Industrial stair rules of thumb

[SocklessJ]

1. Does anyone have any rules of thumb for industrial stairs with grating treads to avoid vibration problems? I've heard C10X15.3 min for stairs with horizontal spans between 15 and 20 ft. C12X20 for anything over 20 ft.

2. Also, does bottom flange bracing (i.e., diagonal L2X2's) help with bounce at all, or is that mainly for strength?

3. Is it typical to evaluate the web of a bent (dogleg) stringer for concentrated forces at the bend?

Thanks

 

[JLNJ]

1. I don't use a rule of thumb - I look at each case. The analysis is pretty simple.

2. Diagonal bracing (which I rarely install) is for horizontal loading. This is what plan bracing does.

3. The dogleg is often the weakest point in the stringer. Of course it needs to be evaluated.

 

[canwesteng]

You should evaluate once and create a standard for use for the client/project/internally. Doesn't make sense to crunch numbers over and over for the same thing. You've got a good starting point already.

 

[SocklessJ]

JLNJ, so if the dogleg needs to be evaluated, would you typically go about this? I'm having some trouble imagining how the forces flow through the joint. Would it be like a panel zone shear check on a column? Without stiffeners this doesn't seem like the best analogy. Anyone have a copy of that new AISC design guide for stairs that is coming out?

 

[JLNJ]

The "knee" often occurs at toward landing where the flexure is somewhat less. You can check the flexure there against a section of the stringer channel with the flanges removed (i.e. web only). Most of the time this will work OK and keep you from needing to reinforce the knee. The web does need to be a CJP welded of course.

If the web-only stresses are too high, a plate welded across the miter will be necessary, kind of like you see in the "knee" of a PEMB frame.