140. Plain Bars. With plain bars, the transmission of stresses is dependent upon the adhesion between the concrete and the steel.. Square and round bars show about the same adhesive strength, but the adhesive strength of flat bars is far below that of the round and square bars. The round bars are more convenient to handle and easier obtained, and have, there fore, generally been used when plain bars were desirable.
141. Structural Steel. Small angles, T-bars, and channels have been used to a greater extent in Europe than in this country. They are principally used where riveted skeleton work is prepared for the steel reinforcement; and in this case, usually, it is desirable to have the steel work self-supporting.
142. Deformed Bars. There are many forms of reinforcing materials on the market, differing from one another in the manner of forming the irregular projections on their surface. The object of all these special forms of bars is to furnish a bond with the concrete, independent of adhesion. This bond formed between the deformed bar and the concrete, is usually called a mechanical bond. Some of the most common types of bars used are the Ransome, Thacker, Johnson, Diamond, Kahn, and Twisted Lug.
The Ransonze or twisted bar, shown in Fig. 13, was one of the first steel bars shaped to give a mechanical bond with concrete. This type of bar is a commerical square bar twisted while cold. There are two objects in twisting the bar—first, to give the metal a mechani cal bond with the concrete; second, to increase the elastic limit and ultimate strength of the bar. In twisting the bars, usually one complete turn is given the bar in eight or nine diameters of the bar, with the result that the elastic limit of the bar is increased from 90 to 50 per cent, and the ultimate strength is increased from 25 to 35 per cent. These bars can readily be bought already twisted; or, if it is desired, square bars may be bought and twisted on the site of the work.
The Thacher bar (Fig. 14) was patented by Mr. Edwin Thacher, M. Am. Soc. C. E. These bars are rolled from medium steel, and range in size from I inch to 2 inches. The cross-sectional area is practically uniform throughout, and all changes in shape of section are made by gradual curves.
The Johnson or Corrugated bar (Fig. 15), with corrugations on all four sides, was invented by Mr. A. L. Johnson, M. Am. Soc. C. E. The corrugations are so placed that the cross-sectional area is the same at all points. The angles of the sides of these corrugations or square shoulders, vary from the axis of the bars not exceeding the angle of friction between the bar and concrete. These bars arc usually rolled from high-carbon steel
having an elastic limit of 55,000 to 65,000 pounds per square inch and an ultimate strength of about 100,000 pounds per square inch. They are also rolled from any desired quality of steel. In size they range from 4 inch to 14 inches, their sectional area being the same as that of commercial square bars of the same size.
The Diamond bar (Fig. 16) was devised by Mr. William Mueser. This bar has a uniform cross-section throughout its length, exerts a uniform bonding strength at every section, and every portion is available for tensile strength. In design, this bar consists of a round bar with interlacing longitudinal semicircular ribs, and without any sharp angles. The Diamond bar is one of the newer types of bars.
The Kahn bar (Fig. 17) was invented by Mr. Julius Kahn, Assoc. M. Am. Soc. C. E. This bar is designed with the assumption that the shear members should be rigidly connected to the horizontal members. The bar is rolled with a cross-section as shown in the figure. The thin edges are cut and turned up, and form the shear members. These bars are manufactured in several sizes.
The Twisted Lug bar (Fig. 1S) is similar in form to the Ransome cold-twisted bar, with the addition of lugs or truncated cones placed at regular intervals along the spirals. These bars are rolled with the lugs, and the twisting is done either while the bars are hot or at any time after they are cold. If the bars are twisted while hot, their elastic limit and ultimate strength are not raised; that is, their physi cal properties are not changed.
Expanded metal (Fig. 19) is made from plain sheets of steel, slit in regular lines and opened into meshes of any desired size or section of strand. It is commercially designated by giving the gauge of the steel and the amount of displacement between the junctions of the meshes. The most common manufactured sizes are as follows: Steel wire fabric reinforcement consists of a netting of heavy and light wires, usually with rectangular meshes. The heavy wires carry the load, and the light ones are used to space the heavier ones. There are many forms of wire fabric on the market.
Table XI is condensed from the handbook of the Cambria Steel Company, and gives the standard weights and areas of plain round and square bars as commonly used in reinforced-concrete construc tion :