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Chicago, Milwaukee & St. Paul Railway, Bridge No. Z-6, Spanning North Branch of Chicago River, South of C, Chicago, Cook County, IL



B&W Photos

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Data Pages


Photo Caption Pages


Item Title


Location
South of C, Chicago, IL

Find maps of Chicago, IL


Created/Published
Documentation compiled after 1968.

Notes
Survey number HAER IL-162
Unprocessed field note material exists for this structure (N652; N967).
Building/structure dates: 1898 initial construction
Significance: The Milwaukee Road's Bridge No. Z-6 may be the only one of its kind ever built, defying the conventional categories of center-bearing and rim-bearing swing bridges. This ingenious design answers the constraints of a small site on a bend in the river. The 175'-2"-long plate-girder span bears on a short segment of roller nest turning at one-half the span's rate. This is accomplished by an unusual drive mechanism with two parallel racks. As a result, the roller nest need only turn through an arc equivalent to half of the span's rotation, reducing the bridge's footprint accordingly.

Subjects
Railroad Bridges
Swing Bridges
Steel Girder Bridges


Related Names
Bates, Onward
American Bridge Works
Chicago, Milwaukee & St. Paul Railway
Canadian Pacific Railroad
Spivey, Justin M., Historian
Lowe, Jet, Photographer


Collection
Historic American Engineering Record (Library of Congress)

Contents
Photograph caption(s): 
1. AERIAL VIEW, LOOKING NNW ALONG NORTH BRANCH OF CHICAGO RIVER. BRIDGE No. Z-6 IN FOREGROUND, CORTLAND STREET BRIDGE BEHIND. BRIDGE No. Z-6 ROTATES CLOCKWISE.
2. AERIAL VIEW, LOOKING DUE EAST.
3. AERIAL VIEW, LOOKING NW.
4. AERIAL VIEW, LOOKING WNW.
5. LOOKING NORTH AT FIXED PLATE GIRDER SPAN ON WESTERN APPROACH. STONE PIER AT CENTER OF FRAME DATES TO PREVIOUS SWING BRIDGE ON THIS SITE.
6. VIEW FROM WESTERN ABUTMENT, SHOWING SIDE ELEVATION OF BRIDGE No. Z-6 IN OPEN POSITION.
7. DETAIL OF SWING SPAN, SHOWING PLATE GIRDER CONSTRUCTION AND PIVOT BEARING BELOW.
8. BALANCE WHEELS AT EASTERN END OF SWING SPAN.
9. OBLIQUE PERSPECTIVE OF SWING SPAN.
10. PIVOT BEARING FOR SWING SPAN.
11. DOUBLE CURVED RACK. UPPER PORTION ROTATES; LOWER PORTION REMAINS STATIONARY. DISCARDED ROLLER NEAR CENTER OF FRAME.
12. WESTERN END OF SWING SPAN, SHOWING ROCKER BEARINGS AND LOCKING MECHANISM.
13. VIEW OF DRIVE TRAIN, SHOWING TWO PINIONS ENGAGING DOUBLE CURVED RACK.
14. LOOKING NW FROM EASTERN ABUTMENT, WITH SWING SPAN IN OPEN POSITION. NOTE BUMPER ON CURVED RACK AT BOTTOM LEFT OF FRAME.
15. LOOKING DUE EAST FROM OPERATOR'S HOUSE, WITH TRAIN APPROACHING BRIDGE.
16. LOOKING SE, WITH SWING SPAN IN MOTION.
17. LOOKING DUE EAST FROM OPERATOR'S HOUSE, WITH TRAIN CROSSING BRIDGE (MOVING TOWARD CAMERA). NOTE JOINT BETWEEN SWING SPAN AND FIXED APPROACH SPAN AT BOTTOM RIGHT OF FRAME.


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