A jack post (screw jack, telepost, adjustable steel column) is a steel post used in the construction trades for temporary support of loads such as ceilings, walls, and concrete formwork, and as

shoring Shoring is the process of temporarily supporting a building, vessel, structure, or trench with shores (Jack post, props) when in danger of collapse or during repairs or alterations. ''Shoring'' comes from ''shore'', a timber or metal prop. Shoring ...

in trenches. They are designed to be able to mechanically telescope to about twice the distance between their pre-drilled adjustment holes. Most examples use removable pins for coarse adjustment and a jack screw for fine adjustments, but many variations exist.

Terminology

Although jack posts are widely standardized, their terminology is not. "Jack post" is just one of many describing the same system: others include any assortment of "adjustable", "steel", "screw", "jack", and "shoring" with "post", "column", "jack", and "prop", depending on region, trade, and precise construction. The "jack" refers to examples with a jack screw to adjust the precise length of the post. They are also known by any number of proprietary names, notably "Acrow prop" in the U.K., after the Acrow Group that introduced them in the UK.

Description

Jack posts are telescopic tubular steel props consisting of two primary parts, both tubular: the main body of the post, and the threaded jack screw or other adjustable fitting on one or both ends. Both ends are normally fitted with flat metal plates on the end, increasing their bearing surface. A recent improvement to Acrow props was to shape this baseplate with notches, allowing

pallet A pallet (also called a skid) is a flat transport structure, which supports goods in a stable fashion while being lifted by a forklift, a pallet jack, a Loader (equipment), front loader, a Jack (mechanical), jacking device, or an erect cra ...

loads of horizontal props to be stacked neatly, rather than randomly piled. Gross adjustment for length is first made by sliding the two sections within each other until they almost fill the gap, inserting a pin through regularly-spaced pre-drilled circular holes to lock them together, then adjusting the screw to the degree of tightness desired. Other designs used two threaded pipes instead of sliding sections, ratechetting or clamping sections, or other similar concepts to lock the system at a specific length. Jack posts are mostly used for

as temporary supports during construction, repair, or alteration work, and should not be confused with

scaffolding Scaffolding, also called scaffold or staging, is a temporary structure used to support a work crew and materials to aid in the construction, maintenance and repair of buildings, bridges and all other human-made structures. Scaffolds are widely u ...

that supplies platforms for workers and materials, nor

Lally column A Lally column is a round or square thin-walled structural steel column filled with concrete, and oriented vertically to provide support to beams or timbers stretching over long spans. Historically, Lally columns were made of steel up to in t ...

s placed as permanent structural supports.

British Standard

Metal props, their size, strength and construction, are now described by a British Standard BS4074. A similar lightweight European prop design exists, these have a maximum capacity of only . Props are made in a range of five BS standard sizes: *size 0 from to , *size 1 from to , *size 2 from to , *size 3 from to , *size 4 from to . The safe load for each prop depends upon the size and extension of the prop. Size 1, 2 and 3 props can take about 34 kN unextended, dropping progressively to less than half of that when fully extended. Size 0 props can take at least 23 kN, whereas size 4 props at most 20 kN dropping to 7 kN at their maximum extension. Props must be loaded concentrically, i.e. vertically for simple weights, to within 25mm.

Seel also

References

{{Reflist Construction equipment