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This guest author post is written by Michael G. Smith, author of the new book Concrete Century: Julius Kahn and the Construction Revolution, from the University of Michigan Press. The book is now available in paperback, and ebook. All are welcome to attend the free book launch on Saturday, October 5th at the The Fisher Building in Detroit. Find more event details at albertkahnlegacy.org/events/save-the-date-concrete-century-book-launch/

At the turn of the 20th century, industrial manufacturing was expanding dramatically while factory buildings remained fire-prone relics of an earlier age. That is, until a 28-year-old civil engineer finally achieved what engineers around the world had unsuccessfully attempted. Julius Kahn invented the first practical and scientific method of reinforcing concrete with steel bars, which finally made it possible to construct strong, fireproof buildings.

Kahn was undoubtedly one of the most important inventors of the 2oth century, and also one of the least well known. Born in Germany, Kahn immigrated to the United States with his family in 1881 to avoid anti-Semitic oppression. By 1902, Kahn was an established civil engineer and a partner with his brother, Albert, in the architecture and engineering firm of Kahn and Kahn.

At the time, commercial and industrial buildings were nearly all constructed of brick and timber, just as they had been for many centuries. Industrial manufacturing, however, was rapidly advancing. The increasing use of highly flammable liquids and gasses in production resulted in fires becoming much more common. Once fire began in a factory of largely timber construction, it was difficult to control and usually consumed the entire building. Losses due to fire were increasing so rapidly that fire insurance costs spiked by 25 percent in 1902.

Beyond the threat of fire, buildings of timber construction were a poor match for the ever larger and heavier machines that were becoming common in manufacturing. Construction of oversize items, such as motor vehicles, required large, open areas for assembly, but the floors in brick and timber buildings were obstructed by numerous support columns that impeded the work flow.

There was a potential solution to the problem of inadequate buildings in the form of concrete. It was fireproof, widely available, and inexpensive. However, because it has no structural strength, it could only be used when fully supported from below, as with a sidewalk or basement floor.

It was apparent that concrete’s shortcoming might be overcome by reinforcing concrete beams with metal rods, making it possible to construct a building of the material. A small number of buildings had been constructed in this manner prior to 1900, but they were considered experimental. The manner and amount of metal embedded in the concrete was based entirely on guesswork; there was no scientific theory to guide engineers. With brick, stone, timber, and steel there were well-established calculations that specified exactly how a structure should be built in order to support a given amount of weight.

To overcome this lack of engineering data, the few architects and engineers that attempted concrete construction used excessive amounts of steel and concrete to assure the building would remain standing. Because the structures were so overbuilt, they were quite expensive to construct and the cost could only be justified by firms that processed highly flammable materials or explosives. There were a few non-industrial structures built in this manner, such as the Leland Stanford Jr. Museum in Palo Alto. Though expensive, concrete was used in place of the far more costly dressed stone from which the museum was originally planned to be built. By treating the surface of the concrete to give the appearance of stone, the cost of the building was reduced.

The problem that vexed engineers and scientists was that concrete behaved unpredictably. In an effort to develop a theory of concrete behavior, numerous tests were conducted using concrete beams reinforced with rods of many types. Square rods, round rods, twisted rods, deformed rods, all were tried, but the results were consistently inconsistent. When a test load was placed on these beams, they would sometimes hold up a great deal of weight, but at other times would fail under a disappointingly small amount. Sometimes the beam would fail due to a large crack opening up along the bottom. At other times the steel reinforcement would slip loose from the concrete allowing the beam to fail. Most puzzling of all was when the concrete beneath the reinforcement rod broke loose from the beam, allowing the rod to separate from it and cause failure.

A professor of engineering at Purdue University, William Kendrick Hatt, performed a wide range of experiments. His work, however, came to naught, with Hatt conceding in a paper published January 1902, “Considering all the elements affecting the strength of reinforced beams, . . . it is evident that the use of refined theories of computation are not justified.” In other words, it was not feasible to develop a theory for determining the construction and strength of a concrete beam.

In spite of Hatt’s conclusion, 28-year-old civil engineer Julius Kahn accomplished exactly what Hatt said couldn’t be done. Working in his brother’s basement in Detroit during the summer of 1902, Kahn not only developed a scientific theory of reinforced concrete, he invented a new type of reinforcement bar that solved the shortcomings of previous attempts.

In 1903 Kahn established a company to manufacture his reinforcement bars. Within months, architects and engineers were putting up building after building using the “Kahn System” of concrete construction. By 1910, more than 5,000 buildings of all types had been constructed. Among them were massive auto factories, hotels, government buildings, department stores, enormous warehouses, and even homes. By solving the riddle of reinforcing concrete so it could be used simply and economically to construct multi-story buildings, Kahn affected nearly every aspect of daily life. Factories became safer and far more efficiently matched to manufacturing requirements, including the moving assembly line. Fireproof hotels of concrete were sought out by travelers who no longer needed to fear being burned alive on an upper floor. Slaughtering and food processing could be carried out in buildings that were more impervious to animal infestation and could be hosed out to maintain cleanliness. Bridges of concrete were safer, substantially less expensive, and required significantly less maintenance than those of steel.

The foundational advances made by Julius Kahn in construction technology were well recognized during his lifetime. Writing in 1906, just three years after Kahn received a patent for his system, Captain John Sewell of the United States Army Corps of Engineers and a leading construction expert credited Kahn with the advances that made concrete construction practical: “Very important advances have been made in the United States . . . by Julius Kahn of Detroit.” Looking ahead Sewell stated that the Kahn reinforcement bar had removed all previous “limitations as to [concrete’s] possible uses” and “this century is likely to be known as the Concrete Age.” Concrete certainly came of age in the last century, in fact, concrete is the most used man-made material on the planet. Yet the man who made it all possible is barely known, or was until the publication of Concrete Century; Julius Kahn and the Construction Revolution. This new book tells the story of how a young Detroiter solved a problem that had confounded the world’s best scientists and engineers.