Sam,
I’m not familiar with using SAP2000 but from previous discussions I don’t believe you can do progressive collapse as such.
You have to create separate models for each assumed mode of failure. Remove a column, adjust loads, perform an analysis. Likewise remove beam, adjust loads perform an analysis.
If you search the SEAint archives a few months back there were some suggestions of software which could automate assessment of progressive collapse.
Regards
B.Tech (mfg & mech), MIIE, gradTIEAust
mailto:sch.tectonic@bigpond.com