Friday, May 3, 2019

Halsted Street Bridges over South Branch

1894 Lift: (Bridge Hunter; Historic Bridges)
1934 Trunnion: (Bridge Hunter; see above Historic Bridges; 3D Satellite)

I'm going to focus on the 1894 lift bridge because it was the first big lift bridge constructed in the world.
Transactions of the American Society of Civil Engineers, Digitized by Google
The 1934 trunnion bridge is another example of the many Chicago-style trunnion bridges that have been built in Chicago. However, this trunnion bridge is of note because it has three truss lines instead of just two so that it is wider than usual.
Street View

On June 21, 1892, the steamer Tioga allided with the Halsted Street Bridge. [Historic Bridges] The War Department specified a width for the navigation channel that precluded replacing the bridge with another swing bridge. This provided John Alexander Low Waddell an opportunity to use his lift bridge design because Chicago city engineers had not yet developed their trunnion bascule bridge design. [HeavyMovableStructures]

Waddell's design had a 130' span that could be lifted 155' clear of mean low water with 217' high towers from the water to the top of the housings. The tower holds "four built-up steel and cast-iron sheaves, 12 ft. in diameter, which turn on 12 in. axles. Over these sheaves pass the 1.5 in. steel-wire ropes (32 in all), which sustain the span. These ropes are double, i.e., two of them are brought together where the span is suspended, and the ends are fastened by clamps, while, where they attach to the counter weights, they form a loop, which passes around a 15-in. wheel or pulley that acts as an equalizer in case the two adjacent ropes tend to stretch unequally....The original design called for the use of two sixty-five horse-power electric motors, but the city of Chicago required a steam engine plant of one hundred and fifteen horse-power instead. The cost of this plant for both operation and maintenance was found to be excessive; and in 1907 electric motors were substituted for the steam engines. Operation by steam had required the services of three engine men, two signal men, four policemen, and one coal shoveler, ten men in all, their combined wages amounting to one thousand dollars per month; and in addition there were one hundred and seventy dollars per month expended for coal, as it was necessary to keep the boilers going at all times during the season of navigation. The cost of the electric power for intermittent service proved to be only one hundred and fifty dollars per month; and the services of only one tender were required, while two had been formerly needed with steam. The change resulted in a saving of over three thousand dollars per annum in the operating expenses. " [Bridge Engineering by J. A. L. Waddell, Digitized by Google, p718]

This photo also shows that some rather large boats traveled pretty far down the South Branch.
Public Domain, LoC via Bridge Hunter

Published prior to 1923 via Bridge Hunter

Bridge Engineering by J. A. L. Waddell, Digitized by Google, p722

Brad Small comment on Bridge Hunter


South Halsted Street Bridge Details including operator's house, rope adjusters, counterweight chains, ship impact protection features (Transactions of the American Society of Civil Engineers, January 1895)
Transactions of the American Society of Civil Engineers, Digitized by Google


Transactions of the American Society of Civil Engineers, Digitized by Google

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