Design of St. Georges Tied Arch Span

The procedure used to determine the preliminary and final designs for a tied arch bridge is presented in this paper. Although the type of structure is not new, having been used in Europe, it is believed that the design introduces a new type in American practice. The structure differs from the usual tied arch in that the ratio of the moment of inertia of the tie girder to that of the arch rib is approximately 13 to 1. With these relative physical properties, the total bending moment taken by the rib and girder together is divided between these two elements, the major part being resisted by the girder. (The distribution of this bending moment has been discussed elsewhere by Nathan M. Newmark, Assoc. M. Am. Soc. C. E.)