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Technical Question-Scissor Stair

C

cymatia

Member
Joined
Sep 9, 2015
Messages
3
Location
New York
We are working on a multiple dwelling structure in reinforced concrete. I would like to ask how does the separation wall (4" cmu) between scissor stairs gets supported. This is an 8 story, including the bulkhead, cellar, and subcellar. The separation needs to happen from the first floor and above. Do you design a support beam at the first floor?

Thank you very much in advance for your help!
 
Welcome,,

Only thing I know about scissors, Is my Mom told me not to run with them,

Give it a few days for reposnes
 
cymatia said:
We are working on a multiple dwelling structure in reinforced concrete. I would like to ask how does the separation wall (4" cmu) between scissor stairs gets supported. This is an 8 story, including the bulkhead, cellar, and subcellar. The separation needs to happen from the first floor and above. Do you design a support beam at the first floor?

Thank you very much in advance for your help!
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Need more information; the support of the wall between the stair does not relate at all to the stair. it is supported on the slab (I assume concrete platform/podium) or directly to the footings below.
 
This is an issue for the architect and the structural engineer on the project to sort out. The building official is only concerned if the support was not provided in a manner consistent with the code provisions.

It is unclear why the question is being asked.
 
Mark K said:
This is an issue for the architect and the structural engineer on the project to sort out. The building official is only concerned if the support was not provided in a manner consistent with the code provisions.

It is unclear why the question is being asked.
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I think this is the architect looking for help
 
Ask the structural engineer. However, the wall will need to have a 2-hour rating, so the 4-inch masonry will need to have the equivalent thickness to provide that rating. If the wall is supported by the floors, then the floors will also need a 2-hour rating.
 
RLGA said:
Ask the structural engineer. However, the wall will need to have a 2-hour rating, so the 4-inch masonry will need to have the equivalent thickness to provide that rating. If the wall is supported by the floors, then the floors will also need a 2-hour rating.
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And that which supports the floor will need a 2-hr rating as well.

I googled scissor stairs and what I found doesn’t look like a good idea for an eight story building.....maybe an eight story grain silo.
 
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Some architects define the scope of the structural engineers work to exclude such things believing they can deal with it without an engineer. Then they try to get some free advice such as by asking a question on this forum.

This problem might be aggravated by the practice of having the stairs designed by the contractor. If they find they need to support part of the wall on the stair framing they will then have to make sure the stair engineer considers the loads from the wall.

I suspect that they will find that it makes more sense to use metal studs instead of CMU. If the building is located somewhere earthquakes are a concern one might question the competence of an architect who uses 4" CMU in the stair well.
 
another thing to consider is that scissor stairs under IBC count as one exit stairway. This may be a moot point since we dont know what the design is, but its one of those items that if not considered early on, could turn into a big headache later.
 
mp25 said:
another thing to consider is that scissor stairs under IBC count as one exit stairway. This may be a moot point since we dont know what the design is, but its one of those items that if not considered early on, could turn into a big headache later.
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I think that might be the intent of the separating wall, or at least that's how I read the OP. To separate the scissor stair into two distinct stairwells.

...but maybe not...
 
tmurray said:
I think that might be the intent of the separating wall, or at least that's how I read the OP. To separate the scissor stair into two distinct stairwells.

...but maybe not...
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Even with a separating wall, they cannot be counted as two separate exit enclosures.
 
Even with a separating wall, they cannot be counted as two separate exit enclosures.
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Our jurisdiction is allowing them. I don't have a copy, but from what I understand, there's language in the 2015 commentary that allows scissor stairs if they are fire separated.
 
2015 1007.1.1 commentary;
"Interlocking stairway that occur over the same building footprint but within separate enclosures are not "scissor stairways" and can count as two independent exits. Due to concern about smoke migration, careful review of the construction details and verification that they meet all the provisions for fire barriers and horizontal assemblies must be made. Of special concern would be the provisions for continuity, penetration and joints."
 
Francis Vineyard said:
2015 1007.1.1 commentary;
"Interlocking stairway that occur over the same building footprint but within separate enclosures are not "scissor stairways" and can count as two independent exits. Due to concern about smoke migration, careful review of the construction details and verification that they meet all the provisions for fire barriers and horizontal assemblies must be made. Of special concern would be the provisions for continuity, penetration and joints."
Click to expand...

If separated they are considered as two separate exit enclosures, but if they are the only two stairs they will probably not meet the separation of exits requirement.
 
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