Effect of vertical irregularity of concrete frame systems on the seismic response modification factor

The analytical model for structures that accounts for all sources of stiffness, P-delta effects, and inelastic response is the most accurate approach for seismic design. The design codes specified factor is known as the response modification factor (R), which represents the ratio between the required base shear forces to keep the structure elastic during the earthquake and the design base shear force considering its inelastic behavior. This study aims to estimate the over strength modification factor (R) for various irregularly of reinforced concrete dual systems at failure using the pushover analysis through the finite element method and compare them with those recommended by the design codes. The structures under investigation were divided into three different heights of 5, 10 and 15 stories. These structures were a dual structural system. Two types of vertical irregularities, classified according to American Society of Civil Engineers (ASCE)/SEI 7-16, have been investigated; soft story and weight (mass). The two types of vertical irregularities were located at three different locations for each type, bottom story, 1/3 from structure height, and 2/3 from structure height. It was concluded that the R coefficient values presented in the current study was not align with those derived from Egyptian or other structural codes.