What it checks
The module designs the cantilevered girder (Gerber) roof system, specifically determining the hinge location that balances the cantilever moment against the back-span moment. It calculates the suspended drop-in span statics and the reactions the scheme hands to each column. The design method utilizes strength-based factored demands for the primary steel checks and provides ASD/NDS-ranked variants for wood design considerations.
The sequence of checks begins with establishing the structural geometry, either by using a user-entered cantilever distance or by running a numeric optimizer to find the hinge location that minimizes the governing envelope moment. The module then applies load patterns, including skip loading across girder and suspended segments, to determine the worst-case contributions at specific locations. Finally, it assembles the load parts to report the governing demands for moments, shears, and hinge reactions.
Inputs
- Geometry - Column spacing (bay_ft, ft) and the cantilever distance each side of the interior column (cantilever_ft, ft), which is ignored when hinge optimization is active.
- Optimization - A flag to find the hinge location that minimizes the governing envelope moment (optimize_hinge, bool).
- Loads - Uniform loads by basic load case (w_dl_plf, plf of girder line).
- Pattern Loading - A flag to skip live, snow, and roof-live loads across girder versus suspended segments (pattern_loading, bool), which defaults to true.
What it reports
- Balance Point - The classic full-load balance point (a_balanced_ft, ft), calculated as bay times (1 minus 1 over the square root of 2) divided by 2.
- Used Cantilever - The cantilever distance actually used (a_used_ft, ft), whether optimized or as entered, and a flag indicating if the numeric optimizer chose it (optimized, bool).
- Column Moment - The governing factored or allowable-side demand (m_column_kipft, kip-ft) for the strength engine.
- Hinge Reaction - The reaction at each end of a suspended segment (hinge_reaction_kips, kips), which sizes the hinge connector hardware.
- Girder Shear - The shear just outside the column on the cantilever side (v_girder_kips, kips).
- Wood Design Variant - The ASD/NDS-ranked demand and CD selection (m_column_nds_kipft, kip-ft) for wood design.
- Load Pattern - The specific load pattern (pattern, String) that produced each variable case's contribution.
Code references
The engine cites Statics (cantilevered girder), ASCE 7-22 combos, and NDS-ranked variants. The suspended span statics are checked at 1.4D so the combo factor is explicit, and the module references the closed-form balance point identity under uniform load.
Limits
The cantilever input is ignored when the hinge optimization flag is active, as the solver determines that value. Turning off pattern loading is considered the unconservative choice, and the results explicitly state this condition. The module does not perform hand-waving for pattern loading effects, as the optimum shifts off the classic point in such cases. Results are engineering aids; the engineer of record is responsible for the design.