Problem in load combination

[ankit.khandelwal]

I am using ROBOT for modelling a cut and cover tunnel section. The whole structure is modeled such that, It is free to move in +Z direction. However, the combination of loads is such that, it creates a net load on section in -Z direction. when I am individually applying the load( then finally using them to create combination), one of the load is such that it creates a net load in +Z direction, and hence creating instability in the solution. So I just want to ask whether there exist any method in ROBOT( as in the case of STAAD we have Repeat Load Command), which analyze a set of loading conditions as though they act concurrently instead of just  combining (in a variety of possible ways) the results that were obtained from the independent analysis of the constituent load cases .

[Rafal.Gaweda]

If your model contains some uplift supports or releases (free to move in Z+) the analysis in Robot is non-linear. Also any combinations defined in Robot are in such case non-linear so they are directly calculated using loads from load cases composing them .

If some simple load cases, composing these combinations, contain loads which do not act independently and  cause instabilities, it is possible to define such load cases as Auxiliary load cases - see below. In such situation such load case is not calculated - but it is used as component of combinations.

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