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RE: Masonry Expansion Joints

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Andrew,

In Florida (no earthquakes, but big wind) the expansion joints for concrete
masonry unit (CMU) walls are generally placed just to add continuity to the
expansion joints (if required) in the steel roof structure.  Aside from
these expansion joints, all other joints will be control joints.  As the CMU
wall ages, the concrete shrinks, and the control joints will open slightly
and allow for what little incremental thermal movement occurs.  

The reason that you don't see the calculated thermal movement in the "real
world" is:
1.  The "real world" CMU wall sits on a wall bearing on earth.  There is no
horizontal joint between the CMU wall above and the foundation below,
therefor as the wall above expands or contracts, it is restrained by the
continuous foundation which will be more thermally stable.  
2.  There is also thermal variation throughout a given height and thickness
of the wall and it will seldom be a uniform  temperature. 

When you read about joints in the masonry technical literature, there is
little mention of expansion joints in CMU walls.  Clay masonry unit walls
are a different story.  Clay units need expansion joints, because they will
expand.  But they expand more due to moisture variation than temperature.

Your comment about compressing the filler material points to the need for
the engineer to evaluate the filler material predicated on the joint detail
and the perceived joint movement.  Properly detailed joints should give many
years of service, but will eventually require maintenance and/or
replacement.

Regards,
Harold Sprague
The Neenan Company


-----Original Message-----
From: PyperEng(--nospam--at)aol.com [mailto:PyperEng(--nospam--at)aol.com]
Sent: Tuesday, August 03, 1999 6:34 PM
To: seaint(--nospam--at)seaint.org
Subject: Re: Masonry Expansion Joints


I note with interest your expertise on masonry buildings. I am curious about

the real need for expansion joints on large commercial retail warehouses in 
Florida eg Home Depot, Builders Square etc. I have found that most rely on 
the control joints at +/-30 ft o.c. with a tendency for expansion joints at 
+/- 250 feet o.c. The National Concrete & Masonry Association says the 
biggest problem they hear about is shrinkage rather than expansion as the 
blocks dry out during the initial periods. Our calculations indicate up to 
one inch expansion for masonry over one hundred feet for a seventy degree 
temp variation. The real world is strange in that common "verbal design 
experience" states if a building takes up more than one sheet then an 
expansion joint is needed! I was seeking a more scientific approach. However

it appears the construction world will continue to make the control joints 
serve as expansion joints. I wonder what happens after the filler is 
compressed and does not expand again. I would welcome any comments. Thank 
you. Andrew Pyper, Florida