Partially restrained moment connection pipe support

[hitch22]

Hi fellow members,

I'm trying to design a pipe support but I'm not sure how to realistically model my idea. This is the situation:

I'm trying to attach an U-shape support underneath an existing platform. Welding is not an option. Due to the width of the existing beam flange, I can only get bolts "within" the connection of the new vertical member and the existing beam. Normally I would model this as a pin connection but I have seen this situation in the field and the supports were not flopping around.

Can someone please give me any hints as to how to approach this problem? I want to estimate deflection. Attached is a diagram to illustrate the situation.

Thank you

 

[paddingtongreen]

Model the joints as fixed and then make them work, that's all you have; a 2" pipe will not add much weight or lateral force. Your main problem might be from a frictional expansion load causing torsion on the support beam although that seems unlikely with only a 2" pipe. If that expansion movement is known to be small, the torsion may be acceptably self-limiting.

Caution. Is it big enough for them to slide another pipe or three onto your support, especially bigger pipes, those sneaky pipers often do that.

Michael.
"Science adjusts its views based on what's observed. Faith is the denial of observation so that belief can be preserved." ~ Tim Minchin

 

[Agent666]

I agree with Paddington, you will find the fixed moments and axial forces in the connection are so small that a thin plate would easily work for the end plate. A thin plate which if the loads were higher you would have no issues with considering it as a nominally 'pinned' detail which you would typically ignore any moment developed. If you have a thick plate and thick flange then it's behaviour will be closer to a fully fixed condition.


A nominally pinned detail may still develop 10-20% of the moment capacity of the section with a thin plate/flange, but to fully mobilise this significant deflection in the plates would have to occur (sufficient to yield them), which in practice isn't really going to occur when you consider how much a column needs to lean over in the case of a pinned column baseplate to get to this condition. So you get some moment, but it's generally ignored in design, but it pays to keep it in the back of your mind that they are developed whether you like it or not!

Something else to consider with the bolting is that in drilling the holes in the beam flange above you are reducing the capacity of the beam above locally. Only an issue if it's working right to the full capacity of the beam, but if you do the numbers on thinner flanged beams a few holes across the section can reduce the plastic modulus of the section by a significant percentage.