OSHA Anchor Requirements 2

[haynewp]

Per OSHA 1926.755(a)(1), all columns require 4 anchors. However, I still see a lot of smaller columns (TS 4x4x3/16) using only 2 bolts at the base, which seems ok for such a small column. Is everyone else using the 4 bolt minimum for all columns sizes?

 

[c2]

Columns weighing less than 300 pounds are exempt from this four bolt OSHA requirment.

 

[Lutfi]

I respectfully disagree with c2. The way I interpret OSHA 1926.755(a)(1), is that all columns require four (4) anchor bolts. I do not see any exceptions where less than four bolts are acceptable. OSHA 1926.755(a)(2) states:

“Each column anchor rod (anchor bolt) assembly, including the column-to-base plate weld and the column foundation, shall be designed to resist a minimum eccentric gravity load of 300 pounds (136.2 kg) located 18 inches (.46m) from the extreme outer face of the column in each direction at the top of the column shaft.”

That part exclusively deals with the size of the weld to resist overturning moment. It does not allow for the use of 2 anchor bolts if they are 300 pounds or less. Four bolts will resist overturning moment due to lateral loads imposed on the column during erection/construction. The challenge I have with the four anchor bolts is physical limitations. I have instances where the four bolts were crowding corners and they had impact on sequence of construction.

If I am mistaken, please let me know. I am always willing to learn.

I hope this helps.

 

[Mattman]

Please see the following thread:

thread507-35572 it, I give links to the entire text of the OSHA regulations.

With regard to the 4 bolt requirement, c2 is right; here are some more details. "Posts", which can have 2 anchor bolts, must be axially loaded or laterally restrained, as well as weighing 300# or less.

OSHA's 4 bolt requirement for columns:
"All columns must be secured with 4 anchor rods (anchor
bolts) and evaluated by a competent person to determine whether guying or bracing is needed. In addition, posts
will be excluded from the 4 anchor rod/bolt requirement by definition."

OSHA's definition of a post:
"Post means a structural member with a longitudinal axis that is essentially vertical, that: (1) weighs 300 pounds or
less and is axially loaded (a load presses down on the top end), or (2) is not axially loaded, but is laterally restrained by the above member. Posts typically
support stair landings, wall framing, mezzanines and other substructures."

Also, as I stated in the previous threead, I strongly recommend the "NISD-SEAA Detailing Guide for the Enhancement
of Erection Safety" for good practice detailing with OSHA compliance.

 

[Stress02]

Does it actually say 4 bolts, or can a properly arranged set of 3 meet the loading requirement?
Trying to work out a corner tube column with offset baseplate. One corner gets no bolt.

 

[CSEllc]

What you need to do is put 2 bolts on each leg of a corner base plate. It really defeats the purpose of requiring the (4) bolts.

 

[SperlingPE]

What was the motivation for the 4 bolt requirement? I believe I read that it had something to do with column failures during construction. Can anyone confirm this? What is the structural engineers obligation as far as adhering to OSHA regulations? We are not the ones on the site doing the work. I think you have to make it possible for the erector to adhere to OSHA, but it is not our obligation to see that the erector does.

 

[jheidt2543]

SperlingPE,

I think you are partially correct, the designer is generally not liable for on site safety and we should say so in our contract documents. However, OSHA does require certain design criteria to be met. For example, the load capacity of a handrail which is specified in the OSHA regulations is the DESIGNER'S responsibility, but the installation is not. Just as the 4 anchor bolt requirement and the 300 lb eccentric load for a column is the DESIGNER's responsibility, but the installation of the column is not.

 

[SperlingPE]

I guess I want to know what is the background of this particular OSHA regulation. I agree that required loads/loadings need to be accounted for. This particular case deals more with erection than it does for design of members. If there was a 2 bolt or 3 bolt base plate design on a job that was overlooked by the EOR, steel detailer, and erector, who is culpable if there was a failure? I think this regulation is in a grey area between design and ways and means. The designer needs to design something that is erectable/buildable. How it gets built/erected is up to another party. I dont' disagree with the intent of thisregualtion. Maybe this requirement should be adopted by AISC and added to the specifications? Currently, I specify 4 bolt minimum base plates.

 

[Stress02]

I envision the reason for the requirement by picturing an ironworker scrambling up a freestanding column; one that is not yet tied in by beams and thereby subject to swaying out of plumb.

 

[CSEllc]

The theory behind the (4) anchor bolt requirement is this:

An iron worker is "climbing up the column, with the 2 anchor bolts scenario, the bolts are usually installed within the web area, about 4 to 5 inches each side of column center. AS the ironworker is climbing, the column base really has no "fixity" in the strong axis of the colun to resist the moment cause by the weight of the iron worker hanging off the side of the column....that';s where the 300 # and 18" eccentricity come into play...with the bolkts at the comn centerline, they "tension fo\rce" is rathger lage even with a small moment, and since the concrete ususlly has not achieved it's 28 day strength, the anchor bolts have pulled out of thge footings/piers/pilasters/ and the columns have collapsed.

Now, take the same column and base plate but put in (4) anchor bolts, the base now has a certain amount of fixity.....definitely more than enough to resist the moment caused by the iron worker.

 

[SperlingPE]

Thank you for the background.
I will continue to specify 4 bolt base plates, but still believe that this is a safety issue that should remain solely with the erector or add it to AISC's specification.

 

[Stress02]

My favorite steel fabricator said that the requirement was directed at fabricators/erectors. But, if you detailed the columns with a 2 bolt baseplate, you are likely to be put on the line for extra charges to meet the standard as well as having the headache of adjusting to the revised detail after the fact.
Better off just going in as a team player.

 

[jheidt2543]

What do you do with the faily frequent condition at a corner column where there is room for only three anchor bolts?