A DLF of 2 is appropriate for a single, instantaneously applied load that does not change once started. In a hammer analysis, you may be applying your load on several elbows and these may be interacting with one another thus showing an effective DLF greater than 2. Also, in CAESAR II, the response due to mass participation above your frequency cutoff does not have the sign sense of the modal responses. That combination may also upset the DLF=2 relationship.
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Dave Diehl