Reynolds Metals

Can someone explain the structural steel beam designation LB21x120?

There are no W,S or M shapes that are 21x120. Is this a custom designation? I cannot find a reference to LB in the Manual of Steel Construction.

Public Comments

1. Strange, generally the second number is weight in pounds per foot...the closest standard size I'm aware of is a W21 X 101, the "LB"? I don't know... could be a W with a larger flange width and web thickness than W21 X 101. Edit: There is a W21 X 122..just found it.
2. Never heard of it. Must be some old obsolete shape, or a custom shape.
3. It is what is called a "historical shape" as designated by AISC and probably dates back to the earlier 20th century (1920s). It is a beam 21 inches deep by 120 lbs/linear foot.
4. E=mc2