SarBear
Structural
- Mar 14, 2022
- 38
Hi everyone,
I have been asked to engineer a set of floating stairs for a residential project. I have attached the PDF from the steel fabricator below. The idea is that the treads are HSS 10x2x1/4, and each tread is to weld to a 1" thick x 10" tall "spandrel" plate that forms the exterior perimeter of the stairs. On the sides of the stairwell this plate will be welded to supporting HSS columns every 3' or so. At the rear of the stairwell the plate will be bolted directly into concrete along its length. These are the different aspects of the stairs that I think I need to look at:
1. The capacity of the HSS treads themselves (easy enough, they are each cantilever beams)
2. The capacity of the weld from the HSS treads to the spandrel plate (easy enough)
3. The capacity of the spandrel plate as it spans between supporting columns and bolts (no idea how to take into account the torsions that are introduced into the plate from each tread)
4. The capacity of the weld from the spandrel plate to the columns (need to get the reactions at each column from #3)
5. The capacity of the columns (can't do this until #3 is done)
6. The connection from the spandrel plate to the supporting I-beam at the top of the stairs (can't do this until #3 is done)
7. The connection from the HSS columns to the concrete slab at the bottom
8. The connection from the HSS columns to the framing at the top (is this needed?)
How would you go about designing these stairs? Some items like #1 and #2 are easy to calculate, but I'm totally lost on how #3 is to be done since each tread is imparting a shear and a torsion to the spandrel plate. I've looked around for hours for some kind of example or design guide but I can't find anything useful. I'd describe the spandrel beam calculation as a "beam fixed at both ends with point loads and torsional loads" if that sounds correct. Do you have any recommendations for examples, software, or guides that I could check out?
I have been asked to engineer a set of floating stairs for a residential project. I have attached the PDF from the steel fabricator below. The idea is that the treads are HSS 10x2x1/4, and each tread is to weld to a 1" thick x 10" tall "spandrel" plate that forms the exterior perimeter of the stairs. On the sides of the stairwell this plate will be welded to supporting HSS columns every 3' or so. At the rear of the stairwell the plate will be bolted directly into concrete along its length. These are the different aspects of the stairs that I think I need to look at:
1. The capacity of the HSS treads themselves (easy enough, they are each cantilever beams)
2. The capacity of the weld from the HSS treads to the spandrel plate (easy enough)
3. The capacity of the spandrel plate as it spans between supporting columns and bolts (no idea how to take into account the torsions that are introduced into the plate from each tread)
4. The capacity of the weld from the spandrel plate to the columns (need to get the reactions at each column from #3)
5. The capacity of the columns (can't do this until #3 is done)
6. The connection from the spandrel plate to the supporting I-beam at the top of the stairs (can't do this until #3 is done)
7. The connection from the HSS columns to the concrete slab at the bottom
8. The connection from the HSS columns to the framing at the top (is this needed?)
How would you go about designing these stairs? Some items like #1 and #2 are easy to calculate, but I'm totally lost on how #3 is to be done since each tread is imparting a shear and a torsion to the spandrel plate. I've looked around for hours for some kind of example or design guide but I can't find anything useful. I'd describe the spandrel beam calculation as a "beam fixed at both ends with point loads and torsional loads" if that sounds correct. Do you have any recommendations for examples, software, or guides that I could check out?
