Snet for a Coped Beam

[EntryLevelEIT]

I need to calculate Snet for a W6 x 12 top coped beam. Values are not listed in table 9-2.

As a check I did a hand calc. for a W8x10, dc=2 in, neglecting the fillets and taking the shapes as true rectangles. My Snet came to be 3.6 in. cubed as opposed to 1.54 in. cubed as listed in AISC table 9.2.

These values are not close as I checked my math twice. Despite neglecting the fillets I doubt that is the reason for the difference in the Snet values. I attached a sheet with calcs, something is off....

Thanks for the help.

 

[nutte]

You calculated S-bottom. Calculate S-top (after fixing Ix) and you'll get the tabulated value. The "d" term in the last A*d^2 should be 1.3375", making Ix=6.42 in^4.

 

[ToadJones]

I didnt check your math, but there are two "ybars" and two "Snets"

ybar 1 = 1.71
ybar 2 = 5.89 -1.71 = 4.18

Snet min = Ix/ ybar max

= 6.18 in4 / 4.18 = 1.48 in^3

You'll S top and S bottom as with any unsymmetrical shape

 

[BAretired]

There is more than that wrong with your calculation. In the expression for Ix, you are adding terms which you should be subtracting. You cannot have Snet (top or bottom) greater than that of the whole beam. Think about it!

BA

 

[sklev]

I'm having a hard time figuring out your d's. I thought that the d was the distance between the middle of the whole piece and the center of the individual part you are looking at. I'm not getting your numbers when I do that, though.

 

[sklev]

Please disregard. I see now.