Custom Section Builder

Create custom cross-sections by drawing from scratch, combining standard shapes, or importing a DXF file. Review calculated results and section stress directly in your browser. Results are calculated using a finite element mesh generated from the section outline and openings, including numerical solutions for torsion, shear, warping, and stress.

Custom Section Builder walkthrough videos

Key Features

  • Point, Line, and Circle Drawing - Create solid and thin-walled shapes
  • Built-Up Sections - Join multiple shapes into one section
  • Holes and Openings - Add circular or freeform openings
  • Section Library - Start from a standard section and edit it
  • DXF Import - Import closed section outlines from CAD
  • Calculated Results - View area, centroid, bending, torsion, shear, and warping values
  • Section Stress - Pro: apply forces and moments, view stress contours, and export a PDF report
  • Save and Reuse - Pro: save editable sections to the cloud and assign them to members in Structural FEA (analysis only; design checks are not supported for drawn sections)

Quick Start

  1. Open the app at /custom-section-builder
  2. Choose units using Metric (mm) or Imperial (in)
  3. Create a section with Draw, Library, Import DXF, or open a previously saved section
  4. Add holes if the section includes openings
  5. Edit the shape using Select, dimensions, and corner radii
  6. Calculate to view results and the section centroid (sign-in required; free accounts get 3 calculations per day)
  7. Review or export the results from the Properties panel (Copy or Excel)
  8. Save the calculated section to the cloud (Pro)
  9. Use it in Structural FEA - Open the section library and choose the saved drawn section to assign it to a member

Drawing a Section

Point Draw

Use Draw > Point draw to place the corners of a freeform shape. Click the first point again to close the outline.

Line Draw

Use Draw > Line draw for sections defined by a centreline and thickness. Set the thickness and inside radius in the Properties panel, then click along the path of the section.

Circle Draw

Use Draw > Circle draw to place a solid circular profile by centre and radius.

Holes

Once the outside shape is closed, use Hole to add a freeform (Point hole) or circular (Circle hole) opening. Holes must remain inside the section.

Editing

  • Select - Move vertices, edges, or complete shapes
  • Edge geometry - Drag an end vertex to change an edge length, and switch selected edges between straight and arc types
  • Corner radius - Add or remove rounded corners at selected vertices
  • Mirror and Rotate - Transform the selected geometry (Mirror Y, Mirror Z, or Rotate 90°)
  • Snap - Choose individual snap targets: vertices, midpoints, edges, angle and direction, and grid.
  • Copy / Paste - Select every vertex of one or more complete shapes, then use Ctrl+C and Ctrl+V (Cmd+C and Cmd+V on Mac)
  • Undo / Redo - Reverse or reapply edits with Ctrl+Z and Ctrl+Y (Ctrl+Shift+Z also redoes)

Tips

  • Merge nodes - Enable vertex snapping and drag one vertex onto another to create a shared node and connected section.
  • Edit a subset - Ctrl-click (Cmd-click on Mac) vertices to add them to the selection, or drag from empty canvas to marquee-select them. You can then move, mirror, rotate, or scale just that selection.
  • Build up a section - Import standard sections from the Library, position them with Select, then use Line draw to add connecting plates or webs.

Library and DXF Import

Choose Library to insert a standard section as editable geometry. If a section is already on the canvas, the new shape is added beside it so the two can be combined.

Choose Import DXF to load a closed 2D section outline. For best results, export only the section profile and remove dimensions, notes, and unrelated drawing views.

Poisson's Ratio

Poisson's ratio (ν) defaults to 0.30 and can range from 0 to 0.499. In the Custom Section Builder, it is used for the warping calculation and recovered transverse-shear stresses; it does not change geometric properties such as area, centroid, or second moments of area.

A saved section's Poisson's ratio does not override the material assigned to its member in Structural FEA. Member stiffness uses that material's properties, including its Young's modulus and shear modulus (or a shear modulus derived from its own Poisson's ratio). The saved section's value is retained for its stress recovery; use the same value as the assigned material and recalculate/re-save when consistency is required.

Results

Click Calculate when the section is closed and connected. The Properties panel displays the calculated values, while the yellow marker shows the centroid on the canvas. Use Copy or Excel to export the results.

Pro users can also apply forces and moments in the Stress tab, view stress contours, and export a PDF report.

Saving and Using in Structural FEA

Pro users can Save calculated sections to the cloud and reopen them later with Saved. Saved sections remain editable, including holes, line thicknesses, and corner radii. Calculate again after editing before re-saving.

Saved drawn sections also appear in the Structural FEA section library (Pro). Assign them to members like any other library section for structural analysis. Drawn sections cannot be used for design checks. If a saved section is outdated, recalculate and save it again in the Custom Section Builder before using it for analysis.

Important Notes

  • The outside boundary must be closed before calculating.
  • Separate shapes must be joined to form one connected section.
  • Composite sections are not supported. The tool models a single homogeneous material only (not multi-material or composite construction).
  • Editing the drawing clears old results; calculate again after making changes.
  • Property calculation requires sign-in. Free accounts get 3 calculations per day; Pro removes the daily limit.
  • Section stress (contours and PDF) and cloud save/load require Pro.
  • Stress contours are for section review and are not a design-code check.