A Guide to Some of the Equations used in Constructing a Suspension Bridge

STUDY OF SUSPENSION BRIDGES

SUSPENSION BRIDGES

THE economic utilization of the materials of construction demands that, as far as possible, the predominating stresses in any structure should be those for which the material is best adapted. The superior economy of steel in tension and the uncertainties involved in the design of large-sized compression members point emphatically to the conclusion that the material of long-span bridges, for economic designs, must be found to the greatest possible extent in tensile stress. This requirement is best fulfilled by the suspension-bridge type.

The superior economy of the suspension type for long-span bridges is due fundamentally to the following causes:

1. The very direct stress-paths from the points of loading to the points of support.

2. The predominance of tensile stress.

3. The highly increased ultimate resistance of steel in the form of cable-wire.

With the exception of the Forth Bridge, the Queensboro Bridge and the Quebec Bridge (under construction), all structures exceeding 1000 ft. in span have been suspension bridges. Table I gives a list of the most notable structures of this type, with their principal dimensions. It is seen from this table that practically all suspension bridges erected after what might be called the experimental period (1796–1876) have spans between the limits of 700 and 1600 ft.

In order to secure information needed in determining