What it checks
The module designs a simple span wood header, either sawn or engineered, for a single species, grade, and size. It supports multi-ply configurations and handles uniform dead and live loads, as well as optional roof live, snow, and wind loads. The design method follows the National Design Specification (NDS) 2018, applying the full adjustment-factor chain including CD, CM, Ct, CF, CL, and Cr to reference values.
The sequence of checks begins with determining the governing load combination and the associated load duration factor. The module then calculates the demands for moment, shear, and deflection. It evaluates bending capacity per NDS §3.3, shear stress per NDS §3.4.2, and bearing perpendicular to grain per NDS §3.10.4. Finally, it checks service-level deflection against the specified limits, reporting the demand-to-capacity ratios for each check.
Inputs
- Geometry - Lumber size string (e.g., "4x10"), number of plies (1–4), clear span (ft), and bearing length at each end (in).
- Loads - Dead load UDL (plf), live load UDL (plf), and optional roof live, snow, or wind load UDLs (plf). Wind load is negative for uplift.
- Adjustment Factors - Wet service (CM), temperature (Ct), incising (Ci), size factors for bending and shear (CF), load duration factor (CD), and repetitive member factor (Cr).
- Deflection Limits - Limit for live load only (e.g., 360 for L/360) and total load (e.g., 240 for L/240).
- Combinations - Optional project load combinations. Supplying these or loads beyond dead and floor live switches the module to the combination engine and derives CD from the governing combination.
- Seismic - Optional SDS value. If provided, the module folds the vertical seismic effect 0.2*SDS*D into seismic combinations.
What it reports
- Governing Combination - The ASD combination that governed the design and the specific load duration factor (CD) applied to it.
- Reactions - The governing support reaction in kips, calculated as the total line load times span divided by two.
- Moment - The maximum moment in kip·ft, compared against the adjusted bending capacity.
- Shear - The shear force at distance d from the face of the support in kips, compared against the adjusted shear capacity.
- Deflection - The deflection due to live load only and total load in inches, compared against the user-specified limits.
- Demand Trace - A text trace explaining how the demands were derived, whether from the closed-form calculation or the combination engine.
- Section Data - The resolved section properties, including total area and the specific section written to the model elements.
Code references
The engine cites NDS 2018 §3.3 for bending, §3.4.2 for shear stress, §3.4.3.1 for shear at distance d from the face of support, §3.10.4 for bearing perpendicular to grain, and Table 4.3.1 for reference value adjustments. It also references NDS Table 2.3.2 for the snow load duration factor and uses the service-level deflection formula 5wL^4 / (384 E I).
Limits
The module assumes a simple span with a single species, grade, and size. It does not handle complex geometries or multiple species in a single header. The seismic effect is only applied if an SDS value is provided; otherwise, it is off. The combination engine is only activated if project load combinations are supplied or if loads beyond dead and floor live are present. Results are engineering aids; the engineer of record is responsible for the design.