Development of Irregularity Index Based on Dynamic Characteristics to Quantify the Vertical Geometric Irregularities

Most of the high-rise buildings in the modern era are irregular in shape due to architectural and aesthetic requirements. But the performance of such buildings during an earthquake varies with the degree of irregularity. According to past studies, the degree of irregularity can be quantified using the parameters based on the geometric configuration of the building and based on dynamic characteristics as well. Two types of geometric irregularities that can be identified in the high-rise buildings are vertical geometric irregularity and horizontal geometric irregularity. However, the present study is focused on vertical geometric irregularity only. The fundamental mode base shear is a kind of dynamic parameter considered in the present study to propose a new index for quantifying the degree of irregularity in selected vertically irregular RC buildings. The study also compares the performance of the existing methods on quantifying the degree of irregularity for the selected irregular buildings. Selected irregular buildings are modeled as planer concrete momentresisting frames using SAP2000 and analyzed for modal analysis. The proposed index can easily quantify the degree of irregularity in vertically irregular RC moment-resisting frames compared to the existing irregularity quantification methods.