from the paper in this link , which is the Belytscko beam. I could not figure out if it is a 3D beam or a 2D one.
if you don't have access to that paper, please check the page 73 on this link.
what confused me was the schematics on the original paper and the second link. in the beginning the general movements start from 3D but I don't see all the DOFs in the above image