A lally column is an height adjustable, thin walled steel column typically of cylindrical cross section used to support construction elements. This kind of column can adjust to meet height requirements by means of a screw-out top plate or courtesy of a telescopic arrangement of inner members. Lally columns are generally used as temporary supports during construction of permanent structural features although they may be left in situ as supplementary columns. The columns are usually fitted with head and foot plates to spread loads and prevent the cylinder from gouging into supported timber.
When new buildings are being constructed and particularly when older buildings need some sort of structural intervention, it is often necessary to install temporary supports under floors or beams. One of the cheapest, quickest and most efficient ways of achieving this temporary support is the lally column. These columns consist of hollow steel pipes fitted with a wide foot plate at the bottom and a height-adjustable mechanism at the top. These mechanisms are usually a screw-out section equipped with a header plate or a series of telescopic inner members which can be pulled out of the outer tube and locked in place when the desired height has been reached. A lally column is also cheap enough to trim the outer pipe and reweld the foot plate if the column is too long.
The term lally column was initially applied to hollow steel columns which were cut to size on site and then filled with concrete to form permanent supports. The first recorded use of this support method occurred in the late 1800s when one John Lally used concrete filled steel cylinders as supports. Often incorrectly referred to as lolly columns, these supports are intended to be temporary measures although they are some times employed on a permanent basis. Lally columns are available in a wide selection of sizes with the smallest being about 12 inches (30 cm) long and giants of 12 feet (3.6 m) or more being common in some construction sectors. The average adjustment range for a lally column is approximately 7 to 7-1/2 feet (about 2 m).
The lally column is often used to support sagging basement and crawlspace floor joists while new pillars or columns are installed. One point that needs to be kept in mind when using this type of temporary support is that the lally column must not be used to lift structures. A suitable jack should be used to lift the structure so that the preadjusted lally column can be placed under it.