2 beams crossing without a column
2 beams crossing without a column
(OP)
Hi, this might be a dumb question but i'll go for it anyways.
If I have 2 beams that are crossed in a corner, for example like this:

And they don't have a column there to support them, what kind of behaviour should I expect on the cross node?
I've made a simple fem (that i will try to perform in sap2000 too) and the result is this:

It's very different to have 2 beams, than a single one, so what could be meaningful to ask here, is, why can't I consider it a single beam with a change of direction?
Thanks for any help
If I have 2 beams that are crossed in a corner, for example like this:

And they don't have a column there to support them, what kind of behaviour should I expect on the cross node?
I've made a simple fem (that i will try to perform in sap2000 too) and the result is this:

It's very different to have 2 beams, than a single one, so what could be meaningful to ask here, is, why can't I consider it a single beam with a change of direction?
Thanks for any help






RE: 2 beams crossing without a column
RE: 2 beams crossing without a column
RE: 2 beams crossing without a column
You can consider it a single beam with a change in direction if you wish to. The reason that this is not generally done is that it generally makes for expensive and inefficient construction. Consider:
1) Your beams would carry a bunch of torsion. Most steel sections are terrible for torsion.
2) You would need moment / torsion connections at the beam intersection. Those will be substantially more expensive to fabricate compared to simple shear connections, particularly if weld testing is required.
3) Your analysis will be much more complex, and much less predictable, with torsional continuity included.
4) If you make the dog leg connection in the shop, the member may be a hassle to ship and erect.
I like to debate structural engineering theory -- a lot. If I challenge you on something, know that I'm doing so because I respect your opinion enough to either change it or adopt it.
RE: 2 beams crossing without a column
I'm surprised you think a model of one geometry can predict the stresses and strains of a different geometry. Rather, you'd have a vertical point load coming down the vertical member into two cantilevered horizontal support beams. The stress model would need to show both ends of the two horizontal beams, their single connection under the vertical, and the supports or anchors of the other two ends.
RE: 2 beams crossing without a column
______________________V
^............"L"............^.......
(ignore the dots, the board wouldn't allow blank spaces easily).
V -- represents the reaction from the other beam at 90-degrees.
^ -- represents support locations
RE: 2 beams crossing without a column
RE: 2 beams crossing without a column
Here you can see the 2 adjacent columns and the cantilever ahead (varanda in most cases means a cantilever)
@racookpe1978 I didn't think it could, just tried it anyways :p Do you know any literature on this?
A few notes, they will be concrete elements, so @Kootk any problems with torsion or connections aren't problematic as long as I can get the real deflection of that node. I don't think a concrete element will behave like 2 different bars. However I have no idea how to analyze it. Is there any kind of literature on this?
RE: 2 beams crossing without a column
1. a. If I assume that north is up on the screen - is there another column farther south, but in line with, the green one? (@ an adjacent frame? @ an opposite side of the building?)
1. b. If yes, can a reasonably sized beam span from this column to the green one?
2. IF the answers to 1a. and 1b. are both yes: why not run the rebar through the column joint at the green column, and all the way to the end to support the zig-zagging concrete beam?
3. When they build your zig-zagging concrete beam in the real world, will they run the rebar continuously along its length? If so, then your model needs to ensure there is full fixity at the zig-zag joint.
It is entirely possible that there are other conditions on your project which make any of the recommendations we give you quite trash-worthy; regardless of your path, make sure you enlist the assistance of a more experienced coworker, supervisor, or senior engineer before you get too deep into the weeds.
Get familiar with your software and be smarter than it is. Make sure you are modeling your joints/boundary conditions to reflect the real world. The software will not do the job for you. If you are getting deflections you do not like, you either have modeled boundary conditions/something else incorrectly, you need larger members, you have incorrect loads, etc. Good luck.
RE: 2 beams crossing without a column
Have you looked at thickening the slab or even maybe doing a P/T design? It should make your formwork and rebar detailing a lot simpler and provide accurate modeling for what the structure wants to do. I'd still keep the column to column beams, but I'd change the cantilevered corner beams to a single diagonal beam from green to red column.