Maximum Deflection in a Beam 1

[Leinster]

What is the maximum deflection in a beam in bending according to AISC Steel Construction Manual 13th edition. I have the manual but cannot find where this is defined? I have heard L/360 but want to be sure.

I want to design roof rafters for a storage tank and want to know the allowable deflection in this case.

 

[WillisV]

The steel construction manual does not provide deflection limits as those are a serviceability limit state, not a strength limit state. The IBC specifies a few basic minimum deflection limits for floors and roofs (of which L/360 or 1" is one); however, these are minimum code limits. The final limits chosen for any project are based on the specific project, situation, materials used, and owner requirements based on engineering judgment and past performance - not code limits.

 

[slomobile]

very well said WillisV...

 

[IFRs]

For a cylindrical aboveground steel storage tank with a uniformly supported bottom use API Standard 650 for petroleum liquids or AWWA D100 for water. Both limit you to ASD design and neither have deflection limits, but both have other requirements. Get the one for your tank or contract with an expert.

 

[rscassar]

What is the magnitude of the weight required to be supported by the steel rafters. Because of the nature of steel design, member sizing is typically governed by stiffness requirements. For roof rafters, I have always employed a span/500 deflection criteria for flat roofs (<4 deg) and span/360 otherwise.