Keywords: field testing, seismic analysis, vulnerability assessment, nuclear facilities.

Seismic assessment of important existing structures that are designed according to prior seismic codes or even without considering any earthquake loading is one of the most important issues for minimizing seismic vulnerability. Within this paper the seismic assessment of an existing building for radioactive waste management is presented. By means of extensive dynamic in-situ measurements followed by finite element analysis a seismic vulnerability analysis was carried out. The non-structural units and fluids in tanks interact with the behaviour of the structure (e.g. where the stiffness or eccentricity significantly contributes to the structural response of the construction), hence the interaction of several machines and fluid structure interaction have to be considered [1]. The application uses a mobile vibration generator for forced vibration testing and offers the possibility of measuring and assessment of the structure as well as the soil conditions with accurate boundary conditions [2,3]. This information is used to obtain modal parameters of the structure for model updating and to obtain initial parameters for considering the soil-structure effects. The stiffness of the springs was further specified as an updating parameter in the modal updating approach. Since the updated model is based on measured results, it represents in a realistic manner the behaviour of the structure during the starting phase of a seismic event. By means of forced vibration tests an adequate frequency range and vibration level could be induced in the structure and surrounding soil surface. The advantages of forced excitation are the short test duration, the good controllability and the favourable signal to noise ratio [4]. With the improved finite element model, earthquake analysis for the local conditions and historical seismic events were carried out. Moreover the following issues were highlighted:

(i)

Considering fluid structure interaction (FSI) allows an adequate simulation of the water behaviour under dynamic excitation and increases the reliability.

(ii)

By using FSI the local dynamic pressure arising from liquid sloshing along the tank walls will be considered in a proper way [5].

(iii)

The analysis results without FSI lead to an overestimation of the deformation and stresses of about 20% for the global system.

(iv)

Post- processing of the transient analysis provides information about simultaneity of bending, shear and axial forces.

(v)

From the finite element analysis many different strengthening possibilities could be investigated and optimised.

(vi)

Using a vibration generator for the Rayleigh wave method is favourable, as the transmission of lower frequencies can be achieved, permitting investigations at greater depths.

1

K. Meskouris, "Baudynamik: Modelle, Methoden, Praxisbeispiele", Ernst & Sohn, Berlin, 1999.

2

M. Karray, G. Lefebvre, "Techniques for mode separation in Rayleigh wave testing", Soils Dynamics and Earthquake Engineering, 29, 607-619, 2009. doi:10.1016/j.soildyn.2008.07.005

3

M. Wathelet, D. Jongmans, M. Ohrnberger, "Surface-wave inversion using a direct search algorithm and its application to ambient vibration measurements", Near Surface Geophysics, 211-221, 2004. doi:10.3997/1873-0604.2004018

4

R. Flesch, M. Ralbovsky, M. Eusebio, A. Campos Costa, M. Oppe, R. Veit, "European Manual for in-situ Assessment of Important Existing Structures", LESSLOSS, IUSS Press July 2007, Report No. 2007/02, Pavia Italy, 2007.

5

H. Liu, D.H. Schubert, "Effects Of Nonlinear Geometric And Material Properties On The Seismic Response Of Fluid-Tank Systems", 2002 ANSYS 10th International Conference and Exhibition, Pittsburgh, PA, April 22-24, 2002.

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