Flexure in Single Angles

[DWHA]

Does anyone know of the provisions in the AISC code for flexure in single angles that do not have equal legs? For my case I have biaxial flexure.
FYI- I am doing an analysis of an existing structure, Why the designer used angles for a member that is in biaxial flexure is beyond me.
Thanks in advance for any help.

 

[Lion06]

13th edition steel manual page 16.1-57 to 16.1-60 (spec F10)
In the Green Book it starts on page 5-309.

 

[UcfSE]

Note for minor axis bending of angles you won't have the LTB check. In this case you check leg local buckling and yielding.

 

[DWHA]

I am not seeing how to check flexure about the geometric axis(axis parallel to a leg) in the code. It is clear for equal leg angles, but not for non-equal leg angles.

 

[UcfSE]

Unequal leg angles are checked about the principal axis only. You would resolve the load into components along the principal axes and check biaxial bending per chapter H. This can be found in the commentary.

 

[UcfSE]

Another note, the exception to checking LTB is when the angle has full/continuous lateral-torsional restraint such that it cannot deflect about its principal axes. If that is the case you check leg local buckling and yielding. This isn't included in the 13th that I can find explicitly though you will get a blurb at the top of 16.1-58. This is better defined imo in the 3rd edition LRFD in the single angle section 16.3-4, section 5.2.1.a.

 

[DaveAtkins]

UcfSE is correct about checking unequal leg angles, and the process is laborious (I finally put it on an Excel spreadsheet). A quick and "dirty" method for checking an unequal leg angle is to assume it is an equal leg angle, with the shorter leg being the leg length.

DaveAtkins

 

[par060]

if you have an unequal leg angle....can you disregard the longer leg and design as if it were an equal leg angle useing the smaler leg angle dimensions?.....