2 vs 4 anchor bolts 1

[WWTEng]

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.

 

[JedClampett]

For what its worth, most of the PEMB columns I see have four bolts. They might be spaced at 4 inches, but there's four there.

 

[msquared48]

I agree from what I have seen too.

Mike McCann
MMC Engineering

 

[nutte]

Jlkells, the distinction you're asking about is that between a "column" and "post."

OSHA definitions in section 1926.751:

https://www.osha.gov/pls/oshaweb/owadisp.show_document?p_table=STANDARDS&p_id=10787

[bold]Column means a load-carrying vertical member that is part of the primary skeletal framing system. Columns do not include posts.[/bold]

[bold]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.[/bold]

An explanation from OSHA:

https://www.osha.gov/pls/oshaweb/owadisp.show_document?p_table=INTERPRETATIONS&p_id=25885

 

[msquared48]

"weighs 300 pounds or less"

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

 

[jlkells]

Ah, very good Nutte. I was not familiar with their definition regarding posts vs. columns. That was the hangup for me.

Thanks for the clarifications everyone, very helpful as always.

 

[jlkells]

And I fully agree with this statement by Nutte:

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.

 

[nutte]

Msquared, there are two cases:

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.