Pre Cast Concrete Staircase support 1

[sithlord382]

Hi All,

Please see attached a rough sketch I have drawn up. I am proposing to install a precast concrete staircase within the loft space.
If you refer to the pdf attached, the red lines spanning up-down the page refer to load bearing walls. As you can see the shape of the staircase is an l shape with the immediate left hand side of the stair case running parallel to a load bearing wall. 2 questions:

1. I am proposing to install 2no. cantilevered beams (shown in green in the attached sketch) that will cantilever off the left hand side load bearing wall (shown in red). The first cantilever beam will support the first flight (imagine if you started from the bottom of the staircase) and the start of the winder. Then as you move up the winder there will be another cantilevered beam that will be positioned higher up on the lhs load bearing wall to provide additional support to the winder and the second flight of staircase. Ultimately is this proposal feasible and any comments would be appreciated.

2. If you refer to the plan, once you are at the top of the staircase, there is a room to the right hand side up on the loft floor. I have shown in purple proposed positions of steel beams to support the hollowcore slabs that make up the loft floor. However how will I support the area shaded in black? Currently I have shown 2 cantilevered beams, 1 that is perpendicular to the beam spanning left to right at the bottom of the plan and the other cantilevered beam is perpendicular to the beam spanning up to down on the page. These 2 canitlever beams will then are perpendicular to each other and will be connected together as shown. Again is this possible? Or will it make more sense to just have 2 cantilevered stubs perpendicular to the main trimmer beam (spanning up to down) for the loft floor hollowcore slabs to sit on.

Thanks in advance,

S

 

[sithlord382]

Hi

Forgot to add the sketch.. Please see below

[URL unfurl="true"]https://res.cloudinary.com/engineering-com/image/upload/v1634571784/tips/STAIRS_hfrayi.pdf[/url]

https://files.engineering.com/getfi...5-95dd-4a3d-be56-37fc0389890f&file=STAIRS.pdf

 

[KootK]

I'll assume that you can't drop a post in the knuckle of the stair.

I feel that the arrangement shown below would be simpler and less prone to deflection problems.

 

[sithlord382]

Koot K,

Many thanks for your repsonse. I have a few questions,

1. With regards to the staircase how do you propose the first flight to second fligh junction is supported? (ie. where they meet perpendicularly?)
2. With regards to the area of the loft floor floor that I am struggling to structural support, could we not cantilever 2 stubs and remove the smaller beam spanning up to down on the sketch? The floor load is probably going to be 4.98kN/m^2(Dead) and 1.5kN/m^2(Imposed). See rough sketch below

 

[KootK]

You're most welcome sithlord.

1. With regards to the staircase how do you propose the first flight to second fligh junction is supported? (ie. where they meet perpendicularly?)

I'd leave that to the premaster if you can. The supported bit might have a couple of steel tubes projecting from it that connect into an edge beam of the supporting landing. Or an underslung connection. Some googling on precast stair connections will likely turn up some ideas.

2. With regards to the area of the loft floor floor that I am struggling to structural support, could we not cantilever 2 stubs and remove the smaller beam spanning up to down on the sketch?

I don't care for any cantilever stubs unless they have a back span like the one that I showed in my sketch. Without that back span, you may get a bunch of torsion in the supporting beam that may be difficult to deal with, both in terms of that beam's torsional strength and the associated deflection in the stub.

 

[sithlord382]

Hi Koot K,

Many thanks for your response and understood.

Just to be clear, when you say back span you are talking about the beam to the right hand side where there will need to be some moment connection designed?

 

[KootK]

Exactly right sithlord.