The "Substructure and bearing elevations are found in the bridge modeler Bridge Object Bent Assignments menu under Bridge > Bridge Objects > Modify/Show Bridge Object > Modify/Show Assignments for Bents > Elevation (Global Z).
Substructure Location, Elevation (Global Z)" refers to is the bearing seat elevation, or the elevation of at the top of the bent cap or abutment cap (this elevation is essentially the bearing seat elevation). "Bearing Assignment, Elevation at Layout Line (Global Z)" refers to is the Z elevation of at the bearing action point of the bearing. Both of these parameters are graphically shown in the "Bridge Seismic Design" manual on . Abutment and bent figures, taken from pages 1-13 and 1-15 . The relevant figures from the manual are reproduced below, for abutment and bent:
Abutment (bearing action point at elevation -49ft, seat at elevation -51ft):
Bent (bearing action point at elevation -49ft, seat at elevation -51ft):
...
of the Bridge Seismic Design manual, are shown in Figures 1 and 2:
Figure 1 - Abutment bearing action point (Z = -49ft) and seat (Z = -51ft)
Figure 2 - Bent bearing action point (Z = -49ft) and seat (Z = -51ft)