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btw, i found this in ACI318-19:

You can find it in books dealing with nonlinear analysis or the research papers dealing with "Failure mechanisms of structures with strong column-weak beam" philosophy. The idea is to enable the frame to maintain its ability to carry gravity loads when it moves into inelastic range. The formation of hinge at the top end of top story column does not inhibit the frame from maintaining its ability to carry gravity loads.

The joint at the top end of column in the top floor does not require this check. The formation of hinge at this location "is part of plan".

You can use truss element to represent equivalent diagonal strut. Yes, you have to provide axial hinge at center. There are different models for strut width according to different conditions of aspect ratios, openings and infill properties. You need to do literature review to select the best model. For instance, Crisafulli and Carr (2007) model can be used for infill with opening For more information, Refer Kumar, M., Khalid, F., & Ahmad, N. (2018). MACRO-MODELLING OF REINFORCED CONCRETE FRAME INFILLED WITH WEAK MASONRY FOR SEISMIC ACTION. NED University Journal of Research, 15(1), 15-38. Nadeem, K., & Mohammad, A. F. RESPONSE OF REINFORCED CONCRETE BUILDING STRUCTURES SUBJECTED TO MULTIPLE SEISMIC SHOCKS.