This model includes parametric construction of the base surface, in white group:
The yellow group trims the base surface using the ‘World XY’ plane, though that is not used in the cyan group, which constructs the step risers and treads.
In principle, the steps are a “simple” use of Contour to guarantee the same step height, but it’s complicated by two issues here:
- Since the high point of the bridge is in the middle, there are two contours for each “step”, one at either end. This calls for some tricky data tree manipulation.
- The middle of the bridge presents other complications. The blue group removes the last set of risers but maybe you prefer to have a flat surface there, between them?
Also, it is possible to get a “Closed Planar Curve” (circle) in the middle, which makes it even more difficult to get that top step (with a hole in it?).