tdellaqu wrote:
how to do this? I tired rotating a beam and trimming the top off in section, but that didn't really work.
I wish I could just drag the node of one corner in section, but it isn't working like that. I need a trapezoid shape in section.

I'm not sure if this question has been answered in the way you expected. Did you want the taper along the length of the beam, or in cross section?

If it's the latter, you can shape many beam objects to a taper using OBJECTIVE's toolset (refer to the attached image). Note that when I refer to the Split or Rotate tools, I mean those under the OBJECTiVE/Tools menu - ArchiCAD's built-in Split and Rotate can't do this:

• 1. Place the selected beam in plan (in this example I used "Precast Beam I 01 11" from the standard ArchiCAD library) and place a section/elevation alongside.
  2) Open the section/elevation and use 'Split' to divide the beam into an upper and lower section.
  3) Use 'Rotate' to incline the lower section to the required taper angle.
  4) Use 'Split' to cut away the unwanted parts of the lower section

The remaining part is optional, depending on whether the tapered beam is also inclined:

• 5) Use 'Rotate' to incline the tapered beam to the required pitch
  6) Use 'Spit' to shape the beam ends to the required angle (as applicable)

The original and tapered beams are shown in the attached image in 2D (image 1) and 3D (image 7). Note that the selected tapered beam adds snappable hotspots long the beam cross-section in 3D, and is correctly represented in 2D (unlike SEO operations).

You can find out more about OBJECTiVE at: http://www.encina.co.uk/objective.html