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3.5.2.1 Friction

Friction may be present whenever the pipe can move, and in the process of moving, rub against a restraint. As noted earlier, the maximum magnitude of the force resisting sliding is equal to Mu times the restraint force, where Mu is the dynamic (i.e., sliding) coefficient of friction. The frictional force is applied along the direction of the pipe movement.

This is a non-linear effect, and requires an iterative solution, since applying a friction load to the piping system alters the results, changing the load at the restraint and the direction of pipe movement. Therefore, friction will have to be calculated again, and re-applied to the system, again changing the results. This continues until the frictional load is unchanged, within a tolerance (which can be adjusted by the user). In the event that there are numerous frictional restraints, this process may take a while (or may even not converge).

Friction restraints have two states: sliding and not sliding. The restraint is not sliding if the force tending to move it is less than F times Mu. The restraint is sliding if the force tending to move it exceeds F times Mu.

Friction is activated at a restraint in CAESAR II by entering a non-zero Mu value.