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Stair Stringer Deflection, 10' rise

Stair Stringer Deflection, 10' rise

Stair Stringer Deflection, 10' rise

(OP)
Loosing my mind on this project. Someone please help

Im building a staircase. Open riser, 2 exposed stringers

First I built a 3.5" wide by 10.25" gluelam oak beam. its really solid, but i used urea PPR glue and my first 3 layers didnt have enough glue, i can see the glue joint is weak in those 3 lamination, it bugs me.

So i went and bought 4x10 structural #1 doug fir beams, planed them down to 3.5 x 9.75

The total rise is 122", total run is 168" so the total stringer length is about 16.5'

I dont want to get to detailed but basically im worried about deflection. There is going to be a glass railing attached to the floor, then to the stair treads, acting as a handrail.

I see from calc i get around 0.34 in deflection with a 50lb live and 15 lbs dead(3" thick white oak treads x 42" wide=heavy)

Every beam i use will get deflection, even an eng lvl.

Is this going to transfer down into the glass railing and put stress onto the glass? Or are the stand off glass fitting designed to allow movement/expansion?

RE: Stair Stringer Deflection, 10' rise

For a stairway, you should be using 100 psf LL.

Mike McCann, PE, SE (WA, HI)


RE: Stair Stringer Deflection, 10' rise

Context first. Is this a residence? For one or two family houses/townhomes you can use 40psf live load. 100psf for every other use.
Regardless, your handrail manufacturer should be well-versed with this situation. The connection types and tolerances for deflection will be manufacturer specific.
Are the beams notched like stringers or do the treads connect to the side?

RE: Stair Stringer Deflection, 10' rise

Building code uses AWC deck guide of 8' between posts if cut stringer or 13'3" if solid. You are 14' so consider mid-span supports.

RE: Stair Stringer Deflection, 10' rise

A residential stair will likely never see 40 psf live load. My gut says you are ok.

RE: Stair Stringer Deflection, 10' rise

(OP)
HI, thanks for responses. render attached.
Heres how i understand it works:

This is residential. The stringer are not notched. 40#LL and i add a 10 dead for treads(white oak). foorprint is about 16x4 or 64 sqft.

64sqft x 50# load = 3200# / 2 stringers = distributed load of 1600lbs per stringer. I round it up to 2200# per stringer for uneven load.
Is this how it works?

When i did some number punching online i found a 2x10 to be fine for my load and span. Im not using spruce 2x10. Im using #1 grade 4x10 Doug-fir which carries an MOE almost 80% more then spruce if i remember.

I cant have support in the middle.

Last night after thinking about all this, i realize that maybe the glass will actually support the stairs a bit, and help prevent that small amount of deflection if some 400# fatty jumps on the mid treads.

The glass is 1/2 or 3/4 tempered laminated low iron, with standoffs on each tread, which will be covered with treads caps.

Thanks for input guys. Even if i dont get exact answer i like hearing opinions and experiences, its helps me worry less.


RE: Stair Stringer Deflection, 10' rise

Quote (fudgemen)

IM not an engineer, i just like to do everything the proper way

Stop. Call a local structural engineer to evaluate this. That is the proper way. There are geometric facets to be considered, not to mention section loss due to notches for your treads and knowledge of properly applying the loads. When your wife (or daughter/son) is walking down those stairs carrying your baby (or grand-baby), do you want to think - man, google and some anonymous guys on a forum helped me build that right, or do you want to know that it was thoroughly investigated and designed by a competent professional?

I don't mean any offense - I'm a DIY'er, too - but some things do need professional consideration.

RE: Stair Stringer Deflection, 10' rise

I agree with phamENG - get a structural engineer involved.

As far as the glass providing support, it can, but only if the the load is applied in the plane of the glass. If load is applied to the standoffs, the results could disastrous. Also, 3/4" glass will add up to 10 psf to the weight.

Rod Smith, P.E., The artist formerly known as HotRod10

RE: Stair Stringer Deflection, 10' rise

Never practice with glass, but I think it has very low tolerance for support deflection (coded in L/xxx"). Check the supplier/manufacture, see if they can provide guidance on deflection limit, and method of connections. With those information on hand, use the deflection limit to figure out required beam depth, round the number up for additional safety.

Agree with all others. DIY is fun, but when the glass railing fails, image what your wife and mother-in-law will say. Not very good, I think.

RE: Stair Stringer Deflection, 10' rise

I'm with XR250. The stair isn't going to explode.

As for deflection fudgemen, the most stringent requirement that the railing could require is "L/360" or 168"/360 = .47 inches, and you're in that range. Someone might suggest that L/600 is a more suitable requirement for glass, but anything that spans a horizontal distance should be built for L/360. If the metal pieces couldn't take that, it would not be used.

RE: Stair Stringer Deflection, 10' rise

The depth of notch and span would be a concern to me as well. I doubt the glass will stiffen the assembly, but it will damp the system so there is less bounce. The holes for the standoffs are oversized and they use rubber to prevent added stress on the glass.

Presumably the stair is built now. Can you mock up a test?

I too have built my own open rise stair, but I used mortise and tenon joinery for the treads and my span is about 1/2 of yours.

RE: Stair Stringer Deflection, 10' rise

(OP)


This is how I built my stringer open riser, this is one I built and removed 6 years later but it's only for 8.5' rise. There is no notching of the 10" stringer. The treads sit on riser block attached to the solid 10" x 3.5" stringers.

I'm professional stair builder. I realize having an engineer spec it would be ideal, but if stairs required engineering then ICC would spec it. This is something that can be figured out on my own with a little effort and time, and help from community.

I will check with glass manufacturer to see if they can supply deflection limits. The glass is a large sheet, 168 inches long by 32 inches at highest top of stairs, it also the handrail.

Good to kno there is rubber washer expansion in the standoffs, I really think that's all that is required.

By the way.... I have since upped the entire stringer to a 4x12 Doug fir beam. Going to pick them up as I type. I'll use the other 4x10 for the bottom stairs, 9' rise.

I'm gonna call this case closed and stop worrying.

Thanks so much guys, first post and it's gave me some insights


RE: Stair Stringer Deflection, 10' rise

I gather you are a builder and not a professional engineer in a different discipline. This forum is not really intended for this type of advice. It is intended for engineers to discuss engineering problems with other engineers.

RE: Stair Stringer Deflection, 10' rise

Quote (fudgemen)

if stairs required engineering then ICC would spec it

That seems like a gross misunderstanding of the intentions and limits of the International Residential Code. Here's a decent article that goes through how limited the IRC is (or was in 2013 - may be a little more comprehensive now) on the topic of stair construction and why it needs more consideration.

RE: Stair Stringer Deflection, 10' rise

(OP)

Quote (phamENG)

Here's a decent article that goes through how limited the IRC is

Have read that article a few times actually. Most recently while researching this issue. You are correct. There are numerous issues which need to be addressed or defined. However i do feel that if it was such a black and white issue, or a vast problem, it would have been added into the new revision, which only a few thing were regarding stair building(as you mentioned).

I think it clear to see im putting every effort into making this overkill. Ive seen guys install 10' rise stairs with a notched 2x12 which leaves like 5.5 inches throat depth. That is unsafe. Its for idiots like this that the code was created, because individuals cared more about the profits then the safety of homeowners.

While you may interpret my stair construction to be unsafe, i can guarantee you that it is not.

RE: Stair Stringer Deflection, 10' rise

Quote (brad805)

if stairs required engineering then ICC would spec it.

Uh nope. This is how your statement should read:

"Anything not prescribed in ICC, either in method or material, requires either an ICC-ES Evaluation Report, or supporting calculations by an engineer."

The number of ICC-ES evaluation reports for stairwell kits is legion. There are even ER's for glass railing systems and glulam's used as beam stringers like the OP is describing.

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