A pressure is a load acting toward the normal of a face of the structure. If there are large deformations in the model and the Include geometric nonlinearity check box is selected under the Study settings section of the current study step, the pressure acts as a follower load. The pressure is then defined with respect to the geometry and, as the geometry deforms locally, the orientation of the load changes. The size of the loaded area can also change as an effect of straining.