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Seismic Slenderness ratios for Steel columns

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Since things seem to be fairly slow, I thought would ask a question that has been bugging me for awhile.  A question, for which I have not gotten any definitive answers. 

 

The question concerns Table I-8-1 of the 2005 AISC seismic detailing specifications (AISC 341-05).  This table lists the limiting element slenderness ratios (h/t, b/t, et cetera) at which an column, beam or brace member can be considered "seismically compact" or "highly ductile".  

Now, some of the member's limiting slenderness will depend on a Ca factor which considers the level of axial load in the member. That makes sense, columns with a high degree of compression can have their flanges and webs and stuff buckle more easily than lightly loaded columns.


Everyone with me so far?  Now, I'll have some members that have two different levels of axial force in them. Some of my column will require that I design them to the regular ASCE load combinations 1.2DL + 1.0 EL.  Other load combinations will require that I also design them to overstrength combinations. 1.2DL + 1.0*Omega*EL.  

When I'm classifying my column as seismically compact, what load combinations am I using, the regular ones only or do I also include the Overstrength ones.  The code doesn't make this particularly clear. 

 

 

Sincerely,  

 

Josh Plummer, SE

 

RISA Technologies

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