Earthquake Response Analysis of Underground Tubular Structure

Abstract

The present paper deals with the vibrational characteristics of the longitudinal and transversal vibration of underground tubular structures subjected to earthquakes. The analytical model is composed of a cylindrical tubular structure of which axis is parallel to the ground surface and the surrounding ground is treated as an infinite homogeneous half space. From the analyses on the structural response to sinusoidal excitation, it was found that the vibration of the structure due to the inertia force will be hardly induced in the ground and that the dynamic motion of structure is strongly dominated by the ground motion. Moreover analyses on the axial and bending strains revealed that the axial strain is proportional to the velocity amplitude of the surrounding ground, while the bending strain is proportional to the acceleration amplitude. The results suggest that the velocity amplitude in the ground is the most significant factor in the aseismic design of underground pipe systems and the acceleration amplitude is of importance for the structures with large diameter such as subway tunnels. Response analyses of strains to strong motion accelerograms have been also performed by making use of the Fourier transform method. The analyses made clear that the effect of structural stiffness on the induced strain level is not so remarkable and the reduction of strain in structure from the strain in surrounding ground is of the order of 10 to 20%. Then the strain in ground is considered to be the upper bound of strain in structures.