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RE: wood frame bldg deformation and windows

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Thanks Paul,
I've been patiently waiting for someone to point this issue out. George
Richards said it, however, not as elegantly. We don't design to protect
windows - we design to prevent collapse or major structural damage.
Broken glass curtain walls are a hazard to pedestrians and I'm sure
cities like Chicago have had their share of problems (I remember when
glass came out of the Hancock Center when I lived in Chicago many years
ago).

I don't mean to be cavalier on this issue either, but it leads into a
discussion that is to be held at the forthcoming BSSC National Meeting
in Atlanta- whether or not we should design buildings based on
performance (the same issues raised by SEAOC's Vision 2000).

As long as the IRC remains a standard for most of the country's
residential design, creating tougher standards that go as far as to
attempt to predict performance will drive the builders away from
engineered products and into the hands of the lowest quality, highest
profit homes. In other words, the quality of construction will take a
greater dive than it did when the 97 UBC was codified. There is an
incentive to reduce the cost of materials and labor so long as it exists
in the code - and this is exactly what the IRC is - a prescriptive
method.

If a home does not meet the provisions of conventional construction, it
does not necessarily disqualify it from being designed prescriptively.
The code has a provision that allows the builder to seek the services of
an engineer to address the non-compliant portion of the building. I
received one of these jobs today - a prescriptive builder with a
non-compliant wall or two.

It isn't a matter of affordability based on the square foot cost of real
estate. The UBC provisions work very nicely for steel, concrete and
masonry buildings - those which we can design stiffness into narrow
panels or columns. Wood doesn't give the design many ways to design
narrow yet stiff panels without resorting to proprietary (and generally
costly) braced frames, cantilevered columns (not practical above one
story) or moment frames. The code is much more predictable with
homogeneous materials and wood does not fit into this category.

IMO, we need to understand that broken glass, and other accoutrements as
part of a building are expendable, non-structural features and the
homeowner has less than reasonable expectations if they believe we can
design wood frame buildings to protect windows from cracking or
breaking.

Even if we get rid of prescriptive methods (and I don't think we should
except in high risk areas), it is still unreasonable to try and predict
the performance of wood frame structures. It's less expensive to educate
the public and focus on improving the quality of the products we
produce.

Regards,
Dennis S. Wish, PE
California Professional Engineer
The Structuralist.Net Information Infrastructure

Website:
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-----Original Message-----
From: Paul Feather [mailto:pfeather(--nospam--at)SE-Solutions.net]
Sent: Tuesday, January 08, 2002 5:57 PM
To: seaint(--nospam--at)seaint.org
Subject: Re: wood frame bldg deformation and windows

I need to jump in here.  Residential windows do not fall under the
requirements of 1633.2.4.2.  1633.2.4.2 is intended for rigid panel
elements
such as precast cladding or prefabricated cladding panels and the
connections of these elements at different floor lines having the
capacity
to accommodate seismic drift without failure of the panel support
connections or the panels themselves.  The references that invoke the
requirements for 1633.2.4.2 are contained in section 1632.2 "For
applicable
forces and Component Response Modification Factors in connectors for
exterior panels and diaphragms, refer to Sections 1633.2.4, 1633.2.8,
and
1633.2.9"  Residential windows can hardly be considered an exterior
panel or
diaphragm.  In fact having a window means there is a hole in the
exterior
panel or diaphragm.

The intent of these provisions was to ensure that large cladding
elements do
not fall off the structure and endanger the public during a seismic
event.
Additionally these provisions are intended to prevent rigid exterior
panels
from binding and acting as unintended shear resisting elements or
failing
from unintended load transfer when supported by more flexible frame
systems.
Read the other five requirements under 1633.2.4.2 and you will realize
that
applying these requirements to a residential window in a wood framed
structure is completely incorrect and taking pieces of the code out of
context.

Paul Feather


----- Original Message -----
From: "Regis King" <steelfishes(--nospam--at)hotmail.com>
To: <seaint(--nospam--at)seaint.org>
Sent: Tuesday, January 08, 2002 4:42 PM
Subject: Re: wood frame bldg deformation and windows


> You think non-conformance with the building code is a "non-issue"?
Seems
a
> little cavalier to me.  I'm sure the difference between 2x and 3x
plates
is
> also a bit of a "non-issue", but you won't soon forget the experience
of
> inadvertantly specifying 2x plates in a high-seismic area, believe me.
>
> Regis
>
>
> >From: "Conrad Guymon" <conrad(--nospam--at)karren.com>
> >Reply-To: <seaint(--nospam--at)seaint.org>
> >To: <seaint(--nospam--at)seaint.org>
> >Subject: Re: wood frame bldg deformation and windows
> >Date: Tue, 8 Jan 2002 15:35:49 -0700
> >
> >Are the windows the full story height?   If they are not, would it be
> >appropriate to use (window height/story height)*Delta M to obtain the
drift
> >differential between the bottom and top of the window?  Would this
reduce
> >the value to something you could handle?  Do you have drift
calculations
on
> >the wood shear walls?
> >
> >It sure seems like this is a non-issue.
> >
> >That's my two cents worth.
> >
> >Conrad
> >----- Original Message -----
> >From: "regis king" <steelfishez(--nospam--at)hotmail.com>
> >To: <seaint(--nospam--at)seaint.org>
> >Sent: Tuesday, January 08, 2002 4:42 PM
> >Subject: wood frame bldg deformation and windows
> >
> >
> > > Have any of the list members had to address the effect of seismic
drift
> >on
> > > the windows of a wood frame apartment building? I am not referring
to
a
> > > large retail window wall system, but rather typical residential
windows.
> >UBC
> > > 1633.2.4.2 includes "elements that are attached to or enclose the
> >exterior".
> > > Most vinyl windows are attached with vinyl flanges on the outside.
I
> >believe
> > > that the vinyl itself has some inherent flexibility, but this is
> >obviously
> > > difficult to quantify. I know that slotted holes can be used.
However,
> >the
> > > slotted holes are not likely long enough to meet the code
requirements
> >if
> >a
> > > residential window is included in UBC 1633.2.4.2. Note that this
same
> > > section requires the greater of Delta M or 0.5 inches. The slot
would
> >have
> > > to be 1" + the width of the screw to qualify. I have never
addressed
> >this
> > > issue and it has been brought up on one of my jobs.
> > >
> > > Thanks in advance for any help.
> > >
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