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Re: roof deck wind screen

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Jeff,

I would take a look at the local governing code first.  I don't know what
code you are under but I can speak some to the BOCA code.

The BOCA code give specific requirements for "updating" the structure for
new live loads and seismic loads but is basically silent on wind.

Section 1614.0 deals with "Existing Buildings".  This section deal
primarily with changes in gravity loads.  Section 1614.2 deals with
additions and basically says an addition "shall not increase the force in
ny structural element of the existing structure by more than 5 percent...",
which I interpret that to mean that if you cause an existing member to be
overstresses by more than 5% by putting on an addition, then the member
must be reinforced.  This would be true for wind or gravity loads.  The
other item of importance in the sections is Section 1614.5, which deals
with changes of occupancy, but this deals mainly with gravity loads.

Section 1610.1.1 deals with additions to buildings with regards to seismic
loading.  It basically states that if the addition increases the forces in
existing members by less than 5% and the addition is designed to meet the
new seismic, then the existing building need not meet new seismic criteria.

The above is rather abbreviated "para-phrasing" of the code, so you might
want to look at it yourself (or if you ask, I can actually type out the
exact wording if you don't have a BOCA).  Also, keep in mind that the code
is a minimum.

After all that hot air, my thoughts...

If the new screen wall increases the stresses in your main lateral system
for wind by more than 5%, then an upgrade of the system might be in order
(a judgement call really).  With regards to seismic, unless that screen
wall is made of masonry (CMU), I would think that it will not change your
overall seismic loads by more that 5%.  Thus, I doubt a seismic upgrade
would be in order due to the screen wall.  Now, the building may be
seismically insufficient regardless of the screen wall...but that is a
completely different can of worms.

Scott

At 04:53 PM 10/28/99 -0700, you wrote:
>Say you have a three story building with a roof deck and the client wants to
>put up a 6 foot high wind screen along 50% of one of the longitudinal
>exterior walls. Would this require a complete upgrade of the lateral system
>in the offending direction? If so, would you not then be obligated to
>consider improvements for seismic loads?
>
>I have seen these wind screens in several places, yet I am sure no one ever
>upgraded the building due to the wind screen.
>
>Jeff Smith
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