1884 7th Street: (Bridge Hunter)
1926,1977,2017 7th Street: (Bridge Hunter; Historic Bridges; HAER; pghbridges; Satellite) Andy Warhol Bridge1890 9th Street: (Bridge Hunter)
That bridge was the first of rehabilitation work that is being done for all three bridges.
They put the color of the bridges up to a vote. The current Aztec gold won. [post-gazette-jul2015] The other choice was to paint the Warhol Bridge silver and the Carson Bridge green. [TripSavvy]
Allegheny County boasts 1,576 bridges that are 8' or more in length. [AlleghenyCounty] Pittsburgh alone has more than 400 bridges. In fact, it has more bridges than the city of Venice. [TripSavvy]
Because the 450', 1,600 tone bowstring trusses of the 6th Street Bridge were still in good shape, the county paid to have them moved to a new bridge in Corapolis, PA. The contractor for the piers of the the Three Sister Bridges, Foundation Co., did it for $316,200 in 30 days.
1926,1993,2020 9th Street: (Bridge Hunter; Historic Bridges; HAER; pghbridges; B&T; Satellite) Rachel Carson Bridge
The 6th Street Bridge is the other of the three sister bridges.
Significance: These structures are the only trio of nearly identical bridges, as well as the first self-anchored suspension spans, built in the U.S. They are among the only surviving examples of large eye-bar chain suspension bridges in America, and furthermore unusual for having been erected using cantilever methods. The bridges' design was a creative response to the political, commercial, and aesthetic concerns of Pittsburgh in the 1920s. [HAER-data]
Since this is looking upriver, we see the 6th, 7th and 9th Street Bridges, respectively.
 |
| Photo taken by Royce and Bobette Haley in May 2016 via both 1926 BridgeHunters |
"The first bridge across the Allegheny was the St. Clair Bridge of 1819 at the site of the current Sixth Street structure. The Hand Street Bridge followed in 1840 at the current Ninth Street Bridge site....The American Institute of Steel Construction called the Sixth Street Bridge (the first to be completed) the Most Beautiful Steel Bridge of 1928." [PittsburghArtPlaces]
Today, these three suspension bridges carry between 12,000 and 23,000 motorists each day. All three Sister Bridges have been painted a bright Aztec gold as an homage to the city’s official colors, and to showcase the bridges’ proximity to Downtown’s “Golden Triangle.” [post-gazette-jan2017]
Or 7,700-11,000 vehicles each day. At 40' clearance, they are the lowest on the Allegheny River. These bridges were built because the predecessor bridges were declared to be too low by the Secretary of War. [AlleghenyCounty, this reference also has a detailed timeline]
 |
| Brad Berkstresser posted Five bridges on a quiet Allegheny river at sunrise |
The 7th Street Bridge replaced an 1884 Gustav Lindenthal designed bridge. So between 1884 and 1892 a Roebling suspension bridge at 6th Street stood a block away from this Lindenthal suspension bridge.
 |
| danepieri via BridgeHunter-1884 |
This view is of the 7th Street Bridge is a representative view of all three bridges. The bridges have plenty of 14" eye-bars in each chord so that it has redundancy. Specifically, the bridge should not fall down if one of the eye-bars breaks like the Silver Bridge did.
 |
| Street View |
When I accessed the satellite images, the 7th Street Bridge was obviously closed for repairs.
 |
| Satellite |
That bridge was the first of rehabilitation work that is being done for all three bridges.
 |
| Michael Baker International |
 |
| 1 of 8 posted by Bridges & Tunnels The Three Sisters Bridges comprise of three self-anchored eyebar suspension bridges across the Allegheny River in Pittsburgh, Pennsylvania. These iconic structures were the result of a compromise with the federal government because of the required horizontal and vertical clearances for the river navigation channel, and because of aesthetic and financial considerations. The bridges received their signature Aztec gold paint in the 1970s. The crossings were listed on the National Register of Historic Places in 1986 and designated as architecturally significant structures by the Pittsburgh History & Landmarks Foundation in 1988. All three have been or are undergoing significant rehabilitation in recent years. B&T shared ▶︎ Check out our extensive article on the Three Sisters Bridges at http://bridgestunnels.com/location/three-sisters-bridges/ |
 |
| Ted Gregory posted [Ted was after the Fort Wayne Bridge, but he also caught the Three Sisters] |
They put the color of the bridges up to a vote. The current Aztec gold won. [post-gazette-jul2015] The other choice was to paint the Warhol Bridge silver and the Carson Bridge green. [TripSavvy]
Allegheny County boasts 1,576 bridges that are 8' or more in length. [AlleghenyCounty] Pittsburgh alone has more than 400 bridges. In fact, it has more bridges than the city of Venice. [TripSavvy]
7th Street (Andy Warhol)
 |
| Jacob H. Ford Photography posted You all have seemed to really enjoy the river reflection shots I've shared the last few days from last Friday evening that I spent on the North Shore, so I decided to share another new one this evening! In this shot here, I wanted to capture the downtown side of the Andy Warhol Bridge looking across the Allegheny River. I also positioned myself so that the Gulg Tower and US Steel Building were nestled above the main suspension cable, and so that the BNY Melon Building was on the other side of the tower of the bridge. There's so many different compositions I could have created, and I just captured a handful that I've seen, and some I came up with on my own (although I'm sure someone out there has silmilar ones to even the compositions I came up with), and I could have lingered for hours, but I captured as many as I could in the time I was there and before the reflection dissapeard due to a light breeze that came in just around the time I was about to leave to head home anyways. Hopefully I get another chance again soon to capture some more amazing reflections in the Allegheny River on the North Shore, but I still have a few that I'll be sharing with you all over the next few days. Be sure to click on the image to view it in its entirety. Enjoy! Photo taken: December 8, 2023 Etsy Store —-> https://jhfordphotography.etsy.com Website —-> https://www.jacobhfordphotography.com/ |
9th Street (Rachel Carson)
 |
| Joseph Flickr via BridgeHunter, License: Creative Commons Attribution-Share-Alike (CC BY-SA) |
I quit watching when it devolved into "talking heads."
The following information comes from HAER-data unless otherwise noted.
The first charter for a bridge was granted on Mar 20, 1810. But it fell through because the Bank of Pittsburgh could not get its charter. The next charter was granted on Feb 17, 1816, for the St. Clair Bridge, the first bridge at the 6th Street location. Toll records show that it opened in 1819. An aqueduct for the state's Pennsylvania Canal was built across this river in 1829 at 11th Street. The third structure across the Allegheny River was the 1840 Hand Bridge. It is known that Lothorp built this bridge, and it is presumed that he built the St. Clair bridge as well. The Hand Bridge was charted in 1867, but the panic of 1837 slowed its construction.
Lindenthal called his 1884 7th Street Bridge design a "suspended arch bridge" because of the diagonal bracing he added between two eye-bar chains. This bridge "gave warning about the anchoring problems that structures at the downtown sites faced. After construction had been completed, the north anchorage proceeded to slip. A repair shoring up the anchorage with additional masonry joined to the structure's first anchor chain resolved the problem, however. Hermann Laub, who had experience working with Lindenthal, completed the repairs."
A streetcar company bought controlling interest of the 9th Street Bridge in 1889. By 1890 they had replaced the wooden spans with iron and steel trusses. Electric streetcar traffic was also a reason why Roebling's bridge was replaced by steel trusses in 1892.
At the interesting turn of the century, not only were the three bridges deemed too low, their piers did not align. So the War Department declared that all three needed to be replaced. It proved difficult to achieve the federally mandated clearance of 47' for the middle 180' without incurring grades over 3% in the shore spans. (Eventually the 3% requirement was relaxed because of the shift from animal-powered to motorized vehicles and the desire to minimize the impact on the shore side structures. All three bridges have approaches with a 4.175% grade.) Several truss designs were considered, some of them movable, before a design was developed that satisfied all of the traditional organizations. But a new 1911 Art Commission ruled that trusses are ugly and that they should build suspension bridges. But the B&O tracks on the north and the proposed boulevard development on the south side did not leave space for anchorages. And the existing two suspension bridges had suffered from anchorage movements. Fortunately, an English-language article describing the 1915 self-anchored bridge over the Rhine at Cologne, Germany became available "just as the county's first truss drawings were rejected as unsuitable."
They rebuilt the 7th and 9th Street Bridges during 1924-26. Then they rebuilt the 6th Street Bridge during late 1926-1928. They increased the disruption of commerce by taking two bridges out of service at the same time because of time pressure exerted by the War Department. The navigation channel was kept open during construction by using a cantilever construction technique. I did not understand how they did that until I found Sheet 2 in the Drawings (below). They did it by adding diagonal support members during construction. Those diagonals turned the eye-bar chain and the stiffening girder into a Howe Truss. They could do this because of the self-anchoring design. Specifically, the stiffening girder was designed to be strong enough to withstand all of the lateral force in the suspension chain. So it was strong enough to act as the bottom cord of a Howe truss. The 6th Street Bridge won the 1928 award for "The Most Beautiful Steel Bridge" constructed in 1928.
 |
| HAER PA,2-PITBU,78A |
Because the 450', 1,600 tone bowstring trusses of the 6th Street Bridge were still in good shape, the county paid to have them moved to a new bridge in Corapolis, PA. The contractor for the piers of the the Three Sister Bridges, Foundation Co., did it for $316,200 in 30 days.
I wish I could have found a photo for when the construction had advanced to building the main span by cantilevering it over the river from the towers.
 |
| AlleghenyCounty Seventh Street (Andy Warhol) Bridge under construction on October 21, 1925. (Courtesy of the Carnegie Library of Pittsburgh) |
JP Diroll Photography posted three photos with the comment: "PITTSBURGH GO BRAGH! Last night's journey to the roof of the Convention Center was really everything I needed to be. I had about an hour and a half all to myself, just to create. It was great. A lucky break to be sure. Once the sun went down, the greens of the bridge really started to shine. And reflect. The greens coming off the river might just be my favorite part of the whole scene."
[It was posted Mar 17, 2024. I presume the bridges are green because of St. Patrick's Day.]
 |
| 1 |
 |
| 2 |
 |
| 3 |
The rehabilitation of the 7th Street Bridge was done 2016-17 and cost $25.4m. 9th Street was rehabilitated in 2019-20 for $23.3m.
No comments:
Post a Comment