In CAESAR II dynamic analysis, modeled restraint friction is replaced with two springs mutually perpendicular to each other in the plane perpendicular to the restraint. The stiffness is based on 1) the restraint's coefficient of friction, 2) the normal load from the static load case identified in the Control Parameters, and 3) the "Stiffness Factor for Friction", also defined in the Control Parameters.
So once you get to dynamics, the (sliding) friction load is based on the calculated position of the pipe times this stiffness - no more mu*N.
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Dave Diehl