During my research, I have read the concept that unbalanced moments in flat slabs being transferred partly by flexure and vertical shear, and it is the basis for ACI code in recommendations on flat plates transferring combined shear and moments. What I want to know is how was the model conceived? ( I mean what made the developers come up with that idea?) what makes the concept valid or how was it proved? Why didn't they make the moment transferred solely by flexure?
I would be happy if someone attaches the original research for the concept?