Bolt Stress

[steris]

I have a Section VIII Div I design where I am trying to size bolts for a very unusually shaped flange. Because of the shape, the load on each bolt is different - both in terms of tensile stress and bending stress. I have experimental data on the resultant load on each bolt. When I examine the calculated stress profile through each bolt, as expected, the bending moment causes the tensile side of the bolt to have a much higher stress than the "compression" side. I use quotes because because the pre-load prevents the bolt from actually going into compression. While examining the stresses in the bolts, I discovered that in some bolts, there are local regions where the max stress (tensile + bending) exceeds the max allowable as given in Table 3 Section IID.

Can a bolt have a local region stressed higher than the given allowable stress? If so, what are the limits? Am I looking at this in too much detail - should I only be comparing (total load)/(root area) to max allowable? I know that for shells and heads you can have a local membrane + bending stress of 1.5*allowable but I do not believe that is applicable to bolts. I know I could "just add more bolts" or "just make the bolts bigger" but I want to understand the intention & application of the code.

Thanks for the help!

Best,
Steris

 

[SnTMan]

steris, the allowables given in Table 3 are for design ONLY. It is recognized that actual assembly and service stress will be higher. This has been discussed numerous times, do a site search for more.

There is no Code imposed limit. The functional limit is typically going to to be some fraction of the bolt yield strength. Such that the members of the joint are not overloaded and that the bolting does not yield in either assembly or service.

Regards,

Mike

 

[ricklts]

SnTMan, you are right on. Steris, refer to what used to be ASME VIII, Appendix S, basically describes exactly what Mike was saying.

Rick