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RE: OSHA 4 bolt anchorage

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>I would appreciate it if you could show me where
>OSHA will allow less than 4 anchor bolts with some
>alternate form of bracing.

Unfortunately, I don't think it does.

As you probably already know, Section 1926.755(a)(1) says "All columns shall
be anchored by a minimum of 4 anchor rods (anchor bolts)." Section
1926.755(a)(4) says "All columns shall be evaluated by a competent person to
determine whether guying or bracing is needed; if guying or bracing is
needed, it shall be installed." So the OSHA regulation defaults to 4 rods,
even in a case where providing 4 will do no more good than 2 and bracing
will likely be needed anyway, such as when the rods are placed all in a
single line to stay within the width of a wall.

On the other hand, cases where the intent cannot be met by providing 4
anchor rods are probably the exception rather than the rule. Note that a
suitable base plate connection and foundation are also critical here - not
technically required in OSHA, but advisable from statics. We put some
guidance on this in the AISC Design Guide #10 Erection Bracing of Low-Rise
Structural Steel Frames.


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