When I've seen this question about stairs and not wanting to see it on story it passes through, it raises several questions.
- in archicad and similar programs, the goal is to model all the 3D elements. Is the stair really not seen on the middle story? Or is it that you would not see all of the stair the upper and lower most sections being obscured by room on this middle story? If so, modeling the stair in sections so it would show only what is visible would be correct. Covering the upper and lowermost sections with a masking fill as David suggests would also work. The downside of the masking fill is it needs maintenance. You will be adjusting its visibility to be behind the elements that you want to obscure it.
-Consider also that the stair will most likely be built in sections if it spans 3 stories. We are creating virtual buildings; creating the stair in sections will mirror the real building.
HTH
Erika
Architect, Consultant
MacBook Pro Retina, 15-inch Yosemite 2.8 GHz Intel Core i7 16 GB 1600 MHz DDR3
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Onuma System
"Implementing Successful Building Information Modeling"