We get asked from time to time how to model a spiral staircase in MecaStack. There is no option to automatically enter the spiral stairway in MecaStack. As a company, Meca has little experience with spiral stairways, and so we don't have a lot of knowledge about how they are usually constructed. We have been asked the question so much that we have attempted to formulate a basic approach to calculating the wind area and weight that would be entered as a General Attachment Uniform into MecaStack in order to attempt to account for the spiral stairway.
We are not experts on this topic, but we have attempted to calculate based upon our knowledge. Our understanding is that a spiral stairway would typically be constructed as shown in this pic.
There are stringers on the outside and inside, and then steps/treads extending up the stringers. Since the geometry is constantly changing given that the stairway follows a helical path, we think that you would calculate two extremes and then take the worst case of the two:
Case 1: Wind perpendicular to the steps and the stringers are basically parallel to the wind and would have minimal wind exposure.
Case 2: Wind perpendicular to the stringer, and the steps are hidden behind the stringer
We calculate these two extremes and then take the larger of the two values, and then add to the wind on the handrails and posts. Attached is an example calculation, and if you use Mathcad we have attached our actual calculation sheet so that you can modify the values as needed.
Again, we are not experts on this and we have not found any published data, and so please use your own judgement when calculating for your own situation.