This bridge was the first Chicago bascule bridge to have a smoothly-curved pony truss design for a movable bridge, and was the generation of trunnion bascule bridges that succeeded the somewhat clunky looking bridge design seen on bridges such as Grand Avenue. The Monroe Street Bridge however still has the clunky looking detail at the ends of the trusses like the Grand Avenue type bascules. Later examples of this bridge design would have a more aesthetically pleasing curved detail at the ends in addition to the smoothly curved detail in the center. The Franklin Street Bridge is one such later example.
The bridge's operating and control panels inside the bridgetender buildings were reportedly the first in the United States to have completely enclosed circuitry so that no exposed copper connections were available for bridgetenders to mistakenly electrocute themselves on.
The navigational vertical clearance of the bridge is 18.7 Feet. The clear span of the bridge is 165.5 feet, while the trunnion-to-trunnion length is 193 feet. The bridge is 60 feet wide.
The Monroe Street Bridge is unique because the engineers had to do some very special technical and mechanical design to get this bridge to fit near to Union Station which was under construction at the time and takes up substantial space below the roadway level of Monroe Street. To ensure that room remained for the Union Station underground facilities, the counterweight, which is under the road on this type of bridge, was changed at one end only. At the west end, engineers used a smaller counterweight using heavier cast iron instead of concrete. The east end however had the standard concrete sized counterweight. There is a more technical description of this available in the HAER entry for this bridge.
On the western end of the bridge, where the smaller counterweight is used, steel blocks used to help counterweight the bridge actually extend above the deck level and are attached to the ends of the trusses. Some of these blocks may be later additions, but a historical photo of the bridge from 1919 does appear to show some counterweight blocks on this end of the bridge. This is likely further indication of the limited space below the roadway and a creative method the city designed to add weight to this end of the bridge. Sometimes over the course of a bascule bridge's history, counterweights would need to be made heavier or lighter, usually in response to changes made to the deck design. On this bridge, the blocks that rest on the west end of the bridge on top of the top chord, do not appear in the 1919 photo and thus appear to be an example of weights added to the bridge at a later date.
The 1919 photo, shown to the right, also shows unusual concrete pillars at the end of the bridge. These appear to have been decorative, but also appear to have contained a "Stop" signal to alert drivers when the bridge was being raised. The arched overhead beams seen in the photo are for holding the cables for the street cars that once were found on numerous Chicago streets. Many of Chicago's movable bridges originally had these arched overhead beams, but all have been removed today.
Main PlaqueWILLIAM HALE THOMPSON
CHARLES R. FRANCIS
COMMISSIONER OF PUBLIC WORKS
DEPUTY COMMISSIONER OF PUBLIC WORKS
THOS. G. PIHLFELDT
ENGINEER OF BRIDGES
CHICAGO UNION STATION CO.
CHICAGO PLAN COMMISSION
ILL. CHAP. AMER. INST. ARCHT'S
FITZSIMONS & CONNELL D. & D. CO.
THE KETLER-ELLIOTT ERECTION CO.
THE ELECTRICAL EQUIPMENT INSTALLED BY C. H. NORWOOD
Rehabilitation PlaqueMONROE STREET BRIDGE
- 2008 -
CITY OF CHICAGO
RICHARD M. DALEY
DEPARTMENT OF TRANSPORTATION
THOMAS G. BYRNE
THOMAS H. POWERS, P.E.
FIRST DEPUTY COMMISSIONER
DIVISION OF ENGINEERING
JOHN YONAN, P.E.
DANIEL BURKE, S.E., P.E.
CHIEF BRIDGE ENGINEER
THOMAS P. AMBRY, AIA
CHRISTOPHER A. KENT, P.E.
CHIEF CONSTRUCTION ENGINEER
FREDDY R. FLORES
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This bridge is tagged with the following special condition(s): Unorganized Photos
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