Seismic qualification by means of indirect methods

Hie indirect method of qualification relies on establishing the similarity of a candidate item to a reference item previously qualified by means of analysis, testing or earthquake experience. To some degree, large quantities of data from earthquake experience, in particular those applicable to the seismic qualification of distribution systems, have been used to justify simpUfication of the analytical evaluation and seismic qualification of such systems . Seismic qualification of cable trays is an example of a simplified analytical evaluation based on data from earthquake experience. 

The seismic input used to quaUfy the candidate item should envelop the design spectra for that item and the seismic input used for the reference item it should also equal or exceed those required for the candidate item. Proper similitude relationships should be considered in input to scale models. The physical and support conditions, the functional characteristics for active items and the requirements for the candidate item should closely resemble those for the reference item. 

The reliable application of indirect methods depends on the appropriate formulation and application of rigorous and easily verifiable similarity criteria. The validation of such criteria and a qualified training of the review team are key issues for the process and should be explicitly recorded in the safety documentation. 

The training records for the engineers who conduct the seismic walkdown and the evidence that appropriate criteria have been met should be collected in the safety documentation for the qualification in accordance with the applicable quality assurance procedures. 

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