Bearing or Contact Stress of Fastener Threads Into Hole

[BenoitJ]

I have two pieces of square steel tubing intersecting in a T configuration. They are connected together by four bolts and two gussets on either sides of the hss tubes. I am curious about how to calculate the bearing stress of the fastener threads into the tubing walls because the tubing is fairly thin. Is there an acceptable stress concentration factor that is utilized in industry? This is not something that was covered in my studies. Any point of reference would be appreciated. Tubing is square 2" x 2" x 1/8". Gusset is 1/4" plate. I attached a couple of pics to better explain what I am up against. Thank you for your help.

 

[tbuelna]

As a general rule you should not load the threaded portion of the bolts in shear. With regards to bearing stress between the bolt bodies and the hole edges in the tube walls, this would depend on factors like bolt/hole fit and how the loads are applied. For example, if a vertical load was applied to the vertical tube member shown in your sketch, then the two vertically aligned fasteners connecting that tube to the gusset would only share the load if they were installed with an interference fit, such as match drilling and reaming the gussets and tubes. And if this is the case, then I believe a fairly simple P/A calculation would suffice for most applications. Just be sure to account for factors like tolerances in the tube wall thickness and chamfers on the hole edges when calculating the bearing surface area of the hole in the tube wall.

 

[desertfox]

Hi BenoitJ

I think I would be concerned about the axial bolt load on the tubing due to bolt tightening, if the bolts are tightened too much then the tube could start to distort.