Staircase - Intermediate Support for Stringers

[Cap07]

I'm designing an interior staircase for an existing building with the stringers spanning about about 13' (horizontal distance). I have to put in an intermediate support for the stringers in order to show them good. My plan is to use a 2x4 support wall in the middle of the staircase. I was going notch the stringers where they rest on the wall (making sure that it's not at a point in the stringers where the depth is at a minimum). Please see the attached jpeg - I've circled in red the detail I'm referring to.

Is an intermediate wall like this a good way to support the stringers?

Also, what is the best way to anchor the support wall's sill plate to the concrete slab (which is probably 4" thick)?

 

[msquared48]

Nothing wrong with using the wall for support.

To anchor the sill plate, eoither shoot the plate to the concrete (Hilti), or use expansion anchors, or screw the plate into lead inserts in the slab. Any will work here.

Mike McCann
MMC Engineering
Motto: KISS
Motivation: Don't ask

 

[Bagman2524]

I'm surprised you need an intermediate support for a 13' span. Stringers typically should be designed for 12' height at a 32.47 deg angle, or about 19' horizontal span. I would see if you could use a bigger stringer. It might be easier than adding an intermediate support wall.

 

[Lion06]

If you're using wood stringers why not use a better species and/or a better grade of lumber?

 

[Cap07]

Mike - thanks for your advice and suggestions, I really appreciate it.

Bagman2524 and StructuralEIT - thanks for your suggestions too. I forgot to mention that the staircase is for a non-residential building, so I'm using a live load of 100 psf. Also, most of the materials for the staircase were obtained before I started working on the project, so I'm trying to get what they already have to work

Thanks again for all of your suggestions, I appreciate them very much.

 

[Ron]

You can do what you propose(although I don't like the idea of notching a tension member subject to repetitive load), but I would look at doubling the stringers.

Keep in mind that if you attach to the wall, you will transfer sound to the wall...that can get annoying for stair sections.

 

[a2mfk]

For new buildings we usually put thickened edges with a bar or two under the landing for crack/settlement control. Maybe do the same under the cripple wall and your landing if you can. Though in reality an uncracked unreinforced slab can take some very large point loads (look at driveways)...

 

[Cap07]

Ron and a2mfk - Thanks for your replies. I was going to double the center stringers, I can't show them good otherwise. This is an existing building, but I'll keep the thickened edge under the landing in mind for new buildings.

Thanks again!