Expansion joint 4

[B.L.Smith]

Dear Friends,

I have a question about nut gap of axial expansion joints.
When should we use rod with outside nut gap in "axial expansion joint"?(As we know outside tied rod can withstand pressure thrust thus I think always using of outside tied rod is preferred)

 

[micalbrch]

Do you mean tie rods (length limiters)? If yes, they are used when reaction forces need to be absorbed.

 

[ione]

A tie rod is used to take pressure thrust force that would be otherwise exerted on the main anchor. If rods are present but axial movement is partly allowed then we are talking about limit road.

http://www.usbellows.com/expansion-joint-catalog/limitrod.htm

 

[B.L.Smith]

Friends At first thank u for your reply.
Always We prefer control pressure thrust. Thus we should tie outside nuts.
ione said:
"If rods are present but axial movement is partly allowed then we are talking about limit road."
When we can use control rod with outside nut gap? (i.e. in which cases axial movement is partly allowed?)

 

[StevenHPerry]

These are good question, it's evident you are thinking about it rather than just slapping an expansion joint in the system and calling it good.

First, be sure we're talking the same language. EJMA and FSA have different and conflicting terminology for expansion joint rods. Are we talking metal or rubber expansion joints?

Regardless of terminology, if there is any axial movement in a non-pressure-balanced expansion joint, the anchors must be designed to withstand the pressure thrust.

- Steve Perry

http://www.linkedin.com/in/stevenhperry

This post is designed to provide accurate and authoritative information in regard to the subject matter covered. It is offered with the understanding that the author is not engaged in rendering engineering or other professional service. If you need help, get help, and PAY FOR IT.

 

[B.L.Smith]

I'm talking about all kind of EJ specially rubber EJ.

 

[rmw]

What you are asking about is used when axial extension is anticipated. The nuts have to be backed off enough to allow for the extension you calculate that you need.

If there is only axial compression to be considered, then the nuts are tight against the tie plate.

rmw

 

[StevenHPerry]

From memory, rubber expansion joints are covered by FSA and any device meant to restrict or distribute movement and/or retain pressure thrust is termed a "control rod."

So, you may use a control rod on a rubber expansion joint without regard for its function. As others have said, back off the nut to allow axial expansion. But your anchors still need to be designed for pressure thrust in my opinion.

On a metallic expansion joint EJMA governs and uses different names for such devices. It would not be proper to say "control rod" for a device that allows a single bellow expansion joint to take axial expansion, though the principle is the same.

- Steve Perry

http://www.linkedin.com/in/stevenhperry

This post is designed to provide accurate and authoritative information in regard to the subject matter covered. It is offered with the understanding that the author is not engaged in rendering engineering or other professional service. If you need help, get help, and PAY FOR IT.