double angle gross area

huangyhg

double angle gross area.
i am trying to model a truss using sap2000. i am unable to understand that in output
why sap can reduce the cross sectional area of double angles. to me the area should be constant
but as i enter different spacing for back to back legs, x-area changes.
i think you are creating your own double angles instead of importing ones from their standard database.
i'm pretty sure your problem comes from the goofy way that sap forces input of double angles.  the "outside width t2" is out to out of angles.  for example, for a standard 2l2x2x3/8, this dimension is 4.375", but for a 2l2x2x3/4, this dimension is 4.75".  
when i first tried to duplicate your error, i kept this dimension the same and modified the "back to back distance" and the area changed.  what i did, in reality, was make the horizontal (in their picture) legs a different length.
i really like a lot of things about sap, but csi never ceases to disappoint when it comes to little booby traps like this one.  etabs is no better.  have to wonder who is in charge of their interface...