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RE: Masonry Expansion Joints[Subject Prev][Subject Next][Thread Prev][Thread Next]
- To: "'seaint(--nospam--at)seaint.org'" <seaint(--nospam--at)seaint.org>
- Subject: RE: Masonry Expansion Joints
- From: Harold Sprague <harold.sprague(--nospam--at)neenan.com>
- Date: Wed, 4 Aug 1999 11:53:08 -0600
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
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