Reinforcing steel may be used in concrete either as individually placed and tied bars, or welded wire fabric. The contractor should know something of the properties of each, and where each is most effectively employed, particularly where the two are given as alternates. The most important properties of a reinforcing bar relate to its performance in tension. For intermediate Grade 40 bars of both axle and billet steel, ASTM requirements can be summarized as follows: minimum tensile strength- 70,000 psi; minimum yield strength- 40,000 psi. For Grade 60, 90,000 and 60,000 psi respectively. Bars being obtainable in a wide range of sizes, from the modest number 3 bar to the hefty, extra large number 18's, is two major grades of steel and in almost any required length up to 60 feet, it is obvious that they are suitable for almost any reinforcing job, particularly in columns, beams, and deep structural members where substantial areas of steel are required to counteract tensile forces. Welded wire fabric offers the contractor the time-saving advantage of prefabricated units of reinforcement, particularly effective where large areas of steel are to be put in place, such as for a thin structural floor slab or slab on ground. The time savings arise in several ways: substitution of many motions involving one by one placement of individual bars with just one sequence of motions covering the placement of a single sheet (or unrolling of a single roll), often covering over 200 square feet at once; elimination of many tieing and securing operations, because the intersecting members of the fabric reinforcement are electrically fused in place at the factory, with the weld strength guaranteed to exceed the strength of the weakest member; and saving in checking and inspection time, because the automatic fabric-making machines assure highly accurate alignment of the reinforcing members and prevent omission of any member.