Industrial History: 1887+1901 GAP Trail/LTV/J&L Connecting Hot Metal Bridge over Monongahela River in Pittsburgh, PA

(Bridge Hunter; HAER; Historic Bridges, Hot Metal; Historic Bridges, Mon Con; PGHbridges; 3D Satellite)

Out-of-service: May 1979. But the bridge remained because it was carrying 20 utility lines including water, steam, gas and power lines. [PA277B]

It now serves vehicles and the Great Allegheny Passage (GAP) Trail.

(Update: the content concerning the Jones and Laughlin Steel mills has been moved to here.)

There are two truss bridges using shared piers. The Monongahela Connecting RR Bridge is on the upstream side and was reopened for road use in 2000. The Hot Metal Bridge was reopened for trail use in 2007. [PGHbridges] When the Mon Con was converted to street use, they removed a very wide shared truss on the north end. [Historic Bridges]

Bryan Rubican posted
The Monongahela Connecting Railroad Bridge and the Hot Metal Bridge, once part of the sprawling J&L Steel complex.
[The upstream side is on the right.]

These two bridges connected the Pittsburgh Works with the South Side Works of Jones and Laufphlin Steel.

Photo from HAER PA,2-PITBU,65C--6 from pa2798

In 1887, a railroad bridge was constructed to link the the two sides of the operation. The upstream side carried two tracks for the Monongahela Connecting Railroad. The downstream side carried a single track used to shuttle hot metal from the furnaces to the rolling mills. Previous to this direct connection, the metal had to be reheated before being worked....Because the bridges share piers and have similar truss designs, the pair are usually referred to simply as The Hot Metal Bridge. It is more accurate to give this name only to the downstream side. The floor of this side has metal plates lining the floor -- protecting the river traffic and the wooden ties from the molten metal and sparks spewing from the opening in the top of each ladle railroad car. [PGHbridges]

The hot metal bridge was added in 1899. [HAER]

Jones & Laughlin Steel Corporation began a program in 1960 to improve steel production. One of the areas was to replace the fleet of 80 ton submarine ladles with 165 ton ladles. This required considerable work on the Hot Metal Bridge in order for the Mon Con to handle the heavier and longer submarine ladles. The first phase was to reduce the dead load. This was accomplished by removing the heavy fire brick trough that made up the deck system and replacing it with a light steel plate covered with granulated slag. This was necessary to prevent any hot metal splashing into the river. This work was done under traffic by company forces. The second phrase was to strengthen the top chord truss members. This was done by drilling holes in the web of the truss members and bolting with high tensile bolts through reinforcing plates. Over 7,000 bolts were placed. The work was designed by Structural Associates of Pittsburgh and erected by company forces. [PA277C]

Kenny Hall posted
" Monongahela 1947...Lawrence Gipe..oil painting

Tim Roolf commented on Kenny's post, cropped
The hot metal bridge, still delivering traffic from the south side to second avenue. Motor vehicles on the left and bikes/pedestrians on the right.

Dave Kuntz Drone Photos posted
Pleased to mention that I got honorable mention for the 2025 Great Allegany Passage photo contest! This photo features a motorboat going under the Hot Metal Bridge in Pittsburgh, which once was a very busy railroad and is now a bike trail and roadway.

Mr. P. Explores posted 18 photos with the comment:

The Hot Metal Bridge crossing the Monongahela River in Pittsburgh is one of the city’s finest surviving pieces of industrial infrastructure; a bridge that once carried glowing, nearly 3,000-degree molten iron between two halves of one of America’s great steelmaking complexes, and today carries cyclists and pedestrians through the remains of that industrial landscape.
The history of the crossing goes back to the Jones & Laughlin Steel Company, whose enormous Pittsburgh Works occupied both sides of the Monongahela. J&L’s Eliza blast furnaces stood on the north side of the river, in what is now the Pittsburgh Technology Center/South Oakland area, while its Bessemer converters, open-hearth furnaces, rolling mills and other facilities spread across the South Side. Before the bridges were built, moving material between the two halves of the plant was considerably more difficult, at one point requiring a railroad-car ferry across the river. J&L organized the Monongahela Connecting Railroad in 1885 to tie its operations together and improve the movement of raw materials and finished products.
The first railroad bridge across the river here opened in 1887. As J&L expanded rapidly during the closing years of the 19th century, however, the company needed something more specialized. Construction of the present Hot Metal Bridge began in 1899, with J&L widening the existing river piers to accommodate the additional structure. The bridge was designed by the structural department of Jones & Laughlin Limited and fabricated and erected by the Edgemoor Bridge Works of Delaware. Company records indicate that it was completed by early 1901 at a cost of $441,882; an enormous industrial investment at the time.
The result was essentially a pair of industrial railroad bridges standing alongside one another on shared piers. Although the entire crossing is commonly called the Hot Metal Bridge today, the bridges originally performed different jobs. The main Monongahela Connecting Railroad bridge handled conventional railroad traffic and movement throughout the sprawling J&L complex, while the downstream Hot Metal Bridge had a far more spectacular purpose: carrying molten iron directly from the Eliza blast furnaces across the river to the steelmaking furnaces on the South Side.
That is exactly where the wonderfully industrial name “Hot Metal Bridge” comes from. “Hot metal” was freshly smelted molten iron, still close to 3,000 degrees Fahrenheit. Special railroad ladle cars carried the glowing liquid iron across the bridge before it had time to cool and solidify. The bridge deck was protected with metal plating because sparks and molten material could spill from the open-topped ladles as they crossed high above the river. It was less a conventional railroad bridge than a moving artery in a gigantic steelmaking machine.
Architecturally, the Hot Metal Bridge is pure industrial engineering. Roughly 1,174 feet [358m] long, it consists of multiple steel truss spans resting upon massive masonry piers, with its largest span measuring about 321 feet [98m]. The trusses were constructed of open-hearth or Bessemer steel, with pin-connected members typical of heavy railroad bridge construction of the period. Rather than attempting to disguise its function with elaborate decoration, practically every visible part of the bridge exists because it had a job to do; carry extraordinarily heavy loads safely across the Monongahela.
And those loads could be extraordinary. At the height of operations, trains reportedly moved approximately 4,300 tons of molten iron across the bridge every day. During World War II, when Pittsburgh’s mills ran around the clock supplying the American war effort, an astonishing amount of the nation’s steelmaking capacity depended upon material crossing this bridge. Estimates cited by the Great Allegheny Passage place it at roughly 15 percent of American steelmaking capacity during the war years.
For generations of Pittsburgh steelworkers, this was not an historic landmark; it was simply part of the workplace. Locomotives, ladle cars, smoke, steam, sparks and molten iron traveled between a landscape packed with blast furnaces, smokestacks, rail lines, cranes, mills and industrial buildings. The bridge existed inside one of the most intensely industrialized landscapes in the United States.
Then came the collapse of Pittsburgh’s traditional steel industry.
Jones & Laughlin became part of LTV during the 1970s, while the region’s enormous integrated steelmaking industry entered its long decline. The Hot Metal Bridge ceased carrying railroad traffic in May 1979 after LTV replaced the South Side open-hearth furnaces with electric-arc furnaces, eliminating the need to move molten blast-furnace iron across the river. The Eliza furnaces were subsequently demolished, and by the 1980s much of the former J&L Pittsburgh Works was shutting down and disappearing.
The landscape surrounding the bridge changed almost beyond recognition. Where blast furnaces and heavy industry once stood north of the river arose the Pittsburgh Technology Center and, farther east, the redevelopment now known as Hazelwood Green. On the South Side, much of the former mill property became SouthSide Works, replacing furnaces and industrial buildings with offices, apartments, stores and other development. Yet remarkably, the bridges remained.
Rather than demolish them, Pittsburgh eventually found new purposes for both structures. The former main railroad bridge was rehabilitated and opened to automobile traffic in 2000, connecting Second Avenue with South 29th Street/Hot Metal Street. The actual downstream Hot Metal Bridge remained unused longer, until a major rehabilitation transformed it into a dedicated bicycle and pedestrian crossing. It reopened in 2007, complete with trail connections and ramps linking the riverfront paths on both sides of the Monongahela.
Today the Hot Metal Bridge has become an important link in Pittsburgh’s recreational trail network and carries the Great Allegheny Passage as it approaches downtown Pittsburgh. Walkers and cyclists now travel the same general route once taken by trains carrying thousands of tons of molten iron. In 2016, the bridge was inducted into the North America Railway Hall of Fame, recognition of the remarkable role it once played in American industry.
Perhaps that is what makes the Hot Metal Bridge such a perfect Pittsburgh structure. It wasn't preserved by freezing it in time or turning it into something completely disconnected from its past. It still works. It still carries people across the Monongahela. Its enormous steel trusses still dominate the riverfront, surrounded by neighborhoods and redevelopment that grew from the remains of the mills it once served.
More than a century ago, glowing iron crossed this bridge on its way to becoming the steel that helped build railroads, skyscrapers, bridges, automobiles, ships and machinery across America. Today you can walk or ride a bicycle through those same trusses and look across a dramatically different Pittsburgh.
The furnaces are gone. The ladle trains are gone. Much of Jones & Laughlin's Pittsburgh Works has vanished. But the bridge remains; an enormous piece of the machinery of the Rust Belt that Pittsburgh managed to give a second life. And what a thing to document on a humid summer afternoon in August! Enjoy the photos and have an excellent Sunday out there, all! -Mr. P.
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