# RE: Plan Irregularity Type 5

• To: <seaint(--nospam--at)seaint.org>
• Subject: RE: Plan Irregularity Type 5
• Date: 06 May 2005 09:44:09 -0700
• Date: Fri, 6 May 2005 09:43:39 -0700
Use this argument:

1: take a shearwall building like a tilt up for simplicity.
2: On the Front of a modern tilt-up, you have many windows and
storefront entrances. On the back you have dock doors, on grade doors,
and man doors.
3: The building is perfectly rectangular in plan.

Now, since the building uses the walls as it's lateral force resisting
system, the rigidity of the back and front walls is obviously different.
If you cut a mirror image through the centerline, you DO NOT have
symmetry by definition. Would the building official classify this as a
type 5 plan irregularity? If so, he/she should be re-assigned.

-gm

-----Original Message-----
From: Paul Crocker [mailto:pcrocker(--nospam--at)reidmidd.com]
Sent: Friday, May 06, 2005 9:34 AM
To: seaint(--nospam--at)seaint.org
Subject: RE: Plan Irregularity Type 5

This is now I understand it, but how does one explain the "or symmetric"
part if... hypothetically... the person asking was a plan reviewer and
they aren't interested in how you view the code, or how it has always
been taken to read, so much as how it is literally written...
hypothetically.  Without the "or symmetric" it makes perfect sense.  It
seems possible that the "or symmetric" is meant to give you one more way
to avoid the Type 5 tag, if the system is non-orthogonal but it is
symmetric, but I can't quite see how that would help make the system
better to the point that some special measure wouldn't still be

Paul Crocker, PE, SE

Not Parallel is correct. Center of Rigidity vs. Center of Mass with
accidental torsion is taking care of the "Non-symmettric" and it's not a
plan irregularity. Use the 100%-30% rule or SRSS analysis.

Hth,
-gm

-----Original Message-----
From: Paul Crocker [mailto:pcrocker(--nospam--at)reidmidd.com]
Sent: Thursday, May 05, 2005 4:01 PM
To: seaint(--nospam--at)seaint.org
Subject: Plan Irregularity Type 5

A question has arisen recently among a few engineers locally about the
meaning of a Type 5 plan irregularity.  I have always thought of this as
a non-orthogal systems irregularity, but looking at ASCE 7-02 Table
9.5.2.3.2, the definition is: "The vertical lateral force-resisting
system elements are not parallel to or symmetric about the major
orthogonal axis of the lateral force resisting system."  The
interpretation, that had never occured to me, is that the "or" in the
sentence means that it applies to either non-parallel systems or
non-symmetric systems.  Since 95% of layouts are not perfectly
symmetric, 95% of buildings would have a Type 5 irregularity.  I have
not understood this to be the meaning of the irregularity, but I don't
see how I can adequately explain the "or symmetric" part.  Does anyone
have any insight into this?

Paul

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