Spread Footing Bearing & Shear Design
Complete spread footing design starting from service loads and allowable bearing pressure. Sizes the footing plan dimensions to satisfy bearing, then checks structural adequacy under factored loads per ACI 318-19. Performs one-way (beam) shear at a critical section d from the column face, two-way (punching) shear at d/2 from the column face, and designs bottom flexural reinforcement.
What this calculates
Required footing size (B × L) from service load bearing check, factored bearing pressure qu, one-way shear demand vs. capacity (φVc = φ·2·√f'c·b·d per Section 22.5), two-way punching shear on the critical perimeter (bo at d/2 from column face per Section 22.6), and required bottom reinforcement As per flexure at the column face.
Inputs
Unfactored column dead load
Unfactored column live load
Column dimension in one direction
Column dimension in the other direction
Allowable net soil bearing pressure
Footing concrete compressive strength
Reinforcement yield strength
Total footing thickness (trial value)
Outputs
Required footing width
Actual service-level bearing pressure
One-way shear demand-to-capacity ratio
Two-way shear demand-to-capacity ratio
Required bottom reinforcement per foot width
Methodology
Footing plan dimensions are sized so the service load bearing pressure q = P/(B·L) ≤ qa. One-way shear per ACI 318-19 Section 22.5: φVc = φ·2·√f'c·bw·d at distance d from the column face. Two-way punching shear per Section 22.6: φVc is the minimum of three expressions involving √f'c, the ratio of column sides (β), and the critical perimeter (bo = 2(c1 + d) + 2(c2 + d)), with φ = 0.75. Flexure per Section 22.2 at the column face with a cantilever projection of (B − c)/2.
Code References
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