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Re: CMU Shear Wall Tension Steel

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Joe,

If I understand your description, then it sounds like the "return" (or
boundary element) extends about 4 ft and the bar is at the end of that
"return".  In other words, it sounds like the bar(s) are 4 ft from the
corner AFTER you have turned from the primary wall into the "return" wall.
If so, then that might be outside of "with in" reason for it to be
effective.  I would take a look at what ACI 318 has on shearwall boundary
elements.  That should at least give you some basic guidance as a starting
point.  Since I don't use those provisions on a regular (or even
infrequent) basis, I don't know them that well.  But, my gut tells me that
4 ft beyond the wall intersection is likely too much.

Regards,

Scott
Adrian, MI


On Fri, 17 Nov 2006, jrgrill(--nospam--at)cableone.net wrote:

>
> Scott,
>
> Thanks for the reply.  I am looking at a remodel where a length of cmu
> wall is going to be removed.  I have no idea if it was intended to be a
> shear wall or not as the building is probably 20 years old at least.  No
> drawings or calculations are available.  At the other end of the wall
> (which is full of openings) there is a 16 ' long cmu wall with returns at
> both ends.  The wall works fine in shear (unreinforced) per code
> requirements in our seismic location.  If I use the 4' return allowed at
> the ends of the walls as allowed for an 8" unit I need 2-#5 bars for
> tension steel (disregarding any intermediate vertical steel).  I will ask
> the contractor to verify the steel, but I'm assuming for now that there
> is a bar at the corners and at 48" o.c., but some of the detailing that I
> am seeing elsewhere it looks as though some thought was put into lateral
> and other design.  If I can use the additional bar which would be at the
> "toe" of the 4' flange then we wouldn't need to add any more steel in the
> wall.
>
> Also, I'm real cranky with the new wind criteria.  A comparison of the 97
> UBC and the IBC for this building has the wind load increasing 26
> percent.  Otherwise, I wouldn't even have this question.  But then I've
> been real cranky with the new wind criteria since it came out.  For
> instance the criteria calcs for "partially enclosed".  Way too much to do
> for our small projects.
>
> Thanks again,
>
> Joe
>
>
>
> On Fri Nov 17 16:28 , Scott Maxwell sent:
>
>       Joe,
>
>       To my knowledge, that answer would be a kind of "yes and no".
>
>       As far as I know, the official answer could be construed as a
>       "no". This
>       is because, to my knowledge, the MJSC (aka ACI 530) does not
>       yet address
>       "boundary elements" of shearwalls. I believe it is on their
>       agenda (it
>       could be in the upcoming 2008 edition...which will have its
>       public comment
>       period sometime this Spring).
>
>       On the other hand, it is something that is addressed and
>       permitted to a
>       degree in ACI 318 (i.e. boundary elements). As such, I don't
>       see why
>       similar principles would not apply to CMU masonry with some
>       modifications
>       (likely minor). So, if you are not looking for a "blessing"
>       of in the
>       code, then I don't see why you could not do it...with in
>       reason.
>
>       Now, since you did not give any definitive specifics of your
>       situation, I
>       won't/can't comment if I think it is "with in reason" in your
>       case.
>
>       Regards,
>
>       Scott
>       Adrian, MI
>
>
>       On Fri, 17 Nov 2006, jrgrill(--nospam--at)cableone.net wrote:
>
>       >
>       > If perpendicular walls at the ends of shear walls are used
>       as flanges at
>       > a shear wall will the tension steel only be that at the end
>       of the "web",
>       > or can the next bar within the "flange" be used as
>       additional tension
>       > steel. I am looking at a remodel where using the additional
>       steel in the
>       > "flange" would be a big help.
>       >
>       > Joe Grill
>       >
>       >
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