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

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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.
Jim Wilson

Harold Sprague <spraguehope(--nospam--at)> 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.

Harold Sprague

>From: Jim Wilson
>To: seaint(--nospam--at)
>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
>Stroudsburg, PA

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