Comparative assessment and recommendations for code‐based identification of vertical stiffness irregularities in reinforced concrete frame buildings

Abstract The poor performance of stiffness irregular buildings during past earthquakes highlights the need to re‐evaluate building code provisions that define irregularity using story stiffness (e.g., IS 1893‐1, NZS 4203, and NBCC 4) or interstory drift (e.g., NBC E.030 and Turkish Earthquake Code [TEC]). It is vital to assess the effectiveness of each provision in detecting irregularities so as to identify the most efficient approach. The spectrum of 2D reinforced concrete moment frame buildings is examined by altering (i) building configurations, (ii) locations of single‐story irregularity, and (iii) locations of successive‐story irregularity. When computing stiffness irregularities, it is required to account for the effect of infill walls as an equivalent infill strut. Based on elastic behavior, IS 1893‐1, NBC E.030, and TEC accurately detect irregularities in buildings that occur in the intermediate stories; yet, the standards do not apply to buildings with irregularities at the bottom or top stories. Nonlinear static and dynamic analyses show that irregularity locations significantly affect building responses. Additionally, dynamic amplification of displacement responses occurs rapidly (~1 to 166 times) in these locations. As a result, the damage is limited to all stories below the irregular story, and it often extends across one to three immediate upper stories. But critical columns have a high demand–capacity ratio around irregular stories (~0.5 to 1.2). It is preferable to detect stiffness irregularity using interstory drift, which involves one to three stories above and below the irregular story; building code recommendations are provided.