Return to index: [Subject] [Thread] [Date] [Author]

RE: [AEC-Residential] QUERY: Wind Load Effects For Small Building Set-Back (ASCE 7-98)

[Subject Prev][Subject Next][Thread Prev][Thread Next]
Bill,
If I am reading this correctly, you do not have a separation between two
buildings but simply a "jog" in the resisting line of shear. If the jog is
approximately 4-feet or less, I would consider the line of shear continuous.
That is to say that I would consider the tributary force to be uniformly
divided into the amount of shear resisting elements that you have in that
one line.

If all of the walls exist on one side of the jog and you need more diaphragm
capacity to meet the demand, you will have to develop the additional
capacity through the diaphragm. You can increase the diaphragm nailing on
one side to pick up the capacity needed to meet the lateral demand but I
would prefer dragging deeper into the diaphragm rather than pushing the
diaphragm to its limit. Just make sure that your connection between walls
(double top plate and up) and drag strut is designed well.

If you are required to provide a rigid analysis, then the offset in the line
of shear will be evaluated by the rotational distribution of shear through
the diaphragm based on the wall location and relative stiffness. I am,
however, assuming that you are referring to a flexible, tributary
distribution only.

The UCBC has a method you may use if you wish to consider the offset an open
front. I'm not sure how many use this method in wood design, but it has been
used with Unreinforced Masonry to compensate for an open-front design. The
URM design considers the setback of the shearwall from the open front based
on calculations which consider the mass of the brick. In the case of wood,
the mass is very low and the setback may calculate much greater.

I don't think I would resort to this method unless you are trying to justify
a small setback. In any case, if you are within say 4 and 6 feet you should
be able to safely combine the lines of shear.

Dennis

-----Original Message-----
From: owner-aec-residential(--nospam--at)polhemus.cc
[mailto:owner-aec-residential(--nospam--at)polhemus.cc]On Behalf Of Bill Polhemus
Sent: Monday, January 15, 2001 4:50 PM
To: seaint(--nospam--at)seaint.org; aec-residential(--nospam--at)polhemus.cc
Subject: [AEC-Residential] QUERY: Wind Load Effects For Small Building
Set-Back (ASCE 7-98)


Here's another question to file under the "Gee I Should Know This But..."

When you have a small building setback breaking up the line a long,
otherwise
continuous wall in a small building, how do you safely account for the
effects
that always arise when you have a discontinuity?

Up until now, this situation has invariably come up such that I felt
justified
in putting a "drag strut" at that point, and calling it a shear-resistant
point
in the structure.

But I have one now that just won't let me justify that expense (as well as
the
time consumption).

The "jog" is only a few feet, less than 10% of the smaller building depth
(perpendicular to the wall line under consideration).

I am tempted to just calculate the diaphragm shear due to wind there, and
check
to make sure the diaphragm has no problem (I'm sure it won't). But I need
some
hand-holding. Is there something I'm failing to take into consideration?

Thanks in advance.
_____________________________
 AEC-Residential - Discussion List for the Residential Building Professional
                     To Subscribe/Unsubscribe, Send Mail to
                   mailto:aec-residential-request(--nospam--at)polhemus.cc
    Leave the Subject Line Blank, put "subscribe" or "unsubscribe" in the
              Body of the Message (without "quotes" of course!)