Slip Joint K2 formula

From reading the App Guide on Slip Joint, there is a formula for K2:

K2 = (100)N/a (N is the NPS, a is the thermal exp., in/100ft)

What's the logic behind this formula?

Can K2 = 1 lb/in be used, after the pushing force passes Fy (like the soil stiffness)? Or K2 = 1 is too small for a typical S.J.?

Bryan

This is an appoximation, the equation was provided by the vendor we were talking to at that time.

A K2 value of 1.0 is probably too small, ask your vendor for a value.