. The Street railway journal . The maximum temperature variation is degs., and thecorresponding change in height of trolley wire is ins. forthe 230-ft. span and ins. for the 270-ft. span. Fig. 12 repre-sents a curve of 425-ft. radius. In this view the use of double-catenary curve pull-offs is illustrated. PROPOSED GENERAL PLAN It was first thought advisable to run the messenger cable overthe bridges. Fig. 11 shows this construction. It is necessary,however, to provide an unobstructed view of the signal ap-paratus, and it is accordingly considered preferable to make thebridge high
. The Street railway journal . The maximum temperature variation is degs., and thecorresponding change in height of trolley wire is ins. forthe 230-ft. span and ins. for the 270-ft. span. Fig. 12 repre-sents a curve of 425-ft. radius. In this view the use of double-catenary curve pull-offs is illustrated. PROPOSED GENERAL PLAN It was first thought advisable to run the messenger cable overthe bridges. Fig. 11 shows this construction. It is necessary,however, to provide an unobstructed view of the signal ap-paratus, and it is accordingly considered preferable to make thebridge high enough to permit the semaphores to be suspendedbelow the truss. Fig. 13 indicates a signal bridge which has been devised fora four-track road carrying, beside the semaphores, the four setsof cables and trolley wires suspended below the truss. Thisconstruction is a decided advantage in erecting, as the cableand trolley wire can be run out along the track and lifted intoplace. Massive porcelain insulators will be used mounted on. FIG. 13.—SIGNAL BRIDGE DEVISED FOR A FOUR-TRACK ROAD character are at present in use on many roads to support sema-phores and other signal apparatus. Fig. II illustrates a section 2500 ft. long of a three-trackroad, one track of which has been equipped with the bridgeconstruction. The double-catenary system is used, each mes-senger being a steel stranded cable. The trolley wireis 000 grooved, and the supporting hangers are placed 10 The average total weight per foot supported by eachcable, including its own weight, is lbs. The vertical sagin the first span, which is 230 ft. long, is ft., and in thesecond span, which is 270 ft. long, ft., both at degs. corresponding tension in the messenger cables is 2300 lbs. The observed variation in heij,ht of trolley wire due to tem-perature change was as follows: TemperatureFahr. Height ot Trolley Wire Above Rails Date SpanNo. 1 Span No. 2 1-16-05 1- 26-05 2- 9-05 °
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Keywords: ., bookcentury1800, bookdecade1880, booksubjectstreetr, bookyear1884
