Analytical and Code-based Assessment of Torsional Irregularity in Low to Medium Rise Buildings

Recent earthquakes have shown that torsional irregularity of buildings is a factor caused collapse of buildings. In previous edition of standard 2800, Iranian code of practice for seismic resistant design of buildings, there was no discussion on torsional irregularity. In the fourth edition, the regulations about this type of irregularity are also included. The aim of this study is to validate the regulations using analytical results and comparison of results with those regulations of other seismic codes. Parameters studied are location of shear walls in the plan, number of stories and number of axes. To study torsional irregularity in the Y plane, shear walls are considered symmetrical and asymmetrical about X and Y axis. Analyzing 96 analytical models, specified that maximum value for torsional irregularity coefficient increases by reducing the number of stories of the building. The upper stories have less torsional irregularity coefficient than the lower stories. The results of rotation angle of floor contrasts to that of torsional irregularity coefficient. A direct relationship proposed to relate the torsional irregularity coefficient and rotation angle of floor.