Catenary Trolley Construction Used on Manhattan Bridge (1917)
Electric Railway Journal · Vol. 49, No. 6 · February 10, 1917 · pp. 240-241.
CATENARY TROLLEY CONSTRUCTION ON MANHATTAN BRIDGE. VIEW OF COMPLETED CONSTRUCTION AND FIRST TWO CARS TO CROSS BRIDGE UNDER NEW OVERHEAD WORK.
Catenary Trolley Construction Used on Manhattan Bridge to Insure Safety. Security Against Damage to Bridge, Good Operating Features and Attractive Construction Obtained by Using Simple Catenary with 90-ft. Pole Spacing.
The Manhattan Bridge Three-Cent Line runs between the corner of Flatbush Avenue and Fulton Street, Brooklyn, N. Y., and the corner of the Bowery and Canal Street, Manhattan. The route is 2 miles long, about half the distance being over the Manhattan Bridge. This line had been operated on the lower-deck tracks of the bridge, but since these tracks were intended to be used by the rapid transit line connecting the subways in Manhattan and Brooklyn, it became necessary to operate the Three-Cent Line on the upper deck. This made it essential to adopt a method of supporting the trolley wire which would give the maximum degree of safety as well as good operating conditions. A construction which would not detract from the attractive appearance of the bridge was also desirable.
The use of the usual span-wire construction was not feasible in this case since a double row of trolley poles would be required and any method of supporting the trolley wire directly from span wires or from poles spaced say 50 ft. apart was considered unsafe since the copper wire, if broken, might come in contact with and burn to a dangerous degree some of the vital members of the bridge. The catenary construction shown in the accompanying illustrations was therefore decided upon, and it has been so installed that if the contact wire should break, the hangers are spaced close enough together to prevent the freed ends of the wire from coming in contact with the steel members of the bridge.
The average pole spacing is 90 ft., the height of the contact wire above the top of the rail is 16 ft., and the distance between the contact wire and the messenger wire at the insulators is 20 in. The details of the length and spacing of the hangers for a typical 90-ft. span are given by the diagram on the. opposite page. A 7/16-in. Siemens-Martin double galvanized, seven-strand steel cable was used as a messenger wire. This was strung in the usual manner, and the sag adjusted so that the middle of each span was 16 ft. 10 in. above the top of the rail. Roebling Brother's No. 000, hard drawn, standard grooved copper wire was used for the contact wire. While stringing this wire it was allowed to rest at the ends of the crossarms, and as the hangers were attached the wire was slipped over the ends of the crossarms. One of the illustrations shows two gangs at work attaching the catenary hangers. The tower cars were made by erecting a scaffolding on an ordinary flat truck.
At the expansion joints of the bridge, steel bar construction is used in place of the catenary. The bar is made in sections, the adjoining ends of which are far enough apart to allow for the expansion and contraction of the bridge. A bronze sleeve of 1/8-in. metal connects the ends of the steel bar and provides the bearing surface for the trolley wheel at these points. A wooden trough provides a suitable protection over the bar. This may be seen under the bridge tower in one of the illustrations.
The drawing giving the details of the steel pole also shows the steady braces which are used at every fourth pole and the taps between the trolley wire and the eight 1,000,000-circ. mil, weatherproof cables which are supported on substantial feeders insulators on each side of the base of the pole. From these feeders, a 250,000-circ. mil, lead-covered cable in 1-1/2-in. metal conduit leads to the feeder switch box, which is located at a convenient height on the pole and contains a 400-amp., quick-break disconnecting switch. The 250,000-circ. mil cable is continued from the switch box to the top of the pole, where it divides into No. 00 weatherproof cables, which connect with the contact wire. It was considered necessary to use lead-covered cable inclosed in metal conduit for the feeder connections on the pole in order to make them doubly safe from possible grounds to the steel poles. The trolley wire is divided into sections by insulated joints, and each section is fed by separate taps from the feeder cables so that each section is an independent electrical unit.
On the approaches to the bridge span-wire construction was used, since the catenary was not necessary for purposes of safety. The drawing in the top, left-hand corner of the page shows the details of this construction, which have been worked out by attaching the trolley wire in such a way as to make the appearance as attractive as possible and in harmony with the catenary construction on the bridge.
Since this construction has been in operation for some time without any trouble developing, it is good evidence that the requirements of safety have been well met. The construction above described was designed by the department of plant and structures, New York City, of which F. J. H. Kracke is commissioner and E. A. Byrne is acting chief engineer, and was built by Peet & Powers of New York.
[Left, top] CATENARY TROLLEY CONSTRUCTION ON MANHATTAN BRIDGE; METHOD OF SUPPORTING TROLLEY WIRE ON BRIDGE APPROACHES WHERE CATENARY WAS NOT NECESSARY FOR PURPOSES OF SAFETY. [Left, Bottom] LENGTH AND SPACING OF HANGERS FOR A TYPICAL 90-FT. SPAN. [Right] DETAILS OF STEEL POLE AND FEEDER CABLES.
CATENARY TROLLEY CONSTRUCTION ON MANHATTAN BRIDGE; DETAILS OF INSULATED JOINT.
CATENARY TROLLEY CONSTRUCTION ON MANHATTAN BRIDGE; CONSTRUCTION GANGS ATTACHING HANGERS BETWEEN MESSENGER WIRE AND TROLLEY WIRE.