Re: Seismic Upgade of Older Structue

Larry,

What code you use depends on whether this is a voluntary retrofit or
one mandated by the AHJ. You say the owner "wishes to upgrade" to
current code. As you allude, you really can't get from a 1920's
building to "current code" without what a friend refers to as a
"blade remodel"--where you lower the blade of a D-7 at one corner of
the building and proceed to the opposite corner.

If the retrofit is voluntary, CBC Chapter 34 says you can do anything
you want (structurally) to the existing building elements as long as
you're not weakening it. I see lots of retrofits that were done
voluntarily where no harm may have been done, but hardly any good was
done either--but there are a whole lot of shiny metal connectors
installed that *look* really impressive to owners, realtors, buyers,
and news media (engineers were not usually involved in these
retrofits).

You're probably looking at new plywood roof sheating, some new
interior shear walls, drag struts here and there, diaphragm chord
reinforcement, roof-to-wall connections, and maybe elements to
reinforce the existing concrete walls for both in-plane and
out-of-plane loads. Fun stuff :-)

Good luck,

Thor Matteson, SE
www.shearwalls.com

>From: Larry Hauer [mailto:lhauer@live.com]
>Sent: Wednesday, November 10, 2010 1:34 PM
>To: Struct. Eng. Assoc.
>Subject: Seismic Upgade of Older Structue
>
>I have been asked to investigate an existing one story commercial
>building =
>with dimensions of 31'x 124' and a wood framed roof and exterior
>concrete w=
>alls. No plans are available, but documentation indicates the
>building was =
>built in the 1920's. The structure is in Southern California.
>
>The owner wishes to seismically upgrade the building to meet current
>code s=
>tandards, (2007 CBC). There are existing materials such as 1x
>straight roof=
> sheathing which has no value in the current code. Am I allowed to
>use valu=
>es for existing materials such as those found in the old 1997 UCBC,
>(Table =
>A-1-D), or maybe values found in some other codes such as the
>Historic Buil=
>ding Code, or are these values no longer valid since these codes are
>obsole=
>te?
>
>Thanks in advance,
>
>Larry Hauer S.E.

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