FAQ: How to model Cross Frames with a back-to-back channel section?
First, on the Utilities ribbon tab, select the Cross Frames tool in the Libraries group, as shown in the screenshot below and in the Help/F1 link:
To create a cross frame template (bentley.com)
Then, as shown in the figures below, at the Cross Frames Library dialog, users can create a customization for the cross-frame by using the Add a new entry with a Name according to the Framy Type selected. After, select the Members, for example, the Bottom Strut in a V-Frame, and scroll in the Template options. L, C, MC, S, W, and WT options are available. Click Update Drawing to see the changes on the screen. Select a C or MC section and the Section Mirror Horizontal to create a Closed Channel.