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jack post
A jack post (telepost, adjustable steel column) is a steel post used in the construction trades for temporary support of ceilings, walls and trenches (shoring). The term "jack post" is one of many describing the same system, other names include any assortment of "adjustable", "steel", "jack" and "shoring" with "post", "column" and "prop", depending on their 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 trade names, notably "lally column" and "Acrow prop". Jack posts are widely standardized.〔For instance, in (BS 4074:1982 )〕
==Description==
Jack posts are telescopic tubular steel props consisting of two primary parts, the main part of the post, and the jack screw or other adjustable fitting on the end. Both ends are normally fitted with flat metal plates on the end, providing additional support area. Most jack posts are split in two near the middle, with the upper end carrying the jack designed to slide within the lower portion. Gross adjustment for length is first made by pulling a pin and sliding the two sections within each other until they almost fill the gap, inserting the pin to lock them, then using the screw to close any remaining gap. Other designs used two threaded pipes instead of sliding sections, clamping sections, or other similar concepts to lock the system at a specific length.
Jack posts are mostly used for shoring: temporary supports during building repair or alteration work, rather than scaffolding: access platforms for workers. A typical use is to support an existing horizontal beam while its original masonry supports are removed or repaired. When masonry itself is to be supported, holes are first knocked through the brickwork and a strong 'needle' or 'strongboy' is placed through the hole. A pair of props are then used, one under each end. Existing windows or doorways may also be supported directly, or via needles. As the plates on the end of the posts are typically small, they offer little sideways support. If there is any sideways force, props should be strutted or 'laced' with scaffolding poles.
抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』
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