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35th Street Pedestrian Bridge (new)

Photos 

Looking east

Photo taken by Roger Deschner in February 2017

License: Creative Commons Attribution-Share-Alike (CC BY-SA)

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BH Photo #379185

Map 

Description 

New, notable bridge, replaced much more humble earlier box-truss and girder bridges.

Unique design may be the only curved cable suspension span in existence. (There are other curved suspension bridges, but they are multiple spans with a curve between, such as Oakland Bay Bridge.) Deck is S-shaped, with one A-shaped tower in the center and one cable. On each half of the deck, the hanger cables extend only to the outer edge of the curve. So each half of the S-curved deck acts structurally like an arch laid on its side, with the cables providing compression as well as vertical support. At the base of the central tower, where the middle of the S-curved deck passes through, the compression forces of the deck halves balance one another. Being self-anchored, the forces at the ends are also balanced, depending more on the strength of the abutments to resist horizontal force, than the strength of the anchorages themselves. It's really a very clever design, visually appealing too. But building it was difficult, requiring extensive falsework to hold the deck up over active rail lines and a highway while the cables were strung. Unlike other suspension bridges, in this case the deck was built first, and then the cables were connected to it. There was no other way to build it.

Facts 

Overview
Self-anchored suspension bridge over Metra Electric Line, South Shore Railroad, Canadian National Railway, South Lake Shore Drive (US 41), and Lakefront Trail, on pedestrian pathway that is an extention of the 35th Street sidewalks
Location
Chicago, Cook County, Illinois
Status
Open to pedestrians only
History
Built 2016
Builders
- James McHugh Construction Co. of Chicago, Illinois
- Teng & Associates Inc. of Wauwatosa, Wisconsin
Railroads
- Amtrak (AMTK)
- Canadian National Railway (CN)
- Chicago, South Shore, & South Bend Railroad (CSS)
- Metra (METX)
Design
Wire/cable self-anchored suspension, using a single main cable hung from a single central tower, supporting only one side of S-curved deck. Structurally, each half of the deck appears to function like an arch laid on its side, with the cables providing compression and rigidity in addition to vertical support.
Dimensions
Total length: 620.0 ft.
Approximate latitude, longitude
+41.83120, -87.60588   (decimal degrees)
41°49'52" N, 87°36'21" W   (degrees°minutes'seconds")
Approximate UTM coordinates
16/449689/4631212 (zone/easting/northing)
Quadrangle map:
Jackson Park
Inventory number
BH 75712 (Bridgehunter.com ID)

Update Log 

  • March 12, 2018: Updated by Roger Deschner: Expanded description of bridge's unique design elements
  • March 10, 2018: New Street View added by Roger Deschner
  • January 28, 2018: New Street View added by Dana and Kay Klein
  • February 19, 2017: Added by Roger Deschner

Sources 

Comments 

35th Street Pedestrian Bridge (new)
Posted August 4, 2017, by Anonymous

One of the photos asks "I wonder what the numbers mean?" (next to each bolt) They would be the tightening sequence. The engineers want the bolts torqued to a very specific torque value, and in the sequence shown to even out the stress on the cable clamp. Then the nuts have "witness marks" so that an inspector can see if the nut has come loose.