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/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
Checked against published worked examples from: ACI 347 formwork practice.
Details, formula, and sources
ScopeA 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.
Formula or tablew = 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.
Source and editionFormwork members analyzed as continuous beams over three or more equal spans, the standard ACI 347 formwork-design approach, by name.
Free accessThe continuous-beam results are public structural mechanics; ACI 347 is available through ACI and its approach is reproduced in free formwork design guides.
What governsEstimate. AHJ and licensed professional govern.
API field namespressure_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