In situ dynamic tests and seismic records on the RHR system building enel IV nuclear plant/caorso (Italy)

Abstract

The tests on the RHR Building of the Caorso Nuclear Plant are part of a program of dynamic tests on large structures sponsored by ENEL, which ISMES is presently carrying out. The main purposes of this program are: • - to collect information on the effectiveness of different excitation methods; • - to set up the most suitable recording and processing technique; • - to compare the experimental results with the computed ones, in view of the validation of the adopted computing schemes. The structure has been excited by a mechanical vibrator delivering sinusoidal forces in a frequency range 2 to 20 cps, in conditions of empty, 1 3 , 2 3 and completely full pools. The response, recorded by 36 velocity transducers was digitally processed by means of a Fourier Analyzer. Moreover, a number of Friuli earthquake aftershocks could be picked up, and the building response recorded in many points. More than ten natural frequencies could be detected, and the related damping and mode shapes determined, in a frequency range from 3 to 16 cps. The structure frequencies determined by tests are lower than the computed ones. The energy content of the seismic excitation, due to the large distance from the epicentral area, is confined within very low frequencies. Some data on the behaviour of the RHR and Reactor buildings could however be obtained. The testing technique adopted, which does not require long testing time and high costs, supplies a large amount of reliable data in case of excitation within the linear range. To account for non-linearities, different testing methods should be used, such as blasting or strong forced vibrations of the foundation. Moreover, the adopted method can fully describe the higher vibration modes, which are of noticeable importance as to the behaviour of mechanical and electric equipment installed in the structure.