Foundation Footing Design

Design spread footings for columns and walls with soil bearing capacity checks.

Design a square footing for a steel column with the following:
- Column: W14×82 steel column
- Dead Load (D): 120 kips
- Live Load (L): 80 kips
- Soil Bearing Capacity: 3,000 psf
- Concrete: f'c = 4,000 psi
- Rebar: fy = 60,000 psi
- Footing Depth: 24 inches below grade
- ACI 318-19 code

Determine footing size and required reinforcement.

SPREAD FOOTING DESIGN (ACI 318-19)

1. LOAD COMBINATIONS
   Factored Load (Service):
   P = D + L = 120 + 80 = 200 kips

2. FOOTING SIZE
   Required Area = P / qa
   A_req = 200,000 lb / 3,000 psf
   A_req = 66.67 SF

   Square Footing:
   B = √66.67 = 8.16 ft
   Use B = 8.5 ft × 8.5 ft (72.25 SF)

3. ACTUAL BEARING PRESSURE
   q_actual = 200,000 / 72.25 SF
   q_actual = 2,769 psf < 3,000 psf ✓ OK

4. FOOTING THICKNESS (One-Way Shear)
   Critical section at d from face of column
   Assume column = 14" × 14"
   V_u = 1.2D + 1.6L = 264 kips
   q_u = 264k / 72.25 = 3.65 ksf

   Shear @ d: V = 3.65 ksf × 8.5 ft × (3.43 ft)
   V = 106.3 kips

   φV_c = φ × 2√f'c × b × d
   φV_c = 0.75 × 2√4000 × 102" × d
   Set V_u = φV_c, solve for d:
   d_req = 20.2"

   Use h = 24", d = 21" (with 3" cover)

5. REINFORCEMENT (Flexure)
   M_u = q_u × B × (B/2 - c/2)²
   M_u = 3.65 ksf × 8.5 ft × (4.25 - 0.583)² / 2
   M_u = 226 kip-ft

   A_s = M_u / (φ × fy × 0.9d)
   A_s = 226 × 12 / (0.9 × 60 × 0.9 × 21)
   A_s = 2.64 in²

   Use 7 - #6 bars each way (A_s = 3.08 in²)
   Spacing = 102" / 7 = 14.6" o.c.

FINAL DESIGN:
✓ 8.5 ft × 8.5 ft × 24" thick footing
✓ #6 @ 14" o.c. each way (top layer)
✓ 3" clear cover
✓ Bearing pressure = 2,769 psf < 3,000 psf

Key Results

Common Use Cases

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