# How to calculate tension force for scattered bolt on plane

1. Dec 9, 2015

### enotyphoon

Please find the attached (http://s23.postimg.org/ropds44ob/Capture.jpg). I know how to get the shear force for each bolt using bolt analysis. But I dont know how to get the tension/compression force of the bolt when it position is not symmetric.

*I already download some excel from internet, but not sure how of how the formula for tension is obtained.(http://s18.postimg.org/nsovgux55/Capture.jpg). searching for original formula before it got as above formula.

Edit: Yb in the second pics is Zb

Last edited: Dec 9, 2015
2. Dec 9, 2015

3. Dec 9, 2015

### enotyphoon

However, from excel result that I have downloaded from engineering edge showed that the value of tension is varying when I change the bolt in z-direction (force(P) applied above plane(distance=y) with direction along x-axis, hence creating Mz=Py). If I'm applying the basic formula same as shown in thread you gave, supposedly tension/compression developed due to moment in z-axis is same although I change the bolt in z-direction.

4. Dec 9, 2015

### JBA

The last post in the above referenced thread states: "Great. I think I got the forces down, just divide the forces by the total bolt area, which is total tensile stress area for the tensile x load and shear stress area for the shear y and z loads.". Alternatively, be sure to use the bolts' thread minor diameter when calculating the area for the the tensile stress on the tension bolts.

5. Dec 10, 2015

### PhanthomJay

The moment Mz is 80 and the outer bolts have tension or compression loads of 80/4(2) = 10 N. No load on center bolts.

6. Dec 10, 2015

### enotyphoon

The answer is 10 when using the formula given. However this excel spreadsheet shows otherwise, the value is 10 only if I put the bolt symmetrical (the 1st column bolt).
If I deviate the bolt as figure above (which is not symmetrical in the first row). The value become 9.10. Here I attached link to excel of bolt group.

http://s000.tinyupload.com/?file_id=09997040759162842171

you can see the formula for axial load at cell S5. So right now I'm confuse which one to follow, But if there is conservative method, please do tell.

*the axis shown is using y-x coordinate. the z axis from the original pics is y-axis in this excel.
this excel is downloaded from http://www.calculatoredge.com/structural/boltgrp.htm

Last edited: Dec 10, 2015
7. Dec 10, 2015

### PhanthomJay

My analysis assumed a rigid base plate such that all bolts an equal distance from the neutral z axis share the same loads under Mz bending moments. I am unsure how that excel calc works, but it indicates less than 10 N load on some bolts and more than 10 N load on others, and non-zero middle bolt loads, implying to me that calcs are based on principal axes rather than the centroidal neutral axes. It's been 50 years since I last fooled with principal axes. I use a factor of safety instead.

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