It will be helpful if a function for applying the hydrostatic forces on plate elements either by selecting a group of plates or a selecting a single plate e.g., the PlateID and the pressure at four corners of the plate. Many a times applying the pressures due to the impulsive and convective seismic forces becomes a tedious job to accomplish manually. Exposing a function to apply the hydrostatic pressure will be much helpful.
Thank you for posting this idea, however, such a function already exists,
OSLoadUI::AddElementTrapPressureEx
Please refer to the OpenSTAAD help documentation for details of this function.