HSS Beam Connection&Local Check 1

[otto_eng]

Hi all!
I have a question related with checking the stress of the flange of a steel hollow section. I have two hollow sections that are attached to the each side of the main hollow section, and both of the side beams are transferring bending to the main beam through a welded connection. I am checking the stress on the side and the top&bottom plate of the main hollow section just to make sure the main beam is locally not failing. I would like to verify if my approach here is valid. I am basically using the prismatic stress approach, and simplifying the connection as I indicate on the attached sketch.
That would be great if I could get some feedback on my approach here.
Many thanks!

 

[271828]

After getting the linear stress distribution, I don't know what to do from there.

I would treat the moment in the side member as a force couple between the side member top and bottom walls. The bottom force will bend the main member wall out-of-plane. Compute the strength for that limit state using the AISC Manual (15th) yield line pattern shown in Figure 9-5(a) and Eq. 9-30. I think that's conservative, but the other option is a yield line analysis derived for this situation.

I like some conservatism on this because -- even if the main member walls are strong enough -- the connection is pretty flexible. Presumably this must behave like a moment connection, so some excessive thickening of the main member walls would be helpful. Years ago, we had a canopy that had a somewhat similar moment connection that was strong enough, but the wall bent enough to let the other member deflect excessively.

 

[bugbus]

I don't necessarily agree with the linear stress distribution. It assumes that the sections remain plane in bending, but given the out-of-plane flexibility of the wall of the main HSS, I think this would be doubtful. More force would be attracted towards the stiffer parts of the wall of the main HSS than the linear assumption would predict, these being towards the two flanges.

I think in reality it will behave more like a force couple similar to 271828's approach, which is also probably a lot simpler to analyse in terms of the out-of-plane capacity of the main HSS web.

 

[DrZoidberWoop]

I agree w/ above guys. If neither of your members are very near their limit states, I'd simplify the analysis and conservatively apply AISC 15th, Eq. 9-34. I might also simplify the triangular stress distribution into a pair of "flange forces," at the upper and lower horizontal surfaces of the beam member, and then check the support against the lower flange force w/ Eq. 9-30.

 

[bkal]

I cannot say for sure that it would answer your problem, but are you aware of a CIDECT publication: DESIGN GUIDE FOR RECTANGULAR HOLLOW SECTION (RHS) JOINTS UNDER PREDOMINANTLY STATIC LOADING (appologies for all capital letters, copy and paste job).

 

[HTURKAK]

Dear loti_eng , the assumption of prismatic stress approach is not reasonable for this case . Triangular stress dist. or a couple force at the flanges of secondary beams as the above posts described ,will be better approach.

I looked to your Internet country domain ( DE). If so, Eurocode 3: Design of steel structures — Part 1-8 is the applicable standard and you are expected to check the punching of the main hollow section and develop a plastic line model to get the capacity of the member.

The attached doc. would be useful to get the concept.

I will suggest you to look ( Eurocode 3 Bemessung und Konstruktion von Stahlbauten. 2, Anschlüsse DIN EN 1993-1-8 mit by By Ulrike Kuhlmann,)

 

[otto_eng]

Thank you all for the information, especially @HTURKAK. I understand it fully after reviewing the associated material. Thanks again!