A plate girder is constructed from steel plate elements which are connected together with welds or bolts. A greater economy of material can be obtained as the designer has the ability to specify the section properties of the stringer to flange thickness. Variation in plate sizes may represent a girder with the least weight; however, this may not be the most economical girder, due to the increase in fabrication costs which are associated with excessive variations in plate sizes. Plate girders gain an advantage over rolled beams as span lengths become great. The box girder is a form of plate girder which utilizes four or five rather than three plates. Since box girders possess excellent torsional stiffness, they do not usually require secondary members to provide bracing
