Seismic — Diaphragm Calculator, ASCE 7-22

What it checks

The module calculates the seismic diaphragm design force at each level of a structure. It applies the design method specified in ASCE 7-22 §12.10.1.1 to determine the governing force for each diaphragm. The process begins by computing the equivalent diaphragm force based on the cumulative ratio of story forces to weights.

Inputs

Seismic Parameters - Design spectral acceleration parameter at short period (g) and seismic importance factor.
Geometry - Diaphragm clear span in the long direction (ft) and diaphragm dimension perpendicular to the lateral load (ft).
Level Data - Weight tributary to the diaphragm (kips), story force from ELF analysis (kips), and total weight from the level up to the roof (kips) for each story, ordered bottom-to-top.

What it reports

Design Diaphragm Force - The governing diaphragm force (kips) for the level.
Lower-Bound Force - The minimum diaphragm force calculated as 0.2 · SDS · Ie · Wpx (kips).
Upper-Bound Force - The maximum diaphragm force calculated as 0.4 · SDS · Ie · Wpx (kips).
Equivalent Force - The force derived from the ratio of cumulative story forces to cumulative weights (kips).
Unit Shear - The average diaphragm unit shear calculated as Fpx / (2·depth) (plf).
Chord Force - The force calculated as M_max / depth, assuming a uniformly-loaded simply-supported diaphragm (kips).

Code references

The engine cites ASCE 7-22 §12.10.1.1 for the calculation of seismic diaphragm forces. The module implements the provisions for the Fpx story-by-story envelope, including the specific floor and cap values defined in the code.

Limits

The module provides approximate diaphragm shears and chord forces. It assumes a uniformly-loaded simply-supported diaphragm for the chord force calculation. It does not account for complex diaphragm behavior or non-uniform loading patterns beyond the specified inputs. Results are engineering aids; the engineer of record is responsible for the design.

This module ships in the desktop app

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