Page 20 - 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

1.18 CHAPTER ONE 1.20

Ratio of yield strength and tensile strength to room-temperature value 1.00

0.80
0.60

0.40
0.20

0.00
0 500 1000 1500 2000 2500
Temperature, °F
(a)

1.20
Ratio of modulus of elasticity to room-temperature value 0.80
1.00

0.60
0.40
0.20

0.00
0 500 1000 1500 2000 2500
Temperature, °F
(b)
FIGURE 1.8 Effect of temperature on (a) yield strength and tensile
strength and (b) modulus of elasticity of structural steels. (Adapted from
data in AISC “Specification for Structural Steel Buildings,” 2005.)

Under long-time loadings at elevated temperatures, the effects of creep must be considered. When
a load is applied to a specimen at an elevated temperature, the specimen deforms rapidly at first but
then continues to deform, or creep, at a much slower rate. A schematic creep curve for a steel sub-
jected to a constant tensile load and at a constant elevated temperature is shown in Fig. 1.9. The ini-
tial elongation occurs almost instantaneously and is followed by three stages. In stage 1, elongation
increases at a decreasing rate. In stage 2, elongation increases at a nearly constant rate. And in stage 3,
elongation increases at an increasing rate. The failure, or creep-rupture, load is less than the load that
would cause failure at that temperature in a short-time loading test.
Table 1.6 indicates typical creep and rupture data for a carbon steel, an HSLA steel, and a con-
structional alloy steel. The table gives the stress that will cause a given amount of creep in a given
time at a particular temperature.
For special elevated-temperature applications in which structural steels do not provide ade-
quate properties, special alloy and stainless steels with excellent high-temperature properties are
available.

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