I have noticed that the RSAP - which uses the Winkler model - often does not take into account the effect of ground water pressure on internal forces in the slab. Perhaps this is not a defect in the program, but simply a feature of this ground model.
When negative reactions occur, it is possible to perform a nonlinear analysis that eliminates the "stripping" - in which case, indeed, the bending moments in combination with water pressure are different from those without pressure.
However, in the case where the building resistances without water pressure are much larger than its values (e.g., the average resistances are 150kPa, with concentrations of 200kPa under the columns and values of about 120kPa in the slab spans - with water pressure, for example, 50/70kPa), the program does not show any differences in the bending moments in the corresponding combinations with and without water pressure.
Is your experience similar?
I ask because the effect of no effect of water pressure on bending moments in the foundation slab is unintuitive. I wonder how the above-described effect of water pressure is taken into account in other foundation models - well, and whether there will be another model in RSAP in the near future.
