Stair Stringer Calculator | StructuralClaw

What it checks

The module designs a single stair stringer as a simply-supported beam of actual slant length. It models the member using statics for a simple span on an incline, with caller-supplied allowables. The design method relies on the specific allowable stresses and deflection limits provided by the user. Loads are specified on the horizontal projection and resolved onto the slant axis. The sequence of checks follows the resolution of these loads into uniformly distributed values along the slant. The module then calculates bending, shear, and deflection based on these resolved loads.

Inputs

Geometry - Horizontal run per flight (ft), total vertical rise per flight (ft), stringer cross-section width (in), and stringer cross-section depth (in).
Material - Material tag ("wood" or "steel"), modulus of elasticity (psi), allowable bending stress (psi), and allowable shear stress (psi).
Loads - Live occupant load on horizontal projection (psf), dead load on horizontal projection (psf), and tributary width per stringer (ft).
Deflection - Live-load deflection denominator and total-load deflection denominator.
Optional - Snow load (plf), roof live load (plf), project load combinations, and Ev toggle (A4, owner spec 09-08).

What it reports

Slant Span - Actual stringer length calculated as the hypotenuse of run and rise (ft).
Inclination - Angle from horizontal (deg).
Slant Loads - Live, dead, and total load along the slant axis (plf).
Max Moment - Maximum bending moment from total load (kip*ft).
Max Shear - Maximum shear from total load (kips).
Section Modulus - Calculated as b*d^2/6 (in^3).
Bending Stress - Actual bending stress (psi) compared against the allowable bending stress (psi).
Bending DCR - Bending demand/capacity ratio.
Shear Stress - Actual shear stress (psi).
Deflection - Live-load and total-load deflection (in) compared against their respective limits (in).
Combo Label - Which combination governed and where its factors came from.

Code references

The engine cites Statics — simple span on an incline, caller-supplied allowables. The material tag sets the self-weight density only. The Ev toggle references A4, owner spec 09-08.

Limits

The material tag is informational only. The number of stringers in the flight is for reference only. Supplying snow or roof live load switches the module onto the combination engine. If no load case beyond dead and floor live is present, the module behaves exactly as it did before. Results are engineering aids; the engineer of record is responsible for the design.

This module ships in the desktop app

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