9.25
- Provided mudsill length (in) 24
- Allowable soil bearing (psf) 2000
You get
- Mudsill area 1.542 ft^2
- Bearing pressure 2,595 psf (OVER allowable)
- Required sill length 31.1 in
Checked against published worked examples from: Government of Alberta.
Details, formula, and sources
ScopeWhether it clears the allowable soil bearing, and the sill length needed if it does not. OSHA 1926.451(c)(2) requires base plates on sound, rigid mudsills. A first-check estimator, not the engineered design.
Formula or tablemudsill_area_ft2 = plank_width_in x plank_length_in / 144; bearing_psf = leg_load_lb / mudsill_area_ft2; required_area_ft2 = leg_load_lb / allowable_psf; required_length_in = required_area_ft2 x 144 / plank_width_in; pass = bearing_psf <= allowable_psf.
Source and editionBearing-pressure identity by name (load / area vs allowable); OSHA 1926.451(c)(2) base-plate and mudsill foundation requirement.
Free accessOSHA 1926.451 is free at osha.gov; the load-over-area bearing check is public statics.
What governsEstimate. AHJ and licensed professional govern.
API field namesleg_load_lb, plank_width_in, plank_length_in, allowable_psf, mudsill_area_ft2, bearing_psf, required_length_in
- Allowable soil bearing from the geotechnical report or a presumptive-load table; 2000 psf is the worked example's value onlygeotechnical
- Mudsill board 9.25 in (a nominal 2x10) in the worked example; the actual plank width and length governOSHA 1926.451(c)(2)