Q.: When renting or purchasing prefabricated column forms, we frequently see the note, "Brace according to industry standards," or similar wording. What are these industry standards, and who sets them up?
A.: It's hard to find a single "industry standard." The American Concrete Institute (ACI) "Guide to Formwork for Concrete (ACI 347R-88)" states the basic idea that braces should be designed to resist all foreseeable lateral loads such as seismic forces, wind, cable tensions, inclined supports, dumping of concrete, and starting and stopping of equipment. It recommends a minimum wind load of 15 pounds per square foot for design, but doesn't offer any specific suggestions for column form braces.
The actual number of braces needed may be affected by size or location of the column in the building. Is it more than one story high? Is it isolated or part of a long line of columns? Do beam, girder, or slab forms frame into the column form? The formwork handbook of one major construction company says simply "column forms must be braced in two directions," and this is about as close as we come to an industry standard for one-story columns.
In his book, Formwork, M. P. Hurst says column forms up to about 20 feet high must be supported on two adjacent sides so that they can be plumbed from two directions.
Another book, Carpentry in Commercial Construction, agrees that column forms must be plumbed and braced in two directions, and adds some specific recommendations: "Bracing is usually accomplished by nailing 2x4's near the top of the form and to a stake driven into the ground. These braces should make an angle of approximately 45 degrees with the horizontal and should be placed on two adjacent sides.... some contractors prefer to use the adjustable brace clamp produced by various manufacturers.... If there are a number of columns in a row, the end columns are braced in two directions with diagonal braces, and the central columns are held with horizontal spacers placed near the top to hold them in one direction. Diagonal braces are needed only in the other direction."
A formwork guide published by The Concrete Society in England (Ref. 4) says that column forms are "aligned, plumbed and stabilized with suitable props, preferably on all faces, to eliminate the possibility of twist" during concrete placement.
- Hurst, M.P., Formwork, Construction Press, New York and London, 1983, page 189.
- Badzinski, Stanley, Jr., Carpentry in Commercial Construction, Prentice Hall, Inc., Englewood Cliffs, New Jersey, 1974, pages 94 and 95.
- ACI Committee 347, "Guide to Formwork for Concrete (ACI 347R-88)," American Concrete Institute, P.O. Box 19150, Detroit, Michigan 48219, 1988, Section 2.2.3.
- Formwork: A Guide to Good Practice, by a joint committee of The Concrete Society and The Institution of Structural Engineers, published by The Concrete Society, London, 1986, page 123.