In RISAFoundation, you can add a vertical offset for slabs or beams. Traditionally, RISA uses centerline analysis which aligns all elements at their centerline. This is a common structural analysis assumption as the loads will get transferred to the centerline even if there is difference in the sizes.
In certain circumstances, it becomes necessary to model the offset because the elements are very different sizes and you need to address the eccentricity.
You can modify the slabs or beams using the Analysis Offset either graphically or in the spreadsheets. The slab or beams can be offset in the downward direction.