Page 14 - Structural Steel Designers Handbook AISC, AASHTO, AISI, ASTM, and ASCE-07 Design Standards

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PROPERTIES OF STRUCTURAL STEELS AND EFFECTS OF STEELMAKING AND FABRICATION

1.12 CHAPTER ONE

1.6 TENSILE PROPERTIES

The tensile properties of steel are generally determined from tension tests on small specimens or
coupons in accordance with standard ASTM procedures. The behavior of steels in these tests is
closely related to the behavior of structural-steel members under static loads. Because, for structural
steels, the yield points and moduli of elasticity determined in tension and compression are nearly the
same, compression tests are seldom necessary.
Typical tensile stress-strain curves for structural steels are shown in Fig. 1.1. The initial portion
of these curves is shown at a magnified scale in Fig. 1.3. Both sets of curves may be referred to for
the following discussion.

Strain Ranges. When a steel specimen is subjected to load, an initial elastic range is observed in
which there is no permanent deformation. Thus, if the load is removed, the specimen returns to its
original dimensions. The ratio of stress to strain within the elastic range is the modulus of elasticity,
3
or Young’s modulus E. Since this modulus is consistently about 29 × 10 ksi for all the structural
steels, its value is not usually determined in tension tests, except in special instances.
The strains beyond the elastic range in the tension test are termed the inelastic range. For
as-rolled and high-strength low-alloy (HSLA) steels, this range has two parts. First observed is a plas-
tic range, in which strain increases with no appreciable increase in stress. This is followed by a
strain-hardening range, in which strain increase is accompanied by a significant increase in stress.
The curves for heat-treated steels, however, do not generally exhibit a distinct plastic range or a large
amount of strain hardening.

FIGURE 1.3 Partial stress-strain curves for structural steels strained through
the plastic region into the strain-hardening range. (From R. L. Brockenbrough and
B. G. Johnston, USS Steel Design Manual, R. L. Brockenbrough & Associates, Inc.,
Pittsburgh, Pa., with permission.)

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