Portal Frame Analysis Wizard

How it calculates

The Portal Frame Analysis Wizard uses a linear elastic finite element analysis engine to solve single- and multi-bay 2D portal frames in any structural material. You specify the frame geometry, member sections, support conditions, and loads; the solver returns full moment, shear, axial, and displacement diagrams across every member and node.

Geometry and supported frame types

Frame geometry is defined by bay width (W_bay), default leg height (H), apex location (X_A), and apex height above the left leg (H_A). Supported configurations include:

• Flat / Monoslope - single-pitch or flat roof
• Gable / Duopitch - symmetric or asymmetric pitched roof
• Circular arch - defined by arch radius
• Tied portal - with an explicit tie member across the column tops

Single-bay and multi-bay (n_bays) frames are both supported. Column base fixity (pinned or fixed) can be set independently for each leg, and interior column connections can also be pinned or fixed.

Member modelling

Each column and rafter segment is modelled as a beam-column element with axial, shear, and bending stiffness derived from the user-supplied Young's modulus (E), cross-section area, and second moment of area. Supported material types include steel, timber, concrete, and cold-formed steel. For truss-form rafters, the chord depth (d_truss) and number of unit panels (n_units) parameterise the equivalent section.

FEA solution and output

The solver assembles the global stiffness matrix from element contributions, applies nodal boundary conditions, and solves for displacements and reactions. Outputs include:

• Bending moment, shear force, and axial force diagrams per member type and per element
• Maximum nodal displacements per member
• Support reactions at column bases (for linking to footing and base-plate calculators)
• Tables of results by element number and by node number

Sign conventions

• Positive bending moment indicates that the bottom or right side of the member is in tension.
• Positive axial load indicates a compressive load.

Load types

Distributed loads can be applied to any member (roof, wall, or floor). Point loads and nodal forces are also supported, and advanced users can apply loads directly by element number. Multiple load cases are evaluated and the governing envelope is reported.

Downstream linking

Column base reactions link directly to footing calculators. Member demands link to beam, column, and connection design calculators - so a change in frame geometry or loading propagates automatically to every linked check without manual re-entry.