built up sections
built up sections
(OP)
When calculating a built-up section, what is the best way to interpret Table B4.1 (13 ed.) B5.1 in the (9th ed)? I am checking the application of angles as stiffeners and am having difficulty determining my final section modulus. The angle is a 3x2x1/4 (A-36) and the housing it is welded to is 12 ga. 304 Stainless Steel. Using the 9th ed. I calc'd the housing contribution to be around 1.5". Do I include my weld size also? Is it correct to align the center of mass of the 1.5" with the center of mass of the welded angle?






RE: built up sections
RE: built up sections
I'm trying to picture what you are doing and like StructuralEIT, I'm not getting it.
If it's a complex built up section, draw it in AutoCAD near the origin.
Convert all of the lines to closed polylines.
Convert all of the closed polylines to regions.
Use the command "massprop" and select all of the regions.
Note where it tells you the center of mass is.
Move the center of mass of your built-up section to the origin (0,0).
Use the massprop command again and select all of the regions.
It should give you everything you need, or a means to calculate it by.
RE: built up sections
RE: built up sections
You say you calc'd the housing contribution to be 1.5". 1.5" of what?
RE: built up sections
You're doing a duct or something similar. The "stiffener" is stiffening up the wall (12 ga SS) of the duct.
If this is the case, it's not really a "stiffener" so to speak. It's a beam that is supporting the pressure generated inside your duct. Even if it's a rectangle, it's acting more like a tension ring. Think of it as putting a rubber band around a balloon, and blowing it up.
Design the angle w/o any consideration of a built up section, for the bending forces coming from the pressure of the duct walls, combined with the tension forces coming from the "vertical" reactions of the angles at each end. The welds from the angle to the duct, braces the compression portion of your angle.
RE: built up sections
Yes, that is what I am doing. However, I have limits imposed by the owner, height and weight. So, I'd like to take into account as much as possible.
RE: built up sections
I understand what you are saying, but, it would not be good engineering judgement to take that into account. Use two-way distribution. You've got a much more rigid section at the top and bottom of the duct (top and bottom duct walls).
RE: built up sections