Product(s):	SACS
Version(s):	All
Area:	Post

Problem

How does SACS calculated the minor axis bending capacity of a Tee section when AISC 360-16 edition is used as design code?

Solution

Let us walk through this discussion with a sample model on which we helped the user to understand the methodology.  

In case of AISC 2016 specification, SACS considers the LTB for T-sections based on Solid Rectangular Bars, which corresponds to F11 of 2016 specification.

If you check SACS post manual Section 3.3.2.2 it is mentioned that lateral torsional buckling and flange local buckling due to minor axis bending of Tee section will be assumed same as solid bars and wide flange sections respectively. Please see the below snap.

But now there might be another confusion as SACS considers the LTB for T-sections based on Solid Rectangular Bars, which corresponds to F11 of 2016 specification. But AISC F11 mentions we don't need to consider LTB for minor axis, but SACS have considered it.

Here SACS is disintegrating the sections into web and flange as individual rectangular bars.

Now, let me try to explain the same with a figure. I tried to develop 2 cross sections of Tee, one with strong flange and the other one with strong web and applied load such that minor axis bending will be generated within the entire section.

Now, in Case1, if you consider the web of the section itself, then you will see the stem will be experiencing “Major” axis bending due to the applied load. Similarly, in Case2, the flange will be experiencing a load which will cause “Major” axis bending to the flange itself. Thus, the global minor axis bending load is simulating local major axis bending to the individual components of the Tee section.

SACS is using LTB for F11.2 (a to c) section, which is mentioned for “Major” axis bending for the individual parts (flange and web) as rectangular bars.

This approach is considered as a conservative design since AISC does not provide any specific guidance for Tee sections minor axis bending.