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RE: PEMB / Masonry expansion joints

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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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