I am modeling a very wide slab (120' x 30') simply supported on two long opposite edges. It would have been a simple one way slab but it has two edge beams on the shorter (30') edges. The slab is 20" deep and the edge beams are 29" deep x 18" wide. I am interested in moments in the edge beams on the shorter edges.
As far as my understanding goes, to vertically offset a beam beneath the slab, rigid links can be inserted between the nodes lying on the shorter edge of the slab plate nodes and the beam nodes lying (29/2 - 20/2) = 4.5" below the plate nodes.
However, this difference being small compared to overall depth of the slab and the dimesnions of the problem in general, can I use thicker plate elements (29" depth) in a few finite element strips at the edges to model edge beams instead of using frame members to model the beams?
Will modeling plate elements of different depth/thickness (20" and 29") introduce some discontinuity in the model that will adversly affect the results? If yes, will introducing using more finite element strips along the shorter edge to gradually increase thickness from 20" to 29" over a 3' width produce more accurate results?
In the real existing structure, the edge beams are 18" wide, however the slab transitions to beam over a 18" wide haunch. This is where the 3' width mentioned above comes from.
Thanks.