Expansion Joint

I tried searching for past posts to look for the answers but I could not find any that helped me.
I am bit confused about the tie rod used in expansion joint. So can anyone clear few queries that I have. I will be very thankful for any answers.
Can anyone explain what is the meaning of tie rod gaps provided by the manufacturers?
What happens when there is no gap in either one of forward or backward direction?
What happens when there is no gaps at all? If there is no gap, will it help the piping system in reducing axial load? and how?
Is expansion joint not useful in tension case?
If the gaps are fully closed due to expansion or compression, what impact will it have in the system?
When the forward gap and backward gap is not fully closed, is the use of expansion joint justified?

I try to answer some of these.
Since you're talking of tie-rods, my answers are based on considering the joint as lateral expansion joint.

-A little gap is provided by most manufacturers to allow the rotation of the tie rods and therefore, the lateral movement.
-A small gap is always required. Also, the bellows' own expansion/contraction needs to be accommodated.
- Expansion joints can both take expansion and contraction.But then these have to axial expansion joints (i.e without tie rods).

Hope it brings some clarity.

Thank you very much.
It was very helpful for me to understand most of the questions that I have asked.
I just want to know a bit more.
If the manufacturer says forward gap 20mm, then does that mean the expansion joint can expand 20mm or is it different than what I am saying?

No.
Tie-rod shall not have that much of gap, technically it should be called limit rod. The capable movement of expansion joint decided by bellow's allowed movement. Contact vendor to get that.

I asked the vendor about the drawing and they sent me these. I am not confused what those gaps are and what is the purpose of those gaps and how to input in softwares like Caesar or Autopipe.

Can anyone explain me about the sketch that I have provided?
I have made an error in the reply above?
"I am now confused what those gaps are and what is the purpose of those gaps and how to input in softwares like Caesar or Autopipe."

The gap you shown can be explained SJ mentioned before. Small gap that compensate error or tollerance. I woudn't want to model them in the software.

As a modelling reference, have a look at the previous post.
http://65.57.255.42/ubbthreads/ubbthread...=true#Post58498