ASCE 7-10 Wind Story Drift Limits for the Lateral Force Resisting System

[jochav52802]

Good day,

I'm looking for direction on how a Structural Engineer would go about determining the story drift limits for the Lateral Force Resisting System for Wind loads.

ASCE 7-10 gives story drift limits for buildings within it's Seismic section, (Chapter-12), but also indicates that the structure must not deflect more than the attaching elements can allow. I don't see anything within ASCE 7-10's Wind load chapters that defines the story drift limits and I've been told that arhitects probably won't know what limits their attaching materials can withstand.

My question is what the typical approach is for a Structural Engineer to determine the story drift requirements for wind loads to ensure the attaching elements don't fail and assure a reasonable level of stiffness for the Lateral Force Resisting System. Maybe I've missed this somewhere, but it seems strange that there aren't clear requirements to follow in the code.

Thanks for your help!

Best regards,

jochav52802

 

[milkshakelake]

Check out CC.1.2 Drift of Walls and Frames. You can use a lower wind speed, because drift isn't really a concern with full level wind. It's all suggestions instead of "code." I personally always use lesser of l/400 or 3/8", which it mentions.

I'd also check joint drift as opposed to story drift. Unlike seismic, which happens in a blue moon, you could have a decent storm every year. If it knocks the building into torsion, story drift would be okay but joint drift could crack the cladding.

Also, if you have a copy of ASCE 7-05, check Appendix C in that one too. It's a little more clear. If I remember correctly, it recommends load combination of D+0.5L+0.7W for checking wind. Though this is tricky because the loads are different in ASCE 7-10 so you have to multiply the ASCE 7-10 service load combo by 0.7 to get the correct one.

Finally, some companies use full wind load for checking drift. It seems overly conservative to me, and happens to decrease the building period due to the extra stiffness so seismic is also affected.

 

[JAE]

Check out this article by AISC:


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