Page 9 - 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

STRUCTURAL STEELS, STEELMAKING, AND FABRICATION 1.7

1.1.5 Bridge Steels
Steels for application in bridges are covered by A709, which includes steel in several of the cate-
gories mentioned above. Under this specification, grades 36, 50, 70, and 100 are steels with yield
strengths of 36, 50, 70, and 100 ksi, respectively. Similar AASHTO grades are designated M270.
The grade designation is followed by the letter W, indicating whether ordinary or high atmos-
pheric corrosion resistance is required. An additional letter, T or F, indicates that Charpy V-notch
impact tests must be conducted on the steel. The T designation indicates that the material is to be
used in a non-fracture-critical application as defined by AASHTO; the F indicates use in a fracture-
critical application. There is also a Grade 50S, where the S indicates the steel must be killed.
A trailing numeral, 1, 2, or 3, indicates the testing zone, which relates to the lowest ambient tem-
perature expected at the bridge site. (See Table 1.2.) As indicated by the first footnote in the table,
the service temperature for each zone is considerably less than the Charpy V-notch impact-test tem-
perature. This accounts for the fact that the dynamic loading rate in the impact test is more severe
than that to which the structure is subjected. The toughness requirements depend on fracture criti-
cality, grade, thickness, and method of connection.
High-performance steels (HPS) are the newest additions to the family of bridge steels. They are
being used increasingly to improve reliability and reduce cost, with approximately 200 bridges in
service in 2005. The initial grade, HPS70W, with a specified minimum yield stress of stress of 70
ksi, has been used most. HPS50W, with a specified minimum yield stress of 50 ksi, has also become
popular. HPS100W, with a specified minimum yield stress of stress of 100 ksi, is available to reduce
thickness where members are highly loaded.

1.2 STEEL-QUALITY DESIGNATIONS

Steel plates, shapes, sheetpiling, and bars for structural uses—such as the load-carrying members in
buildings, bridges, ships, and other structures—are usually ordered to the requirements of ASTM A6
and are referred to as structural-quality steels. (A6 does not indicate a specific steel.) This specifi-
cation contains general requirements for delivery related to chemical analysis, permissible variations
in dimensions and weight, permissible imperfections, conditioning, marking and tension and bend
tests of a large group of structural steels. (Specific requirements for the chemical composition and
tensile properties of these steels are included in the specifications discussed in Art. 1.1.) All the steels
included in Table 1.1 are structural-quality steels.
Steel plates for pressure vessels are usually furnished to the general requirements of ASTM A20
and are referred to as pressure-vessel-quality steels. Generally, a greater number of mechanical-
property tests and additional processing are required for pressure-vessel-quality steel.

1.3 STEEL SHEET AND STRIP FOR STRUCTURAL APPLICATIONS

Steel sheet and strip are used for many structural applications, particularly for cold-formed structural
members for residential and light commercial building construction (Chap. 9). The facade of many
high-rise structures is supported by cold-formed sheet steel systems and interior partitions are often
built with steel C-sections. The stressed skin of transportation equipment is another application of
such material. Tensile properties of several sheet steels are presented in Table 1.3. Many of them are
available in several strength levels, with a specified minimum yield point from 25 to 80 ksi. Some
grades may not be suitable for all applications, depending on the ratio of tensile strength to yield
point and other considerations (Chap. 9).
ASTM A606 covers high-strength low-alloy, hot- and cold-rolled steel sheet and strip with
enhanced corrosion resistance. This material, available in cut lengths or coils, is intended for struc-
tural and other uses where savings in weight and improved durability are important. It may be
ordered as Type 2 or Type 4, with atmospheric corrosion resistance approximately two or four times,

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