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Re: 1997 UBC Question

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Regarding UBC-97, Section 1632, Formula (32-2)...

The ratio hx/hr need not be taken as greater than 1, even if the component is
above the roof.  This has been made explicit in the IBC and is consistent with
the original intent of NEHRP Technical Subcommittee 8, from which the formula

Also, in NEHRP-97 and the IBC, the coefficient 3 has been reduced to 2.  This
is because the higher acceleration magnifications tend to occur only during low
level earthquakes.

John V. Loscheider, S.E.
Loscheider Engineering Co.
Renton, Washington

**********  ORIGINAL MESSAGE  **********

From: "Ritter, Mike" <mritter(--nospam--at)>
To: "'seaint(--nospam--at)'" <seaint(--nospam--at)>
Subject: 1997 UBC Question

List members,

I could use a little help interpreting the 97 UBC.  A colleague has
prepared a set of calculations to evaluate an elevated piece of
equipment, and has used section 1632 of the 97 UBC (Lateral Force on
Elements of Structures, Nonstructural Components and Equipment Supported
by Structures).  Specifically I have a question regarding the definition
of hx and hr.  hr is defined as the structure roof elevation with
respect to grade.  Is this the main building structure roof elevation or
the equipment structure roof elevation?  It appears that the ratio of hx
and hr is to make the seismic demand larger if the equipment is higher
in the building (makes sense) but I can read the hx definition two ways.

Anybody got the answer?

Thanks in advance,

Michael Ritter, PE