Effect of Torsional Irregularity on Seismic Performance of Steel Moment Resisting Frame Structures

This paper examines the seismic damage of three-dimensional steel moment-resisting frame (SMRF) structures affected by torsional irregularities. Six steel ۳-D SMRF structures with varying degrees of irregularity were evaluated using incremental dynamic analysis (IDA) to determine their dynamic capacity. The aim of the study was to develop a quantifiable damage index based on the results of IDA. The yield point and the point of loss of lateral bearing (collapse threshold) on the IDA curve of each record were used to calculate the proposed damage index, which ranges from ۰ to ۱ and can be calculated individually in two horizontal directions. The study evaluated the feasibility of a meaningful match between the momentary torsion and the predicted damage by charting the ratio between these two quantities against the damage index findings. The analysis of the average damage at different levels of mild, medium, and high damage, as well as the comparison of the average damage index between the design accelerations corresponding to the return periods of ۴۷۵ and ۲۴۷۵ years, revealed a general trend towards higher damage in structures with greater irregularity.

Keywords:

Incremental dynamic analysis (IDA) , Torsional Irregularity , Steel moment resisting frame (SMRF) , Damage index , Seismostruct software