Structural Sections:

Eq. (8) may be rewritten in the form,

where k_x & k_y are radii of gyration of the area of section around the axes of x & y, respectively.

For zero stress at the point, we must have

Figure

For an I-section, the four corners shall be the limiting points, where x′ = b/ 2  and y′ = d/2

Therefore, we have

 Eq. is the equation of the bounding line which restriction the deviation of load from the centroid for no change in the sign of the stress, for I-section. The equations of the three other bounding lines shall be similar, therefore, forming a rhombus having the principal axis of I-section as diagonals, as illustrated in Figure.