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

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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