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Many CAESAR II users question how to solve the friction problem. Unfortunately, things are not as simple as you would initially imagine.
There are two approaches to solving the friction problem. First, insert a force at the node which must be overcome for motion to occur, or second, insert a stiffness which applies an increasing force up to the value of Mu * Normal force. CAESAR II uses the restraint stiffness method. (An excellent paper on this subject is "Inclusion of a Support Friction Into a Computerized Solution of a Self-Compensating Pipeline" by J. Sobieszczanski, published in the Transactions of the ASME, Journal of Engineering for Industry, August 1972. A summary of the major points of this paper can be found below.)
Ideally, if there is motion at the node in question, the friction force is equal to Mu * Normal force. However, since we have a non-rigid stiffness at that location to resist the initial motion, the node can experience displacements. The force at the node will be the displacement * the stiffness. If this resultant force is less than the maximum friction force (Mu * Normal force), the node is assumed to be "not sliding," even though we see displacements in the output report.
The maximum value of the force at the node is the friction force, Mu * Normal force. Once this value is reached, the reaction at the node stops increasing. This constant force value is then applied to the global load vector during the next iteration to determine the nodal displacements.
Basically, here is what happens in a "friction" problem:
By increasing the friction stiffness in the setup file, the displacements at the node will decrease to some degree. This may cause a re-distribution of the loads throughout the system. However, this could have adverse affects on the solution convergence.
If problems arise during the solution of a job with friction at supports, reducing the friction stiffness will usually improve convergence. Several runs should be made with varying values of the friction stiffness to ensure the system behavior is consistent.
Summary of J. Sobieszczanski's ASME Paper
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