Flitch Beam Calculator, NDS 2018 / AISC ASD §F1/§F4

What it checks

The module designs a flitch beam, a composite member consisting of a steel plate and wood sandwich. It calculates transformed-section flexure, shear, and deflection, with load shared by stiffness. The design method follows NDS 2018 and AISC ASD, utilizing strength and service limit state principles as implied by the cited codes. The sequence of checks begins with determining internal forces for the specified support condition under combined uniform and midspan point loads. The module then evaluates stress and deflection at the governing load combination. It applies the appropriate load-duration factor based on the active load cases, such as dead, live, snow, or roof live loads.

Inputs

Geometry and Loads - Support condition, uniform load (klf), midspan point load (kips), and span length (ft).
Optional Load Cases - Snow load (plf) and roof live load (plf). Supplying snow load switches the module onto the combination engine.
Combinations - Project load combinations. If absent and no load case beyond dead and floor live is present, the module uses the default path.
Seismic - Ev toggle (SDS). If provided as a value greater than zero, it folds the vertical seismic effect into every seismic combination.

What it reports

Governing Combination - The specific load combination that governed the design and the source of its factors.
Duration Factor - The load-duration factor actually applied to the design loads.
Stress Check - One stress check result at the governing combination, indicating the member's capacity relative to demand.
Internal Forces - Maximum absolute moment (kip-ft) and shear (kips) for the given support condition.
Deflection - Deflection calculated using a multiplier on the simple-span baseline, adjusted for non-simple spans with approximate stiffness reductions.

Code references

The engine cites NDS 2018 §3.3 / §3.4.2 and AISC ASD §F1 / §F4. These standards govern the transformed-section analysis and the specific flexure and shear checks performed by the module.

Limits

The module assumes the load sharing is based on stiffness. If no snow or roof-live case is supplied, the module takes the old path exactly, using D + L unfactored at the supplied C_D. The conversion to the combination engine is opt-in. If the Ev toggle is None, the vertical seismic effect is off. Results are engineering aids; the engineer of record is responsible for the design.

This module ships in the desktop app

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