Seismic Fragility Assessment of Rc Frame Structures Under Main Shock- Aftershock Sequences Using Incremental Dynamic Analysis

Abstract

Earthquakes are major unpredictable natural phenomenon which often results in major disasters. In any real earthquake, shaking occurs in sequence of foreshocks, main shock and aftershocks. These repeated earthquakes may occur several times with in even few hours or minutes leaving very limited time between occurrences of tremors. This may hamper the re-occupancy and restoration activities of structures in post disaster situations. When structures are subjected to repeated earthquakes, structural damages gets further accumulated which results in degradation in stiffness and strength characteristics of structural members. Generally, Aftershocks may have smaller magnitude than main shock but it may have higher peak ground acceleration, longer time duration than main shock. Hence, after a major earthquake, it is important to check whether damaged buildings can continue to be occupied, also keeping threat of aftershocks in consideration. This study is mainly focused on fragility assessment of RC framed structure designed according to the Nepal National Building codes of practice under single and repeated ground motions. Incremental dynamic analysis is performed using SAP2000. Results obtained in this study are evaluated in terms of lateral displacement, residual displacement, and maximum inter-story drift ratio for particular peak ground acceleration. Depending on the results it is concluded that repeated earthquakes have significant effects on seismic responses of structure. It is also found that seismic vulnerability considerably increases when structure is exposed to sequence earthquake.