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RE: Design ground accelerations

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Michael Bryson wrote:
"Fire the geotech and find one who will design to the minimum code
requirements, not beyond them."



Maybe we need to step back and look at what is being asked for and what type
of building we are applying it to.  

First, the original poster identified the structure as a fire house which
would place it in the essential services category. 

Second, the building Code is a set of MINIMUM, not MAXIMUM requirements.

Third, while I agree that the geotechnical engineer has gone beyond what I
have found to be normal practice, he has apparently considered the nature of
the building to be designed and in his own way tried to clarify what ground
motions would apply to what level of safety.  I would hope he did this in
consultation with the owner and structural engineer (although it sounds like
the structural engineer and geotechnical engineer weren't talking in this
instance).  If there is a provision in the geotechnical report the
structural engineer is concerned about, he needs to talk with the
geotechnical engineer BEFORE going to plan check.  Plan checkers do read
submittals and the better ones do understand what is presented.

Fourth, if we as structural engineers never go beyond minimum code
requirements, we are doing our clients a disservice.  That stated, we should
be discussing the level of performance with our clients, educating them on
what it means and following their instructions (based on their reasonably
informed decision) using the building code as the MINIMUM acceptable level
of service.

Fifth, the 1997 UBC, cited as the controlling code, states in Section
1629.4, "Seismic hazard characteristics for the site shall be established
based on the seismic zone and proximity of the site to active seismic
sources, site profile characteristics and the structure's importance
factor."  This provision allows for greater design forces if, in the opinion
of the project team (including the Owner, structural engineer, geotechnical
engineer and the architect (sigh!)), a greater seismic hazard exists. If the
project criteria, as presented by the project team to the plan checker, call
for a higher level of design, I think the plan checker is within his rights
under this section, to ensure that a consistent level of design is used
relative to the seismic hazard. Without more available information, we
shouldn't be second guessing the geotechnical engineer.  Rather, we should
be talking with him or her to ensure we are all speaking the same language
and have the same project goals in mind.

Sixth, if it were my community, I wouldn't want MY fire station being
designed to the MINIMUM code provisions if it is truly to be functional
after a major earthquake.  Fred Turner of the Seismic Safety Commission has
done some remarkable studies of the failure of fire doors (presumably
designed to code) to operate following a variety of earthquakes.  A simple
door failure can take out critical response crews for a considerable period
of time in the important first hours immediately following an earthquake.
Failure of the structure can take out these crews for an even longer time.

So Michael, before you "fire the geotech" for designing to greater than
MINIMUM CODE REQUIREMENTS, you might want to understand what he is saying.
He may be saving your butt by making the project design appropriate for the
intended use, one that will perform as intended.  On the other hand, he may
be unduly conservative.  Either way, you won't know if you don't talk with
him.  It is just common courtesy.

Regards,
Bill Cain SE
Oakland CA

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