- In PipingDesign@yahoogroups.com, "Tony Paulin" <tony@p...> wrote:
> New seismic deisgn documents from about 1997 on have been tending
toward
> significant increases in the design inertial load constants for
piping and
> pressure vessels because of failures in some unrelated components
and an
> extension of the design basis period. We are seeing Code documents
in draft
> form that will increase seismic g loads by three times or more over
values
> used in pre 1997 documents. This posting is to query is to see if
anyone
> has experienced seismic failures of supports or piping components
due
> purely, or at least in large part, to the inertial loading of the
pipe. The
> majority of seismic failures that we have reviewed were caused by
the
> relative movement of pipe or supports and not due to inertial
loads. If this
> is universally the case, then increasing g loads is probably not
the way to
> address these failures and will only serve to increase
unnecessarily the
> cost of piping systems subject to seismic loads.
>
> Comments or references appreciated.
> Regards,
> Tony Paulin
My experience supports your conclusion.
Many seismic failures were the result of seismic anchor motion at
equipments or at the supporting structures where the designer had
originally assumed rigid. A large vessel/Structure may be rigid, but
in a seismic event, this anchor point moves independently from the
pipe (different natural frequnecies). When the seismic movements of
the anchor and the pipe are out of phase, failure can occur. The
inertia of the pipe coupled with that of the anchoring points may be
enough to cause failure.
Examples:
Pacific Lumber Company powerhouse; Calif.
Stanford University Cogen; Calif.
Univ of Calif San Francisco cogen; Calif.
Tsuruga NPP; Japan
Wolsong NPP; Korea
I have not seen seismic failure purely because of the inertial
loading of the pipe.
Received on Tue May 27 18:51:00 2003