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Re: Seismic forces from industrial equipment

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With respect to the 1997 UBC.

The system you described is not a building or an element of a structure.
It is a Nonbuilding Structure.  The structure type is probably a
Cantilevered-Column Type Structure (Select R = 2.2 from Table 16-P),
although it may be an  "All Other" structure (Select R = 2.9 from Table
16-P).  Calculate the fundamental period of your system in each direction.
Determine the design base shear in each direction.

If you pedestal is considered rigid (T < 0.6 seconds), like a wall pier in
the transverse direction or a big block, refer to Section 1634.2.  The
design base shear is determined by Eq. 34-1.

If your pedestal is considered flexible (T > 0.06 seconds), like a wall
pier in the longitudinal direction or a tee-support, refer to Section
1634.5.  The design base shear is determined by Eq. 30-5, with a maximum
determined by Eq. 30-4, and minimums determined by Eq. 34-2.  If you are in
Seismic Zone 4, you must also check minimum Eq. 34-3.

The above is consistent with petrochemical industry practice.

Rick Drake, SE
Fluor Daniel, Aliso Viejo, CA

*******************************************





RajSTC(--nospam--at)aol.com on 09/06/2000 02:44:45 PM

Please respond to seaint(--nospam--at)seaint.org

To:   seaint(--nospam--at)seaint.org
cc:

Subject:  Seismic forces from industrial equipment



Seismic criteria in ASCE 7 and UBC are tailored for building structures.
ASCE 7-93 specifically excludes industrial towers, equipment, etc., from
its
provisions. UBC 1997 has increased the confusion that existed in previous
versions.  So far, I was using some judgment in estimating seismic forces
for
horizontal tanks supported on concrete pedestals.  The error in judgment,
if
any, would not affect the design in lower seismic zones because wind loads
would more likely to be the governing lateral force.  However, for heavier
tanks, the error in estimating seismic force may be less desirable.

Any suggestions for estimating seismic forces from industrial equipment
such
as horizontal tanks supported on concrete pedestals?

P. Rajendran
Service & Technology Corporation
105 SW Penn
Bartlesville, OK 74003
Ph: 918 336 8161  FAX: 918 336 8265

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