a The tabulated values are based on ASTM standards. b 1 in. = 25.4 mm; 1 ksi = 6.9 MPa = 70.3 kg/cm2.

c Structural Grade 80 of A653, A875, and A1008 steel and Grade 80 of A792 are allowed in AISI Specification under special conditions. For these grades, Fy = 80 ksi, Fu = 82 ksi, and elongations are unspecified. See AISI Specification for reduction of yield point and tensile strength.

For type H of A1003 steel, the minimum tensile strength is not specified. The ratio of tensile strength to yield strength should not be less than 1.08.

e For A1011 steel, the specified minimum elongation in 2-in. gage length varies with the thickness of the steel sheet and strip. The elongation in 8-in. gage length is for thickness below 0.23 in.

Specification [7] for computing the tensile yield point of corners and the average full-section tensile yield point for design purposes.

6.4.3 Modulus of Elasticity, Tangent Modulus, and Shear Modulus

The strength of cold-formed steel members that are governed by buckling depends not only on the yield point but also on the modulus of elasticity, E, and the tangent modulus, Et. A value of E = 29,500 ksi (203 GPa or 2.07 x 106 kg/cm2) is used in the AISI Specification for the design of cold-formed steel structural members. This E value is slightly larger than the value of 29,000 ksi (200 GPa or 2.04 x 106 kg/cm2), which is used in the American Institute of Steel Construction (AISC) Specification for the design of hot-rolled shapes. The tangent modulus is defined by the slope of the stress-strain curve at any given stress level as shown in Figure 6.5b. For sharp-yielding steels, Et = E up to the yield, but with gradual-yielding steels, Et = E only up to the proportional limit, fpr (Figure 6.5b). Once the stress exceeds the proportional

Strain, e

/pr = proportional limit

Strain, e

FIGURE 6.5 Stress-strain curves of steel sheet or strip: (a) sharp-yielding and (b) gradual-yielding (courtesy of Yu, W.W. 1991).

0 0

Post a comment