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Green Bay Road Bridge

Green Bay Road Trusses

   


Green Bay Road Bridge

Primary Photographer(s): Nathan Holth

Bridge Documented: April 14, 2013
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Key Facts

Facility Carried / Feature Intersected
Green Bay Road Over Railroad (Union Pacific)
Location
Lake Bluff: Lake County, Illinois
Construction Date and Builder / Engineer
By Builder/Contractor: Unknown

Technical Facts

Rehabilitation Date
1988
Main Span Length
70 Feet (21.3 Meters)
Structure Length
170 Feet (51.8 Meters)
Roadway Width
26 Feet (7.9 Meters)
Spans
3 Main Span(s)
NBI Number
49680215346

Historic Significance Rating (HSR)

Bridge Documentation

View Archived National Bridge Inventory Report - Has Additional Details and Evaluation

This bridge was sadly demolished and replaced in 1988, however the only good news is that the extremely unusual and highly significant truss webs of the bridge were placed on the replacement bridge as decorations. These trusses have several unusual details. The double-Warren truss configuration is unusual, especially in the Chicagoland area. However the most unusual feature is what looks like "archways" over the cantilevered sidewalks. Although these elements include decorative knee braces with punch-out decorations, these "archways" are not decorative features. They are actually the outriggers for the pony truss, designed to provide lateral stability. The use of outriggers was a common way to stabilize pony trusses that did not get enough lateral stability from the trusses themselves. However, if it was desired to design a pony truss with outriggers, but also with cantilevered sidewalks, a practical problem developed. The outriggers would stick out into the sidewalk, or the sidewalk would have to be extended out beyond the outriggers which would be an inefficient design. As such, the designers of this bridge simply placed the outriggers outside of the cantilevered sidewalk, and connected them to the top of the truss via overhead beams. This produced the "archways" seen on the bridge.

Based on style, the bridge could be as old as the 1890s. If so, it is also significant as an early surviving example of a rivet-connected truss bridge.

The bridge trusses make efficient use of materials at the expense for a more complicated design. Diagonal members become increasingly lightweight toward the center of the truss, representing the distribution of loads within the truss web.

Note: The bridge dimensions given are for the replacement bridge. The length, width and span number of the historic bridge would have been different. The bridge is likely wider than the original, and where the current bridge is three spans, the original bridge may have been single span (just the truss) or there may have been flanking approach spans of some sort.

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