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Earthquake + Short circuit ?

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Gentlemen,
 
More than once I have come to this subject, when dealing
with industrial projects involving Electric-Power facilities.
The specific issue arises in the design of foundations for a
turbo-generator, in a highly seismic area. Among the loads
affecting the system, we may handle operation loads
( in steady-sate and start-up conditions ), short-circuit and
seismic loads, in this case.
 
Now, for combos to produce loading cases for design, 
operation loads + seismic loads, is a case to be considered,
as it is also the short-circuit + op. ( usually the higher loads ), but
the criteria that I have seen ist not considering simultaneously,
the earthquake and the short-circuit, i.e. short-circuit + seismic
loads is not a case to be considered. The very small fraction
of time for the short-circuit lasting ( less tha 1 sec ), as compared
with the strong phase of the quake, is one of the factors supporting
this approach. On the other side, I have been told by electric
engineers, that there are no reports of short-circuits produced
because of the quake, in these facilities. Nevertheless I knew of
some calculations that were considering this loading case.
 
If someone has an opinion and/or knows of any recommendations,
code or provisions addressing this point, I will appreciate the
information. 
 
Regards,
 
Raúl Labbé S.E.