If you take a look at one of the clarification attempts at the 300# requirement, it appears to me that the interpretation is that a minimum 300# X 1.5' resisting moment (not just the 300# here) is required to be verified for the connection, in addition to furnishing (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
