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South Bridge (Stone Facing)

Animal Bridge

South Bridge (Stone Facing)

Primary Photographer(s): Nathan Holth

Bridge Documented: September 8, 2011

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Key Facts

Facility Carried / Feature Intersected
US-41 (Coast Guard Drive) Over Jackson Park South Lagoon
Location
Chicago: Cook County, Illinois: United States
Construction Date and Builder / Engineer
1904 By Builder/Contractor: Thomas E. Hill and Engineer/Design: Peter J. Weber

Technical Facts

Rehabilitation Date
2003
Main Span Length
47 Feet (14.4 Meters)
Structure Length
49 Feet (15 Meters)
Roadway Width
67.3 Feet (20.51 Meters)
Spans
1 Main Span(s)
NBI Number
16619727260

Historic Significance Rating (HSR)
View Information About HSR Ratings

Bridge Documentation

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

View Historic American Engineering Record (HAER) Documentation For This Bridge

HAER Drawings, PDF

View A Series of Advertisements For The Trussed Concrete Steel Company

View A Historical Book About The Trussed Concrete Steel Company

View Three Julius Kahn Patents For Reinforced Concrete

Note: The historic bridge once at this location was demolished and replaced in 2003. The bridge seen here is modern and not historic. This HistoricBridges.org listing refers to the historic stone facing that was salvaged from the placed on this modern bridge.

About The Former Historic Bridge - Today Demolished

Kahn Trussed Bar

Constructed in 1904, the bridge at this location was an exceedingly rare example of a concrete arch bridge which used a type of concrete reinforcing patented by Julius Kahn of the Trussed Concrete Steel Company of Detroit, Michigan. This unique type of concrete reinforcing had a comb-like appearance and had bars that had smaller bars that extended out at an angle from the main bar. The idea of having these angled bars extending from the main bar was to produce a structural effect similar to how a truss works to transfer loads. This system was patented by Julius Kahn in 1902, so the system was relatively new when the bridge was built. Kahn's unusual reinforcing system was one of a number of unusual methods of reinforcing concrete that were developed and patented in the first decade of the 20th Century. At this time, reinforced concrete construction (often called concrete-steel construction) was relatively new and so engineers were inventing and patenting their own ideas for what the best reinforcement method was. Kahn's reinforcing was used at least occasionally on bridges, but it appears to have been far more popular for building construction, based on the content of the company's advertisements.

Kahn Building Products Trussed Concrete Steel Company

The replacement of this historic bridge resulted in the loss of this extremely rare reinforced concrete bridge. It is not known how many other bridges if any might survive in the country that have Kahn reinforcing. It does not appear that Chicago salvaged any of the reinforcing during the demolition of the bridge. At the very least, it would have been nice to salvage some of the concrete and reinforcing and create an interpretive display near the bridge that would have explained the reinforcing and its significance.

Kahn System of Reinforced Concrete

About The Current Bridge

Animal Bridge Replacement

The bridge seen today is a modern precast arched rigid-frame. The bridge's structure is not historic or noteworthy. However the unique stone facing that was part of the 1904 historic bridge was salvaged and placed on the new bridge and this facing is itself historically and aesthetically significant. It appears that the new bridge's superstructure was designed to match the shape of the historic arch, because the stones line up on the new bridge. The stone facing is unique because it features detailed sculptures that stick out from the stone and include hippopotamus heads, faces, and a boat. These unique details were designed to compliment the themes of wind and water at the park.

The result of this replacement project was that the structural features and technological significance of the historic bridge were destroyed completely, however the historic bridge's architectural features and aesthetic significance was preserved.

Kahn Concrete Reinforcement Drawing

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Photo Galleries and Videos: South Bridge (Stone Facing)

 
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Maps and Links: South Bridge (Stone Facing)

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