Bolt strength problem. Need help!

Hello dear Engineer,

I have this bolt strength problem and I am trying to understand the concept.

Assume, there is a plate of thickness t and diameter D. It has to hold a cable load of force P. How many bolts do we need to have on this plate to carry the load P.

(the way I look at the problem and what I have done so far is find the tensile strength of bolts from shigley, use a factor of safety, and use normal stress formula to find the diameter of the bolts, but the number of bolts can be arbitrary?) The problem I am having is that the number of bolts can be anything as long as the strength is met. Right?

This is just an example. If you have these type of problems solved, please let me know. The concept is about finding the number of bolts on a plate to hold certain cable force. Thank you 

Engineer_562 said:

Hello dear Engineer,

I have this bolt strength problem and I am trying to understand the concept.

Assume, there is a plate of thickness t and diameter D. It has to hold a cable load of force P. How many bolts do we need to have on this plate to carry the load P.

(the way I look at the problem and what I have done so far is find the tensile strength of bolts from shigley, use a factor of safety, and use normal stress formula to find the diameter of the bolts, but the number of bolts can be arbitrary?) The problem I am having is that the number of bolts can be anything as long as the strength is met. Right?

This is just an example. If you have these type of problems solved, please let me know. The concept is about finding the number of bolts on a plate to hold certain cable force. Thank you 

Click to expand...

Essentially that is theoretically true but of course your bolt diameter may become unfeasible.  In a real world scenario, the designer would present a mounting configuration from which you would derive the correct bolt size given the load.  Also from a practical aspect, consider the torque required for proper application of the bolt.  If the torque is very high, special tools may be required in which case it is beneficial to have additional bolts of lesser torque.

There's almost always more than one way to solve a problem. as long as you're reasonable in your solution, and your solution does in fact work, and you have met all of the parameters and restraints given, then you likely aren't going to get failed or unacceptable for having one more bolt than they were thinking. keep in mind, one parameter might be the minimum number of bolts etc. 

Thank you for your reply ramnares and tj PE.

I agree. OR The diameter of the bolt has to be given in order to find the number of bolts needed because that way we can find the max allowable stress for each bolt and divide that by the total load.

An alternative problem might include a bolt pattern that resists a compound load, so that the loads on each bolt are not identical. In that case,  you would need to find a way to determine the worst case bolt loads and apply your safety factors there.