The Allowable Stress Design (AISC-ASD) 9th Edition provides detailed provisions for designing steel stair systems that are safe and long-lasting while complying with code requirements. This Excel sheet automates the design of steel stair components including stringers, treads, risers, and landings under typical occupancy live loads and self-weight.
Steel Stair Design Components
A structural steel stair consists of several elements that must each be sized and checked:
- Stringers: The inclined beams that carry the treads. Typically W-shapes, channels, or plates, stringers must be checked for bending, shear, and deflection.
- Treads: The horizontal walking surfaces. Plate treads or grating panels are checked for bending between stringers.
- Landings: Flat intermediate platforms, designed as beams or plates spanning between stringers or support framing.
- Connections: Weld or bolt connections at the top and bottom supports must transfer both vertical load and horizontal thrust.
Design Loads Applied
Per AISC-ASD 9th Edition and applicable building codes:
- Live load: 100 psf (4.8 kN/m²) for public assembly stairs; 60 psf (2.9 kN/m²) for private residential stairs
- Dead load: Self-weight of steel sections plus any architectural finishes
- Concentrated load check: 300 lb (1.33 kN) point load at mid-span of treads
AISC-ASD 9th Edition Design Method
The allowable stress design approach checks that calculated stresses under service loads do not exceed the code-defined allowable values:
- Allowable bending stress Fb = 0.66Fy for compact sections (typical W-shapes)
- Allowable shear stress Fv = 0.40Fy
- Deflection limit: L/360 under live load for treads and L/240 for stringers
Modern Context: ASD 9th vs LRFD for Stair Design
Although LRFD (Load and Resistance Factor Design) is now the dominant design method in the United States for structural steel, the AISC-ASD 9th Edition remains relevant for renovation projects, facilities with existing ASD-based documentation, and some international jurisdictions. This Excel sheet provides a compliant and transparent design workflow for engineers who need to work within the ASD 9th framework.
