erected as described for short-span and medium suspension bridges, and their use as suspended falsework for the construction of the main cables built up from straight wires spliced to form continuous lines reaching around and around the anchorage pins and adjusted to the proper catenary curve and elevation as they are successively laid. These are grouped first into strands and then into the main cables; and the stiffening trusses and the roadways are erected on them by means of simple travelers.

Suspension bridges having eye-bar chains could be erected in a similar manner from a temporary, suspension-falsework platform.

Arch Spans

Very short arch-spans should be erected like girder spans, and handled as units by any convenient apparatus. Medium and long spans are generally erected on falsework or by the cantilever method. As in the case of ordinary truss spans, erection on falsework is economic when practicable; and for arches of the plate-girder or solid-rib type this method can hardly be replaced by any other, when the spans are of any considerable length. Care must be taken, however, to brace the falsework thoroughly so as to resist the oblique stresses and thrusts that are produced by unequal loading as the inclined sections of girders are assembled, unless particular pains are taken to arrange them so as to maintain balanced reactions throughout the erection. Plate-girder arch-spans up to 510 feet long have been erected on falsework.

Truss arch-spans may be erected by the cantilever method, which has been employed successfully for most of the large spans and up to the greatest present maximum of about 1,000 feet clear opening. By this method the top chords of the semi-spans which are built simultaneously are tied back to sufficient anchorages with adjustable connections so that the spans may be revolved around their skewback hinges in order to make the center connection at the crown.

Erection Plant

A very important feature in the economics of bridge erection is the design and operation of the special plant provided for handling the heavy members in the field. It has been found good, economic practice to expend large sums in the construction of plant for the erection of a single structure, and for the equipment of the field force with special machinery and power appliances of great capacity. This apparatus is so costly that none but the most important construction-companies keep it in stock; and the existence of available plant of this nature is often an important factor in the design of the structure and in the award of the construction contract. Among the important standard appliances for bridge erection are derrick cars, derricks, hoisting engines,  and  riveting  machinery  that,  in  general,  are  applicable  for