Question
When I solve my LimitState:RING problem the solution is sometimes reported as *unknown*. What does this mean? Can it be avoided?
Solution
There are several possible causes for *unknown* solutions:
The solver is unable to find a valid solution
Very occasionally, the third-party solver used to carry out the optimization calculations in LimitState:RING is unable to reach a valid solution. In such cases an *unknown* result is returned. The cause is generally related to the complexity of the problem, so you may want to try reducing the number of blocks or load cases.
The geometry is such that a valid solution is prevented
In some circumstances the model geometry is the cause of the problem. Generally an *unknown* is given when the springing contact surfaces (those at the very ends of each span) are absolutely horizontal. This is normally as a result of specifying user-defined intrados and extrados end points with the same 'y = 0.0' value (see the attached file, 2_Span_Unknown.ring, for an example). To prevent this from occurring, ensure that the extrados y positions are slightly higher (e.g. 0.05).
