Anchor bolt design / "effective bearing length" meaning & calculat 1

[dannyo]

I am trying to verify some equations relating to the design of anchor bolts on the saddle of a horizontal vessel in a seismic / wind load design situation.

My understanding is that anchor bolt design is governed by one of three load cases including: longitudinal load, shear load, and transverse load.

Assuming these are correct, my question lies in the transverse load case. The book I'm using has a 6 step method of analyzing the transverse load on the anchor bolts. I have not been able to verify the author's design method or any of the equations he uses.

If anyone could inform me the origin of the following equation and any references I could find additional information, I would greatly appreciate it.

I am mainly confused about what is called the "bearing length" (Y) It is calculated by solving the following equation for Y:

Y^3 + K1*Y^2 + K2*Y + K3 = 0

where Y has units of (inches / cm / etc...) and K1, K2, K3 are all factors relating mainly to the moment force produced by the seismic / wind event.

If my question is unclear, please respond and I will try to provide any additional information.

Thanks a million in advance!

 

[chichuck]

danyo,
I'm a first time visitor to this forum. I realize your post is about a year old, but I do recognize that formula. It comes directly out of a book titled "Design of Welded Structures", by Omer Blodgett. It was published years ago by the Lincoln Arc Welding Foundation, it is probably out of print.

That formula is the main equation in the method used to calculate the bearing pressure under a column baseplate that has an axial (compressive) load combined with an overturning moment.

The bearing length referred to is this. The combination of compressive load and overturning results in a bearing stress that varies linearly from max at the "toe" of the baseplate, to zero some distance back of that. Farther back, there is no effective bearing on the baseplate. Although it has not actually lifted off the concrete or grout, the effective contact stress is zero. The "Y" value in that equation is the length of the baseplate that does have a compressive stress on it's bottom. If you can get Blodgett's book, the complete method is included there. You can follow it along, he provides definitions for all input terms, all the three K values. That will allow you to solve that cubic equation by trial and error to get the value of Y. From that, you can calculate the maximum compressive stress on the bottom of the baseplate, the tension in the hold down bolts on the 'backside', bending stresses in the baseplate on both the front(compressive) side and on the back (tensile)side. The method in Blodgett's book is specific to structural columns with an "H" shape, what structural engineers refer to as a wide flange. The method could probably be modified slightly and/or adapted to a case for a vessel saddle. I have an excel spreadsheet that does all the calculations for this method, if you are interested, I'd be glad to share.

Regards,

Tim Heup, PE