Bell-ring vibration response of nuclear containment vessel with attached-mass under earthquake motion

There are two types of vibrations, such as 'Beam-type vibration' and 'Bell-Ring type vibration', of nuclear containment vessels as axisymmetric thin shell structures. Up to this time, the seismic analysis for such thin axisymmetric shells mostly has been performed only to the 'Beam-type vibration'. Because, in fact, the response participation factor for the 'Bell-Ring type vibration' under seismic motion is zero when the shell structure is in perfectly axisymmetric shape. However, as in nuclear containment vessels, when the thin axisymmetric shell has several attached heavy masses such as the equipment hatch or the man holes, seismic responses of 'Bell-Ring type vibration' are caused unexpectedly large and become remarkably more important than the 'Beam type vibration'. For the seismic analysis of 'Bell-Ring type vibration', there was the method of analysis advocated by H. Shibata. This method was the approximate uncoupled analysis using the natural mode shapes of unweighted perfect axisymmetric shell, on the assumption that the effect of the attached mass might be very small to their natural modes. However, for some models, the responses of 'Bell-Ring type vibration' calculated were noticeably smaller than the experimentally obtained results. The seismic response analysis of the 'Bell-Ring type vibration' coupled with the 'Beam type vibration' though the attached masses is given with the new consideration. The results show good agreement between the theoretical calculation and the experiment