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RE: Design ground accelerations

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RE: US Army Corps of Engineers TI 809-04  It is a
seismic performance code.  It is not perfect, but it is the only thing out
there for new buildings.  It is free, and it also includes examples.  One of
the examples is a fire station.

The structural design is not all that difficult, the real issue (and cost)
is how "significant damage" is defined.  If the components are to be
seismically qualified, you will have to get into seismic qualifications like
ICBO AC 156.  

You may want to assure elastic performance for the 0.6g event, and allow for
nonlinear performance for the 0.8g event.  Using a response modification
factor of 1.25 assures an essentially elastic structure.

It is actually better to link the 2 performance levels to 2 distinct
probabilities as opposed to 2 acceleration levels, and determine the ground
motion response spectra for those probabilities.

Harold O. Sprague

> -----Original Message-----
> From:	Lynn [SMTP:lhoward(--nospam--at)]
> Sent:	Wednesday, September 11, 2002 3:23 PM
> To:	seaint(--nospam--at)
> Subject:	Design ground accelerations
> We have received plan check corrections on a Fire
> Station we designed.  The governing Code is the 1997
> UBC.
> The plan checker has sited a section in the
> Geotechnical report called "seismic shaking", that says
> the building should be designed for .6g without
> suffering significant damage, and .8g without
> structural collapse. 
> The plan checker then goes on to site the California
> Building Standards Administrative Code as requiring
> that the building be designed for the ground
> accelerations given in a Geologic Hazards Evaluation.
> The plan checker is asking for additional structural
> calculations showing that the building is able to
> withstand peak ground accelerations of .6g's without
> significant damage, and .8g's without structural
> collapse.
> What we have done is just used the 1997 UBC, taken into
> account the near source factors, and factored again for
> an essential facility.  Beyond that, I am not sure we
> are required to do anything.
> The language used by the plan checker seems to relate
> more to NERHP provisions and the IBC design
> methodology.
> Has anyone else come up against this, and if so, what
> have you done to satisfy the plan checker.
> Thanks
> Lynn

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