Q: How do I avoid a *locked* solution?

Question

When solving a LimitState:RING problem, the output window reports:

Adequacy factor = not found at load case number X

(Key: locked = geometrically locked for given load case)

What can I do?

Solution

A geometrically *locked* solution occurs when the applied load can be increased indefinitely without a failure occurring in the bridge - this is most often encountered when a vehicle in a load case does not transfer any load to the bridge (i.e. it is too far to the left or right side). Another reason may be a very thick arch with infinite crushing strength.

Assuming a lack of loading is the reason for the *locked* result, to resolve the situation you can:

1. Set up the file initially such that the loading at the left hand side just touches the bridge structure over the left side and the loading at the right just touches over the right side. This should avoid you getting a *locked* result by ensuring that the bridge is loaded in every case, or...
2. Examine the results for each load case in the output window and delete ALL those that report (locked) as a result of the loading not affecting the bridge.

Note

As the load case name is a user-definable entity, the load case number reported in the output pane may not necessarily be the same as the name shown in the drop-down box in the Load Cases dialog. To ensure you are deleting the correct load case number, look to the right of the drop-down box (e.g. 11/40 is load case number 11 out of a total of 40).