Seismic Behavior of Tunnel Form Reinforced Concrete Buildings with Mass Irregularity in Elevation

Non-uniform mass distribution in elevation is one of the main sources of irregularity in buildings that could lead to concentration of nonlinear deformations followed by local or global damage to buildings during earthquake excitation. Considering lack of accurate information about behavior of tunnel form RC buildings in preceding earthquakes, it is required to evaluate vulnerability of such buildings with mass irregularity in elevation. In this research, seismic behavior of tunnel form RC buildings with heights of 5 and 10 stories, having different patterns of non-uniform mass distributions in elevation is studied in the nonlinear deformation range. For this purpose, seismic performance levels of understudied buildings under design earthquake are determined using time history analysis as well as pushover analysis. Fragility curves are developed by analytical approach for different hazard levels. The results show excellent performance of this structural system and placement in immediate occupancy performance level under maximum design earthquake Iranian seismic code (standard No. 2800). Moreover, modal vibration response of the system is not influenced by building height and height-wise mass distribution pattern. It seems that the provision No. 5 of regulations issued by Road, Housing & Urban Development Research Center of Iran pertaining to design and construction of tunnel form RC buildings, which stipulates that this type of buildings have to be regular in elevation, is so strict and conservative for the studied models with selected patterns of mass irregularities.