Page 27 - Structural Steel Designers Handbook AISC, AASHTO, AISI, ASTM, and ASCE-07 Design Standards

Brockenbrough_Ch01.qxd 9/29/05 4:59 PM Page 1.25

PROPERTIES OF STRUCTURAL STEELS AND EFFECTS OF STEELMAKING AND FABRICATION

STRUCTURAL STEELS, STEELMAKING, AND FABRICATION 1.25

are fillet welded to both the web and the flange, with the cutout in the corners of the continuity plate
at least 1.5 by 1.5 in, and the fillet welds stopped short by a weld length from the edges of the cutout.
Groove welding is unnecessary. Similarly, tests also showed that web doubler plates should be fillet
welded, and that they do not need to be in contact with the column web. Design details should follow
the requirements of the AISC “Specification” and the recommendations given in its Commentary.

1.18 VARIATIONS IN MECHANICAL PROPERTIES

Tensile properties of structural steel may vary from specified minimum values. Product specifica-
tions generally require that properties of the material “as represented by the test specimen” meet cer-
tain values. ASTM specifications dictate only a limited number of tests per heat (in each strength
level produced, if applicable). If the heats are very large, the test specimens qualify a considerable
amount of product. As a result, there is a possibility that properties at locations other than those from
which the specimens were taken will be different from those specified.
For plates, a test specimen is required by ASTM A6 to be taken from a corner. If the plates are
wider than 24 in, the longitudinal axis of the specimen should be oriented transversely to the final
direction in which the plates were rolled. For other products, however, the longitudinal axis of the
specimen should be parallel to the final direction of rolling.
For structural shapes with a flange width of 6 in or more, test specimens should be selected from
a point in the flange as near as practicable to two-thirds the distance from the flange centerline to the
flange toe. Prior to 1997–1998, the specimens were taken from the web.
An extensive study commissioned by the American Iron and Steel Institute (AISI) compared
yield points at various sample locations with the official product test. The studies indicated that the
average difference at the check locations was −0.7 ksi. For the top and bottom flanges, at either end
of beams, the average difference at check locations was −2.6 ksi.
Although the test value at a given location may be less than that obtained in the official test, the
difference is offset to the extent that the value from the official test exceeds the specified minimum
value. For example, a statistical study made to develop criteria for load and resistance factor design
showed that the mean yield points exceeded the specified minimum yield point F y (specimen located in
web) as indicated below and with the indicated coefficient of variation (COV):
Flanges of rolled shapes: 1.05F y , COV = 0.10
Webs of rolled shapes: 1.10F y , COV = 0.11
Plates: 1.10F y , COV = 0.11

Also, these values incorporate an adjustment to the lower “static” yield points.
For similar reasons, the notch toughness can be expected to vary throughout a product. (R. L.
Brockenbrough, Chap. 1.2 in Constructional Steel Design—An International Guide, R. Bjorhovde
et al., eds., Elsevier Science Publishers, New York.)

1.19 CHANGES IN CARBON STEELS ON HEATING AND COOLING*

As pointed out in Art. 1.11, heating changes the tensile properties of steels. Actually, heating changes
many steel properties. Often, the primary reason for such changes is a change in structure brought
about by heat. Some of these structural changes can be explained with the aid of an iron-carbon equi-
librium diagram (Fig. 1.13).

*Articles 1.19 through 1.27 are adapted from a previous edition written by Frederick S. Merritt, Consulting Engineer, West
Palm Beach, Fla.

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