FOUNDATION ANALYSIS OF A LARGE NUCLEAR ISLAND FOR SOIL CASES

摘要

This paper describes the foundation analysis of a large nuclear island resting on soft and medium soil sites to obtain forces and moments for basemat foundation design. The Nuclear Island (NI) under study consists of Reactor Building, Containment, four Safeguard Buildings and a Fuel Building resting on a common basemat. The analysis model consists of dynamic (SASSI) finite element model superstructure with the common basemat shell elements replaced by solid elements. The model has soil spring dashpot elements in the three translational directions at the bottom to idealize the soil column behavior and sidewall spring elements that idealize the active, at-rest and passive states of earth pressure caused by the movement of the NI sidewalls against the embedded soil mass. The model represents the sliding interface between the foundation concrete basemat and the underlying soil using 3D contact elements and allows for basemat uplift through compression only vertical springs. The model is loaded with static loads (100% dead loads, 25% live loads, 75% precipitation loads, hydrostatic forces/buoyancy and at-rest soil pressure) before a nonlinear time-history analysis is performed for the soil cases. In-column ground motions at the bottom of the NI common basemat foundation level obtained from SHAKE91 in the three translational directions are used as the input motions to the nonlinear time-history analysis. The dynamic response of the ANSYS model is benchmarked against the results from the SASSI model for validation. The forces and moments obtained from this model are to be used for structural design.