aisc 13th ed. table 4-12 eccentrically loaded single angles

huangyhg

aisc 13th ed. table 4-12 eccentrically loaded single angles
i have been looking into using table 4-12 in aisc 13th ed. does anyone use this? seems a bit conservative but i would like to get other opinions. i have a truss modeled up using risa. the  diagonals in the truss are single angles. taking member forces from my model i looked in table 4-12 to comply with 13th ed., but according to the tables for eccentrically loaded single angles (which is what i would have) the sizes to satisfy these tables are about double the weight as what i would usually design with. i am just wondering if this would be overly conservative to figuire out axial load in angles and choose size from table 4-12? i am thinking we really are inbetween table values from 4-12 & 4-11 (eccentrically & concentrically loaded single angles).

this is usually a (lateral) torsional buckling problem...

have you tried to apply the provisions of aisc 13th e5?  it has been a while since i have used this but it allows you to ignore the effects of eccentricity if you meet the criteria and use a modified effective length. if you have any bending, you will need to apply f10 and h1.1.
i assume that e5 results should match up with table 4-12 but i haven't checked. let us know what you find if you compare them.  
the tables of 4-12 were developed based on the provisions of f10 and h1.1 under combined principal axis bending as discussed in the paper by sakla (engineering journal 2001 q3).  
as blackmaddog said, for eccentric axial load you can also use e5 to determine a modified effective length in lieu of using the combined axial/bending method.  it is actually quite suprising how different the results can be (the e5 method seems to be much less conservative if applicable).   
blackmaddog & willisv
thanks for the valuable information. this is exactly what i was looking for!!