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RE: Shielding

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Gabe,

In order to consider shielding from an adjacent building you would need
to have testing done in a boundary-layer wind tunnel:  

ASCE 7-95 Commentary:  "Due to the lack of reliable analytical
procedures for predicting the effects of shielding provided by buildings
and other structures ... reduction in velocity pressure due to shielding
are not permitted under the provisions of 6.4.2.  However this does not
preclude the determination of shielding effects ... by means of the wind
tunnel procedure in 6.4.3"

Of course the testing might show that the adjacent buildings increase
the wind forces due to channeling and buffeting rather than providing
shielding.

Ed Marshall, PE
Simons Engineering,
Atlanta

> -----Original Message-----
> From:	Bohm, Gabriel [SMTP:GBohm(--nospam--at)kticorp.com]
> Sent:	Wednesday, September 09, 1998 8:16 PM
> To:	'seaint(--nospam--at)seaint.org'
> Cc:	Riddick, Gene
> Subject:	Shielding
> 
> Your help is requested with the following wind loading situation. 
> 
> I have five identical buildings, spaced 16 feet apart. Building height
> is 120 feet. Building width is 60 feet - this is the dimension
> perpendicular to the wind direction. The dimension parallel to the
> wind
> direction is 20 feet. The buildings are in perfect alignment, such
> that
> the first one effectively shields the other four. 
> 
> Normally, we would design one of the five buildings treated as a
> self-supporting entity subjected to full wind loading, then simply
> build
> five such structures, with or without interconnecting struts. The
> client, of course, understands the cost implications of this approach.
> 
> This time, it's different - the client insists that we take advantage
> of
> wind load reduction due to shielding, and wants the five buildings to
> be
> interconnected and treated as one large structure.
> 
> ASCE 7-95, paragraph 6.5.4, prohibits shielding, but the client
> guarantees that the five buildings will always stay together. If so,
> using shielding makes sense. A call to ASCE confirmed that paragraph
> 6.5.4 is not gospel. Unfortunately, ASCE 7-95 does not address wind
> loading for series of buildings. Here are my questions:
> 
> 1. Is it OK to apply wind loads only on the windward wall of building
> 1
> and leeward wall of building 5?
> 
> 2. Is it reasonable to assume that, as the wind goes around the
> buildings, vacuum will develop in the spaces between the buildings,
> which in turn will generate suction on all interior wall surfaces? 
> 
> 3. If my above assumptions are incorrect, what would be the correct
> approach for applying wind loads?
> 
> Many thanks,
> 
> Gabe Bohm
> San Dimas, California
> 
> 
> 
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