I am currently doing my master thesis on a topic and am having little conclusion in my initial research.

My topic summarized is analyzing the a tall structure with multi level basements fixed as a cantilever with varying base conditions at 1) the ground/grade level 2) substructure/basement level and 3) foundation. All with varying lateral moment distribution I need to analyze the effect and difference in taking the effective height from the basement/substructure level as oppose to the ground level and document what importance/consequence there is in considering this fixity.

Im assuming this is closely relative to backstay effects?
I will also need to model this situation using deep foundation/geotechnical software.

Theres much literature to consider here including soil-substructure-structure interaction and basement modelling but there is quite scarce past literature on the effective heights for tall buildings with basements/substructures.

Can someone please advise on how this topic can be addressed and how to approach this study? what in particular methods should i use to analyze and define this importance in considering effective height?