A Simple Model for Calculating the Fundamental Period of Vibration in Steel Structures

Most international codes allow the use of an equivalent static lateral forces method for practical design of real structures to withstand earthquake actions. This method requires the calculation of an approximation for the fundamental mode period of vibrations of these structures and several empirical equations have been suggested. Most of these equations are not considering the effect of semi-rigid connections and provide only a crude approximation to the required fundamental periods. In this paper, a new formula to calculate a satisfactory approximation of fundamental period of the structure is proposed. This formula takes into account the effect of semi-rigid connections, mass and the stiffness of the structure. In order to verify the accuracy of the proposed formula, several examples are presented in which the fundamental mode periods of several structures have been calculated utilizing the proposed formula and the conventional empirical equations. Comparing the obtained results with those obtained from a well known computer program STAAD.PRo has shown that the proposed formula provides a more accurate estimation of the fundamental period of the structures.