Leveling nuts affecting tensile capacity of anchor bolts.

[beamer]

I have an engineer in our office who has been told the statement that leveling nuts under a building column base plate should not be used if the anchor bolts are intended to take tension loads. Is this an AISC or OSHA issue or some other requirement? We don't know how to respond to this individual. They are asking the engineer to make this statement on the drawings.

Thanks for any help.

 

[dougantholz]

There is only one instance that I could think of where this would be a problem. If you specify pre-tensioned anchor bolts then leveling nuts would clamp at the base plate giving you tension in the bolt across the base plate but no where else. I would recomend not using pretensioned anchor bolts with leveling nuts, as snug tight would be sufficient. You shouldn't have to worry about the nut working itself loose if it is barried in concrete. If you are worried you could always have the threads damaged to prevent spinning off the nuts.
HTH
Doug

 

[beamer]

There is nothing special about the bolts. A36, snug tight. No pretensioning of the bolt required.

 

[whymrg]

Try to contact AISC Steel Solution Center. Phone 312-670-5449, e-mail: solutions@aiscmail.com, or find link at

http://www.aisc.org

(

http://www.aisc.org/faq_search.asp?...=TECHNICAL+QUESTIONS+ABOUT+STRUCTURAL+STEEL).

They should know.

 

[dlew]

beamer,

My worry about using leveling nuts under building columns, has always been that the anchor bolts would try to carry the downward forces, producing compression in the anchor bolts and bending moment in the base plate.

I have read in the past several articles from the AISC in this subject, but I do not remember their title or where I read them. If I find any of them, I would let you to know.

Good luck
AEF

 

[evelrod]

I think you are overly concerned about the effects of compression on the anchor bolts with leveling nuts. As long as they have vertical loads within design limits( as well as shear) and are PROPERLY grouted, then there should be no problems . Here in Los Angeles I have personally replaced small columns in a hospital damaged by the Northridge earthquake that were literally torn from their baseplates. The baseplates were not buckled and the drypacks were still as originally installed. The building collapsed, but not due to anchor bolt problems.
At any rate, leveling bolts are used SOP for just about all applications where buildings do not exceed a few floors. In the taller highrise, other methods of locating the base of the column at proper elevation are commonly used . One example---December, 1969,Arco/BofA towers Los Angeles, 55 floors and 7 basements--- the base plates for the core columns were set with 4 leveling bolts drilled through the plate (5'square X 14 " thick). Once the grout had cured, the bolts were removed.

Sorry, I am getting a bit off topic. A lot of 'fun' memories.


Rod

 

[dlew]

I agree with Evelrod that leveling nuts under base plates of "lightly" loaded columns are not a problem.
But I would not use leveling nuts under the base plate of columns with high compressive loads because of the following reasons:
1) The base plates are designed for a uniform load under the "b" by "n" area immediately under the column. Leveling nuts are hard points under the base plate, and as such tend to carry considerable more load that the surrounding grout, increasing the bending moments in the base plate.
2) Why to use leveling nuts under the base plate when they could be located very easily on the perimeter of the base plate as shown on Fig 14-6 of the AISC's LRFD Manual. Or for heavier columns, as Evelrod described in his posting.

AEF