Metal staircase attachment - no beam 3

[mechemi]

First, I'm a mechanical engineering student, so I'm not familiar with the US building codes pertaining to this issue. This is also not coursework, but curiosity.

I have encountered a staircase in an industrial setting that is anchored at one end to diamondplate only. One side of the staircase end rests directly on diamondplate (is welded), several inches from the nearest beam connection. The other side of the same staircase end rests on air, next to diamondplate, with a 3" weld between them that would be subjected to shearing through the weld thickness. There are flanges on the diamondplate but no beam supporting it at the staircase.

My gut feeling is that a metal staircase should be connected beam-to-beam at both ends, and that diamondplate should not be used as a primary structural support. However, I don't know where to look to verify this. I found guidelines on the construction of the actual staircase but not regulations on how it would be attached.

Can someone direct me to the appropriate resource, or give me some guidance backed by more experience than I have?

 

[KootK]

Your gut feeling is quite right. Stair stringers are generally set out such that they bear on primary framing (beams, slabs, etc.) for support. The stairs that you've described sound like junk.

You're not likely to find a regulation specifically prohibiting the crappy connection details that you've encountered. And part of the reason for that is that, under the right circumstances, one could support a stair case from connections to the floor plate alone. It would be weird, and would require some calculation to justify it, but it could be done.

An excellent reference on stairs can be downloaded for free here: Link. It will tell you a good deal about how stairs are typically detailed but it won't supply a prohibition on the kind of connection details that you're seeing.

The greatest trick that bond stress ever pulled was convincing the world it didn't exist.

 

[mechemi]

Unfortunately, I am describing the floor plate (well, landing plate) connection of the top flight of a stairs-landing-stairs assembly. So it's possibly worse than you're thinking. The stairs are supported stringer-to-beam at the top, and the staircase itself is standard metal industrial stairs (two closed box beams with flanged risers), but it seems bad to support any load by shear through a weld thickness.

(Gosh, I hope I'm describing this correctly..)

And if the weld doesn't fail in shear, then the weight of the stairs + live load is creating a load on the edge of the diamondplate, inducing a moment since the nearest support is several inches away. The diamondplate does have edge flanges which seems to be the only reason it has not bent already.


Thank you for the link, I'm reading through it now.

 

[Ron]

mechemi....my gut feel is you are right, but a sketch or photo of the issue would be helpful.

Providing support through weld shear is common, but there are situations where it should not be done.

 

[KootK]

You'll find it takes a fair bit to shock an experience structural engineer mechemi. As bad as you think your stairs are, I've got a bottle of scotch that says the ones in the shaft I walk up every day on my way to work are worse. Engineers of record often delegate the design of non-architecturally significant stairs to the steel suppliers. And skill can very a great deal from one steel supplier to the next.

The greatest trick that bond stress ever pulled was convincing the world it didn't exist.

 

[JStephen]

That's not the normal way things are done, but that doesn't mean it CAN'T be done that way, either. There is obviously some strength in the plate and in the weld, whether it's adequate would be a matter of crunching through the numbers. If the numbers don't easily work out, it would likely be easier to load-test the stairs than to make a more extensive analysis.

On the weld itself- shear strength is several thousand psi, so it doesn't take much weld to support a set of stairs if it's in the right place and the right configuration.

 

[mechemi]

 

[KootK]

Huh. It's cleaner and more purposeful looking than I'd imagined. And I see what you mean about the stiffening flanges. The lower stringer connection is unconventional too with that little HSS projection. It's hard to tell if this is the handiwork of an incompetent boob or a rogue stair genius.

The greatest trick that bond stress ever pulled was convincing the world it didn't exist.

 

[MikeHalloran]

Guesstimating from photos of modest resolution:

It looks like the OSHA toeplate is formed up from a serious deck plate, and the diamond plate is a mere veneer over that.

If the stair stringer is welded to the end of the toeplate, it could be okay, unless the weld is as ugly as that between the bottom of the stringer and the deck edge.

OR, I could be completely misinterpreting what I'm not quite seeing.




Mike Halloran
Pembroke Pines, FL, USA

 

[mechemi]

I'm not sure what a toeplate is, sorry. Is that what I'm calling a flange? A bend in the diamondplate that sticks up some 4"?

The stair stringer is only attached to the diamondplate at bottom. The stair stringer at right is some 6" from the beam piece connected to the bottom set of stairs, and is about 6" forward of the small metal plate that connects the 2" hollow tubing frame to the diamondplate. The flange, or toeplate, is cut before the stair stringer and there is no attachment between that flange and the stringer.

On the left, the only connection is the 3" horizontal weld to the edge of the diamondplate.

I did have a laugh at "rogue stair genius", thanks.

 

[KootK]

Oh no, I'm quite serious mechemi. Notice how the platform is point supported by those little standoff plates. And how there are those intentional daylight gaps in the treads. Those metal stairs in the link that I shared are generally utilitarian eyesores, relegated to dank stair shafts and left to rust out back with the dock levelers. But this... this is someone's feature stair. It's an attempt to speak to future generations via the medium of stair art/porn.

And yes, Mike's kick plate is your upturned "flange". Mike raises the excellent point that the floor landing appears to be made of two plates: a thicker plate on the bottom with a 4" upturn, and the diamond plate on the top with the 1.5" downturn. Can you confirm that? As Mike has alluded, it would seem logical for the designer to have intended for there to be a vertical weld connecting the toe plate to the end of the stringer.



The greatest trick that bond stress ever pulled was convincing the world it didn't exist.

 

[mechemi]

No, there is only one plate, which, bent different directions, forms both the kick-plate and the flange. It is just a single thickness of diamondplate.

I can get a better picture from the top, but my memory says the toe plate isn't connected to the stair stringer at all and the only support on that stringer end is the weld visible in the photos.

This is actually the second poorly constructed staircase I've found at the same facility. The other featured the top of a staircase + platform supported only through shear on a weld about 3' wide. At the time I found it, the weld was cracking and daylight was visible through 1/3 of its length. I can post an Inventor file of that one... an emergency work order was issued and gussets were added the same night, but it too is using diamondplate as primary support. I was satisfied that the gussets prevented immediate collapse but I plan to recommend other modifications.

 

[IFRs]

This is a poor detail.

Here is my opinion ( the preceding was not opinion ):
It looks marginally strong enough now.
It is unlikely that an inspector would fail it.
It is not likely to fail tomorrow.
In the future, when things corrode, get bumped and vibrated from use, I see trouble.
If it is in a high traffic area, I'd fix it RIGHT NOW.
If it gets used once in a blue moon, detail the fix and put it on the maintenance department's list of things to do.

Finally, pat yourself on the back for finding it, don't become jaded if the owner tells you to stuff it and keep your eyes and ears open!

 

[racookpe1978]

It is a jobsite "oops-we-cut-the-floorplate-too-short-well-slide-the-stair-sideways-a-bit-and-I'll-fill-the-gap-up" ...

The stairs are holding up because they have not fallen down yet because only two lightweight people at a time have walked down the stairs while they are not carrying any load and have been quietly walking. NOT a building evacuation after an earthquake, fire, windstorm when the stairwell is loaded top-to-bottom with people rushing to evacuate because there is no elevator service!

Look again under the floorplate or decking. That decking becomes a "beam" because it has a turned-up 4 inch section on one side and a turned-down 2 inch section immediately under the stairs, right.

(Please! everybody QA me and my logic on this!)

But that bent deckplate is supporting half the weight of the next staircase riser we know for sure - and probably part of the next staircase turning platform, and maybe even part of the next riser section above that platform. There is no sign of additional structure, nor of how many more flights of stairs are being loaded through the force "track" from top to bottom.

Can the OP provide a photo of the entire stair?

But that platform that we do see is being held up by what looks like two angle iron point supports under it. So the load starts at the very far edge of the platform steel, is transmitted across the plate as a cantilevered beam with the stress being resisted by the 4 inch vertical "up" bent edge and the 2 inch bent "down" edge, and then that plate is being supported by two tiny angle braces about 24 - 30 inches away from the edge.

 

[mechemi]

But that bent deckplate is supporting half the weight of the next staircase riser we know for sure

Yes, this is exactly my concern. This staircase sees what I'd guess is "moderate" use (like you said, probably not more than 2 people at once, on the order of 10s of trips per hour).

and probably part of the next staircase turning platform, and maybe even part of the next riser section above that platform

There is one platform above which is beam supported, and where the staircase stringer is connected directly to the beam. There are no riser sections above this, fortunately.

I will go in this weekend and try to get more detailed photos.

But that platform that we do see is being held up by what looks like two angle iron point supports under it. So the load starts at the very far edge of the platform steel, is transmitted across the plate as a cantilevered beam with the stress being resisted by the 4 inch vertical "up" bent edge and the 2 inch bent "down" edge, and then that plate is being supported by two tiny angle braces about 24 - 30 inches away from the edge.

That's mostly correct (the right idea at least), but there are at least 4 of these small angle iron point supports on this half of the platform. There are two nearer supports - one about 6" behind the right stair stringer, the other is about 12-16" behind and to the right of the left stair stringer. So the weight of the stairs + load on the corner of the plate is resting on cantilevered diamondplate. The diamondplate is only resisting the moment through the two flanges, which are about 4" and 1.5".

 

[msquared48]

I am not as concerned about the connection and placement of the inside riser as the outside riser, where all bearing, shear, bending, and torque from the outside riser is being transferred to the metal plate through a single horizontal weld. This is just plainly a very badly "designed" connection, and I use the word "designed" very loosely here.

As a minimum, there needs to be additional support directly from the column to the outside stair stringer.

Oh, by the way, do does this firm fabricate metal stairs for a business?

Mike McCann, PE, SE (WA)

 

[mechemi]

No, this facility is not involved in structural design or fabrication at all. They manufacture a food product. I doubt if they even have a structural engineer or civil engineer on staff - they probably hire one only for larger building projects. This staircase probably resulted from Maintenance being asked to add a staircase over a weekend.

I agree, I don't really like the connection at right but it's the connection at left that mostly concerns me - both that the weld could corrode or fatigue and fail in shear, and that there is a more significant bending moment on the platform. I would guess that failure would occur if the 1.5" flange buckled at the edge in compression, because there is no attachment between the toe plate and the stair stringer.

 

[Ron]

The material looks like stainless steel, but could be aluminum. If aluminum, this conditions needs to be corrected immediately!

As IFRs and others noted, this is an awful detail. The weld used to fill the gap is somewhat of a fillet weld under both longitudinal and vertical shear. As Mike H. noted, if the stringer is welded to the toe plate, that helps.

The plate is cantilevered and under a typical required design load of 100 psf, the corner will exhibit a lot of deflection, thus twisting the poorly conceived weld even more. Not good.

A structural engineer needs to look at this and design a proper repair.

 

[mechemi]

I don't feel I'm qualified to do a proper analysis or detail a modification. I checked and we don't have a structural engineer on staff, but contract with a local structural engineer for designs requiring a stamp. I've contacted a site manager and Monday we will be contacting that engineer to detail a modification.

I appreciate the comments here, it's nice to have my concern validated.

 

[mechemi]

I believe the staircase is steel and not aluminum. To my knowledge we don't use aluminum at all in our facility, we use either powder coated soft steel, stainless or some other type of steel.