<p>The Park-Ang damage model is widely used in evaluating structural damage status, but the interactions between compression and biaxial drift still need to be determined. This study takes 42 steel columns, of which sections are H-shaped and box-shaped, as research objects, load conditions of one-directional drift, biaxial drift, and combinations of compression and drift have been analyzed. An equivalent damage index <i>D</i>_<i>eq</i>, which is the sum of the 0.42 power of drift damage in two perpendicular directions, is proposed based on the Park-Ang model. And the denominator coefficient <i>α</i> and its calculation equations are proposed to consider the global second-order effect. Furthermore, a 5-story steel frame is taken as a case study, and the damage index marks the failure time of the middle column in each story according to this method.</p>