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.

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)

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
  • Dimensions - Enter exact edge lengths and arc sizes
  • Corner radius - Add or remove rounded corners at selected vertices
  • Mirror and Rotate - Transform the selected geometry (Mirror Y, Mirror Z, or Rotate 90°)
  • Grid snap - Snap to the grid, vertices, midpoints, and edges
  • Undo / Redo - Reverse or reapply edits with Ctrl+Z and Ctrl+Y (Ctrl+Shift+Z also redoes)

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.

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.