2 vs 4 anchor bolts
2 vs 4 anchor bolts
(OP)
I understand that minimum 4 ABs for a column base plate is an OSHA requirement. I have an existing job from 1955 where we need to replace the base plate for an exterior column due to significant corrosion (column to be removed/shored etc). These existing baseplates were installed with 2 ABs. Can we replace the baseplate with just two ABs or do I have to use 4 per the new requirements? The only issue with using 4 ABs is that the existing pier would have to be enlarged to accommodate 4 ABs.
The column is a W10x49 with gravity load of 8 kips max.
The column is a W10x49 with gravity load of 8 kips max.






RE: 2 vs 4 anchor bolts
if the loading on the strucutre increased, and you had to add a new column ... would you use 2 AB or 4 ?
Quando Omni Flunkus Moritati
RE: 2 vs 4 anchor bolts
RE: 2 vs 4 anchor bolts
Quando Omni Flunkus Moritati
RE: 2 vs 4 anchor bolts
You may have a problem with the inspector, but for an application like this, I wouldn't feel uncomfortable using only two anchor bolts (provided, of course, there isn't any sort of lateral/uplift loading on the column)
RE: 2 vs 4 anchor bolts
RE: 2 vs 4 anchor bolts
http://www.osha.gov/pls/oshaweb/owadisp.show_docum...
I don't see any exceptions for the 4 anchor bolt rule.
RE: 2 vs 4 anchor bolts
RE: 2 vs 4 anchor bolts
RE: 2 vs 4 anchor bolts
I meant to say.
I don't think the
twofour bolt rule applies. The 4 bolt rule is to provide added stability against a column toppling over until it's sufficiently braced.I must be getting senile.
The other day I got an e-mail about something I ordered and was wondering why they couldn't find my address; turns out I used my zip code from 20 years ago
RE: 2 vs 4 anchor bolts
RE: 2 vs 4 anchor bolts
RE: 2 vs 4 anchor bolts
All more the reason to use 2 anchor bolts...
Is there an OSHA inspector in the area and can you explain that there is no stability issue, the col is existing and is not going to topple...
Dik
RE: 2 vs 4 anchor bolts
EIT
www.HowToEngineer.com
RE: 2 vs 4 anchor bolts
RFreund, the limit you refer to is 300 pounds. And at 49 pounds per foot, it won't take long for the W10x49 to exceed that.
RE: 2 vs 4 anchor bolts
RE: 2 vs 4 anchor bolts
EIT
www.HowToEngineer.com
RE: 2 vs 4 anchor bolts
RE: 2 vs 4 anchor bolts
I also looked at the interpretations of code section 1926.755(a)(1) but didn't see any exceptions.
Basically what I am wondering is, why are pre-engineered metal building manufacturers allowed to get away with 2-bolts at all of their pinned base connections...
Please let me know if I am missing something... Thanks!!
John
RE: 2 vs 4 anchor bolts
May 27, 2004
Mr. L. Carlos Garcia
Project Manager
Urban Associates LP
1400 Geronimo
San Antonio, TX 79925
Re: Under Part 1926 Subpart R, is it permissible to field-weld a column to a base plate that has four anchor rods welded to its bottom side and is already embedded in the footing?
Dear Mr. Garcia:
This is in response to your telephone call of March 24, 2004, to the Occupational Safety and Health Administration (OSHA) in which you ask about the requirements for securing a column to a foundation under 29 CFR Part 1926 Subpart R (Steel Erection). We have paraphrased your questions below:
Question (1): This question has to do with a procedure for erecting steel columns on concrete footings. The scenario is as follows: A steel base plate with four ½" diameter headed studs welded to its bottom side is embedded in a concrete footing. Once the concrete meets the strength specified in Part 1926 Subpart R, the steel column is lowered by crane onto the base plate. While still attached to the crane, the column is braced in two directions (i.e., east-west and north-south). The column is then attached to the plate with a continuous ¼" weld. After the column is field welded, employees in aerial lifts will remove the crane hook and guy wires.
Photograph indicating procedure for erecting steel column using four pre-attached anchor rods attached to the column, and that assembly is embedded into the concrete footing.
Section 1926.755(a)(1) requires four anchor rods. Is it permissible under §1926.755 to use this installation procedure?
Answer:
Section 1926.755 "Column Anchorage" states:
(a) General requirements for erection stability. (1) All columns shall be anchored by a minimum of 4 anchor rods (anchor bolts).
(2) 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 (.46 m) from the extreme outer face of the column in each direction at the top of the column shaft. * * *
The intent of §1926.755(a)(1) and (2) is to ensure the stability of a column during the erection process. These hazards are addressed in part by the requirement that the column be "anchored by a minimum of 4 anchor rods."
However, §1926.755(a)(1) does not specify the manner in which the four anchor rods must be attached to the column. So long as the column anchoring system meets the strength criteria in (a)(2) and has four anchor rods, the assembly meets the requirements of §1926.755(a)(1). (emphasis added)
In your scenario, the four anchor rods are pre-attached to the base plate, and that assembly is embedded in the concrete footing. Once the concrete has reached the strength required under §1926.752, the column is placed on the steel plate, and pre-attached guy wires are used to brace it. The column is then field welded with continuous weld to the embedded base plate. At that point the column is anchored to the footing with four anchor rods. The requirement in §1926.755(a)(1) is thus met once the column is welded to the base plate. So long as the column in your scenario, after the anchorage assembly is completed, can resist a 300-lb. eccentric gravity load in all directions, the column anchorage will satisfy the stability requirements of §1926.755(a)(1) and (2).
If you need additional information, please do not hesitate to contact us by fax at: U.S. Department of Labor, OSHA, Directorate of Construction, Office of Construction Standards and Guidance, fax # 202-693-1689. You can also contact us by mail at the above office, Room N3468, 200 Constitution Avenue, N.W., Washington, D.C. 20210, although there will be a delay in our receiving correspondence by mail.
Sincerely,
Russell B. Swanson, Director
Directorate of Construction
Personally, I think the site needs to be updated with most of the clarification answers in the order of 7 years old or older.
In metal buildings, some of the columns, particularly in end wall (wind) columns under an end wall mainframe, do not see vertical loads greater than 300#, if only this vertical load this is in fact a definition of a "post". In this circumstance, (2) bolts could be used.
Personally, I think greater latitude needs to be made here if it can be shown that the column base arrangement can handle the eccentricity required. The intent of the code should be to use 4 bolts if that eccentricity criteria cannot be met or shown. Otherwise two bolts are OK.
That being said, I think that small required eccentricity for a typical mainframe column is very, very low.
Mike McCann
MMC Engineering
RE: 2 vs 4 anchor bolts
RE: 2 vs 4 anchor bolts
Mike McCann
MMC Engineering
RE: 2 vs 4 anchor bolts
OSHA definitions in section 1926.751: https://www.osha.gov/pls/oshaweb/owadisp.show_docu...
Column means a load-carrying vertical member that is part of the primary skeletal framing system. Columns do not include posts.
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.
An explanation from OSHA: https://www.osha.gov/pls/oshaweb/owadisp.show_docu...
RE: 2 vs 4 anchor bolts
So that is the difference here. Thanks for the clarification nutte.
Few columns in a structure, secondary or otherwise, will weigh less than 300#.
For PEMB end wall wind columns of back to back light gage metal C's, this could apply though.
Mike McCann
MMC Engineering
RE: 2 vs 4 anchor bolts
Thanks for the clarifications everyone, very helpful as always.
RE: 2 vs 4 anchor bolts
nutte (Structural)
21 May 13 12:35
What is most frustrating about this problem is that a general erection requirement (properly brace columns during erection) has led to a prescriptive engineering requirement (provide 4 anchor bolts) that sometimes leads to ridiculous results, with no apparent way out for special cases. I've seen small miscellaneous posts detailed with 4 anchor bolts all on one side of the post. "OSHA wants 4, I gave 'em 4." I don't see any benefit here.
There is no way an OSHA erection req't should be dictating structural engineering design.
RE: 2 vs 4 anchor bolts
1) Members that receive axial load, but weigh less than 300 pounds, can be considered posts.
2) Members that are vertical, but do not receive axial load, can be considered posts. Think of a vertical element acting like a wind girt. These do not have to weigh less than 300 pounds to be considered posts.