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# Re: How to model for flexible diaphragm analysis?? Help

• To: <seaint(--nospam--at)seaint.org>
• Subject: Re: How to model for flexible diaphragm analysis?? Help
• From: "Greg Smith" <strusup(--nospam--at)gte.net>
• Date: Fri, 30 Jul 1999 08:59:10 -0500

```This is the thread that I was addressing in the two part post about mass.
Sorry to confuse.

Greg
-----Original Message-----
From: Seaintonln(--nospam--at)aol.com <Seaintonln(--nospam--at)aol.com>
To: seaint(--nospam--at)seaint.org <seaint(--nospam--at)seaint.org>
Date: Friday, July 23, 1999 2:15 PM
Subject: How to model for flexible diaphragm analysis?? Help

>In the past I would break a complicated geometry down into smaller blocks
and
>analyze each separately - accumulating the shears at the junction of each
>block. If I have a structure with skewed walls or if the roof is at a
skewed
>angle from another block, I would have isolated this area and designed it
for
>lateral movement normal to its angle.
>
>The '97 code suggests that we split the design into flexible and then rigid
>(torsion) analysis and compare the results from each - increasing the shear
>as needed due to torsion.
>This poses a bit of a problem as it becomes easier to model the whole
>structure for rigid diaprhagm and shearwall distribution since it produces
a
>point for Center of Mass, Rotation and where the lateral load is to be
>applied.
>
>Is it still valid to break apart the flexible diaphragm analysis to account
>for the difficulties of skewed sections and leave the Torsional analysis as
>the complete system?
>
>If not, can anyone suggest how to set up the flexible model as a whole and
>how I would distribute shear to the skewed sections? Would I simply place
>gridlines in the two major axis runing through the center of skewed walls
and
>taking tributary areas btween gridlines and finding the priniple vectors
for
>each of the skewed walls???
>