Determining Shear Stress on Bolts

[stinlin]

So as you can see, the drawing I've attached shows two bolts through those 3 plates. There are the shown forces acting on the plates, and the maximum allowed shear stress is given to be 110 MPa. You're supposed to determine the minimum diameter required for the bolts. Also, the forces are assumed to be evenly distributed amongst the two bolts.

So I can ask my TA how to solve this problem, so I'm not entirely asking for a solution...What I want to know is really the theory of this. If I'm looking at the bolt alone, there are 3 forces acting on it, no? If that's the case, then how do I go about applying t = V/A?

Can I get an explanation of how to look at the bolt and determine the shear force? Thanks!

 

[Pyrrhus]

What do you know about planes of shears?

In your example each bolt will have 2 planes of shears, making the bolt in a double shear state. Which means each of the shear forces will be equal to the half of the total load transmitted per bolt.

With this in mind you know the total load is simply 80 Newtons, and for a bolt the average shear stress will be equal to the shear force divided by the cross section of the area where it acts. You have the total load, you have the allowed shear stress, and the only unknown is the diameter, so simply by using the equation you have stated, you can solve for the diameter of the bolts.

Remember: you have 2 cross section areas, because you have two bolts (which should be accounted in A).