The Bridge Delta Girder: Single-Webbed and Double-Webbed

The specifications of the American Association of State Highway Officials (AASHO) govern the construction of the great majority of highway bridges in the United States. These specifications determine the dimensions and general relationship of parts in steel girders. Since compliance with these specifications is the sine-qua-non condition upon which allotment of Federal participating construction funds is based, deviations from these requirements are rare. Yet it is a fact that the standard plate girder as produced by the AASHO specifications is not satisfactory in all respects. It is too flexible, too limber, too lacking in lateral stiffness. The 1959 AISC National Engineering Conference paper presented by Mr. E. L. Durkee of the Bethlehem Steel Company, dealing with bridge erection problems, is an earnest plea for providing lateral stiffness in steel members. Of course, after installation of cross-bracing, bottom lateral bracing and a top roadway slab, the plate girder serves admirably, but it can not be said to do so in the early stages of bridge construction.