REINFORCED CONCRETE Reinforced concrete is .usually, though some what inaccurately, defined as a combination of steel and concrete in which the steel takes the tension and the concrete the compression. For example, if one or more steel rods be imbedded near the tension side of a concrete beam, the steel will resist the tension and the concrete the compression. Concrete is stronger in compression than in tension, while steel is stronger in tension; and hence in the above combination each material is serving the purpose for which it is best adapted.
The preceding definition of reinforced concrete is defective since the steel is sometimes employed to resist shear, as at the ends of short or heavily loaded beams, and is also sometimes employed to take direct compression, as in columns. Furthermore, steel is sometimes embedded in concrete to prevent contraction cracks due to changes of temperature. Therefore, it is more exact to say that reinforced concrete is concrete having metal embedded in it so that the two materials assist each other in supporting the stresses imposed upon the structure.
The term reinforced concrete does not include those combinations of steel and concrete in which the steel is designed to carry all of the load, as, for example, a steel column encased in concrete. In such combinations the concrete is intended only to protect the steel from corrosion and fire, the steel being designed to support the concrete as well as the other loads; but in reinforced concrete the proportions and positions of the steel and the concrete are designed to distribute the loads between the two materials.
Formerly there was a great diversity of names applied to this combination of steel and concrete, among them being steel-con crete, armored concrete, and concrete-steel; but in the last few years the term reinforced concrete has been almost universally adopted.
Apparently the first use of reinforced concrete was in a row-boat built by J. L. Lambert in France in 1850. This boat was exhibited at the Paris Exposition in 1855, and in 1902 was still in good condition and in use. In 1865, Jean Monier, a French
man, made large concrete flower-pots which were strengthened by an embedded wire net; and in 1867 he took out a patent for reinforced concrete flower-pots, pipes, tanks, etc. Later he took out patents for the use of reinforced concrete in bridge construction; and in 1875 built a reinforced concrete arch-bridge, probably the first in the world. Monier is frequently referred to as the father of reinforced concrete construction. However, reinforced concrete construction had made but little progress in Europe before 1887, but after this date it made rapid progress—at first chiefly through the efforts of Hennebique.
In 1875, W. A. Ward built a dwelling at Port Chester, N. Y., in which the walls, floors, and roof were made of reinforced concrete. This building was in perfect condition in 1905. However, rein forced concrete construction made practically no progress in America until 1885-90 when Ransome built a reinforced concrete arch-bridge and several notable reinforced concrete buildings in and near San Francisco. Reinforced concrete construction was not extensively used in America before 1900.
Since the uses described above, many systems of reinforce ment have been proposed and many patents have been granted; and reinforced concrete has come into extensive use in all kinds of engineering and architectural construction. Reinforced concrete has been more extensively used in Europe than in America, chiefly because during the last three decades of the last century the price of cement was much more favorable to the development of concrete construction in Europe than in America; but the recent develop ment of the portland-cement industry in America has greatly stimu lated the use of concrete, and in the last few years reinforced con crete has been extensively used in America. The use of reinforced concrete is the most important step in structural engineering since the introduction of steel for building purposes.