RECIPROCITY THEOREM AND SEISMIC LOADS IMPACTING RIGID BASEMENT IN COMPLEX SOIL ENVIRONMENT

摘要

Platform model of the soil-structure system with lumped frequency-dependent soil springs is widely used in seismic analysis of NPP structures with rigid basements. However, for embedded basements it is not easy to link lumped seismic loads for this model to the free-field motion. Further difficulties arise in case rigid basement is surrounded by finite volume of the modified soil spoiling the horizontal layering of the initial soil foundation (this case is called "complex soil environment"). The author derives both continuous and mesh solutions for this case, using the reciprocity theorem extended to the frequency domain. In addition to the contact surface of the basement one has another surface limiting the volume of the modified soil. Contact problems with vibrating rigid basement are solved for the modified soil foundation with a new soil in a finite volume around the basement and "empty" outcropped volume (inside the embedded basement). As usual, response forces at the contact surface of the rigid basement are obtained and used to calculate integral impedances. Besides, the response displacements at the second "flexible" surface are also obtained. They are used to average the free-field seismic motion in the initial soil foundation at the second surface, and the result is equal to the lumped seismic load impacting the first surface (according to the reciprocity theorem). This analytical result is in good agreement with previously used mesh algorithms, but helps to develop new algorithms, saving computational resources.