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Blackburn Point Road Bridge

Blackburn Point Road Bridge

Primary Photographer(s): Rick McOmber

Bridge Documented: March 23, 2010

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Key Facts

Facility Carried / Feature Intersected
Blackburn Point Road (CR-789) Over Gulf Intracoastal Waterway
Osprey: Sarasota County, Florida: United States
Construction Date and Builder / Engineer
1925 By Builder/Contractor: Unknown

Technical Facts

Rehabilitation Date
Main Span Length
142 Feet (43.28 Meters)
Structure Length
142 Feet (43.28 Meters)
Roadway Width
15.7 Feet (4.79 Meters)
1 Main Span(s)
NBI Number

Historic Significance Rating (HSR)

Bridge Documentation

This bridge is one of a small number of surviving swing truss bridges in Florida. Among this small number there is considerable variety, but a few of them appear to share the same standard plan. The Blackburn Point Road Bridge is an example of that standard plan. The design consists of trusses with rolled i-beams for the top chord and end post. Diagonal and vertical members are all built-up beams composed of two angles and battens. There is no v-lacing or lattice on any built-up beams.

The Blackburn Point Road Bridge in particular has an unusual detail that was observed. All the shop rivets (those rivets placed before the bridge parts were shipped to the site) have cone-shaped rivet heads. This design is nearly unheard of in bridge truss construction, although these rivets were used in boiler and tank construction as well as occasionally in caisson construction. In contrast, those rivets on the bridge placed in the field (during on-site assembly) are the standard round-head rivets.

This swing bridge still operates for boats.

The bridge has been rehabilitated, and some rivets were replaced with bolts and there are other welded repairs and alterations present. Otherwise however, the bridge retains its original appearance and design. Among the surviving truss swing bridges in Florida, this one appears to be one of the best in terms of structural condition. The bridge is only considered functionally obsolete in the National Bridge Inventory (because it is a narrow, one-lane bridge) but is not listed structurally deficient. Florida has an extremely small number of historic metal truss bridges. The preservation of each surviving example must be considered essential.


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