Centerbeam

Centerbeam flatcars, centerbeams, center partition railcar, or "lumber racks"[1] are specialty cars designed for carrying bundled building supplies such as dimensional lumber, wallboard, and fence posts. They are essentially bulkhead flatcars that have been reinforced by a longitudinal I-beam, often in the form of a Vierendeel truss, sometimes reinforced by diagonal members, but originally in the form of stressed panels perforated by panel-lightening "opera windows", either oval-shaped or egg-shaped.