This Architectural Drawing of Details of girder in AutoCAD, dwg file. a horizontal main structural member (as in a building or bridge) that supports vertical loads and that consists of a single piece or of more than one piece bound together. A girder is a large and deep type of beam that is used in construction. It is typically capable of longer spans and taking greater loads than a normal beam, and is often used as a main horizontal structural support for smaller beams, such as in bridge construction. For more details and information download the drawing file.