Tuesday, November 29, 2016

Hell Gate Bridge

Albert R Brecken posted
Section of the Hell Gate Bridge that spanned the Easr River as viewed without the massive "portal" towers at each end of the span.
Arch bridges push out as well as down on their abutments. I always assumed the portal towers provided mass to help resist the outwards forces. But this indicates that they are just decorative. The bridge was completed in 1916 when railroads could afford to spend money on decoration. I then assumed that this must be one of the places in New York where the bedrock is at the surface so they could easily anchor the bridge to bedrock. But then I learned that caissons had to be sunk 90 feet to reach bedrock. [nycroads] I wonder how much of the expense for building to decorative portals was used to build foundations for all of that masonry.


 Historic Bridges
In fact, the bearing is mounted to the base at almost a 45-degree angle indicating the arch does push out about as much as the weight of the arch pushes down.

It was the longest steel-arch bridge in the world when built, and it "was named after the narrow channel of strong waters and dangerous rocks in the East River running underneath the structure (known as Hell Gate)." [parachute] "The Hell Gate Bridge would be the last NYC bridge to collapse if humans disappeared, taking at least a millennium to do so.... Built by the Pennsylvania Railroad between 1912 and 1917 for the purpose of connecting the Pennsylvania and New Haven railways, its 20,000 tons of steel spans 1,107 feet from the shore of Astoria to the Bronx's Ward Island." [gothamist]

I've seen both 1916 and 1917 for completion dates. This project finished in 1916, but evidently additional track work was needed before through trains could use this project:
The arch bridge, the two smaller bridges and the viaduct were completed in September 1916. On March 9, 1917, the first Pennsylvania Railroad train - the Federal Express service between Washington and Boston - went over the Hell Gate Bridge, completing the first uninterrupted rail service between the two cities. [nycroads]
Library of Congress: HAER NY,31-NEYO,167--18
I did not realize until I saw some of the HAER photos on the Bridge Hunter site that the approach viaducts are non-trivial structures in their own right.
Library of Congress: HAER NY,31-NEYO,167--16
Little Hell Gate Bridge now spans land instead of water. Historic Bridges notes:
It uses a design that is rare anywhere, but almost unheard of in North American, the inverted bowstring truss. It is a deck truss where the bottom chord takes on an arch-like shape.
The reason this unusual design was chosen was as unusual as the design itself: the engineer wanted to give a greater clearance for boats near the piers. This is odd because boats usually would want to pass under the bridge as far away from the piers as possible.
I was able to manipulate a 3D Satellite image to capture much of the length of the structure. Historic Bridges estimates it to be 3.6 miles long based on a diagram of the East River Bridge Division of the New York Connecting Railroad.

3D Satellite
THE HELL GATE BRIDGE TODAY: The Hell Gate Bridge, which today has the 17th longest main steel arch span in the world, continues to play a central role in rail transportation in the Northeast. Only three of the four tracks are used on the bridge. The two south tracks carry Amtrak Northeast Corridor trains, while the north inner track carries CSX and Norfolk Southern (the owners of the former Conrail routes) freight trains. The north outer track is no longer in operation. [nycroads]
oldnyc has several pictures including a couple of the Randall Island Viaduct and one of a bearing.

Dave Frieder has an interesting collection of photos of this and other bridges in the New York area.

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