Tensile capacity/minimum engagement 8

[RMPE]

Need to find the tensile capacity of a bolt in a tapped hole condition.

Lifting a tank that has 6-3/8" tapped holes about 3/8" deep. Tank flange is Cu-Ni and weighs about 5,000 lbs. Considering FS of 2 on lift and additional 20% for prying action on bolt heads. Therefore I need a 2,000 capacity per bolt (looking at A307 or Grade 5 if available). We have a lifting lug (1" thick plate) that will be bolted to the flange via the six bolts.

How much thread engagement do I need for full capacity of the bolt (assuming steel base material)?

Can I calculate the reduced capacity if less than optimal thread engagement?

How do I determine capacity of connection based on shear strength of actual base material?

 

[CoryPad]

peteSwift,

hrehman7 is correct - m[sub]eff[/sub] is the axial length/height of the internal threads that are engaged with the external threads.





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[hrehman7]

CoryPad,
Per 'Handbook of Bolts & Bolted Joints, Bickford/Nassar, pg 175', Length of threads in a 90 deg countersink contributes 40% of shear strength. How does meff takes this into account? Is this c’sink depth added to clamp length lk or thread engagement meff? I could not find any treatment of c’sink (c’fer) on tapped holes in VDI 2230 latest edition. VDI also added 0.8P to meff. Any comments on this?
Many Thanks

 

[CoryPad]

hrehman,

m[sub]eff[/sub] does not account for countersinks. The nut height m = m[sub]eff[/sub] + x, where x is the length of countersinks, etc. VDI 2230 February 2003 edition does not show this, rather it references Alexander [48] on page 86. This is the same source on page 175 of Bickford & Nassar.

Regarding the additional 0.8 P, they added it with research from 1995. I have not seen the source, but my understanding is that the 0.8 P accounts for the non-uniform axial force distribution in helical threads. I am trying to get some of the new references from the journal Konstruktion that are shown in VDI 2230, but the publisher won't return my email messages. If I learn more, I will share it.





Please see FAQ731-376 for tips on how to make the best use of Eng-Tips Fora.

 

[dulmant]

CoryPad,

This 0,8xp gave me a lot of truble; I don't know if you remember but I brought this up a while ago and you were kind enough to point me in the right direction. However, at the time you left this detail out and my preliminary calculations didn't consider it. Later, when I got the February edition of VDI 2230 I included the 0,8xp into my calculations and that on itself made me change the bolts grade.

As I said before, there is not much information on the load distribution over the engagement threads, but I think they introduced it not because of this but because the first and the last threads, being incomplete, may not take much load.

I think it is important and I would be grateful if you would share the info you may get on this, I will do the same if I find any, should you be interested.

Thank you again,

Dulmant.