(
Bridge Hunter;
Historic Bridges;
HAER;
PGHbridges;
3D Satellite)
The main tied-arch span is 620'. You can barely see part of the
J&L Hot Metal Bridge under the center of the deck.
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HAER PA,2-PITBU,31--3
3. Charles W. Shane, Photographer, April 1970. VIEW LOOKING FROM THE SOUTHWEST. - Brady Street Bridge, Spanning Monongahela River at South Twenty-second Street, Pittsburgh, Allegheny County, PA |
The total length of the bridge is quite long because it goes bluff-to-bluff over highways and railroads. Because of those bluffs, Pittsburgh can avoid have to build movable bridges.
As we have come to expect, it used to go over more railroads than it does now.
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| 1969 Pittsburgh East Quad @ 1:24,000 |
I first noticed the tied-arch bridge in this image.
Scanning those J&L notes, I found an overview of the 1896 bridge.
The description in BridgeHunter is a quote of the significance in the HAER: "The Brady Street Bridge, contracted by the Schultz Bridge & Iron Co. of Pittsburgh, was a steel-riveted, through-highway bridge. The structure consisted of a tied arch for the central span with a suspended deck, and two through-trusses for the side spans. The bridge was the second to be owned by the city and the first free bridge in Pittsburgh." [
HAER-data, p2] I'm surprised there are no comments on BridgeHunter correcting this description. The new bridge is a tied-arch bridge. The bridge built by Schultz Bridge was "a continuous truss and thus unusual in its day." [
HAER-data, p24. Footnote 77 is referenced, which is: "On authority of George S. Richardson, the Pittsburgh bridge engineer."] Other sources have called the bridge a 3-hinged arch and a cantilever. But "the engineer, Marcel Fertig, examined the bridge for the State in the 1960's and found that the channel span was a continuous truss." [
HAER-data, p28]
I emphasized that it was a continuous truss because both Bridge Hunter and the Significance description in the HAER have it wrong. But I also emphasized it because I recognized that it looked continuous even though it was obviously built a long time ago. I wonder if this is the oldest continuous truss bridge that I've seen. They were quite rare before computers were developed because the stress computations for the truss members is much more difficult than for multiple simple trusses.
This bridge was built using what is now called Accelerated Bridge Construction. ("The main span was constructed on floats moored on the river bank and the superstructure was swung into position on 24 November." [
HAER-data, p27]) I wonder if this is the first example of using that technique with such a large span.
The new bridge was built just downstream from the old bridge.
Note the piers for the new bridge in the above photo with no visible construction activity. That is because construction was halted for over a year because Pittsburgh did not want to pay its share for the large interchange in Soho. [
HAER-data, p28] That interchange was probably a surprise expense because the 6-lane bridge was originally (
1963) planned to be part of a new expressway that went between the north side of the Allegheny River and the south side of the Monongahela River. See
PGHbridges for more information on the need for a convoluted interchange on the north side of this bridge. The change in plans from a crosstown beltway to a local bridge also explains why a 6-lane bridge ends at
a stoplight interchange on the south side. I noticed that "bridge to nowhere" dynamic when I first looked at a satellite image.
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