Allowable deflection for other structural steel

[cgstrucg]

Hello,

I have designed an elevated platform on top of a building. As per ASCE, I used L/360 as deflection limit for all the beams in my design. Do we have to use the same factor for columns? My platform design is governed by Wind Load.

Thanks

 

[JAE]

Deflection control is a purely serviceability issue - not a code/strength issue.

Since this sounds like a pure steel platform out in the air, the only deflection control is what you might see appropriate for human comfort walking on it.

Without a full blow vibration analysis or something like that - your use of L/360 for vertical LL deflection would be OK.

For lateral sway - for structures like this - I'd probably lean also to L/360 or L/400.

Check out Eng-Tips Forum's Policies here:
faq731-376

 

[Lomarandil]

L/360 for the columns (for wind) is possibly tighter than you need, unless you have finishes to protect (etc.). Not a bad starting point though.

----
just call me Lo.

 

[Hokie93]

I typically use a wind speed based on a lesser mean recurrence interval (MRI), say 10-year or 25-year MRI, for lateral deflection (drift) computations. Wind speed charts for various mean recurrence intervals are provided in the Commentary to ASCE 7-10 Appendix C. You should, of course, evaluate the sensitivity to movement of the equipment supported by the platform. With the reduced wind pressure, I would then aim for a drift limit in the H/300 to H/400 range, provided the equipment or your client have not imposed a more strict limit.