Why divide elastic deflection by I (asce 7-05, 12.8.6)

[almadelibertad]

ASCE 7 requires deflections to be checked by multiplying the elastic deflection by the deflection amplification factor and dividing by the importance factor. What is the purpose for dividing by the importance factor? Just applying quick knee jerk logic, one would assume that as we increase the importance factor for a more critical structure, we would want tighter requirements. However, this larger importance reduces our design deflections - WHY?

 

[sandman21]

Deflection limits are a serviceability issue not a life safety issue, arbitrarily reducing allowable deflection limits does not increase life safety.

 

[frv]

sandman is correct.

btw.. "horizontal" deflections are usually referred to as "Drift" (I got bit confused when I read the title of your post)

 

[Lion06]

Additionally, the "service" wind load doesn't change for a higher I. It's an attempt to bump up the wind loads that the structure is designed for based on strength. To get that back down to "real" service winds for drift, you would divide by I (it's not exact given second order effects and the like, but it's close enough).