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Re: Diaphragm

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Ashraf,
For a building that size, I would put in X-bracing in the roof. The CISC has stated that for large buildings, diaphragm action is not reliable. However some eminent engineer (Galambos?) has disagreed with that.
Gary

Ashraf, Mohammed (Qatar) wrote:
Thanks GM. I am using IBC 2003 code.
A brief description of building is given below for your info.
The building is of 107x60 m in plan size and maximum 17m height with
roofs at different levels.
The columns are of concrete and most of the beams are of steel. Roof is
of steel deck type. I have about 7 braced frame in the x-direction (107m
is in x-direction). The span of frames vary from 10 to 22m. In the
y-direction there are 7 columns @ a spacing of 10m. Only 3 bays are
braced. The height of braced bay is 8m and span is 10m.
The maximum size of diaphragm comes around 60x22m. What can I do to make this system more rigid?. Since I am using Open Web
Joists to support metal deck, does bridging help me to make the system
more rigid?.
Thanks and regards
Ashraf

-----Original Message-----
From: Gerard Madden, SE [mailto:gmadden(--nospam--at)maddengine.com] Sent: Saturday, May 27, 2006 9:43 AM
To: seaint(--nospam--at)seaint.org
Subject: RE: Diaphragm

Most likely not. I'm assuming the walls are concrete or steel braced
frame.
Unless the metal deck has concrete fill, it will be considered flexible
diaphragm. See the UBC/IBC for the definition of Rigid Diaphragms and
Flexible
Diaphragms. The deflection of the diaphragm would need to be less 2.5
times
the deflection of the vertical resisting elements of the lateral system
to consider it rigid and at best your would have a partially rigid
diaphragm
but with those plan dimensions, you would need several interior lines of
lateral resistance and you must also be careful to make sure that your
diaphragm
span ratios are not too great to violate whatever code your structure
falls
under.

-gm
-- Original Message --
Subject: Diaphragm
Date: Sat, 27 May 2006 09:14:22 +0300
From: "Ashraf, Mohammed (Qatar)" <mohammed.ashraf(--nospam--at)worleyparsons.com>
To: <seaint-ad(--nospam--at)seaint.org>
Cc: <seaint(--nospam--at)seaint.org>
Reply-To: <seaint(--nospam--at)seaint.org>



"This email is to be read subject to the disclaimer at the end of this
message
or attached to this message."

Hello all,

I have building of 107mx60m in plan size and maximum height of 17m.

The roof is of seamless metal deck from Bemo USA or other manufacture.

The metal deck is supported by open web joists. The maximum span of
joists is 22m.

Can I take this deck as rigid diaphtragm?.

Thanks in advance,

Ashraf




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