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History

Rebar inside the Leaning Tower of Nevyansk

Reinforcing bars in masonry construction have been used since at least the 15th century (2,500 meters of rebar was used in the Château de Vincennes). During the 18th century, rebar was used to form the carcass of the Leaning Tower of Nevyansk in Russia, built on the orders of the industrialist Akinfiy Demidov. The cast iron used for the rebar was of high quality, and there is no corrosion on the bars to this day. The carcass of the tower was connected to its cast iron tented roof, crowned with one of the first known lightning rods. However, it was not until the mid-19th century that rebar displayed its greatest strengths with the embedding of steel bars into concrete, thus producing modern reinforced concrete. Several people in Europe and North America developed reinforced concrete in the 1850s. These include Joseph-Louis Lambot of France, who built reinforced concrete boats in Paris (1854) and Thaddeus Hyatt of the United States, who produced and tested reinforced concrete beams. Joseph Monier of France is one of the most notable figures for the invention and popularization of reinforced concrete. As a French gardener, Monier patented reinforced concrete flower pots in 1867, before proceeding to build reinforced concrete water tanks and bridges.

The Alvord Lake Bridge in San Francisco's Golden Gate Park

Ernest L. Ransome, an English engineer and architect who worked in the United States, made a very significant contribution to the development of reinforcing bars in concrete construction. He invented twisted iron rebars, which he initially thought of while designing self-supporting sidewalks for the Masonic Hall at Sockton, California. His twisted rebar was, however, not initially appreciated and even ridiculed at the Technical Society of California, where members stated that the the twisting would weaken the iron. In 1889, Ransome worked on the West Coast mainly designing bridges. One of these, the Alvord Lake Bridge in San Francisco's Golden Gate Park, was the first reinforced concrete bridge built in the United States. He used twisted rebar in this structure.

At the same time Ernest L. Ransome was inventing twisted steel rebar, C.A.P. Turner was designing his "mushroom system" of reinforced concrete floor slabs with smooth round rods and Julius Kahn (inventor) was experimenting with an innovative rolled diamond-shaped rebar with flat-plate flanges angled upwards at 45° (patented in 1902). Kahn predicted concrete beams with this reinforcing system would act in bending like a Warren Truss, and also thought of these rebars as shear reinforcement. Kahn's reinforcing system was built in concrete beams, joists, and columns. The system was both praised and criticized by Kahn's engineering contemporaries: C.A.P. Turner voiced strong objections to this system as it could cause catastrophic failure to concrete structures. He rejected the idea that Kahn's reinforcing system in concrete beams would act as a Warren Truss and also noted that this system would not provide the adequate amount of shear stress reinforcement at the ends of the simply supported beams, the place where the shear stress is greatest. Furthermore, Turner warned that Kahn's system could result in a brittle failure as it did not have longitudinal reinforcement in the beams at the columns. This type of failure unfortunately manifested itself in the partial collapse of the Bixby Hotel in Long Beach, California and total collapse of the Eastman Kodak Building in Rochester, New York, both during construction in 1906. It was, however, concluded that both failures were the consequences of poor quality labor. With the increase in demand of construction standardization, innovative reinforcing systems such as Kahn's were pushed to the side in favor of the concrete reinforcing systems seen today.