Analysis of Irregular Structures under Earthquake Loads

Behavior of a multi-storey building during strong earthquake motion depends on structural configuration. Irregular configuration either in plan or in elevation is recognized as one of the major causes of failure during earthquakes. Thus irregular structures, especially the ones located in seismic zones are a matter of concern. Structures generally possess combination of irregularities and consideration of a single irregularity may not result in accurate prediction of seismic response. The choice of type, degree and location of irregularities in the design of structures is important as it helps in improving the utility as well as aesthetics of structures. Hence, the present study addresses the seismic response of reinforced concrete structures possessing various combinations of irregularities. A nine-storeyed regular frame is modified by incorporating irregularities in various forms in both plan and elevation to form 34 configurations with single irregularity and 20 cases with combinations of irregularities. Along with the regular configuration, 54 irregular configurations are analyzed and compared. All the frames are subjected to seismic loads and the response of the structures is computed numerically. It is observed that irregularity considerably affects the seismic response. Out of various types of single irregularities analyzed, stiffness irregularity is found to have maximum influence on the response. Among the cases having combinations of irregularities, the configuration with mass, stiffness and vertical geometric irregularities has shown maximum response. The results of this study would aid in designing of irregular structures judiciously without compromising their performance.