Evaluation of seismic behavior of steel frames with non - parallel system irregularity using nonlinear dynamic analysis

Many structures exhibit Non-orthogonal systems irregularity based on architectural design, which is a type of torsional irregularity. This paper evaluates the inelastic response of multi-story steel moment resisting frames with this type of irregularity. A parametric investigation is carried out on six building models exhibiting coupled behavior in lateral and torsional response with various degrees of torsional irregularity. Maximum inter-story drift and peak global roof drift were adopted as critical response parameters. Non-linear time-history analysis method was performed using ۷ ground motion records for prediction of the seismic response of the frames. The results indicate a higher recordto- record variability in time history response as a result of higher mode effects for the structural models studied. The results also indicate that it is essential to undertake nonlinear dynamic analysis to design structures with irregularity in plan and to capture nonlinear mechanisms and post-earthquake residual displacements for structures with non - parallel systems irregularity.