MD&M Problem #125

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jmsander

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Hi all,

I know it's last minute, but I'm stuck on understanding where this solution is coming from.

I solved the problem using the equations from MERM 53-18.  I know that

shear = F*e*r / J

where   J = r^2 * A

So what I don't understand is where the book is getting a value of "2" for A. According to MERM, A is the area of the bolt, which in this case should be .1419?

Any help/insight would be much appreciated!!!

IMG_0071 (1).JPGIMG_0072 (1).JPG

 
The bolt size is extraneous information to the problem. Problem asks for total shear as a force, not as shear stress.

Direct shear is the applied load divided by the bolt count. Secondary is shear is found from summing the moments about the bolt group centroid.

 
Thank you so much.  So to solve for the secondary shear = M*r / J , what area is J being calculated for, that would give a value of "2"?

 
It is the summation of bolts so it is N bolts * r^2.  There are two bolts total that experience secondary shear (the middle bolt doesn't since it lies on the centroid) so N = 2.  r = 6 so r^2 = 36.

 
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