You have to partition the boundary at the point where the slope changes from linear to horizontal, and then define an analytical field for the linear part of the distribution.
To define a partition, in the Part or Assembly module, go to Tools->Partition
To define an analytical field, in the Interaction or Load module, go to Tools-Analytical Field->Create and create a linear analytical fiel.
Captain, Infrastructure Engineer, Hellenic Ministry of National Defence
Civil Engineer, M.Sc., Ph.D. candidate, NTUA
Email: [hidden email]