Through the end of next week a handful of bridges on the Chicago River will be tested ahead of the annual spring lift, where sailboats parade out to Lake Michigan for summer sailing season.
The tests, which started March 17 and run through April 1, are done to make sure the bridges are working and will close the roads to pedestrians and vehicles for five hours starting after morning rush hour at 9:30 a.m. and ending at 2:30 p.m. The Chicago Department of Transportation, which operates the bridges, conducts the testing. During the tests, officials make sure the bridges function normally and inspect electrical components, mechanical systems and motors, as well as the structural integrity, balance and backup systems.
What makes hundreds of feet of steel bridge rise into the air? “The coolest thing is this is all pretty low tech,” said Jim Phillips, a retired civil engineer who runs the site www.chicagoloopbridges.com. “It’s just gears and fifth-grade physics.”
Phillips, who worked in the defense industry and taught at a junior college in New Mexico, moved to Chicago with his wife, Pat Armell, in 2009. “I’ve always had a thing for bridges,” he said. When Phillips’ fascination grew over the Chicago River structures, he went looking for a source of information. He discovered there wasn’t a central place and got to work making one. He also has published a digital book, “Two Miles — Eighteen Bridges: A walk along the Chicago River.” Over the course of his research, he’s met the people who operate the bridges and some who sail through.
What does an engineer think of the spectacle? “Sometimes the best solution is not the most complex one.”
The schedule for the spring lift will be released in early April, CDOT said.
Bridge test schedule
- Dearborn Street Bridge: 9:30 a.m. to 2:30 p.m. Thursday, March 24
- State Street Bridge: 9:30 a.m. to 2:30 p.m. Monday, March 28
- Wabash Avenue Bridge: 9:30 a.m. to 2:30 p.m. Tuesday, March 29
- Columbus Avenue Bridge: 9:30 a.m. to 2:30 p.m. Wednesday, March 30
- Michigan Avenue Bridge: 10 p.m. Thursday, March 31, to 5 a.m., Friday, April 1
Bridge locations
The bridge tests will be done once the overnight test of the Michigan Avenue Bridge is expected to be finished at 5 a.m. April 1.
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Navy
Pier
Bridge
MADISON
MICHIGAN
ASHLAND
Lake
Michigan
HALSTED
ROOSEVELT
LAKE SHORE
STATE
18TH
CERMAK
1 mile
Canal Street
Marina
Chicago
Yacht Yard
How the Michigan Avenue Bridge opens
The Michigan Avenue Bridge, aka the DuSable Bridge, is a “Chicago-type, double-leaf, trunnion bascule bridge” design. A bascule bridge is a family of drawbridges that use massive counterweights to assist in the rising of each bridge leaf. Because the counterweights are balanced with the bridge weight, it takes a relatively small amount of energy to raise and lower the 4,300-ton bridge. Also, both sides of the parallel bridge can be operated independent from one another.
Components of the bridge
- Bridge tender house: Where the operator sits and can observe the bridge. It extends 3 1/2 stories above the water level.
- Rack: A steel curved gear bar driven by rotational motion applied by the pinion, translating rotational motion into linear motion.
- Motor: Each leaf of the bridge is operated by four 110 horsepower DC electric motors, which open the bridge in one minute. A driveshaft runs from the motor to the gears that drive the pinion.
- Heel lock: Can lock the bridge in position so wind doesn’t sway it.
- Counterweight: Each side contains a fixed 4 million-pound counterweight composed of individual 450-pound cubic-foot steel blocks.
- Brake: Stops the rack and pinion when applied.
- Pinion: A circular gear that engages the rack and is powered by the motor.
- Trunnion: Axle or pivot point that supports the bridge weight. They can support a load of 800 tons.
- Counterweight pit: Area to accommodate the counterweight when the bridge lifts. The pit measures 95 feet by 67 feet with a depth of 40 feet.
- Leaf: One side or portion of the steel bridge that extends over the river.
Sources: www.chicagoloopbridges.com, Chicago Department of Transportation, National Park Service
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