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Answer: You could replace each stage (or sequence of stages) for which you need to perform the design by a standalone staged construction load case that would be using stiffness at the end of a load case for the previous stage. Then the design load combination can be created for these new load cases that essentially represent the individual stages in the construction stage analysis.
How can I obtain results only for a certain stage of a staged construction load case?
Extended Question: For each stage, the stage construction results are cumulative, ie. they incorporate forces from all the previous stages. How can I, without manually subtracting results for individual steps, obtain results only for a given stage?
Answer: You could replace the stage construction load case by a chained sequence of staged construction load cases, each of which would be using stiffness at the end of the previous load case. The results for a single stage could be then obtained by setting up a load combination that would include the current load case with a scale factor of 1 and the previous load case with a factor of -1.