The Probert Encyclopaedia of Architecture

GIRDER

In architecture a girder is a main beam; a straight, horizontal beam to span an opening or carry weight, such as the ends of floor beams, etc. and hence, a framed or built-up member discharging the same office, technically called a compound girder.
The term girder is also applied in architecture to a small circular band around a column - like the steel band around an old wooden barrel (which is also called a girder).
Research Girder