Sunday, March 19, 2017

The Dock Bridge

So, I'm kind of a sucker for big industrial age steel constructs, and when I saw this photo in a pile of dollar photos, it went into the "buy" stack. Why? Because as an engineering marvel for its time, it's cool, that's why.

I had no idea of where this was, but a bit of searching, starting with Wikipedia's page on lift bridges, quickly showed that this is the Dock Bridge over the Passaic River between Harrison and Newark, NJ, and is on both the National and New Jersey Registers of Historic Places.

The bridge was originally built by the Pennsylvania Railroad as part of a $42 million passenger transportation project, and included Newark's Penn Station at Raymond Plaza, off to the right of our view. The west span (closest to the camera in our photo) was dedicated with appropriate pomp and circumstance for that era on March 24, 1935. At the time it was built, it was the longest three-track lift bridge in the world, with a span of 230 feet.

The east span, which opened in 1937, is actually a double bridge, with two tracks on one span and a third on the other. Today, the bridge is owned and operated by Amtrak, with the west span carrying three Amtrak Northeast Corridor tracks, and the east span hosting two PATH tracks and an Amtrak/NJ Transit track. Closed, the bridge provides a 24-foot clearance over the mean high-water mark (the Passaic River at this point is influenced by the daily tides), while fully open, the clearance is 135 feet. It takes between 15 and 20 minutes for the bridge to lift, allow a barge to pass, and then lower back into place.

According to the National Register of Historic Places documentation,
Aerial photo by Jack Boucher, April 1977; part of a NPS aerial
survey of historic places (Federal Gov't work, public domain)
Dock Bridge is the only vertical lift bridge on the Northeast Corridor railroad route. The structure is unique because of the operation of six tracks on three bridges with two lift spans. Dr. J.A.L. Waddell was one of the first to patent a simplified and improved design of vertical lift bridge in the United States. Vertical lift bridges of small spans and low lifts were constructed in Europe at a fairly early date, but no vertical lifts of any size were constructed until the late 19th century. The consulting engineering firm for the construction of this structure, Waddell & Hardesty, used the patent of Dr. Waddell in the design of the bridge.

This type is economical in construction and operation and has proven efficient in heavily trafficed areas because the span can be opened in less time than is required for a swing bridge. In addition, the span can be partially raised when height requirements are low. Heavy railroad traffic between New York City and Newark and the frequent openings necessary on the Passaic River make this structure critical to the operation of the Northeast Corridor railroad system. The machinery and electrical systems which were specifically designed for this bridge have not been significantly altered since their installation. Earle Gear and Machine Company of Philadelphia was the contractor for the machinery and the electrification was done by Gibbs & Hill.

Dock Bridge is an exceptionally important Pennsylvania Railroad engineering accomplishment. This lift bridge is an unusual engineering design in terms of its massiveness and double bridge lifts which operate independently. There are no other comparable railroad bridges in New Jersey, and it is one of the few double lift bridges in the country.

For those interested in some of the more technical details, the register also includes the following:
Aerial photo by Jack Boucher, April 1977; part of an NPS
aerial survey of historic places
(Federal Gov't work, public domain)
Dock Bridge over the Passaic River in Newark, New Jersey, a through-truss liftbridge, was constructed in 1935 by Waddell & Hardesty, Consulting Engineers, after the patent of Dr. J.A.L. Waddell. It was constructed for the Pennsylvania Railroad with T.W. Pinard, Chief Engineer of the railroad.

The structure consists of two deck girder approach spans 94 feet and 64 feet long, respectively; a through Warren truss, with verticals, lift span 230 feet long and two deck girder approach spans 64 and 68 feet long, respectively. Bridge A8.50 carries three tracks and C8.50 carries one track. PATH trains are carried on a separate span. The bridges are side by side and operate independently. This bridge has two sets of lift towers supporting three lift towers. The south towers support two bridge structures. Each span has the moving machinery located at the center of the span on the top chord of the trusses.
The substructure is 24 feet above mean high water and the abutments and piers are concrete with stone facings. There are timber fenders on both sides of the channel at the rest piers.

The main drive motors are 260-horsepower DC series wound electric motors. There are electro-hydraulic trustor brakes on each motor. The motors are geared through common spur reduction gears on shafts which transmit power to the cable drums. Cables run over the cable drums to the end of the span where they pass over an idler sheave to the bridge sheave. The bridges are raised and lowered by uphaul and downhaul cables. The counterweight cables are attached to the top chord of the trusses and run over sheaves. There is a 150 horsepower gasoline engine in the machinery house of each span. This engine serves as an emergency power source. There are compressors in the operator's house basement for bridge floor and rail locks. There are AC motor DC generator sets in the operator's house at the north shore. The bridge operator occupies the fifth floor of this house. The operator's level contains the signal interlock box, track model board, reversing drum controllers, and navigation light control. There is a cable tunnel below the river for cables carrying single-phase and 3-phase 4150-volt AC. The operator's level is the top floor of the five-level house on the north shore. The other floors contain railroad electrical equipment.

This photo provides a sense of scale to the massive bridge, as Amtrak's Vermonter crosses,
approaching Newark's Penn Station.
Photo by Tony Jin, used under CC-BY-SA 3.0 license.

A panaramic view of the Passaic Riverfront and the Dock Bridge in June 2015 on Wikimedia. The large tank in the background is gone.
Photo by Tony Jin, used under CC-BY-SA 3.0 license.

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