Abstract
This study is focused on developing a damage-based design procedure for torsionally coupled moment-frame structures under earthquake ground motion. The core idea is selecting a design value for the Park-Ang damage index and determining a target maximum drift ratio under torsion to be input to a displacement-based design procedure. The target drift ratio is calculated using the results of an extensive incremental dynamic analysis. In each round of analysis, the damage index and maximum drift ratio of the structure are determined as a couple. It makes it possible to derive an equation for the maximum drift ratio as a function of the damage index, by regression analysis. An almost linear relation is shown to be present between the two for the whole practical range of torsional mass eccentricity, with a very good correlation. Moment frame buildings having 5 and 10 stories, are shown to meet the sample damage index value for zero, 5 and 10 percents of eccentricity ratio.