A.B. Design: ôEquivalent Area Methodö vs. ôApproximate Methodö

[iv63]

I am checking existing vertical vessel anchor bolts and using a very well known approximate method for bolt tension 4M/(D*N)-W/N anchor bolts are overstressed. In the attached numerical example of “Equivalent Area Method” found in Dennis Moss’ “Pressure Vessel Design Manual” maximum stress in A.B. is 12.10ksi while using an approximate method I am getting 4*3034/(8.75*20)-194/20=59.65 k/bolt / 3.715in2 = 16.06ksi. Can I use this “Equivalent Area Method” instead of approximate method?
Thank you.
iv

 

[JStephen]

I am not aware of any standard that specifies exactly how the anchor bolt loads are to be calculated for vessels, which leaves it up to the designer. The assumption is that you use a rational method that is either commonly used or supported by some degree of logic or experiment.

Wind loads and seismic loads have been adjusted through the years, and it may be worthwhile to investigate if the anchors in question need to meet the latest standards, or the standards that were applicable when they were built.

It may be worthwhile to look into the allowable stress for the anchor bolts. App. D of ACI-318 includes steel srength requirements for the bolts, which will be higher than that used under many older standards.

Also note that the current App. D gives fairly low allowable loads for pull-out capacity of hooked bolts.

 

[JoshPlumSE]

Yes, I believe you can use the equivalent area method. It looks like the same basic method I've used in the past. Then again, I originally learned this by working at the same company as Dennis Moss.

FYI: The best reference on this subject that I have found is the technical manual that Dan Horn (the original author of ERITower/RISATower/TnxTower) put together for monopole base plate design.

http://www.towernx.com/downloads/Technical_Manual_MP_BasePL.pdf

This document is more focused on base plate design than anchor design. But, the two subjects are very much tied to each other. You might find this reference useful as it evaluates a number of different methods and comes up with some basic recommendations. Even if you only look at the list of references, it should still be of some use.