Wind drift requirement for shallow story heights

[VA-Struct-Engr]

Hello everyone.
I am designing a 10-story cold-formed steel (CFS) bearing wall residential building in Mid-Atlantic region. Cladding mostly consists of metal panel and brick. The lateral system is CFS flat strap braced frames. I am looking at building wind drift, designing for 10-year MRI (per ASCE 7-10 Commentary to Appendix C). I am limiting the overall building drift to H/500. Typically, I would limit the story drift to maximum of H/500 or 3/8”, however, my floor-to-floor height is only 9’-8” in this building (floor structure is shallow). H/500 for this height is 0.23”, which seems conservative to me, so I am thinking of reducing this requirement to H/360 (0.32”). Does anyone have any thoughts on this? Does it seem reasonable to reduce the floor-to-floor drift requirement or should I stick with H/500?
Thank you for your inputs in advance.

 

[phamENG]

From an inter-story serviceability standpoint that's probably okay - 0.4" is considered the point where you really start braking stuff.

But then if you're building this in Tysons Corner you may need to meet a higher standard for nicer/more fragile finishes and the quality of construction people paying that much for a place to live often expect.

Flat strap for a 10 story building? Yikes. Is that really working? I've done flat strap for single and two story buildings and the connections get unpleasant.

 

[VA-Struct-Engr]

@Pham, I have used flat straps for a 9 story CFS building before. At bottom floors, member sizes get to be pretty large, 12" wide x 16-ga straps with HSS chord members, but it can be done. Also, trick is to make the connection to the podium/foundation, as uplift forces get to be very high.

 

[phamENG]

Good for you. (And I don't mean that sarcastically.) Can I ask what metro you're in? DC/NOVA, Richmond, or Hampton Roads? (Feel free to decline - I'd understand completely.)

 

[phamENG]

Nice. I'm mostly in Hampton Roads, but have picked up a few small, niche jobs in your area.

 

[VA-Struct-Engr]

Good.
Where does the 0.4" come from? I have seen it a couple of times, but have not seen a reference for where it comes from.

 

[phamENG]

I've heard for a long time, too. It's mentioned in this article in Structure but they don't directly cite a source. If I come across a better reference I'll let you know.

 

[Lomarandil]

My guess? It's 10mm.

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just call me Lo.