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Sheilding

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Gabriel Bohm wrote:
>>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?

<<<
If your client wants to treat these buildings as a group,
then you should change the distance between buildings to
something smaller than 16 feet.  I agree with an earlier
post that wind tunnel tests should be conducted to verify
the amount of shielding benefit from these buildings at that
distance.

The end buildings have an aspect ratio of 6 to 1 with only
20 feet to resist the lateral forces.  Depending on the
lateral system chosen, the seismic design of the middle
buildings may not require a large increase to accomodate
the wind design.

If your client still wants to treat these buildings as a group
ask this question:  If a fire, earthquake or other natural
disaster damages one of the buildings to the point where it
needs to be replaced, is your client going to tear down all
of the buildings?  If not, then you still need to have the
other buildings designed without considering the sheilding.