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RE: PEMB / Masonry expansion joints

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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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