Cozzone question

[bf109g]

I am working on determining maximum strength of a part we've been making for 30 years. All previous analyses have applied a load to the part to see if it can take it.

The cross section I have are two 1" high x .4" wide rectangles spaced at 4.5" with a .318" hole drilled parallel to the neutral axis and .375" from the bottom of the section. I am doing analysis similar to Bruhn page C3.8, Example 4 and can get a k1 of 1.5 for the upper section, but I get a k2 of less than 1 for the lower section. The upper section is critical under the worst load case - I don't think I have a strength problem with the part. I just want to analyze it correctly.

I've never come across a k value less than 1 before. I believe I can use Fb for the upper section and Ftu for the lower section. Does this sound reasonable?

 

[rb1957]

i've never seen k < 1 ... i'm certain that by definition it can't be (so i suspect a calc problem) ... a rectangle section with a small piece removed should be darn close to 1.5.

 

[bf109g]

That's what I'm thinking, too. Shouldn't be too far off 1.5, if at all.

Something's squirrelly here, I just haven't found it yet.