Free Vibration Analysis of Symmetric and Asymmetric RCC Structures

Abstract

Abstract Symmetric and asymmetric structures behave differently under external loads even though they are of an equal number of stories or equal in dimensions. It is necessary to estimate the dynamic properties of the asymmetric structures carefully to avoid failure. Modal analysis for symmetric and asymmetric multi-storied reinforced concrete (RC) buildings is very essential to assess the dynamic characteristics of the structure. The plan asymmetric buildings with the shift of core from a central position to different positions and vertical asymmetry with the mass variation in vertical direction and setback stories are considered for the present study. Flexural beam elements are modelled to represent the columns. Two translations i.e., longitudinal, and transverse displacements of the building and rotation about the vertical axis of the structure are taken as global degrees of freedom at each node. The distance between the mass center and stiffness centre on each floor is taken as eccentricity. A finite element model is developed using MATLAB code to estimate the natural frequencies. Different RCC structures of 5 to 20-storied buildings are modelled by developing global stiffness and mass matrices based on the member connectivity. Eigen-value technique is used to estimate the natural frequencies. From the study it is observed that the natural period in asymmetric structures is found more than the symmetric building. The structure with setback also showed larger natural period.