I have modelled a 4 storey Steel frame in Seismostruct 2016 and I ran a Dynamic Time-History Analysis for specific seismic event (scale=1.0, completed successfully). Next, I ran an Incremental Dynamic Analysis for the same frame using the same seismic input applying the factors 0.1, 1.2, 0.1 for start, end and step scaling factors respectively, and the model completed the first 6 steps of analysis (up to scale 0.6) and then stopped, as it was “unable to apply the next step load”. Without changing the aforementioned model, I just applied the following scaling factors 0.1, 1.2, 0.05 (start, end and step respectively) and again my model completed the first 6 step of analysis (reaching 1.35 scale), but was unable to continue.
I would like to ask why this thing happens, and whether I need to change any parameters in order to make my model run all the steps (i.e. convergence criteria, iterative strategy etc.).
Thank you in advance,