How to model a "concentrated" area load on top of a larger area 2

[Hurly26]

All,

A colleague and myself are trying to figure out how you would go about applying a load to an area that you have drawn in SAP2000. The steel structure model is built and all of the appropriate assigns are in place. This is a 3 story building with the first and second floors being covered in concrete. What we're trying to figure out now, is how we go about modeling a null (no physical properties) area on top of this concrete. We can't model the areas on top of the beams alone because the areas are smaller than the center to center spacing of the beams. The way it's drawn in now, the null area is in the same plane as the concrete floor and only one portion of any of these null areas rests on a beam. When the analysis is run, SAP2000 is assuming these null areas are only supported on the beams instead of being on the concrete and so, any portion of the null area that isn't over the beam is showing massive deflections on the scale of billions which is obviously incorrect. Furthermore, a simple glance at the shear diagrams or deflected shape is proving that the loads are not going through the concrete and then distributed to the beams as intended.

If you have any thoughts on the matter, I would greatly appreciate them.

Thank you

 

[stressed]

When you say steel "covered with concrete" are you referring to concrete cladding/fireproofing on the steel beams, or do you mean concrete slab? If concrete slab, what are you trying to accomplish with the None (null) area load? you didn't say how you modeled the concrete floor. Did you use shell elements?

If cladding on the beams, just assign it as a distributed load to the beams.

If you need to assign load to an existing shell (slab) you will need to make sure that your shell is meshed/divided in order assign load to specific areas. Edit menu>Edit areas>Divide areas and use Mesh by gridlines and mesh by lines should help you with this meshing. Once you have meshed your slab, assign area distributed load to selected areas. No need to work with None/null property areas that I can see. ETABS uses None areas for adding load. I don't believe SAP2000 functions the same way.

Be aware that SAP2000 distributes area load based on mesh points. If for example, you modeled the slab as one big area covering many beams, those beams would not get any load from the slab unless they intersected with a slab mesh point. When assigning area load there are a couple of options - uniform load assigns two-way, Uniform to frame distributes one-way.

 

[Hurly26]

Stressed,

Thanks for the reply. I would comment back and respond to the questions you initially asked but you went on in your post and ended up providing me with the solution I needed as well as answers to other problems I hadn't asked so there's no point anymore.

Thanks again!