Page 13 - 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 1.11

yield point of up to 50 ksi is available for shaped tubes and up to 46 ksi for round tubes. A500 Grade
B and Grade C are commonly specified for building construction applications and are available from
producers and steel service centers. A500 tubing may not be suitable for dynamically loaded elements
in welded structures where low-temperature notch-toughness properties are important.
A 501 tubing is a hot-formed carbon-steel product available as hot rolled or hot dip galvanized.
It provides a yield point equal to that of A36 steel in tubing having a wall thickness of 1 in or less.
A618 tubing is a hot-formed HSLA product that provides a minimum yield point of up to 50 ksi.
The three grades all have enhanced resistance to atmospheric corrosion. Grades Ia and Ib can be used
in the bare condition for many applications when properly exposed to the atmosphere.
A847 tubing covers cold-formed HSLA tubing and provides a minimum yield point of 50 ksi. It
also offers enhanced resistance to atmospheric corrosion and, when properly exposed, can be used
in the bare condition for many applications.

1.5 STEEL CABLE FOR STRUCTURAL APPLICATIONS

Steel cables have been used for many years in bridge construction and are occasionally used in build-
ing construction for the support of roofs and floors. The types of cables used for these applications
are referred to as bridge strand or bridge rope. In this use, bridge is a generic term that denotes a
specific type of high-quality strand or rope.
A strand is an arrangement of wires laid helically about a center wire to produce a symmetrical
section. A rope is a group of strands laid helically around a core composed of either a strand or
another wire rope. The term cable is often used indiscriminately in referring to wires, strands, or
ropes. Strand may be specified under ASTM A586, wire rope, under A603.
During manufacture, the individual wires in bridge strand and rope are generally galvanized to pro-
vide resistance to corrosion. Also, the finished cable is prestretched. In this process, the strand or rope
is subjected to a predetermined load of not more than 55% of the breaking strength for a sufficient
length of time to remove the “structural stretch” caused primarily by radial and axial adjustment of
the wires or strands to the load. Thus, under normal design loadings, the elongation that occurs is
essentially elastic and may be calculated from the elastic-modulus values given in Table 1.5.
Strands and ropes are manufactured from cold-drawn wire and do not have a definite yield point.
Therefore, a working load or design load is determined by dividing the specified minimum breaking
strength for a specific size by a suitable safety factor. The breaking strengths for selected sizes of
bridge strand and rope are listed in Table 1.5.

TABLE 1.5 Mechanical Properties of Steel Cables

Minimum breaking strength, kips,* Minimum modulus of elasticity, ksi,*
of selected cable sizes for indicated diameter range
Nominal Zinc-coated Zinc-coated Nominal diameter Minimum
diameter, in strand rope range, in modulus, ksi
1 30 23 Prestretched
/ 2
3 68 52 zinc-coated strand
/ 4
9
1 122 91.4 1 / 2 to 2 / 16 24,000
5
1 276 208 2 / 8 and over 23,000
1 / 2
2 490 372 Prestretched
3 1076 824 zinc-coated rope
4 1850 1460 3 / 8 to 4 20,000
*Values are for cables with Class A zinc coating on all wires. Class B or C can be specified where additional
corrosion protection is required.

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