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Re: Is it a shearwall or not??? Need some help

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Dennis,

I think your analysis is valid but as I think someone else has already said,
that wall may not be aware that it is not a shear wall -- Mother Nature
being the ultimate arbiter of disputes between engineers and the physical
word.  Before I would proceed on the assumptions you outline I would want
to:

(a) see the building to verify that it appeared to be in good condition (fee
or gross external evidence of significant damage or defect),

(b) advise my client of the fact that even though I could probably get a
building official to agree to allow him to make the penetration without
reinforcing the interior wall the net effect would likely be a reduction in
the structure's grand total overall ability to absorb energy in future
earthquakes,

(c) advise my client that my design was going to be based on the assumption
that the original design and all subsequent modifications had been made
responsibly and per applicable codes so as to give him or her the
opportunity to advise me if they knew of any reason to think this might not
be true, and

(d) verify that the project did not involve a change in use or occupancy
that would trigger a "whole building" analysis or upgrade.

Drew

----- Original Message -----
From: "Dennis Wish" <dennis.wish(--nospam--at)gte.net>
To: <aec-residential(--nospam--at)polhemus.cc>
Cc: "SEAINT Listservice" <seaint(--nospam--at)seaint.org>
Sent: Thursday, November 02, 2000 9:15 AM
Subject: Is it a shearwall or not??? Need some help


> I have a small project which I need some advice. Because I am on the
SEAINT
> list in digest format, I would appreciate it if anyone who responds can
send
> it to me directly at admin(--nospam--at)structuralist.net. Here is the problem:
>
> The building is a concrete commercial building about 50 years old, two
> stories - 45-feet deep by 38-feet wide. The roof and floors are framed
from
> a center wall parallel to the 38-foot width. This means that the floor
> framing does not exceed 19-feet on either side of the interior bearing
wall.
>
> At the second floor, this partition is the full depth of the diaphragm -
> roughly 45-feet and is sheathed in gypsum board on both sides. On the
first
> floor, this interior bearing wall is less than 35 feet long with various
> openings. It is sheathed with gypsum on one side and paneling on the
other.
>
> The client wants to place a 27-foot opening in the second floor wall to
join
> the two office spaces.
>
> Problem:
> Inasmuch as there are no existing drawings or analysis, I am afraid that
if
> the wall were designed for shear (150 plf times two sides or 300 plf) I
> would be redirecting the shear into the exterior concrete wall sections.
The
> problem is that the second floor exterior walls are sufficient for shear,
> but the first floor is glass storefront with minimal shear resistance in
the
> form of a cantilevered panel that sits back 8-feet from the glass front.
>
> Assumption.
> I need to know if the conclusion I wish to draw is a valid assumption:
>
> The first floor bearing wall (interior) is significantly weaker than the
> second floor wall if shear is considered - about 1/4 of the second floor
> wall capacity. I would assume that the wall, although bearing, is not
> designed to transfer shear from the roof to the foundation since the first
> floor wall would never be able to meet the demand.
>
> It is possible that the building had been remodeled numerous times and
shear
> removed with each attempt, however, I don't believe I need to go further
> than to assume the building to be laterally stable at the time I started
> work on it. Therefore, I would treat this second floor wall as only a
> bearing partition and make the opening.
>
> The problem of trying to recreate the shear at the second floor is more
> difficult as the opening at the second floor occurs above the solid
portion
> of wall below - leaving me a difficult time trying to beef up the second
> floor panels and tying them down (uplift and compression).
>
> The size and ratio of the building plan is such that an interior shearwall
> at the second floor would not be necessary. It is also unusual for a
> building this size to use an interior shear wall when the owners of
> commercial structures like to leave room for the potential of removing or
> opening up the space at each level.
>
> Question:
> Does my assumption seem to be valid - that is, assume the wall is not a
> shearwall and simply provide the header and post connections to transfer
> down to the first floor foundation.
>
>
> Regards,
> Dennis S. Wish, PE
> Structural Engineering Consultant
> structures(--nospam--at)engineer.com <mailto:structures(--nospam--at)engineer.com>
> (208) 361-5447 E-Fax
> ICQ #95561393
>
>