Portal Frame (2D FEM) Calculator, ASCE 7-22

What it checks

The module performs a two-dimensional finite element analysis of portal or moment frames. It models planar structures using three degrees of freedom per node: horizontal displacement, vertical displacement, and rotation. The solver supports inclined members and calculates member forces, joint displacements, and story drifts. The design method relies on linear elastic stiffness matrices and optional geometric stiffness iterations for P-Delta effects. It does not apply strength or service limit state factors directly but provides the raw structural response data required for these checks. The sequence of checks involves solving for global displacements, recovering local member end forces, and evaluating story drift ratios against specified limits.

Inputs

Geometry - Element lengths in inches and orientation angles in radians.
Section Properties - Cross-sectional area in square inches and moment of inertia in fourth powers of inches.
Material - Modulus of elasticity in ksi.
Loads - Joint loads and member uniformly distributed loads in kips per linear foot, with positive values indicating downward gravity.
Stability - Total gravity axial load in kips, used for informational purposes and not automatically applied to the solver.
Drift Criteria - Drift limit as a ratio, such as 0.020 per ASCE 7-22 §12.12.1.

What it reports

Member Forces - Local end forces for each element, including axial, shear, and moment components.
Displacements - Global node displacements in horizontal and vertical directions and rotations.
Story Drift - The calculated drift ratio for the frame, compared against the user-defined drift limit.
P-Delta Coefficient - The stability coefficient theta, calculated as Px·Δ / (Vx·hsx) per ASCE 7-22 §12.8.7.
Reactions - Support reactions recovered from the penalized stiffness matrix solution.
Amplification - Indication of whether P-Delta amplification is measurable, typically triggered when theta exceeds 0.10.

Code references

The engine cites ASCE 7-22 §12.8.7 for the P-Delta stability coefficient and ASCE 7-22 §12.12.1 for story drift limits. The module utilizes the 2D FEM method to generate the data required for these specific code clauses.

Limits

The module is limited to two-dimensional planar analysis and does not account for out-of-plane behavior. The total gravity axial load input is informational and is not automatically applied to the structural model. The solver assumes linear elastic material behavior and does not include plasticity or nonlinear material models. Results are engineering aids; the engineer of record is responsible for the design.

This module ships in the desktop app

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