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# Bolt calculation

## Bolt calculation

(OP)

My colleague calculated a safety factor of 1.31. Is my calculation correct?

### RE: Bolt calculation

You have a bending moment and axial compression on the bolt which is going to generate tensile stress on one side of the bolt (M/S - P/A) and compression stress on the other edge of the bolts (M/S + P/A) , but I don't see a section modulus calculated, so at a glance, I would say there's no way it's right.

Rod Smith, P.E., The artist formerly known as HotRod10

### RE: Bolt calculation

The forces are not in equilibrium.

BA

### RE: Bolt calculation

Wait, is this supposed to be supported at point "M"?

Rod Smith, P.E., The artist formerly known as HotRod10

### RE: Bolt calculation

The "M" is confusing. Not sure why you'd take a moment about there instead of along the vertical axis of the CG. Doesn't make physical sense to me.

### RE: Bolt calculation

(OP)
Point M is the assumed pivot point under headwind when the fastener starts to loosen.

### RE: Bolt calculation

Assuming the area exposed to wind is correct, and it's only about the size of a small tissue box (0.0144 m^2 = 22.32 in^2), and your support assumptions are valid (which is what I would be scrutinizing closely), the calculations appear to be correct; strength of the bolt shouldn't be an issue. The fatigue on the supporting material at Point M (it will experience millions of stress cycles), is another matter entirely, but since you haven't given us any information about that, there's no way for us to assess it.

Rod Smith, P.E., The artist formerly known as HotRod10

### RE: Bolt calculation

#### Quote (TGK07)

Point M is the assumed pivot point under headwind when the fastener starts to loosen.

What is your basis for that assumption?

You need to address boundary conditions and equilibrium before you can solve the problem.
1. FA has no force to balance it, so does not satisfy equilibrium.
2. The second equation (for FA) is incorrect as it neglects the contribution of FS.

To answer your initial question, your solution is not correct. Given the magnitude of the applied force, it seems unlikely that your colleague's solution is even in the ballpark.

BA

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