The use of frequency-independent soil-structure interaction parameters

Abstract The validity of approximating frequency-independent foundation impedance functions by constant parameters was evaluated for nuclear power plant structures. The soil-structure interaction system with the frequency-dependent impedances was analyzed using the Foss method to uncouple the equations of motion; this closely follows the method developed by Jennings and Bielak. The interaction system with the constant impedances was approximately analyzed by the normal mode method using equivalent modal damping values computed according to a procedure developed by Tsai. The above two methods were applied to simplified containment structural models founded on an idealized elastic half-space, the shear wave velocities being taken to be 600, 1150, 2000 and 10 000 ft/sec. The results such as frequencies, damping, and in-structure response spectra were then compared. It was concluded that frequency-independent foundation impedances can be adequately used for plant sites having relatively deep and uniform overburdens.