Question on the seismic design manual [for steel; i.e. AISC 341]. 2

[3doorsdwn]

One thing I'm not quite following in this is: what to do for strength calculations (moment, axial, etc.) if the section is seismically non compact. There is criteria in the 13th edition for design when an element is non-compact, but I'm not sure it is applicable here because compact/noncompact criteria is different seismic considerations (vs. normal day to day loads). Thoughts?

I suppose one obvious thing to do is select a section that is seismically compact. But I thought I'd ask.

 

[OCI]

The seismic design manual has strict guidelines on compactness for steel members. These are requirements for members in a steel lateral system utilizing R>3 or as required by local codes. The methods for determining the nominal strength (moment, axial, ect.)in the 13th edition manual based on compactness is a seperate issue which also has to be adhered to. Basicly the seismic design manual tells you certain members have to be seismicly compact (above and beyond the 13th edition). I hope that was clear and some one will correct me if im wrong.

 

[3doorsdwn]

Right, but what I am asking is: how do you go about determining the strength of sections that are NOT seismically compact. Are they just worthless (i.e. zero strength)?

 

[sandman21]

If the section is required to be seismically compact, then it must be, anything outside of that is not permitted. The code requires this compactness to prevent unwanted failure modes.

 

[3doorsdwn]

thanks sandman

 

[ChipB]

As OCI was trying to point out if R is less than or equal to 3, you don't need to worry about it. It's when it gets above 3.

Also as OCI was trying to point out, it only applies to the members that are part of your Seismic Force Resisting System. i.e. Columns, drag struts, and bracing.

 

[sandman21]

It only applies where specifically mentioned in AISC 341, columns are not always included in this category and drag struts do not need to meet this requirement.