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RE: Building corner wind effect - when is a corner a corner?

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ASCE 7-02 Page 44 shows that walls have vertical corner zones only.  The corner zone does not continue along the top edge of the wall.  Figure 6-17 on page 67 shows the same thing.
 
If I wasn't clear when I originally mentioned roof edge, I was trying to describe the leeward edge at the top of the wall.  That is where BOCA 1609.8.2 does indicate there are corner/end zones for C&C, but ASCE does not.
 
Jim

Harold Sprague <spraguehope(--nospam--at)hotmail.com> wrote:
Jim,

I am not sure which issue of ASCE you have, but the ASCE 7-02 page 44 shows
the corner zone for components and cladding.

Regards,
Harold Sprague


>From: Jim Wilson
>Reply-To:
>To: seaint(--nospam--at)seaint.org
>Subject: RE: Building corner wind effect - when is a corner a corner?
>Date: Tue, 14 Sep 2004 19:30:12 -0700 (PDT)
>
>ASCE 7 seems remiss in not visually depicting the roof edge as a corner
>zone. The figures are quite clear that only the vertical corners receive
>corner effects. I agree with my limited knowledge of wind testing that the
>roof edge IS a corner, but it could more easily be argued the other way,
>given what is in the figures.
>
>And thanks for the update on ASCE 7-05. I'll start surcharging my clients
>now.
>
>Thanks,
>Jim Wilson
>
>
>Harold Sprague wrote:The edge of the roof is a
>corner. BOCA never developed a commentary. The
>ASCE develops commentary. The other point that should be made is that if
>you design per the 1993 BOCA, you will have pressures that are too low. The
>ASCE 7 underwent very marked changes in the mid and late 1990's due to
>Hurricane Andrew. We were wrong, and the ASCE needed help. We switched
>over to 3 second gust and changed the way local pressures were calculated
>especially on fasteners.
>
>I would suggest that you require a Factory Mutual I-90 roof. That should
>keep you out of the code problems and get you the performance that you
>need.
>
>By the way, I am in San Francisco Friday and Saturday working on the next
>evolution of the seismic section of the ASCE 7-05. I think that you will
>like the improvements.
>
>Regards,
>Harold Sprague
>
> >From: Jim Wilson
> >Reply-To:
> >To: seaint(--nospam--at)seaint.org
> >Subject: Building corner wind effect - when is a corner a corner?
> >Date: Fri, 10 Sep 2004 11:04:33 -0700 (PDT)
> >
> >ASCE 7-02 Figures 6-3 and 6-17 illustrate that the end zone of a wall
> >receives a higher negative wind loading for components and cladding. But
> >there is no end zone treatment along the leeward edge of the roof.
> >
> >BOCA Figure 1609.8.2, on the other hand, does treat the roof edge as a
> >building corner for components and cladding. My intuition tells me that
> >BOCA is right on this, but I would otherwise prefer to follow the more
> >current recommendations in ASCE.
> >
> >To complicate my interpretation more, I am designing to the Mass Building
> >Code which is modeled on BOCA 1993. They provide tabulated wind pressures
> >by elevation, zone (location within the state) and exposure. Corner type
> >areas are defined as "The salient corner shall be defined as the vertical
> >surface located within a distance of 1/10 the least width of the
>structure,
> >but not more than ten feet, from a prominent (salient) corner." A
> >"prominent (salient) corner "sounds like it should include the roof edge.
> >
> >Thus my question - When is the roof edge considered a "corner" for
> >increased wind loads on components and cladding? I have already concluded
> >and designed my system for corners at the roof. But now that the
> >contractor did not install the roof edge as if it were a "corner".....
> >
> >Jim Wilson, PE
> >wilsonengineers(--nospam--at)yahoo.com
> >Stroudsburg, PA
> >
> >
>
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