Bolt Group Ip
Bolt Group Ip
(OP)
I am trying to figure out how to calculate how to calculate the moment of inertia of a bolt group. In accordance with page 7-9 or AISC 13th edition Ip=Ix+Iy in units of in4/in2
Are you suppose to include the bolt area in the calculation of Ix and Iy? The way the units are written (in4/in2) I wouldn't thinks so, but then again, if you don't, you are not truly getting Ix or Iy of the bolt group.
Are you suppose to include the bolt area in the calculation of Ix and Iy? The way the units are written (in4/in2) I wouldn't thinks so, but then again, if you don't, you are not truly getting Ix or Iy of the bolt group.






RE: Bolt Group Ip
Similar to calculating the section modulus of a line of weld. When I do this I use a unit width of 1 for the weld, resulting in a value of in3/in, then when I divide the moment by the section modulus, I get a value of kip/in.
RE: Bolt Group Ip
RE: Bolt Group Ip
RE: Bolt Group Ip
DaveAtkins
RE: Bolt Group Ip
I think you need to be careful if you exclude the bolt area for the calc, as dave notes the units are "odd". With "odd" units you have to use the result in a correspondingly "odd" manner, ie you'll be adding the bolt area later in the calc or else understanding that the later calcs (using this "odd" result) know that using this inertia (I got tired on writing "odd") results in bolt force rather than stress (as in the usual bending calc ... My/I).
another day in paradise, or is paradise one day closer ?
RE: Bolt Group Ip
1. Ignore the Ix and Iy of the bolts
2. Assume bolt area is 1 to simplify the calculation of “Ip”. The actual Ip should be the calculated “Ip” times bolt area.
RE: Bolt Group Ip
RE: Bolt Group Ip
another day in paradise, or is paradise one day closer ?
RE: Bolt Group Ip
I originally included the area of the bolt in my calculation and in the end, has different answers for the loads in my bolts vs the calculation eliminating area from the equation. The way the process is written, I believe they don’t want you to include the area in the Ix and Iy calculations .
RE: Bolt Group Ip
but with that equation you're limited to that assumption (not that it is a real problem in the real world).
another day in paradise, or is paradise one day closer ?
RE: Bolt Group Ip
I've always treated it like just like a pile group problem. (I.e. independent of cross sectional area.)
RE: Bolt Group Ip
I agree: the force distribution among the bolts is not related to bolt area.
RE: Bolt Group Ip
another day in paradise, or is paradise one day closer ?
RE: Bolt Group Ip
As has been mentioned, in the realm of traditional building/bridges structural engineering, if you're using different size bolts in one connection (really, different size bolts in any given type of connection), you're just asking for trouble of a half-dozen different flavors.
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RE: Bolt Group Ip
If you aren't getting the same answer then I believe there is an error somewhere in your calculation. You should get the same force distribution if your bolt area is 1 or any other value.
RE: Bolt Group Ip
another day in paradise, or is paradise one day closer ?