# Stairs on a curved surface

Hello everyone!
I’m trying to reproduce this bridge on grasshopper but, definitely for inexperience, I think that the workflow is too long and complex.

I would like to build the stairs directly in Grasshopper, but I don’t know if it may be more simple in Rhino. Any advise? I find my workflow a little bit long, I want it to be more optimized

Ciao Diego!

Your .gh is a bit messy…
Can you explain what would be the workflow?
What you have for initial input? A curved surface?
Then you want starting making steps from the outside or from inside?
What is the logic to use between the steps?

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Yeah, I think so too. I skipped creation of the curved base surface and focused on the steps, using internalized copies of yours (‘Srf_1’ and ‘Srf_2’). There are probably simpler ways to do this using RelItem but I ran out of patience with that. Also, there are creative decisions to be made about what to do at the top, in the center of the bridge. I skipped that too, or rather, made a simplistic assumption.

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I try to reply with some sketches. I think that the workflow must be divided in function of the two surfaces (intrados and extrados). On the first surface will be applied the structure and on the second one will be applied the steps. Unfortunately, at the moment, I can’t understand the logic between the steps, so I made them measuring them on the original drawing.

Thank you! I’ll try with your advice and I’ll post the result!

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:

1. 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.
2. 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?).
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