Composite Beam Design Problem!

[SteelStructureDesign]

Hello all,

I am a new ETABS user. When I design composite beams and a steel frames together, the final sections seems strange. I mean columns, composite beams and short beams seems smaller than usual, but long steel frame beams are bigger than usual. You can see following final sections and added picture which shows sections.

Is this sections seems normal according to your experiences? Or is it because of any mistake? I will be glad if you help me.

Columns (6 meter) : HE340A etc.
Long Beams (20 meter) : HE1000-488 etc.
Short Beams (6 meter) : IPE450 etc.
Composite Beams (20 meter) : IPE600

Thanks already now...

 

[slickdeals]

I noticed something in your model that has nothing to do with your post, but thought I should mention. A brace frame is essentially a vertical truss, and I think you will be better off assigning their bases as pinned supports so that you don't have to detail the connection to carry moment and axial force.

 

[slickdeals]

From what your screenshot looks like, it seems like you have run only a steel frame design (meaning no composite action). I think the beams that are shown in white (with no sizes) are the composite beams. All other beams are non-composite.

For a beam to be designed as a composite beam, ETABS has the following limitations:
1. It has to be a I shaped beam
2. It has to be in its strong axis
3. It has to be a single span with pinned ends.

 

[SteelStructureDesign]

Hello again,

Thank you for your interest. But I do not get exactly the answer to my question. I would like to inform you more about my model.

My braces are already pinned. But whatever I do, ETABS dont accept my brace sections except very big sections. It must be because of pressure stresses. So generally I dont take into consideration what etabs says me about braces. If you have any better suggestion I can try to do it.

I think it is not possible to show composite beams sections and steel frame sections at the same display screen after desining. But I designed composite beams also before stell frame and the results were as I told above. So I dont think that any mistake about my designing. If you have any idea about my sections. Do they seems normal or strange to you? If they seems really strange, I wonder where I would make mistakes.

Thanks again.
Latif

 

[ishvaaag]

I think what we see and what you say look some possibly a reasonable solution (it depends on loads etc), but I don't see the result be neccessarily abnormal. My suggestion is that you check the model in other program trying to imitate the restrictions and code used is ETABS; being similar, you should get similar members. The biggest beams connected to columns are surely due to their participation in the lateral system; and whilst you don't have a model that allows for the integritiy between the slab and composite and main beams be represented (something that many times is not wanted, preferring the division of behaviours in vertical and lateral systems) likely you won' be seeing abatement of the dissimilar sizes between composite long beams and main beams. You will get more "elastic" behaviour when the general continuity is represented but then you must inspect if you are providing anywhere the means to deliver such continuity, for a case like this meaning more than anything detailed investigation of the shear interfaces (studs etc) and tensile stresses in the slabs.