Formwork Stud / Wale Maximum Spacing
The stud, wale, and shore spacing a formwork member can span under the concrete pressure.
Example
You enter
- Form pressure (psf) 600
- Tributary width (in, spacing of what it supports) 12
- Member width b (in, dressed) 1.5
- Member depth d (in, dressed) 3.5
- Allowable bending Fb (psi, duration-adjusted) 1000
- Allowable shear Fv (psi) 180
- Modulus E (psi) 1600000
- Deflection limit denominator (360 = L/360) 360
You get
- W lb per (in) 50
- Section modulus (in³) 3.0625
- Moment inertia (in⁴) 5.35938
- Span bending (in) 24.7487
- Span shear (in) 21
- Span deflection (in) 41.0308
- Max spacing (in) 21
Details, formula, and sources
A form member is a continuous beam over three or more supports, so the span comes from three exact continuous-beam results - M = wL^2/10, V = 0.6wL, and deflection wL^4/145EI - each inverted and the smallest governing. A 2x4 stud under 600 psf at 12-in tributary allows 24.7 in by bending and 41.0 by deflection but only 21.0 by SHEAR, which is the one that governs short deep form members and the one people skip.
w = pressure x tributary / 144; bending L = sqrt(10 Fb S / w); shear L = (2/3 Fv b d)/(0.6 w); deflection L = cbrt(145 E I/(w x denominator)); the smallest governs.
Formwork members analyzed as continuous beams over three or more equal spans, the standard ACI 347 formwork-design approach, by name.
The continuous-beam results are public structural mechanics; ACI 347 is available through ACI and its approach is reproduced in free formwork design guides.
Estimate. AHJ and licensed professional govern.
Field names used by the API: pressure_psf, tributary_in, width_b_in, depth_d_in, fb_psi, fv_psi, e_psi, deflection_denominator, w_lb_per_in, section_modulus_in3, moment_inertia_in4, span_bending_in, span_shear_in, span_deflection_in, max_spacing_in
- Three or more spans continuous-beam coefficients wL^2/10, 0.6wL, and wL^4/145EI apply to that case onlycontinuous-beam analysis / ACI 347 practice
- Dressed and adjusted dimensions dressed, Fb and Fv already adjusted for short load durationuser input, stated in the field labels
- Shear governs short members the check most often skipped and most often controllingworked example in the tile