# NCEES practice MD&M #124 and 125



## katiejune (Mar 29, 2017)

Im hoping someone can help my mom-brain fog on these two. My answers are not matching.

For #124, I get the area of the bolt to be .196in^2 but the book gets .142

For #125, I'm not sure what this equation they are using for secondary shear force is coming from. I was thinking I would use the polar moment of inertia equation with J=sum(r^2*A) but not sure how their J=6*36?

thanks!!

posting both questions and answers below, or I will try to


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## katiejune (Mar 29, 2017)




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## JHW 3d (Mar 29, 2017)

*#124:* 0.142 in² is the tensile stress area for a 1/2-13 bolt. It's a table lookup. See Table 53.5 in MERM13.

*#125: *Direct Shear is from the 500# load applied downward, divided by all three bolts. Secondary shear is based on the forces required to balance the moment of the offset load. 500#*19in (to center of bolts)... since you have a simple pattern, you might recognize that reax forces on A and C form a couple to balance the moment load. *I have no idea where their actual equation comes from*, but I used: 500#/3x + 500#*19in/(6in*2x) = 958.3 lbf.


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## katiejune (Mar 30, 2017)

Thank you so much. I am using MERM12 and the table is 51.5 on page 51-10 if anyone else reads this and needs it.

Have a great day and I appreciate the guidance!


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