Ductility demands of low-, mid- and high-rise steel buildings with medium and deep columns

In order to reduce drifts in steel buildings located in high seismicity areas, structural engineers use deep columns despite what reported in some studies in the sense that deep columns can prematurely twist. In other studies, on the other hand, the use of deep columns is encouraged. The behavior of steel buildings with deep columns subjected to cyclic loading has been experimentally studied, but the effect of dynamic characteristics of strong motions and buildings, as well as the associated ductility demands, have not been considered. In this research, the seismic responses of steel buildings with medium columns are calculated in terms of drifts and ductility demands and compared to those of similar buildings with equivalent (same weight) deep columns. Results indicate that the drifts of the models with medium columns may be up to 60% larger than those of the models with deep columns implying that the drifts may significantly be reduced if deep columns are used. The reduction in terms of local ductility demands on beams may be up to 70%, but for the case of columns of high-rise buildings, the reduction is negligible. The reductions in story ductility demands are smaller than those of local ductility, as expected. Although it is generally accepted that nonlinear time history analysis is the most accurate and reliable analysis procedure, pushover analysis is broadly used to estimate seismic responses in terms of different parameters; however, the story ductility demands obtained from pushover while using deep columns are much larger than those of dynamic analysis.