Stair Tread - Horizontal Component of Load

[bookowski]

I'm doing some cantilever stair treads. The treads are a built up T and easily work for the vertical loads for serviceablility and strength. It's a residential stair so loading is relatively light.

I'm curious about the horizontal direction. Does anyone have any guidance on a load (or % of vertical load) that is used horizontally? I would think it's a fairly small component of the vertical, would 25% be conservative (75#)? I think it's fine but just wondering about the stair tread feeling like it's swinging under service conditions.

 

[Ron]

I would use the horizontal component of the angle of the stairs. No other criterion that I know.

 

[BAretired]

If you are referring to a sway force, there is no specified requirement. In the Canadian code, the sway load for bleachers is 0.3kN/m (20plf) parallel and 0.15kN/m (10plf) perpendicular to the bleacher. I suppose you could apply that to a stair tread although the two situations are not the same.

BA

 

[paddingtongreen]

What is the greatest coefficient of friction between shoe and stair? could someone running lock their heel on the edge of the tread? If you know that, you have the proportion of the vertical. And yes, horizontal stiffness is important if you want people to use the stair. I would apply the load to the cantilever end of the tread.

Michael.
Timing has a lot to do with the outcome of a rain dance.

 

[a2mfk]

This is all about servicability, not strength, as I assume the treads having been designed for gravity loading will be overdesigned (most likely) for lateral loads. In lieu of any other code related info, I would probably apply a 50lb load at the very end and keep the deflection very low, like 1/8". You would have to be doing something strange to a staircase to apply a 50 lb lateral load but anyway...

Having designed lots of stairs as a specialty engineer, I would be concerned with the handrail design on this one. And the torsion on your stringer and the end connections. That could be really difficult if the rest of your structure is wood!

 

[slickdeals]

Don't forget to add the combination of moment due to vertical load and lateral load from handrail acting simultaneously when sizing your moment connection at the cantilever.

 

[csd72]

The worst case I would expect would be the same as a handrail load.

 

[bookowski]

There doesn't seem to be a consensus. The railing load seems pretty conservative to me. I can't imagine what you would do to impose that load horizonally on the tread. I'm going to check 20% of the vertical load at the tip as a horiz force and call it a day. Thanks for the input.

 

[Bagman2524]

I would also consider seismic loads. Especially if the stairs are egress stairs.

 

[csd72]

bookowski,

sorry I meant to sa that that was the upper bound that I would expect. 20% sounds reasonable to me.