Steel plate stair stringer and guardrail 1

[Mart Johnson]

Hi,

I have been assigned to analyze and design a stair which the stair is an open stair with just steel plate acting as both stringer and guardrail. Does anyone has any idea what is the common steel thickness? I looked up online, it seems like 1" thick of steel plate acting both stringer and guardrail.

In term of analyzing it, could I analyze the steel plate separately? Meaning I analyze the steel plate in vertically first to check the tread's load and then I analyze the steel plate horizontally to check the 50plf (guardrail)?

All opinions are welcome, I am here to learn.

 

[JedClampett]

I don't understand how you're using the plate as a stringer and handrail, but one inch thick is too thick.

 

[MIStructE_IRE]

Have you a sketch?

 

[RPMG]

For MC12x14.3, Iy = 1.00 in^4.
For PL12x1", Iy = 1.00 in^4.

I'm not going to finish that out to completion with a lateral-torsional buckling math proof, but I know lateral-torsional buckling is largely dependent of the Iy of the compression region. I realize that the typical assumption is that stair sections are braced by treads, but stairs are generally framed with channels or tube steel. I say 1" seems reasonable.

 

[Mart Johnson]

Hi JedClampett, MIStructE_IRE, RPMG

I dont have a sketch but the link below is the idea of the stair. It will have no stringer at all.

 

[KootK]

1) your nifty treads will have to provide rotational restraint to the plate stringers.

2) I do feel that it is reasonable to separate your vertical stringer design from your guardrail design. Alternately, You could do a little von misses style checking if you feel that an event that might max out both functions is likely enough to warrant consideration.

 

[MIStructE_IRE]

I agree with Koot. I’d separate the design of the stringer from the balustrade - even if they’re made as one, I think its reasonable to separate the design.

Inch thick solid plate will be a serious weight to lift and get into position. I would have thought 10mm would be plenty - but watch your lateral deflection of the balustrade.

 

[Boiler106]

For all those doubting this, i have seen this design using about 1/2" thick stringers in a newer public parking garage at Crocker Park in Westlake, Ohio just outside of Cleveland.

Creeped me out, but seemed as solid as could be. Sure, stiffness and ltb are two very different things, but they were there, in use.

Edit: I should point out that the stringers were acting as just stringers and did not form the guardrail

 

[KootK]

@Mart Johnson: what's going on at the wall side of the treads? Is this one of those deals where there's an HSS stringer buried in the wall etc?

 

[Mart Johnson]

Really appreciate for all the inputs.

KootK: No, there is no stringer either. The treads will be sitting on solid blockings and the blockings will be nailed to studs.

 

[RPMG]

If this is connected to a wall on once side and plate stringer on the other, then I would understand using a thinner plate.

As for a 1" plate weight, that's like 600 lb opposed to 300 or 400 lb. I wouldn't worry about it.

 

[human909]

I would consider that aesthetics and guardrail safety would dominate here rather than structural support of the treads. Half inch aka 10-12mm thick plate, ~200mm deep plate is very typical here for stairways in industrial buildings here. The treads keep it all together.

1" seems crazy thick structurally. But if you are after a clean aesthetic you likely need something about that to provide appropriate lateral resistance for the guardrail.

 

[Ron]

Let's think a minute....If the 1" plate also serves as a guardrail, it would have to be 42 inches high above the tread plus the necessary stringer depth. That means that it will weigh something like 150 lbs per linear foot. It would take a crane to install it in a very limited space. Compare that with a typical MC10x8.4 plus a steel baluster rail...all with a dead weight of less than 25 lbs/ft. Even if you used a plasma cutter to create guardrail voids of 3-3/4" spacing, the weight is still high. Seems like a waste of time, material, and money.

LTB will certainly be an issue if you go the void route and should be checked in both cases. The guardrail/stringer combination acts as a deep beam.

 

[gte447f]

A star for Ron for applying rational, logical, common sense. Unless this is a "monument stair" where budget is no issue (including paying a substantial premium for innovative structural engineering design), I would say the idea should be discounted immediately. Ironically, it was probably proposed by bean counters.

 

[LittleWheels]

It is a pity you can't roll the top of the guardrail to form a flat rail. Even inch wide steel plate edge is uncomfortable to hang onto compared to something wider, if you actually need to hang onto the guardrail for stability.