This may be a dumb question; but, when modeling a u-bolt restraint, besides the lateral restraints (and there is generally a small gap on the sides), does a u-bolt provide axial restraint?

I have maintained that the pipe is not restrained axially, no matter how tight the bolts are tightened, especially during thermal expansion. While it may not be able to "freely" slide axially, it will.

The u-bolt could be double nutted and specifically state that the bolts NOT be tight that could be OK. But plants personnel generally will tighten anything that is loose. Axial stops could be added to the pipe at the u-bolt to prevent axial movement.

Can a friction be applied? probably if one were to know the force of the u-bolt against the pipe. Depends on how tight the bolts are.

Anyway, just looking for some thoughts.

Ugh, I hate u-bolts some days. In general a pipe will slide through a u-bolt unless it is really tightened down. I would recommend adding a Mu = 0.3 for the friction to the +Y part of the support model.

In practice I also specify nuts on both sides of the structural steel so the u-bolt is not tightened against the pipe. If they can leave a gap between the top of the pipe and the u-blot that is best.

I hope that helps,
Duncan

I hate U-bolt too, it has been widely used in many sites, and casued so many problems. Because of friction, its behaviour cannot be predicted.

I don't use tighten U-bolt as an axial restraint. If there are two tighten U-bolts installed in a straight line, it could act as an axial restraint and cause buckling. As you mentioned, plate or another attachment provided for restraint the axial movement.

Of course, if possible, try not to use U-bolts especially pipe is high temperature, thin wall, small size.

Dear Stressers
I have a model of pipe lenght ~ 1000 m and temperature 50°C.
I have on all long pipe only u -bolts

Can I model it as Guide and Y restrain ??
Should I left some gaps on Guides (1 mm per side) or do it without gaps.
I assume that a coeficient of friction Mu=0.3 is okey ??

Thanks for all helps and answers
I never do a model with U-bolts.

Regards
___________________________________
Adrian

Get a detail of your u-bolts or create one. They come in standard sizes or whatever size you want them to.

They can be tightened down or they can be specified to have a gap on the sides and the top.

Friction will be whatever your client or employer decides to use for the material(s) in question. U-bolts can come in low-friction variants on the bottom, after all.

Generally speaking, u-bolts are best for use to prevent your pipe from walking or flying off due to wind, but not actual hard points to prevent thermal movement.

Thanks Michael for Answer.
I know that I need detail information about the U-Bolt.
But I asked generally:
Is it good thinking about a model of U-Bolt.
For example horizontal pipe with axis in X direction
Guide Y
Guide Z
I know that I have a Mu=0.3 Steel to Steel.
And I left the X direction free.

It is generally good idea to model a U-Bolt support ?

Yes, it is obligatory to model your U-bolts.

The answer as to how you should model U-bolts for new designs is "as close as you can get to reality to provide adequate evidence that the configuration will not fail." For forensic analysis, "as close to reality as possible based on the evidence you have available."

I would recommend modeling the U-bolts in CAESAR with the gaps per their detail drawings, with the resistances of the supports, unless you have compelling evidence that these absence of these values will not negatively impact the analysis from reality.