Nonlinear rocking analysis of nuclear reactor buildings

In this paper, the dynamic behavior of BWR (MARK-I) type nuclear reactor building is studied considering a geometrical nonlinearity based on the uplift of the base mat with the EL CENTRO 1940 earthquake applied as the input. The responses for the following two cases of inputs are compared. Case 1) Its NS (Max. 0.5 g) and UP-DOWN (Max. 0.3 g) components are applied simultaneously as the horizontal and vertical inputs respectively. Case 2) Only its NS (Max. 0.5 g) component is applied as the horizontal input. In respect to the maximum response horizontal accelerations, only a small difference is seen between Case 1) and Case 2). The vertical response accelerations are fairly large regardless whether the vertical input is considered or not. They are generated by the uplift phenomena of the base mat and are strongly amplified by rebond effect. The vertical input has little influence on the maximum response vertical accelerations. In case of the conventional seismic design, where by the simple combination of the maximum response overturning moment obtained by linear analysis for a horizontal input with a maximum acceleration of 0.5 g and static vertical force of gravity g plus and/or minus 0.3 g, the building results in an overturn. However, in case of the nonlinear dynamic analysis by simultaneous inputs for the horizontal direction with the maximum acceleration of 0.5 g and for the vertical direction with the maximum acceleration of 0.3 g, it is quite stable against an overturn. (author)