What it checks
The module designs the Main Wind Force Resisting System (MWFRS) for low-rise buildings using the ASCE 7-22 Chapter 28 Envelope Procedure. It applies this method only to structures that meet the Section 26.2 low-rise definition, specifically those with a mean roof height of 60 ft or less and a height that does not exceed the least horizontal dimension. The module refuses to produce pressures for buildings outside this scope rather than using figures that do not cover them.
The calculation sequence begins by verifying the low-rise gate. If the building passes, the module determines the velocity pressure profile and internal pressure coefficients. It then calculates the envelope pressure coefficients for each zone, interpolating values based on the building's aspect ratio and roof angle. The results provide the design pressures required for the structural analysis of the MWFRS.
Inputs
- Geometry - Building width (B), length (L), and mean roof height (h) in feet.
- Wind Speed - Basic wind speed (V) in miles per hour (mph).
- Site Conditions - Exposure category (A, B, C, or D) and ground elevation in feet.
- Roof Configuration - Roof angle (theta) in degrees and enclosure type (enclosed or partially enclosed).
- Structural Layout - Number of stories and diaphragm top override elevation in feet.
What it reports
- Low-Rise Status - A boolean verdict indicating whether the building meets the Section 26.2 definition for the Envelope Procedure.
- Velocity Pressure - The qz value in pounds per square foot (psf) at various heights, derived from the wind speed and exposure.
- Internal Pressure - The internal pressure coefficient (GCpi) based on the building's enclosure type.
- Envelope Coefficients - The pressure coefficient (GCpf) for each zone, interpolated between the 0.5 and 1.0 columns of the reference figure.
- Zone Pressures - The final design pressures for each building zone, combining external and internal effects.
- Base Shear - The net base shear in kips, calculated as external-only per the owner ruling.
- Story Forces - The distributed wind forces at each story level for the structural model.
Code references
The engine cites ASCE 7-22 Chapter 28 for the Envelope Procedure and Section 26.2 for the low-rise definition. It utilizes Table 26.11-1 for exposure constants, Table 26.10-1 for the velocity pressure exposure coefficient, Table 26.13-1 for internal pressure coefficients, and Figure 28.3-1 for envelope pressure coefficients. The velocity pressure calculation follows Equation 26.10-1, and the ground elevation factor is derived from Table 26.9-1.
Limits
The module refuses to calculate pressures for buildings that exceed the 60 ft mean roof height or have a height greater than the least horizontal dimension. It does not support the Directional Procedure for all heights, which is handled by a separate module. The base shear reported is external-only, as internal pressure coefficients cancel across the envelope. Results are engineering aids; the engineer of record is responsible for the design.