Friday, December 7, 2012

Florida Keys Bridge #20 Old Seven Mile Bridge

Old Seven Mile Bridge
December 7, 2012, Rob Hickman, Keith Nelson


Historic Old Seven Mile Bridge

Also called:
Knights Key- Pigeon Key Bridge
Pacet Channel Bridge
Knight's Key Bridge
Seven Mile Bridge (local reference)
Pigegon Key Bridge
Moser Channel Bridge

Overview: Concrete Arch and Deck Girder bridge over Moser Channel on Old US 1 with a through truss swing span (removed), now used as a Fishing Pier and observation deck in Marathon
NBI Structure Number: 900020
Location: Marathon, Monroe County, Florida
Feature Carried: Old alignment of US 1, former Florida East Coast Railway
Feature Crossed: Intracoastal Waterway
History: Originally built by the railroad in 1912. Rehabilitated in 1938. Replaced in 1982 with a modern bridge, but most of the original bridge (with a few spans removed for shipping) intact. Part of the bridge is now used for fishing.
Type: Beam
Subtype: Steel deck girder, (Warren through truss swing span over Moser Channel removed in 1982)
Recognition: Posted to the National Register of Historic Places on August 3, 1979
Length: Main Span: 80 ft, Total: 10480 ft
Builder or Contractor: William Krome, Joseph Meredith, Florida East Coast Railway, American Bridge Co. (Steel Fabricator), Terry and Tench Company (Contractor); rebuilt by B. M. Duncan (Chief Engineer)
Sufficiency: 15%
Status: Closed to vehicular traffic in 2008, in use for pedestrians, future uncertain
Notes: The Old Seven Mile Bridge (Knights Key-Pigeon Key-Moser Channel-Pacet Channel Bridge) is the longest of the original Florida East Coast Railway (FECR) Bridges. The bridge was designed and built in four sections: Knight's Key Bridge, Pigeon Key Bridge, Moser Channel Bridge, and Pacet Channel Viaduct. Unlike most of the FECR bridges in the keys, only the Pacet Channel Viaduct consists of concrete arches, as seen in the picture. The rest of the bridge is composed of steel deck girders spans. Steel girders were more economical for most of this crossing, due to a deeper channel that makes longer spans more efficient. As with the other keys bridges, the bridge's deck was widened when it was converted to vehicular use in 1938. The rails from the railroad were used as railings. Once the replacement bridge opened in 1982, several spans of the old bridge were demolished, including the one to the west of the Pigeon Key ramp. Since the new bridge does not cross Pigeon Key, the Knight's Key-Pigeon Key Bridge and ramp were retained to provide vehicular access to the island. Therefore, the bridge was divided into two sections. The Knights Key-Pigeon Key Bridge continued to provide vehicular access to Pigeon Key until 2008, when it was closed to traffic. It may be rehabilitated in the future. Currently (2009) it is just open to pedestrians. According to the Historic American Engineering Record, ''At the time the Florida East Coast Railway constructed this bridge it was acclaimed as the longest bridge in the world, an engineering marvel. It was the most costly of all Flagler's bridges in the Key West Extension. Since the beginning it has served as the one and only vital link between Miami and Key West. The logistics of assembling labor and materials and overcoming the difficulties presented by deep water, normal tides and hurricanes attest to the engineering and management skills of those connected with its construction.
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