is it possible that You are asking for Frame Components rather than Weldments?
To create frames from "lines" is a matter of Strutural Frames function.
See tutorial about it.
i can't find any command called "frame". i was looking for a icon like a square window called "frame" and it's still kept in ST9. i can't find it in ST10.
as mentioned by @rbhaskin it is only available in assembly, but if Your are talking from weldmentss I anyway thought You to be in an assembly.
But have You used the Command Finder?
This tool certainly is one of the most ignored but nevertheless greatest helpers we have.
... and from there the help icon will directly lead YOu to the appropriate icon and function, from where again YOu directly can start the help page