it looks like you're using beams only
you'd have to add something like a shell or solid to apply a pressure to. (the beam doesn't really have a surface area to apply the pressure to so that it could be converted to a force at the nodes)
option 2, convert your pressure to a force and apply appropriately
Thank you, that is what I figured I should do... I just multiplied the pressure by the tributary width of the beam and applied the load as a uniformly distributed load on each beam.