Round Pattern/Bolted Flange Connection

[hungrydinosaur]

Hi All,

I am trying to do an analysis on a structure, where some part has pipe to pipe connection (bolted with flanges). The structural beam analysis software I am using does not allow to model flanges or bolts. So the flange joint can only be input as beams with a node joint, and I will have to do hand calculations for the bolt joint. Can anyone tell what values I need to take for the hand calculations? I would be having the forces and moments in each of the members, so which values do I consider for a conservative calculation? Please see attached.

Thanks in advance.

HD

 

[kiskertlugas]

You can use Consteel software to design such a moment splice connection.

 

[hungrydinosaur]

Thanks Kiskertlugas.

 

[MacGruber22]

Can anyone tell what values I need to take for the hand calculations?

Sounds like a bit of a loaded question but I will try.

The max of:
The forces and moments at this node + some reasonable percent higher. I use 10% for most of my connections where reactions come directly from an FEA program. Sometimes enveloping the forces and moments provides this coservatism too.
The minimum required splice forces/moments required by your governing design code. Though, if this value is 25% or less of the section capacities, I would want to use something closer to 50%.

You may need to consider fatigue and prying action on the bolts (if the flange is not rigid enough). Analysis of bolt forces using the elastic method is a conservative way to go (Link)

What kind of structure is this member a part of? How confident are you in the calculated loads? These are also questions that may drive how conservative you should be with that splice.


"It is imperative Cunth doesn't get his hands on those codes."

 

[BUGGAR]

How will you analyze the joint for stiffness to see if it is valid as a rigid node in your computer model? Is this significant?

 

[racookpe1978]

How would a flanged joint (welded like a pipe fitting) not be rigid against bending?

 

[MacGruber22]

How would a flanged joint (welded like a pipe fitting) not be rigid against bending?

If the flange plate is not thick enough, it will allow rotation. AISC Flange Angled Partially Restrained moment connections comes to mind.

"It is imperative Cunth doesn't get his hands on those codes."

 

[racookpe1978]

More likely to not actually "bend" the flange or pipe then, but I can certainly see the flange plate itself rotate several degrees on the structure as the bolt holes (which are significantly! oversized compared to structural bolt holes to let pipes be made up in the field!)

 

[MacGruber22]

To add on my previous comment - I suspect that your connection will be generally more rigid to moment resistance than the idealized partially restrained beam moment connection due to the continuity of the ring. Though for simplicity, keeping the bolts close to the pipe (possibly at the minimum tightening clearance) and providing a flange plate thickness that precludes bolt prying action would be conservative, I think. Using the prying action model for clip angles based on a bolt tributary width (arc length) would be my initial thought. If you feel comfortable with that, it sounds cheaper to fabricate a heavy flange than adding stiffeners. You will have some iteration to do, but I think good detailing makes this connection fairly straightforward to count on as rigid in the model.

The other thing you can do is release the moment rigidity at the joint in the model and see where the loads "redistributed" to. I often find that worrying about modeling fixity of column base plates is meaningless when either a) there wasn't much moment being attracted in the first place or b)changing it to pinned doesn't cause other stuff to fail elsewhere.

Also sounds like pre-tensioning is needed for torsion and shear based on racookpe1978's comment.

"It is imperative Cunth doesn't get his hands on those codes."

 

[BUGGAR]

Why are you using a pipe flange to make a structural connection?