Adjustable steel columns, also known as telescopic steel columns, beam jacks and screw jacks, are hollow steel members designed to provide structural reinforcement or support. A threaded mechanism is attached that is used to adjust the height of the post according to the appropriate elevation.
They are usually installed in basements as the structural members underneath the main floor carry the most weight. In some parts of Canada and USA, adjustable steel columns are also called lally columns, although this term normally pertains to columns that are filled with concrete and non-adjustable. They are manufactured as single-piece unit, or as multi-part assemblies also known as telescopic steel columns.
In order to function properly, adjustable steel columns must:
• Have diameter of 75mm (3 inches) or greater. As per 2012 International Residential Code (IRC), Section R407.3, columns (including adjustable steel columns) "shall not be less than 3-inch diameter standard pipe." Although columns smaller than 75mm contravene the IRC, they are not necessarily substandard or defective. A 100mm diameter column is considered defective if it buckles when the load is exceeded; whereas a 2½-inch column may be sufficient to support the load it is intended to carry. Structural engineers must be consulted to confirm whether the adjustable steel posts are of sufficient diameter and length.
• Be protected by rust-inhibitive paint. According to IRC Section R407.2: “All surfaces (inside and outside) of steel columns shall be given a shop coat of rust-inhibitive paint, except for corrosion-resistant steel and steel treated with coatings to provide corrosion resistance.” It is hard to identify if the paint applied is rust-inhibitive. However, visible rusts indicate absence of protective coating and therefore constitute a probable defect. Rust-inhibitive paint may not be needed in arid environments where rust is not as much of a concern.
• Be straight. The recommended maximum lateral deflection between the bottom and top of the post should not exceed 25mm. However, tolerable lateral deflection is affected by several factors, such as the diameter and length of the column. The column must also not bend at its mid-point. Excessive deflection is an indication that the column cannot bear the overlying load of the house structure. There must be no cracks in upstairs walls. Such condition could be a sign of a column failure.
• Be mechanically connected both to the floor below and beam above to provide additional resistance against lateral deflection. However, we cannot confirm whether such connections exist if they are covered by concrete and ceiling materials.
• Be properly tightened. No more than 3 inches of the screw thread should be exposed.
Republished from: “Adjustable Steel Columns”, Green Building, Pilipino Express.