I-95 New Haven Harbor Crossing Corridor Improvement Program

-	Contract A - State Street Station
-	Shore Line East Station Improvements

Long Wharf Improvements

GNHWPCA

-- Contract B --

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Extradosed Bridge

The new Pearl Harbor Memorial Bridge will be the first extradosed cable stayed bridge constructed in the United States. The extradosed system is a hybrid design that is a marriage between a concrete cable stressed girder bridge, of which a good example is the Baldwin Bridge (I-95 over the Connecticut River), and a cable stayed bridge. Some examples of cable-stayed bridges are the new Charles River Crossing Bridge in Boston, Massachusetts and the Sunshine Skyway Bridge in Tampa, Florida.

This extradosed system is a hybrid design that is a marriage between a concrete cable stressed girder bridge and a cable stayed bridge.

In this new type of bridge the wire carrying cables are placed outside the girders and up on the main concrete towers as opposed to inside the concrete boxes. However, the cables are not placed high up on tall towers, as would be the case with a conventional cable stayed bridge.

With a typical cable stayed bridge most of the load (weight of the bridge deck, girders, cars and trucks) is carried through the cables, up to the top of the towers and then down through the towers to the foundations. In an extradosed bridge both the girders and the wire cables carry the load. A portion of the load is carried back through the girders to the towers and the remaining portion is carried by the cables up to the top of the towers and then back down through the towers to the foundations. As a result we have a very efficient load-carrying bridge with superior aesthetic qualities due to the exposed cables and concrete towers above the bridge roadway surface.

Some other characteristics of extradosed cable stayed bridges are:

An extradosed bridge lends itself to longer spans (the distance between foundation supports) than a conventional girder bridge. This was a benefit for the design of the Pearl Harbor Memorial Bridge in that the new bridge will have a longer main span than the existing bridge. This allowed the new bridge foundations to be built without interfering with the existing bridge foundations, which have to remain in service to carry traffic during construction of the new bridge. Also, the longer main span will benefit boat and barge navigation below the bridge by providing a wider navigation channel.
The tower height above the bridge deck is much less than that of a cable stayed bridge. This was important for the new bridge in that the new bridge towers could not restrict flight traffic from the nearby Tweed New Haven Airport.
The stay cables (wire strand cables which go up to the concrete towers) need no tension adjustment as would be required for a conventional cable stayed bridge. This will result in reduced future maintenance costs for the extradosed bridge.
The girder depth of an extradosed bridge is less than that of a standard girder bridge (see diagram). This allows for a longer span length while not impacting the profile of the bridge deck roadway.

Request a copy of the report (CD-ROM): Extradosed Bridge Technology in Japan, containing details of an investigative delegation to Japan (Sept. 2001) and select technical papers. Please indicate the intended use of the report. The report is 2.7MB; if you are not capable of receiving a file of this size, provide a contact name and mailing address.

Reprinted from The Bridges Over Kiso & Ibi River Brochure, Japan Highway Public Corporation.

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