F rom its founding in 1764, St. Louis was the premier city in the American Midwest—a posi-tion that strengthened after the 1803 Louisiana Purchase opened up the vast American interior for

settlement. Given its location at the junction of the Mississippi and Missouri rivers, St. Lou-is became the essential connection point for freight traffic with the arrival of steamboats in the 19th century. Many different kinds of boats were required to traverse different sections of the Mississippi, Missouri, and Illinois rivers.

“It was kind of like an airline hub. Everyone had to put into port,” says Rob Moore, Ph.D., the historian of the National Park Service’s Jefferson National Expansion Me-morial in St. Louis.

But as boats gave way to trains, the city’s spirit as a commer-cial center was best exemplified by one of the great engineers in American history—James Buchanan Eads—a self-educated boat cargo salvager who, through intelligence, vision, and per-sistence, designed the revolutionary Eads Bridge across the Mis-

sissippi. The bridge represented a series of firsts: the first major bridge to use predominantly steel for its structural system, the first to use pneumatic caissons, and one of the first built using the cantilevered construction method.

St. Louis’s geographic advantage was ac-cepted “almost as a divine right,” wrote histo-rian and urban planner Robert W. Jackson in his book Rails Across the Mississippi: A History of the St. Louis Bridge (University of Illinois Press, Champaign, Illinois, 2001). But success bred complacency. By midcentury the railroad was gaining ground, and St. Louis underestimat-

ed its importance. Chicago, however, had not and became a major rival.

The first railroad connected East St. Louis, Illinois, just across the river, to the East Coast in 1857, but getting goods into the city posed a problem. Entrepreneurs employed steamboat ferries and even ferries carrying train cars, but nei-ther was a cost-effective substitute for bringing cargo directly across by rail.

[42] C i v i l E n g i n e e r i n g N O V E M B E R 2 0 1 7

A Pioneering Structure: The Eads Bridge

The bridge’s steel arches were built back-to-back

and held in place by guy wires that passed over temporary towers erected atop the piers.

. Hi s to ry Le s s on.

After the Civil War, the city arrived at a turning point. St. Louis was un-der tremendous pressure to maintain its status as a trade hub. “The idea of bridging the river was thought by a lot of visionary people in St. Louis to be a real necessity,” Moore says. But entrenched river interests did not want to see railroads cut into their business.

The man who would design the bridge was neither a bridge builder nor a formally trained engineer. Born in Indiana, Eads came with his fam-ily to St. Louis in 1833 at the age of 13. The family was penniless, and the boy peddled apples on the street be-fore he got a clerk’s job with dry goods merchant Barrett Williams. Williams opened his private library to Eads, who pro-ceeded to educate himself.

As a young man, Eads served as a purser on a steamboat carrying iron between St. Louis and Galena, Illinois. “Steamboats were a great form of transportation but not very long lived,” says Moore. There were hundreds of wrecks a year along the inland waterway, Moore notes. Although the river was relatively shallow, averaging 12 ft in depth, wrecks were difficult to find because of the sandy river bottom.

So salvaging cargo from those wrecks became lucrative work. Eads built special steamboats with twin hulls, much like a catamaran, according to Moore. From the center of the vessel, his crew could lower cranes to recover sunken cargo. He also developed a diving bell that allowed him to “walk” in the river and find wrecks. He later contributed design work to a series of ironclad gunboats for the Union Navy, predat-ing the more famous ironclads involved in the 1862 Civil War naval battle between the Union Monitor and Confeder-ate Merrimack.

Eads was a trusted voice on matters of the river, but he had no experience as an engineer. So why was he tasked with designing the bridge that would secure St. Louis’s future?

Some suggest Eads was appointed as bridge designer by the St. Louis and Illinois Bridge Company, the bridge builder, but Jackson maintained that Eads “took over” control of the com-pany through sheer force of will. He earned the confidence of others be-cause of his “drive, determination, or-ganizational abilities, and capacity for handling complex construction prob-lems,” Jackson wrote. He “probably knew more about the nature of the Mississippi River than any man alive,” and he also had the support of two re-spected, German-born engineers, Col. Henry Flad and Charles Pfeiffer.

According to Henry Petroski, Ph.D., P.E., Dist.M.ASCE, the Aleksan-

dar S. Vesic professor of civil engineering at Duke University and author of several books—including Engineers of Dreams: Great Bridge Builders and the Spanning of America (Alfred A. Knopf, New York, 1995)—Eads reasoned that an upright arch bridge could be economical-ly competitive with a suspension bridge “if it

could be made of a material whose capacity to carry a load without yielding in compression was not so inferior as was that of iron to its capacity to carry a load in tension.” There was such a material: cast steel.

But steel had never been used in any large structure before; according to Jackson, it was a “radical design that shattered engineering precedent.” Steel was thought to be “unsuitable for long-span bridges by virtually every engineer in America and Europe due to its high cost, the difficulties of its fabri-cation, and the belief that it became brittle in cold weather,” Jackson wrote.

Steel was stronger than iron, which could not have with-stood the stresses needed for a bridge of this magnitude, but Eads was nonetheless surrounded by skeptics. Andrew Carn-egie’s Keystone Bridge Company won the contract to pro-duce the steel for the bridge. But Carnegie’s engineering

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Although not formally educated as an engineer,

James Buchanan Eads designed the revolution-ary bridge in St. Louis that bears his name.

The completed bridge, which was 4,600 ft long, was designed to allow ferries and steam-

boats to pass beneath the deck. (The statues atop the piers were designed but not built.)

consultant held that Eads’ plan was “unsafe and imprac-tical.” And, as Moore points out, “Carnegie’s Keystone works couldn’t produce steel couplings without bubbles or inter-nal flaws.”

This might be why Carnegie was so reluctant. “Every-one would know where that steel came from and who was to blame,” says Moore. In the end, steel was used for most of the bridge deck structure, though wrought iron was used for the bridge couplings.

There were other challenges, too. Eads was worried about the amount of scour that the river might cause, so he insisted that the piers and abutments be founded on bedrock. This would mean that on the Illinois side, the bridge piers would have to extend as deep as 93 ft. On a trip to Europe, Eads saw builders in France using pneumatic caissons to construct a bridge in the Allier River near Vichy. Eads brought the idea back to the United States, and the Eads bridge became the first in the nation to use pneumatic caissons.

The first caisson at the Eads Bridge was sunk in October 1869. According to Jackson, the “air chamber inside the cais-sons would be about nine feet high and divided into three compartments, each connected by a permanent opening. The caisson would be composed of oak timbers, with riveted plate iron covering the entire outer surface. When properly caulked, each caisson would be air- and watertight. Pumps would force compressed air into the chambers at a pressure great enough to keep the water out.”

The caissons were the largest and deepest that had ever been dug, and their installation repre-sented the first significant use of com-pressed air to enable caissons to withstand increasing water pressures as they were sunk. But no one knew what effects such caissons would have on those working in-side of them, especially as they were sunk ever deeper beneath the riverbed.

The experience inside the caisson was surreal. There was a constant, loud hiss of escaping pressurized air. Normal con-versation sounded like high-pitched squawking. When workers tried to blow out candles, the flame would sometimes bounce off the roof and relight the can-dles. For a while, Petroski wrote, the caissons themselves became tourist at-tractions. In his book, he quoted one visi-tor who described going inside one as a nearly mythic visit to the underworld:

“Shrouded in a mantle of vapor, labored the workmen there loosening the sand; dim flickered the flames of the lamps, and the air had such a strange density and moisture that one wan-dered about almost as if he were in a dream.”

Workers were well compensated at $4 a day—twice what workers on land were making—but they had to con-tend with the often deadly prospect of working literally under high pressure. Workers began to complain of stom-ach pains, headaches, nausea, and paralysis. Decompression sickness—or “the bends”—occurs when nitrogen dissolves in the bloodstream at high atmospheric pressure; when the workers returned to the surface without taking enough time for decompression, the bubbles worked their way out of the bloodstream, bursting blood vessels and blocking the sup-ply of oxygen to vital organs, sometimes causing them to shut down.

Eads and his physician tried to improve the working con-ditions. He cut the working day to two 45-minute shifts. And he allowed eight minutes of decompression time for 50 lb of pressure; unbeknown to Eads, this wasn’t enough. On the project, 119 workers developed the bends. Of those, 13 died, two were permanently disabled, and 77 others were severely affected.

Eads and his crew also had their hands full designing the bridge’s cantilever procedure. Once the piers were built, arches were begun and extended from “either side of the central piers, supporting the heavy mass by guy wires that passed over tem-porary towers erected atop the piers—until the arch was com-

pleted and could support itself,” according to Petroski.

Engineers also used “hydraulic rams to adjust cable tensions, thus effectively em-ploying the cantilever principle to support balanced back-to-back arch sections until the completed arches could support them-selves,” Petroski wrote.

All that was left was to place the key-stone section to complete the steel arches. Unfortunately, by the summer of 1873, according to Petroski, unseasonably high temperatures had expanded the metal just enough to make the gap too small for the keystone piece. Engineers built a wooden trough along the length of the arch and packed it with ice to try to get the steel to contract. It didn’t work.

Eads developed the solution. As Petroski explained, Eads used a “screw

[44] C i v i l E n g i n e e r i n g N O V E M B E R 2 0 1 7

The caissons were the largest and deepest that had ever been dug, and their installation represented the first

significant use of compressed air to enable caissons to withstand increasing water pressures as they were sunk.

Engineers built a wooden trough

along the length of the arch and

packed it with ice to try to get the

steel to contract. It didn’t work.

mechanism capable of raising the completed arch a few inches, so that the supporting ca-bles could be slackened and could be removed. By cutting the ends off the too-long arch ribs, threading them, and inserting the screw mech-anism into the sprung arch, it was possible to close the arch” by September.

Bridge construction began in 1869 and was completed in 1874. The bridge was 4,600 ft long, with a 520 ft long center span and two side spans of 502 ft apiece. It contained two decks: an upper deck for pedestrians, wagons, and streetcars, and a lower deck for trains. (Eads also designed a tunnel system connecting the bridge to the train station in St. Louis. After decades of in-activity, these tunnels now serve the city’s light-rail system.)

The opening festivities, on July 4, drew 150,000 people and included a huge parade through the town, as well as marching bands and fireworks. General William Tecumseh Sherman drove in the last spike and opened the bridge. “It was very successful,” says Moore. “They ran 14 locomotives out on the bridge at the same time to test the span, and they even had an elephant walk across the bridge” to prove to the masses that it would hold.

The bridge cost $6.5 million; unfortunately, it was not a commercial success. Chicago had wrested economic control of the region, and within a few years, a single company con-trolled the railroad and the ferry in St. Louis. Crossing the river remained expensive, and Eastern financiers (including J.P. Morgan, who eventually took ownership of the bridge) took home most of the profits. By 1878 the bridge was los-ing money and was sold at public auction to pay off creditors.

But the strength of its design allowed the bridge to flour-ish within the transportation system of the city. The bridge’s

train tracks still serve a line on the city’s light-rail system. The bridge’s upper deck has long since been converted to vehicular use.

A significant, $48 million rehabilitation of the bridge began in 2012. According to a fact sheet from Metro, the agency that operates the St. Louis region’s public transit system, crews installed more than 1.16 million lb of steel to replace struts, bracing, and other sup-port steel that dated back to the 1880s. Nine

layers of paint, rust, and corrosion were blasted from the bridge, and more than 7,500 gal of a multilayer anticorro-sion coating were applied. Workers completed about 1,200 structural repairs to the bridge and rebuilt the concrete that supports the road deck. The work, completed in 2016, is expected to extend the life of the bridge by 75 years. (Read “Transit Agency Repairs Historic Eads Bridge,” Civil Engi-neering, March 2013, pages 18, 20, and 22.)

From the beginning people called it Eads’ Bridge or the Eads Bridge—one of the few major structures in the world, Petroski notes, that was named for its engineer. ASCE accord-ed the bridge landmark status in its Historic Civil Engineer-ing Landmark Program in 1971.

At the time of its completion, Eads was characteristically bold about the bridge’s future. “The bridge will exist just as long as it continues to be use-ful...to the people who come after us, even if its years should number those of the pyramids.” —t.r. witcher

T.R. Witcher is a contributing editor to Civil Engineering.

N O V E M B E R 2 0 1 7 C i v i l E n g i n e e r i n g [45]

Witcher

The Eads Bridge in St. Louis was the first major bridge to use predomi-

nantly steel for its struc-tural system, the first to use pneumatic caissons, and among the first to use the cantilevered construction method.

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