Evaluating Seismic Response of Underground Structures Based on the Beam on Dynamic Visco-Elastic Foundation Theory

Underground structures, which are located in seismic zones, should undergo static loads induced by the ground and dynamic earthquake-induced forces. Cross section of the underground structures is usually less than the wavelength of input ground motion. Therefore, semi-static or semi-dynamic methods can be used in cross sectional analysis of these types of structures. In this paper, based on the beam on dynamic visco-elastic foundation theory, a new analytical method was developed to determine the shear deformations of the buried box structures. The proposed method is able to consider the characteristics, such as frequency of the ground motion and the damping ratio, in calculating the seismic displacements, which is less considered in the past analytical methods that was introduced by other researchers. The results of the proposed method indicate that the seismic deformation of underground structures is considerably dependent to damping ratio and frequency of ground motion as well as mechanical and geometrical properties of the surrounding medium and structure. In addition, in some frequencies, the results of the new method indicate good general agreement with the methods developed by other researchers. Nonetheless, according to the effect of the frequency, in some frequencies, remarkable differences are observed.