Direct Answer
Camber is a deliberate upward curve built into a beam during fabrication to offset the beam's expected dead-load deflection in service. When the dead load is applied, the beam deflects downward and ideally reaches a nearly flat profile. Camber is specified in inches at midspan and is typically ordered when dead-load deflection exceeds L/300.
Full Explanation
Camber is introduced by cold-press cambering — applying force to the beam to permanently deform it upward — or, less commonly, by heat cambering. AISC recommends not specifying camber for beams shorter than about 25 feet because the residual stresses from rolling often provide natural camber in that range. Common camber rule of thumb: 75% of calculated dead-load deflection. Camber must be clearly called out on the shop drawing with a midspan dimension and tolerances (typically ±1/4" per AISC).
What This Means for Your Shop
Camber must be specified on the shop drawing, not verbally. The fabricator orders cambered beams from the mill or sends straight beams to a cambering shop. Cambering after galvanizing is not possible, so sequence matters. Over-cambered beams can cause floor problems; under-cambered beams result in visible sag.
Common Mistakes
Specifying camber on short beams (under 25 feet) where it is impractical. Also: not accounting for construction loads that will be applied before the dead load reaches design value, which can flatten a beam before the slab is poured.
Recommended Process
Have your engineer calculate dead-load deflection for every beam and flag those requiring camber. Include camber callout on the shop drawing piece mark sheet with tolerance. Verify received material with a straightedge or optical level before sending to the shop floor.