FLRJOIST draws an I-section as real surfaces — a timber I-joist with its flanges and web, or a steel beam — lying along the X axis from a point you pick.
What FloorJoist does
Useful for a 3D framing model, for checking clearances against ductwork and services, and for cutting a section anywhere along it.
What it is made of: twelve 3D faces — the top and bottom of each flange, the two sides of each flange, and the four sides of the web. That closes the shape completely, so it hides properly and shades properly, which a set of lines never does.
How to use it
- Load the routine with
APPLOAD, or put it on your support file search path. - Type
FLRJOIST. - Pick the start point and give the depth, length, flange width and web thickness.
- Say whether you want the ends capped — they are open by default.
How it works
The ends are left open, because a joist is nearly always cut by something or runs into a hanger. Say so and the two end caps are added.
Faces alone define the shape; edges are optional and off by default. Drawing eighteen lines and sixteen 3D faces over the top of them makes every edge in the model two objects deep. On a floor of forty joists that is over a thousand objects that need not exist, and it makes the edges look heavy when shaded.
Notes and limits
- It draws along the X axis from the picked point. Rotate or set a UCS for anything else.
- Ends are open unless you ask for caps.
- Edges are off by default, so the model stays light.
- One undo group covers the whole member.
Download and details
| Name | FloorJoist — draw an I-joist or steel beam as real 3D surfaces |
| Download | FloorJoist.lsp — 8.9 KB, plain AutoLISP source. Downloads directly; no zip to unpack. |
| Type | AutoCAD AutoLISP routine |
| Command | FLRJOIST |
| Requires | nothing beyond a CAD platform with AutoLISP. |
| Source size | 8.9 KB, 209 lines |
| Error handling | Yes — a *error* handler restores every system variable it changed, on cancel as well as on error. |
| Undo | The whole operation is wrapped in a single undo group, so one U reverses all of it. |
| Compatibility | AutoCAD (any release with AutoLISP), BricsCAD, ZWCAD, GstarCAD, ProgeCAD and other IntelliCAD-based platforms. AutoCAD LT needs a LISP enabler. No .NET, no ObjectARX, no installer. |
| Author | YZ, August 2026 |
| Licence | Free to use, supplied “as is” with no warranty. |
References
- HOUSESHELL LISP — the shell these frame into
- FACEHOLE LISP — cutting openings through 3D faces
- Wisey’s Steel Shapes — true published steel section profiles in 2D
- More free AutoLISP routines on this site
- Wisey’s Steel Shapes — free structural steel section drawing program