PSI - Issue 14

Siva Naveen E et al. / Procedia Structural Integrity 14 (2019) 806–819 Siva Naveen E, Nimmy Mariam Abraham, Anitha Kumari S D / Structural Integrity Procedia 00 (2018) 000–000

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incorporated by changing the vertical and horizontal configurations of the regular frame. Apart from the regular case, 54 irregular configurations are analyzed, out of which, 34 cases possess single irregularity and 20 possess combination of irregularities.

4.1. Configurations having single irregularity

Vertical irregularities include mass, stiffness and vertical geometric irregularities whereas horizontal irregularities include re-entrant corner and torsional irregularities. The 24 frame configurations with single vertical irregularity along with the regular configuration and the 10 configurations having single plan irregularity are shown in Figures 1a and 1b respectively. For all the cases analyzed, bay length and number of storeys are kept constant. The details of various irregularities incorporated in each case are as follows:  Mass irregularity (MI) Four different cases of mass irregularity (MI-1 to MI-4) are adopted for the analysis. Irregularity is introduced by increasing the mass of a particular storey. For MI-1 and MI-2, the mass is increased at 4th storey by 1.5 and 2 times respectively than the regular frame. For MI-3 and MI-4 the mass is increased at second and seventh storeys by 1.5 and 2 times respectively.  Stiffness Irregularity (SI) Ten different cases of stiffness irregularities (SI-1 to SI-10) are considered for the analysis. Irregularity is introduced by reducing the number of columns, increasing the length of the columns or changing the cross section area of the columns. For the cases SI-1 and SI-9, number of columns is reduced from 28 to 12 with respect to the regular frame. For SI-2, SI-3, SI-4 and SI-5 cases, the length of the columns is increased. For SI-6, rectangular columns are replaced with circular columns for the first two floors, without changing the total cross sectional area of the columns. For SI-7, rectangular columns are replaced with circular columns for the first two floors, with increased total cross sectional area of the columns. For SI-8, the cross sectional area of the columns for first two floors is increased to 0.056m×0.042m from 0.051m×0.038m. For the first two floors, the cross sectional area is more compared to the remaining floors. For SI-10, the number of columns was reduced to 12 and the length of the columns was increased to 0.458 m from 0.229 m. Table 3 shows the percentage reduction in storey stiffness with respect to adjacent storey, at the location of irregularity.  Vertical Geometric Irregularity (VGI) Ten different cases of vertical geometric irregularity (VGI-1 to VGI-10) are considered for the analysis. Irregularity is introduced by varying vertical configuration along the height. For the cases VGI-1, VGI-2, VGI-3, VGI-7, VGI-9 and VGI-10, the horizontal dimension of the lateral resisting force system is reduced as shown in Figure 1a. For the cases VGI-4, VGI-5, VGI-6 and VGI-8 lateral dimension is increased.  Re-entrant Corner Irregularity (REC) Re-entrant corner irregularity is introduced by varying plan configuration of the frames. Seven different cases (REC-1 to REC-7) are considered for analysis.  Torsional Irregularity (TI) Torsional irregularity is introduced by varying vertical structural elements. Three different cases (TI-1 to TI-3) are selected for the analysis. For case TI-1, irregularity is incorporated by introducing circular columns of size 0.06m. For case TI-2, irregularity is incorporated by introducing two shear walls of thickness 0.042m at the corner of the building. For the case TI-3, irregularity is incorporated by introducing columns of different types of cross sections, two columns of dimensions 0.06m×0.04m, one column of dimensions 0.055 m×0.04m, sixteen columns of dimensions 0.051m×0.038m and two columns of dimension 0.05m×0.035m along with two shear walls of thickness 0.042m at the corner.