### Allowable Column Stress for Buildings

The AISC specification for allowable-stress design (ASD) for buildings provides two formulas for computing allowable compressive stress

*Fa*, ksi (MPa), for main members. The formula to use depends on the relationship of the largest effective slenderness ratio*Kl*/*r*of the cross section of any unbraced segment to a factor*Cc*defined by the following equation and Table 1Where:

*E =*modulus of elasticity of steel

= 29,000 ksi (128.99 GPa)

*Fy =*yield stress of steel, ksi (MPa)

When

*Kl*/*r*is less than*Cc*,
Table 1 |

The effective-length factor

*K*, equal to the ratio of effective column length to actual unbraced length, may be greater or less than 1.0. Theoretical*K*values for six idealized conditions, in which joint rotation and translation are either fully realized or nonexistent, are tabulated in Figure 1.
Figure 1 |

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