Comparison of response acceleration methods suggested by different standards

The Chinese specifications, "Code for seismic design of urban rail transit structures" and "Standard for seismic design of nuclear power plants", give two response acceleration methods for the seismic analysis of underground structures. The difference lies in the determination of the effective inertial acceleration. The former calculates the horizontal effective inertia through free-field shear stress. However, the latter directly uses the free-field acceleration as the effective inertial acceleration. Their applicability is evaluated through the theoretical analysis and numerical examples, and the horizontal effective inertial acceleration calculated by the two methods is compared and studied with the site type, shear wave velocity and ground motion intensity. The research results show that whether to consider the damping of the soil is the main source of the difference in the calculation of the two response acceleration methods, and the stiffness ratio (wave velocity ratio) of the adjacent soil layers is also the source of the difference. The difference of the horizontal effective inertia calculated by the two standard methods decreases with the increase of shear wave velocity, and increases with the increase of ground motion intensity. When the site conditions are poor or the ground motion intensity is high, the horizontal effective inertial acceleration calculated based on the shear stress is more reasonable. The displacement obtained by this calculation is consistent with the calculated result by the dynamic time history method, thus it has better calculation accuracy. A new response acceleration method for calculating the effective inertial acceleration through free-field displacement is also proposed-displacement-based response acceleration method. The characteristics of using the free-field displacement to determine the effective acceleration and the calculation accuracy when used in the response acceleration method are discussed and compared, and it is preliminarily verified that the displacement-based response acceleration method has good calculation accuracy and wider adaptability.