Calculate design load capacity of concrete slabs, beams, columns, and footings using ACI 318-2026 strength design — with φ-factors, reinforcement, and IBC 2024 compliance check.
ACI 318-2026 uses the Strength Design Method: φRn ≥ U, where U = 1.2D + 1.6L is the governing factored load combination per ASCE 7-22. The strength reduction factor φ reflects failure mode ductility — 0.90 for ductile flexural failures, 0.65 for brittle column compression, 0.75 for shear. Capacity depends on concrete strength f'c, effective steel area As, member dimensions, and span. Normal-weight concrete (150 pcf) and Grade 60 rebar (fy = 60,000 PSI) are assumed throughout.
This calculator provides preliminary estimates only using simplified ACI 318-2026 equations. All structural concrete design in the USA must be performed or reviewed by a licensed PE per IBC 2024. Results assume idealized support conditions, Grade 60 rebar, normal-weight concrete, and no seismic or wind demand. Do not use these results in place of engineered structural drawings.
| Slab / Thickness | f'c | Steel | Span / Subgrade | Capacity | Use |
|---|---|---|---|---|---|
| SOG 4″ | 3,000 | Fiber / WWF | k = 100 pci | 300–500 PSF | Residential garage |
| SOG 6″ | 4,000 | #4 @ 12″ | k = 100 pci | 600–900 PSF | Warehouse / commercial |
| SOG 8″ | 4,000 | #5 @ 12″ | k = 200 pci | 1,200–1,600 PSF | Heavy industrial |
| Struct. Slab 6″ | 4,000 | #4 @ 12″ | 12 ft span | 100–150 PSF | Residential floor |
| Struct. Slab 8″ | 4,000 | #5 @ 10″ | 14 ft span | 175–250 PSF | Commercial floor |
| Column Size | f'c (PSI) | Steel Ratio | φPn (kips) | Application |
|---|---|---|---|---|
| 10 × 10″ | 4,000 | 1% | ~142 kips | Residential / light commercial |
| 12 × 12″ | 4,000 | 2% | ~224 kips | Standard commercial |
| 16 × 16″ | 5,000 | 3% | ~508 kips | Mid-rise commercial |
| 24 × 24″ | 6,000 | 4% | ~1,350 kips | High-rise / transfer |
SOG slabs transfer load directly to subgrade — governed by the Westergaard method and modulus of subgrade reaction k. They typically carry 200–2,000+ PSF. Structural slabs span between supports — governed by ACI 318 flexural strength φMn — and carry 40–300 PSF depending on span. The two require completely different design approaches.
ACI 318-2026 Section 9.6.1: As,min = max(3√f'c/fy, 200/fy) × bw × d for beams. For 4,000 PSI / Grade 60: ρmin ≈ 0.0033. For slabs: temperature/shrinkage steel ρ = 0.0018Ag per Section 24.4.3. Columns: ρmin = 1%, ρmax = 8% (Sections 10.6.1). Minimum steel ensures ductile behavior and crack control.
Short column equations apply when slenderness kl/r ≤ 22 (braced frame, tied column). For a 12×12″ column, r = 0.30 × 12 = 3.6″, so limit = 22 × 3.6 = 79.2″ ≈ 6.6 ft. Taller columns require moment magnification per ACI 318-2026 Section 6.2.5 — which can reduce effective capacity by 20–40%.
ASCE 7-22 minimum live loads: Residential floors 40 PSF · Offices 50 PSF · Retail 75–100 PSF · Light storage 125 PSF · Heavy storage 250 PSF · Parking (passenger) 40 PSF · Driveways / trucks 250 PSF. Slab and beam design must meet or exceed these minimums for legal occupancy per IBC 2024.