Need a book? Engineering books recommendations...
RE: Reinforced Concrete Blockwork Construction[Subject Prev][Subject Next][Thread Prev][Thread Next]
- To: "'seaint(--nospam--at)seaint.org'" <seaint(--nospam--at)seaint.org>
- Subject: RE: Reinforced Concrete Blockwork Construction
- From: "Jeffery Seegert (x 485)" <jbseegert(--nospam--at)matrixti.com>
- Date: Tue, 27 Jul 1999 11:02:56 -0400
In Reply. -----Original Message----- From: Harold Sprague [mailto:harold.sprague(--nospam--at)neenan.com] Sent: Tuesday, July 27, 1999 10:16 AM To: 'seaint(--nospam--at)seaint.org' Subject: RE: Reinforced Concrete Blockwork Construction "But in the US the knock-out units are very common." Yes. This is very true. But it is also true that CMU fabricators prefer to produce U-block. First of all it contains less overall concrete so the manufacturing/curing process is shorter. There is less wear and tear (friction) on the molds when they are withdrawn. This results in lower maintenance costs (for mold replacement and downtime to replace molds). The original purpose of knockout block was to allow the installation of materials such as conduit, piping, other such items in partially grouted walls. A knockout block tends to be more expensive (a couple cents per block does add up) than a U-block. I'm sure all the contractors would prefer to pay the extra money just to convert them to U-block All these factors basically means that the U-block is also very common and will be for a long time to come. In fact, I had the opportunity to work with the designers/inventors of the "Ice-Block" system which uses U-shaped polystyrene blocks with horizontal and vertically reinforced/grouted cells at 16" o.c. The system was originally developed on the west coast back in the early 1990's and was based conceptually on the CMU "U" style block. "For many years the NCMA and the USACE have had details showing the use of the knock out bond beams in partially grouted walls. The NCMA and USACE standard details do not show "U" shaped bond beams except at lintels. The NCMA even has a video tape showing the proper installation and grouting using the knock out bond beams." I wouldn't know why these organizations ignore the existence of bond beam U-block installation. Possibly that it is the same procedure as using knockout block. But even ACI 530 Commentary shows examples of U-block being used in a normal bond beam application. "I have seen many jobs where the "U" shaped bond beams are shown on drawing details, but the masons routinely replace them with the knock out units without calling the architect or engineer." There is no real structural difference between a "knock-out" block and "U-block with the same material properties. So I frequently see the substitution of for "U-block" also. "Another advantage is that the masons can replace regular CMU with a knock-out unit, but they can not replace them with a "U" shaped unit." Advantage? U-block is only used to install horizontal reinforcement with solid grouting. It would never be expected (even by the masons) to be used in a normal condition. "The only bond beams used on the west coast are the lintel "U" shaped bond beams, but the only reason is the predominance of fully grouted masonry walls. Where partially grouted walls are the norm, you will see the use of the knock-out bond beams." The ONLY? Come on now. That's a pretty broad reaching statement. With all of your experience I'm sure you realize that many methods of construction are used in all areas of the country and world. Just because the predominant method of construction in your area is what you have explained does not mean it is the "only" method.
- Prev by Subject: RE: Reinforced Concrete Blockwork Construction
- Next by Subject: RE: Reinforced Concrete Blockwork Construction
- Previous by thread: RE: Reinforced Concrete Blockwork Construction
- Next by thread: RE: Reinforced Concrete Blockwork Construction