Three Sisters Bridges

The Three Sisters Bridges are three iconic eyebar suspension bridges over the Allegheny River in Pittsburgh, Pennsylvania.

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The Three Sisters Bridges are three nearly identical eyebar suspension structures over the Allegheny River between downtown and the North Shore of Pittsburgh. The designs were the result of a compromise with the federal government because of the required horizontal and vertical clearances for the river navigation channel. ¹ The structures were also the result of aesthetic and financial considerations, and the lack of adequate anchorage points along the river banks.

The River and Harbor Act, passed by Congress in 1899, required the Secretary of War to declare bridges over navigable bodies of water in violation if they posed an obstruction to the free navigation of such waters because of insufficient height or width. ^{2 3} Local district engineer Captain William L. Sibert reported that the bridges were not in compliance, but he was overruled by the Secretary of War Elihu Root in 1904. A 1911 ruling by the Bixby Board, a War Department committee, stated that the structure would not need to be razed to meet height requirements. That primarily influenced Allegheny County’s decision to purchase the bridges from their respective private owners through a bond issue that March.

In 1915, Secretary of War Newton D. Baker determined that the Sixth, Seventh, and Ninth Street bridges had insufficient vertical clearance and needed to be raised. ³ In 1917, seeing no traction toward the matter, he imposed deadlines for raising the bridges.

For boats needing 32.6 feet of clearance, typically steamboats with lowered stacks, navigation was impossible for periods ranging from 14 days at Thirtieth Street to 105 days at Sixth and Ninth Streets, and for the entire year at Sixteenth and Forty-Third Streets. ² Additionally, uneven pier placements in the river made for dangerous conditions because of the river’s swift currents and frequent fluctuations in water level. These considerations proved instrumental in determining specifications that the bridges would need to meet by the 1920s.

Raising funds for the project to raise or rebuild the Sixth, Seventh, and Ninth Street bridges was a daunting task, as the municipal government had gained a reputation for corruption. ² Voters were suspicious of undesignated allocations for public works projects such as last-minute bond proposal that was initiated by the county in 1920. The Chamber of Commerce recommended that a $35 million bond election be postponed until 1921 to make its specific details available to the public.

Unfortunately, voters rejected the 1921 bond issue that would have supplied $35 million for the bridges, among other projects. ² Mistrust in government resulted in reform candidates being elected who had promised to clean up local government, but their inexperience and a lack of connections led to the bridge project being postponed. Ironically, those reform-minded officials were voted in 1924 out by candidates that promised the bridges, among other projects, would benefit all of Pittsburgh’s citizens. In that same year, voters approved a $29.2 million bond issue to finance the construction of new bridges, roadways, and municipal buildings. ^{2 3}

Four design proposals were initially evaluated. One included a circa 1910 design by F. A. Glafey, the former chief designing engineer of the Keystone Bridge Company and of the American Bridge Company. ² Another plan from A. A. Henderson proposed reusing the existing bridge and propping it on jacks that could be raised or lowered depending on water levels. This idea was rejected by the War Department as a single jack’s malfunction would make the entire bridge inoperable.

In order to avoid fines from the War Department for noncompliance, the county began preparing plans in 1923 and by 1924, began razing the Seventh Street Bridge. ² The War Department forced the county to begin work on the Ninth Street Bridge despite local opposition to the inconvenience and pleas for time extensions.

Engineers prepared several options using steel trusses to meet the vertical and horizontal navigation clearances and ultimately recommended three: a conventional lift structure with a platform nestled under the northern span provided the Baltimore & Ohio Railroad sufficient clearance below street traffic at the River Avenue and Federal Street intersection; a fixed truss structure with a parabolic top chord with a main span of 410 feet, two other main spans, and two approach spans; and a continuous truss structure at Sixth and Ninth Streets designed by the city Bureau of Architecture and a cantilever structure designed by Rutan, Russel & Wood at Seventh Street. ² The plans were the cumulation of compromise between a dozen organizations.

The proposals went to the Art Commission for suggestion and approval. ² The advisory body, created by the state in 1911 to approve bridges in the city costing more than $25,000, was expected to sign off on the project. Instead, it vetoed the plans, taking issue with aesthetics, desiring bridges that would not mar the downtown skyline with metal structures above the deck.

Under the auspices of the Department of Public Works, architect Stanley L. Roush, chief engineer Vernon R. Covell, design engineer A.D. Nutter, and consulting engineer T.J. Wilkerson, ³ an eyebar suspension bridge was proposed at all three crossings. ^{2 3} The renderings were considered unrealistic from an engineering perspective and the plans had to be substantially reworked. ² With the railroad right-of-way on the northern shore and a planned boulevard on the southern shore, engineers lacked adequate anchorages. They considered whether the bridge’s own forces could provide a system of support, with the piers bearing all vertical forces, after examining literature and reports of similar bridges in Cologne, Germany. The bridge types would be the first built in the United States.

After it was decided to erect the suspension bridge with a cantilever method, the county advertised the bids for construction and awarded the contract for the three bridges’ superstructure to the American Bridge Company and the substructure to the Foundation Company of New York. ² By building all three bridges at a single price and with relative uniformity, the county was able to save $500,000 off of the project budget.

Sixth Street Bridge

The first petitioners to build bridges across the Allegheny and Monongahela rivers received charters on March 20, 1810, but they lapsed because of a lack of progress owing to the state legislature’s issues with chartering banks within the state. ² Specifically, the legislature had refused a charter application from the Bank of Pittsburgh in 1810, which had promised to fund the proposed bridge projects with $20,000. New charters for the Allegheny Bridge Company were finally obtained on February 17, 1816.

The St. Clair Bridge, a covered Theodore Burr arch truss crossing constructed by a local contractor named Lothrop for $80,000, opened over the Allegheny River in late 1819. ^{1 2} Located along St. Clair Street (later Sixth Street), it boasted a total length of 1,037 feet with four spans each 185 feet in length, another that was 170 feet in length, and another that was 137 feet in length. ² Iron bars one inch in diameter provided vertical ties between the floor system and the arches. Stone piers supported the spans which were joined to each other by removable iron bolts in case a particular span needed repairs.

The opening of the bridge was celebrated with a banquet that was eaten across the entire length of the structure. ² The Allegheny Bridge Company showed consistent profits, with the rate of dividends increasing steadily from 3% in 1823 when it was first paid to 15% by the mid-1840s.

A charter supplement in 1857 allowed for the bridge to be replaced, and the St. Clair Bridge was completely reconstructed between 1857 and 1860 with a suspension bridge designed by John A. Roebling. ² Only some stone was saved for reuse. The new structure, built at the cost of $300,000, nearly doubled the largest span lengths of the previous iteration, with two main spans of 344 feet between two approach spans of 177 feet and 171 feet. It had a deck with of 40 feet with a roadway width of 20 feet with two eight-foot sidewalks.

Subsequent to the reconstruction, the company became known as the Suspension Bridge Company and it marketed itself more aggressively while reducing the tolls to a penny for male pedestrians and nothing for female pedestrians, while also publicizing incentives rewarding companies whose members committed to using the bridge. ² It paid off with dividends increasing in the years after the bridge reopened.

In 1868, Pittsburgh annexed the East End and renamed city streets, preferring for numbered sequences over names of founders or landmarks. ² The St. Clair Bridge became more simply the Sixth Street Bridge.

In the 1870s, two street railway tracks were added but the advent of heavier and wider electric streetcars in 1890 overburdened the bridge. ² While still in good structural shape, the exterior strands on the cables were showing excessive wear while the iron components were corroding from steamboat smoke.

In the early 1890s, the Allegheny Bridge Company sought to rebuild the Sixth Street Bridge to accommodate heavier and wider electric streetcars, along with providing additional space for passenger and vehicular loads. ² After a design competition was held, the Lohse system of inverted arches was selected. It would include a three-hinged inverted arch in the lower chords. But before any work could begin, the bridge company changed its mind on the design, instead selecting a simpler pin-connected bowstring truss design by Theodore Cooper.

The Drake & Stratton Company received a contract for substructure work while the Union Bridge Company received a contract for superstructure work. ² The new bridge was completed at the cost of $560,000 in 1892. It included two main spans flanked by approach spans of 105 feet and 48.6 feet in length.

The River and Harbor Act, passed by Congress in 1899, required the Secretary of War to declare bridges over navigable bodies of water in violation if they posed an obstruction to the free navigation of such waters because of insufficient height or width. ² It was determined that the Sixth Street Bridge, with a vertical clearance of 33.4 feet above the Davis Island pool, needed to be raised by 13.6 feet. A 1911 ruling by the Bixby Board, a War Department committee, stated that the bridge would not need to be razed to meet height requirements, and influenced Allegheny County’s decision to purchase the bridge from the Allegheny Bridge Company. Work on raising the bridge was mandated to begin by 1919 with completion by 1920.

The Secretary of War specified that the Sixth Street Bridge would need three spans between present abutments with at least 400 feet of horizontal clearance between piers, with 47 feet of vertical clearance above the Davis Island pool which had to be maintained for at least 180 feet. ²

The advent of World War I delayed the start of work until April 2, 1920, but it received a two-year extension. ² Finally, in March 1924, work on the Sixth Street Bridge began by the Foundation Company and the American Bridge Company. It was decided that the superstructure would be reused in Coraopolis, twelve miles away, saving the county $350,000. Under the guise of the Foundation Company, workers removed half of the roadway at a time, leaving pedestrian areas accessible until the structure itself needed to be moved, in order to minimize disruptions for nearby residents who relied on the bridge.

Instead of shifting the spans off piers for lowering, the Foundation Company lowered the old structure in position, lopping off the masonry and rigging temporary supports while the superstructure was lowered with straps and jacks. ² Workers made a pontoon out of two pairs of barges which carried the bridge down the Allegheny and Ohio Rivers. When workers reached the Manchester Bridge, they had to adjust the structure to fit under it. After supporting the bridge under the floor beams, they disassembled the top chord and stabilized each panel point on the trusses. Reversing the process and using the same jacks and straps, the superstructure was raised on new piers and abutments and the process was finished 30 days after the project began.

Meanwhile, the Foundation Work completed the substructure of the new Sixth Street Bridge four months ahead of schedule. ² The American Bridge Company fabricated two-fifths of the superstructure in its Ambridge shop during the winter. The new Sixth Street Bridge opened for pedestrians on the downstream sidewalk on September 14, 1928, ^{2 3} and was completely open to everyone else on October 19. ²

The crossing was named the “Most Beautiful Steel Bridge of 1928” by the American Institute of Steel Construction. ¹

The Sixth Street Bridge was painted in its signature Aztec gold in 1975. ³ The crossing was listed on the National Register of Historic Places in 1986 and designated as an architecturally significant structure by the Pittsburgh History & Landmarks Foundation in 1988.

In August 1998, the Sixth Street Bridge was renamed the Roberto Clemente Bridge after the legendary Pittsburgh Pirates player, the first Latin American and Caribbean player to be inducted into the National Baseball Hall of Fame. ³

The Roberto Clemente Bridge closed for a $34.4 million rehabilitation on February 14, 2022, and is expected to reopen in December 2023. ⁵ Work will involve replacing the corroded tie-down system at the ends of the bridge with four steel pins with self-lubricating bronze washers in an attempt to create a seal from water. ⁴ The tie-downs comprised of a couple of eyebars that passed down through the bottom of the piers to engage the weight of the pier to hold the end of the bridge down. Other work will involve replacing the deteriorated steel buckle plate structural deck with reinforced concrete and replacing thousands of rivets with high-strength bolts with button heads to mimic the look of rivets.

Seventh Street Bridge

In a bid to compete with the popular Sixth and Ninth Street bridges, the North Side Bridge Company was formed. ² It hired famous bridge builder Gustav Lindenthal to design a stiffened chain suspension bridge at Seventh Street. Three towers carried chains supporting two main spans of 320 feet each and two approach spans of 165 feet each. A pair of eye bars instead of wire comprised the chains which provided a stiffness that lacked in traditional wire suspension crossings. Lindenthal referred to it as a suspended arch bridge because of the unusual web bracing between the top and bottom chains. The new Seventh Street Bridge opened in 1884.

The River and Harbor Act, passed by Congress in 1899, required the Secretary of War to declare bridges over navigable bodies of water in violation if they posed an obstruction to the free navigation of such waters because of insufficient height or width. ² It was determined that the Seventh Street Bridge, with a vertical clearance of 35 feet above the Davis Island pool, needed to be raised by 12.1 feet. A 1911 ruling by the Bixby Board, a War Department committee, stated that the bridge would not need to be razed to meet height requirements, and influenced Allegheny County’s decision to purchase the bridge from the North Side Bridge Company. Work on raising the bridge was mandated to begin by September 28, 1918, with completion by 1920.

The Secretary of War specified that the Seventh Street Bridge would need three spans between present abutments with at least 350 feet of horizontal clearance between piers, with 47.1 feet of vertical clearance above the Davis Island pool which had to be maintained for at least 180 feet. ²

The advent of World War I delayed the start of work until April 2, 1920, but it received a two-year extension. ² Finally, in September 1924, the Seventh Street Bridge was razed and construction for the new eyebar suspension bridge began by the Foundation Company and the American Bridge Company. Erection began in July 1925 with the driving of wood piles to place metal bents on both sides of the main span, with the last girder being installed in February 1926. The bridge was opened for traffic on June 17. ^{2 3}

The Seventh Street Bridge was painted in its signature Aztec gold in 1975. ³ The crossing was listed on the National Register of Historic Places in 1986 and designated as an architecturally significant structure by the Pittsburgh History & Landmarks Foundation in 1988.

On March 18, 2005, the Seventh Street Bridge was renamed the Andy Warhol Bridge after the famous Pittsburgh-born visual artist and filmmaker. ³ The crossing was officially rechristened with a day-long celebration coinciding with the 10th anniversary of the nearby Andy Warhol Museum.

The Andy Warhol Bridge underwent rehabilitation in 2016-18 at the cost of $25.5 million. ³ Work involved replacing the corroded tie-down system at the ends of the bridge with four steel pins with self-lubricating bronze washers in an attempt to create a seal from water. ⁴ The tie-downs comprised of a couple of eyebars that passed down through the bottom of the piers to engage the weight of the pier to hold the end of the bridge down. Other work involved replacing the deteriorated steel buckle plate structural deck with reinforced concrete and replacing thousands of rivets with high-strength bolts with button heads to mimic the look of rivets.

Ninth Street Bridge

In 1835, the St. Clair Bridge and the Pennsylvania Canal provided the only crossings over the Allegheny River between Pittsburgh and Allegheny. ² A charter granted in 1836 permitted the Pittsburg & Allegheny Bridge Company to construct a third structure, joining Hand Street (later Ninth Street) in Pittsburgh with Chestnut Street (also known as Greyasoto Lane and later Anderson Street) in Allegheny. The company selected Pagan, Alston & Company to erect stone work for the cost of $37,000, paid an unknown contractor $10,000 for the approaches, and hired Le Baron & Lothorp for the superstructure for the cost of $33,000. Also included in the construction project was a bridge to carry the West Pennsylvania Railroad over the Pennsylvania Canal on the Allegheny side (near Canal Street), paving of a road from the canal to the river crossing, and a tunnel through the Allegheny approach to make way for the Pittsburg & Western Railway tracks.

The economic Panic of 1837 slowed construction, but the company continued foundation work while it awaited better financial conditions. ² Local opposition, fearing that cross-river construction would intensify floods on the river, forced bridge work to cease until 1838 when the company guaranteed that its structures would not impede river flows.

The Hand Street Bridge finally opened in 1840. ² The covered Burr arch truss, the third largest in the nation, boasted a total length of 990 feet with a single span of 190 feet and four spans each 200 feet long. Three lines of arch trusses divided the roadway into two sections each 11 feet wide. Cantilevered sidewalks added seven feet to each side of the bridge.

Ice damaged a pier on the Hand Street bridge in 1857 so severely that the crossing had to be closed to traffic until repairs could be completed. ² In 1868, Pittsburgh annexed the East End and renamed city streets, preferring numbered sequences over names of founders or landmarks. ² The Hand Street Bridge became more simply the Ninth Street Bridge.

In 1889, the Pleasant Valley Electric Street Railway Company purchased controlling stock in the Pittsburgh & Allegheny Bridge Company, allowing the entity to dictate a new Ninth Street Bridge to its specifications. ² The railway provided funds to construct a riveted steel and wrought iron Pratt through truss bridge with room for four streetcar tracks. Work began on the crossing by the Iron City Bridge Company in 1889 and was completed by the fall of 1890. The new crossing boasted room for four streetcar tracks, and three main spans of 205 feet each flanked by approach spans of 152.6 feet and 80 feet.

The River and Harbor Act, passed by Congress in 1899, required the Secretary of War to declare bridges over navigable bodies of water in violation if they posed an obstruction to the free navigation of such waters because of insufficient height or width. ² It was determined that the Ninth Street Bridge, with a vertical clearance of 33.6 feet above the Davis Island pool, needed to be raised by 13.7 feet. A 1911 ruling by the Bixby Board, a War Department committee, stated that the bridge would not need to be razed to meet height requirements, and influenced Allegheny County’s decision to purchase the bridge from the Pittsburgh & Allegheny Bridge Company. Work on raising the bridge was mandated to begin by September 28, 1918, with completion by 1920.

The Secretary of War specified that the Ninth Street Bridge would need three spans between present abutments with at least 350 feet of horizontal clearance between piers, with 47.5 feet of vertical clearance above the Davis Island pool which had to be maintained for at least 180 feet. ²

The advent of World War I delayed the start of work until April 2, 1920, but it received a two-year extension. ² Finally, in March 1924, the Ninth Street Bridge was razed and construction for the new eyebar suspension bridge began by the Foundation Company and the American Bridge Company. Erection began in July 1925 with the driving of wood piles to place metal bents on both sides of the main span. The bridge was opened for traffic on November 26. ^{2 3}

The Ninth Street Bridge was painted in its signature Aztec gold in 1975. ³ The crossing was listed on the National Register of Historic Places in 1986 and designated as an architecturally significant structure by the Pittsburgh History & Landmarks Foundation in 1988.

On April 22, 2006, the Ninth Street Bridge was renamed the Rachel Carson Bridge after Springdale native and Chatham University alum who became a renowned environmentalist and author who sparked the creation of the U.S. Environmental Protection Agency. ³

The Rachel Carson Bridge underwent rehabilitation in 2019-20 at the cost of $23.3 million. ⁵ Work involved replacing the corroded tie-down system at the ends of the bridge with four steel pins with self-lubricating bronze washers in an attempt to create a seal from water. ⁴ The tie-downs comprised of a couple of eyebars that passed down through the bottom of the piers to engage the weight of the pier to hold the end of the bridge down. Other work involved replacing the deteriorated steel buckle plate structural deck with reinforced concrete and replacing thousands of rivets with high-strength bolts with button heads to mimic the look of rivets.

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Gallery

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Details

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Sources

1. “Three Sisters Bridges, Sixth Street Bridge, Spanning Allegheny River at Sixth Street, Pittsburgh, Allegheny County, PA.” Library of Congress.
2. Hawley, Haven. “Three Sisters Bridges, Spanning Allegheny River at Sixth, Seventh & Ninth Streets, Pittsburgh, Allegheny County, PA.” Library of Congress, Aug. 1998.
3. “History of the Sister Bridges.” Allegheny County Public Works and Facilities Management.
4. “No. 9 – Andy Warhol (7th street) bridge rehabilitation.” Roads & Bridges, 5 Nov. 2018.
5. “Roberto Clemente Bridge to close on Feb. 14 for bridge rehabilitation project, expected to reopen in Dec. 2023.” WTAE, 2 Feb. 2022.