Parametric Study on the Variation of Time Period of RC MRF Buildings

Abstract

The time period of buildings is an important criterion for the design of new buildings and an assessment of existing ones. As per Indian Standards, the fundamental time period is a parameter for evaluating seismic base shear. Time periods calculated by codal provisions are extensively used in practice though there exists a scope for further improvement in the methods. IS codes provide empirical relations for calculating the time period of a building that generally depends on the height and least lateral dimensions of a building. However, for bare frame buildings, the fundamental period is considered as a function of height only. But only the height of a building may not be sufficient to explain the variations in the time period. Apart from the height, the time period depends on many other parameters such as stiffness of the structure, number of bays in both directions, plan area of the building, the orientation of the building (longitudinal or transverse direction). This study aims to understand the effects of various parameters on the fundamental time period of a reinforced concrete (RC) building with moment resisting frames (MRF). For this purpose, a detailed parametric study of the time period is done by creating models of RC MRF buildings, and eigenvalue analysis is performed using the SEISMOSTRUCT 2020 software. By changing the parameters, variation in the time period in different models is studied. The values of the time period obtained from these analyses and the values of the time period obtained as per the IS code are compared. This study proposes that there exists a possibility to assimilate various factors discussed here, in the time period formula given Indian Standards, to obtain more accurate values of the fundamental time period of a building.