High Strength Structural Steel

Steel is employed as the structural frame in various forms of construction (bridges, buildings, etc.), as well as in reinforced portland cement concrete structural members. The composition and engineering properties of the steels used in these diverse applications vary substantially. Although a detailed examination of all structural quality steels is beyond the scope of this text, the main grades, types, and classes of these steels will be briefly described.
As noted previously, structural steels are classified on the basis of strength (class or grade) as well as composition (type). For example, the composition and selected properties of some (1) structural carbon steels (ASTM A-36M), (2) high-strength, low-alloy manganese vanadium steels (ASTM A-441/A-572M), and (3) high-yield strength, quenched and tempered alloy steels (ASTM A-514M) are provided in Table 13.2 and Fig. 13.15. The differences in strength and ductility among the various types can be significant, and the selection of appropriate steel should be based on the end use of the structural element.
Steels used as reinforcing elements in portland cement concrete structural members are available in several forms and with a variety of properties. Distinction must be made between (1) plain and deformed reinforcing bars (Fig. 13.16(a)), (2) wire for welded wire fabric (Fig. 13.16(b)), and (3) bar, wire, and strand (Fig. 13.16(c)), for prestressing. Gradings and selected properties are presented in Table 13.3, and typical stress-strain curves are shown in Fig. 13.17. The time-dependent behavior of steels is of interest in prestressed members, where relaxation of the steel reduces its stress level with time, as shown in Fig. 13.18. Note that the stress loss is greater for higher prestress levels (see Chapter 7).