As Per IBC Vertical Deflection Limit L/120 Is It Reasonable ???

[TekEngr]

i am designing a steel portal frame for industrial shed , which is 36 meter in clear span , as per IBC code allowable vertical roof deflection limit is L/120 (not supporting ceiling ) against Dead + Live Load and L/180 against live load which means allowable deflection for my portal frame is 300 mm and 200 mm ,so my question is that is it reasonable to consider these limit ?? 300mm and 200mm deflection looks too much.

i guess practically this much deflection can be seen with naked eyes, however i know roof live load is not permanent load for my structure but still against dead load vertical displacement can be visible if i consider these deflection limits. does these kind of structures allow us visibility of roof frame vertical deflection in piratical/actual??

 

[Ron]

What you are referencing is a code mandated minimum requirement. As the design engineer, you can set the deflection limit anywhere you want above that. L/180 or L/240 would probably look better from a deflection standpoint.

 

[r13]

You should slope the roof to the effect of dead load. Roof live load is transient event, I wouldn't worry that, except for possibility of ponding.