Bellows EJ spring rate 1

[Nukie]

I am a little confused about the bellows expansion joint spring rate.

What really is the ANGULAR spring rate?
Does a Lateral movement affect or create an ANGULAR movement?

Thanks for your time

 

[kstaylor]

A bellows for an expansion joint has 4 different spring rates or stiffnesses depending on the type of movement that is to be absorbed. The names of these stiffnesses, the type of movement to be absorbed, and USCS units are as follows:

1. Axial, axial extension or compression, lbf/in.
2. Lateral, the two ends remain parallel but have a lateral offset in the centerline at each end, lbf/in.
3. Angular, the bellows is "bent" or rotates through a small angle, lbf/in./degree.
4. Torsional, a torque is applied about the centerline of the bellows causing a "twist" in the bellows, lbf/in./degree.

The lateral movement causes two separate angulations or bends within the set of convolutions of the bellows.

For further details of how to calculate the various spring rates or stiffnesses for a bellows see the Standards of the Expansion Joint Manufacturers Association (EJMA). They have a website (

http://www.ejma.org)

and offer a publication titled A Practical Guide to Expansion Joints as well as the EJMA Standards.

Are you experiencing trouble with a particular joint or just looking for information?