Many years ago, the typical way of modelling an expansion joint was to code right to the center of the joint and add the expansion joint terms (stiffnesses) at the center. For example, if I have an expansion joint running from 100 to 110, I might run a rigid element from 100 to the midpoint at 105 and then another rigid element from 106 to the other end at 110 and specify the "zero-length" xj terms between 105 and 106.

Many xj manufacturers list bending "flexibility" rather than bending stiffness in their catalog. This bending flexibility is what you enter for a "zero length" xj in a beam element program like CAESAR II rather than bending stiffness. Use bending stiffness for "finite length" xj's. If you enter axial and lateral stiffness for finite length joints in CAESAR II, CAESAR II program will calculate the appropriate number. But you have to have the correct flexible length of the joint specified.

As I am using these terms - bending stiffness is four times bending flexibilty.