Long span stringer deflection limit for vibration

[cec17]

I am designing an industrial stair which exceeds the IBC 12' vertical rise since it's for infrequent maintenance access. The stringers are fairly long because of this, +/- 21' in length.

I am getting a full service deflection of 0.188" at midspan. It equates to L/1500 which is extremely small, but I'm wondering about vibration. Generally my rule of thumb is about 1/4" max deflection on "long" span members (over 15') for detecting vibration - so I believe this is fine. Just wanting some opinions from others in similar situations. It also should be considered this industrial access stair may never see 60psf live load anyways.

 

[AskTooMuch]

I haven't checked but does that meet osha or other requirement for being too long without landing regardless how infrequent it's used.

 

[human909]

You've said it yourself L/1500 is extremely small. That stiffness should ensure you are good. I've often had stringers 6m long and never had issues. My preferred member for longer stringers is a 230PFC (230mm deep). A span on depth of 26 is normally reasonably stiff for walkway loads.

 

[XR250]

I can't imagine anyone in an industrial setting caring about that.

 

[271828]

In that setting, it would have to vibrate a lot to get anybody's attention. I don't think there are published methods to check this specific case.

You could do a quick check on the natural frequency using the AISC Design Guide 11 Section 4.3. If the frequency is over about 10 Hz, then I certainly wouldn't worry about it. If it's 2-3 Hz, then I might considering increasing the stringer sizes to increase the frequency.

You could also compute the acceleration using that same section. The tolerance limit is bound to be extremely high, at least 5 %g.