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RE: PEMB / Masonry expansion joints

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Bill,
When the AISC developed Design Guide #3 it was predicated solely on the serviceability of single story structures. That is where the serviceability concept of the the 10 year wind was introduced. Keep in mind that a 10 year wind velocity will have about 75% of the pressure generated from a 50 year wind velocity. It would not be overly conservative to design the frame for a h/200 lateral drift for the full 50 year wind.

The L/600 was a limit that came from studies from the Brick Institute of America, and is what the BIA recommends. Hardly any solid brick walls are used today so a conflict of interest is unlikely with the BIA. The L/720 is also the recommendation of "Technics - Steel Stud / Brick Veneer Walls", by Trestain and Rouseau for The Canadian Mortgage and Housing Corporation (CMHC).

The only published documents that have pushed the L/360 for brick is the one generated by The Metal Lath / Steel Framing Association. Obviously they have a vested interest in pushing for wider use of metal studs as opposed to brick with a CMU back-up.

Some years ago, I had panels tested for water infiltration and wind, and it led me to the same conclusion of the BIA. The underwriters on that particular building would not underwrite the building for any greater panel deflection.

Regards,
Harold Sprague




From: "Sherman, William" <ShermanWC(--nospam--at)cdm.com>
Reply-To: <seaint(--nospam--at)seaint.org>
To: <seaint(--nospam--at)seaint.org>
Subject: RE: PEMB / Masonry expansion joints
Date: Fri, 20 May 2005 09:39:45 -0400

I agree with much of what Harold wrote below, but I personally question
the use of 10-year wind speeds for serviceability checks. That seems
find if you are only concerned about "comfort" of occupants due to sway,
but if you are concerned about cracking of masonry, I feel that 50-year
wind speeds should be used if the building has a 50 year design life.
Thus, I prefer an H/200 limit on drift using full code wind pressures.

While limits of L/600 to L/720 make sense for vertical deflection of
masonry supports, I'm not sure that should apply to lateral supports. A
masonry wall is very stiff in-plane but has some flexibility
out-of-plane. I feel that limits of L/240 to L/360 would be reasonable
for lateral supports.

William C. Sherman, PE
(Bill Sherman)
CDM, Denver, CO
Phone: 303-298-1311
Fax: 303-293-8236
email: shermanwc(--nospam--at)cdm.com


> -----Original Message-----
> From: Harold Sprague [mailto:spraguehope(--nospam--at)hotmail.com]
> Sent: Thursday, May 19, 2005 10:57 AM
> To: seaint(--nospam--at)seaint.org
> Subject: RE: PEMB / Masonry expansion joints
>
> Jim,
> There are several considerations that I would suggest for
> consideration.  It is important to note that this is a
> servicability issue, and not a life safety issue.  Therfor
> the building code is not much help.
>
> Lateral Drift:
> The standard for Butler Manufacturing for a masonry clad
> building is h/100.
> I would suggest that you obtain the AISC Design Guide #3
> "Serviceability Design Considerations for Low-Rise
> Buildings".  Reference p 17.  I prefer to limit the drift of
> the frame to h/200.  With proper detailing one can design to
> h/100.  It really does not cost that much to require an
> increase in frame stiffness when you look at the cost per
> square foot of the building.  Keep in mind that this drift
> limit is for a 10 year wind not a 50 year wind.
>
> Horizontal deflection:
> There is a lot of controversy on this issue, and the
> opiinions vary depending on who's is citing the research.
> The light guage people claim that you can go to L/360.  But
> the same research (the Clemson Study) cited by others would
> indicate L/720.  I have a bit of heart burn with the research
> itself because of the types of mortar either used or not
> properly cited.  N mortar is much better for crack healing
> than S mortar.  But that is another issue.  The Canadian
> Mortgage and Housing Corporation (CMHC) did an independent
> evaluation and suggests L/720.  But again, this is a
> serviceability issue, and this would suggest a 10 year wind.
> My preference is to use L/600 with a 50 year wind.  This is
> about the same as a L/720 with a 10 year wind.  The L/600 is
> consistant with the Brick Institute of America
> (BIA) recommendation.
>
> Vertical deflection:
> Obviously this one is L/600 as mandated by most building
> codes. You can go more with proper detailing, but why fight it?
>
> There have been several good articles in The Magazine of
> Masonry Construction on this issue.
>
> PS Use G-90 galvanized studs.
>
> Regards,
> Harold Sprague
>
>
>
>
> >From: Jim Wilson <wilsonengineers(--nospam--at)yahoo.com>
> >Reply-To: <seaint(--nospam--at)seaint.org>
> >To: seaint(--nospam--at)seaint.org
> >Subject: PEMB / Masonry expansion joints
> >Date: Thu, 19 May 2005 06:42:13 -0700 (PDT)
> >
> >If a metal building is designed to H/100 lateral displacement, is it
> >appropriate to size the vertical expansion joints in the
> masonry facade
> >at the building's corners for an equal amount of movement?
> >
> >For example, 20ft tall building, masonry walls to 12ft tall.
>  Lateral
> >displacement = 2.4" at roof level, 1.44" at top of masonry.
> Expansion
> >joints in masonry should provide for 1.5"(1.44") lateral movement.
> >
> >This seems obvious, but is there anything else to it that I
> am missing?
> >
> >TIA,
> >Jim Wilson
> >Stroudsburg, PA

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